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Activation and functionalization of carbon-hydrogen bonds catalysed by oxygen ligated iridium metal complexes

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Activation and functionalization of carbon-hydrogen bonds catalysed by oxygen ligated iridium metal complexes

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Content ACTIVATION AND FUNCTIONALIZATION OF C-H BONDS CATALYSED BY OXYGEN LIGATED IRIDIUM METAL COMPLEXES by Gaurav Bhalla A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment o f the Requirements for the Degree DOCTOR OF PHILOSOPHY (CHEMISTRY) December 2005 Copyright 2005 Gaurav Bhalla Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 3220086 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. ® UMI UMI Microform 3220086 Copyright 2006 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DEDICATION TO MY PARENTS Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS First of all, I would like to extend my gratitude to Professor Roy A. Periana for a very stimulating and exciting journey o f research. This wouldn’t have been possible without his guidance, endless support and positive criticism. Surely, his followings will help me in the long run in making me a better scientist. I would also like to thank Professor George A. Olah and Professor G. K. Surya Prakash for their excellent support and encouragement. Their profound knowledge in both chemistry and philosophy has truly inspired me and thus will be ideal role models for me to follow in life. I must acknowledge all the past and present members of Periana group from whom I have learned a lot o f things, both scientific and non scientific. I personally acknowledge Dr. Xiang Yang Liu and Oleg Mironov who really helped me from the very beginning. My thanks are also due to other members including Dr. Antek G. Wong-Foy, Cj Jones, Dr. K. J. H. Young, William, Vadim, Somesh, Steve and Brian. I am grateful to our collaborators Professor W. A. Goddard, III, Dr. Jonas Oxgaard, Smith and Jason at Beckmann Institute, CALTECH, for their help in DFT calculations. I extend my personal gratitude to Professor William C. Kaska at UCSB for his valuable suggestions and insights. I also thank Professor Flood and Paul Boothe for their insight and help regarding iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. kinetic experiments. Professor Bau and Professor K. Shing are recognized for their valuable time as Ph.D. committee members. Muhammed Yousufuddin, Dr. I. Tsyba and Dr. Nam Nhat Ho are accredited for their help in X-Ray crystallography. I am thankful to Thomas Gadda for his help in TGA analysis. I also thank Dr. Thomas Mathew and Chiradeep Panja for their helpful discussions and generous loans of chemicals. I would also like to thank many other friends and colleagues including Mihir, Jinbo, Ryan, Shashi, Asanga, Sean, Srikant, Paulin, Iris, Kim, Bhavna, Christian, Anton, Ulrika, Habiba and others. I thank other staff members of the chemistry department, especially Michele, Heather and Jessy for their kind support. Allan and Jim are also acknowledged for their technical help with NMR and glass blowing. All this wouldn’t have been possible without the support of my wife, Pooja Bhalla, who helped me in every possible manner. Being a chemist herself, I had the priviledge to exchange a lot of chemistry ideas with her. Last but not the least; I convey my deep appreciation to my parents. Without their word of encouragement and support, this wouldn’t have been possible. Thus, are the ideal role models for me to follow in my life. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS DEDICATION................................................................................................... ii ACKNOWLEDGEMENTS.............................................................................. iii LIST OF SCHEMES......................................................................................viii LIST OF FIGURES..........................................................................................xi LIST OF TABLES..........................................................................................xiv ABSTRACT................................................................................................. xviii 1 Introduction..............................................................................................1 1.1 Introduction to C-H Activation................................................................................1 1.2 C-H Activation by Electrophilic M echanism........................................................ 5 1.2.1 Electrophilic C-H activation by H g .................................................................................................. 6 1.2.2 Electrophilic C-H activation by Pt(II).............................................................................................11 1.2.3 Electrophilic C-H activation by A u ................................................................................................ 14 1.2.4 Electrophilic Oxidative Carbonylation o f C-H bonds by P d(II).............................................17 1.3 C-H Activation by Oxidative Addition Mechanism...........................................22 1.3.1 Functionalization based on Oxidative Addition M echanism ..................................................... 23 1.3.2 Iridium in an Oxygen ligand Environment............................................ 25 1.4 References.................................................................................................................30 2 Alkane and Arene C-H Activation Catalyzed by an O-Donor, bis-acetylacetonato Iridium (III) Complex..........................................33 2.1 Introduction..............................................................................................................33 2.2 Results...................................................................................................................... 36 2.2.1 Synthesis o f CH3-Ir(III)(acac-0,0)2(P y )........................................................................................36 2.2.2 Stoichiometric C-H Activation o f Alkanes and A renes............................................................37 2.2.3 Proposed Mechanism for C-H Activation...................................................................................... 40 2.2.4 Catalytic H/D E xchange......................................................................................................................41 2.3 Experimental Section.............................................................................................. 44 2.4 References.................................................................................................................67 v Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 Mechanistic Details of 0-Donor Ir(lll) Complexes: C-H Activation Studies with Benzene........................................................ 70 3.1 Introduction...............................................................................................................70 3.2 Results and Discussion........................................................................................... 74 3.2.1 Synthesis and Characterization o f (acac-0,0)2lr(III) Complexes............................................74 3.2.2 Dynamic Behavior o f Dinuclear Complexes, [(acac-0,0)2Ir-R]2............................................78 3.2.3 Reactions o f the Dinuclear Complexes, [(acac-0,0)2lr-R]2, with Ligands...........................81 3.2.4 Ligand (L) Substitution Chemistry o f (a ca c-0 ,0 )2Ir(R)(L) C om plexes................................84 3.2.5 Trans-Cis Isomerization o f (acac-0,0)2lr(R )(Py)........................................................................ 87 3.2.6 C-H Activation o f Arenes by (a ca c -0 ,0 )2Ir(R)(L)......................................................................95 3.3 Conclusion..............................................................................................................116 3.4 Experimental Section............................................................................................ 118 3.5 Reference................................................................................................................ 157 4 Anti-Markovnikov, Hydroarylation of Olefins Catalyzed by a bis-acetylacetanato Iridium (III) Complex......................................... 161 4.1 Introduction.............................................................................................................161 4.2 Results and Discussion......................................................................................... 166 4.2.1 Stability o f O-Donor Spectator L igands.......................................................................................166 4.2.2 Rates o f Various (acac-0,0)2lr(III) C om plexes.........................................................................169 4.2.3 Thermodynamic vs Kinetic control................................................................................................ 172 4.2.4 Dinuclear or Mononuclear Active Catalyst?................................................................................175 4.2.5 Reaction Order o f Substrates........................................................................................................... 178 4.2.6 Evidence for Proposed Mechanism.................................................................................................180 4.2.7 Rate Determining Step....................................................................................................................... 189 4.2.8 Why are Olefinic Products not Produced in CH Activation with Ir Com plexes? 190 4.3 Conclusion..............................................................................................................199 4.4 Experimental Section............................................................................................ 199 4.5 References...............................................................................................................213 5 Hydrovinylation of Olefins catalyzed by an Iridium Complex via C-H Activation................................................................................ 215 5.1 Introduction.............................................................................................................215 5.2 Results and Discussion.........................................................................................216 5.2.1 Synthesis o f Vinyl-lr(acac)2-P y ...................................................................................................... 217 vi Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.2.2 Catalytic Hydrovinylation............................................................................................................... 218 5.2.3 DFT Calculations for Hydrovinylation........................................................................................ 220 5.3 Experimental Section........................................................................................... 222 5.4 References..............................................................................................................233 6 Alkane and Arene C-H Activation Catalyzed by an O-Donor, bis-tropolonato Iridium (III) complex................................................235 6.1 Introduction............................................................................................................235 6.2 Results.................................................................................................................... 238 6.2.1 Synthesis o f CH3-Ir(lI])(trop-0,0)2(P y )......................................................................................238 6.2.2 Stoichiometric C-H Activation o f Alkanes and A renes.......................................................... 241 6.2.3 Catalytic C-H Activation and Comparison with bis Acac com plex.....................................242 6.3 Experimental Section........................................................................................... 244 6.4 References..............................................................................................................260 7 Anti-Markovnikov, Hydroarylation of olefins Catalyzed by a bis-tropolonato ligated Iridium (III) Complex................................. 264 7.1 Introduction............................................................................................................264 7.2 Results.................................................................................................................... 268 7.2.1 Synthesis o f Ph-Ir(trop-0,0)2(P y ).................................................................................................268 7.2.2 Hydroarylation and Comparison with bis Acac Complex...................................................... 269 7.2.3 DFT Calculations Comparing Acac and Trop Complexes..................................................... 271 7.3 Experimental Section........................................................................................... 275 7.4 References..............................................................................................................276 Bibliography................................................................................................ 278 vii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF SCHEMES Scheme 1.1. Generalized Catalytic Scheme For Generating Products Based on the C-H Activation Reaction. 2 Scheme 1.2. Examples of some of the reported C-H activation systems with catalytic systems that generate functionalized products (boxed). 3 Scheme 1.3. Different mechanisms for alkane C-H bond activation. 5 Scheme 1.4. C-H bond activation by electrophilic mechanism. 6 Scheme 1.5. Methane activation by HgSC>4 . 7 Scheme 1.6. Possible Transition States for Generation of Methanol from CH3 HgX. 9 Scheme 1.7. Methane activation by (bpym)PtCl2 11 Scheme 1.8. Acetic acid formation using (bpym)PtCl2 with CEU and CO. 13 Scheme 1.9. Proposed mechanism for methane oxidation by the Pt(bpym)Cl2 /H 2 S0 4 . 14 Scheme 1.10. Methane oxidation using Au. 16 Scheme 1.11. Methane oxidation to acetic acid using Pd. 18 Scheme 1.12. Proposed tandem catalysis mechanism for the oxidative condensation of methane directly to acetic acid. 2 1 Scheme 1.13. Some Notable C-H Activation Complexes based on OA Mechanism. 22 Scheme 1.14. Ir(PCP)H2 catalyzed dehydrogenation of Alkanes. 23 Scheme 1.15. Friedel Craft’s Alkylation. 24 Scheme 1.16. Murai Reaction Catalyzed by Ru Complex. 25 viii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Scheme 1.17. Oxygen transfer on Iridium center using polyoxoanion (Klemperer) 26 Scheme 1.18. Scheme 1.19. Scheme 2.1. Scheme 2.2. Scheme 2.3. Scheme 2.4. Scheme 2.5. Scheme 2.6. Scheme 3.1. Scheme 3.2. Scheme 3.3. Scheme 3.4. Scheme 3.5. Scheme 3.6. Scheme 3.7. Scheme 3.8. Reported Examples of Ir(V) Complexes. 27 Examples of Oxygen donor Ligands. 28 Schematic illustration of possible 7i-donor involvement of the non-bonding electrons on O- donor ligands in C-H Activation reactions with oxidative addition character. 35 Synthesis of CH3 -Ir-Py 36 Stoichiometric C-H Activation with CH3 -Ir-Py 38 Stoichiometric C-H Activation with [CH3 -Ir] 2 40 Proposed mechanism for the C-H activation of alkanes and H/D exchange reactions catalyzed by CH3 -Ir-Py 41 H/D Exchange 42 Proposed reaction mechanism of H/D exchange and hydroarylation of olefins catalyzed via arene C-H activation by [(acac-0 ,0 )2 lr(R)(L)] and [Ir(|i- acac-0 ,0 ,C3 )(acac-0 ,0 )(R) ] 2 Complexes. 73 Synthesis of Family of O-Donor, bis-acac Ir(III) Complexes. 75 Fluxional Behaviour 80 Pyridine Exchange. 85 Trans-Cis Isomerization for Ph-Ir-Py. 8 8 Possible C-H activation pathway involving the trans intermediate, R-Ir-D. 97 C-H Activation of Benzene with R-Ir-Py. 101 Ratio of rate laws for isomerization and C-H activation. 114 ix Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Scheme 3.9. Ratio of rate laws for isomerization and C-H activation. 116 Scheme 4.1. Possible dependence of L on TOF 176 Scheme 4.2. Possible Reaction products with (3 hydride Elimination. 192 Scheme 4.3. Kinetic Scheme for CH Activation and a to p 1 3C- Migration 1 9 7 Scheme 5.1. C-H Activation and Cossee-Arlman Mechanisms for Olefin Oligomerization. 216 Scheme 5.2. Synthesis of Vinyl-Ir-Py 217 Scheme 5.3. Proposed Mechanism for hydrovinylation using Vinyl-Ir-Py. 219 Scheme 6.1. Synthesis of CH3 -IrT -Py. 239 Scheme 6.2. Stoichiometric C-H Activation Reactions of CH3 - IrT Py with RH to Generate R-IrT -Py. 242 Scheme 7.1. Hydroarylation of unactivated arenes with unactivated olefins. 265 Scheme 7.2. Comparison of Acac and Tropolone. 267 Scheme 7.3. Synthesis of Ph-IrT -Py from CH3 -IrT -Py. 269 x Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES Figure 1.1. Figure 2.1. Figure 2.2. Figure 3.1. Figure 3.2. Figure 3.3. Figure 3.4. Figure 3.5. Figure 3.6. Figure 3.7. Figure 3.8. Figure 3.9. Figure 3.10. Figure 3.11. Time dependent product formation for Pd catalyzed oxidative condensation of methane to acetic acid. ORTEP drawing of CH3 -Ir-Py. ORTEP drawing of CftHi ,-Ir-Py. ORTEP diagram of Complex Ph-Ir-Py. ORTEP diagram of Complex PhCH2 CH2 -Ir-Py. Variable temperature observed (Left) and calculated (right) ’H NMR Spectra for [CH3 -Ir]2 . Plot of k0 b s versus [Py] for pyridine exchange with Ph-Ir-Py. Eyring plot for pyridine exchange with Ph-Ir-Py (■) and CH3 -Ir-Py (A ). Possible unimolecular (U) and bimolecular (B) mechanism for Trans-Cis isomerization of Ph-Ir- Py. First order Plots for Trans-Cis isomerization of Ph- Ir-Py Plot of k0 b s vs l/[Py] for Trans-Cis isomerization of Ph-Ir-Py. H/D exchange between CfiHf, and Tol-dg catalyzed by Ph-Ir-Py and cis-Ph-Ir-Py at 160°C. Possible C-H activation pathways involving reaction of benzene with R-Ir-Py species. Eyring plot for the reaction of CH3 -Ir-Py ( ♦ ) with C6 D6 at [Py]/[C6 D6] = 0.045. kc0 rr = kob s x [Py]/ [C6 D6 ], A = PhCH2 CH2 -Ir-Py. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 3.12. Figure 3.13. Figure 3.14. Figure 3.15. Figure 3.16. Figure 4.1. Figure 4.2. Figure 4.3. Figure 4.4. Figure 4.5 Figure 4.6. Figure 4.7. Figure 4.8. Figure 4.9. Figure 4.10. Figure 4.11. First order plots for Pyad d e d for C-H activation of PhCH2 CH2 -Ir-Py at 140°C. 104 Plot of k0 b s vs 1/Py for C-H activation of PhCH2 CH2 -Ir-Py at 140°C. 105 A plot of kobs vs [C6 H6 ] at 120 °C with 107 Possible reaction coordinate for reaction of CH3 -Ir- Py with 1,3,5-C6 D3 H3. 109 Theoretical calculations of trans-cis isomerization and C-H activation. Boxed values are the experimental value for that step. 113 Comparison of the conventional two step method and a single step method to generate saturated linear alkyl benzene’s. 162 Proposed Reaction Mechanism of H/D Exchange and Hydroarylation of Olefins Catalyzed via Arene C-H activation by R-Ir-L and [R-Ir] 2 Complexes. 165 Thermal Treatment of (acac-0,0)Ir(III) Complexes with Various Acids 168 ORTEP diagram of [CH3 COO-Ir]2. 168 ORTEP drawing of Ph-Ir-CH3 OH. 169 No Rearrangement of isopropyl to n-propylbenzene under catalyst. 173 Turn over number (TN) vs 1/Py Equivalents. 177 Olefin Dependence on Hydroarylation 179 Benzene dependence on Hydroarylation 180 Insertion Products of olefins with Ph-Ir-Py 186 Combined Experimental (boxed) and DFT (solvated and gas phase) AH Values. 190 Xll Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 4.12. Figure 4.13. Figure 5.1. Figure 5.2. Figure 6 .1. Figure 6.2. Figure 6.3. Figure 7.1. Figure 7.2. Possible products expected from heating CH3 1 3 CH2 -Ir-Py in C6D6 to generate ethane by C-H Activation. Time Dependent 1 3 C NMR spectra for the reaction of CH3 1 3CH2 -Ir-Py (-9 ppm) with C&D 6 to form 1 3CH3 CH2 -Ir-Py (18 ppm) and 2 regioisomers of ethane ( 8 ppm) ORTEP projection of Vinyl-Ir-Py. Calculated AH surface for the hydrovinylation of alkenes (shown only for ethylene) catalyzed by Vinyl-Ir-Py through C-H activation (solid black line) and Cossee Arlman mechanism (dotted blue line). Comparison of A cac-0,0 and T rop-0,0 Ligands ORTEP drawing of CH3 -IrT -Py. Comparison of Catalytic C-H Activation of Trop- 0 ,0 and A cac-0,0 Complexes. Calculated (B3LYP/LACVP**) energy profile of Ir(trop) 2 and Ir(acac) 2 catalyzed hydroarylation. TS3 194 195 217 221 237 240 244 272 274 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES Table 2.1. Table 2.2. Table 2.3. Table 2.4. Table 2.5. Table 2.6. Table 2.7. Table 2.8. Table 2.9. Table 2.10. Table 2.11. Table 3.1. H/D exchange With C6 D6 Catalyzed by CH3 -Ir-Py 43 Crystal data and structure refinement for IrCi6 0 4N 1H2 2 (CH3 -Ir-Py). 55 Atomic coordinates ( x 10 ^) and equivalent isotropic displacement parameters (A^x 1 0 ^) for Ir Ci6 0 4 N 1H2 2 (CH3 -Ir-Py). 56 Bond lengths [A] and angles [°] for IrCi6 0 4N]H2 2 (CH3 -Ir-Py). 57 Anisotropic displacement parameters (A^x 10^) for Ir C 1 60 4 NiH 2 2 (CH3 -Ir-Py). 59 Hydrogen coordinates ( x 1 0 ^) and isotropic displacement parameters (A^x 1 0 3) for IrC,6 0 4 NiH 2 2 (CH3 -Ir-Py). 60 Crystal data and structure refinement for C2 1H 3 0 IrNO4 (C6 H 1 1-Ir-Py). 61 Atomic coordinates (x 10 ^) and equivalent isotropic displacement parameters (A^x 1 0 ^) for C2 iH3 0 IrNO4 (C6 Hji-Ir-Py). 62 Bond lengths [A] and angles [°] for C2 iH3 0 IrNO4 (C6 H n -Ir-Py). 62 Anisotropic displacement parameters (A^x 10^) for C2 iH3 0 IrNO4 (C6 Hi i-Ir-Py). 65 Hydrogen coordinates (x 1 0 ^) and isotropic displacement parameters (A^x 1 0 3) for C2iH3oIrN04 (C6Hn-Ir-Py). 66 Methane isotopomer ratio obtained from reaction of CH3 -Ir-Py with various solvents. 110 x iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table Table 3.2. Line Broadening studies. 132 3.3. Dissociative Pyridine Exchange studies with Ph-Ir- Py. 133 3.4. Eyring Plot for Pyridine Exchange with Ph-Ir-Py. 134 3.5. Eyring Plot for Pyridine Exchange for CH3 -Ir-Py. 135 3.6. Dependence of Trans-Cis Isomerization of Ph-Ir- Py on Pyridine Concentration. 136 3.7. Kinetics for C-H Activation of C6 D6 with CH^-Ir- Py at constant [C6 D 6/Py]. 137 3.8. Dependence of Benzene C-H Activation on Pyridine Concentration. 139 3.9. Arene Concentration Dependence on Rate of C-H activation of Benzene with Cy-di i -Ir-Py. 140 3.10. Crystal data and structure refinement for Ph-Ir-Py. 144 3.11. Atomic coordinates ( x 1 0 ^) and equivalent isotropic displacement parameters (A^x 1 0 ^) for Ph-Ir-Py. 145 3.12. Bond lengths [A] and angles [°] for Ph-Ir-Py 145 3.13. Anisotropic displacement parameters (A^x 1 0 ^) for Ph-Ir-Py. 147 3.14. Hydrogen coordinates ( x 10^) and isotropic displacement parameters (A^x 10 3) for Ph-Ir-Py. 148 3.15. Crystal data and structure refinement for PhCH2 CH2 -Ir-Py. 149 3.16. Atomic coordinates ( x 10^) and equivalent isotropic displacement parameters (A^x 1 0 ^) for PhCH2 CH2 -Ir-Py. 150 3.17. Bond lengths [A] and angles [°] for PhCH2 CH2 -Ir- Py. 151 xv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.18 Table 3.19 Table 4.1 Table 4.2. Table 4.3. Table 4.4. Table 4.5. Table 4.6. Table 4.7. Table 4.8. Table 5.1. Table 5.2. Table 5.3. Anisotropic displacement parameters (A^x 1 0 ^) for PhCH2 CH2 -Ir-Py. Hydrogen coordinates ( x 1 0 ^) and isotropic displacement parameters (A^x 1 0 3) for PhCH2 CH2 -Ir-Py. Hydroarylation of propylene catalysed by various Ir(acac) 2 complexes3 Thermodynamic and Experimental data for hydroarylation with various olefins. Insertion Products of olefins with Ph-Ir-Py Crystal data and structure refinement for Ci7 H2 2 Ir0 5 (Ph-Ir-CH3 OH). Atomic coordinates ( x 10 ^) and equivalent isotropic displacement parameters (A^x 1 0 ^) for Ci7 H2 2 Ir0 5 (Ph-Ir-CH3 OH). Bond lengths [A] and angles [°] for Ci7 H2 2 Ir0 5 (Ph-Ir-CH3 OH). Anisotropic displacement parameters (A^x 1 0 ^) for Ci7 H2 2 Ir0 5 (Ph-Ir-CH3 OH). Hydrogen coordinates ( x 10^) and isotropic displacement parameters (A^x 10 3) for Ci7 H2 2 Ir0 5 (Ph-Ir-CH3 OH). Crystal data and structure refinement for Ci7 H2 2 IrN 04. (Vinyl-Ir-Py) Atomic coordinates ( x 10 ^) and equivalent isotropic displacement parameters (A^x 1 0 ^) for C 1 7H2 2 IrN 0 4 (Vinyl-Ir-Py). Bond lengths [A] and angles [°] for C 1 7H2 2 IrN 0 4 (Vinyl-Ir-Py). 154 155 170 174 186 206 207 208 210 211 227 228 229 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 5.4. Table 5.5. Table 6.1. Table 6.2. Table 6.3. Table 6.4. Table 6.5. Table 7.1. Anisotropic displacement parameters (A^x 1C )3) for Ci7 H2 2 lrN 0 4 (Vinyl-Ir-Py). Hydrogen coordinates ( x 10^) and isotropic displacement parameters (A^x 1 0 3) for irvinylm. Crystal data and structure refinement for C2 oHi8 IrN 0 4 (CH3 -IrT -Py) Atomic coordinates (x 10 ^) and equivalent isotropic displacement parameters (A^x 1 0 ^) for C2 0 H 1 8IrNO4 (CH3 -IrT -Py). Bond lengths [A] and angles [°] for C2 oHi8 IrN 0 4 (CH3 -IrT -Py). Anisotropic displacement parameters (A^x 10 ^) for C2 0 H]8 IrNO4 (CH3 -IrT -Py). Hydrogen coordinates ( x 10^) and isotropic displacement parameters (A^x 1 0 ^) for C2 0 Hi8 IrNO4 (CH3 -IrT -Py). Hydroarylation of olefins by Ir Complexes3. 231 232 253 254 255 258 259 270 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT This dissertation describes the usage of oxygenated ligand sets such as acetylacetone (acac) and tropolone (trop) on Iridium metal for the activation of the C-H bonds of alkanes and arenes and functionalization such as hydroarylation and hydrovinylation of olefins. Chapter 1 introduces various mechanisms of C-H activation and functionalization of alkanes. Some of the notable results from our group that convert alkanes (methane) via electrophilic substitution mechanism to generate alcohols and acid have been summarized. Other class of mechanisms such as Oxidative addition mechanism for C-H activation with Iridium in an oxygenated environment is discussed. Chapter 2 summarizes the first examples of air and water stable O- donor ligated, late metal complexes, (acac-0 ,0 )2 lr(R)(L), based on the simplest P-diketonate, acetylacetonate that are competent for alkane C-H activation. These complexes are efficient catalysts for H/D exchange reactions with alkanes and arenes. Chapter 3 describes the mechanism of the C-H activation reaction with R-Ir-Py, discussed in Chapter 2, with benzene, which has been shown to proceed via four key steps: A) pre-equilibrium loss of pyridine that generates a trans-5-coordinate, square pyramidal intermediate, B) unimolecular, xviii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. isomerization of the trans-5-coordinate to generate a cis-5-coordinate intermediate, C) rate determining coordination of this species to benzene to generate a discrete benzene complex and D) rapid C-H bond cleavage step. Chapter 4 summarizes the usage of the homogeneous Ir catalyst described in Chapter 2 and 3 for the anti-Markovnikov, hydroarylation of unactivated olefins, which has been shown to operate by arene C-H activation followed by olefin insertion. Chapter 5 describes olefin oligomerizations catalyzed by O-donor Ir complexes via a mechanism that involves olefin activation by C-H bond activation as opposed to a Cossee-Arlman type migratory mechanism. Chapter 6 summarizes the synthesis of a O-donor, bis-tropolonato Ir(III) complex that efficiently activates the C-H bonds of alkanes and arenes. The new complex is 50 times faster for catalytic C-H activation than the bis- acetylacetonate O-donor Iridium (III) analogue, described in Chapter 2. Chapter 7 describes the synthesis of a related O-donor, bis-tropolonato Ir(III) organometallic analogue, (trop-0 ,0 )2 lr(Ph)(Py), described in Chapter 4 as an active catalyst for the anti-Markovnikov hydroarylation of unactivated olefins. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 Introduction 1.1 Introduction to C-H Activation The development o f new, selective, energy efficient chemistry for the direct, oxidative conversion of alkanes at temperatures below 250 °C is one of the most challenging and potentially important problems in contemporary catalytic science today. ’’2 g Success in this field could lead to a new paradigm in energy and petrochemical technologies in the 2 1 st century that are environmentally and economically superior and allow the vast reserves of natural gas to be employed directly as feedstocks for fuels and chemicals. However, the direct, catalytic, oxidative conversion of alkanes at lower temperatures to products, such as versatile alcohols, presents many challenges. Suitably designed homogenous complexes have been identified that can coordinate to and cleave the C-H bond of alkanes at low temperatures and with extraordinary selectivity via the C-H activation reaction. 2 This reaction is of particular interest from a scientific as well as an economic viewpoint as it could be utilized to design the next generation of low temperature, selective, hydrocarbon oxidation catalysts based on a generalized catalytic sequence shown in Scheme 1.1. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Scheme 1.1. Generalized Catalytic Scheme For Generating Products Based on the C-H Activation Reaction. Despite the large body of work on the C-H activation reaction that has been generated over the last three decades, to date relatively few catalytic systems that are based on this approach have been reported which allow the direct conversion of alkanes to useful products such as alcohols or other oxygenated products. This is likely due to the challenges associated with designing complexes that A) react by the C-H activation reaction, B) generate functionalized products in a catalytic sequence and C) are stable to the oxidizing conditions required for the oxidative functionalization reaction. Some of the notable homogeneous complexes that catalyze the activation of alkanes and functionalization to products are shown in Scheme 1.2. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ir— CO Shilov Bergm an G raham W atson [(Por)2Rh"]2 C p X H W ayland W hitesides Flood Hartwig G oldberg Lau R 3R ... I ...'P R 3 p r , V Pd(II) Sen u - H Z r = N R Me3P L , PM e3 W. D .Jo n e s w; G reen W olczanski H g (II) P eriana Bergm an G oldm an, Je n s e n , K aska « v s P eriana c CH: l ® Bercaw P eriana Scheme 1.2. Examples of some of the reported C-H activation systems with catalytic systems that generate functionalized products (boxed). Most of the organic chemistry, characterized by mild reaction conditions and high reaction selectivity, can be classified as inner-sphere coordination chemistry at carbon centers; i.e. chemistry that occurs within the first-coordination sphere of three, four and five coordinate carbon species. While the coordination chemistry of carbon in functionalized organic molecules is well-developed, the coordination chemistry of alkanes is much less so and is characterized by reactions with super acids, super bases, free-radicals or carbenes. These very reactive species are either generated under high energy conditions, or with high energy precursors and are 3 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. generally not amenable to efficient syntheses with alkanes as starting materials. The C-H activation reaction can also be classified as a coordination reaction of alkanes with some reactive species, “M”, that takes place within the inner-sphere of the carbon to generate a M-C intermediate without the involvement of high energy species such as ffee-radicals, carbocations or carbanions. An important consequence of the coordination characteristics of the C-H bond activation reaction are low activation barriers and remarkable selectivities. Thus, the C-H activation reaction of alkanes has been reported at temperatures below 0°C and with greater selectivity for primary over tertiary C-H bonds, arene C-H over alkane - y C-H bonds, and reactions of alkanes over alcohols. The high rate of the C-H activation reaction results partly from formation of strong M-C bonds that compensate for the cleavage of the strong C-H bonds (thermodynamics) and availability o f appropriate orbitals on the central atom, M, that ensure good overlap in the transition states (kinetics). Various mechanisms of C-H activation are shown in Scheme 1.3. Coupled with the possibility for oxidative conversion of the M-C intermediate to functionalized products with regeneration of “M”, the C- H activation reaction can provide a basis for the development of the next generation catalysts for the atom and energy efficient conversion of alkanes directly to useful products. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. M ---------X + C --------H M H \ / C Alkane Com plex - x - i t / \ M H 'C M C + H X Electrophilic Substitution - x - f t / \ ^ / j iiii< ■ 11<i■ i< 11ai J-J . V - x / \ M H \ / C Oxidative Addition t > x / M - H ""c M C + H X Sigm a Bond M etathesis x / / \ - V " - M / X H 1,2 Addition X M ""C H ""M X t -> • X M C + H M X M etalloradical Scheme 1.3. Different mechanisms for alkane C-H bond activation. 1.2 C-H Activation by Electrophilic Mechanism Alkane C-H activation can be compared to Wacker reaction which is an inner-sphere process. 2 9 As identified in the Wacker reaction (activation, functionalization and reoxidation), following steps can also be seen in catalytic, alkane C-H activation and functionalization systems that operate with electrophilic catalysts. Thus, the coordination of the double 5 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. bond of the olefin to electrophilic Pd(ll) followed by cleavage of the coordinated double bond by nucleophilic attack of water can be compared to C-H Activation of CH4 by an Electrophilic Substitution (ES) pathway, as shown in Scheme 1.4. En+—sol C-H ACTIVATION C-H coordination CH4 sol .... H Sol CH, n+ C-H Cleavage 1/2 0 2 + 2 H OXIDATION E (n-2)+ FUNCTIONALIZATION CH3OH + H+ Scheme 1.4. C-H bond activation by electrophilic mechanism. 1.2.1 Electrophilic C-H activation by Hg C-H bond activation has been demonstrated with the “soft,” powerful electrophilic species, [XHg]+, generated by dissolving HgX2 salts in strongly 6 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. acidic solvent such as sulfuric acid or Triflic acid. These stable, active oxidation catalysts that operate via the alkane C-H activation reaction utilize metals that can be readily dissolved with suitable oxidants to generate “soft”, electrophilic, oxidizing metal cations in poorly coordinating solvents. Reasoning that “soft”, electrophilic, oxidizing, third or second row metal cations, MX, could form relatively stable covalent bonds to methyl groups and M-CH3 intermediates that can subsequently be oxidized, use of soluble Hg(II) cations in sulfuric acid as an •j effective catalyst for the selective oxidation of methane to methanol. Thus, reaction of methane (500 psig) with 96% sulfuric acid at ~180°C containing 20mM concentration of Hg(HS0 4 ) 2 efficiently generates methanol at concentrations of ~1 M with selectivities >90% and yields of -40% based on added methane, Scheme 1.5. The reaction can be carried out in triflic acid to generate methyl triflate, but in this case the reaction is stoichiometric in Hg(II) which serves as both the catalyst and stoichiometric oxidant. H gS 0 4 CH4 + H2S 0 4 — [7 — r ---- ► CH 3OH + S 0 2 + H20 H2OVJ4 Scheme 1.5. Methane activation by HgS04. As shown in Scheme 1.4, the proposed mechanism of the Hg system is characterized by the same three steps: C-H activation of methane, functionalization 7 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the CH3 -Hg to generate methanol and the reoxidation of the resulting Hg(I) - 2 species. This system seems to be the simplest case of C-H activation of methane by an ES pathway. It is proposed that the soft and powerful electrophilic species, [XHg]+, is generated upon dissolution of HgX2 salts in hot sulfuric acid and readily reacts with methane. It seems likely that the high solvation energy of the proton in sulfuric acid and the formation of the strong Hg-CH3 bond are the driving force of this step. The intermediacy of the CH^HgX species in this step is confirmed by the direct observation of this species in the reaction media.3 , 4 It is also found that approximately the same catalytic activity (TOF) is obtained with the use of CHsHgX directly in place of HgSC>4 . Additionally, under the reaction conditions, independently synthesized CHsHgX is readily converted to both methane, methanol and the reduced Hg2 (II) species (Hg2 X2 ). It is interesting to speculate on how the methanol is formed in this reaction. Kinetic studies show that the rate of formation of CH3 OH is independent of the concentration of added Hg(II). This rules out a free Hg(II)-assisted bimolecular electrophilic substitution pathway as shown in Scheme 1.6 . It is also well known that Hg(II) with strong field ligands such as CH3 - adopts a linear, two coordinate geometry. This would suggest that a concerted reductive elimination is unlikely. On the basis of preliminary theoretical and experimental studies, we propose that the reaction occurs by solvent assisted heterolysis of the [CH3 -Hg]+ species with simultaneous capture of the departing incipient fragment, CH3+, by H2SO4 (or by either HSO4' or H20 ) to generate 8 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CH3 OSO 3 H, or CH 3 OH and Hg(0). The Hg(0) is not observed because Hg(II) is known to react rapidly with Hg(0) to generate Hg2 (II), which is observed. Kinetic studies on [CH 3HgX] in sulfuric acid show that the activation energy of the functionalization step is higher than that for the C-H activation step. The Hg2 (II) species generated in the functionalization step has been shown to reoxidize to Hg(II) in hot sulfuric acid. Experiments suggest that Hg2 (II) is the resting state of the catalyst and suggests that the oxidation step is rate-determining in the overall catalytic cycle. It should be noted that the possibility of a free-radical pathway operating concurrently has been suggested by other researchers. 5 However, based on the observation of high yields and selectivities and that added oxygen does not change the reaction rates or selectivities, we do not believe that free-radical pathways play a significant role in this system. HX * - X H g + - I a+ X H g — C H 3 / \ a+ X H g — C H 3 L HX HX _ U nim olecular solvent B im olecular Electrophilic A ssisted H eterolysis Substitution Scheme 1.6. Possible Transition States for Generation of Methanol from CH 3 HgX. The basis for the high selectivity in this system, confirmed by both theoretical and experimental results, is that the active catalyst [XHg]+ reacts at 9 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. least 1000 times faster with the C-H bonds of methane compared to the those of CH3 OH, which exists primarily as the protonated, or sulfated forms, [CH3 0 H 2 ]+ or CH3 OSO 3 H respectively, in sulfuric acid. This greater reactivity of the methane C-H bonds compared to those of methanol can be traced to substantially lower reactivity of the electrophilic [XHg]+ catalyst towards the C-H bonds of methanol, which due to the electron withdrawing effect of protonation or sulfonation are substantially less electron rich than those of methane. The properties of Hg(II) that lead to this efficient reaction with methane in strongly acidic media can be described as “soft”, “redox active” and “electrophilic”. These properties are also shared by the late third and second row elements of the periodic table due to their high Zeff, high principal quantum number and large size. Consistently, we have found that the cations (bpym)PtCl2 , Au(III), Au(I), Tl(III) and Pd(II) all react readily with methane in strongly acid media to generate methanol presumably via an ES C-H activation reaction mechanism. Consistent with the important electrophilic properties, all of these systems are inhibited by good ligands such as water or methanol or anions such as HSOT or Cf. 10 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.2.2 Electrophilic C-H activation by Pt(ll) Durring the 1970’s Shilov published extensively on the reactions of typically carried out at < 100°C with chloride salts of Pt(II) as catalyst and the chloride salts of Pt(IV) as the oxidant in aqueous hydrochloric acid as solvent. Typical reaction yields, based on added methane are less than 3% with >90% selectivities to methanol and methyl chloride. The reaction was proposed to proceed via a C-H activation reaction to generate alkyl platinum intermediates in reactions with alkanes and later studies by other are consistent with this proposal. 7 This system is one of the first systems that was proposed to operate via the C-H activation reaction and to generate potentially useful functionalized products. The key disadvantages of the Shilov system were the low rates (catalyst tum-over- frequency, TOF of <10' 5 s’1 ), short catalyst life (tum-over-number, TON of < 20) and the use of Pt (IV) as a stoichiometric oxidant. alkanes in aqueous solutions of platinum(II) complexes. 6 The reactions are CH4 + H 2 S 0 4 c h 3o h + s o 2 + h 2o h 2 s o 4 Scheme 1.7. Methane activation by (bpym)PtCl2 11 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. One of the advantages of the use of transition metals for the C-H activation reaction is that, as a result of the multiple available coordination sites, spectator ligands can be utilized to mediate the chemistry of the metal center. Utilizing ligands and alternative oxidants with Pt(II), a very efficient catalyst for the oxidation of methane to methanol based on the C-H Activation reaction was developed. This system, dichloro(K-2-{2,2’-bipyrimidyl})platinum(II), Pt(bpym)Cl2 , is stable and active for the conversion of methane to methanol in concentrated sulfuric acid (Scheme 1.7) with yields of over 70% methanol (based on added methane) with selectivities of >90% with a catalyst TOF of ~10" 3 s' 1 at o 500 psig of methane. The Pt(bpym)Cl2 complex is stable in hot concentrated sulfuric acid for weeks and catalyst TON of > 300 have been observed without decomposition. The chemistry is applicable to higher alkanes and reactions with ethane lead to the generation of ethylene glycol. Reactions with higher alkanes are less selective but oxygenated products can be obtained. The key issues with this system for alkane oxidation are the slow rates (TOF of ~1 s’ 1 are desirable) and the inhibition of the catalyst by water and methanol that limit concentration of products to -1.5 M. It has been estimated that at concentrations below -3 M, the cost of separation of the products from sulfuric acid is not economical. To overcome this separation issue, the possibility of using this stable, active system to generate acetic acid by the oxidative carbonylation reaction shown in Scheme 1.8 is being examined. Initial studies indicate that in the presence of low levels of CO, 12 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the oxidation of methane with the Pt(bpym)Cl2 / H 2 SO4 system can be selectively diverted to generate acetic acid instead of methanol. 9 0 n W n Y \ T p l NWN C O CH4 + C 0 C F 3 S 0 3H> C H 3C ° 2 H + s ° 2 + H20 Scheme 1.8. Acetic acid formation using (bpym)PtCl2 with CH4 and CO. Experimental and theoretical studies are consistent with the Pt(bpym)Cl2 system proceeding via the electrophilic substitution (ES) C-H activation reaction mechanism shown in Scheme 1.9. 1 0 This is likely due to the increased electrophilicity of the metal upon protonation of the bpym ligand. Consistent with the proposed formation of a Pt-CH 3 intermediate, when the reactions are carried out in D2SO4, multiple deuterium incorporation occurs into both methane and methyl products. Experimental and theoretical studies show that the high stability of Pt(bpym)Cl2 complex is likely due to the unique structure and composition of the bpym ligand . 1 0 These studies show that the bpym ligand is protonated in strongly acidic media which prevents decomposition from irreversible formation of insoluble (PtCb)^ or Pt black formation. The presence of two nitrogens in the same aromatic ring in the bipyrimidine ligand, along with the chelate structure, 13 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. allows electronic communication between these N-centers and prevents loss of the ligand that could result from exhaustive protonation of all the ring nitrogens. Consistent with this proposal, while (PtCl2 )« and Pt black are both insoluble in hot sulfuric acid, addition of one equivalent of bpym ligand leads to dissolution and generation of an active and stable catalyst. Significantly, this dissolution is not observed with simpler ligands such as bipyridine. ^ Sol ........... H 2S O 4 mA n > ^ ' " C l - HCI ch 3o h ^ Functionalization]/ h2o - 7 N y N .............. .. H N ^ N ^ P'^ [ S 0 H Sol N^-N. HN N I I .1 2 HSO 4' c h 4 . .. c i -PC '[CH4] 2 HSO4' CH Activation /" N ,., „„C1 ( >tC"" V H H h 2S 0 4 H S 04‘ ? I ,„ o s o 3h -Y ^ C H HN | v -'n 3 OSO3H “ 1^1 u N y N Cl hn""n^ ^CH3 ■ n + H S 04‘ o I, Electrophilic Substitution Oxidation 3 H 2S0 4 S 0 2 + 2 H20 Scheme 1.9. Proposed mechanism for methane oxidation by the Pt(bpym)Cl2/H2S04 . 1.2.3 Electrophilic C-H activation by Au Gold is unique in that in most catalytic systems based on “soft”, redox cations, only one oxidization state of the redox pair is typically active for C-H 14 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. activation. However, both Au 1 and Au111 oxidation states can be active for C-H activation and oxidative functionalization because Au1 (d1 0 , two-coordinate) and III R Au (d , square planar) are isoelectronic and isostructural with the neighboring cations, Hg11 and Pt11 respectively, which are known active catalysts. Consistently, Au1 ", formed by dissolution of AU2 O3 in sulfuric acid 1 1 selectively produces methanol with concurrent production of gold metal. Since sulfuric acid is incapable of oxidizing and dissolving gold metal the reaction is stoichiometric in Au(III). This emphasizes two key issues which must be addressed in developing a catalytic system based on electrophilic Au cations; A) a system must be chosen that can maintain Au in a soluble, cationic state and B) the system must not contain nucleophiles that can coordinate to and inhibit methane coordination to the electrophilic Au cations. It has been identified that selenic acid/sulfuric acid mixtures meet these requirements. Thus, selenic acid (H 2 Se0 4 ) is also almost as acidic as sulfuric acid I2 , !3, and consequently it was considered that neither the acid nor the conjugate base, HSeC>4 _, should inhibit catalysis by blocking coordination of methane to the metal center' Equally importantly SeV I is a more powerful oxidizing agent than SV I (E° = 1.5V Se0 4 2 7 H 2 Se0 3 ; E° = 0.17V S0 4 2- /H2SO3) and, selenic acid is known to oxidize gold metal. 1 3 Recently, solutions of selenic acid in 96 % sulfuric acid containing Au metal have been shown to efficiently oxidize methane to methanol according to the stoichiometry shown in Scheme 1.10. This system is quite efficient and at 180°C with -25 mM of Au and 400 psig of methane, methanol concentrations of 350 mM 15 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. can be obtained with selectivity of 80-95% and -10% yields, based on added methane, are observed. 1 4 With added SO3 (increasing the effective acid concentration) product concentrations of 650 mM, selectivities in excess of 90%, methane conversions of -28% and methanol yields of -25% , based on added methane, can be observed. By carrying out the stoichiometric oxidation of methane to methanol with Au 111 from 100 to 200°C an estimate of the overall activation barrier was determined to be -30 kcal m ol'1 . CH4 + H2Se0 4 — — *► CH3OH + H2Se0 3 + H20 Scheme 1.10. Methane oxidation using Au. Theoretical calculations suggest that the C-H activation steps are rate determining in both cycles as consistent with the requirement for strongly acidic solvent for reaction. However, these energetics do not take into account the relative concentrations of the Au 111 and Au 1 cations in solution. The concentration of Au1 should be significantly lower than Au111 in the presence of excess oxidant, SeV I. The oxidative functionalization step is found to be viable with a Auin-CH 3 intermediate and proceeds with a low barrier (10.7 kcal m o l1 ) via an SN 2 type attack on the methyl group by a free bisulfate ion as was similarly found for reaction of the Hg°-CH 3 and PtIV -CH 3 intermediates. 16 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.2.4 Electrophilic Oxidative Carbonylation of C-H bonds by Pd(ll) After Pt(II), Pd(II) is the other system most examined for the oxidation of alkanes. Thus, Sen reported that Pd(CF3 C C > 2 ) 2 in CF3 CO 2 H will react stoichiometrically with methane to generate the corresponding methyl esters, where Pd(II) plays the role of catalyst and oxidant.1 5 In later developments, it was shown the use of Cu(II)/0 2 /C 0 with Pd black on carbon in CF3 CO 2 H at 85°C allows the catalytic conversion of methane to the methyl ester in ~2% yield based on added methane, at high selectivity and a calculated TOF of 0.02 s'1 and TON of >3000.1 5 The CO in this system is a sacrificial reductant and is consumed in reactions with O2 to presumably generate the active catalyst. While co-reductants could be expected to generate reactive peroxo species that could initiate free- radical reactions that would be characteristic of the high reactivity observed at the relatively low temperatures (~85°C), studies by Sen suggests that free radicals are not involved in this Pd catalyzed reaction. Sen has also shown that Rh salts in a complex system containing CO in heptafluorobutyric acid oxidize methane to both methanol and acetic acid. The oxidation of methane to methanol, ethanol and acetic acid were also reported with this Rh system. Recently, Herrmann reported a related bis-carbene Pd(II) based system that oxidized methane to the ester in CF3 CO 2 H at 80°C using persulfate (K2 S2 O 8) as the stoichiometric oxidant. Yields 17 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the methyl ester of -4% based on added methane (assuming >90% selectivity) and TOF of 0.06 s" 1 were calculated from a reported TON of 3 0 .1 6 Pd(II) will react with methane in sulfuric acid to generate methanol with O low efficiency. However, in addition to methanol, we recently reported that the PdS0 4 /H 2 S0 4 system will efficiently catalyze the oxidative condensation of two methane molecules to generate acetic acid 1 7 as shown in Scheme 1.11. There have been reports of Pd(II) to catalyze the coupling of methane with CO , 1 8 CO2 1 9 * y a or carboxylic acids to generate acetic acid. However, what is interesting about the PdSC>4 /H 2 S0 4 system for the oxidative condensation of methane to acetic acid is that this reaction proceeds without the need fo r added CO or other carbon sources. Labeling studies employing 1 3CH4 show that 1 3CH 3 1 3C C > 2 H is the major product and unambiguously show that both carbons of acetic acid are derived from the added methane in this one-pot reaction. This is intriguing because this is formally an eight-electron process and clearly cannot proceed via one-step. Pd(ll) 2 CH4 + 4 H2S 04 -------- — — ► CH3COOH + 4 S 02 + 6 H20 H2 SO 4 Scheme 1.11. Methane oxidation to acetic acid using Pd. The reaction is reasonably efficient and -12% yield of acetic acid based on added methane with a selectivity of -90% to acetic acid can be obtained. The 18 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reaction stops after ~ 2 0 turnovers presumably due to catalyst deactivation and the formation of Pd(0). Product formation versus time is shown in Figure 1.1. 80 2 0 - • CO X = OH, 0 S 0 3H (28) 4 16 0 8 12 Time (hr) Figure 1.1. Time dependent product formation for Pd catalyzed oxidative condensation of methane to acetic acid. This direct, oxidative condensation of methane to acetic acid in one-pot could be competitive with the current three step, capital intensive process for the production of acetic acid based on methane reforming to CO, methanol synthesis from CO and generation of acetic acid by carbonylation of methanol. However, key improvements required with the PdS0 4 /H 2 S0 4 system will be to develop more stable, faster and selective catalysts. While it is possible that sulfuric acid could be utilized industrially as a solvent and oxidant for this reaction, it would be desirable to replace sulfuric acid with less corrosive materials. Based on the experimental and theoretical studies of the reaction mechanism, it is believed that the reaction proceeds via an ES C-H activation reaction to generate Pd-CH 3 intermediates, followed by an oxidative carbonylation 19 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 + reaction. Interestingly, it is possible that the catalyst is a Pd(CO)* species that may be generated by slow overoxidation of the methanol produced from the in-situ 1 oxidation of methane. Some evidence for this is that added CO as well as added 1 o i 'j CH 3 OH (in separate experiments) both react with CH4 to generate 1 2CH 3 ,3 C 0 2 H. Moreover, addition of 1 2CH 3 0 H to a ,3 CH4 reaction mixture generates primarily 1 3CH 3 1 2C0 2 H. Interestingly, while low levels of CO (added or produced by in situ methanol oxidation) is incorporated into the generation of acetic acid, addition of higher concentrations of CO essentially shuts down the reaction and rapid formation of Pd black and CO2 is observed. These observations are all consistent with the proposed tandem-catalysis mechanism shown in Scheme 1.12. Central to this proposal is that the reaction proceeds via several parallel reaction steps as might be expected for a formal eight electron coupling of two methane molecules to acetic acid. The observation that the reaction is effectively stopped by high concentrations of added CO but proceeds at low levels of CO can be explained if the rate limiting step is reoxidation of Pd(0) by sulfuric acid. From independent experiments we have found that under high CO pressure conditions the rate of formation of Pd(0) is much higher that the reoxidation of Pd(0) by sulfuric acid and the observed reaction inhibition under high pressures of CO is most likely due to loss of the active Pd(II) catalyst. However, under low CO conditions, the rates of Pd(0) reoxidation by sulfuric acid and Pd(II) reduction (from reactions with methane, methanol as well as CO) are presumably balanced and the reaction can be 20 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. maintained. These results are intriguing and suggest that CO insertion is particularly facile under these conditions of C-H activation. This could suggest that oxidative carbonylation of alkanes may be a particularly effective means of coupling C-H activation with a useful M -C functionalization reaction. This chemistry has recently been revisited, verified, and extended with the use of Cu(II) 0 1 as a cooxidant by Bell et al. CO XPd-CCH XPd-CH CH. PdX- * ■ Pd Metal Pd(0) SO CO Pd-CO CO CO Scheme 1.12. Proposed tandem catalysis mechanism for the oxidative condensation of methane directly to acetic acid. 21 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.3 C-H Activation by Oxidative Addition Mechanism Indeed, the first indications for C-H activation came from the reactions with Iridium centers especially of arylphosphine ligands via orthometalation reactions. Bergman and Janowicz were the first ones to show the intermolecular C-H activation reactions using Cp*Ir(PMe3 )H2 . Using photolysis, a very highly reactive molecule was generated after the loss of hydrogen, which would then react with alkanes to yield alkylhydrido Iridium complexes (Scheme 1.13). Other notable systems based on Iridium for C-H activation are shown in Scheme 1.13 and all have been shown to follow an oxidative addition mechanism. All these complexes are efficient C-H activation catalyst as evident fromH/D exchange but lack functionalization. H Bergman Graham Bergman Carmona Scheme 1.13. Some Notable C-H Activation Complexes based on OA Mechanism. 22 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.3.1 Functionalization based on Oxidative Addition Mechanism Catalysts based on ES pathways are not the only stable, active systems that operate by alkane C-H activation and functionalization. In the case of the (PCP)IrH 2 system, which is the one of the most efficient system known for the low temperature dehydrogenation of alkanes (conversion of alkanes to olefins, Scheme 1.14)2 2 C-H activation has been shown to operate by an OA, (3-hydride elimination sequence. This catalyst is quite stable and reaction of alkanes can be carried out at reasonable rates at temperatures above 200°C where both hydrogenation (transfer of hydrogen to an olefin as hydrogen acceptor) and “acceptorless” dehydrogenation (loss of hydrogen gas) is observed. While many systems are known that can cleave C-H bonds by OA mechanism and may also be capable of (3-hydride elimination reactions, it is likely that an important property of the catalyst is the unique, high thermal stability imparted by the tri-dentate, PCP ligand and strong Ir-C and Ir-P bonds. Scheme 1.14. Ir(PCP)H 2 catalyzed dehydrogenation of Alkanes. 23 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. As shown in Scheme 1.1, the general scheme for generating functionalized products involves C-H activation followed by oxidation or insertion of small molecules (CO or olefins). Based on differences in mechanism of Electrophilic substitution (ES) and oxidative addition (OA) mechanism, one could expect some novel selectivity (regio, stereo, enantio) in the products. An example where one can witness this difference is the Friedel craft’s based alkylation, where one observe 1 0 0 % branched product, as the mechanism proceeds via carbocations (Scheme 1.15). Scheme 1.15. Friedel Craft’s Alkylation. Whereas novel selectivity is observed in the case of Murai reaction, 2 3 which is the hydroarylation of olefins, proposed to go via chelation assisted, C-H activation. This reaction is catalyzed by Ru(H 2 )(CO)(PPh3 ) and the mechanism is shown in Scheme 1.16. This complex is very high yielding reaction and results primarily in linear alkylated benzenes. One of the limitations is the requirement of the acetyl group which is needed for the reaction to proceed. As shown in mechanism, this assists in C-H activation of the benzene followed by insertion of the olefin. 24 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Q CH, + <sJ?Xv'S i(O E t)2 1 : 1 ratio R u (H )2(C O )(P P h 3)3 T o lu en e 135 C , 1 h r S i(O E t)2 H ig h Y ie ld RuH2(C O )(PPh3)3 ? Ru R u Scheme 1.16. Murai Reaction Catalyzed by Ru Complex. 1.3.2 Iridium in an Oxygen ligand Environment Most of the catalysis using Iridium compounds has typically exploited neutral, soft donor ligands such as phosphines, arsines, cyclopentadienes, etc. Iridium in atypical environment such as oxygen could support very active catalysts and may actually be more akin to the environment that exists around a metal when it is supported on an oxide support. Finke’s and Klemperer’s2 4 group have attached polyoxoanions on Iridium metal centers and suggest some novel reactivity with molecular oxygen to yield a 25 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. oxometallacyclobutane unit derived from insertion of oxygen into the M-C bond (Scheme 1.17). The mechanism has been proposed through coordination of oxygen, which then bridges with another Iridium center. This undergoes internal oxidation whereby the oxygen atoms are inserted into Ir-C bonds to complete the transformation. This suggests that placing an Iridium metal center in this environment might provide the platform to do some unusual catalytic reactions. Analogous oxygen atom transfer from the Ir(III) oxo complex, [C5 Me5 )Ir(0 )]2 , to PPh3 has also been observed. 2 5 2 © h o o X -R a y 0 2 1,2 d ic h lo ro e th a n e H O O 2 © X -R a y M e c h a n is m / 0 2 2© / Ir(P 30 9) O. 'O 4 © O . N . 4 © Ir(P 3O o) 2© X -R a y Scheme 1.17. Oxygen transfer on Iridium center using polyoxoanion (Klemperer) 26 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Crabtree has also investigated the oxygen donor ligand effect on the Iridium centers using the ligand “triso” (HC(Ph2P=0), shown in Scheme 1.18. Crabtree’s group showed that this ligand could stabilize the Iridium in not only +1 oxidation state but also in +3 and +5 as well. Well all these cases involving insertion and stabilization of high oxidation state Iridium complexes suggest that lone pair donation might be involved and help in C-H activation and oxidation chemistry. There are lots of oxygen donor ligands available in literature as shown in Scheme 1.19. These ligand sets provide an oppourtunity to control or tune the reactions of interest either by changing the electronics or by changing the sterics. For example, one might expect a difference in reactivity with acetylacetone (acac) and tropolone, on the basis of their different bite angle. Given the ubiquity of the OA mechanism, most of the systems shown in Scheme 1.2 operate by this mechanism, it would be desirable to identify complexes that operate via this mechanism and that are stable to the protic, thermal, oxidizing conditions required E s te r u e la s , e t. a l., O r g a n o m e t a l l i c s , 1 9 9 6 , 8 2 3 . T a n k e , R . S .; C r a b tr e e , R . H . B e r g m a n , e t. a l., O r g a n o m e ta llic s , 1 9 9 1 , 4 1 5 . J . A m . C h e m . S o c . 2 0 0 0 , 1 8 1 6 . Scheme 1.18. Reported Examples of Ir(V) Complexes. 27 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. for functionalization of alkanes to alcohols or other insertion reactions such as olefin. In such an effort to develop new stable motifs that operate via the OA pathway and that may lead to the development of new, stable oxidation catalysts, we have been exploring the use of O-donor ligands. AcAc Tropolone Ethyl Maltol PR, HO Klaui's Ligand Grim's Triso Crabtree's Hydroxy Catecholates Acetophenone Calixarenes Scheme 1.19. Examples of Oxygen donor Ligands. Significant progress has been made in incorporating the C-H activation reaction into a catalytic sequence to develop stable, active, selective systems for the conversion of alkanes to functionalized molecules. Considering the state of knowledge today, while there is some understanding of the C-H activation reaction in poorly coordinating media such as strong acid solvents, less is known about facilitating the C-H activation reaction of alkanes in coordinating media such as 28 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. water, and significantly less is understood of the other required catalytic steps that involve redox reactions. In particular, a greater level of fundamental understanding is required to develop catalysts that A) react with alkanes via the C-H activation reaction at useful rates in desirable solvents such as water, B) generate M-R intermediates that can be oxidatively functionalized at useful rates with practical oxidants to generate a range of useful products, C) show broader compatibility between the C-H activation and the oxidative functionalization steps, D) are thermally stable to the reaction conditions required for generating useful products, E) are selective for generation of the desired products and F) utilize practical oxidants that directly or indirectly utilize oxygen as the final oxidant. Developing a basic understanding of these steps could lead to the development of the next generation of hydrocarbon conversion catalysts and a new paradigm in energy and petrochemical technologies. 29 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.4 References (1) (a) Methane Conversion by Oxidative Processes, Wolf, E. E.; Ed.; Van Nostrand Reinhold; New York, 1992. (b) Catalytic Activation and Functionalization o f Light Alkanes. Advances and Challenges, Derouane, E. G.; Haber, J.; Lemos, F.; Ribeiro, F. R.; Guisnet, M.; Eds.; Nato ASI Series, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1997. (c) “Catalytic Conversion of Methane to More Useful Chemicals and Fuels: a Challenge for the 21st Century.” Lunsford, J. H. Catalysis Today, 2000, 63, 165. (d) Periana, R. A. C&E News, 2001, 79, 287. (e) Natural Gas Conversion II, Curry-Hyde, H. E.; Howe, R. F. Eds. Elsevier, New York, 1994. (2) (a) Amdtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H. Acc. Chem. Res. 1995, 28, 154. (b) Shilov, A. E.; Shulpin, G. B. Activation and Catalytic Reactions o f Saturated Hydrocarbons in the Presence o f Metal Complexes, Kluwer Academic; Dordrecht, 2000. (c) Jia, C.; Kitamura, T.; Fujiwara, Y. Acc. Chem. Res. 2001, 38, 633. (d) Jones, W. D. Acc. Chem. Res. 2003, 36, 140. (e) Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2001, 19, 2437. (f) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507. (g) Periana, R. A.; Bhalla, G.; Tenn III, W. J.; Young, K. J. H.; Liu, X. Y.; Mironov, O.; Jones, C.; Ziatdinov, V. R. J. Mol. Cat. A- Chem. 2004, 220, 7. (3) (a) Snyder, J. C.; Grosse, A. V. US Patent 2493038, 1950. (b) Periana, R. A.; Taube, D. J.; Evitt, E. R.; Loftier, D. G.; Wentcek. P. R. Science, 1993, 259, 340. (c) Periana, R. A.; Taube, D. J.; Evitt, E. R.; Loftier, D. G.; Wentcek, P. R.; Voss, G.; Masuda, T. Stud. Surf. Sci. Catal. 1994, 81, 533. (4) CH 3 HgX species is also an intermediate of sulfonation of methane in oleum. See; Sen, A.; Benvenuto, M. A.; Lin, M.; Huston, A. C.; Basickes, N. J. Am. Chem. Soc. 1994, 116, 998-1003. (5) Basickes, N.; Hogan, T. E.; Sen, A. J. Am. Chem. Soc. 1996,118, 13111. (6) (a) Shilov, A. E. Activation o f Saturated Hydrocarbons by Transition Metal Complexes, Riedel, Dordrecht, 1984. (b) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879. (7) For Example see; Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507. (8) Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T.; Fujii, H. Science, 1998, 280, 560. 30 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (9) Periana, R. A.; Mironov, O.; Taube, D.; Bhalla, G.; Jones, C. Science, 2003, 301,814. (10) (a) Kua, J.; Xu, X.; Periana, R. A.; Goddard, W.A. Ill Organometallics, 2002, 21, 511. (b) Xu, X.; Kua, J.; Periana, R. A.; Goddard, W.A. Ill Organometallics, 2003, 212, 2057. (11) (a) Wickleder, M. S.; Esser, K. Zeitschrift fuer Anorganische und Allgemeine Chemie, 2002, 62, 8911; (b) Wickleder, M. S.; Buchner, O. Zeitschrift fuer Naturforschung, B: Chemical Sciences, 2001, 56, 1340. (12) (a) McDaniel, D. H.; Steinert, L. H. J. Am. Chem. Soc. 1966, 88, 4826; (b) Wasif, S. J. Chem. Soc. A, 1967, 1, 142; (c) Hussein, M. A.; Iskander, G. M.; Nour, M. M.; Wasif, S.; Zeidan, H. M. J. Chem. Soc., Dalton Trans: Inorg. Chem., 1982, 9, 1645. (13) Greenwood, N. N.; Eamshaw, A. Chemistry o f the Elements, second edition, Butterworth-Heinemann, Oxford, 1997, p. 782. (14) Jones, C.; Taube, D.; Ziatdinov, V. R.; Periana, R. A.; Nielsen, R. J.; Oxgaard, J.; Goddard III, W. A. Angew. Chem. Int. Ed., 2004, 43, 4626. (15) (a) Sen, A. Acc. Chem. Res., 1998, 31, 550. (b) Lin, M.; Hogan, T.; Sen, A. J. Am. Chem. Soc. 1997, 6048. (16) Muehlhofer, M.; Strassner, T.; Herrmann, W. A. Angew. Chem. Int. Ed. 2002, 41, 1745. (17) Periana, R. A.; Mironov, O.; Taube, D.; Bhalla, G.; Jones, C. Science, 2003, 301, 814. (18) (a) Olah, G. A.; Molnar, A. Hydrocarbon Chemistry (Wiley, New York, 1995). (b) Lin, M.; Sen, A. Nature, 1994, 368, 613. (c) de Rege, P. J. F.; Gladysz, J. A.; Horvath, I. T. Adv. Synth. Catal. 2002, 344, 1059. (19) Nizova, G. V.; Shul'pin, G. B.; Suss-Fink, G.; Stanislas, S. Chem. Commun. 1998, 1885. (20) Reis, P. M. Angew. Chem., Int. Ed. 2003, 42, 821. (21) Zerella, M.; Mukhopadhyay, S.; Bell, A. T. Chem. Commun. 2004, 1948. (22) (a) Xu, W; Rosini, G. P.; Krogh-Jespersen, K; Goldman, A. S.; Gupta, M; Jensen, C. M.; Kaska, W. C. Chem. Commun. 1997, 23, 2273 (b) Liu, F; 31 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S. J. Am. Chem. Soc. 1999, 121, 4086. (c) Kanzelberger, M; Singh, B; Czerw, M; Krogh- Jespersen, K; Goldman, A. S. J. Am. Chem. Soc. 2000, 122, 11017. (d) Goettker-Schnetmann, I.; White, P.; Brookhart, M. J. Am. Chem. Soc. 2004,126, 1804. (23) (a) Murai, S. Nature 1993, 366, 529. (b) Kakiuchi, F.; Murai, S. Acc. Chem. Res. 2002, 35, 826. (24) Day, V. W.; Klemperer, W. G.; Lockledge, S. P.; Main, D. J. J. Am. Chem. Soc. 1990, 2031. (25) McGhee, W. D.; Foo, T.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc. 1988,110, 8543. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 Alkane and Arene C-H Activation Catalyzed by an O-Donor, bis-acetyiacetonato Iridium (III) Complex 2.1 Introduction As discussed in Chapter 1, the oxidative conversion of fossilized hydrocarbons to energy and useful materials are foundational technologies. Currently, these conversions operate at high temperatures that ultimately lead to excessive emissions and high costs. Catalysts based on C-H activation1 show potential for the development of new hydrocarbon conversion chemistry that can be substantially more efficient given the lower temperature and enhanced selectivity. While many alkane and arene C-H activation systems are known, relatively few have been reported to allow efficient catalysis to generate functionalized products. Some of the most efficient catalysts reported for the low-temperature, selective conversion of hydrocarbons directly to useful products, for example alcohols, alkyl arenes and carboxylic acids, generally operate by coupling of the C-H activation and functionalization steps as shown in Scheme 1.1. Some key challenges to designing effective catalysts that operate via this sequence of reactions are: a) avoiding inhibition of the C-H activation reaction by desirable solvents, products and reactants, b) generating functionalized products in a catalytic sequence and c) stabilizing the catalysts to the conditions required for functionalization.lh 33 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Complexes based on Ir are among the most active reported for the C-H activation reaction. We have been investigating the design of homogeneous catalysts based on Ir and other late transition metal complexes4 using O-donor ligands such as acetylacetonate (acac),5 tropolone,6 aryloxides,7 catechols,8 hydroxyacetophenone, etc., to stabilize the complexes to the reaction conditions required for generating functionalized products. Compared to the N, C or P-donor ligands generally utilized for C-H activation,9 O-donor ligated complexes may have the potential for higher thermal, protic and oxidant stability given the expected covalent character of oxygen-metal bonds with the late transition metals and the lower basicity of oxygen.1 0 Another key reason for study of these ligands is that the known Tt-donor,1 1 electronegative and “hard” characteristics of O-donor ligands could lead to electronic differences at the metal center that result in significant changes in chemistry compared to complexes based on N, P and C-donors. Thus it could be anticipated that O-donor ligands might: a) facilitate access to higher oxidation states, via hard/hard interactions or 7t-donation during catalysis that may be required for the functionalization step shown in the generalized catalytic cycle, Scheme 1.1 , b) moderate the electron density, by the interplay of a-withdrawing and 7C-donating properties at the metal center and reduce the possibility of the solvent, product or reactant inhibition that is generally observed with very electron-rich or electron-poor metal centers and c) facilitate C-H activation reactions with electron-rich, late transition metal complexes that take place via 34 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 9 “oxidative addition” or insertion pathways. Recent theoretical and experimental evidence has been presented for C-H activation reactions facilitated by 7U-donation through phenyl-Ir interactions.1 3 As O-donor ligands directly attached to a metal center can be efficient 71-donors,1 1 it is likely that O-donor, d6, 5-coodinate, square pyramidal motifs would exhibit ground state destabilization from non-bonding O- p7t to M-djr, filled-filled repulsions or so-called “7 1-conflict” n ’ 1 4 as well as stabilization of the non-bonding O-pJi electrons by back interactions into the formally empty metal-d7t orbitals when the M-C and M-H bond are formed by C-H Activation, either in a transition state or as an intermediate (the metal is now formally d4, Ir(V)), Scheme 2.1. This stabilization is analogous to the pi-donor effects of alkoxide ligands with late transition metals that facilitate binding of CO or oxidative addition to H 2 trans to the O-donor ligand as shown by Caulton.1 1 Destabilization Stabilization Filled 0-p-7t to filled M -d- n repulsion Filled 0-p-7r to empty M -d- n Interaction Scheme 2.1. Schematic illustration of possible 7t-donor involvement of the non bonding electrons on O-donor ligands in C-H Activation reactions with oxidative addition character. 35 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Given these considerations, it was important to establish whether well- defined, O-ligated late transition metal complexes could activate alkane C-H bonds. Herein, we report a well-defined, O-ligated, late transition metal Ir complex that can activate alkane C-H bonds. 2.2 Results 2.2.1 Synthesis of CH3 -Ir(III)(acac-0,0)2 (Py) The Methyl-Ir(III) complex, CH 3 -Ir(III)(acac-0 ,0 )2 (Py), CH3 -Ir-Py, have been used as the model complex to show the reaction with alkanes (RH) via C-H activation to generate the corresponding alkyl-Ir complexes, R-Ir-Py, (RH = cyclohexane and n-octane). CH3 -Ir-Py has been synthesized from Ir(acac- C3 )(acac-0 ,0 )2 (H2 0 ), Acac-Ir-H 2 0 , by treatment with (CH 3 )2 Hg or (CH 3 )2Zn to provide [CH 3 -Ir ] 2 followed by addition of pyridine, in good yields (70%) as shown in Scheme 2.2. Complex CH3 -Ir-Py is air stable and has been fully characterized by 'H, 1 3C-NMR spectroscopy, elemental analysis and X-ray structural studies. ORTEP drawing is shown in Figure 2.1. M eoH a , or M e2Z n C H 3 [CH3 -Ir]2 Scheme 2.2. Synthesis of CH3 -Ir-Py 36 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.1. ORTEP drawing of CH 3 -Ir-Py. Thermal ellipsoids are at the 50% probability level. Hydrogen atoms omitted for clarity. Selected bond lengths (A°): Irl- C4, 2.041(6); Irl-N l, 2.181(4). 2.2.2 Stoichiometric C-H Activation of Alkanes and Arenes Heating CH 3 -Ir-Py in neat cyclohexane at 130°C for 3h yields the corresponding Ir-cyclohexyl complex, CeHn-Ir-Py, as shown in Scheme 2.3. 'H- NMR analysis of the crude reaction mixture has shown that the reaction is essentially quantitative. Complex C 6 H n-Ir-Py, could be isolated from the reaction mixture and fully characterized by *H and 1 3C-NMR spectroscopy and elemental and X-Ray structural analyses. An ORTEP drawing of CeH n-Ir-Py is shown in Figure 2.2. 37 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CH 130°C + RH -► - CH N. N. R-lr-Py H RH = H Scheme 2.3. Stoichiometric C-H Activation with CH3-Ir-Py Consistent with the stoichiometry shown in Scheme 2.3, when the reaction is carried out in a sealed NMR tube with cyclohexane-J/2 , mono-deuterated methane is observed based on gas chromatography-mass spectroscopy (GC-MS) analysis. These observations unambiguously show that complexes based on the O- ligated, (acac-0 ,0 )2 lr(III) motif can activate alkane C-H bonds. To our knowledge, this is the first well-defined, late-metal, O-donor ligated complex that shows this reactivity for alkane C-H activation. 38 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 2.2. ORTEP drawing of CeHn-Ir-Py. Thermal ellipsoids are at the 50% probability level. Hydrogen atoms omitted for clarity. Selected bond lengths (A°): Irl- C4, 2.060(7); Irl-N l, 2.225(6). Other hydrocarbon substrates that react by C-H activation with CH 3 -Ir-Py are shown in Scheme 2.3. Thus, heating a solution of CH3 -Ir-Py in mesitylene at 130 °C for 3 h results in the formation of a single new species. ]H and 1 3 C NMR spectroscopy analysis of the crude mixture in CDCI3 shows clean formation of the Ir-mesityl, R-Ir-Py, R = mesityl, (Scheme 2.3) in which only the benzylic C-H bond is activated. The reaction with benzene and acetone cleanly provided the corresponding Ir-phenyl and Ir-acetonyl derivatives. These materials have also 1 1 T been isolated and characterized by H, C NMR spectroscopy and elemental analysis. The reaction with n-alkanes, exemplified by n-octane, could not be fully 1 1 characterized and H and C NMR spectroscopy shows that several Ir-octyl products (presumably resulting from 1° and 2° C-H bond activation) are produced that could not be separated and quantified. 39 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. [CH3-Ir]2 is found to be much more reactive for the reaction of alkanes, reacting at much more lower temperatures. For example, [CH3-Ir]2 reacts with mesitylene within 3 h at 100°C with mesitylene as solvent to yield [Mes-Ir]2 as a dinuclear species as clearly evident from 'H NMR spectroscopy as shown in Scheme 2.4., which reacts with pyridine at room temperature to give Mes-Ir-Py in quantitative yields. Although with substrates such as cyclohexane, no clear dinuclear species is formed, hence pyridine was used in all these studies to keep a track of ligand. [CH3-Ir]2 [Mes-Ir]2 Mes-Ir-Py Scheme 2.4. Stoichiometric C-H Activation with [CH3-Ir]2 2.2.3 Proposed Mechanism for C-H Activation The alkane C-H activation reactions (Scheme 2.3) in the corresponding alkane solvent are retarded by added free pyridine. As shown in Scheme 2.5, a plausible mechanism for the C-H activation may involve initial loss of pyridine, trans to cis isomerization to generate a 5 coordinate, cw-intermediate, cis-2, that 40 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cleaves alkane C-H bonds via a 7-coordinate oxidative addition intermediate or transition state, 3, or sigma-bond metathesis transition state (not shown) . 15 Details of these mechanistic studies are provided in next chapter. 1-R HY DY 3-D RD RH Scheme 2.5. Proposed mechanism for the C-H activation of alkanes and H/D exchange reactions catalyzed by CH3-Ir-Py 2.2.4 Catalytic H/D Exchange Having established that O-ligated, late metal complexes can stoichiometrically activate the C-H bonds of alkanes, we examined the catalytic activity o f this class of complexes with hydrocarbons. 41 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cat RH + DY w RD + HY Scheme 2.6. H/D Exchange Analysis by GC/MS and NMR spectroscopy show that CH3 -Ir-Py efficiently catalyze H/D exchange between C6 D6 and hydrocarbons, including alkanes, according to Scheme 2.6, RH = hydrocarbon, Y = C6 D 5 (Table 2.1, entries 1 - 5). The reactions are clean and no catalyst decomposition is observed, showing that these systems are thermally stable and activate alkane C-H bonds reversibly. ]H NMR analysis of the crude reaction mixtures after heating shows that the resting state of the catalyst in the reaction with C6 D 6 is Ph-d5 -Ir-Py Control experiments with added drops of Hg metal (to test for catalysis by reduced metals) show no change in rate. Consistent with the presumption of stoichiometric 1 -j C-H activation reactions with n-octane, C NMR analysis of the C6 D6 /n-octane reaction mixture after catalysis shows deuterium incorporation into all the positions of n-octane with higher selectivity for the 1 ° positions. 42 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.1. H/D exchange With CeDg Catalyzed by CH3 -Ir-Pya Entry No. Substrate TONb TOFb (*10' 3 sec'1 ) 1 Cyclohexane 240 10 2 Methane 123 1.7 3 n-Octane 43 2.9 4 Benzene 1210 675 5 Acetone 72 43 a All reactions were carried out at 180°C using CH3 -Ir-Py as the catalyst (2 - 20mM). b See experimental section for details. Consistent with the expected protic stability of O-donor ligands preliminary results show that CH3 -Ir-Py is thermally stable (to loss o f the O- ligated acac ligands) in protic media such as D2 O, CH3 CO2 D, and CF3 CO2 D and remains active for C-H activation and catalysis in these media. Thus, reaction of 0.1 ml of mesitylene with 1 mL of CF3 CO2 D containing 10 mM o f CH3 -Ir-Py show H/D exchange (according to Scheme 2.6, Y = CF3 CO2 , RH = mesitylene) of only the benzylic C-H bonds with a TOF of ~10' 3 s' 1 at 160°C. These H/D exchange reactions in protic media are being examined in greater detail. In summary, we demonstrate that well-defined, late metal, O-ligated complexes are competent for alkane C-H activation, exhibit high thermal and protic stability and are efficient catalysts for H/D exchange reactions with alkanes. 43 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. We are currently investigating the oxidative functionalization of O-donor M-R complexes and new O-donor complexes that activate C-H bonds. 2.3 Experim ental Section G eneral Considerations: All air and water sensitive procedures were carried out either in a Vacuum Atmospheres inert atmosphere glove box or using standard Schlenk techniques. All solvents used were reagent grade or better. THF was dried over sodium/benzophenone ketyl and distilled under nitrogen. All deuterated solvents (Cambridge Isotopes), HgMe2 (Strem), and ZnMe2 (Aldrich) were used as received. GC/MS analysis was performed on a Shimadzu GC-MS QP5000 (ver. 2) equipped with cross-linked methyl silicone gum capillary column (DB5). The retention times of the products were confirmed by comparison to authentic samples. NMR spectra were obtained on a Bruker AC-250 spectrometer at 250.13 MHz (!H) and 62.90 MHz ( 1 3C) or on a Bruker AM-360 spectrometer at 360.14 MHz (!H) and 90.57 MHz ( 1 3C). All coupling constants are reported in units of Hz. Elemental analyses were done by Desert Analytics Laboratory; Arizona. 44 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. n H 1. Synthesis of [C-acac-Ir(0,0-acac)2(H2 0 )] (Acac-Ir- H2 0 ): To a round-bottom flask equipped with a reflux condenser vented to an oil bubbler IrCl3 (H2 0 )x (1 g, 2.82 mmol, 54.11% Ir), 10 mL of 2,4-pentanedione (9.75 mmol) and 1 g of NaHCC>3 (11.9 mmol) were added. The mixture was heated to gentle reflux with stirring for 48 h. During this time a yellow solid precipitated from solution. The reaction mixture was cooled to room temperature and the solid was collected on a frit. The solid was washed thoroughly with dichloromethane to remove excess of 2,4-pentanedione and Ir(acac)3 . The remaining yellow solid was dissolved in -200 mL H20 at room temperature under vigorous stirring and the resulting solution was filtered. The solution was concentrated under vacuum to yield 500 mg (35%) of title complex as a yellow-orange powder. 'H NMR (D2 0): 8 5.53(s, 2H, O-acac CH), 5.47(s, 1H, C-acac CH), 1.90(s, 12H, O-acac CH3 ), 1.73(s, 6 H, C-acac CH3 ). '^ { 'H } NMR (D2 O/10%CD3 OD): 8 217.9(C-acac, C=0), 188.0(O-acac, C=0), 104.5(O-acac, CH), 50.0(C-acac, CH), 33.2(C-acac, CH3, 28.3(0-acac, CH3 ). Anal. Calcd: C, 35.50; H, 4.57. Found: C, 35.20; H, 4.39. 45 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2. Synthesis of [CH3 -lr(0,0-acac)2 (Py)] (CH3-Ir-Py) using ZnMe2 : In the glove box a re-sealable Schlenk tube was charged with Acac-Ir-H2 0 (342 mg, 0.674 mmol) and THF (100 mL) was added. To this was added a toluene solution of ZnMe2 (2.0 M toluene, 740 pL, 1.48 mmol). The Schlenk tube was then sealed, removed from the glove box, and placed in a 90°C oil bath for 4h. The resulting slightly cloudy orange solution was cooled to room temperature whereby a small amount of a white precipitate settled out. The solution was poured onto water (200 mL), extracted with CH2CI2 (2 x 100 mL), and then dried over Na2S 0 4. Filtration followed by removal of solvent in vacuo yielded a yellow solid in 75-80% yield, which was characterized as [CH3 -Ir]2. Dissolution of the yellow solid with a minimum of pyridine, followed by gentle warming, resulted in the title compound, CH3-Ir-Py. After removal of excess pyridine, the product was recrystallized from dichloromethane and hexanes. Alternative synthesis of CH3-Ir-Py using HgMe2: To a mixture containing 100 mg (0.197 mmol) of Acac-Ir-H2 0 in 10 mL of methanol, 60 pL (0.25 mmol) of dimethylmercury (HgMe2) was added. The mixture was heated at 80°C for 2h. The solvent was removed in vacuo. The resulting orange precipitate was treated with excess of pyridine and gently warmed. Excess pyridine was removed under vacuum. CH3-Ir-Py was recrystallized from dichloromethane and hexanes at 253K and obtained in 60-70% yield. 46 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ]H NMR (CDCI3 ): 5 8.44(dd, 3 JH H = 5.00, 4 JH h = 1.5, 2 H, o -H py), 7.81(tt, 3 JH H = 8.0, 4 Jhh = 1.5, lH ,p -//p y ), 7.37(t, 3 JC H = 6.50, 2H, m -tfpy), 5.29(s, 2H, O-acac- C3tf), 1.81(s, 12H, 0-acac-CH3 ), 1.65(s, 3H, CH3 ). 1 3C{]H} NMR (CDC13 ): 5 183.6(0-acac, C=0), 149.9(o-C Py), 137.2(p-C Py), 125.2(w-C Py), 103.0(0-acac, CH), 27.1 (O-acac, CH3 ), -27.1(CH3 ). Analysis (Calc.): C, 39.66; H, 4.58; N, 2 89 Found: C, 39.88; H, 4.55; N, 2.79. 3. Synthesis of C 6 H n-Ir-Py: A re-sealable Schlenk tube was charged with CH 3 -Ir-Py (29.9 mg, 0.062 mmol) and cyclohexane (5 mL). The resulting suspension was thoroughly degassed before being placed under an atmosphere of Ar. The tube was sealed and then heated to 130°C in an oil bath for 3 h. After a few minutes of heating, the solid dissolved to yield a clear orange- yellow solution that darkened over the course of the reaction to clear red-orange. After cooling to room temperature, the solvent was removed to yield an orange solid in quantitative yields as determined by NMR. X-Ray quality crystals were grown from ethylacetate and pentanes at 253K. Elemental analysis is complicated by the deliquescent nature of the solid in the absence of solvent. 'H NMR (CDCI3 ): 47 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 8.34 (dd, 3 JH h = 6.25, 4 JH H = 1 - 0 0 , 2 H, o -H py), 7.76 (tt, 3 JH H = 7.50, 4 JH H = 1 - 0 0 , 1H, p-H py), 7.31 (t, 3 Jhh = 6.25, 2H, m -H py) 5.18 (s, 2H ,0- acac-C3 H), 3.11 (tt, 3 J h h = 1 2 .0 , 5 Jh h = 5.25, 1 H, Ir-C//C 5 HU), 1.74 (s, 1 2 H, O-acac-C//3 ), 1.62-0.92 (m, 11H, Ir-CHC5//ii). NMR (CDC13 ): 8 182.59 (O-acac, C=0), 149.38 (o-C py), 137.04 (p-C py), 124.76 (m-C py), 103.21 (acac-C3 H), 35.99 (Ir- CHC5 H 1 1), 28.58 (Ir-CHC5 Hn), 28.51 (Ir-CHC5 H n ), 27.35 (0-acac-CH3 ), 9.31 (Ir-CHCjHn). Anal. Calcd: C, 45.64; H, 5.47; N 2.53. Found: C, 44.31; H, 5.03; N, 2.19. O 0 4. Synthesis of Acetonyl-Ir-Py: A re-sealable Schlenk tube was charged with CH 3 -Ir-Py (29.9 mg, 0.062 mmol) and acetone (5 mL). The resulting clear solution was thoroughly degassed before being placed under an atmosphere of Ar. The tube was sealed and then heated at 130°C in an oil bath for 3 h. After a few minutes of heating, the clear orange-yellow solution darkened over the remaining course of the reaction to give a clear red-orange solution. After cooling to room temperature, the solvent was removed to yield an orange solid in quantitative yields as determined by NMR. X-Ray quality crystals were grown from ethylacetate and pentanes at 253K. ]H NMR (CDC13 ): 8 8.45 (dd, 3 Jhh = 6.4, 48 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 Jh h = 2 .0 , 2 H, o-H py), 7.90 (tt, 3 JH H = 8.50,4 JH H = 2 .0 , lH,p-Hpy), 7.31 (t, 3 JH H = 6.4, 2H, m -H py), 5.38 (s, 2H, O-acac-C3 //), 3.90 (s, 2H, Ir-C//2), 1.96 (s, 12H, O-acac-C//3 ), 1.81 (s, 3H, Ir-CH2 -CO-C//3 ). NMR (CDC13 ): 6 225.0(acetyl C=0), 184.53 (O-acac C=0), 149.70 (o-C py), 137.64 (p-C py), 125.10 {m-C py), 103.05 (0-acac-C 3 H), 30.78 (Ir-CH2 -CO-CH3 ), 27.21 (O-acac- CH3 ), 11.52 (Ir-CH2 -CO-CH3 ). Anal. Calcd: C, 41.05; H, 4.59; N, 2.66. Found: C, 40.97; H, 4.83; N, 2.36. 5. Synthesis of M esityl-Ir-Py: A re-sealable Schlenk tube was charged with CH 3 -Ir-Py (32.0 mg, 0.066 mmol) and mesitylene (5 mL). The resulting clear orange solution was thoroughly degassed before being placed under an atmosphere of Ar. The bomb was sealed and then heated to 130°C in an oil bath for 3h. After cooling to room temperature, all solvent was removed in vacuo leaving an orange solid of M esityl-Ir-Py in quantitative yields as determined by NMR. The sample was recrystallized from dichloromethane and hexanes at 253 K. 'H NMR (CDC13 ): 8 8.38(dd, 3 JH H = 5.00, 4 JH H = 1-5, 2H, o-H py), 7.73(tt, 3 JH H = 8.0, 4 Jhh = 1.5, 1H, p-H py), 7.28(t, 3 JH H = 6.50, m-H py), 6.65(s, 2H, o-Mesityl H), 6.60(s, 1H, p-mesityl H), 5.13 (s, 2H, O-acac-C3/7), 3.99(s, 2H, Ir-CH2- mesityl), 2.19(s, 6 H, Aromatic C //3 ), 1.70(s, 12H, O-acac-C//3 ). 1 3C{1H} NMR 49 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (CDCI3 ): 8 183.6(0-acac, C=0), Aromatic Region (Phenyl and Pyridine 21.1 {O-acac, CH3 ), 21.8 (aromatic methyls), 2 .4 (CH2 -Ir). Analysis (C, H, N): charged with [CH3 -Ir]2 (32.0 mg, 0.0394 mmol) and mesitylene (10 mL). The resulting solution was thoroughly degassed before being placed under an atmosphere of Ar. The bomb was sealed and then heated at 130 °C in an oil bath for 3 h. After a few minutes of heating the solid dissolved to yield a clear yellow solution that remained through out the course of the reaction. After cooling to room temperature, all solvent was removed in vacuo to yield a yellow solid. This was taken up in a minimum amount of CH2 CI2 , precipitated with hexanes under vigorous stirring and then cooled to -25 °C. The cooled solution was decanted and the solid was washed with hexanes and dried in vacuo to afford 24.4 mg (60.7%) of [Mes-Ir]2 as an analytically pure yellow powder. 'H NMR (CDCI3 ): The dimer is not fluxional in CDC13 at ambient temperatures. 8 6.74 (br s, 4H, 1- CH2 -3 ,5 -(CH3 )2 C6/ / 3 ), 6.72 (br s, 2 H, l-CH 2 -3 ,5 -(CH3 )2 C6/ / 3 ), 5.33 (br s, 2 H, resonances): 153.0, 150.2, 137.6, 136.7, 127, 125.4, 124.0, 103.6 (O-acac, CH), Calc: C, 48.96; H, 5.14; N, 2.38. Found: C, 47.36; H, 4.90; N, 2.44. 6. Synthesis of [Mes-Ir]2 A re-sealable glass bomb was 50 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. acac-C3 H), 4.80 (s, 2H, p-acac-C3tf ), 4.03 (s, 4H, l - C / ^ X C T ^ Q f t ) , 2.20 (s, 12H, l-C i/2 -3 ,5 -(CH3 )2 C6 H3 ), 1.83 (br s, 12H, acac-CH3), 1.64 (br s, 12H, p-acac- CH fy 1 3C{’H} NMR (CDCI3 ): 5 192.55 (acac C=0), 182.91 (p-acac C=0), 149.24 (l-CH 2 -3,5-(CH3 )2 C6H3), 136.70 (l-CH2-3,5-(CH3)2 C6 H3 ), 127.73 (1-CH2 - 3 ,5 -(CH3 )2 C6 H3 ), 125.03 (l-CH 2 -3 ,5 -(CH3 )2 C6 H3 ), 103.64 (acac-C3 H), 78.40 (p- acac-C3H), 28.63 (acac-CH3 ), 27.20 (p-acac-CH3 ), 21.19 (l-CH 2 -3 ,5 -(CH3 )2 C6 H3 ), 6.52 (l-CH 2 -3,5-(CH3 )2 C6 H3 ). Anal. Calcd: C, 44.78; H, 4.94. Found: C, 44.83; H, 4.96. H/D exchange: Catalytic H/D exchange reactions were quantified by monitoring the loss of deuterium in C6D6 or by the increase of deuterium into C6H6 by GC/MS analyses. This was achieved by deconvoluting the mass fragmentation pattern obtained from the MS analysis, using a program developed on Microsoft EXCEL. An important assumption built into the program is that there are no isotope effects on the fragmentation pattern of the benzenes due to replacing H with D. Fortunately, because the parent ion o f benzene is relatively stable towards fragmentation, it can be used reliably to quantify the exchange reactions. The mass range from 78 to 84 (for benzene) was examined for each reaction and compared to a control reaction where no metal catalyst was added. The program was calibrated with known mixtures of benzene isotopomers. The results obtained by this method are reliable to within 5%. Thus, analysis of a mixture of C6 H(„ C6D 6 and C6 H5 D] prepared in a molar ratio of 40: 50: 10 resulted in a calculated 51 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ratio of 41.2(C6H6 ): 47.5(C6D6): 9.9(C6H5Di). Catalytic H/D exchange reactions were thus run for reaction times in order to be able to detect changes >5% in exchange. CH3-Ir-Py was the catalyst used to carry out the H/D exchange between various substrates and deuterium sources. H/D exchange between cyclohexane and benzene: For analytical reasons discussed above, cyclohexane-di2 was used with benzene-do and the deuterium incorporation into benzene was monitored using GC-MS. A typical reaction was carried out in a 10 mL Schlenk tube, to which 3.5 mM of CH3-Ir-Py was added to a solvent mixture of benzene and cyclohexane-dn (2:1 molar ratio). (These relative concentrations were employed to keep an equal number of protons and deuterium that simplified the MS analyses and deconvolution). The Schlenk tube was sealed and freeze-pump-thawed two times. The tube was then immersed in a temperature regulated oil bath and the liquid phase sampled regularly under argon. The solution remained homogenous through out the reaction and no signs of decomposition were observed. !H NMR spectroscopy of the residue confirmed the CH3-Ir-Py as the main species (>90%). H/D exchange between Benzene-do-Benzene-d6: In a typical lOmL Schlenk tube, 2mM of CH3-Ir-Py was added followed by equal volumes of C6 H6 and CeD6 (0.5mL each). The Schlenk tube was sealed under an inert atmosphere of Ar and the liquid phase monitored regularly using GC-MS. Typically, an aliquot of the 52 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reaction mixture was sampled before heating. Deconvolution of the mass peak ratios from this mixture at t = 0 min gives the initial mol % of benzene and benzene-d6 . Analysis by GC-MS and deconvolution of the reaction mixture at various reactions times shows the scrambling of the H and D ’s between the benzene. The amount of deuterium incorporation is calculated from the decrease in the C6H6 mol ratio. H/D exchange between acetone and benzene: Acetone-c^ was used with benzene-do and the deuterium incorporation into benzene was monitored using GC-MS. In a typical reaction, 10 mM of CH3-Ir-Py was added to a solvent mixture of benzene and acetone-d6 (1:1 molar ratio) in a lOmL Schlenk tube. The Schlenk tube was sealed and freeze-pump-thawed two times. The tube was then immersed in a temperature regulated oil bath and the liquid phase sampled regularly under argon. H/D exchange between benzene and methane: In a typical 3 mL stainless steel reactor, 6 mM of catalyst, CH3-Ir-Py was loaded followed by 1 mL of C6 D6. The reactor was thoroughly flushed with argon before pressurizing with methane (600psi, 6 . 6 M). The reactor was then immersed in a temperature regulated oil bath heated to 180°C and the gas phase sampled regularly. The gas phase was analyzed using GC-MS. A deconvolution spreadsheet (calibrated with known mixtures of 53 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the methane isotopomers) was used to determine the molar ratio of methane isotopomers, CH4, CH3D, CH2D2, CHD3 and CD4. H/D Exchange between benzene and n-Octane: In a J-young style NMR tube, 20mM of CH3 -Ir-Py was dissolved in 0.5mL of benzene-d6 . 25 p.L of n-Octane was added (substrate : cat = 20:1) and the tube heated in an oil bath at 180°C for 1 - 5 24 hr. C NMR analysis of the crude reaction mixture after reaction clearly shows the incorporation of deuterium into both the 1° and 2° positions (the 1 3 C signals show the characteristic increase in multiplicity due to exchange of H for D). From the relative intensities of the 1 3 C resonances it can be estimated that the -CH3 group is more deuterated than the CH2 positions. X-ray Crystallography. Diffraction data for CH3 -Ir-Py and CgHn-Ir-Py was collected on a Bruker SMART APEX CCD diffractometer with graphite- monochromated Mo K a radiation (k= 0.71073 A). The cell parameters for the Ir complex were obtained from the least-squares refinement of the spots (from 60 collected frames) using the SMART program. A hemisphere of the crystal data was collected up to a resolution of 0.75 A, and the intensity data was processed using the Saint Plus program. All calculations for structure determination were carried out using the SHELXTL package (version 5.1)1 6 . Initial atomic positions were located by direct methods using XS, and the structure was refined by least- squares methods using SHELX. Absorption corrections were applied by using 54 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SADABS.1 7 Calculated hydrogen positions were input and refined in a riding manner along with the attached carbons. Table 2.2. Crystal data and structure P y). Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 27.50° Transmission Factors Refinement method Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I>2sigma(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole refinement for IrCi604NiH22 (CH3-Ir- C 16H 22 IrN1 0 4 484.55 298(2) K 0.71073 A Triclinic P-l a = 8.4259(9) A ot=97.389(2)° b = 9.7219(10) A p = l08.005(2)° c = 11.3004( 12) A 7^92.259(2)° 869.96(16) A3 2 1.850 Mg/m3 7.689 mm-1 468 0 .3 8 x 0 .2 0 x 0.0 7 mm3 2.12 to 27.50°. -10<=h<= 10, -12<=k<=9, -14<=1<=12 5328 3704 [R(int) = 0.0199] 92.6 % min/max ratio: 0.605 Full-matrix least-squares on F2 3704 / 0 / 205 1.022 R1 = 0.0308, wR2 = 0.0746 R1 = 0.0336, wR2 = 0.0761 0.0000(4) 1.503 an d -1.205 e.A’3 55 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.3. Atomic coordinates ( x 10^) and equivalent isotropic displacement parameters (A^x 10^) for Ir C 1 6O4 N 1H2 2 (CH3-Ir-Py). U(eq) is defined as one third of the trace of the orthogonalized UU tensor. X y z U(eq) Ir(l) 1626(1) 2257(1) 7624(1) 40(1) N (l) 2490(5) 176(5) 7478(4) 42(1) 0 (1 ) 3960(4) 3125(4) 8525(4) 50(1) 0 (2 ) 1715(5) 2424(4) 5887(3) 54(1) 0 (3 ) 1524(5) 2159(4) 9363(3) 49(1) 0 (4 ) -722(5) 1406(4) 6736(4) 52(1) C (l) 6435(8) 4506(8) 8808(8) 82(2) C(2) 4822(8) 3756(6) 7970(7) 63(2) C(3) 4345(9) 3746(6) 6658(7) 65(2) C(4) 2941(9) 3129(6) 5734(6) 62(2) C(5) 2695(12) 3278(9) 4376(7) 100(3) C(6) 256(11) 2071(8) 10929(6) 77(2) C(7) 142(8) 1857(6) 9559(5) 53(1) C(8) -1362(8) 1390(7) 8633(7) 65(2) C(9) -1736(7) 1151(6) 7336(7) 60(2) C(10) -3446(8) 571(8) 6496(9) 89(3) C (ll) 1843(7) -743(6) 6461(5) 62(2) C(12) 2284(10) -2080(7) 6320(7) 77(2) C(13) 3467(8) -2517(7) 7286(6) 72(2) C(14) 4180(11) -1576(8) 8351(7) 92(3) C(15) 3660(9) -267(7) 8409(6) 71(2) C(16) 732(8) 4177(6) 7697(6) 60(1) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.4. Bond lengths [A] and angles [°] for IrC]604N]H22 (CH3 -Ir-Py). Ir(l)-0(1) Ir(l)-0(3) Ir(l)-0(4) Ir(l)-0(2) Ir(l)-C(16) Ir(l)-N (l) N (l)-C (l 1) N (l)-C (15) 0(1)-C (2) 0(2)-C (4) 0(3)-C (7) 0(4)-C (9) C (l)-C (2) C(2)-C(3) C(3)-C(4) C(4)-C(5) C(6)-C(7) C(7)-C(8) C(8)-C(9) C(9)-C(10) C(11)-C(12) C(12)-C(13) C(13)-C(14) C(14)-C(15) 2.007(4) 2.007(3) 2.009(4) 2.014(4) 2.041(6) 2.181(4) 1.314(7) 1.331(7) 1.281(8) 1.286(7) 1.281(7) 1.279(7) 1.491(9) 1.409(10) 1.368(10) 1.510(9) 1.508(8) 1.385(9) 1.387(9) 1.499(8) 1.369(8) 1.359(9) 1.369(9) 1.362(9) 0 (l)-Ir (l)-0 (3 ) 84.41(16) 0 (l)-Ir (l)-0 (4 ) 179.27(13) 0 (3 )-Ir(l)-0 (4 ) 95.17(16) 0 (l)-Ir (l)-0 (2 ) 95.21(16) 0 (3 )-Ir(l)-0 (2 ) 178.08(14) 0 (4 )-lr (l)-0 (2 ) 85.20(17) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.4. Continued 0 ( 1 )-Ir( 1 )-C( 16) 0(3)-Ir(l)-C (16) 0(4)-Ir(l)-C (16) 0(2)-Ir( 1 )-C( 16) 0(1 )-Ir(l)-N (l) 0 (3 )-Ir(l)-N (l) 0(4 )-Ir(l)-N (l) 0(2)-Ir( 1 )-N( 1) C (16)-Ir(l)-N (l) C (11 )-N( 1 )-C( 15) C (11)-N (l)-Ir(l) C( 15)-N( 1 )-Ir( 1) C (2)-0(1)-Ir(l) C (4)-0(2)-Ir(l) C (7)-0(3)-Ir(l) C (9)-0(4)-Ir(l) 0(1)-C (2)-C (3) 0(1)-C (2)-C (1) C(3)-C(2)-C(l) C(4)-C(3)-C(2) 0(2)-C (4)-C (3) 0(2)-C (4)-C (5) C(3)-C(4)-C(5) 0(3)-C (7)-C (8) 0(3)-C (7)-C (6) C(8)-C(7)-C(6) C(7)-C(8)-C(9) 0(4)-C (9)-C (8) O(4)-C(9)-C(10) C(8)-C(9)-C(10) N (l)-C (l 1)-C(12) 90.1(2) 89.4(2) 89.3(2) 88.7(2) 92.06(15) 91.75(15) 88.54(16) 90.14(15) 177.61(18) 115.5(5) 121.5(4) 123.1(4) 122.4(4) 120.9(4) 121.6(4) 121.9(4) 124.1(6) 115.4(7) 120.4(6) 129.7(6) 126.5(6) 113.3(7) 120.1(6) 125.3(5) 113.9(6) 120.7(6) 129.7(6) 125.3(5) 113.5(6) 121.1(6) 124.6(5) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.4. Continued C(13)-C(12)-C(l 1) 119.0(6) C(12)-C(13)-C(14) 117.6(6) C(15)-C(14)-C(13) 119.3(6) N (l)-C (15)-C (14) 123.9(6) Symmetry transformations used to generate equivalent atoms: Table 2.5. Anisotropic displacement parameters (A^x 10^) for Ir C 1 6O4 N 1H2 2 (CH3 -Ir-Py). The anisotropic displacement factor exponent takes the form: -2n^[ h^ a*2(jl 1 + ... + 2 h k a* b* ] U 1 1 U22 u 3 3 U 2 3 U 1 3 u 1 2 lr(l) 38(1) 39(1) 38(1) 4(1) 7(1) 1(1) N (l) 39(2) 45(2) 37(2) 5(2) 8(2) 2(2) 0 (1 ) 41(2) 48(2) 55(2) 3(2) 11(2) -2(2) 0 (2 ) 65(2) 53(2) 42(2) 12(2) 10(2) 5(2) 0 (3 ) 53(2) 52(2) 41(2) 5(2) 15(2) 2(2) 0 (4 ) 42(2) 53(2) 52(2) 0(2) 3(2) 2(2) C (l) 52(4) 62(4) 126(6) -11(4) 32(4) -12(3) 0(2) 54(3) 42(3) 95(5) -5(3) 34(3) 3(3) 0(3) 83(4) 40(3) 86(5) 4(3) 52(4) -5(3) 0(4) 86(5) 45(3) 74(4) 21(3) 46(4) 16(3) 0(5) 156(8) 95(6) 75(5) 44(5) 62(5) 28(6) 0(6) 117(6) 64(4) 71(4) 13(3) 59(4) 13(4) 0(7) 70(4) 42(3) 58(3) 11(2) 32(3) 11(3) 0(8) 62(4) 55(4) 84(4) 2(3) 35(3) 1(3) 0(9) 42(3) 47(3) 84(4) 4(3) 11(3) 2(2) 0(10) 40(3) 74(5) 128(7) -14(5) 5(4) -8(3) 0(11) 64(4) 56(3) 49(3) -2(3) -3(3) 14(3) 0(12) 93(5) 50(4) 66(4) -12(3) -1(4) 13(3) 0(13) 83(5) 49(4) 79(5) 14(3) 17(4) 19(3) 59 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.5. Continued C(14) 114(6) 78(5) 60(4) 11(4) -12(4) 40(5) C(15) 84(4) 59(4) 47(3) 0(3) -11(3) 21(3) C(16) 56(3) 51(3) 70(4) 5(3) 16(3) 7(3) Table 2.6. Hydrogen coordinates ( x 10^) and isotropic displacement parameters (A^x 10 3) for IrCi604NiH22 (CH3 -Ir-Py). X y z U(eq) H(1 A) 6212 5343 9259 124 H(1B) 7118 4736 8310 124 H(1C) 7012 3920 9396 124 H(3) 5099 4233 6380 78 H(5A) 1968 2508 3838 149 H(5B) 3759 3288 4230 149 H(5C) 2 2 0 2 4132 4197 149 H(6A) 1335 1847 11427 115 H(6B) -602 1478 11050 115 H(6C) 107 3025 11183 115 H(8) -2255 1209 8926 78 H(10A) -3927 1224 5945 133 H(10B) -4146 406 7001 133 H(10C) -3360 -289 6006 133 H (11) 1029 -465 5789 74 H(12) 1780 -2681 5573 93 H(13) 3782 -3423 7225 86 H(14) 5010 -1827 9027 111 H(15) 4152 355 9144 86 H(16B) 532 4419 8487 72 H(16C) -297 4162 7021 72 H(16A) 1539 4854 7618 72 60 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.7. Crystal data and structure refinement for C2 iH3 oIrN0 4 (C6Hi r Ir- Py) Identification code Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 27.47° Transmission Factors Refinement method Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I>2sigma(I)] R indices (all data) Largest diff. peak and hole gcycm C21 H30 Ir N 0 4 552.66 123(2) K 0.71073 A Monoclinic C2/m a = 16.0199(18) A a= 90°. b = 11.1848(13) A p= 102.917(2)° c = 12.1863(14) A y = 90°. 2128.3(4) A3 4 1.725 Mg/m3 6.298 mm-1 1088 0.1 x 0.1 x 0.05 mm3 1.71 to 27.47°. -20<=h<=20, -10<=k<= 14, -14<=1<=15 6376 2473 [R(int) = 0.0393] 96.1 % min/max ratio: 0.827 Full-matrix least-squares on F2 2 4 7 3 / 0 / 139 1.244 R1 = 0.0382, wR2 = 0.0719 R1 = 0.0471, wR2 = 0.0740 2.055 an d -1.971 e.A'3 61 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.8. Atomic coordinates (x 10^) and equivalent isotropic displacement parameters (A^x 1 (P) for C2 iH3 oIrN0 4 (CfiHn-Ir-Py). U(eq) is defined as one third of the trace of the orthogonalized U 1 .] tensor. X y z U(eq) Ir(l) 1379(1) 0 2530(1) 22(1) 0 (1 ) 1475(2) 1216(4) 3772(3) 35(1) 0 (2 ) 1235(2) 1197(3) 1275(3) 29(1) N (l) -31(4) 0 2382(5) 30(2) C (l) 1370(3) 2325(6) 3552(6) 40(2) 0(2) 1256(4) 2861(6) 2491(6) 45(2) C(3) 1218(3) 2315(6) 1453(5) 38(2) 0(4) 2694(4) 0 2779(6) 24(2) 0(5) 3085(3) 1111(6) 2338(5) 36(1) 0(6) 4068(4) 1110(6) 2623(6) 42(2) 0(7) 4404(5) 0 2191(7) 42(2) 0(9) -1444(5) 0 1322(8) 47(2) 0(10) -1754(6) 0 2289(8) 59(3) 0(11) -1199(5) 0 3308(8) 45(2) C(12) -336(5) 0 3314(6) 39(2) 0(13) -580(5) 0 1382(6) 37(2) 0(14) 1168(5) 3079(7) 432(6) 61(2) 0(15) 1387(5) 3108(7) 4570(6) 63(2) Table 2.9. Bond lengths [A] and angles [°] for C2 iH3 oIrN0 4 (CftHn-Ir-Py). Ir(l)-0(2)#1 2.008(4) Ir(l)-0(2) 2.008(4) Ir(l)-0(1) 2.015(4) Ir(l)-0(1)#1 2.015(4) Ir(l)-C(4) 2.060(7) 62 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.9. Continued Ir(l)-N (l) 0(1)-C (1) 0(2)-C (3) N (l)-C (13) N (l)-C (12) C (l)-C (2) C (l)-C (15) C(2)-C(3) C(3)-C(14) C(4)-C(5) C(4)-C(5)#l C(5)-C(6) C(6)-C(7) C(7)-C(6)#l C(9)-C(13) C(9)-C(10) C (10)-C (ll) C (ll)-C (12) 0 (2 )# l-Ir (l)-0 (2 ) 0 (2 )# 1 -Ir( 1 )-0 ( 1) 0 (2 )-Ir (l)-0 (l) 0 (2 )# 1 -Ir( 1 )-0 ( 1 )# I 0 (2 )-Ir (l)-0 (l)# l 0(1)-Ir(l)-0(1)#1 0 (2 )# I -Ir( 1 )-C(4) 0(2)-Ir(l)-C (4) 0(1)-Ir(l)-C (4) 0 ( 1 )# 1 -Ir( 1 )-C(4) 0 (2 )# 1 -Ir(l)-N (l) 0 (2 )-Ir(l)-N (l) 0 (1 )-Ir(l)-N (l) 2.225(6) 1.272(8) 1.270(7) 1.334(9) 1.333(9) 1.400(9) 1.514(8) 1.393(9) 1.497(8) 1.541(7) 1.541(7) 1.535(8) 1.495(7) 1.495(7) 1.370(11) 1.377(12) 1.357(12) 1.381(11) 83.7(2) 177.79(15) 95.66(16) 95.66(16) 177.79(15) 84.9(2) 92.94(18) 92.94(18) 89.20(18) 89.20(18) 89.80(16) 89.80(16) 88.09(16) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.9. Continued 0 (1)#1-Ir(l)-N (l) 88.09(1 C(4)-Ir( 1 )-N( 1) 176.3(2) C (l)-0(1)-Ir(l) 121.0(4) C (3)-0(2)-Ir(l) 121.9(4) C (13)-N(l)-C (12) 119.0(7) C (13)-N (l)-Ir(l) 121.7(5) C (12)-N (l)-Ir(l) 119.3(5) 0(1)-C (1)-C (2) 126.6(6) 0 ( 1 )-C( 1 )-C( 15) 114.4(6) C(2)-C( 1 )-C( 15) 119.0(6) C(3)-C(2)-C(l) 128.3(6) 0(2)-C (3)-C (2) 126.1(6) 0(2)-C (3)-C (14) 114.8(6) C(2)-C(3)-C(14) 119.1(6) C(5)-C(4)-C(5)#l 107.4(6) C(5)-C(4)-Ir(l) 115.5(3) C (5)#l-C (4)-Ir(l) 115.5(3) C(6)-C(5)-C(4) 113.4(5) C(7)-C(6)-C(5) 110.6(5) C(6)#l-C(7)-C(6) 112.3(7) C(13)-C(9)-C(10) 120.5(8) C(11)-C(10)-C(9) 119.6(8) C (10)-C (ll)-C (12) 117.1(8) N (l)-C (12)-C (l 1) 123.6(7) N (l)-C (13)-C (9) 120.1(7) Symmetry transformations used to generate equivalent atoms: #1 x,-y,z Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.10. Anisotropic displacement parameters (A^x 1(P) for C2iH3oIrN0 4 (C6Hn-Ir-Py). The anisotropic displacement factor exponent takes the form: -2n^[ h^ a*2fjl 1 + ... + 2 h k a* b* ljl2 ] U 1 1 U2 2 U33 U2 3 U 1 3 U 1 2 Ir(l) 23(1) 27(1) 17(1) 0 5(1) 0 0 (1 ) 30(2) 45(3) 28(2) -14(2) 5(2) 1(2) 0 (2 ) 31(2) 32(2) 23(2) 4(2) 5(2) 0(2) N (l) 30(3) 34(4) 28(4) 0 16(3) 0 C (l) 27(3) 42(4) 50(4) -17(3) 4(3) 2(3) C(2) 41(4) 27(3) 65(5) -4(3) 9(3) 1(3) C(3) 27(3) 36(4) 50(4) 8(3) 3(3) 3(3) C(4) 22(4) 34(5) 17(4) 0 6(3) 0 C(5) 25(3) 47(4) 36(3) -3(3) 8(2) -3(3) C(6) 36(3) 49(4) 45(4) -9(3) 15(3) -11(3) C(7) 29(4) 65(7) 37(5) 0 17(4) 0 C(9) 25(4) 78(8) 37(5) 0 4(4) 0 C(10) 31(5) 96(9) 52(6) 0 14(4) 0 C (ll) 32(4) 67(7) 37(5) 0 14(4) 0 C(12) 31(4) 68(7) 18(4) 0 4(3) 0 C(13) 30(4) 58(6) 20(4) 0 2(3) 0 C(14) 65(5) 44(4) 72(5) 33(4) 14(4) 4(4) C(15) 60(5) 63(5) 59(5) -34(4) -4(4) 20(4) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.11. Hydrogen coordinates (x 10^) and isotropic displacement parameters (A^x 10 3) for C2 iH3 0 IrNO 4 (C6H n-Ir-Py). x y z U(eq) H(2) 1198 3707 2476 54 H(4) 2918 0 3613 29 H(5A) 2878 1153 1510 43 H(5B) 2881 1836 2664 43 H(6A) 4279 1820 2282 51 H(6B) 4282 1159 3449 51 H(7A) 4241 0 1358 50 H(7B) 5037 0 2419 50 H(9) -1833 0 608 56 H(10) -2354 0 2242 71 H (11) -1395 0 3988 54 H(12) 62 0 4020 47 H(13) -372 0 711 44 H(14A) 1748 3286 361 91 H(14B) 850 3812 507 91 H(14C) 873 2640 -239 91 H(15A) 1335 2606 5211 95 H(15B) 908 3674 4403 95 H(15C) 1929 3550 4756 95 66 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.4 References (1) (a) Shilov, A. E.; Shul’pin, G. B. Activation and Catalytic Reactions o f Saturated Hydrocarbons in the Presence o f Metal Complexes, Kluwer Academic; Dordrecht, 2000. (b) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879. (c) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507. (d) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem. Res. 2002, 35, 44. (e) Crabtree, R. H. Chem. Rev. 1995, 95, 987. (f) Davies, J. A.; Watson, P. L.; Liebman, F.; Greenberg, A. Selective Hydrocarbon Activation', VCH: Toledo, 1990. (g) Jones, W. D. Topics in Organometallic Chemistry, 1999, 3, 9. (h) Periana, R. A.; Bhalla, G.; Term III, W. J.; Young, K. J. H.; Liu, X. Y.; Mironov, O.; Jones, C.; Ziatdinov, V. R. J. Mol. Cat. A- Chem. 2004, 220, 7. (2) For some examples, see: (a) Jia, C.; Kitamura, T.; Fujiwara, Y. Acc. Chem. Res. 2001, 34, 633. (b) Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. Rev., 2002, 102, 1731. (c) Wolf, D. Angew Chem. Int. Ed. Eng. 1998, 37, 3351. (d) Kakiuchi, F.; Murai, S. Topics in Organometallic Chemistry 1999, 3, 47. (e) Periana, R. A.; Mironov, O.; Taube, D.; Bhalla, G.; Jones, C. Science, 2003, 30, 814. (f) Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T.; Fujii, H. Science, 1998, 280, 560-564. (f) Periana, R. A.; Taube, D. J.; Evitt, E. R.; Loffler, D. G.; Wentrcek, P. R.; Voss, G.; Masuda, T. Science, 1993, 259, 340-343. (g) Chen, H. Y.; Schlecht, S.; Semple, T. C.; Hartwig, J. F. Science, 2000, 287, 1995-1997. (h) Liu, F.; Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S. J. Am. Chem. Soc. 1999, 121, 4086-4087. (i) Jones, W. D. Science, 2000, 287, 1942. (j) Sen, A. Acc. Chem. Res. 1998, 31, 550. (k) Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2001, 19, 2437. (3) (a) Amdtsen, B. A.; Bergman, R. G. Science, 1995, 270, 1970. (b) Zhu, K.; Achord, P. D.; Zhang, X.; Krogh-Jespersen, K.; Goldman, A. S. J. Am. Chem. Soc. 2004, 126(40), 13044. (c) Ishiyama, T.; Takagi, J.; Hartwig, J. F.; Miyaura, N. Angew. Chem., Intl. Ed. 2002, 41(16), 3056. (d) Ben- Ari, E.; Gandelman, M.; Rozenberg, H.; Shimon, L. J. W.; Milstein, D. J. Am. Chem. Soc. 2003, 125(16), 4714. Gutierrez-Puebla, E.; Monge, A.; Nicasio, M. C.; Perez, P. J.; Poveda, M. L.; Carmona, E. Chem Eur. J. 1998, 4(11), 2225. (4) Liu, X. Y.; Tenn, III, W. J.; Bhalla, G.; Periana, R. A. Organometallics, 2004, 23, 3584-3586. (5) Mehrotra, R. C.; Bohra, R.; Gaur, D. P. Metal (3-Diketonates and Allied Derivatives, Academic press, 1978. 67 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (6 ) (a) Muetterties, E. L.; Wright, C. M. J. Am. Chem. Soc. 1965, 8 6 , 4706. (b) Muetterties, E. L.; Wright, C. M. J. Am. Chem. Soc. 1965, 87, 21. (c) Muetterties, E. L.; Roesky, H.; Wright, C. M. J. Am. Chem. Soc. 1966, 8 8 , 4856. (d) Narbutt, J.; Krejzler, J. Inorg. Chim. Acta 1999, 286, 175. (7) Bradley, D. C.; Mehrotra, R. C.; Rothwell, I. P.; Singh, A. Alkoxo and Aryloxo Derivatives o f Metals, Academic Press, 2001. (8 ) (a) Pierpont, C. G.; Buchanan, R. M. Coord. Chem. Rev. 1981, 38, 45. (b) Pierpont, C. G.; Lange, C. W. Prog. Inorg. Chem. 1994, 41, 331. (c) Martin, R. Handbook o f Hydroxyacetophenones, Kluwer, 1997. (9) For example see: (a) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem. Res. 2002, 35, 44. (b) Jones, W. D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91. (c) Wang, C. M.; Ziller, J. W.; Flood, T. C. J. Am. Chem. Soc. 1995, 117, 1647. (e) Zhong, H. A.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2002, 124, 1378-1399. (f) Johansson, L.; Ryan, O. B.; Tilset, M. J. Am. Chem. Soc. 1999, 121, 1974. (g) Fekl, U.; Goldberg, K. I. Adv. Inorg. Chem. 2003, 5454, 259. (h) Liu, F. C.; Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S. J. Am. Chem. Soc. 1999, 121, 4086. (i) Nuckel, S.; Burger, P. Angew. Chem. Int. Ed. 2003, 42, 1632. (10) (a) Bryndza, H. E.; Tam, W. Chem. Rev. 1988, 8 8 , 1163-1188. (b) Bergman, R. G. Polyhedon, 1995, 3221-3237. (c) Mayer, J. M. Polyhedron, 1995, 3273. (11) (a) Lunder, D. M.; Lobkovsky, E. B.; Streib, W. E.; Caulton, K. G. J. Am. Chem. Soc. 1991, 113, 1837. (b) Flood, T. C.; Lim, J. K.; Deming, M. A.; Keung, W. Organometallics 2000, 19, 1166. (c) Riehl, J.; Jean, Y.; Eisenstein, O.; Pelissier, M. Organometallics 1992, 729. (d) Poulton, J. T.; Folting, K.; Streib, W. E.; Caulton, K. G. Inorg. Chem. 1992, 31, 3190. (12) (a) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th ed.; John Wiley & Sons: New York, 1988, 1189-1194. (b) Collman, J. P. Acc. Chem. Res. 1968, 1, 136 (c) Tellers, D. M.; Skoog, S. J.; Bergman, R. G.; Gunnoe, T. B.; Harman, W. D. Organometallics 2000, 19, 2428. (d) Tellers, D. M.; Bergman, R. G. J. Am. Chem. Soc. 2000, 122, 954. (e) Owen, J. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2004, 126, 8247. (13) Krogh-Jespersen, K.; Czerw, M.; Zhu, K.; Singh, B.; Kanzelberger, M.; Daiji, N.; Achord, P. D.; Renkema, K. B.; Goldman, A. S. J. Am. Chem. Soc. 2002, 124, 10797. 68 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (14) (a) Holm, R. H. Chem. Rev. 1987, 87, 1401. (b) Bates, P. A.; Nielson, A. J.; Waters, J. M. Polyhedron 1987, 6 , 163. (c) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc. 1988, 110, 8729. (d) Cummins, C. C.; Baxter, S. M.; Wolczanski, P. T. J. Am. Chem. Soc. 1988, 110, 8731. (e) Parkin, G.; Bercaw, J. E. Polyhedron 1988, 7, 2053. (f) Herrmann, W. A. Angew. Chem, Int. Ed. 1988, 27, 1297. (g) Bryndza, H. E.; Domaille, P. J.; Paciello, R. A.; Bercaw, J. E. Organometallics 1989, 8 , 379. (h) Chao, Y. W.; Rodgers, P. M.; Wigley, D. E.; Alexander, S. J.; Rheingold, A. L. J. Am. Chem. Soc. 1991, 113, 6326. (i) Rachidi, I. E. I.; Eisenstein, O.; Jean, Y. New J. Chem. 1990, 14, 671. (j) Caulton, K. G. New J. Chem. 1994, 18,25. (15) Related Ir(V), seven coordinate intermediates have been proposed and observed in CH Activation by Ir(III) complexes, (a) Webster, C. E.; Hall, M. B. Coord. Chem. Rev. 2003, 238-239, 315-331. (b) Klei, S. R.; Tilley, T. D.; Bergman, R. G. J. Am. Chem. Soc. 2000, 122, 1816. (16) Sheldrick, G. M. SHELXTL, version5.1; Bruker Analytical X-ray System, Inc.: Madison, WI, 1997. (17) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 Mechanistic Details of 0-Donor Ir(lll) Complexes: C-H Activation Studies with Benzene. 3.1 Introduction As mentioned in Chapter 1 and 2, catalysts based on the C-H activation reaction show potential for the development of new, selective, hydrocarbon oxidation chemistry. 1 A central consideration in the design of such C-H activation based catalysts is the choice of ligands. The ligands generally acceptable for C-H activation reactions range from C-donor, e.g. cyclopentadienyl ligands, to mono and multi-dentate P- or N-donor ligands, to chelating NC or PC type ligands. We have been particularly interested in O-ligated, late transition metals as such complexes could exhibit protic and oxidant stability given the lower basicity and higher electronegativity of O compared to N, C or P. Another key reason for study is that the electronegativity and “hardness” of O-donor ligands could allow access to higher oxidation states during catalysis that could facilitate the oxidative functionalization reactions of M-R intermediates to functionalized RX products in a catalytic cycle. Previously in Chapter 2, we reported first examples of a d6, O-donor ligated Ir complex, (acac-0 ,0 )2 lrin(R)(L), (acac-0,0 = K2-0,0-acetylacetonate, L = ligand), R -Ir-L, (where -Ir- is understood to be the trans-(acac-0 ,0 )2 lr(III) motif throughout this paper unless specified and L is a ligand such as pyridine, Py) 70 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. that shows stoichiometric and catalytic C-H activation and H/D exchange of alkanes and arenes3 Some experimental. 4 and theoretical5 studies of this O-donor complex, R-Ir-L, have been reported, and a proposed mechanism for the C-H activation and hydroarylation catalysis based on arene C-H activation is shown in Scheme 3.1.(Hydroarylation is discussed in next chapter) While O-donor ligands have been utilized with early and late transition metals, 6 to our knowledge these are the first, well-defined, O-ligated, late transition metal complexes that activate alkane and arene C-H bonds. These late metal, O-donor complexes catalyze reactions with hydrocarbons and show significantly higher thermal stability at temperatures above 200 °C to oxidizing, acidic conditions compared to complexes based on C, N and P ligands. Other unique characteristics are that, unlike more electron rich systems, these O-donor complexes are not severely inhibited by substrates such as olefins and water and do not generate olefinic products that would be expected from (3-hydride elimination reactions. These are intriguing characteristics and, as discussed above, may be related to the a-acceptor and 7i-donor properties of the O-donor ligands. Given the potentially useful characteristics of these O-donor, bis-acac-0,0, Ir(III) complexes, we embarked on a detailed study of the stoichiometric chemistry of this class of compounds. The scope of this work includes the development of a detailed understanding of the reaction chemistry of these complexes, R-Ir-L, with an emphasis on providing a molecular picture of the C-H activation and other reactivity of these complexes as examples of the class of late transition metal, O- 71 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. donor, organometallic complexes. A particular focus of this study is to determine if the C-H activation reactions of this novel class of organometallic complexes proceed by inner-sphere processes involving substrate coordination as has been found with most other systems that exhibit the C-H activation reaction . 1 A desirable outcome from these studies will be to utilize this information to rationally design new, more effective, thermally, protic and oxidant stable O-donor catalysts for hydrocarbon conversion. 72 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. C-H ACTIVATION HYDROARYLATION PhCH2CHr Ir-L Scheme 3.1. Proposed reaction mechanism of H/D exchange and hydroarylation of olefins catalyzed via arene C-H activation by [(acac-0 ,0 )2 lr(R)(L)] and [Ir(|i-acac- 0 ,0 ,C3 )(acac-0 ,0 )(R ) ] 2 Complexes. 73 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.2 Results and Discussion 3.2.1 Synthesis and Characterization of (acac-0,0)2lr(lll) Complexes The various complexes examined in this study were synthesized as shown in Scheme 3.2. All the complexes were fully characterized by 'H, 1 3 C NMR spectroscopy, elemental analyses and/or high-resolution mass spectrometry. In selected cases, the compounds were also characterized by X-ray crystallography. These compounds are (both aryl and alkyl, with and without P-CH bonds) stable at room temperature to air and protic solvents such as water and methanol. Importantly, the (acac-0 ,0 )2 lr(III) motif is very stable and, remarkably, refluxing complexes in acid solvents such as acetic or trifluoroacetic acids in air does not lead to loss of the acac-0,0 ligands. This oxidation and protic stability is likely to arise from the octahedral geometry and the lower electropositivity at an Ir center with four electronegative O-donor ligands. 74 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IrCl\ 1M) + Acac-H NaHCQ3 ■H,0 |Acac-C-Ir]2 = & > < „ HgR2 or ZnR2 O H / H Acac-C-lr-H20 .0. Ph-Ir-H20 H H Py (R=acac) =51 (R=Ph) R R = CH3, |CH3 -Ir]2 R = PhCH2CH2, |PhCH2CH2-Ir|2 R = CH3CH2, |CH3CH2 -Ir]2 R = Acac, Acac-C-Ir-Py R = CH3, CHj-Ir-Py R = C6H5, Ph-Ir-Py R = PhCHjCHj, PhCH2CH2-Ir-Py R = CH3CH2, CHjCH2 -Ir-Py Scheme 3.2. Synthesis of Family of O-Donor, bis-acac Ir(III) Complexes. 3.2.1.1 Dinuclear Complexes, [(acac-0,0)2 Ir-R]2 Synthesis of the bis-acac-0,0 Ir(III) complexes begins with the mononuclear bis-acac-0,0 Ir(III) complex, Acac-C-Ir-H2 0 , that can be obtained in high yield from a modification of the procedure reported by Bennett7 for the dinuclear complex, [Ir(|i-acac-0 ,0 ,C3 )(acac-0 ,0 )(acac-C 3 )]2 , [Acac-C-Ir]2. Treatment of Acac-C-Ir-H2 0 with ZnR 2 or HgR2 (R = alkyl = CH 3 , CH 3 CH2 and PhCH 2 CH2) (Scheme 3.2), leads to the corresponding dinuclear bis-acac-0,0 Iridium organometallic complexes [R-Ir]2 , in high isolated yields. For example, treatment of Acac-C-Ir-H2 0 in THF with Zn(CH 3 ) 2 leads to the formation of the 75 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. dinuclear complex, [Ir(p-acac-0 ,0 ,C3 )(acac-0 ,0 )(CFl3 )]2, [CH3Ir]2 in 75% yield. The characteristic bridging acac ligands in these dinuclear iridum complexes is a common feature of these P-diketonate complexes. 8 3.2.1.2 Mononuclear Complexes, (acac-0,0)2 Ir(R)(L) The mononuclear complexes R-Ir-Py can be obtained from the corresponding dinuclear complexes, [R-Ir]2 by treatment with pyridine or in the case of R = Acac-C and R = Ph, by treatment of the Acac-C-Ir-H2 0 with Py, or Ph2Hg followed by Py, respectively. The reactions of the dinuclear alkyl complexes [R-Ir]2, (R = CH3 ), (R = CH 2 CH 2 Ph) and (R = CH 2 CH3 ) with pyridine result in the quantitative formation of the corresponding mononuclear complex, R- Ir-Py. The yellow pyridine complexes CH3-Ir-Py, Ph-Ir-Py, PhCH2CH2 -Ir-Py and CH3CH2 -Ir-Py were all characterized by ’H and 1 3 C NMR spectroscopy, elemental analysis, FAB mass spectrometry and in selected cases, by single crystal 1 13 X-Ray crystallography. H and C NMR spectra of these complexes are consistent with a trans-octahedral geometry. In no cases were any cis-(acac- 0 ,0 ) 2 Ir(R)(L) complexes observed or isolated in these preparations. FAB mass spectral analyses of CH3-Ir-Py, Ph-Ir-Py, PhCH2 CH2 -Ir-Py and CH3CH2 -Ir-Py show an M+ ion of appreciable intensity. Generally, the most intense fragment is derived from the loss of the pyridine, [M-Py]+. These complexes show a general trend of ion peaks for the loss of Py and the hydrocarbyl substituent, i.e., [M+ ], 76 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. [M-Py]+ and [M-Py-R]+. For instance, the Ph-Ir-Py complex shows m/z 547.1, 468.1 and 391.1 which correspond to [M+ ], [M-Py]+and [M-Py-Ph]+, respectively. X-Ray crystallography of selected complexes was carried out to confirm the structure of these complexes. The ORTEP projections of Ph-Ir-Py and PhCH2CH2-Ir-Py are shown in Figure 3.1 and Figure 3.2 respectively. The crystal structure of the Ph-Ir-Py is disordered. As a result, the molecule lies on a center of symmetry necessarily causing the phenyl group or the pyridine group to be disordered. The Ir-N bond length can be used to estimate the trans influence of the hydrocarbyl substituent. As expected, the data suggests that alkyl groups are better trans-donors than aryl groups: the Ir-N distances for CH3-Ir-Py and PhCH2CH2-Ir-Py at 2.181 and 2.165 A respectively. C(6) 0 (2) N (l) Figure 3.1. ORTEP diagram of Complex Ph-Ir-Py. Selected. Bond Angles (°): C(6)-Ir(l)-N(l): 180.0; 0 (l)-Ir(l)-0(2): 95.45(18); 0(2)-Ir(l)-N (l): 90.1(2); C(4)-0(2)-Ir(l): 120.7(4). 77 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 3.2. ORTEP diagram of Complex PhCH2 CH2 -Ir-Py. Selected Bond Lengths (A) and Angles (°):Ir(l)- C(16): 1.956(13); Ir(l)-N (l): 2.165(7); C(16)-Ir(l)- 0(1): 91.7(4); C(16)-Ir(l)-N(l): 176.5(4); 0(1)- Ir(l)-N (l): 90.4(3). 3.2.2 Dynamic Behavior of Dinuclear Complexes, [(acac-0,0)2lr- R]2 As communicated earlier in chapter 2, both the mononuclear and dinuclear (acac-0 ,0 )2 lr(III) complexes are active catalysts for C-H activation and olefin hydroarylation with anti-Markovnikov selectivity.(Scheme 3.1) There is precedent 78 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. for catalysis by dinuclear complexes with possible cooperativity between the metal centers. 9 However, given the expected strong trans influence and the weakened -j Ir(|i-acac-0,0,C ) bridging bond in the [R-Ir] 2 dinuclear complexes (where R is alkyl), we anticipated that reactions would be initiated by facile dissociation to generate mononuclear, coordinatively unsaturated, 5-coordinate, square pyramidal intermediates, R-IrD (where □ is used as a symbol for a vacant site throughout this paper). Mechanisms involving C-H activation111 and olefin insertion 1 0 are typically inner-sphere, coordination reactions that generally require a vacant coordination site on the metal for coordination of the C-H substrate, and substantial evidence can be cited for a dissociative mechanism for octahedral complexes, especially for those of Ir(III) . 11 Consistent with these considerations and the observed catalytic activity of these dinuclear complexes for the hydroarylation reaction and catalytic H/D exchange, we find the stability of the dinuclear complexes is highly dependent on the nature of the R group. For example, dinuclear complexes with electron withdrawing groups such as chloro,4 c [Cl-Ir] 2 or acac-C, [acac-C-Ir]2 , are stable at room temperature and show well- defined 'H NMR resonances for two pairs of methyl (12 H ’s each) and two methines (2 H ’s each). However, dinuclear complexes with more electron donating alkyl groups, such as [CH3-Ir]2, [CH3CH2 Ph-Ir] 2 and [CH3CH2 -Ir] 2 are only stable below room temperature and show dynamic behavior by NMR at room temperature that can be best explained by facile formation of the coordinatively unsaturated, 5-coordinate intermediates, R-IrlU, as shown in Scheme 3.3. It is 79 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. possible these intermediates could be 6 -coordinate, solvento complexes, but as will be discussed later, this is not consistent with the chemistry of these complexes. The 'H NMR resonances of the methyl and methine groups in the acac-0,0 ligands of the dinuclear complex, [CH3-Ir]2, in tol-dg are broad peaks ( 1 . 8 and 5.1 ppm, respectively) at room temperature. At lower temperatures, these signals decoalesce, and at 253 K, the NMR spectrum shows two singlets for two pairs of methyl (1.76 and 1.46 ppm, each 12 H ’s) and two methine resonances (5.19 and 5.02 ppm, each 2 H ’s) that are consistent with a stable dinuclear complex with bridging acac ligands. Similar dynamic behavior was observed for the alkyl complexes, [PhCH2 CH2 -Ir]2 and [CH3CH2 -Ir]2. Line broadening analysis was carried out for [CH3-Ir]2 in tol-dg using the methyl and the methine resonances. The exchange rates were obtained in the slow-exchange region from the width of the NMR signals at half height. 1 2 R R = CH3, [CH3-Ir]2 R = CH2CH2Ph, [PhCH2CH2-Ir]2 R = CH2CH3, [CH3CH2-Ir]2 R-Ir-D Scheme 3.3. Fluxional Behaviour 80 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The activation parameters: AH* = 17.8 (± 1) kcal/mol, AS* = 12.7 (± 2) eu and AG* (T=298K) = 14.1 (± 0.5) kcal/mol, were derived from a linear regression analysis of the Eyring plot using rate data obtained from 253-333 K. A qualitative analysis was also carried out using WIND NMR, and the observed and calculated 'H NMR spectra1 3 of [CH3-Ir] 2 are shown in Figure 3.3. The positive AS* (> 10 eu) value is consistent with a dissociative reaction mechanism 1 4 of the dinuclear complexes, [R-Ir]2 to presumably generate two coodinatively unsaturated, 5- coordinate, square pyramidal species, R-Ir-D. Figure 3.3. Variable temperature observed (Left) and calculated (right) ’H NMR Spectra for [CH3-Ir] 2 in 10 K increments. Only the spectral area of interest is shown. 3.2.3 Reactions of the Dinuclear Complexes, [(acac-0,0)2lr-R]2, with Ligands As anticipated from the proposed facile dissociation of the dinuclear complexes, these compounds react rapidly at room temperature with added ligands 81 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. such as pyridine or CH3 OH to quantitatively generate the corresponding trans-6 - coordinate, mononuclear octahedral complexes on mixing (Scheme 3.2). This is readily apparent by NMR analysis, as only one methyl (12 H ’s) resonance and one methine (2 H ’s) resonance are observed upon reaction of the dinuclear complexes with these ligands. While reactions of the dinuclear complexes with strong field ligands such as pyridine lead to 6 -coordinate monomeric species, R-Ir-L (L = Py), that can be isolated from solution, 6 -coordinate monomeric complexes formed from reaction with weak field ligands such as L = CH 3 OH can only be observed in solution (by NMR analysis) and are not sufficiently stable to isolate without decomposition back to the dinuclear complexes. Interestingly, attempts to generate the olefin complexes showed that olefin complexes, R-Ir-L (L = olefin), are also very labile. Thus, treatment of [CH3 -Ir] 2 in tol-d8 with 1 atm of ethylene shows no reaction by NMR, and only the broad peaks resulting from the dynamic equilibrium between the 6 -coordinate dinuclear and 5-coordinate mononuclear complexes are observed. However, on cooling the reaction mixture to 253 K, in addition to the stable dinuclear complex, a new set of resonances consistent with a trans-6 -coordinate, mononuclear olefin complex, CH3 -Ir-L (L - C2H4), can be observed by ’H and I3C NMR. Theoretical calculations show that the coordination of the ethylene only has a AH of -7.5 kcal/mol, indicating that the magnitude of the AS term will control whether the five or six coordinate species forms, with increased temperature drastically favoring the five coordinate complex. 82 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Consistent with the importance of the trans-effect, treatment of the dinuclear complexes with the weaker trans-effect acac-C ligand, [Acac-C-Ir]2 , in CDCI3 with ethylene (2-10 atm) at room temperature, does lead to the formation of a stable, trans-6-coordinate, mononuclear, octahedral complex that could be assigned to Acac-C-Ir-C 2 H 4 . However, as in the case of CH 3 -Ir-C 2 H4, all attempts at isolation were unsuccessful, presumably due to facile loss of ethylene. This lack of formation of stable olefinic complexes is in stark contrast to more electron rich complexes such as those based on more electron rich Ir(III) complexes with Cp or phosphine ligands that readily form stable olefinic complexes. While the ease of formation of coordinatively unsaturated intermediates in these dinuclear and mononuclear complexes may be largely due to the strong trans-effect of the strong-field alkyl groups on the stability of the Ir-C2 H4 bond or the bridging acac, it is possible that this may also be due to the so-called “cis- effect” resulting from the lone pair effects on the O-ligands.1 1 , 1 5 This effect, whereby 7i-donor ligands can labilize cis-groups, is presumed to operate by donation of the non-bonding 7 1-electrons into the empty metal orbital remaining after dissociation of ligands cis to the 7i-donor. Since the generation of coordinative unsaturation is critical to coordination catalysis, this could be an important characteristic of O-donor ligands and we are exploring the magnitude and scope of this possibility. 83 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.2.4 Ligand (L) Substitution Chemistry of (acac-0,0)2lr(R)(L) Complexes Pyridine exchange in the mononuclear complexes, R-Ir-Py, where R is alkyl or phenyl, is quite facile at room temperature. As expected on the basis of the trans-effect and the previous bond length data, the alkyl complexes are significantly more labile than the aryl analogues. Addition of 5 eq. of Py-ds to a CDCI3 solution of Ph-Ir-Py or CH3-Ir-Py at room temperature, leads to rapid Py exchange and formation of Ph-Ir-Py- d5 or CH3-Ir-Py-d5 on mixing, as shown in Scheme 3.4. At low temperatures, the rate of exchange is sufficiently slow on the NMR time scale to allow the reaction kinetics to be followed from the generation of free Py-Hs at various concentrations of Py-ds (under pseudo first order conditions). Kinetic studies, Figure 3.4, show that the reaction rate is essentially independent of added excess pyridine (52 mM-172 mM) for Ph-Ir-Py as expected for a dissociative process from an octahedral Ir(III) complex. The activation parameters for the rate of exchange for Ph-Ir-Py were estimated to be AH* = 22.8 ± 0.5 kcal/mol; AS* = 8.4 ± 1.6 eu; and AG*2 9 8 k = 20.3 ± 1 .0 kcal/mol, Figure 3.5. The pyridine exchange for CH3-Ir-Py was similarly found to be dissociative, with activation parameters of AH* = 19.9 ± 1.4 kcal/mol; AS* = 4.4 ± 5.5 eu; and 4 . + AG+ 2 9 8 k _ 18.6 ± 0.5 kcal/mol, Figure 3.5. The previously reported values of AH+ calculated by DFT methods5 for the loss of Py from Ph-Ir-Py (20.1 kcal/mol) and CH3-Ir-Py (17.3 kcal/mol) to generate the coordinatively unsaturated, 5- 84 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. coordinate, square pyramidal complexes, R-Ir-D are consistent with these experimental values. The generation of these 5-coordinate intermediates from the R-Ir-Py complexes by loss of Py is more unfavorable than in the case of the dinuclear complexes, and no dynamic behavior is observed by NMR below 100 °C. These facile exchange reactions of Ir(III), octahedral complexes are unusual, although not unique,1 6 and as discussed above, are likely due to the combination of the trans-influence of the hydrocarbyl group on the pyridine and the Tt-donor, O- ligands cis to the Py. R R Room Temperature CDC13/Py-D5 R= Ph; Ph-Ir-Py R = CH3; CH3-Ir-Py R= Ph; Ph-Ir-Py-d5 R = CH3; CH3-Ir-Py-ds Scheme 3.4. Pyridine Exchange. 85 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.001 0.0008 - 0.0006 - 0.0004 - 0.0002 - 100 [Py] (mM) 150 200 Figure 3.4. Plot of kobS versus [Py] for pyridine exchange with Ph-Ir-Py. o .o)32 0.0034 0 .0036 0 .0038 -10 - t -12 R2 = 0.9997 -14 - = 0 .9916 -16 1/T (1/K) Figure 3.5. Eyring plot for pyridine exchange with Ph-Ir-Py (■) and CH3-Ir-Py (A ). 86 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.2.5 Trans-Cis Isomerization of (acac-0,0)2lr(R)(Py) As discussed above, the (acac)2 lr(R)(L) complexes are typically synthesized and isolated only as the trans isomer, and it is this isomer that is utilized in these studies. However, a central premise in the proposed reaction mechanism for hydroarylation and H/D exchange is that the trans-(acac- 0,0)2lr(R)(L) complexes are capable of isomerization to a cis-configuration that is required for both the olefin insertion and C-H activation steps as seen in Scheme 1 7 3.1. Related rearrangement has been shown for tris-acac complexes, but no data was available on the barriers for such rearrangements with the bis-acac-0,0 Ir(III) complexes used in the catalytic studies. Earlier theoretical calculations5 predicted that the cis-Ph-Ir-Py complex should be more stable than the trans-Ph-Ir-Py isomer (by ~3 kcal/mol), and that the calculated barrier to trans-cis isomerization (AH* = 42.0 kcal/mol for Ph-Ir-Py) should be sufficiently high as to preclude the observation of this isomerization at room temperature and typical temperatures and reaction times employed during synthesis. To show feasibility for the trans-cis isomerization, we investigated the conditions required to generate the cis-Ph-Ir-Py complex from the trans complex, Ph-Ir-Py, Scheme 3.5. The reactions were carried out in medium pressure NMR tubes (with added Ar as an inert gas to prevent solvent refluxing) at 180 °C. To avoid issues of C-H activation reactions of the solvent, we examined the reaction of trans-complex, Ph-ds-Ir-Py, in C6 D6 where the reactions with the solvent would 87 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. be kinetically silent. The reaction progress was monitored by 'H resonances of the methyl groups of the acac-0,0 ligands in the starting trans-complex, Ph-Ir-Py, which appear as one peak that integrates to 12 protons relative to two methine protons. Importantly, control experiments showed that conversion of the trans complex, Ph-Ir-Py to the deuterated trans-complex, Ph-ds-Ir-Py, which is rapid in CfrDf,, does not change these m ethyl-acac-0,0 resonances. However, as the trans- cis isomerization destroys the C2 V symmetry of the molecule, the formation of the cis-complex should be readily evident in the 'H NMR. Importantly, we find that the trans-cis isomerization proceeds cleanly and quantitatively (by NMR analysis) on heating the Ph-Ir-Py complex to 180°C for 12 hr. This shows that, consistent with the theoretical predictions, the cis-Ph-Ir- Py is more stable than the Ph-Ir-Py. In order to isolate and identify the cis isomer, the reaction was carried out on a preparative scale in C6H6. The isolated cis-Ph-Ir-Py complex has been fully characterized by 'H and I3C NMR Ph-Ir-Py cis-Ph-Ir-Py Scheme 3.5. Trans-Cis Isomerization for Ph-Ir-Py. 88 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. spectroscopy and elemental analysis. ]H and 1 3 C NMR spectra of the complex are consistent with cis-octahedral geometry. 3.2.5.1 Mechanism of Trans-Cis-Isomerization of (acac- 0 ,0 ) 2 Ir(R)(Py) Given the central importance of this trans-cis isomerization in the C-H activation and hydroarylation catalysis of these complexes, we examined the isomerization of the Ph-Ir-Py complex in greater detail. In our previous theoretical study of this process,5 two mechanisms were found to be competitive in a study of the olefin complexes, R-Ir-Ol (01= olefin); a dissociative mechanism, where trans-cis isomerization occurs with a monomolecular transition state and an associative mechanism, where the trans-cis isomerization is facilitated by coordination of olefin. The first of these related mechanisms for the isomerization of the Ph-Ir-Py complex is shown in Figure 3.6 (solid line). In this mechanism, the 5-coordinate, square pyramidal intermediate, Ph-Ir-d, generated by reversible, dissociative loss of pyridine, undergoes a unimolecular (U), trans-cis isomerization to generate a 5-coordinate cis-intermediate, cis-Ph-Ir-d, that reacts with free pyridine to generate cis-Ph-Ir-Py (TS1 -> TS2 -> TS3). An alternative is a direct, bimolecular (B), associative reaction of free pyridine with the 5- coordinate trans-complex, Ph-Ir-d, to directly generate the cis-Ph-Ir-Py (TS1 -> TS4), also shown in Figure 3.6 (dashed line). 89 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. k, -Py n o - 1 ^ K I ^ 1+ Py fast Ph-Ir-Py ,-.-0 ^ I 0: Ph-Ir-D B _ k,k4[PhIrPy] kobs= ^ rateT C = k k-' 4 + Py ■ 3 +Py cis-Ph-Ir-Py k3[ P y ] » k _2 k_2 » k 3 [py] rateu _ k,k2 k3[PhIrPy] k_,(k3 [Py] + k_2) k i ^ P ^ k_,[Py] = k,k2 °b s k_,[Py] rateT C = „ _ k,k2 k3[PhIrPy] k - l k -2 k1 k2 k3 °b s k_,k_2 TS3 rateu _ k,k2 k3[PhIrPy] T C k_,(k3[Py] + k_2) T S 2 1 (46.5) cis-Ph-Ir-D k ,k 4[PhIrPy] E T S l Ph-Ir-D (20 . 1) Ph-Ir-Py (0.0) cis-Ph-Ir-Py (-2 .9 ) Figure 3.6. Possible unimolecular (U) and bimolecular (B) mechanism for Trans-Cis isomerization of Ph-Ir-Py. Predicted rate laws for trans-cis isomerization via the dissociative (solid line) and associative (dashed line) mechanisms are shown along with the calculated enthalpies in parenthesis. 90 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The predicted rate laws for the two possibilities are shown in Figure 3.6 (using a pre-equilibrium treatment for the trans-intermediate, Ph-Ir-d, and a steady state approximation for the cis intermediate, cis-Ph-Ir-d). As can be seen, only one set of conditions, via the pathway involving a unimolecular, trans-cis isomerization of Ph-Ir-d (TS1 TS2 -> TS3) when the formation of the 5- coordinate cis-Ph-Ir-d intermediate is rate determining (k 3[Py] » k _ 2), leads to a predicted inverse dependence of the kobS on added pyridine. If the formation of the cis-Ph-Ir-d is slow but reversible (k_2» k 3[Py]) or if the bimolecular pathway (TS1 TS4) is followed, the reaction rate should be independent of added pyridine. The experimental results are shown in and Figure 3.8. As can be seen, the rate of isomerization of Ph-Ir-Py to cis-Ph-Ir-Py in benzene at 180°C shows an inverse dependence on added pyridine over a range of 10 to 60 equivalents and is consistent with trans-cis isomerization following the unimolecular pathway (TS1 -> TS2 -> TS3, Figure 3.6) involving the rate determining formation of the 5-coordinate intermediate, cis-Ph-Ir-d. As can be seen from the rate law, it is possible that at very low concentrations of pyridine, k_2 » k3 [Py] , reaction via cis-Ph-Ir-d could also be expected to be independent of pyridine as under these conditions it is plausible that the unimolecular isomerization of cis-Ph-Ir-d back to the trans-intermediate, Ph-Ir-d, would be faster than trapping by pyridine. The observation that the last data point in Figure 3.8 (lowest pyridine concentration) deviates significantly from a straight line 91 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. through the other two points and the origin may indicate the onset of this behavior albeit three data points are not sufficient to establish this trend. Theoretical calculations also show that the barrier for reaction through TS4 is 4.5 kcal/mol lower in energy on the AH surface, Figure 3.6 (values in parenthesis). However, the T*AS term is expected to favor the dissociative mechanism, (assuming AAS(TS2 - TS4) <9.9 e.u. at 373K) and the reaction should proceed through TS2 and largely rate determining formation of the cis-5-coordinate intermediate, cis- Ph-Ir-d.. This energy diagram would lead to the prediction that the rate of exchange of pyridine from the cis-complex, cis-Ph-Ir-Py, would be expected to be substantially lower than from the trans-complex since exchange of the cis-complex would require generation of cis-Ph-Ir-d which is calculated to be -20 kcal/mol higher than the corresponding trans-intermediate. This is indeed the case and while the trans-complex, Ph-Ir-Py, exchanges with Py-ds on mixing at room temperature exchange is only observed with the cis-Ph-Ir-Py above 140° C. 2.5 2 1.5 1 0.5 0 R2 = 0.9907 R2 =0.9177 R2 =0.9784 0 5000 10000 15000 20000 25000 30000 time (s) | ♦ 1.25M___________ A 2.5M_____________■ 0.5M_________ j Figure 3.7. First order Plots for Trans-Cis isomerization of Ph-Ir-Py. 92 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.5 2.5 1/[Py] (1/M) Figure 3.8. Plot of kobs vs l/[Py] for Trans-Cis isomerization of Ph-Ir-Py. These results suggest that if C-H activation reactions with trans-(acac- 0,0)2lr(R)(L) complexes require coordination to the cis-intermediate, cis-R-Ir-D, that the trans-cis isomerization could be expected to be an important contributor to the overall reaction rate in reactions from the trans-complexes. These results are also potentially relevant to design considerations for improved catalysts based on these trans-(acac-0,0)2 Ir(III) organometallic species. Many reactions require two mutually cis- sites for reaction. This geometry is typically achieved through the use of cis-tetradentate or use of tripodal ligands. An alternative strategy is to access this geometry with octahedral metal complexes having cis-bis-bidentate spectator ligands either from the cis or trans-configurations. However, a fundamental issue with such a strategy that could lead to decreased reactivity is that the trans configuration could be more stable than the cis and/or the barriers for isomerization can be significant. Before this study, given the known kinetic 93 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. inertness of Ir complexes, we regarded this to be likely with the trans-(acac-0 ,0 ) 2 Ir(III) complexes, and considered that the reactivity could be improved by designing cis-restricted bis-acac-0,0 ligand motifs. Importantly, however the observation that the cis-(acac-0,0)2lr(Ph)(Py) complex is more stable than the trans-isomer now indicates that such a strategy may not lead to improved rates for C-H activation for this complex. Indeed, depending on the relative stability of the trans and cis bis-acac-0,0 Ir(III) complexes (~3 kcal/mol for the pyridine complexes as discussed above and comparable for the olefin complexes5 on the basis of theoretical calculations), the cis-complexes could be less active (in the case of the pyridine complex) or comparable (in the case of the olefin complexes) assuming that TS2 and TS3 are comparable in energy. These predictions are being investigated and preliminary results show that rate of C-H activation of benzene with cis-Ph-Ir-Py is slower than the corresponding trans-isomer. Thus, while the trans-isomer catalyzes H/D exchange between Tol-dg and C6H6 with a TOF of 1 x 10"2 sec"1 (TN-50 after 2 h) at 160 °C, the cis-Ph-Ir-Py exhibits at TOF of 2 x 10"4 sec"1 (TN~1 after 2 h) under these conditions (Figure 3.9). This drop in rate consistent with the predicted ground state differences between trans and the more stable cis- Ph-Ir-Py These results are encouraging and suggest that other readily available cis or trans octahedral complexes with bis-bidentate spectator ligands may allow access to two mutually cis-sites without significant kinetic penalty. We are currently expanding our study of other bis-bidentate octahedral metal complexes for C-H activation and other reactivity studies.1 8 94 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80.0 60.0 40.0 20.0 0.0 50 100 150 time/min ♦ Ph-Ir-Py a Cis Ph-Ir-Py Figure 3.9. H/D exchange between and Tol-dg catalyzed by Ph-Ir-Py and cis-Ph-Ir-Py at 160°C. 3.2.6 C-H Activation of Arenes by (acac-0,0)2lr(R)(L) 3.2.6.1 Rate Laws for Plausible Mechanisms of Arene C-H Activation by (acac-0,0)2 Ir(R)(L) We define the C-H activation reaction as a reaction between a C-H bond and species MX that proceeds via coordination chemistry and without the involvement of free-radicals to generate M-C intermediates. As a result of the coordination characteristics of the C-H activation reaction, it is generally observed to be composed of two steps: coordination of the C-H bond to the metal to generate an intermediate alkane or arene complex followed by a C-H cleavage step to generate the M-C intermediate. ’ Given the facile rate of ligand exchange with these (acac-0,0)2lr(R)(L) complexes, it is plausible that the C-H activation reaction proceeds via the coordinatively unsaturated, trans-5-coordinate 95 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. intermediate, R-Ir-D. From this intermediate two general pathways for C-H activation can be considered. One possibility is that the benzene coordination occurs before the trans-cis isomerization. In this case, benzene could react directly with the trans intermediate, R-Ir-D, by coordination and C-H cleavage leading to a seven- coordinate, Ir(V), intermediate or transition state that then undergoes rearrangement and loss of RH to generate the Ph-Ir-L product as shown in Scheme 3.6. However, this pathway seems unlikely, as attempts at investigating this pathway by DFT calculations indicate that the intermediate or transition state resulting from C-H oxidative addition trans to the R group in the trans intermediate R-Ir-D could not be located, with all geometries collapsing back to R-Ir-D. Attempts at constraining pertinent geometry parameters such as Ir-C and/or Ir-H distances all revealed substantial energy increases on the order of >50 kcal/mol. The unfavorable C-H activation with this coordinatively unsaturated trans-intermediate, R-Ir-D, is most likely due to a combination of two effects: A) the destabilizing trans-effect of the R group and B) the inflexibility of the trans acac ligands, caused by the extended aromatic system generated over the two, six- membered rings, which is necessarily perturbed if the rings are scissored away to make room for an oxidative addition. 96 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. >=^o. R I „.iO- r lr c i j ^ o - L R -Ir-L - o . Ph I c r ^ | L Ph-Ir-L Fast + L -L -RH + L R -Ir-D Ph Scheme 3.6. Possible C-H activation pathway involving the trans intermediate, R -Ir-d. The more likely mechanisms for the C-H activation reaction from the 5- coordinate, trans-intermediate, R -Ir-d are shown in Figure 3.10, involving coordination of benzene cis to the R group during the C-H cleavage step. On the basis of the trans-cis isomerization studies of the Ph-Ir-Py complex, it could be anticipated that the most likely pathway would involve a unimolecular trans-cis isomerization of R -Ir-d to cis-R-Ir-d, followed by benzene coordination to generate a cis-R-Ir-PhH benzene intermediate complex, C-H cleavage and loss of RH (TS5 TS6 -> TS7 TS8). Such a pathway is consistent with the observations that the cis-Ph-Ir-Py complex undergoes both Py exchange and C-H activation at slower rates than the trans (vide infra), earlier theoretical calculations5, and the studies on C-H activation with alkyl-Ir(III) complexes3 that 97 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. show a requirement for cis-orientation for H transfer. However, there is no requirement that cis-benzene coordination is similar to trans-cis isomerization of the Ph-Ir-Py complex, and pathways involving bimolecular reactions e.g., TS9 and TS10, between benzene and R-Ir-D can be proposed for the CH activation as shown in Figure 3.10. In all cases the reaction rates are expected to show an inverse dependence on pyridine, given the low experimentally measured barrier (AG = ~20 kcal/mol) for loss of pyridine from R-Ir-Py, while the dependence on benzene can be more complex. These dependences and other aspects of the kinetics of the C-H activation reaction were examined in an attempt to distinguish between these possible pathways. 98 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ksk8[RlrPy][PhH] k = k 5k 8[PhH ] k.5 [Py] k_,[Py] PhH, - RH + Py cis-R-Ir-D R-Ir-Py Ph-Ir-Py rateU _ k5 k6 k7[RIrPy][PhH] C H k_5[Py](k7[PhH] + k_6) _k,k 6[RIrPy] rdie^u —----------------------- k_5[Py] k5 k6 k7 [RIrPy][PhH] k 5 k8[RIrPy][PhH] I r - TS10 \ - " ”159 „ ksk6 k7[RIrPy][PhH] C H k_5 [Py](k7[PhH] + k_6) TS6 TS7 TS8 TS5 / cis-R-Ir-D cis-R-Ir-PhH R -Ir-D R-Ir-Py - RH Ph-Ir-Py Figure 3.10. Possible C-H activation pathways involving reaction of benzene with R-Ir-Py species. 99 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.2.6.2 Products of Arene C-H Activation with (acac- 0 ,0 ) 2 Ir(R)(L) As mentioned earlier, these thermally, protic and oxidant stable O-donor Ir(III) complexes readily undergo stoichiometric C-H activation of arenes and alkanes. The reaction of R-Ir-Py with C6D6 at 130°C for 1 h leads to irreversible loss of RD and quantitative formation of Ph-ds-Ir-Py (based on *H and 1 3 C NMR by comparison to independently synthesized and fully characterized Ph-Ir-Py). This reaction is general and can be carried out with Acac-C-Ir-Py, Ph-Ir-Py, CH3 -Ir-Py, CH3 CH2-Ir-Py and PhCH2CH2-Ir-Py as shown in Scheme 3.7. Thus, when the reaction of CH3 -Ir-Py is carried out in C6D6 at 130°C for lh, the quantitative formation of CH3 D and Ph-ds-Ir-Py has been confirmed by GC/MS (of the gas and liquid phase) and ]H NMR spectroscopy using trimethoxybenzene as an internal standard. The higher deuterium isotopomers of methane, CHn D4 _ n, were not observed under the reaction conditions even after longer reaction times. This shows that the generation of methane under these conditions is essentially irreversible (at higher temperatures, reaction with methane can be observed). Indeed, theoretical calculations for the replacement of methyl for phenyl is •5 ^ exothermic by ~15 kcal/mol. ’ Similarly, heating other alkyl complexes (PhCH2 CH2-Ir-Py and CH3 CH2-Ir-Py) in neat C6D6 led to the quantitative and irreversible formation of the corresponding mono-deuterated hydrocarbons, PI1CH2CH2D and CH3CH2D, respectively, and Ph-d5-Ir-Py. In the case of 100 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reaction of PhC H 2 CH 2 -Ir-Py, only the PI1 CH2 CH2 D regio-isotopomer is formed as determined by ]H NMR of the reaction products. Interestingly, unlike the alkyl-Ir complexes, treating Ph-Ir-Py with tol-dg for short times (-20% conversion to minimize post H/D scrambling o f the benzene product since this reaction is reversible) led to the formation of multiple deuterated isotopomers of benzene rather than only the mono-deuterated product, C6 H 5D. This observation of multiple deuterium incorporation into the benzene eliminated from Ph-Ir-Py on treatment with tol-dg is characteristic of the generation of intermediate arene complexes in a rate determining step during C-H activation reactions.1 9 To examine this possibility and elucidate the details of the C-H activation reactions we turned to kinetic studies. Scheme 3.7. C-H Activation of Benzene with R-Ir-Py. 101 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.2.6.3 Activation Barrier for C-H Activation using CH3 -Ir-Py The CH3 -Ir-Py complex was used to obtain the barrier for arene C-H activation. Due to the poor solubility of the Ph-Ir-Py in benzene and overlapping aromatic resonances in the 'H NMR, the arene C-H activation barrier with this complex could not be accurately obtained. As previous studies showed that the C- H activation was inhibited by added pyridine, the activation barriers were obtained at constant pyridine concentrations. The temperature dependence of the reaction was examined over the range of 140-180°C in neat C6D6 at a constant pyridine concentration ([PyMCftDe] = 0.045). The reaction follows clean first order kinetics, and to determine the reaction rates, 'H NMR spectroscopy of the methyl resonances of the acac-0,0 ligands was used to monitor the irreversible disappearance of the CH3 -Ir-Py starting material and the formation of the Ph-ds- Ir-Py product for three half lives. Activation parameters were obtained from an Eyring plot as shown in Figure 3.11. The activation entropy (AS*) was estimated to be 11.5 (±3.0) eu along with a AH* of 41.1 (±1.1) kcal/mol and AG* 2 9 8 of 37.7 (±1.0) kcal/mol. The PhC H 2 CH 2 -Ir-Py complex was found to react at essentially the same rates as CH3-Ir-Py and as can be seen in Figure 3.11, the experimentally determined rate for arene CH activation with PhCH2CH2-Ir-Py shows similar temperature dependence to that of CH3-Ir-Py. The previously calculated C-H activation barrier5 for a pathway proceeding via a cis-intermediate was found to be 102 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ~ 43 kcal/mol (AH3 ') for the PhC H 2 CH 2 -Ir-Py and is consistent with the value obtained in this experimental study. 21.00 - ■ f c 19.00 - R2 = 0.9988 15.00 0.0021 0.0022 0.0023 0.0024 0.0025 1/T (1/K) Figure 3.11. Eyring plot for the reaction of CH3 -Ir-Py ( ♦ ) with C6 D6 at [Py]/[C6 D6 ] = 0.045. kc0 rr = kobs x [Py]/ [C6 D6 ], A = PhCH2 CH2-Ir-Py. 3.2.6.4 Dependence of C-H Activation on Pyridine Concentration If the C-H activation reaction proceeded, as proposed in Figure 3.10, from the 5-coordinate trans-intermediate, R-Ir-D, then the C-H activation should show an inverse dependence on added pyridine as shown in the possible rate laws. To confirm this, the rate of the C-H activation reaction of PhCH2 CH2-Ir-Py was obtained in the presence of 15 to 44 equivalents of pyridine (223 mM to 669 mM), Figure 3.12 and Figure 3.13. The reactions are clean and quantitatively generate 103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the trans-complex, Ph-ds-Ir-Py. There are very little complications at these concentrations of pyridine with C-H activation of the pyridine. The rate of formation of the cis-complexes (R-Ir-Py, R = Ph or Alkyl) is slower than the C-H activation reaction at 140 °C and is not observed on the time scale of these experiments. As can be seen, the rate of C-H activation shows an inverse dependence on added pyridine. This is consistent with the C-H activation reaction proceeding via the formation of the trans-5-coordinate complex, PhCH 2 CH 2 -Ir-D , that is formed by prior, rapid, reversible, dissociative loss of pyridine and is consistent with either rate law shown in Figure 3.10. 0.6 -[ 0.5 - 0.4 - R2 = 0.9688 0 5000 10000 15000 20000 25000 30000 time (s) ♦ 223mM ■ 446mM A 669mM Figure 3.12. First order plots for P y added for C-H activation of PhCH 2CH 2 -Ir-Py at 140°C. 104 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.40 R2 = 0.996 1.60 - 0.80 - 0.00 Figure 3.13. Plot of kobs vs 1/Py for C-H activation of PhC H 2CH2 -Ir-Py at 140°C. 3.2.6.5 Arene Substrate Concentration Dependence As can be seen in Figure 3.10 from the various possible mechanisms and associated rate laws for arene C-H activation, there is the possibility that the reaction could show a direct dependence, independence or more complex dependence on the benzene concentration. Both arene dependent and independent • 90 91 kinetics has been reported for arene for C-H activation. ’ To begin to distinguish between these possibilities, we examined the dependence of the arene C-H activation rate on the arene substrate concentration. A key challenge in carrying out such a study is to identify an inert solvent that could be used as a diluent for the benzene substrate. Due to a combination of reactivity and solubility issues, solvents such as fluoropyridine, hexafluorobenzene or trifluoroethanol 105 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. could not be utilized. Instead, we utilized a strategy of carrying out the C-H activation reactions in cyclohexane-di2 solvent using the Cy-dn-Ir-Py (where Cy- d] i is the perdeuterated cyclohexyl group), with varying amounts of added excess C6D6 (1600 mM - 5600 mM to ensure pseudo first order reaction conditions). Under these conditions, any reactions with the solvent would be degenerate and kinetically silent. The reactions were followed by analyzing the loss of the Cy- dn-Ir-Py relative to trimethoxybenzene as an internal standard at 120 °C, and the results are shown in Figure 3.14. The Ph-ds-Ir-Py product was not completely soluble under these reaction conditions, and to ensure that loss of Cy-dn-Ir-Py resulted only from formation of Ph-ds-Ir-Py, CD2 CI2 was added after reaction to dissolve all products and the trimethoxybenzene was used as an internal standard to ensure that Ph-ds-Ir-Py produced accounted for >95% of the reacted Cy-dn-Ir- Py The lack of unreacted Cy-dn-Ir-Py after long reaction times ensured that the reaction to generate Ph-ds-Ir-Py was irreversible under the reaction conditions and simple first order plots could be used to obtain the rate constants. As can be seen from Figure 3.14, the C-H activation reaction shows a linear dependence on the benzene concentration that indicates that benzene is involved prior to or in the rate determining step. This observation rules out the k k unimolecular possibility that k 7[ P h H ] » k _ 6, k o b s = — 5 6 , (Figure 3.10), and k_5[Py] shows that, unlike the case with isomerization of Ph-Ir-Py, that (at least at the concentrations of benzene examined) the formation of the cis-5-coordinate 106 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. intermediate, cis-R-Ir-D, can not be the rate determining step and that benzene is involved in the rate determining step for arene C-H activation. Indeed, this observation does not provide any evidence for the formation of a cis-5-coordinate intermediate, cis-R-Ir-D, or indicate whether an arene complex is formed, if the C-H cleavage step is rate determining or if the C-H activation reaction is concerted from the trans-5-coordinate intermediate, R -Ir-d. To distinguish between these possibilities, we turned to studies of the kinetic deuterium isotope effects on the C- H activation reactions of R-Ir-Py. 0.003 R? = 0 .9562 0.002 ■ * 0.001 2000 600 0 80 0 0 Figure 3.14. A plot of kobS vs [CeHe] at 120 °C with Cy-du-Ir-Py. 107 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.2.6.6 Isotope Effects on the Rate of C-H Activation with (acac- 0,0)Ir(R )(L) Complexes As discussed above, the observation that the reaction of Ph-Ir-Py with tol- dg leads to multiple deuterated benzenes is most consistent with the C-H activation reaction proceeding via the formation of an intermediate arene complex, followed by rapid and reversible C-H cleavage before loss of the arene. To examine this possibility in greater detail, we turned to the now classic method, developed by W. Jones, of providing evidence for the intermediacy of arene complexes by comparison of the deuterium kinetic isotope effect (KIE) on the relative rates of C- H activation when reactions are carried out with a mixture of and with 1,3,5-trideuterobenzene.1 9 Three possibilities for the C-H activation of benzene with CH3 -Ir-Py can be considered with respect to the formation of arene complexes as shown in Figure 3.15: A) a concerted process without the involvement of an arene-complex (TS5 TS10), B) rate determining C-H cleavage proceeding via an arene complex, cis-CH3-Ir-PhH, (TS5 TS9 TS11 or TS5 -> TS6 -> TS7 ->TS11) that is kinetically indistinguishable by KIE from case A, and C) rate determining trans to cis isomerization and benzene coordination followed by rapid C-H cleavage (TS5 TS6 TS7 TS8). As can be seen if C-H cleavage is rate determining, case A or B, both the C6D6/C6H6 mixture as well as neat 1,3,5-C6D3H3 will be expected to show a normal kinetic isotope effect. However, if an arene complex is formed in a rate determining step 108 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and followed by faster C-H cleavage (case C), only the reaction with 1,3,5-C6D3 H3 will show a normal KIE; the reaction with C6D6/C6H6 will show no KIE. Ph-Ir-Py Figure 3.15. Possible reaction coordinate for reaction of CH3-Ir- Py with 1,3,5-C6 D3 H3. As discussed above, the reaction of CH3-Ir-Py with CeD6 proceeds quantitatively and irreversibly to produce only CH3 D. Thus, analysis of the CH4 :CH3 D ratio produced from C-H activation with CH3-Ir-Py provides a convenient method of determining the KIE for C-H activation with this complex. The C-H activation reaction was carried out by reaction of CH3-Ir-Py at 110°C with neat l,3,5-CeH3 D3, a 1:1 (molar) mixture of C6H6/C6D6 and neat C6D6 as 109 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. solvents in separate reactions. In all three cases, the methane generated was analyzed by GC-MS, and the molar ratios of the methane C H ^C f^D isotopomers were determined by deconvolution of the mass peaks based on actual response factors and fragmentation patterns from pure samples of CH4 and CH3 D. Since it is known that these (acac-0,0)Ir(III) complexes will catalyze H/D exchange between arenes, the reactions were carried out for three half lives and GC-MS analysis of the various solvents after reaction confirmed that no significant extent of H/D scrambling had occurred in the CeDg-CcHg mixture or 1,3,5-C6H3D3 solvents. The results are shown in Table 3.1. Table 3.1. Methane isotopomer ratio obtained from reaction of CH 3 -Ir-Py with various solvents. SOLVENTS Isotopomer8 c 6 d 6 1,3,5-C6 H 3 D3 C^Hfi: C 6 D6 (1 : 1 molar mixture) c h 4 0 76 50 c h 3 d 1 0 0 24 50 a See experimental section for details. As discussed above, the observation that only CH3D was produced in the reaction with neat C6 D6 ruled out any error that could be introduced from post H-D exchange of the generated methane. 2 2 Control experiments in neat C6 H6 also confirmed that only CH4 is generated. As can be seen, no kinetic isotope effect is 110 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. observed for the CeDe/CeHe mixture since a 1 : 1 ratio of CH ^C f^D is produced. This result effectively rules out pathways via TS10 and TS11 that involve C-H cleavage in the rate determining step. The rather large kinetic isotope effect (considering the temperature of 110°C) of 3.2 (±0.2) that is observed with 1,3,5- C6H 3 D3 suggests that the reaction proceeds via TS5 -> TS6 TS7 -> TS8 or TS5 -> TS9 -> TS8 that involve rate determining coordination of benzene, followed by rapid CH cleavage. These results provide strong evidence that intermediate arene complexes are involved in the C-H activation with the O-donor (acac-0 ,0 )2 lr(R)(L) complexes and that C-H activation with these O-donor complexes are inner-sphere processes involving substrate coordination. 3.2.6.7 Does The C-H Activation Reaction Proceed via a Cis-5- Coordinate Intermediate? Importantly, these KIE and kinetic studies do not address the question of whether the formation of these intermediate arene complexes are generated via the formation of the cis-5-coordinate intermediate cis-R-Ir-D (TS5 -> TS6 -> TS7, Figure 3.15), or directly, in an associative step from the trans-5-coordinate intermediate, R-Ir-D (TS5 -> TS9, Figure 3.15). The trans-cis isomerization studies of the Ph-Ir-Py complex provide evidence for the rate determining formation of such cis-intermediates, vide-supra. Since the formation of the cis- benzene complex, cis-R-Ir-PhH, is essentially the same process as the formation 111 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the cis-Pyidine complex, cis-Ph-Ir-Py, it is likely that formation of the benzene complex also proceeds by formation of the cis-5-coordinate intermediate, cis-R-Ir- □ , and that this should constitute the bulk of the barrier for the reaction with benzene. If this is the case, the rate constant for C-H activation should be similar to the rate constant for the trans to cis-isomerization for these complexes (obtained when the reaction rates are corrected for benzene and pyridine concentrations). This has been examined both theoretically and experimentally. Theoretical results for the reaction of CH3 -Ir-Py with benzene, summarized in Figure 3.16, show that these rates constants should be comparable as the formation of cis-R-Ir-D is found to be the slowest step in both reactions. The cis/trans isomerization has a AH* = 44.6 kcal/mol, while C-H activation has a AH* = 43.4 kcal/mol. AS terms are expected to be of similar magnitude, as the total number o f molecules does not change. 112 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 44.6 (TS) X ' 0^|\ f t \ -Ct° / \39.6 43.4 (TS) 27.7, 'CH .17.3 ■CH , - Pyr + Pyr .+ Pyr 41.1 19.9 -2.9 •CH. i-15.8 Figure 3.16. Theoretical calculations of trans-cis isomerization and C-H activation. Boxed values are the experimental value for that step. Experimentally, the rates of the trans-cis and C-H activation have been obtained under identical conditions (180 °C and pyridine to benzene ratio of 0.045) where the trans-cis isomerization shows an inverse dependence on pyridine, and the C-H activation a direct dependence on benzene. Taking the ratio of the appropriate cases of the rate laws, Figure 3.10, and assuming these reactions proceed via the formation of the cis-5-coordinate intermediate, Scheme 3.8, allows the ratio of the rate constants for the C-H activation, k C H and trans-cis isomerization, k T C to be compared. As can be seen, this ratio is ~ 1. It may be 113 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. considered that this specific comparison is not entirely valid as different complexes, the Ph-Ir-Py and the CH3-Ir-Py, are utilized in the trans-cis isomerization and CH activation reactions, respectively. However, extrapolation of the equilibrium constants for the loss of pyridine from Ph-Ir-Py and CH3 -Ir-Py show that at 180°C the values are comparable, ~0.7 E-9 and -2.0 E-9, respectively, and we anticipate that the trans-cis isomerization step should be energetically similar for these complexes. This suggests that the comparable rate constants for these reactions are consistent with the C-H activation and trans-cis reactions proceeding via a common intermediate, the cis-5-coodinate intermediate, cis-R-Ir- □ and that the energetics of benzene coordination to this species, TS10 and k/7 (Figure 13 and 18), do not significantly contribute to the activation barrier for CH activation. Rate law for CH activation Rate law for trans-cis isom erization ( k_6 » k 7[PhH] ) ( k3[P y ]» k_2) r a t e cH k C H [R lrPy] [PhH] [Py] kT C [PhIrPy] rate^c _ k T C [PhIrPy] ratec uH ~ k C H [R lrP y lP h H ] k C H rate^H 8x10 4 k T C _ rate^c [PhH ]_ 4.5xlO~5[11.2]_ 0 6 - ^ Scheme 3.8. Ratio of rate laws for isomerization and C-H activation. 114 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A comparison of the rates for trans-cis isomerization and C-H activation via the cis-R-Ir-D intermediate also explains why no cis-R-Ir-Py species are detected under typical C-H activation conditions with R-Ir-Py (-140 °C and no added Py). Under these conditions, the appropriate rate law for the trans-cis isomerization is that shown in Scheme 3.9, where because of the low concentration of pyridine the reaction is independent of pyridine (k. 2 » k3[Py], Figure 3.6) while the rate of C-H activation remains inversely dependent on pyridine and directly dependent on benzene (k.6 « k7[PhH], Figure 3.10). Thus, assuming that the rate constants, k jc and for these steps are comparable, at comparable concentrations of complexes the relative rates of trans-cis isomerization to C-H activation would be given by [Py]/[PhH] which, based on the experimental equilibrium values for pyridine dissociation from R-Ir-Py is - 10'6. This low value is consistent with the observation that no cis-products are detected after the C-H activation reaction is complete. At higher pyridine concentrations, the ratio of these rates would be expected to become comparable (as the rate law changes to those shown in Scheme 3.9 and both reactions become independent of added pyridine), and the trans-cis isomerization should be observed along with C-H activation. This is observed experimentally and at pyridine concentrations above 1 M, the cis-Ph-Ir-Py is observed during the C-H activation of benzene with CH3 - Ir-Py. However, clean kinetics could not be obtained under these conditions as the reaction is complicated by CH activation of pyridine. 115 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rate law for CH activation Rate law for trans-cis isomerization ( k_6 » k 7[PhH] ) ____________ ( k_2 » k3[Py])_ u _ ^cH [^ rPy][^^H] rate^c =k*c[PhIrPy] [Py] rateyc k;c [PhIrPy][Py] [Py] 1Q _6 rate“„ kc„[RIrPy][PhH] [PhH] Scheme 3.9. Ratio of rate laws for isomerization and C-H activation. 3.3 Conclusion The chemistry of novel (acac-0,0)2lr(R)(L) organometallic complexes has been examined in detail. The dinuclear, [R-Irh, as well as mononuclear complexes, R-Ir-L, have been found to be labile complexes that are in equilibrium, via dissociative processes, with trans-5-coordinate species, R-Ir-D, that are key intermediates in the substitution chemistry of these complexes. These R-Ir-L complexes have also been shown to undergo trans-cis isomerization via a rate determining, unimolecular isomerization of R-Ir-D to cis-R-Ir-D, followed by rapid reaction with substrates. Bimolecular pathways involving direct reaction of the substrate with the trans-intermediate, R-Ir-D, are not consistent with the experimental or theoretical results. Arene C-H activation with these O-donor complexes has been shown to occur via an inner-sphere process that involves substrate coordination and 116 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. intermediate formation of an arene complex, followed by C-H cleavage. While ligand exchange reactions readily occur via the trans-5-coordinate intermediate, R- Ir-D, both experimental and theoretical results are consistent with the C-H activation reaction requiring further reaction of R-Ir-D to generate the cis intermediate, cis-R-Ir-D befor reaction. Experimental and theoretical studies are consistent with the formation of this species constituting the bulk of the barrier for the C-H activation reactions and serve to explain why the rates of trans-cis isomerization and C-H activation are comparable. Overall the C-H activation reaction with R-Ir-Py has been shown to proceed via four key steps: A) a pre equilibrium loss of pyridine that generates a trans-5-coordinate, square pyramidal intermediate, R-Ir-D, B) a largely rate determining, unimolecular, isomerization of the trans-5-coordinate to generate a 5-coordinate intermediate, cis-R-Ir-D, C) coordination of benzene to this species to generate a discrete benzene complex, cis-R-Ir-PhH and D) rapid C-H cleavage step. Kinetic isotope effects on the CH activation comparing reaction with a mixture of C6 H6 /C6 D6 (KIE = 1) and 1,3,5- C6 H3 D3 (KIE ~ 3) are consistent with the C-H activation occurring via rate determining arene coordination, followed by rapid C-H cleavage. In addition to showing that common O-donor ligands can be utilized in the design of efficient, stable C-H activation catalysts capable of functionalization reactions, these studies show that the use of readily available, bis-chelating O- donor ligands, based on the acac-0 , 0 ligands, may be used to access coordination reactions, such as C-H activation, that require two mutually cis-sites for reaction. 117 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. These O-donor complexes are effective hydroarylation catalysts, and it will be interesting to rationalize the results of the current studies with the various catalytic steps of the hydroarylation reaction. For example, if mutually cis-sites are required for the olefin insertion step, then the rate of the trans-cis isomerization could be expected to be a lower limit for the catalytic rate starting from the trans complex while the rate for loss of pyridine would be expected to be the lower limit starting from the cis-complex. 3.4 Experim ental Section General Considerations. Spectroscopy. Liquid phases of the organic products were analyzed with a Shimadzu GC-MS QP5000 (ver. 2) equipped with a cross-linked methyl silicone gum capillary column, DB5. Gas measurements were performed using a GasPro column. The retention times of the products were confirmed by comparison to standards. NMR spectra were obtained on a Bruker AC-250 (250.134 MHz for 'H and 62.902 MHz for 1 3 C), a Bruker AM-360 (360.138 MHz for ]H and 90.566 MHz for 1 3 C) or on a Varian Mercury 400 (400.151 MHz for ]H and 100.631 MHz 1 for C) spectrometer. Chemical shifts are given in ppm relative to TMS or to residual solvent proton resonances. All carbon resonances are singlets unless otherwise mentioned. Resonances due to pyridine are reported by chemical shift and multiplicity only. All pyridine complexes showed similar coupling constants 118 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (3 J = 5.00, 4J = 1.5, o-H py; 3 J = 8.0, 4J = 1.5, p-H py; 3 J = 6.50, m-H py). The temperature of the probe was monitored using methanol or ethylene glycol samples with an added trace of concentrated aqueous hydrochloric acid. Errors in reported temperatures are ±2°C at a maximum. Fast atom bombardment (FAB+ ) mass spectrometry was carried out using a VG ZAB-SE, high resolution double- focusing mass spectrometer at PASAROW Mass Spectrometry laboratory at UCLA using Nitrobenzene alcohol (NBA) as the matrix. Materials and Analyses. All manipulations were carried out using glove box and high vacuum line techniques. Benzene, benzene-d6, toluene-dg and THF were purified by vacuum transfer from sodium benzophenone ketyl. CD2 CI2 and pyridine were dried by vacuum transfer from CaH2. Synthetic work involving Iridium complexes was carried out in an inert atmosphere in spite of the air stability of the complexes. Reagent-grade chemicals and solvents were used as purchased from Aldrich or Strem. Complex [Acac-C-Ir]2 , 7 Acac-C-Ir-H20 , 3 Acac-C-Ir-Py, 3 Ph-Ir-H20 , 3 Ph-Ir-Py, 3 diethylmercury2 3 and bis-(2- phenethyl)mercury2 4 were prepared as described in the literature. Elemental analyses were done by Desert Analytics laboratory, Arizona. 119 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. [Ir(|i-acac-0,0,C3 )(acac-0,0)(CH3 )]2 [CH3-Ir]2: M ethod A: In the glove box, a Schlenk flask fitted with a Teflon valve was charged with acac-C-Ir-H2 0 (342 mg, 0.675 mmol) and suspended in THF (100 mL). To this, was added a toluene solution of ZnMe2 (2.0 M toluene, 370 pL, 0.740 mmol). Upon addition, the solution developed a slight orange color. The flask was then sealed, removed from the glove box, and placed in a 60°C oil bath for 2 h. The resulting slightly cloudy orange solution was cooled to room temperature whereby a small amount of a white precipitate settled. The solution was poured onto water (200 mL), extracted with CH2C12 (2 x 100 mL), and then dried over Na2S C > 4 . Filtration, followed by removal of solvent in vacuo, yielded a solid. Addition of acetone and precipitation with ether at -25°C afforded a bright yellow solid. The clear yellow solution was decanted and the solid dried in vacuo, to afford [CH3 -Ir] 2 as an analytically pure bright yellow powder (205 mg, 75% yield). Comparable yields were obtained when [acac-C-Ir] 2 was used. M ethod B: A solution of acac-C-Ir-H2 0 (340 mg, 0.674 mmol) in methanol was added to a Schlenk flask fitted with a Teflon valve. To this, dimethylmercury (55 pL, 0.7 mmol) was added through a syringe. The reaction flask was heated to 60°C for 2 h and then cooled to room temperature. The resulting solution was vacuum transferred to leave a crude orange powder. The 120 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. crude reaction mixture was loaded on a silica gel column and eluted with THF to afford [CH3-Ir]2 as yellow powder (220 mg, 80% yield). 'H NMR (CDCI3 , RT): Due to the fluxional nature of the dinuclear complex in CDCI3 at ambient temperature, the bridging and non-bridging acac resonances are broadened. 8 5.40 (br s, 4H, acac-C3 H), 1.96 (s, 6 H, Ir-C /^), 1.83 (br s, 24H, acac-CH3 ). !H NMR (CDC13, -33 °C): 5 5.50 (s, 2H, O-acac-C 3 tf), 5.34 (s, 2H, |i-acac-C 3tf), 1.89 (s, 6 H, Ir-Ctf3 ), 1-88 (s, 12H, O-acac-CH3 ), 1.77 (s, 12H, |i-acac-Ctf3 ). 1 3C{]H} (CDC13, -27 °C): 8 191.55 (|i-acac C=0), 183.14 (O- acac C=0), 103.79 (0-acac-C 3H), 81.56 0i-acac-C 3 H), 28.53 (fX-acac-CH3 ), 27.32 (0-acac-CH3 ), 21.31 (Ir-CH3 ). ]H NMR (CD3 OD): 8 5.46 (s, 2H, C3 //), 1.76 (s, 12H, acac-Ci/3), 1-75 (s, 3H, CHi). ,3 C{!H} NMR (CD3 OD): 5 184.3 (acac C=0), 103.8 (acac-C3H), 26.4 (acac-CH3), -34.9 (CH3 ). Anal. Calcd. for C2 2 H3 4 lr2 0 8: C, 32.58; H, 4.23. Found: C, 31.87; H, 3.94. Ph p h [Ir(|i-acac-0 ,0 ,C3 )(acac-0 ,0 )(CH2 CH2 Ph) ] 2 [PhCH2 CH2 -Ir] 2 - [PhCH2 CH2-Ir] 2 was synthesized according to Method B with acac-C-Ir-H2 0 (100 mg, 0.197 mmol) in 10 mL of methanol and using bis-(2- phenethyl)mercury (100 pL, 0.25 mmol). The crude reaction mixture was purified 121 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. using column chromatography (silica gel) using a gradient solvent (100% THF to 1:1 THF-Ether) and recrystallized from a mixture of CH2 CI2 and hexanes. The title compound was isolated as an orange powder (60mg, 60% yield). 'H NMR (CDCI3 ): (-10 °C) 5 7.1-7.35 (m, 10H, Ph), 5.52 (s, 2H, O-acac-C3 H), 5.42 (s, 2H, p-acac- C3 H), 3.10 (m, 4H, Ph-CH2), 2.3 (m, 4H, It-CH2), 1.92 (s, 12H, O-acac- C //3 ), 1-85 (s, 12H, p-acac-C//3 ). 1 3C{!H} (CDCI3 , -10 °C): 5 191.53 (p-acac C=0), 183.19 (O-acac C=0), 143.35 (Ph), 128.37 (Ph), 128.32 (Ph), 125.32 (Ph), 104.05 (O-acac-C3 FI), 82.19 (p-acac-C3 H), 37.05 (Ph-CH2), 28.69 (p-acac-CH3 ), 27.36 (0-acac-CH3 ), 4.16 (Ir-CH2). *H NMR (CD3 OD): 6 7.05 -7.15 (m, 5H, Ph), 5.50 (s, 2H, acac-C3tf), 3.02 (m, 2H, Ph-Ctf2), 2.05 (m, 2H, Ir-CH2), 1.79 (s, 12H, acac-CH3). ^Cl'HKCDsOD): 6 184.2 (acac C=0), 146.1 (Ph), 128.9 (Ph), 125.5 (Ph), 103.9 (acac CH), 38.9 (CH2 -Ph), 26.6 (acac CH3 ), -8.5 (Ir-CH2 ). Anal. Calcd. for C3 4 H4 6 0 8 Ir2: C, 42.22; H, 4.79, Found: C, 42.68; H, 4.48. k [Ir(p-acac-0,0,C )(acac-0,0)(CH 2 CH3 ) ] 2 [CH3 CH2 - Ir]2: [CH3 CH2-Ir] 2 was synthesized similarly from acac-C-Ir-H2 0 (200 mg, 0.394 mmol) and diethylzinc (360 pL, 1.1 M in toluene) using Method A or using diethylmercury (43 pL, 0.4 mmol) using Method B. [CH3 CH2-Ir] 2 was isolated in 75-80% yields. 'H NMR (CDC13, -10 °C): 5 5.47 (s, 2H, O-acac-C3 H), 5.37 (s, 122 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2H, (X-acac-C3 H), 2.87 (q, 3 J = 7.4, 4H, Ir-CH2 ), 1.86 (s, 12H, 0-acac-Ctf3 ), 1-76 (s, 12H, (X-acac-Ci/3), 0.31 (t, 6 H, 3 J = 7.4, CH3 ). (CDC13, -10 °C): 5 190.67 (|X-acac C=0), 182.73 (O-acac C=0), 103.87 (0-acac-C 3 H), 83.11 (|X-acac- C3H), 28.56 (|X-acac-CH3 ), 27.37 (0-acac-CH3 ), 15.79 (CH3 ), -4.44(Ir-CH2). CH3 o i 0 [Ir(0,0-acac)2 (CH3 )(Py)] (CH3 -Ir-Py): CH3 -Ir-Py was synthesized from [CH3 -Ir] 2 (100 mg, 0.123 mmol) in CHC13 and pyridine (1 mL, 12.3 mmol). Isolated Yield: 115 mg, >95%. ]H NMR and 1 3 C NMR were consistent with the earlier reports. 3 FAB+ MS: m/z (%) 485.1 (8 ) [M+ ], 406.1 (100) [M-Py]+, 391.1 (14) [M-Py-CH3]+. [Ir(0,0-acac)2 (Ph)(Py)] (Ph-Ir-Py). Ph-Ir-Py was synthesized similarly from [Ph-Ir-H20 ] as described earlier. FAB+ MS: m/z (%) 547.1 (14) [M+ ], 468.1 (100) [M-Py]+, 391.1 (17) [M-Py-Ph]+. 123 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ^ [Ir(0,0-acac)2 (CH2 CH2 Ph)(Py)] (PhCH2 CH2-Ir-Py). PhCH2CH2-Ir-Py was synthesized similarly from [PhCH2 CH2 -Ir] 2 (100 mg, 0.206 mmol) in 10 mL of methanol and pyridine (1 mL, 12.3 mmol). Isolated yield: 120mg, >95%. ]H NMR (CD2 C12 ): 5 8.41 (d, 2H, o-H Py), 7.83 (t, 1H, p-H Py), 7.39 (t, 2H, m -f/Py), 7.20 (m, 4H, Ph), 7.07 (m, 1H, Ph), 5.27 (s, 2H, acac- C3 //), 2.75 (m, 2H, Ph-C//2), 2.24 (m, 2H, lr-CH2 ), 1.75 (s, 12H, acac-Ci/3 ). 1 3 C {]H} NMR (CD2 C12 ): 5 183.6 (acac C=0), 149.6 (o-Py), 137.2 (p-Py), 128.3 (Ph), 128.1 (Ph), 125.0 (m-Py), 124.5 (Ph), 103.2 (acac C3 H), 37.4 (CH2 -Ph), 27.2 (acac CH3 ), -2.4 (CH2 -Ir). Anal. Calcd. for C2 3 H2 8 N 0 4Ir : C, 48.07; H, 4.91; N, 2.44. Found: C, 48.24; H, 4.75; N, 2.54. FAB+ MS: m/z (%) 575.1 (13) [M+ ], 496.1 (100) [M-Py]+, 391.1 (16) [M-Py-CH2 -CH2 -Ph]+. rO. I ■ o > S [Ir(0,0-acac)2 (CH2 -CH3)(Py)] (CH3 CH2 -Ir-Py): CH3 CH2-Ir-Py was synthesized similarly from [CH3 CH2-Ir] 2 (100 mg, 0.119 mmol) in CHC13 and pyridine (1 mL, 12.3 mmol). Isolated yield: 110 mg, >95%. ’H NMR (C6 D6): 5 8.69 (d, 2H, o -H py), 6.80 (tt, 1H, p -//p y ), 6.60-6.75 (m, 2H, 124 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. m-H py), 5.08 (s, 2H, acac-C3 //), 3.50 (q, 3 J= 7.6, -CHi-lr), 1.60 (s, 12H, acac- CHi), 1.25 (t, 3H, 3J= 7.6, C T /rO ^-h O ^C ^H } NMR (C6 D6): 8 182.69 (acac C=0), 149.57 (o-Py), 136.32 (p-Py), 124.38 (m-Py), 102.76 (acac-C3 H), 26.66 (acac-CH3 ), 15.99 (CH3 ), -10.56 (CH2 -Ir). Anal. Calcd for C 1 7H2 4N 0 4 Ir: C, 40.95; H, 4.85; N, 2.81. Found: C, 41.38; H, 4.95; N, 2.70. FAB+ MS: m/z (%) 499.1 (10) [M+ ], 420.1 (100) [M-Py]+, 391.1 (17) [M-Py-CH2 -CH3 ]+. r i v i e 3 CH3 -Ir-(0,0-acac)2 -PMe3 (CH3 -Ir-PMe3 ): 1M solution of trimethylphosphine in toluene was added to [CH3 -Ir] 2 (32 mg, 0.04mmol) dispersed in 10 mL of benzene. The solution was gently warmed to 60°C to get a homogeneous solution. All the volatiles were removed to give the title compound in quantitative yields. The complex was recrystallized using CH2 Cl2 /hexanes at 253 K. *H NMR (CD2 C12): 8 5.26(s, 2H, CH), 1.75(s, 12H, acac- CH3 ), 1.15(d, 9H, JP H = 7.7 Hz, PMe3 ), 0.98(d, 3H, JP H = 8.1 Hz, Ir-CH3 ). 3,P (’H) ( 1 4 6 M H z , CD2 C12): 5 -28.6. 'H NMR (C6 D6 ): 5 5.02(s, 2H, CH), 2.03(d, 3H, JPh = 8 .1 H z , Ir-CH3 ), 1.55(s, 12H, acac- CH3 ), 0.99(d, 9H, JP H = 7.1 Hz, PMe3 ). 1 3 C ('H) (CD2 C12 ): 8 184.52(s, O-acac, C=0), 102.5(s, O-acac, CH), 26.6(s, O-acac, CH3 ), 11.9 (d, JP C = 19.7 Hz, PMe3 ), -2.0 (d, JP C = 124.7 Hz, Ir-CH3 ). 125 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 CH3 -Ir(acac)2 -PPh3 (CH 3 -Ir-PPh 3 ): The above procedure was repeated using triphenylphosphine. *H NMR (CD2 CI2 ): 8 7.30-7.4l(m, 15H, PPh3 ); 4.99 (s, 2H, acac-CH); 1.56 (s, 12H, acac-CH3 ); 1.3(d, 3H, JP .H = 7.4Hz, Ir- CH3 ). 1 3C{'H}. NMR (CD2 CI2 ): 8 184.3 (s, acac C=0); 134.5 (d, JP .C = 10.8 Hz, o- or m-PPh3 ); 132.7 (d, JP .C = 29.4 Hz, i-PPh3 ); 129.8 (s, p-PPh3 ); 128.4 (d, JP .C = 9.3 Hz, o- or m-PPh3 ); 102.8 (s, acac-CH ); 26.6 (s, acac-CH3 ); -2.4 (d, JP _ c = 112Hz, Ir-CH3). 3 1 P (‘H) (146MHz): 8 -1.2. C H 3 Ph-Ir(acac)2 (Pyp'C H 3 ) Ph-Ir-PypC"3: To 50mg of Ph-Ir- h 2 o in dichloromethane, 30 |lL of 4-picoline was added and was gently warmed to get a homogenous solution. To this ether was added to precipitate the title compound in >95% yield. The compund was washed with hexanes and dried in vacuo to give a yellowish powder. !H NMR (CDC13 ): 8 8.37(d, 2H, o-H Py), 7.23(d, 2H, m -H Py), 6.97-7.02(m, 5H, Ph-lr), 5.14 (s, 2H, acac-CH), 2.43(s, 3H, CHS -Py), 1.80 (s, 12H, acac-Ci^)- ^ C l’H} NMR (CDC13 ): 8 184.6(0-acac C=0), 149.3(o-Py), 136.0(p-Py), 125.9(m-Py), 131.9(Ph), 125.3(Ph), 123.0(Ph), 103.4(0- acac CH), 27.2(0-acac CH3 ), 21.2(Py-CH3 ). 126 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CH, ^ CH3 -Ir(acac)2-CO (CH3 -Ir-CO): To a solution of [CH3 -Ir] 2 in benzene, CO gas was bubbled. Quantitative amount of the title complex was formed. ]H NMR (CDC13 ): 5 5.41 (s, 2H, acac-CH), 1.99 (s, 12H, acac-CH3 ), 1.08 (s, 3H, CH3 -Ir). 1 3C{'H} NMR (CDC13 ): 8 184.45 (acac-CO), 174.80 (Ir-CO), 102.34 (acac-C3H), 26.65 (acac-CH3 ), 8.82 (CH3 -Ir). 'H NMR (Tol-d8 ): 5 5.01 (s, 2H, acac-CH), 1.65(s, 3H, CH3 -Ir), 1.61(s, 12H, acac-CH3 ). Due to instability of these complexes, analytical analysis was not carried out. 0 0 Ph-Ir(acac)2-CO (Ph-Ir-CO): To a solution of Ph-Ir-HaO in benzene, was bubbled CO till a homogenous solution is observed. *H NMR (CDC13 ): 8 7.02-7.18 (m, 5H, Ph-Ir), 5.24 (s, 2H, acac-CH), 1.95 (s, 12H, acac- CH^. 1 3C{'H} NMR (CDC13 ): 8 188.25 (acac-CO), 175.10 (Ir-CO), 133.04 (Ph), 126.4(Ph), 125.08(Ph), 103.03 (acac-C3 H), 26.66 (acac-CH3). Due to instability of these complexes, analytical analysis was not carried out. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cis-[Ir(0 ,0 -acac)2 (Ph)(Py)] (cis-Ph-Ir-Py): A 3 mL stainless steel autoclave equipped with a glass insert and a magnetic stir bar was charged with 1 mL of benzene containing Ph-Ir-Py (10 mg, 0.02 mmol). The autoclave was pressurized with an additional 2.96 MPa of Argon. The autoclave was heated for 12 h in a well-stirred heating bath maintained at 180°C. The autoclave was cooled thereafter, and the solvent was transferred in a Schlenk flask whereby the solvent was removed in vacuo. Isolated yield: 9 mg, >95%. ]H NMR (CD2 C12 ): 5 8.21 (d, 2H, o-H py), 7.71 (t, lH,/>-/7py), 7.17 (t, 2H, m-H py), 6 . 8 8 (t, 2H, m -H Ph), 6.82 (t, 1H, p -H Ph), 6.71 (d, 2H, o-H Ph), 5.34 (s, 1H, acac- C3 H), 5.29 (s, 1H, acac-C3 H), 1.94 (s, 3H, acac-CH3), 1.87 (s, 6 H, acac-CH3 ), 1.77 (s, 3H, acac-Ci/3 ). 1 3C{]H} NMR (CD2 C12): 8 186.48 (acac C=0), 185.80 (acac 0= 0), 184.67 (acac C=0), 184.21 (acac C=0), Phenyl and pyridine Carbons: 171.07, 154.41, 137.21, 136.98, 131.20, 129.30, 128.84, 126.03, 125.05, 122.76, 102.72 (acac-C3 H), 101.30 (acac-C3H), 28.75 (acac-CH3 ), 27.91 (acac-CH3 ), 27.37 (acac-CH3 ), 27.26 (acac-CH3 ). Anal. Calcd. for C2 iH2 4 N 0 4 Ir: C, 46.14; H, 4.43; N, 2.56. Found: C, 46.08; H, 4.55; N, 2.50. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. \ Cis Ir(acac)2 (Ph)(CO) (Cis Ph-Ir-CO): The above procedure was repeated using 500 psig of CO in benzene. Quantitative formation of the title complex was formed. !H NMR (C6 D6): 5 7.68(d, 3 J = 7.3, 2H, o-H Ph), 7.29(t, 2H, m-H Ph), 7.13(t, 1H, p-H Ph), 5.07 (s, 1H, acac-C3 //), 4.93(s, 1H, acac- C3 //), 1.72(s, 3H, acac-C//3 ), 1.69(s, 3H, acac-C//3 ), l-65(s, 3H, acac-C//3 ), 1.62(s, 3H, acac-C//3 ). 1 3C{]H} NMR (C6 D6 ): 5 190.25 (acac C=0), 187.93 (acac C=0), 187.40 (acac C=0), 186.21 (acac C=0), 162.51(Ir-C=0), 136.58(Ph), 127.76(Ph), 125.60(Ph), 122.52(Ph), 102.65 (acac-C3 H), 101.79(acac-C3H), 28.15 (acac-CH3 ), 27.02 (acac-CH3 ), 26.85 (acac-CH3), 26.81 (acac-CH3 ). ]H NMR (CD2 CI2 ): 5 6.97-7.12(m, 5H, Ph), 5.49 (s, 1H, acac-C3 //), 5.48(s, 1H, acac-C3 //), 2.08(s, 3H, acac-C//3 ), 2.06(s, 3H, acac-C//3 ), 2.05(s, 3H, acac-C//3 ), 1.94(s, 3H, acac-C//3 ). ^C l'H } NMR (CD2 C12): 5 190.50 (acac C=0), 187.82 (acac C=0), 187.52 (acac C=0), 186.53 (acac C=0), 161.61(Ir-C=0), 136.24(Ph), 127.37(Ph), 125.05(Ph), 122.33(Ph), 102.27 (acac-C3 H), 101.60(acac-C3 H), 28.38 (acac-CH3 ), 27.29 (acac-CH3 ), 27.09 (acac-CH3 ), 27.02 (acac-CH3 ). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cis-[Ir(0,0-acac)2 (2-PhPy)] (cis Ir-2-PhPy): To 400 mg (0.78mmol) of A cac-Ir-H20 in CH3 OH, 600 mg (1.54mmol) of 2-(pyridin-2’- yl)phenylmercuric chloride25 was added. The solution was refluxed for 2 h at 60 °C and was monitored using TLC with 1:1 mixture of ethylacetate and hexane. The reaction mixture was kept in the refrigerator, which lead to the precipitation of the unreacted mercury compound. The remaining solution was concentrated under vacuum and loaded on to a silica gel column and was eluted using hexane and ethylacetate as an eluent. The main fraction was again recrystallized using ethylacetate and hexane at -20°C, which resulted in yellow crystals. Isolated yield = 150 mg (35%). ’H NMR (CD2 C12): 6 8.34 (d, 3 J = 6.0, 1H, o-tf py), 7.82 (d, 3 J = 8.2, 1H, m-H py), 7.65 (m, 2H, m & p-H py), 7.29(d, 3 J = 7.2, 1H, m -//P h), 7.1- 6.9(m, 3H, o, m & p -//P h ), 5.42 (s, 1H, acac-CH), 5.37(s, 1H, acac-CH), 2.08(s, 3H, acac-Ctf3 ), 2.01(s, 3H, acac-CH3 ), 1.64(s, 3H, acac-Ctf3 ), l-58(s, 3H, acac- C //3 ). 1 3C{'H} NMR (CD2 C12): 5 185.91 (acac C=0), 185.57 (acac C=0), 184.65 (acac C=0), 183.88 (acac C=0), Phenylpyridine Carbons: 171.07, 150.90, 146.77, 144.76, 138.42, 134.55, 129.34, 124.13, 122.74, 121.76, 118.45, 102.56 (acac- CH), 101.35(acac-CH), 29.01 (acac-CH3 ), 27.49 (acac-CH3 ), 27.21 (acac-CH3 ), 26.65 (acac-CH3 ). Anal. Calcd. for C2 ]H2 2 N 0 4 Ir: C, 46.31; H, 4.07; N, 2.57. 130 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Found: C, 46.50; H, 4.03; N, 2.61. FAB+ MS: m/z (%) 545.2 (100) [M]+, 446.1 (25) [M-acac]+. Deuterium Kinetic Isotope Effect on Arene C-H activation with CH3- Ir-Py: Three 2 mL thick glass screw cap vials containing septa were loaded with 5 mg (0.01 mmol) of CH3 -Ir-Py in parallel. To these vials, 0.5 mL of C6 D6 , 1,3,5- C6 H3 D3 and a 1:1 molar mixture of C6 H6 and C6 D6 were introduced. The vials were freeze-pump-thawed thrice and fdled with Argon gas. The vials were immersed in a 110°C oil bath and the gas phase was sampled for three half lives and analyzed on a GC-MS equipped with a Gas Pro column. The molar ratio of the liberated methane isotopomers was deconvoluted using a spreadsheet. The solution remained homogeneous throughout the reaction, and no signs of decomposition were observed. The liquid phase was analyzed to make sure that no deuterium scrambling had occurred. 131 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.2. Line Broadening studies. The mononuclear-dinuclear equilibrium was measured in the slow exchange region from the width of the NMR signals at half height using eq: 1/ xa = 7i(ce»A - w ° A ) where xa is the residence time in site A and cda and g>°a are the line widths in the presence and in the absence of exchange, respectively. co°a was measured at a temperature where the signals were not exchanging on the NMR time scale. The experimental line widths were corrected by subtracting the line width of TMS to minimize the effect of instrumental line-broadening. Values of the rate constants at various temperatures were used to obtain AG* and the Arrhenius parameters using the Eyring Plot. T/K (ioA- w " a ) /Hz Kobs/S ' 1 253 0 0 258 0.73 2.29 263 1.47 4.62 268 3.23 1 0 , 2 273 6.48 20.4 278 10.36 32.56 283 18.66 58.65 288 29.91 94.00 Eyring Plot for Line Broadening studies. 334 1035 0 .0 0 3 6 0 .0 0 3 7 0 .0 0 3 8 y = -8 9 7 7 .4 x + 3 0 .1 4 7 R P = 0 .9 9 5 8 0 .0 339 1/T AH* = 17.8 ± 1 kcal/mol, AS* = 12.7 ± 2 eu, AG* (T=298K) = 14.1 ± 0.5 kcal/mol. 132 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.3. Dissociative Pyridine Exchange studies with Ph-Ir-Py. A stock solution of Ph-Ir-Py in CDCI3 (5 mM) was made and transferred to four oven-dried NMR tubes. Py-d5 (52-156 mM) was added to these NMR tubes at low temperature and then subjected to pre cooled (273 K) NMR studies. The intensity of the bound or free pyridine was plotted against time using the Mercury 400 NMR machine. 10eq (52mM) 20eq (104mM) 33eq ( 172mM) time (s) At -Ln(Ao/At) At -Ln(Ao/At] At -Ln(Ao/At) 31.96 85 0 65 0 82 0 90.92 89 0.045985113 68 0.04512 83 0.012121361 149.9 91 0.06820825 70 0.074108 87.8 0.068342253 208.8 95 0.111225635 72.9 0.114701 89.5 0.087519378 267.8 98 0.142316222 74 0.129678 92 0.11506933 326.7 102 0.182321557 78 0.182322 95 0.147157644 385.7 110 0.257829109 83.2 0.24686 98 0.178248231 444.7 111 0.266878945 89.8 0.323198 103 0.228009741 503.6 113 0.284736562 89.2 0.316494 101 0.20840127 562.6 121 0.353139289 92 0.347401 103 0.228009741 621.5 130 0.424883194 94.8 0.377382 106 0.256719847 680.5 135 0.462623522 98 0.41058 116 0.346870944 739.5 138 0.484602429 95.1 0.380542 115 0.338212881 798.4 145 0.534082486 98.3 0.413637 120 0.380772496 857.4 150 0.567984038 104 0.470004 128 0.445311017 916.3 155 0.60077386 105 0.479573 128 0.445311017 975.3 160 0.632522559 100 0.430783 125 0.42159449 1034 181 0.755845775 118 0.596297 130 0.460815203 1093 185 0.777704569 110 0.526093 137 0.513261679 1152 185 0.777704569 120 0.613104 143 0.556125383 1211 190 0.804372816 117 0.587787 144 0.563094052 1270 200 0.85566611 122 0.629634 146 0.576887374 1329 206 0.885224912 130 0.693147 149 0.597227059 1388 205 0.880358723 122 0.629634 155 0.63670587 1447 209 0.899682995 127 0.6698 155 0.63670587 First Order Plots and Kobs vs [Py] for Py Exchange for Ph-Ir-Py at 273 K. R = 0.9896 0.9504 R = 0.9884 M04mM 5 00 1000 1500 200 0 time (s) 172mM ♦ 52mM 0.001 0 .0008 - 0 .0006 - 0.0004 - 0.0002 - 100 150 200 [Py] (mM) 133 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.4. Eyring Plot for Pyridine Exchange with Ph-Ir-Py. 290 K 283 K 297K time (s) At -Ln( At/Ao) At -Ln( At/Ao) time At -Ln(At/Ao) 30.91 37.1 0 64.5 0 30.91 92 0 91.82 29.5 0.229226706 58.9 0.090824 61.82 66.5 0.324586629 152.7 25.8 0.363242478 57.8 0.109676 92.73 42.6 0.769934324 213.6 20.2 0.607934365 54.1 0.175831 123.6 32.7 1.034413499 274.5 18.3 0.70671591 52 0.215422 154.6 22.8 1.395028041 335.5 14.6 0.932595441 50.4 0.246674 185.5 21 1.477266139 396.4 13 1.048667612 40.3 0.470314 216.4 18 1.631416819 457.3 10.5 1.262241712 44.8 0.364457 247.3 15 1.813738376 518.2 8.84 1.434330093 40.5 0.465363 278.2 14 1.882731247 579.1 8.03 1.530432442 33.9 0.64325 309.1 9.8 2.239406191 640 8.17 1.513148061 33.1 0.667132 340 8 2.442347035 700.9 6.88 1.684998318 30.1 0.76214 370.9 7.5 2.506885557 761.8 6.43 1.752642431 31.9 0.704059 401.8 7 2.575878428 822.7 4.74 30.8 0.739151 883.6 6.12 1.802054873 30.5 0.748939 944.6 5.5 1.908868877 23.6 1.005419 1005 4.5 2.109539573 24.6 0.963919 1065 3.41 2.386904678 23.3 1.018212 1127 2.93 2.538614547 23.2 1.022513 1188 3.05 16 1249 2 2.920469789 17.5 1.304464 1310 1.9 2.971763083 21.4 1371 1.8 3.025830305 14.8 1.472038 1432 13.8 1.541997 3.5 R = 0.9754 R = 0.960: 2.5 R = 0 .9722 0.5 R = 0.9881 1000 1500 500 time (s) 277K X 297K ♦ 290K ■ 283K Eyring Plot for Pyridine Exchange for Ph-Ir-Py. T (K) I 1/T kobs Ln(K/T) 277 ! 0.00361 0.0004 -13.448064 283 0.003534 0.001 -12.553202 290 | 0.003448 0.0026 -11.622125 297 j 0.003367 0.0071 -10.6413931 0.0 -10 • )32 0.0034 0.0036 0.0 )38 R2 = 0.9997 -J -14 -16 1/T (1/K) AH* = 22.8 ± 0.5 kcal/mol, AS* = 8.4 ± 1.6 eu, AG* (T=298K) = 20.3 ± 0.5 kcal/mol 134 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.5. Eyring Plot for Pyridine Exchange for CH3-Ir-Py. Dissociative Pyridine Exchange studies with CH3 -Ir-Py. A stock solution of CH3 -Ir-Py in CDCI3 (5 mM) was made and transferred to four oven-dried NMR tubes. Py-ds (52-156 mM) was added to these NMR tubes at low temperature and then subjected to pre cooled (264-281 K) NMR studies. The intensity of the bound or free pyridine was plotted against time using NMR. 264K 272K 281K tim e (s) At -Ln(At/Ao] tim e (s) At -Ln(At/Ao] tim e (s) At -Ln(At/Ao) 30.91 38 0 30.91 79 0 30.91 10 0 91.82 31 0.203599 71.82 73 0.078988 61.82 6 0.510826 152.7 29 0.27029 112.7 62.8 0.229493 92.73 4 0.916291 213.6 27.7 0.316154 153.6 41.4 0.646167 123.6 2 1.609438 274.5 24.9 0.422718 194.5 37.1 0.755831 154.5 0.89 2.419119 335.5 21 0.593064 235.5 28.1 1.033678 185.5 0.5 2.995732 396.4 18.6 0.714425 278.4 25 1.150572 216.4 0.2 3.912023 457.3 19.9 0.646866 317.3 18.9 1.430286 518.2 14.9 0.936225 358.2 16.4 1.572167 579.1 16.1 0.858767 399.1 15 1.661398 640 12.7 1.095984 440 14 1.730391 700.9 13 1.072637 480.9 13.6 1.759378 761.8 12.5 1.111858 521.8 10.7 1.999204 822.7 11 1.239691 562.7 883.6 9.21 1.417296 603.6 644.7 5.87 2.599593 685.5 3 3.270836 R = 0.9639 R = 0 .9 7 ! 600 800 1000 T (K ) 264 272 281 1/T k o b s j Ln(k/T) i 0 .0 0 3 7 8 8 0 .0 0 3 6 7 6 0 .0 0 3 5 5 9 0 .0 0 1 6 0 .0 0 4 2 0 .017 -1 2 .0 1 3 7 -1 1 .0 7 8 5 -9 .7 1 2 9 = 19.9 ± 1.4 kcal/mol, AS* = 4.4 ± 5.5 eu, AG1 (T=298K) = 18.6 ± 0.5 kcal/mol t * -7 ■®0p33 -11 - -13 -15 *00036 0.0039 R2 = 0.9416 1/T (1/K) f IT -', AH1 135 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.6. Dependence of Trans-Cis Isomerization of Ph-Ir-Py on Pyridine Concentration. A stock solution of Ph-Ir-Py in CeD6 (15 mM) with trimethoxybenzene (1 mM) as internal standard was added to three 5 mm J-young NMR tube fitted with a valve. To each of them, Py-ds, ranging from 0.5 - 2.5 M equivalents, was added. The NMR tube was heated with added argon pressure (100-150 psig) in a well stirred oil bath maintained at 180 °C during which the samples were analyzed by 'll NMR spectroscopy. The reactions were monitored for 2-3 half lives. 0.5M 1.25 M 2.5 M Time (s) -Ln(At/Ao) Time (s) -Ln(At/Ao) Time (s) -Ln(At/Ao) 0 0 0 0 1800 0 1200 0.000 1200 0 3600 0.184086 5400 0.250 5400 0.044742 7200 0.394168 9420 0.427 9420 0.110169 10800 0.724862 15300 0.571 15300 0.211548 14400 0.967679 21900 0.679 21900 0.31659 18000 1.29755 21600 1.475528 25200 1.701462 28800 1.914759 R = 0.990. R2 = 0.9177 R = 0.9784 5000 10000 15000 20000 25000 30000 time (s) ♦ 1.25M ▲ 2.5M a 0.5M [Py] 1/[Py] kobs kobsx10-5 0.5 2 0.000044 4.4 1.25 0.8 0.00003 2.8 2.5 0.4 0.000014 1.3 7 6 5 4 3 2 1 0 0.5 15 2 2.5 0 1 1/[Py] (1/M) 136 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.7. Kinetics for C-H Activation of C6 D6 with CH 3 -Ir-Py at constant [C6 D6 /Py], A stock solution of CH3-Ir-Py was made in C6D6 (17 mM) with added Pyridine-ds (510 mM) and trimethoxybenzene (5 mg) as internal standard. 200 |iL of this solution was added to a 5 mm thick J-young NMR tube fitted with a valve to which Argon (100-150 psig) was added. The NMR tube was heated in a well- stirred oil bath maintained at a temperature (140-180°C) during which the sample was analyzed by 'H NMR spectroscopy. The reaction was monitored for 3 half lives. 148 C 159 C 179 C time (s) -Ln(At/Ao] tim e (s) -Ln(At/Ao) time (s) -Ln(At/Ao) 0 0 0 0 0 0 1800 0.107496 900 0.082972 120 0.176654 4200 0.139367 2700 0.281758 240 0.247311 7500 0.217868 4500 0.442112 540 0.384734 10200 0.300359 6480 0.538559 900 0.699193 14100 0.454189 8100 0.775522 1200 1.039833 17700 0.520686 9900 0.972099 1500 1.22385 21600 0.654717 25200 0.690989 R2 = 0 .9869 R2 = 0.9896 S 0.8 i 0.6 -J 0.4 0.2 = 0.98 4 4 6 4 5000 10000 15000 20000 25000 30000 time (s) ♦ 148 C ■ 159 C ▲ 179 C 137 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.7. Continued Tem p C Tem p (K) 1/T kobs kobs x Py/[Bz] (s '1 * [-LN(kcorr/T)] 179 452 0.002212 0.000823 3.74759E-05 16.31 169 442 0.002262 0.000329 1.49816E-05 17.20 159 432 0.002315 0.000095 4.32589E-06 18.42 148 421 0.002375 0.000029 1.32054E-06 19.58 139 412 0.002427 0.000009 4.09821 E-07 20.73 21.00 - 19.00 - R? = 0.9988 17.00 - 15.00 0.00215 0.00225 0.00235 0.00245 0.00255 1/T (1/K) Eyring Plot for the reaction of CH3-lr-Py (♦ ) with C6D6 at [Py]/[C6D6 ] = 0.045. k c o n - = kob s x [Py]/ [C6D6 ], A = PhCH2CH2-lr-Py. AH* = 41.1 ±1.1 kcal/mol, AS* = 11.5 ± 3.0 eu, AG* (T=298K) = 37.7 ± 1.0 kcal/mol 138 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.8. Dependence of Benzene C-H Activation on Pyridine Concentration. A stock solution of PhCH 2CH 2 -Ir-Py in C6D6 (15 mM) with trimethoxybenzene (1 mM) as internal standard which was added to three 5 mm J- young NMR tubes fitted with a valve. To each of them, Py-ds, ranging from 72 mM to 217 mM was added. The NMR tube were heated with added argon pressure (100-150 psig) in a well stirred oil bath maintained at 140°C during which the samples were analyzed by ’H NMR spectroscopy. The reaction was monitored for 2-3 half lives. 15eq(223mM) 30eq(446mM ) 45 eq (669mM) Time (s) At/Ao -Ln(At/Ao) Time (s) At/Ao -Ln(At/Ao) Time (s) At/Ao < c 0 1.00 0 .0 0 0 0 1.00 0 .0 0 0 0 1.00 0 .0 0 0 1200 0.98 0.015 1200 0.99 0.007 1200 0.98 0.019 3600 0.94 0.060 3600 0.97 0.027 3600 0.97 0.027 7200 0.89 0.113 7200 0.92 0.083 7200 0.95 0.054 11280 0.81 0.215 11280 0.89 0.115 11280 0.92 0.081 15300 0.74 0.294 15300 0.86 0.147 15300 0.90 0.105 18900 0.69 0.369 18900 0.82 0.194 18900 0.88 0.123 21600 0.66 0.421 21600 0.80 0.221 21600 0.88 0.130 25680 0.61 0.492 25680 0.77 0.265 25680 0.87 0.145 0.56 0.48 y = 2E-05x R2 = 0.9969 y = 1E-05x o 0.32 < r 0.24 _ l ' 0.16 5000 10000 15000 20000 25000 30000 tim e (s) ♦ 223mM ■ 446mM A 669m M 2.40 R2 = 0.996 1.60 0.80 0.00 139 [Py] (M) 1/P y j K obs x 10-5 (s-1) 0 .2 2 3 0 7 6 9 2 3 j 4 .4 8 2 7 5 8 6 2 1 j 1.92 0 .4 4 6 1 5 3 8 4 6 j 2.2 4 1 3 7 9 3 1 [ 1.02 0 .6 6 9 2 3 0 7 6 9 j 1 .4 9 4 2 5 2 8 7 4 I 0 .6 2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.9. Arene Concentration Dependence on Rate of C-H activation of Benzene with Cy-dn-Ir-Py. 5 mg of C y-dn-Ir-Py along with 1 mg of trimethoxybenzene as internal standard was added to three 5 mm J-young NMR tubes fitted with a Teflon valve. To these, varying amounts of CgDg and C6 D 12 were added {[CgDg] = 1600-5600 mM}. The NMR tubes were heated with added argon pressure (100-150 psig) in a well stirred oil bath maintained at 120°C during which the samples were analyzed by 'h NMR spectroscopy. The reactions were monitored for 2-3 half lives. After the reaction, CD2 CI2 was added to dissolve all Ph-d5 -Ir-Py produced, and the trimethoxybenzene was used as an internal standard to ensure that Ph-ds-Ir-Py produced accounted for >95% of the added Cy-dn-Ir-Py. 5600mM 3733mM 1600mM rim e (s) At/Ao -Ln(At/Ao) Tim e (s) At/Ao -Ln (At/Ao) Tim e (s) At/Ao -Ln(At/Ao) 0 78.13 0 0 63.61 0 0 128.93 0 300 45.1 0.549492 300 50 0.240748 300 115 0.114337 600 28 1.02617 600 36 0.569252 600 100.22 0.251902 900 14 1.719317 900 27 0.856934 900 95.45 0.300667 1200 6.11 2.548447 1200 18.87 1.215197 1200 76.87 0.517154 1500 11.75 1.688917 1500 68.59 0.631123 1800 7.5 2.137868 1800 62.53 0.723623 R2 = 0.9801 = 0 .9846 = 0 .9868 500 1000 1500 2000 25 0 0 time (s) ■ 3733mM A 1600mM ♦ 5600mM 140 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.9. Continued 0.003 0.0025 = 0.9562 [C6H6 ] (mM) I kobs (s'1 ) 0.002 - 0.0015 5600 0.002 3733 1600 0.0011 0.0004 0.0005 - 8000 2000 6000 H-D Exchange between C6H6 and toluene-dg: Catalytic H-D exchange reactions were quantified by monitoring by the increase of deuterium into C6H6 by GC/MS analyses for Ph-Ir-Py and cis-Ph-Ir-Py (5 mM) using toluene-dg as the deuterium source at 160°C. This was achieved by deconvoluting the mass fragmentation pattern obtained from the MS analysis, using a program developed on Microsoft EXCEL. The mass range from 78 to 84 (for benzene) was examined for each reaction and compared to a control reaction where no metal catalyst was added. The program was calibrated with known mixtures of benzene isotopomers. The results obtained by this method are reliable to within 5%. Catalytic H/D exchange reactions were thus run for reaction times in order to be able to detect changes >5% in exchange. Com putational Methodology: All calculations were performed using the hybrid DFT functional B3LYP as implemented by the Jaguar 5.0 or 5.5 program package.2 6 This DFT functional utilizes the Becke three-parameter functional2 7 (B3) combined with the correlation functional of Lee, Yang, and Par2 8 (LYP), and 141 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. is known to produce good descriptions of reaction profiles for transition metal containing compounds.2 9 ,3 0 The iridium was described by the Wadt and Hay3 1 core-valence (relativistic) effective core potential (treating the valence electrons explicitly) using the LACVP basis set with the valence double-^ contraction of the basis functions, LACVP**. All electrons were used for all other elements using a modified variant of Pople’s3 2 6-31G** basis set, where the six d functions have been reduced to five. Implicit solvent effects of the experimental benzene medium were calculated with the Poisson-Boltzmann (PBF) continuum approximation,3 3 using the parameters s = 2.284 and rso iv = 2.602A. Due to the increased cost of optimizing systems in the solvated phase (increase in computation time by a factor of ~4) solvation effects were calculated here as single point solvation corrections to gas phase geometries, except for cases where a vacant coordination site is created. Allowing relaxation in solvent did not change the relative energies more than 1 kcal/mol for species where the coordination remained constant; however, in cases where the coordination changed, the relaxation can account for up to 4 kcal/mol. All geometries were optimized and evaluated for the correct number of imaginary frequencies through vibrational frequency calculations using the analytic Hessian. Zero imaginary frequencies correspond to a local minimum, while one imaginary frequency corresponds to a transition structure. 142 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. To reduce computational time, the methyl groups on the acac ligands were replaced with hydrogens. Control calculations show that relative energies of intermediates and transition structures change less than 0.1 kcal/mol when methyl groups are included. X-ray diffraction data were collected on a Bruker SMART APEX CCD diffractometer with graphite monochromated M o-Ka radiation (X , = 0.71073 A). The cell parameters were obtained from the least-squares refinement of the spots (from 60 collected frames) using the program SMART. A hemisphere of data was collected up to a resolution of 0.75A. The intensity data were processed using the program Saint-Plus. All calculations for the structure determination were carried out using the SHELXTL package (version 5.1).3 4 Initial atomic coordinates of the Ir atoms were located by direct methods, and structures were refined by least- squares methods. Empirical absorption corrections were applied using the program SADABS. Calculated hydrogen positions were input and refined in a riding manner along with their attached carbons. A summary of the refinement details and the resulting parameters are given in supporting information. The crystal structure of the Ph-Ir-Py is disordered. As a result, the molecule lies on a center of symmetry necessarily causing the phenyl group or the pyridine group to be disordered. 143 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.10. Crystal data and structure refinement for Ph-Ir-Py. Identification code Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 27.52° Transmission factors Refinement method Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I>2sigma(I)J R indices (all data) Largest diff. peak and hole acacm C21 H24 IrN 0 4 546.61 298(2) K 0.71073 A Monoclinic P2(l)/n a = 8.1041(9) A a = 90°. b = 9.6690(10) A (3=94.113(2)° c = 13.2092(14) A y = 90°. 1032.39(19) A3 2 1.758 Mg/m3 6.491 mm-1 532 0.94 x 0.57 x 0.494 mm3 2.61 to 27.52°. -10<=h<=9, -11 <=k<=l 2, -15<=1<=16 6140 2266 [R(int) = 0.0312] 95.0 % min/max ratio: 0.629 Full-matrix least-squares on F2 2 2 6 6 / 0 / 126 1.261 R1 = 0.0407, wR2 = 0.0900 R1 = 0.0467, wR2 = 0.0926 1.323 and -0.949 e.A'3 144 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.11. Atomic coordinates ( x 10^) and equivalent isotropic displacement parameters (A^x 1C )3) for Ph-Ir-Py. U(eq) is defined as one third of the trace of the orthogonalized U’ J tensor. X y z U(eq) Ir(l) 0 5000 5000 35(1) 0 (2 ) 847(6) 4631(4) 3622(3) 37(1) 0 (1 ) 1945(5) 6167(5) 5515(3) 36(1) N (l) 1195(7) 3205(6) 5573(4) 37(1) C (l) 4487(9) 7288(8) 5472(7) 53(2) 0(2) 3132(8) 6412(7) 4977(6) 40(2) 0(3) 3302(9) 5963(8) 3992(6) 49(2) 0(4) 2213(9) 5156(7) 3380(5) 43(2) 0(5) 2629(13) 4741(10) 2318(6) 69(3) 0(6) 1195(7) 3205(6) 5573(4) 37(1) 0(7) 1117(9) 1983(8) 5047(6) 46(2) 0(8) 1883(10) 802(8) 5420(7) 54(2) 0(9) 2764(11) 817(9) 6333(7) 60(2) 0(10) 2851(11) 2040(10) 6888(6) 61(2) 0(11) 2078(10) 3220(8) 6495(5) 48(2) Table 3.12. Bond lengths [A] and angles [°] for Ph-Ir-Py Ir(l)-0(1)#1 2.016(4) Ir(l)-0(1) 2.016(4) Ir(l)-0(2) 2.022(4) Ir(l)-0(2)#1 2.022(4) lr(l)-C (6)#l 2.102(6) Ir(l)-N (l)#l 2.102(6) Ir(l)-N (l) 2.102(6) 0(2)-C (4) 1.279(9) 145 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.12. Continued 0(1)-C (2) 1.259(8) N (l)-C (l 1) 1.367(9) N (l)-C (7) 1.370(9) C (l)-C (2) 1.499(9) C(2)-C(3) 1.389(10) C(3)-C(4) 1.392(10) C(4)-C(5) 1.520(10) C(7)-C(8) 1.375(10) C(8)-C(9) 1.357(12) C(9)-C(10) 1.390(12) C (10)-C (ll) 1.385(11) 0(1 )# 1 -Ir( 1 )-0 ( 1) 0 (l)# l-I r (l)-0 (2 ) 0 (l)-Ir (l)-0 (2 ) 0(1 )#1 -Ir(l )-0 (2 )# 1 0(1)-Ir(l)-0(2)#1 0 (2 )-Ir(l)-0 (2 )# l 0 ( 1 )# 1 -lr( 1 )-C(6)# 1 0(1)-Ir(l)-C (6)#l 0(2)-Ir(l)-C (6)#l 0 (2 )# 1 -Ir( 1 )-C(6)# 1 0 ( 1 )# 1 -Ir( 1 )-N( 1 )# 1 0(1 )-Ir(l )-N (l )#1 0 (2 )-Ir(l)-N (l)# l 0 (2 )# 1 -Ir( 1 )-N( 1 )# 1 C (6)#l-Ir(l)-N (l)#l 0 (1)#1-Ir(l)-N (l) 0 ( 1 )-lr( 1 )-N( 1) 0(2 )-Ir(l)-N (l) 0 (2)#1-Ir(l)-N (l) C (6)#l-Ir(l)-N (l) 179.999(1) 84.56(18) 95.44(18) 95.44(18) 84.56(18) 179.999(1) 90.7(2) 89.3(2) 89.9(2) 90.1(2) 90.7(2) 89.3(2) 89.9(2) 90.1(2) 0.0(4) 89.3(2) 90.7(2) 90.1(2) 89.9(2) 180.000(1) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.12. Continued N (l)# l-Ir (l)-N (l) 180.000(1) C (4)-0(2)-Ir(l) 120.7(4) C (2)-0( 1 )-Ir( 1) 121.7(4) C(11)-N(1)-C(7) 117.6(6) C( 11 )-N( 1 )-lr( 1) 120.7(5) C (7)-N (l)-Ir(l) 121.7(5) 0(1)-C (2)-C (3) 127.0(6) 0(1)-C (2)-C (1) 115.2(6) C(3)-C(2)-C(l) 117.8(6) C(2)-C(3)-C(4) 128.1(7) 0(2)-C (4)-C (3) 127.0(6) 0(2)-C (4)-C (5) 112.3(7) C(3)-C(4)-C(5) 120.7(7) N (l)-C (7)-C (8) 122.1(7) C(9)-C(8)-C(7) 120.4(8) C(8)-C(9)-C(10) 118.8(8) C(11)-C(10)-C(9) 120.0(8) N (l)-C (l 1)-C(10) 121.2(7) Symmetry transformations used to generate equivalent atoms: #1 -x,-y+ l,-z+ l Table 3.13. Anisotropic displacement parameters (A2x 102) for Ph-Ir-Py. The anisotropic displacement factor exponent takes the form: -2n^[ h2 a*2ljl ^ + ... + 2 h k a* b*U 12] U 1 1 u 2 2 U 3 3 U 2 3 U 1 3 U 1 2 Ir(l) 31(1) 43(1) 31(1) -3(1) 4(1) -5(1) 0(2) 43(3) 33(2) 34(2) -2(2) 11(2) -3(2) 0(1) 36(2) 35(2) 39(2) -7(2) 3(2) -5(2) N (l) 35(3) 39(3) 37(3) 2(3) 8(2) -4(2) 147 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.13. Continued C (l) 38(4) 42(4) 78(5) -8(4) 9(4) -11(3) C(2) 37(3) 29(3) 54(4) -1(3) 1(3) -8(3) C(3) 40(4) 52(4) 56(4) -5(4) 16(3) -11(3) C(4) 48(4) 41(4) 42(4) 2(3) 10(3) 8(3) C(5) 73(6) 92(7) 46(5) -7(4) 25(4) -5(5) C(6) 35(3) 39(3) 37(3) 2(3) 8(2) -4(2) C(7) 46(4) 46(4) 45(4) 0(3) 4(3) -4(3) C(8) 53(5) 35(4) 76(6) 4(4) 14(4) -6(3) C(9) 72(6) 50(5) 59(5) 20(4) 14(4) 17(4) C(10) 63(5) 78(6) 41(4) 16(4) 1(4) 10(4) C (ll) 55(4) 55(5) 34(3) -6(3) 2(3) 6(4) Table 3.14. Hydrogen coordinates parameters (A^x 10 3) for Ph-Ir-Py. ( x lO^) and isotropic displacement X y z U(eq) H(1 A) 4464 8186 5162 79 H(1B) 5537 6858 5388 79 H(1C) 4330 7380 6182 79 H(3) 4265 6235 3704 58 H(5A) 2765 3756 2289 104 H(5B) 3637 5185 2159 104 H(5C) 1748 5019 1837 104 H(7) 523 1954 4429 55 H(8) 1797 -12 5045 65 H(9) 3301 24 6583 72 H(10) 3427 2065 7522 73 H (11) 2212 4052 6837 58 148 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.15. Crystal data and structure refinement for PhCH 2CH2-Ir-Py. Identification code Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 27.52° Transmission factors Refinement method Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I>2sigma(I)] R indices (all data) Fargest diff. peak and hole iretphpm C23 H28 IrN 0 4 574.66 153(2) K 0.71073 A Monoclinic P2(l)/n a = 8.3752(12) A oc= 90°. b = 19.188(3) A P= 96.132(2)° c = 14.088(2) A y = 9 0 ° . 2251.0(6) A3 4 1.696 Mg/m3 5.959 mm-1 1128 0.39 x 0.04 x 0.01 mm3 2.12 to 27.52°. -10<=h<= 10, -22<=k<=24, -16<=1<=18 13453 5012 [R(int) = 0.0550] 97.0 % min/max ratio: 0.445 Full-matrix least-squares on F2 5 0 1 2 /0 /2 6 6 1.038 R1 = 0.0564, wR2 = 0.1334 R1 = 0.0914, wR2 = 0.1472 3.744 an d -2.422 e.A’ 3 149 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.16. Atomic coordinates ( x 10^) and equivalent isotropic displacement parameters (A^x 1(P) for PhCH 2 CH 2 -Ir-Py. U(eq) is defined as one third of the trace of the orthogonalized U 1 . ! tensor. X y z U(eq) Ir(l) 10234(1) 1251(1) 3317(1) 33(1) 0 (1 ) 11342(9) 1313(3) 4652(5) 44(2) 0 (2 ) 11984(8) 1756(3) 2711(5) 40(2) 0 (3 ) 8502(7) 752(3) 3933(4) 34(1) 0 (4 ) 9094(7) 1200(3) 1983(4) 34(1) N (l) 11402(8) 264(4) 3113(5) 33(2) C (l) 13170(15) 1714(7) 5919(8) 68(4) 0(2) 12639(13) 1662(6) 4853(8) 48(3) 0(3) 13546(12) 1984(5) 4190(8) 48(3) 0(4) 13208(11) 2012(5) 3204(8) 42(2) 0 (5) 14395(12) 2377(5) 2647(9) 55(3) 0(6) 5942(12) 288(5) 4064(8) 51(3) 0 (7) 7155(11) 624(5) 3464(7) 38(2) 0 (8) 6694(11) 728(5) 2504(7) 39(2) 0(9) 7648(11) 990(5) 1822(6) 33(2) 0(10) 6908(13) 1041(6) 801(7) 49(3) 0(11) 11328(11) -277(5) 3712(7) 38(2) 0(12) 11989(12) -917(5) 3582(8) 45(2) 0(13) 12749(13) -1035(6) 2773(9) 53(3) 0(14) 12841(12) -487(5) 2147(8) 48(3) 0(15) 12188(11) 130(5) 2336(7) 40(2) 0(16) 9052(16) 2114(6) 3479(8) 69(4) 0(17) 9539(14) 2691(6) 4169(9) 67(4) 0(18) 8292(13) 3249(5) 4265(7) 45(2) 0(19) 7916(12) 3734(5) 3569(7) 48(2) C(20) 6697(14) 4202(5) 3604(9) 55(3) 0(21) 5835(15) 4202(7) 4394(10) 69(4) 150 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.16. Continued C(22) 6178(14) 3736(7) 5100(8) 61(3) C(23) 7395(13) 3262(6) 5040(7) 50(3) Table 3.17. Bond lengths [A] and angles [°] for PhCH 2 CH 2 -Ir-Py. Ir(l)-C(16) 1.956(13) Ir( 1 )-0 ( 1) 2.010(6) lr (l)-0 (3 ) 2.011(6) Ir(l)-0(4) 2.017(6) Ir(l)-0(2) 2.021(6) Ir(l)-N (l) 2.165(7) 0(1)-C (2) 1.281(12) 0(2)-C (4) 1.273(11) 0(3)-C (7) 1.269(11) 0(4)-C (9) 1.274(10) N (l)-C (l 1) 1.342(11) N (l)-C (15) 1.360(11) C(l)-C (2) 1.523(14) C(2)-C(3) 1.409(15) C(3)-C(4) 1.388(14) C(4)-C(5) 1.503(13) C(6)-C(7) 1.532(12) C(7)-C(8) 1.380(13) C(8)-C(9) 1.406(12) C(9)-C(10) 1.507(12) C(11)-C(12) 1.368(13) C(12)-C( 13) 1.382(15) C(13)-C(14) 1.381(14) C(14)-C(15) 1.342(13) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.17. Continued C(16)-C(17) 1.500(14) C(17)-C(18) 1.512(14) C(18)-C(19) 1.364(14) C(18)-C(23) 1.391(14) C(19)-C(20) 1.364(14) C(20)-C(21) 1.391(16) C(21)-C(22) 1.345(17) C(22)-C(23) 1.375(15) C (16)-Ir(l)-0(1) 91.7(4) C (16)-Ir(l)-0(3) 87.4(4) 0 (l)-Ir (l)-0 (3 ) 84.6(3) C (16)-Ir(l)-0(4) 87.4(4) 0 (l)-Ir (l)-0 (4 ) 179.0(2) 0(3 )-Ir(l)-0 (4 ) 95.0(2) C (16)-Ir(l)-0(2) 92.4(4) 0 (l)-Ir (l)-0 (2 ) 94.8(3) 0(3 )-Ir(l)-0 (2 ) 179.4(3) 0(4 )-Ir(l)-0 (2 ) 85.6(2) C (16)-Ir(l)-N (l) 176.5(4) 0(1 )-Ir(l)-N (l) 90.4(3) 0(3 )-Ir(l)-N (l) 89.9(2) 0 (4 )-Ir(l)-N (l) 90.6(2) 0 (2 )-Ir(l)-N (l) 90.3(2) C (2)-0(1)-Ir(l) 122.3(7) C (4)-0(2)-Ir(l) 122.2(7) C (7)-0(3)-Ir(l) 120.6(6) C (9)-0(4)-Ir(l) 121.8(6) C(11)-N(1)-C(15) 114.8(8) C(1 l)-N (l)-lr (l) 122.7(6) C (15)-N (l)-Ir(l) 122.4(6) 0(1)-C (2)-C (3) 126.0(9) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.17. Continued 0(1)-C (2)-C (1) 113.8(10) C(3)-C(2)-C(l) 120.2(10) C(4)-C(3)-C(2) 127.8(10) 0(2)-C (4)-C (3) 126.6(10) 0(2)-C (4)-C (5) 115.7(9) C(3)-C(4)-C(5) 117.7(9) 0(3)-C (7)-C (8) 128.5(9) 0(3)-C (7)-C (6) 113.5(9) C(8)-C(7)-C(6) 118.0(9) C(7)-C(8)-C(9) 127.0(9) 0(4)-C (9)-C (8) 126.2(9) O(4)-C(9)-C(10) 115.8(8) C(8)-C(9)-C(10) 118.0(8) N (l)-C (l 1 )-C (l 2) 124.3(9) C(11)-C(12)-C(13) 119.1(10) C( 12)-C( 13)-C( 14) 117.6(10) C(15)-C(14)-C(13) 119.6(10) C( 14)-C( 15)-N( 1) 124.6(10) C(17)-C(16)-Ir(l) 126.5(9) C( 16)-C( 17)-C( 18) 115.9(10) C(19)-C(18)-C(23) 116.7(9) C( 19)-C( 18)-C( 17) 121.9(10) C(23)-C(l 8)-C(l 7) 121.3(10) C(20)-C(19)-C(18) 122.7(10) C(19)-C(20)-C(21) 118.9(11) C(22)-C(21 )-C(20) 120.2(11) C(21)-C(22)-C(23) 119.7(11) C(22)-C(23)-C(18) 121.8(11) Symmetry transformations used to generate equivalent atoms: Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.18. Anisotropic displacement parameters (A2x 1(P) for PhCH 2 CH 2 - Ir-Py. The anisotropic displacement factor exponent takes the form: - 2 n \ h2 a*2U n + ... + 2 h k a * b * U 12] U 1 1 u 2 2 U 3 3 u 2 3 U 1 3 u 1 2 Ir(l) 23(1) 41(1) 34(1) -1(1) -4(1) 2(1) 0 (1 ) 43(4) 49(4) 36(4) -2(3) -11(3) 14(3) 0 (2 ) 31(4) 37(3) 50(4) 7(3) -5(3) -6(3) 0 (3 ) 19(3) 52(4) 30(3) 3(3) 3(2) 12(3) 0 (4 ) 23(3) 47(4) 29(3) 2(3) -3(2) -3(3) N (l) 17(4) 47(4) 34(4) 1(3) -2(3) -1(3) C (l) 52(8) 97(9) 47(7) -17(6) -24(6) 14(7) 0(2) 34(6) 54(6) 52(7) -12(5) -19(5) 20(5) C(3) 24(5) 51(6) 66(7) -10(5) -14(5) 7(4) 0(4) 18(5) 42(5) 65(7) -8(5) -3(4) 1(4) 0(5) 29(6) 42(6) 92(9) 1(6) -3(5) -10(4) 0(6) 35(6) 66(7) 54(7) 19(5) 17(5) -5(5) 0(7) 30(5) 45(5) 42(6) -5(4) 12(4) 6(4) 0(8) 21(5) 55(6) 43(6) -2(5) 9(4) 0(4) 0(9) 20(5) 40(5) 38(5) 2(4) -2(4) -1(4) 0(10) 31(6) 78(7) 37(6) -1(5) -8(4) -3(5) 0(11) 29(5) 47(5) 36(5) -1(4) -2(4) -5(4) 0(12) 35(6) 44(5) 53(6) -2(5) -5(5) -6(4) 0(13) 28(5) 49(6) 78(8) -20(6) -7(5) 6(4) 0(14) 28(5) 62(7) 53(6) -20(5) 4(5) -2(5) 0(15) 26(5) 61(6) 33(5) 0(5) 2(4) 0(5) 0(16) 81(9) 90(9) 37(6) -22(6) 5(6) -45(7) 0(17) 45(7) 79(8) 75(9) -23(7) -12(6) 18(6) 0(18) 47(6) 45(6) 43(6) -15(5) -3(5) 11(5) 0(19) 35(5) 63(6) 46(6) -9(6) 15(4) -5(5) C(20) 49(7) 37(6) 76(8) -3(5) -6(6) 0(5) 0(21) 42(7) 75(8) 88(10) -49(8) -6(6) 22(6) 154 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.18. Continued C(22) 37(6) 96(9) 49(7) -15(7) 5(5) 2(7) C(23) 42(6) 72(7) 36(6) -8(5) -2(5) -2(6) Table 3.19. Hydrogen coordinates ( x 10^) and isotropic displacement parameters (A^x 10 3) for PhCH 2 CH 2 -Ir-Py. x y z U(eq) H(1 A) 13801 2140 6048 101 H(1B) 13829 1308 6123 101 H(1C) 12222 1728 6270 101 H(3) 14505 2210 4448 58 H(5A) 15415 2122 2716 82 H(5B) 14570 2853 2891 82 H(5C) 13973 2395 1971 82 H(6A) 6411 -135 4370 76 H(6B) 4965 166 3652 76 H(6C) 5676 616 4556 76 H(8) 5618 611 2281 47 H(10A) 7475 1397 467 74 H(10B) 5774 1171 788 74 H(10C) 6994 590 485 74 H (11) 10780 -210 4261 45 H(12) 11926 -1275 4042 54 H(13) 13193 -1478 2653 63 H(14) 13363 -546 1586 57 H(15) 12281 499 1896 48 H(16A) 8909 2336 2841 83 H(16B) 7968 1969 3620 83 H(17A) 10513 2916 3970 81 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3.19. Continued H(17B) 9835 H(19) 8527 H(20) 6442 H(21) 5001 H(22) 5583 H(23) 7628 2482 4806 81 3747 3039 57 4522 3096 66 4533 4436 83 3735 5637 73 2935 5542 60 156 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.5 Reference (1) (a) Jia, C.; Kitamura, T.; Fujiwara, Y. Acc. Chem. Res. 2001, 633 and references therein, (b) Jones, W. D. Acc. Chem. Res. 2003, 36, 140. (c) Shilov, A. E.; Shul’pin, G. B. Activation and Catalytic Reactions o f Saturated Hydrocarbons in the Presence o f Metal Complexes Kluwer Academic; Dordrecht, 2000. (d) Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2001, 19, 2437. (d) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507. (2) (a) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem. Res. 2002, 35, 44. (b) Jones, W.D.; Feher, F.J. Acc. Chem. Res. 1989, 22, 91. (c) Harper, T.G.P; Shinomoto, R.S; Deming, M.A; Flood, T.C. J. Am. Chem. Soc. 1988, 110, 7915. (d) Wang, C.M.; Ziller, J.W.; Flood, T.C. J. Am. Chem. Soc. 1995, 117, 1647. (e) Holtcamp, M.W.; Labinger, J.A.; Bercaw, J.E. J. Am. Chem. Soc. 1997, 119, 848. (f) Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T.; Fujii, H. Science 1998, 280, 560. (g) Johansson, L.; Ryan, O.B.; Tilset, M. J. Am. Chem. Soc. 1999, 121, 1974. (h) Fekl, U.; Goldberg, K.I. Adv. Inorg. Chem. 2003, 5454, 259. (i) Liu, F. C.; Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S. J. Am. Chem. Soc. 1999, 121, 4086. (j) Nuckel, S.; Burger, P. Angew. Chem. Int. Ed. 2003, 42, 1632. (3) Wong-Foy, A. G.; Bhalla, G.; Liu, X. Y.; Periana, R. A. J. Am. Chem. Soc. 2003,125, 14292. (4) (a) Matsumoto, T; Taube, D. J.; Periana, R. A.; Taube, H.; Yoshida. H. J. Am. Chem. Soc. 2000, 122, 7414. (b) Matsumoto, T.; Periana, R A.; Taube, D. J.; Yoshida, H. J. Mol. Catal. A. 2002, 180, 1. (c) Matsumoto, T.; Yoshida, H. Catal. Lett. 2001, 72, 107. (5) (a) Oxgaard, J.; Muller, R. P.; Goddard III, W. A.; Periana, R. A. J. Am. Chem. Soc. 2004, 126, 352. (b) Oxgaard, J.; Goddard III, W. A. J. Am. Chem. Soc. 2004, 126, 442. (c) Oxgaard, J.; Periana, R. A.; Goddard, W. A. Ill, J. Am. Chem. Soc. 2004,126, 11658. (6) (a) Griffith, W. P. Coord. Chem. Rev. 1970, 5, 459. (b) Besecker, C. J.; Day, V. W.; Klemperer, W. G. Organometallics 1985, 4, 564. (c) LaPointe, R. E.; Wolczanski, P. T.; Van Duyne, G. D. Organometallics 1985, 4, 1810. (d) Grim, S. O.; Sangokoya, S. A.; Colquhoun, I. J.; McFarlane, W.; Khanna, R. K. Inorg. Chem. 1986, 25, 2699. (e) Klaeui, W.; Muller, A.; Eberspech, W.; Boese, R.; Goldberg, I. J. Am. Chem. Soc. 1987, 109, 164. (f) Burk, M. J.; Crabtree, R. H. J. Am. Chem. Soc. 1987, 109, 8025. (g) Burk, M. J.; Crabtree, R. H. J. Am. Chem. Soc. 1987, 109, 8025. (h) 157 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fryzuk, M. D.; Montgomery, C. D. Coord. Chem. Rev. 1989, 95, 1. (i) Power, P. P.; Comments Inorg. Chem. 1989, 8, 111. (j) West, B. O. Polyhedron 1989, 8, 219. (k) Tanke, R. S.; Crabtree, R. H. J. Am. Chem. Soc. 1990, 112, 7984. (1) Lunder, D. M.; Lobkovsky, E. B.; Streib, W. E.; Caulton, K. G. J. Am. Chem. Soc. 1991, 113, 1837. (m) Poulton, J. T.; Folting, K.; Streib, W. E.; Caulton, K. G. Inorg. Chem. 1992, 31, 3190. (n) Johnson, T. T.; Huffman, J. C.; Caulton, K. G. J. Am. Chem. Soc. 1992, 114, 2125. (o) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239. (p) Sharp, P. R. J. Chem. Soc., Dalton Trans. 2000, 2647. (q) Cinellu, M. A.; Minghetti, G. Gold Bull. 2002, 35, 11. (7) Bennett, M. A.; Mitchell, T. R. B. Inorg. Chem. 1976,15, 2936. (8) (a) Swallaw, A. G.; Truter, M. R. Proc. Roy. Soc. London, 1960, A252, 205. (b) Ingrosso, G.; Immirzi, A.; Porri, L. J. Organomet. Chem., 1973, 60, C35. (9) (a) Fryzuk, M. D.; Jones, T.; Einstein, F. W. B. Organometallics 1984, 3, 185. (b) Burch, R. R.; Shusterman, A. J.; Muetterties, E. L.; Teller, R. G.; Williams, J. M. J. Am. Chem. Soc. 1983,105, 3546. (10) Crabtree, R. H. The Organometallic chemistry o f the Transition Metals', 3rd Ed., John Wiley & Sons, 2001, p 174. (11) (a) Basolo, F.; Pearson, R. G. Mechanisms o f Inorganic Reactions', John Wiley: New York, 1968. (b) Wilkins, R. G. The Study o f Kinetics and Mechanisms o f Transition Metal Complexes'. Allvn and Bacon: Boston. MA. 1974. (c) Langford, C. H.; Gray, H. B. Ligand Substitution Processes', W. A. Benjamin: New York. 1965. (d) Tobe. M. L. Inorganic Reaction Mechanism: Nelson: London, 1972. (e) Atwood; J. D. Inorganic and Organometallic Reaction Mechanisms', Brooks/Cole Publishing Co.: Monterey, CA, 1985. (12) Gunther, H. NMR Spectroscopy, Second Edition; John Wiley & Sons Limited: West Sussex, England, 1995; pp. 335-346. (13) NMR spectrum calculations were carried out using WINDNMR 7.1.6. Author: Hans J. Reich, Department of Chemistry, Wisconsin. (14) Atwood, J. D. Inorganic and Organometallic Reaction Mechanisms', Wiley-VCH: New York, 1997, p 13 158 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (15) (a) Jordon, R. B. Reaction Mechanisms o f Inorganic and Organometallic Systems', Oxford University Press, New York; 1998. (b) Davy, R. D.; Hall, M. B. Inorg. Chem. 1989, 28, 3524. (c) Flood, T. C.; Lim, J. K. Deming, M. A. Organometallics, 2000,19, 2310. (16) Riiba, E.; Simanko, W.; Mereiter, K.; Schmid, R. and Kirchner, K. Inorg. Chem. 2000, 39, 382. (17) Fay, R. C.; Amal, Y. G.; Klabunde, U. J. Am. Chem. Soc. 1970, 92, 7056. (18) Bhalla, G.; Periana, R. A. Angew. Chem. Int. Ed. 2005, 44, 1540. (19) (a) Jones, W. D. Acc. Chem. Res. 2003, 36, 140. (b) Jones, W. D.; Feher, F. J. J. Am. Chem. Soc. 1986, 705,4814-4819. (20) (a) Tellers, D. M.; Bergman, R. G. Cand. J. Chem., 2001, 79, 525-528. (b) Tellers, D. M.; Yung, C. M.; Amdtsen, B. A.; Adamson, D. R.; Bergman, R. G. J. Am. Chem. Soc. 2002,124, 1400. (21) (a) Johansson, L.; Tilset, M. J. Am. Chem. Soc. 2001, 739. (b) Johansson, L.; Tilset, M. Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2000, 10846. (22) Methane can exchange with benzene at elevated temperatures and lead to higher isotopomers of methane as reported, reference 3. (23) Gilman, H., and Brown, R. E., J. Am. Chem. Soc., 1929, 51, 928. (24) (a) Criegee, R.; Dimorth, P.; Schempf, R. Chem. Ber., 1957, 90, 1337. (b) Rozema, M. J.; Rajagopal, D.; Tucker, C. E.; Knochel, P. J. Organomet. Chem., 1992, 438, 11. (c) Gilman, H., and Brown, R. E. J. Am. Chem. Soc., 1929, 51, 928. (25) (a) Constable, E. C.; Leese, T. A. J. Organomet. Chem. 1987, 335, 293. (b) Black, D. St. C.; Deacon, G. B.; Edwards, G. L.; Gatehouse, B. M. Aust. J. Chem. 1993, 46, 1323. (c) Parish, R. V.; Wright, J. P.; Pritchard, R. G. J. Organomet. Chem. 2000, 596, 165. (26) Jaguar 5.0, Schrodinger, Inc., Portland, Oregon, 2000. (27) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (28) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785. 159 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (29) Baker, J.; Muir, M.; Andzelm, J.; Scheiner, A. In Chemical Applications o f Density-Functional Theory, Laird, B. B., Ross, R. B., Ziegler, T., Eds.; ACS Symposium Series 629; American Chemical Society: Washington, DC, 1996. (30) Niu, S.; Hall, B. M. Chem. Rev. 2000,100, 353. (31) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299. (b) Goddard, W. A., Ill Phys. Rev. 1968, 174, 659. (c) Melius, C. F.; Olafson, B. O.; Goddard, W. A., Ill Chem. Phys. Lett. 1974, 28, 457. (32) (a) Hariharan, P. C.; Pople, J. A. Chem. Phys. Lett. 1972, 16, 217. (b) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654. (33) (a) Tannor, D. J.; Marten, B.; Murphy, R.; Friesner, R. A.; Sitkoff, D.; Nicholls, A.; Ringnalda, M.; Goddard, W. A., Ill; Honig, B. J. Am. Chem. Soc. 1994,116, 11875. (b) Marten, B.; Kim, K.; Cortis, C.; Friesner, R. A.; Murphy, R. B.; Ringnalda, M. N.; Sitkoff, D.; Honig, B. J. Phys. Chem. 1996,100, 11775. (34) Sheldrick, G. M. SHELXTL, version 5.1; Bruker Analytical X-ray System, Inc.: Madison, WI, 1997. (35) Blessing, R. H. Acta Crystallogr. 1995, A51, 33. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 Anti-Markovnikov, Hydroarylation of Olefins Catalyzed by a bis-acetylacetanato Iridium (III) Complex 4.1 Introduction The Friedel-Crafts reaction is one of the cornerstones of organic chemistry for the generation of C-C bonds.1 The reaction is very efficient and proceeds with a high degree of regiocontrol to give the Markovnikov products that is controlled by the relative stabililty of incipient carbocationic intermediate. Given importance of this reaction in organic chemistry and the common occurrence of the Aryl-Akyl C-C bond it would be useful to develop reaction strategies to: (A) control the regiochemistry, (B) control the stereochemistry and (C) replace the strong Lewis acids utilized as catalyst in these reactions with non-acidic species that are more tolerant to a broader range of functional groups. One strategy to accomplishing this is to develop new generations of catalysts that do not operate via the carbocationic mechanisms. Such a strategy could be based on the C-H activation reaction. The C-H activation reaction is a facile reaction that is possible with a wide range of substrates and involves reactions with metal complexes that lead to M-C species as intermediates. Since this reaction does not involve the formation of radicals or charged carbon intermediates, catalysts based on the C-H Activation reaction are not required to be acidic and the formation of planar carbocations are avoided. Consequently, the potential exists for a wide range of functional 161 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. tolerance, complementary regio-selectivity to the Friedel-Crafts reaction as well as possible steroselectivity in the formation of C-C bonds. As discussed in earlier chapters, significant advances in the chemistry of the hydrocarbons have been made since the 1970’s. Particularly relevant to the development of low temperature, selective, heteroatom hydrocarbon functionalization catalysts have been made. Extensive research work has been carried out in the field of homogeneous metal complexes that cleave the C-H bonds of unactivated hydrocarbons at low temperatures and with extraordinary selectivity. However, relatively few metal complexes can carry out the selective • 3 functionalization of alkane C-H bonds. Reported systems that catalyze reactions between olefins and arene C-H bonds typically generate unsaturated products.4 Saturated products are generally produced in two steps involving Friedel Craft’s acylation followed by reduction as shown in Figure 4.1. Notably a chelation- assisted reaction of olefins with heteroaromatic ketones catalyzed by Ru is practically exploited.5 R Friedel Craft's Acylation Reduction Figure 4.1. Comparison of the conventional two step method and a single step method to generate saturated linear alkyl benzene’s. 162 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Recently a novel, binuclear complex, [Ir(|a-acac-0,0,C3 )(acac-0,0)(acac- •3 C )]2 , [Acac-Ir]2 , that catalyzes the only reported example of anti-Markovnikov, hydro-arylation of unactivated olefins by unactivated arenes to produce saturated alkyl arenes was reported.6 Subsequently, in the earlier chapters, it was shown that mononuclear species of the R-Ir(acac)2 L family were the active catalysts H-D exchange reactions and follow the same reaction pathway as shown in Figure 4.2.7 7 o Experimental and theoretical studies, involving the C-H activation studies reveal that (A) all the dinuclear and mononuclear complexes follow the same mechanistic steps and share catalytic steps, (B) Initiation step involve either the cleavage of the dinuclear or the loss of the ligand L from the mononuclear species in a dissociative process to generate the 5-coordinate site, (C) These complexes undergo trans-cis isomerization of the acac groups to generate the active site, (D) C-H activation and trans-cis isomerization goes through a common intermediate, (E) C-H activation is not the rate determining step and (F) bis bidentate ligands can be employed to access the benefits of a tetradentate ligand. DFT studies delineate a complex interplay between C-H activation and olefin insertion for this family of complex, where one is facilitated at the expense of other.8 This has been the case in the recently shown Ru(II) complex, Tp- Ru(Ph)(CH3 CN)(CO), which is also an active hydroarylation catalyst.9 Both the Ir(acac) and Ru(Tp) complex have been shown to proceed through common steps for hydroarylation.8 163 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Given the broad potential utility of efficient catalysts for olefin hydroarylation, the wide availability of O-donor ligands, the unique properties of this first example of an O-donor late transition metal catalyst and the limited study of O-donor ligands with late transition metals for C-H activation reactions we have begun a systematic study of this class of homogeneous complexes. The focus has been on structure-function relationships based on variations in the metal center1 0 and the O-donor ligands. In later chapters, the chemistry have been extended to a bis tropolonato Ir(III) analogue, which has been shown to be a faster C-H activation catalyst and shows a comparable hydroarylation reactivity.1 1 It was presumed that the reaction operated by electrophilic arene C-H bond activation and hydroarylation, although no mechanistic work has been Z L reported. It is important to understand the basis of operation of this unique catalyst as most other systems that catalyze reactions between olefins and arene C- H bonds typically generate unsaturated coupled products.4 By avoiding the formation of achiral carbocation intermediates, hydro-arylation of olefins via C-H bond activation has the potential for broad applicability given the possibility for both unusual regioselectivity as well stereoselective C-H and C-C bond formation. 164 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. C-H ACTIVATION HYDROARYLATION PhCH2CH2-Ir-L Figure 4.2. Proposed Reaction Mechanism of H/D Exchange and Hydroarylation of Olefins Catalyzed via Arene C-H activation by R-Ir-L and [R-Ir] 2 Complexes. 165 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. However, given the low rates of [Acac-Ir]2 (tum-over-frequency (TOF) of 10‘3 s'1 at 200 °C, a key requirement will be to develop more active catalysts. To guide the design of more efficient catalysts we sought to determine the reaction mechanism with an initial focus on whether: A) Acetylacetonate ligands are thermally and protic media stable? (B) What are the rates of various R-Ir(acac)2 -L complexes with different “R” and “L” groups? (C) Is the given reaction under thermodynamic or kinetic control? (D) Does the reaction proceeded directly via the dinuclear Ir complex, [Acac-Ir]2, or alternatively a mononuclear species, (E) what is the reaction mechanism proceeded via a C-H activation reaction and olefin insertion (F) Why are no unsaturated products observed? (G) How thermally stable are these complexes? 4.2 Results and Discussion 4.2.1 Stability of O-Donor Spectator Ligands Given the observed high thermal stability of these (acac-0,0)2lr(III) catalysts for the hydroarylation reaction (see below) it is unlikely that the catalysis is due to decomposition reactions of the complexes. However, as it known that O- donor ligands are more labile than N or P ligands it was important to examine the possibility that the P-diketonate ligands were not being lost by thermolysis or protonolysis. To investigate this we examined the possibility of exchange 166 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reactions between the coordinated acac-ligands and free, substituted p-diketones as well as stronger protic acids. Thus, refluxing [Acac-C-Ir] 2 or Acac-C-Ir-HiO in neat hexafluoro acetyl acetone (BP = 70°C) for 3 h leads to the quantitative formation and isolation of the corresponding dinuclear complex, [HFacac-Ir]2 , -j where the acac-0.0 ligands remain intact and only the C-donor ligand, acac-C , has been replaced, Figure 4.3. Similarly, refluxing [Acac-C-Ir] 2 or Acac-C-Ir- H2 0 with other stronger acids, HX, (X = Cl, OCOCH3 and OCOCF3 ) for 3 hr lead to quantitative isolation of the corresponding dinuclear complexes, again with the 1 13 acac-0,0 ligands intact. These complexes have been characterized by H and C NMR spectroscopy, elemental analyses and selected ones by X-ray crystallography. ORTEP diagram of [CH3 C O O -Ir] 2 is shown in Figure 4.4. The [Cl-Ir] 2 dinuclear complex, Figure 4.3, has been previously reported to be formed from [Acac-C-Ir] 2 by treatment with excess of benzoyl chloride. As these reactions could be successfully carried out in the air as well as under nitrogen, these complexes are speculated to be reasonably stable to oxygen even at elevated temperatures. 167 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o o [Acac-C-lr]2 X = Cl, [Cl-lr]2 X = OCOCH3 , [CH3COO-lr]2 X = OCOCF3 , [CF3COO-lr]2 o o Cp3, [HFacac-lr]2 Figure 4.3. Figure 4.4. Thermal Treatment of (acac-0,0)Ir(III) Complexes with Various Acids ORTEP diagram of [CH3 C O O -Ir]2 . Two molecules of chloroform and one molecule of water omitted for clarity. Selected bond lengths and bond angles are: Ir(l)-0(3) 1.993(7); Ir(l)-0(4) 2.003(7); Ir(l)-0(5) 2.019(6); Ir(l)-0(6) 2.032(7), Ir(l)-0(1) 2.069(8). 0(3)-Ir(l)-0(4) 94.9(3); 0(3)-Ir(l)-0(5) 85.5(3); 0(4)- Ir(l)-0(5) 176.6(3); 0(3)-Ir(l)-0(6) 175.8(3); 0(4)-Ir(l)-0(6) 85.4(3); 0(5)-Ir(l)-0(6) 94.0(3); 0 (3 )-Ir(l)-0 (l) 86.6(3); 0(4)- Ir(l)-0(1) 86.9(3); 0 (5 )-Ir(l)-0 (l) 89.7(3); 0 (6 )-Ir(l)-0 (l) 89.2(3). 168 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.2.2 Rates of Various (acac-0,0)2lr(lll) Complexes All the O-donor complexes shown in Figure 4.2, catalyze, at varying rates, the hydroarylation reaction of propene with benzene and the results are shown in Table 4.1. The most active catalyst being Ph-Ir-I^O. The ORTEP drawing is shown in Figure 4.5 with methanol as the ligand. The most important conclusion from this data is that while the various complexes operate at different rates, that all exhibit the same anti-Markonikov regioselectivity showing a preference for n- propyl to iso-propyl benzene in a 61:39 molar ratio. Figure 4.5 ORTEP drawing of Ph-Ir-CH^OH. Thermal ellipsoids are at the 50% probability level. Hydrogen atoms omitted for clarity. Selected bond lengths (A°): Irl-Cll, 1.972(5); Irl-0 4 , 1.994(3). 169 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 4.1 Hydroarylation of propylene catalysed by various Ir(acac) 2 complexes3 [Complex] TOFb (x 10-4 Entry Complex Additive L:B mmol s'1 ) 1 [Acac-Ir]2 — 5 110 61:39 2 Acac-Ir-H2 0 — 5 100 61:39 3 Acac-Ir-Py — 5 24 61:39 4 Acac-Ir-Py — 10 22 61:39 5 Acac-Ir-Py — 30 22 61:39 6 Ph-Ir-Py — 5 32 61:39 7 Ph-Ir- H2 0 — 5 130 61:39 8 Ph-Ir-Py Acac 5 15 61:39 9 Ph-Ir-Py H20 5 36 61:39 aAll reactions were carried at 180°C for 30min with 0.96 MPa of propylene with added 1.96 MPa of added nitrogen. bTOF = [mols of product/mols of catalyst x reaction time] As can be seen in Table 4.1, these catalysts differ either in the R group or L group attached to the (acac)2 lr(III) motif. Also, both the mononuclear complexes, Ph-Ir-H2 0 and Ph-Ir-Py are active catalysts with Ph-Ir-H2 0 being as active as [Acac-C-Ir]2, while Ph-Ir-Py is less active. These complexes can be considered as precursors which are in equilibrium with the active catalyst cis-Ph-Ir-C2 H4 170 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. since the regioisomer distribution of the products are same. For example, all [R- Ir(III) (acac)2 L] complexes, irrespective of nuclearity, show the identical linear to branced (L:B) (61:39) product ratio with propylene. Similarly, a constant L: B product ratio (98:2) is obtained when styrene is employed. These constant product selectivity with all the (acac)2 lr(III) complexes strongly reflect that the same active catalytic species (albeit at different concentrations) is formed from [Acac-C-Ir]2 , Acac-C-Ir-H20 , Acac-C-Ir-Py, Ph-Ir-H2 0 or Ph-Ir-Py. Using the reaction rates of hydroarylation catalysed by these (acac)2 lr(III) complexes, a similar correlation has been drawn between the free energies of the various catalyst precursors and TOF, strongly supporting the presence of a common catalytic step and a common o rate determining step. As the reaction of Ph-Ir-H2 0 or Ph-Ir-Py seemed to indicate that neither y-C bonded acac nor water was essential to catalysis we confirmed this by examining the effect of added free acetyl acetone (acac-H) and water on the catalytic activity of Ph-Ir-Py using dry benzene. As can be seen in Table 4.1, (entries 8 and 9) neither added acac-H nor water has any effect on the product selectivity of Ph-Ir-Py and therefore, the further studies have been limited to Ph- Ir-H2 0 or Ph-Ir-Py. Although with added acac, the rate reduces to half, suggesting a detrimental effect to the catalysis rate. Infact, we observe this as a consistent trend where acids such as acetic acid, trifluoroacetic acid, hydrochloric acid, etc. strongly retard the reaction rate. These observations suggest that these 171 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. acids react with the “active form” of the catalyst, thereby reducing the catalyst concentration of the active catalyst, hence a drop in TOF. 4.2.3 Thermodynamic vs Kinetic control A key distinguishing feature of these catalysts is the Anti-Markonikov regioselectivity in the olefin hydroarylation reactions as opposed to analogous Friedel-Crafts conditions, which gives markovnikov addition product. While this dramatic difference could support the conclusion that these catalysts operate via different mechanism, one should note that 40:60 ratio o f iso- and n-propyl benzene is essentially the same value expected from thermodynamic control. As the ratio of alkyl arene products with propylene is very close relative to thermodynamic stabilities of these isomers (based on DFT calculations8 and thermodynamic 1 2 tables ) we examined whether the reaction is under thermodynamic control for this particular olefin or not. For the hydroarylation to be under thermodynamic control it is required that a facile pathway be available for the intramolecular interconversion of the n- propyl and isopropyl benzene isomers on at least the same time scale and under the same reaction of the hydroarylation reaction. Importantly, such alkyl arene isomerizations must not be accompanied by intermolecular trans-alkylation (reactions that transfer alkyl groups between different arenes) because in that case the predictred thermodynamic products would be expected to be polyalkyl arenes 172 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. that are not observed. However, to test this possibility that under hydroarylation conditions that a selective, intramolecular alkyl arene isomerization catalyst is generated, we examined the possibility that isopropyl benzene in the presence of benzene and the catalyst, Ph-Ir-Py, under reaction conditions for the hydroarylation reaction could rearrange to the thermodynamically more stable isomer, n-propyl benzene (Figure 4.6). GC/MS analysis of the resulting reaction mixture showed that essentially no reaction occurred and that while unreacted isopropyl benzene was observed, no n-propyl benzene was generated. To further mimic the reaction conditions, the reaction was repeated but in this case, in the presence of ethylene gas, to rule out the possibility that the active catalyst for this isomerization is only generated in the presence of olefins. In this reaction, while ethyl benzene is observed (indicating an active hydroarylation catalyst is formed) the isopropyl benzene again remains unchanged and no n-propyl benzene is observed. These experiments rule out the possibility that the anti-Markovnikov reaction selectivity stems from thermodynamic control during the hydroarylation and that results with propylene are coincidental. \ / [Ph-Ir-Py] 180°C Figure 4.6. No Rearrangement of isopropyl to n-propylbenzene under catalyst. 173 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. We believe that this is fortuitous as the reactions with styrene also lead to 98:2 ratio of 1,2-diphenyl ethane : 1,1 diphenyl ethane, while the thermodynamic control would predict > 99% of 1,1-diphenyl ethane (Table 4.2). Similarly, reactions with isobutylene generate the products in 82:18 ratio, while thermodynamic control would predict 2-methylpropyl benzene and tert-butyl benzene in. 97:3 ratio. All these results strongly suggest that the reaction is not under thermodynamic control. Table 4.2. Thermodynamic and Experimental data for hydroarylation with various olefins. R R k k R [Ph-Ir-Py] ► 180°C k k Linear Branch Olefin Thermodynamic Data Experimental Data Linear Branch Linear Branch Propylene 60 40 61 39 Styrene 1 1000 98 2 Isobutylene 97 3 82 18 174 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. It is interesting to note that the same regioisomers are observed as in the well documented Heck reaction. The common step being the insertion of olefin into M-Ph bond, which controls the selectivity of the products. Interplay of electronic and steric factors are suspected to control the selectivity of these products. 4.2.4 Dinuclear or Mononuclear Active Catalyst? In the initial report of hydroarylation by the (acac-0,0)2lr(III) complexes, we utilized the dinuclear complex, [Acac-C-Ir]2 , as the catalyst. Subsequently, we have found that the mononuclear complexes shown in Table 4.1 (Ph-Ir-L, Acac- C-Ir-L (L=H20, Py) etc.) are active catalysts. While this suggests that the active catalyst is a mononuclear (acac^Ir complex, it could be speculated that the active catalyst could be a dinculear Ir species that is formed under the reaction conditions. The lability of the dinuclear complexes to dissociation to stable 5- coordinate square pyramidal complexes (or 6-coordinate solvento complexes) for other related complex, [CH3-Ir]2 , occurs with an activation barrier of 14.1 kcal/mol based on the dynamic NMR study of these complexes, as well as the facile conversion of these complexes to stable mononuclear complexes are also inconsistent with the dinuclear complexes as the stable, active catalysts.7 175 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. An examination of the predicted rate laws for a dinuclear catalyst versus a mononuclear ligated catalyst and the dependence of the catalysis rate on the concentration of added L can provide evidence against this possibility. If we presume that the active catalyst is a dinculear complex [M-M] and that the mononuclear [M-L] and dinuclear species are in equilibrium during reaction then the rate law will be proportional to [M-L] /[L] assuming steady state approximations (Scheme 4.1). This is reasonable if the equilibrium constant for formation of the dinuclear complex, M-M, or the amount of L formed from dissociation of M-L is small formed from, are both small. Consistent with these assumptions VT-NMR analysis of a C6D6 solution of Ph-Ir-Py at 100°C showed no detectable amounts of free pyridine or dinuclear complex. These results are also consistent with theoretical calculations that indicate that both the reactions are endoergic reactions with AG > 5 kcal/mol. 2 M-L m-M ► Products +2L Rate = kobs [M-L]2 [L]2 TOF = Rate = knhJM-Ll [M-L] [L]2 M-L — M * - Products +L Rate = kobs 1 M~L1 [L] TOF = Rate = ^obs [M-L] [L ] Scheme 4.1. Possible dependence of L on TOF 176 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. With these considerations plotting TOF (TOF = Rate/MLa ; MLa = ML) •j vs. [1/L ] should yield a straight line if the catalyst is the dinuclear complex M-M, Scheme 4.1. On the other hand, if the active catalyst is the 5-coordinate mono nuclear species [M] generated by the loss of L from added M-L, then plotting TOF vs. [1/L] should yield a straight line at constant [M-L]. As can be observed in Figure 4.7, for [Ph-Ir-Py] with added Py, the TN vs [1/L] plot yields a straight line ruling against an active dinuclear catalyst. Similar trend is observed when plotting TOF vs 1/Py equivalents. 0.4 - 0.05 0.15 0.2 0.25 0.3 1/Py Equivalents 0.35 0.4 Figure 4.7. Turn over number (TN) vs 1/Py Equivalents. Analysis of the bond distances in the crystal structure the dinuclear complex, [Acac-C-Ir] 2 are also consistent with the observed lability of these compounds to mono-nuclear complexes. Thus, the Ir-C (bridged acac) bond distance of 2.329(6) A is much longer than the normal Ir-C sigma bond, which 177 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. usually fall in the range around 2.00-2.20 A. Compared to this, the Ir-C (y-acac) bond distance is 2.165(6) A, which suggests bond breaking of Ir-C (bridged acac) to generate a mononuclear Ir (III) (acac-0 ,0 )2 (C3 -acac) species is a facile process and it is unlikely that the dinuclear complexes would be sufficiently stable under the reaction conditions to be the active catalyst. 4.2.5 Reaction Order of Substrates 4.2.5.1 Dependence on olefin The hydroarylation of olefins to generate monoalkyl arenes is typically carried out at ~200°C with 5 - 1 0 mM catalyst in arene both as reactant and as solvent. Generally ~ 10-20 mol % olefin is used as co-reactant. As shown in Figure 4.8, under these conditions using Ph-Ir-Py as catalyst, the olefin shows complicated dependence on olefin. The initial increase in the TN is consistent with the reaction being first order in styrene as shown by the linear dependence on the styrene olefin concentration up to 3M. The inhibition at higher concentrations has been reported earlier and has been shown to be relevant to the catalysis. 8 , 6 178 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 5 4 3 2 1 0 1 2 3 4 5 Styrene / [M] Figure 4.8. Olefin Dependence on Hydroarylation 4.2.5.2 Dependence on Benzene The reaction order in benzene was determined using cyclohexane with Ph- Ir-Py as catalyst. Thus, as shown in Figure 4.9, the reaction rate decreases linearly upon dilution of benzene that would be expected for a first order dependence on benzene. The assumption that cyclohexane was inert was based on the other observation that no net reaction was observed between olefin and cyclohexane in the presence of Ph-Ir-L catalyst. 179 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. B enzene/M Figure 4.9. Benzene dependence on Hydroarylation 4.2.6 Evidence for Proposed Mechanism The reaction mechanism of the hydroarylation reaction catalyzed by the O- donor, (acac)2 lr(III) complexes is shown in Figure 4.2. As previously shown, the trans complexes are the kinetic product that is isolated during synthesis, but on heating lead to the quantitative formation of the cis product, which is the thermodynamic product. 7 These observations clearly show the involvement of cis species in the mechanistic cycle. The reaction mechanism is proposed to proceed via three key steps: A) Pre-equilibrium or isomerization step(s) that generates the “active catalyst independent of which R-Ir-L complex is used to catalyze the reaction,” B) an olefin insertion step and C) a C-H activation step. An important prediction of the proposed mechanism is that the two the two key cis- intermediates, cis-Ph-Ir-Ol and cis-PhCH2 CH2 -Ir-Bz are proposed to be in 180 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. equilibrium with the corresponding trans-R-Ir-L complexes, where L is an added ligand. This is important as this allows entry into the proposed catalytic cycle from the trans-complexes that can be readily synthesized. We have been unable to synthesize or isolate the “active catalysts” on the catalytic cycle. Of course, alternative mechanisms can be postulated for the alkylation of arenes with olefins. This type of alkylation reaction is well known in organic chemistry for Friedel-Crafts alkylation of arenes that proceeds via the generation of cabocation intermediates. The Friedel-Crafts reaction is catalyzed by Lewis acids and it can be proposed that the (acac)2 lr(III) complexes are “soft” Lewis acids, 1 especially given the recent precedent fo r the use o f transition metal complexes such as Au, Pt and Pd as general Lewis acids fo r catalyzing reactions 1 ^ between alkene/alkyne and arenes. However, the central observation that the hydroarylation reaction catalyzed by the (acac)2 lr(III) complexes generates alkyl arenes with anti-Markovnikov regioselectivity would tend to rule out mechanism occurring via carbocation intermediates. Several other observations also rule against a carbocation type reaction mechanism that would be catalyzed by Lewis acids: A) With classical Lewis acid catalyzed reactions, alkyl arenes are more reactive than the parent arenes toward alkylation; in the (acac)2 lr(III) catalyzed hydroarylation alkyl benzenes are less reactive. B) Lewis acid catalyzed reaction are typically inhibited by greater than one equivalent of water relative to the catalyst. However, the (acac)2 lr(III) catalysts are not inhibited by addition of several equivalents of water (Table 4.1, entries 6 and 9). C) Lewis acids readily 181 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. catalyze the exchange of alkyl groups between alkyl arenes. However, the (acac)2 lr(III) complexes do not catalyze reactions of diethylbenzene with benzene to generate mono-ethyl benzene under hydroarylation conditions. D) The reaction rates of lewis acid catalyzed reaction strongly correlate with the strength of the Lewis acid. However, while IrCh could be expected to be a stronger Lewis acid than the (acac)2 lr(III) complexes, IrCl3 does not catalyze the hydroaylation reactions under identical conditions. Additionally, the observation that other readly available Ir catalysts show no hydroarylation activity strongly suggest a unique catalytic activity for the (acac)2 lr(III) complexes. The central approach taken to elucidating the reaction mechanism is to synthesize well-defined complexes that are proposed to be involved in the catalytic cycle and to show that the chemistry of these complexes are consistent with the observed catalysis with respect to rate and selectivity and the observed resting state of the catalyst from hydroarylation. Furthermore, answering some of the particular questions would help understanding the mechanism and improving the yields. For instance, (A) What is the rate limiting step? B) What is the Selectivity determining step ? (C) why is the reaction selective for hydroarylation to generate saturated products ? (D) Why doesn’t this undergo B-Hydride elimination to provide unsaturated products? To answer these, the mechanism has been divided mainly into three sections which constitute the Pre-equilibrium steps, olefin insertion and C-H activation. 182 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.2.6.1 Pre-Equilibrium Steps As can be seen from Figure 4.2, it is proposed that these are all the various R-Ir-L as well as dinculear, [R-Ir]2, complexes examined are catalyst precursors that in a series of pre-equilibrium steps, that can involve ligand loss, trans-cis isomerization, arene C-H activation and olefin coordination, lead to the same active catalyst, cis-Ph-Ir-Ol, independent of the starting complex. Mechanisms involving C-H activation 2 and insertion are typically inner-sphere reactions and as such require a vacant coordination site on the metal for coordination of the substrate. The O-donor complexes utilized in this study are 18 electron, 6 - coordinate octahedral complexes of one of the most substitutionally inert metals, Ir(III). As shown in Table 4.1, the ligand “L” of the O-donor (acac)2 lr(R)(L) complexes significantly influence the rates of the catalytic hydroarylation reaction. Strongly donating ligands such as pyridine (Table 4.1, Entry 3-6) severely inhibits the catalysis whereas labile ligands such as CH3 OH and H20 (Table 4.1, Entry 7) are weaker inhibitors. These TOF have been correlated to the relative energies of these molecules and these have been shown to be due to the difference in the ground states. 8 Strong evidence for pre-equilibrium, dissociative loss of ligand, L has been shown previously, 7 where exchange of free pyridine with coordinated pyridine with Ph-Ir-Py and CH3 -Ir-Py, is rapid at room temperature and independent of 183 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the concentration of added free Py, as expected for a dissociative process. The activation parameters for the rate of exchange for Ph-Ir-Py were also estimated to be AH* = 22.8 ± 0.5 kcal/mol; AS* = 8.4 ± 1.6 eu; and AG*2 9 8 k = 20.3 ± 1.0 kcal/mol and similarly, pyridine exchange for CH 3 -Ir-Py was found to be dissociative, with activation parameters of AH* = 19.9 ± 1.4 kcal/mol; AS* = 4.4 ± 5.5 eu; and AG*2 9 8 k = 18.6 ± 0.5 kcal/mol. This rapid rate relative to the hydroarylation catalysis is consistent with the ligand loss being a pre-equilibrium step. 4.2.6.2 Olefin Insertion To generate the proposed active catalyst cis-Ph-Ir-Ol, olefin coordination is required. We propose that occurs in a manner similar to conversion of the trans- Ph-Ir-Py to cis-Ph-Ir-Py. However, while olefin complexes can be observed by in situ NMR spectroscopy, attempts at generating and isolating such olefin complexes with various trans-R-Ir-L complexes have failed, presumably due to the instability of the olefin complexes. Thus, NMR analyses show that addition of ethylene to the dinculear complex, [Acac-Ir]2 , does lead to a new mononuclear complex containing a coordinated ethylene. However, attempts at isolating the complex have failed. This instability of the olefin complexes is consistent with the lability of the Py and H2 O complexes to substitution at room temperature. Olefin 184 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. doesn’t coordinate strongly with these O-donor complexes as other pi acids such as Py and CO do, so as to isolate an olefin complex. A key step of the proposed reaction mechanism is the olefin insertion step with the Ph-Ir intermediate, cis-Ph-Ir-Ol. This is the step proposed to result in the preferred anti-Makovnikov regioselectivity for olefin hydroarylation. To examine the feasibility of this step we examined the stoichiometric reaction of Ph-Ir-Py with various olefins as shown in Figure 4.10. The regioselectivity of the olefin is remarkable as it leads to the formation of the anti-markovnikov product. The reaction was typically carried out by reaction of 15 mmol Ph-Ir-Py with olefins such as propylene, ethylene, styrene and 1 -hexene in liquid protiated mesitylene, at 180 °C for 20 min. After reaction the gas and liquid phases were analyzed by GC/MS to identify and quantify the organic reaction products. The solvent was then removed and the non-volatile reaction products were dissolved in CDCI3 and analyzed by NMR. The formation of benzene is expected based on the known CH activation of solvents by R-Ir-Py complexes. As can be seen, Ph-Ir-Py treated with olefins such as styrene in mesitylene, leads to the formation of both dihydrostilbene and 2,2-diphenylethane in 98:2 ratio along with free benzene in 60% yield. Similarly, reaction with 1-hexene also leads to the formation of 1- Phenyl hexane and 2-phenyl hexane in 69:31 ratio and free benzene. As can be seen in all these cases, these stoichiometric reactions of Ph-Ir-Py with olefins result in the same ratio of branced to linear alkyl arene products observed in olefin hydroarylation catalysis. 185 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I ■X d - n B n R = H, CH3, Ph, C4 H 9 Figure 4.10. Insertion Products of olefins with Ph-Ir-Py Table 4.3. Insertion Products of olefins with Ph-Ir-Pya R A (% ) B (% ) A : B C (% ) Hb — c h 3 c 40 27 61:39 33 Ph 39 1 98:2 60 C4H9 50 25 69:31 25 All reactions carried out with 15mmol of Ph-Ir-Py in 1mL of mesitylene at 180 °C for 20min. b Carried out with 2 MPa of ethylene c Carried out with 0.96Mpa of propylene with 2 MPa of N2. As can be seen from the reaction stoichiometry, Figure 4.10, a hydrogen donor would be required for the generation of alkyl arenes. In the proposed catalytic reaction mechanism this is provided by the arene co-reactant in the CH 186 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. activation step or through olefin itself via vinylic C-H bond activation. However, benzene (or other aromatic solvents such as toluene) could not be utilized as a hydrogen donor in the stoichiometric reaction of Ph-Ir-Py with propylene because Ph-Ir-Py exchanges more rapidly with arene solvents via rapid CH activation. Consequently, the phenyl group would be lost before olefin insertion could occur if olefin insertion is rate limiting. Thus, to carry out these reactions, mesitylene was used. Control experiments showed that the olefin hydroarylation reaction with benzene and propylene catalyzed by Ph-Ir-Py could be carried out in the presence of added mesitylene suggesting the mesitylene did not significantly alter the hydroarylation chemistry. NMR spectra’s of these reactions show that the organometallic complex after the reaction is either the Mes-Ir-L1 4 or Vinyl-Ir-L, 15 both of which have been characterized earlier, the latter being the major product. This is also indicated by various experiments as follows. (A) There was significant amount of deuterium incorporation in the ethylene ( 1 0 %) when C&D 6 was employed for hydroarylation. (B) Along with the stoichiometric amount of product, small traces of coupling of olefins were also observed which could arrive from the hydrovinylation of olefins. This has been shown to be the case for any R- Ir-L; in an inert solvent, will catalyse the hydrovinylation of olefins. The mechanism has been shown to be via C-H activation and not via Cossee-Arlman migratory insertion. 15 187 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.2.6.3 C-H Activation Step n Ample evidence for this step has been reported earlier and is also observed in the facile, clean reaction of R-Ir-Py with benzene at to generate the Ph-Ir-Py complex. The activation parameters (AS* =11.5 ± 3.0 eu; AH* = 41.1 ± 1.1 kcal/mol; AG*2 9 8 k = 37.7 ± 1.0 kcal/mol) for CH activation were obtained using CH3 -Ir-Py as starting material at a constant ratio of [Py]/[C6D6] = 0.045.7 The PhCH2CH2-Ir-Py complex was found to react at essentially the same rates as CH3 -Ir-Py and showed similar temperature dependence. Also, to determine whether the reaction between benzene and propylene was occuring via benzene C-H activation to generate phenyl-Ir intermediates, we sought to isolate and identify the predominant Ir species present after catalysis. NMR analysis of crude reaction mixtures catalyzed with 5 mole % Acac-Ir-Py, after removal of volatiles, led to the isolation of a phenyl-Ir(III) species, Ir(Ph)(acac-0,0)2(pyridine), Ph-Ir-Py, in -65% yield based on added Acac-Ir-Py. The identity of this material has been confirmed by comparison to the independently synthesized complex. The identical material is formed when catalysis is carried out with Acac-Ir-H2 0 , followed by addition of pyridine and isolation. To confirm that Ph-Ir-Py was in fact involved in the catalysis, the catalytic activity of this and the related complex, Ph-Ir-H2 0 (both prepared by independent syntheses, were examined. As can be seen in Table 4.1, Ph-Ir-Py (entry 6) was found to be as active as Acac-Ir-Py (entry 3) while Ph-Ir-H20 188 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (entry 7) was found to be slightly more active than [Acac-Ir] 2 or Acac-Ir-HiO. Critically, these bis-acac-0,0, phenyl-Ir(III) complexes also gave the same branched to liner ratios of products with propylene indicating that the same catalytic species are involved. 4.2.7 Rate Determining Step Carrying out the reaction of ethylene and benzene at various temperatures leads to an estimate of the activation barrier of -30 kcal/mol. The reaction is quite selective for ethyl benzene and diethyl benzene is only seen at low levels later in the reaction. Importantly, only para and meta diethyl benzenes are observed in an -1:2 ratio. Carrying out the catalysis with ethylene and CeDg shows no kinetic isotope effect, which is consistent with earlier observations as C- H activation is not rate determining. Under these conditions, only low levels of deuterium incorporation (-5% ) into unreacted ethyelene is observed. Activation parameters for stoichiometric C-H activation was estimated to be - 41.1 kcal/mol (AH) (Figure 4.11). This actually corresponds to the trans-cis isomerization barrier calculated theoretically as shown in Figure 4.11. The overall barrier for hydroarylation is the trans-cis isomerization. In the absence of such trans-cis barrier, olefin insertion is suggested to be the rate limiting step compared to C-H activation. This is being experimentally investigated in our labs. 189 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 2 .0 TS1 4 4 . 3 "Si r “ 34.0 \ 0> f T 2 3 .3 ' V C ^ 22.6 A TS 3 + CcH -16.3 OR * + c 2 h4 Figure 4.11. Combined Experimental (boxed) and DFT (solvated and gas phase) AH Values. 4.2.8 Why are Olefinic Products not Produced in C-H Activation with Ir Complexes? It is well know that metal-alkyl complexes possessing |3-CH bonds are susceptible to facile P-hydride elimination reactions.1 6 However, no olefinic products are observed in the hydroarylation reactions between benzene and n ethylene, or styrene, catalyzed by these O-donor complexes. Additionally, in the stoichiometric C-H activation reactions of PhCH2 CH2-Ir-Py and CH3 CH2 -Ir-Py with benzene, analysis of the liquid and gas phases of these reactions by NMR and 190 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. GC/MS showed that no olefinic products such as styrene or ethylene (either free or complexed to Ir) or Ir-hydride products are formed. Such products would be expected from irreversible (3-hydride elimination reactions from the coordinatively unsaturated, cis-5-coordiante intermediate, cis-PhCH2 CH 2 -Ir-D or cis-CH3CH2 - Ir-D (Scheme 4.2). This complete lack of olefinic products could suggest that (3- hydride elimination reactions to generate olefinic intermediates either do not occur or are reversible and unproductive. The observation that only PhCH2CH2 D is quantitatively formed from the stoichiometric C-H activation of CgD6 with PhCH 2CH 2 -Ir-Py could suggest that (3-hydride elimination reactions do not occur. However, this result would also be observed if the (3-hydride elimination from PhCH 2CH 2 -Ir-Py, was reversible, unproductive and significantly more stable than the branched alkyl, PhCH(CH3 )-Ir-Py product and/or if C-H activation from PhCH 2 CH 2 -Ir-Py was competitive with the (3-hydride elimination reactions. Given these plausible possibilities the selective formation of PhCH2 CH2D from CH activation of with PhC H 2 CH 2 -Ir-Py does not rule out the possibility that reversible, unproductive, (3 -hydride elimination reactions occurs in these O-donor complexes. 191 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. PhCH2CH2 -Ir-Py cis-PhCH(CH3 )-Ir-Py cis-PhCH2CH2 -Ir-Py PhCH2 — CH2D PhCHD—CH3 Scheme 4.2. Possible Reaction products with P hydride Elimination. Since metal alkyl possessing P-CH bonds that do not react to generate olefins would be useful in a variety of catalytic reactions (polymerization, hydroarylation, etc.) or in preventing catalyst inhibition from the generation of stable olefin complexes, the absence of these products is an important characteristic difference of the chemistry of these O-donor complexes compared to more electron rich or electron poor complexes. To understand the basis for this lack of products from expected P-hydride elimination reactions we sought to determine if this was because p-hydride elimination reactions: (A) are slower than the CH activation reactions or (B) do occur but are reversible and unproductive. In 192 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1-2 i - j order to examine these possibilities the a- C-lablled complex, CH3 CH2-Ir-Py, was synthesized and the C-H Activation with CeDf, examined, Figure 4.12. This ethyl-Ir complex was chosen as an alkyl-Ir-L complex that would not show a steric or electronic bias to possible 1,2-Ir-carbon rearrangements that could result from reversible (3-hydride elimination reactions because the olefin is symmetrical. CH 3 1 3 CH 2 -Ir-Py was synthesized using 1 3 C-labelled Et2 Hg. As shown in Figure 4.12, if reversible P-hydride reactions does occur with CH 3 1 3 CH 2 -Ir-Py this could be expected to lead to migration of the 1 3 C-label from the a to the p-positions and formation of the 1 3CH3CH2 -Ir-Py regio-isotopomer. Additionally, carrying out this reaction in C6D6 as the reaction solvent could be expected to lead to two regio- isotopomers of ethane, 1 3 CH3 CH2 D and l3CH2 DCH3 (formed by C-D activation of the C(£)(i solvent and loss of ethane) if reversible P-hydride elimination did occur 13 13 or only CH2 DCH3 if no C-migration occurred. Importantly, measurements of the rate of 1 3 C migration in the 1 3 C-labelled CH3 1 3CH2-Ir-Py and/or the relative ratio of the two regio-isotopomers of ethane could both be expected to provide information on the relative rates of reversible P-hydride elimination versus benzene C-H activation. Thus, for example, if the reversible P-hydride reaction is fast compared to benzene C-H activation, then it could be anticipated that approximately equal amounts of Ir-CH2 1 3 CH3, Ir-1 3 CH2 CH3 as well as 1 3 CH3 CH2 D and 1 3 CH2 DCH3 would be observed upon arene C-H activation reaction to generate 1 3 C,2 H-ethane and Ph-Ir-Py. 193 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. L = Pyridine Figure 4.12. Possible products expected from heating CH 3 1 3 CH 2 - Ir-Py in C6D6 to generate ethane by C-H Activation. As reported earlier,7 treatment of C H jC Ih-Ir-Py with CeD6 at 110 °C leads to quantitative and irreversible formation of Ph-d5 -Ir-Py and mono- deuteroethane (C2H5D) by the stoichiometry. This formation of mono- dueteroethane is also observed upon CH activation of C6 D6 with the l3C-labelled 194 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. complex, CH 3 I3 CH 2 -Ir-Py. However, monitoring the progress of the C-H activation reaction by 1 3 C {1H} (with sufficiently long relaxation delay to afford IT 1 accurate integration of the C resonances) and H NMR yielded additional information. As shown in Figure 4.13, a time dependent study of the reaction 13 13 progress shows evidence for the migration of the C label of CH 3 CH 2 -Ir-Py (~ - 9 ppm) from the a to the (3-position, resulting in a formation of the (3-1 3 C regio- isotopomer, 1 3 CH 3 CH 2 -Ir-Py (-18 ppm). (X T ........ I iX L C6P6 C L M D \ + D Ph-Ir-Py CH3*C H 2-lr-Py *CH3CH2-lr-Py All T65 1 3 5 1 0 5 7 5 "45 1 5 15 10 0 -10 -15 -ti= 0 m in Figure 4.13. Time Dependent 1 3 C NMR spectra for the reaction of CH 3 1 3 CH 2 -Ir-Py (-9 ppm) with CeD6 to form 1 3 CH 3 CH 2 -Ir-Py (18 ppm) and 2 regioisomers of ethane ( 8 ppm) 195 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. It is also clear from Figure 4.13, that a steady concentration of the 1 3 - isomer, 1 3 CH3CH 2 -Ir-Py, is attained that is substantially lower than the amount of CH3I3CH 2 -Ir-Py present. This indicates that: a) reversible |3-hydride elimination most likely occurs and accounts for the a to (3-migration of the 1 3 C-label of 1 1 CH3 CH2 -Ir-Py and b) importantly, the lack of formation of equimolar amounts CH31 3 CH2 -Ir-Py and 1 3 CH3CH 2 -Ir-Py as ethane is lost with concomitant C-H activation of the benzene solvent, strongly indicates that the a to (3-migration of 1 3 the C-label is slower than the CH activation of benzene and formation of ethane and Ph-ds-Ir-Py. This result is confirmed by analysis of the dissolved ethane that is produced from arene CH activation. Thus, both regio-isotopomers of mono-2H, IT IT C-ethane (8ppm composed of a singlet from CH3 CH2 D and a 1:1:1 triplet from 2 H-I3C coupling in 1 3 CH2 DCH3,) are generated from the CH activation of C6D6 as shown in Figure 4.13. Simulation of this pattern readily shows that the predominant ethane product is 1 3 CH2 DCH3 with ~ 16 mol % of l3CH3CH2 D and that this ratio is essentially constant over the course of the reaction to generate ethane. Analyses by 'H NMR confirm these results and show (on the basis of the methyl resonances due to the (acac)2Ir resonances) that Ph-ds-Ir-Py is the only new (acac)2Ir product formed on loss of ethane. 196 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CH3-1 3CH2-Ir-Py 13 CH3-CH2-Ir-Py kcH PhH Ph-d5 -Ir-Py + c h 3 -1 3 c h 2d kcH PhH Ph-d5 -Ir-Py + c h 2 d -1 3 c h 3 J[CH 3 13CH2D] [CH3 13CH2 D] k C H [PhH] 1 4 C H 2D,3CH3] [CH2 D13CH3] 0.16 kC H [CH3 13CH2 D] 0 5 k 6 [CH2D13CH3 ][PhH] Scheme 4.3. Kinetic Scheme for C-H Activation and a to p 1 3 C- Migration Kinetic analysis of a reaction scheme, Scheme 4.3, assuming the steady state approximation for the formation of I3 CH3 CH2-Ir-Py and that the CH activation reaction is a bi-molecular reaction dependent on the concentration of benzene while the 1 3 C migration occurs via a unimolecular p-hydride elimination reactions pathway allows the ratio of rate constants for the C-H activation to P- hydride elimination (kcH : kp) to be estimated to be ~0.5 from the relative ratios of l3CH2 DCH3 and 1 3 CH3CH2 D produced during reaction. 197 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. These results are consistent with the theoretical predictions 8 that these O- donor Ir-alkyls do undergo reversible (3-hydride elimination reactions but that such reactions are unproductive. The theoretical calculations indicated that that while P-hydride elimination could occur to generate intermediate olefin hydrides that the reactions are reversible and unproductive because the barrier for dissociative loss of olefin from the saturated, 6-coordinate, 18 e' olefin hydride intermediates was higher than the C-H activation step. This comparable value for C-H activation and P-hydride elimination would seem to suggest a common rate determining intermediate for both processes as was seen for the C-H activation and trans-cis isomerization reaction. As in that case, this intermediate is most likely the cis-5-coordinate species, cis-R-Ir-D , where R = CH3CH2-. Theoretical calculations confirm that the barriers for p-hydride elimination and CH activation with CH 3 CH 2 -Ir-Py are comparable and proceed via the cis-Et-Ir-D intermediate. These findings should be contrasted to the closely resembled electron rich Ir(III) complex, [Cp*(PMe3 )IrMe(OTf), which undergo irreversible p-hydride 1 7 elimination. Also, closely related molecule TpIr(olefin) 2 have been shown to transform into Ir(III) vinyl hydride isomers, [TpIr(CH=CH2 )H(C2 H4 )] which are thermodynamically favoured.1 8 These results point to an important characteristic of these O-donor complexes, that is, even though the loss of olefin from these complexes are kinetically uphill, as a result of the P-hydride elimination reaction to generate olefinic metal complexes are reversible rather than being irreversible. 198 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Knowing that the olefin insertion is reversible, one could potentially exploit this result to carry out the insertion reactions of olefins. This is being currently investigated to take advantage of these O-donor complexes. 4.3 Conclusion The O-donor (acac)2Ir(R)(L) catalysts are active and stable catalysts for the hydroarylation of unactivated olefins with unactivated arenes. All the O-donor complexes shown at varying rates, catalyze the hydroarylation of unactivated arenes with unactivated olefins. These are stable to very high protic media and thermal conditions. These hydroarylation reactions are not under thermodynamic control and nature of the catalyst is mononuclear in nature. The hydroarylation of ethylene with can be carried out in neat benzene at temperatures of -200 °C with T 1 catalyst TOF of -1 0 ' s' . Initial mechanistic studies suggest that the mechanism involves pre quilibrium steps followed by insertion of olefin which then undergoes CH activation of benzene. Also, labelling studies unequivocally suggest that these complexes undergo P hydride elimination. 4.4 Experim ental Section General Considerations. GC analysis was performed with a shimadzu GC-MS QP5000 (ver. 2) equipped with cross-linked methyl silicone gum capillary 199 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. column, DB5. The retention times of the products were confirmed by comparison to standards. NMR spectra were obtained on a Bruker AM-360 spectrometer, measured at 360.138 MHz for ’H and 90.566 MHz for 1 3 C or on a Bruker AC-250 spectrometer, measured at 250.134 MHz for 'H and 62.902 MHz for ,3 C. Chemical shifts are given in ppm. Elemental analyses were done by Desert Analytics laboratory, Arizona. Synthetic work was carried out under air. Reagent- grade chemicals and solvents were used as purchased from Aldrich or Strem 1 T chemicals. CH3 CH2I was purchased form Cambridge Isotopes Inc. and was used as received. Complexes R-Ir-L, [R-Ir] 2 and cis R-Ir-L7 , 1 9 diethylmercury2 0 were prepared as described in the literature. To a mixture containing 100 mg (0.197 mmol) of Acac-Ir-I^O in 10 mL of CHCI3 1 mL (12.3 mmol) of Pyridine was added. The mixture was heated at 60°C for 1 minute to generate a homogenous solution and was filtered. Solvent was removed in vacuo to give quantitative yield of Complex Acac-Ir-Py (112mg, 100%). 'H NMR and 1 3C{'H} NMR (CDCI3 ) were consistent with that were o o Synthesis of Ir(0 ,0 -acac)2(C-acac)(Py) (Acac-Ir-Py). 200 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reported. Anal. Calcd: C, 42.24; H, 4.61; N, 2.46. Found: C, 41.95; H, 4.65; N, 2.74. Synthesis of Ir(0,0-acac)2 (Ph)(H2O) (Ph-Ir-H20 ). 100 mg (0.197 mmol) of Acac-Ir-H20 was added to a 6 mL mixture of CH3 OH and H20 (2:1) followed by 71 mg (0.2 mmol) of HgPh2 in lOmL of acetone. The mixture was stirred for 5 minutes. Complex Ph-Ir-H2 0 formed immediately as yellow crystalline in 70% yield (67 mg). ’H NMR (THF-d8 ): 5 6.65(m, 3H, Ph), 6.57(m, 2H, Ph), 5.21(s, 2H, CH), 1.77(s, 12H, CH3 ), '^ { 'H } NMR (THF-d8 ): 6 184.5(s, O-acac, C=0), 136.3(s, Ph), 125.3(s, Ph), 122.9(s, Ph), 103.0(s, 0-acac, CH), 26.6(s, O-acac, CH3 ). Anal. Calcd: C, 39.58; H, 4.36. Found: C, 39.88; H, acac)(OCOCH3 ) ] 2 [CH3 COO-Ir]2: To 100 mg (0.197 mmol) of Acac-Ir-H2 0 in 10 mL of CH3 OH, 1 mL (17.4 mmol) of acetic acid was added. The mixture was heated at 60 °C for couple of minutes to get a homogenous solution and was filtered. Solvent was removed in vacuo to give yellow coloured solid. Isolated 4.44. OCOCH3 0 C 0C H 3 Synthesis of [Ir(p-0,0,C 3-acac)(0,0- 201 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. yield: 170mg, >95%. ]H NMR (CDC13 ): 5 5.85(s, 2H, O-acac C3 H), 5.68(s, 2H, p- acac C3 H), 2.17(s, 12H, O-acac CH3 ), 2.08(s, 12H, p-acac CH3 ), 1.96(s, 6H, acetate CH3 ). 1 3 C{]H} NMR (CDC13 ): 8 217.7(p-acac C=0), 185.6(0-acac C=0), 180.2(acetate C=0), 102.9(O-acac C3 H), 41.1(p-acac C3 H), 29.9(p-acac CH3 ), 26.7(0-acac CH3), 23.6(acetate CH3 ). Anal. Calc: C, 32.0;H, 3.81. Found:C, 31.36; H, 3.76. FAB+ MS: m/z (%) 899.10 (15) [M+H]+, 839.50 (35) [M- OCOCH3]+, 779.47 (10) [M- 2(OCOCH3 )]+. OCOCF3 — Synthesis of [Ir(p-0,0,C 3 -acac)(0,0- acac)(OCOCF3 )]2: To 100 mg (0.197 mmol) of Acac-Ir-H20 in 10 mL of CH3OH, 1 mL (12.8 mmol) of trifluoroacetic acid was added. The mixture was heated at 60 °C for couple of minutes to get a homogenous solution and was filtered. Solvent was removed in vacuo to give quantitative yield (190mg, >95%). ]H NMR (CDC13 ): 5 6.00(s, 2H, O-acac C3 H), 5.73(s, 2H, p-acac C3 H), 2.19(s, 12H, O-acac CH3 ), 2.14(s, 12H, p-acac CH3 ). NMR (CDC13 ): 8 219.2(p- acac C=0), 186.6(0-acac C=0), 177.8(acetate C=0), 102.8(O-acac C3 H), 67.9(p- acac C3 H), 36.8(p-acac CH3 ), 26.5(0-acac CH3 ), 30.4(CF3). 202 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Synthesis of [(CH3-1 3 CH2 )Ir(0,0-acac)2]2 [CH3 1 3 CH2-Ir]2: [CH3 1 3CH2 -Ir] 2 was synthesized similarly from acac-C-Ir-H 2 0 (97 mg, 0.19 mmol) and 1 3 C enriched diethylmercury (630 mg, 0.24 mmol) . 7 The crude reaction mixture was developed on a preparatory silica TLC plate with THF: ether (1:1) as an eluent. After pumping off the solvent, the solid was redeveloped on a preparatory silica TLC plate using 1:1:2 THF: CH2 C12: hexanes. The orange band Rf = 0.87 was scraped off and extracted with CH2 C12 and THF. The solvent was pumped off to yield an orange powder (0.04 lOg, 51% yield). (For simplicity, CD3OD was chosen) ]H NMR (CD3 OD): 5 5.47 (s, 2H, acac-C3 H), 2.83 (dq, 'JC h = 128.5, 3 Jhh =7.7, - 1 3CH2 -Ir), 1.76 (s, 12H, acac-CH3 ), 0.198 (m, 3H, CH3 - 1 3CH2- Ir) 1 3 C {*H} few scans (CD3 OD): 8 -17.59 (s, - 1 3CH2 -Ir). Synthesis of [Ir(0,0-acac)2 (1 3CH2 CH3 )(Py)] (CH31 3 CH2 -Ir- Py): CH3 1 3CH2 -Ir-Py was synthesized from [CH3,3CH2 -Ir]2 (lOOmg, 0.119 mmol) in CHCI3 and pyridine (1 mL, 12.3 mmol) . 7 Isolated Yield: 115 mg, >95%. H NMR (C6 D6 ): 8 8.69 (d, 2H, o-Py), 6.84 (t, 1H, p-Py), 6.56 (t, 2H, m-Py), 5.10 203 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (s, 2H, acac-C3 H), 3.47 (dq, 2H, ‘Jch = 125.3, -1 3 CH2-Ir), 1.60 (s, 12H, acac-CH3), 1.23 (m, 3H, CH3-1 3 CH2-Ir). 1 3 C {’H} NMR (C6 D6 ): 5 182.69 (acac C=0), 149.57 (o-py), 136.32 (p-py), 124.38 (m-py), 102.76 (acac-CH), 26.66 (acac-CH3 ), 15.99 (d, ‘Jcc = 34, CH3), -10.56 (-1 3 CH2-Ir). Reaction Procedure for the Olefin Arylation: A 3 mL stainless steel autoclave, equipped with a glass insert and a magnetic stir bar was charged with 1 mL of dry, distilled benzene and 3-5 mg (5 mmol, -0.1 mol %) of catalyst (unless otherwise mentioned). The reactor was degassed with nitrogen, pressurized with 0.96 MPa of propylene and an additional 2.96 MPa of nitrogen. It was heated to 180 °C for 30 minutes. The liquid phase was sampled and the product yields were determined by GC-MS using methyl cyclohexane as an internal standard that was introduced into the reaction solution after the reaction. Insertion Reactions of Olefins with Ph-Ir-Py: A 3 mL stainless steel autoclave, equipped with a a glass insert and a magnetic stir bar was charged with distilled 1 ml of mesitylene and 15 mg of Ph-Ir-Py. The autoclave was heated at 180 °C for 10 min after adding olefin. The liquid phase was sampled and the product yields were determined by GC-MS using methyl cyclohexane as an internal standard, introduced into the reaction solution after the reaction. Following are the amount of olefin added in the above insertion reactions: 2 MPa 204 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of ethylene, 0.96 MPa of propylene with an extra 2 MPa of nitrogen, 0.25 mL of Styrene with 2 MPa of nitrogen and 0.25 mL of 1-hexene with 2 Mpa of nitrogen. Reaction Procedure for substrate Dependence (Olefin): A 10 mL glass schlenk flask fitted with a Teflon valve, equipped with a magnetic stir bar was charged with dry, distilled benzene (typically 1 mL) and 3-5 mg (5 mmol, -0.1 mol %) of catalyst from a stock solution. To it was added varied amount of styrene (typically 0.1 to lmL) and 20 pL of methylcyclohexane, added as internal standard. The valve was closed and was heated to 180 °C for 30 minutes. The liquid phase was sampled and the product yields were determined by GC-MS. Reaction Procedure for substrate Dependence (Benzene): A 10 mL glass schlenk flask fitted with a Teflon valve, equipped with a magnetic stir bar was charged with dry, distilled styrene (typically 0.6 mL) and 3-5 mg (5 mmol, ~0.1 mol %) of catalyst from a stock solution. To it were added benzene (0.1 to 1 mL) and cyclohexane (0.1 to 1 mL) and 20 pL of methylcyclohexane, added as internal standard. The valve was closed and was heated to 180 °C for 30 minutes. The liquid phase was sampled and the product yields were determined by GC-MS. 205 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 4.4. Crystal data and structure refinement for Cnf^IrOs (Ph-Ir- CH3 OH). Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions Volume Z Density (calculated) Absorption coefficient F(000) Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 28.00° Refinement method Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I>2sigma(I)] R indices (all data) Extinction coefficient Fargest diff. peak and hole C 17H 22 Ir 0 5 498.55 296(2) K 0.71073 A triclinic P-1 a = 9.0258(9) A c^66.070 b = 10.7983(11) A (3=69.305 c = 11.1929(11) A .y=75.076 924.43(16) A3 2 1.791 Mg/m3 7.242 mm-' 482 2.07 to 28.00°. -11 <=h<= 11,-14<=k<= 10, -14<=1<=8 5587 3853 [R(int) = 0.0196] 86.6 % Full-matrix least-squares on F2 3853 /0 /214 1.026 R1 = 0.0278, wR2 = 0.0650 R1 = 0.0306, wR2 = 0.0663 0.0000(3) 1.098 and -0.601 e.A’ 3 206 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 4.5. Atomic coordinates ( x 10^) and equivalent isotropic displacement parameters (A^x 10^) for C17H22ITO5 (Ph-Ir-CH3OH). U(eq) is defined as one third of the trace of the orthogonalized Uh tensor. X y z U(eq) Ir(l) 2110(1) 3419(1) 3764(1) 44(1) 0 (1 ) 2694(4) 1527(3) 4989(3) 53(1) 0 (2 ) -270(3) 3371(3) 4524(3) 50(1) 0 (3 ) 1514(4) 5362(3) 2633(3) 51(1) 0 (4 ) 4461(3) 3480(3) 3056(3) 49(1) 0 (5 ) 2068(5) 4207(4) 5347(4) 68(1) C (l) 2301(9) -623(6) 6656(7) 86(2) 0(2) 1653(6) 730(5) 5802(5) 57(1) 0(3) -7(7) 1048(5) 5971(5) 63(1) 0(4) -858(6) 2278(5) 5385(4) 52(1) 0(5) -2652(6) 2414(6) 5765(6) 71(1) 0(6) 1907(8) 7581(5) 1055(6) 69(2) 0(7) 2561(6) 6137(4) 1778(4) 49(1) 0(8) 4218(6) 5748(5) 1475(5) 57(1) 0(9) 5046(5) 4515(5) 2087(4) 49(1) 0(10) 6846(6) 4329(6) 1611(6) 66(1) 0(11) 2192(5) 2707(5) 2370(4) 49(1) 0(12) 3386(6) 1638(5) 2089(5) 60(1) 0(13) 3417(8) 1116(6) 1131(5) 75(2) 0(14) 2295(9) 1633(7) 416(6) 81(2) 0(15) 1135(8) 2674(7) 661(5) 76(2) 0(16) 1077(6) 3196(6) 1617(5) 61(1) 0(17) 2762(11) 3512(9) 6401(8) 114(3) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 4.6. Bond lengths [A] and angles [°] for CnffolrOs (Ph-Ir-CHsOH). Ir(l)-C (l 1) 1.972(5) Ir(l)-0(4) 1.994(3) Ir(l)-0(1) 2.004(3) Ir(l)-0(3) 2.010(3) Ir(l)-0(2) 2.017(3) Ir(l)-0(5) 2.241(3) 0(1)-C (2) 1.276(5) 0(2)-C (4) 1.282(5) 0(3)-C (7) 1.276(5) 0(4)-C (9) 1.272(5) 0(5)-C (17) 1.382(7) C (l)-C (2) 1.488(7) C(2)-C(3) 1.409(7) C(3)-C(4) 1.381(7) C(4)-C(5) 1.505(7) C(6)-C(7) 1.508(7) C(7)-C(8) 1.401(7) C(8)-C(9) 1.382(7) C(9)-C(10) 1.507(6) C (11 )-C(l 6) 1.402(7) C(11)-C(12) 1.417(7) C(12)-C(13) 1.389(7) C(13)-C(14) 1.377(9) C(14)-C(15) 1.370(9) C(15)-C(16) 1.378(8) C(1 l)-Ir(l)-0 (4 ) 90.94(15) C( 11 )-Ir( 1 )-0 ( 1) 90.94(16) 0 (4 )-Ir (l)-0 (l) 84.78(12) C (11 )-Ir( 1 )-0 (3 ) 92.91(16) 0 (4 )-Ir(l)-0 (3 ) 95.28(12) 208 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 2.4. Continued 0 (l)-Ir (l)-0 (3 ) 176.15(11) C( 11 )-Ir( 1 )-0 (2 ) 90.70(15) 0 (4 )-Ir(l)-0 (2 ) 178.35(11) 0 (l)-Ir (l)-0 (2 ) 95.02(13) 0 (3 )-Ir( 1 )-0 (2 ) 84.81(12) C(1 l)-Ir(l)-0 (5 ) 178.85(14) 0 (4 )-Ir(l)-0 (5 ) 88.07(13) 0 ( 1 )-Ir( 1 )-0 (5 ) 88.40(13) 0 (3 )-Ir(l)-0 (5 ) 87.75(13) 0(2 )-Ir(l)-0 (5 ) 90.29(13) C (2)-0(1)-Ir(l) 122.4(3) C (4)-0(2)-Ir(l) 121.8(3) C (7)-0(3)-Ir(l) 122.3(3) C (9)-0(4)-Ir(l) 121.4(3) C (17)-0(5)-Ir(l) 125.9(4) 0(1)-C (2)-C (3) 125.7(4) 0(1 )-C (2)-C (l) 114.9(5) C(3)-C(2)-C(l) 119.4(5) C(4)-C(3)-C(2) 128.4(4) 0(2)-C (4)-C (3) 126.2(4) 0(2)-C (4)-C (5) 114.2(4) C(3)-C(4)-C(5) 119.6(4) 0(3)-C (7)-C (8) 125.4(4) 0(3)-C (7)-C (6) 115.3(4) C(8)-C(7)-C(6) 119.3(4) C(9)-C(8)-C(7) 127.9(4) 0(4)-C (9)-C (8) 127.3(4) O(4)-C(9)-C(10) 113.9(4) C(8)-C(9)-C(10) 118.8(4) C(16)-C(l 1)-C(12) 115.8(5) C(16)-C(l l)-Ir(l) 123.0(4) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 4.6. Continued C(12)-C(l l)-Ir(l) 121.2(4) C(13)-C(12)-C(l 1) 121.1(5) C( 14)-C( 13 )-C( 12) 120.9(6) C(15)-C(14)-C(13) 119.2(5) C(14)-C(15)-C(16) 120.7(6) C(15)-C(16)-C(l 1) 122.3(5) Symmetry transformations used to generate equivalent atoms: Table 4.7. Anisotropic displacement parameters (A^x 1()3) for CnH^IrOs (Ph-Ir-CH3OH). The anisotropic displacement factor exponent takes the form: h^ a*2\J^ 1 + ... + 2 h k a* b* ljl2 ] U 1 1 U2 2 U 3 3 U2 3 U 1 3 U 1 2 Ir(l) 43(1) 39(1) 44(1) -13(1) -5(1) -7(1) 0 (1 ) 54(2) 42(2) 51(2) -9(1) -11(1) -7(1) 0 (2 ) 44(2) 49(2) 51(2) -18(1) -3(1) -9(1) 0 (3 ) 52(2) 40(2) 55(2) -12(1) -14(1) -4(1) 0 (4 ) 45(2) 43(2) 53(2) -14(1) -8(1) -10(1) 0 (5 ) 74(2) 72(2) 67(2) -38(2) -26(2) 9(2) C (l) 99(5) 49(3) 80(4) 4(3) -22(3) -10(3) 0(2) 71(3) 43(2) 49(2) -14(2) -10(2) -11(2) 0(3) 69(3) 56(3) 55(3) -14(2) -2(2) -25(2) 0(4) 51(2) 60(3) 49(2) -24(2) -2(2) -20(2) 0(5) 57(3) 78(4) 75(3) -27(3) -3(3) -24(3) 0(6) 90(4) 47(3) 69(3) -8(2) -37(3) -8(3) 0(7) 61(3) 40(2) 45(2) -15(2) -13(2) -9(2) 0(8) 68(3) 47(3) 51(3) -9(2) -13(2) -18(2) 0(9) 51(2) 50(2) 46(2) -20(2) -7(2) -14(2) 0(10) 52(3) 68(3) 72(3) -24(3) -1(2) -21(2) 210 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 4.7. Continued C(ll) 46(2) 48(2) 42(2) -13(2) 1(2) -13(2) C(12) 61(3) 57(3) 57(3) -23(2) -3(2) -9(2) C(13) 89(4) 67(3) 63(3) -35(3) 9(3) -22(3) C(14) 109(5) 91(5) 56(3) -38(3) -2(3) -45(4) C(15) 84(4) 92(4) 60(3) -21(3) -16(3) -42(3) C(16) 55(3) 66(3) 59(3) -17(2) -11(2) -21(2) C(17) 146(7) 108(6) 125(6) -64(5) -88(6) 34(5) Table 4.8. Hydrogen coordinates ( x 10^) and isotropic displacement parameters (A^x 10 3) for C n ^ I r O s (Ph-Ir-CH3OH). x y z U(eq) H(1A) 3106 -1073 6079 129 H(1B) 1453 -1175 7197 129 H(1C) 2762 -496 7244 129 H(3) -607 338 6553 75 H(5A) -3110 3165 6090 107 H(5B) -3010 1586 6468 107 H(5C) -2979 2578 4980 107 H(6A) 1109 7563 681 104 H(6B) 2758 8042 334 104 H(6C) 1437 8057 1691 104 H(8) 4837 6398 776 69 H(10A) 7259 4121 2362 99 H(10B) 7205 5156 906 99 H(10C) 7221 3592 1261 99 H(12) 4162 1280 2553 72 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 4.8. Continued H(13) 4205 408 970 90 H(14) 2324 1280 -225 97 H(15) 379 3033 177 91 H(16) 271 3897 1768 73 H(17A) 2116 2833 7099 172 H(17B) 2841 4145 6772 172 H(17C) 3810 3077 6064 172 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.5 References (1) Olah, George A. Friedel-Crafts and Related Reactions. Vol. I. General Aspects.; Vol. II. Alkylation and Related Reactions. Part 1.; Part 2.; 1964, 1031 pp.; 658 pp.; 703 pp. Interscience (Div. of Wiley), New York (2) (a) Jones, W. D. Acc. Chem. Res. 2003, 36, 140. (b) Shilov, A. E.; Shul’pin, G. B. Activation and Catalytic Reactions o f Saturated Hydrocarbons in the Presence o f Metal Complexes Kluwer Academic; Dordrecht, 2000. (c) Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2001, 19, 2437. (d) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507. (e) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem. Res. 2002, 35, 44. (f) Jones, W.D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91. (g) Amdtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H. Acc. Chem. Res. 1995, 28, 154. (h) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879. (i) Jones, W. D. Science, 2000, 287, 1942. (j) Crabtree, R. H. Chem. Rev. 1995, 95, 987. (k) Jones, W. D. Acc. Chem. Res. 2003, 36, 140. (1) Jones, W. D. Topics in Organometallic Chemistry, 1999, 3, 9. (m) Kakiuchi, F.; Murai, S. Topics in Organometallic Chemistry 1999, 3, 47. (3) Jia, C.; Kitamura, T.; Fujiwara, Y. Acc. Chem. Res. 2001, 34, 633. (4) Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. Rev., 2002,102, 1731. (5) (a) Murai, S.; Kakiuchi, F.; Sekine, S.; Tanaka, Y.; Kamatani, A.; Sonoda, M.; Chatani, N. Nature 1993, 366, 529. (b) Murai, S.; Chatani, N.; Kakiuchi, F. PureAppl. Chem. 1997, 69, 589. (6) (a) Matsumoto, T; Taube, D. J.; Periana, R. A.; Taube, H.; Yoshida. H. J. Am. Chem. Soc. 2000, 122, 7414. (b) Matsumoto, T.; Periana, R A.; Taube, D. J.; Yoshida, H. J. Mol. Catal. A. 2002, 180, 1. (c) Matsumoto, T.; Yoshida, H. Catal. Lett. 2001, 72, 107. (7) (a) Bhalla, G.; Liu, X. Y.; Oxgaard, J.; Goddard III, W. A.; Periana, R. A. J. Am. Chem. Soc. 2005, In Press, (b) Periana, R. A.; Liu, X. Y.; Bhalla, G. Chem. Commun. 2002, 3000. (8) (a) Oxgaard, J.; Muller, R. P.; Goddard III, W. A.; Periana, R. A. J. Am. Chem. Soc. 2004, 126, 352. (b) Oxgaard, J.; Periana, R. A.; Goddard, W. A. Ill, J. Am. Chem. Soc. 2004,126, 11658. (c) Oxgaard, J.; Goddard III, W. A. J. Am. Chem. Soc. 2004,126, 442. (9) (a) Lail, M.; Arrowood, B. N.; Gunnoe, T. B. J. Am. Chem. Soc. 2003, 125, 7506. (b) Lail, M.; Bell, C. M.; Conner, D.; Cundari, T. R.; Gunnoe,T. B.; Petersen, J. L. Organometallics, 2004, 23, 5007. 213 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (10) Liu, X. Y.; Tenn, III, W. J.; Bhalla, G.; Periana, R. A. Organometallics 2004, 23, 3584-3586. (11) (a) Bhalla, G.; Periana, R. A. Angew. Chem. Intl. Ed. 2005, 44, 1540. (b) Bhalla, G.; Oxgaard, J.; Goddard, III, W. A.; Periana, R. A. Organometallics 2005, 24, 3229. (12) Chemical reaction software “Outokumpu HSC Chemistry for windows” ver. 4, Finland. (13) (a) Karshtedt, D.; Bell, A. T.; Tilley, T. D. Organometallics 2004, 23, 4169. (b) Viciu, M. S.; Stevens, E. D.; Petersen, J. L.; Nolan, S. P. Organometallics 2004, 23, 3752. (c) Youn, S. W.; Pastine, S. J.; Sames, D. Org. Lett. 2004, 6, 581-584. (14) Wong-Foy, A. G.; Bhalla, G.; Liu, X. L.; Periana, R. A. J. Am. Chem. Soc. 2003,125, 14292. (15) Bhalla, G.; Oxgaard, J.; Goddard, III, W. A.; Periana, R. A. “Hydrovinylation of olefins catalyzed by an Iridium Complex via C-H Activation” (submitted). (16) (a) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications o f Organotransition Metal Chemistry', University Science Books: Mill Valley, CA, 1987. (b) McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem. Soc. 1976, 6521. (c) Burger, B. J.; Thompson, M. E. Cotter, W. D.; Bercaw, J. E. J. Am. Chem. Soc. 1990, 1566. (17) (a) Burger, P.; Bergman, R. G. J. Am. Chem. Soc. 1993, 10462. (b) Stoutland, P. O.; Bergman, R. G. J. Am. Chem. Soc. 1988, 5732. (18) Slugovc, C.; Padilla-Martinez, I.; Sirol, S.; Carmona, E. Coordn. Chem. Rev. 2001, 129. (19) Bennett, M. A.; Mitchell, T. R. B. Inorg. Chem. 1976, 15, 2936. (20) Gilman, H., and Brown, R. E., J. Am. Chem. Soc., 1929, 51, 928. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 Hydrovinylation of Olefins catalyzed by an Iridium Complex via C-H Activation 5.1 Introduction Carbon-carbon bond-forming reactions are among the most important types of bond constructions in organic chemistry. One potentially important class of such reactions that has been reviewed1 is the hydrovinylation of olefins catalyzed by [Ni -H] species that forms the basis of current commercial technologies. The generally accepted mechanism for hydrovinylation involves a Cossee-Arlman type migratory insertion of olefins into a cationic metal hydride intermediate that subsequently undergoes (3 -hydride elimination to yield product, Scheme 5.1.3 Other mechanisms involving metallacyclopentane intermediates have also been postulated.4 Mechanisms involving catalytic C-H activation to generate metal- vinyl intermediates followed by olefin insertion, Scheme 5.1, should also be possible. However, to our knowledge while complexes have been reported that show both stoichiometric olefin C-H activation5 and olefin insertion6 no efficient catalysts that operate by this mechanism have been reported. A likely reason is that many complexes that undergo C-H activation may be inhibited by high olefin concentrations. Herein, we report evidence for catalytic olefinic oligomerization via a C-H activation mechanism. 215 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cossee-Arlman Mechanism C-H Activation Pathway Scheme 5.1. C-H Activation and Cossee-Arlman Mechanisms for Olefin Oligomerization. 5.2 Results and Discussion In earlier chapters, O-ligated complex, (acac-0,0)2lr(III)(CH3 )(Py), (acac- 0 ,0 = K2-0,0-acetylacetonate, Py = pyridine), CH3 -Ir-Py, [where -Ir- is understood to be (acac-0,0)2lr(III) throughout this paper] was demonstrated to activate alkanes stoichiometrically and catalyses the isomerization and hydroarylation of olefins with arenes to generate alkyl benzenes.7 Herein the vinyl-Ir (III) derivative, Vinyl-Ir-Py, is shown to insert olefins and catalyse the oligomerization of olefins via a proposed C-H activation pathway. 216 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.2.1 Synthesis of Vinyl-lr(acac)2-Py Vinyl-Ir-Py was synthesized from Acac-Ir-HiO, by treatment with divinylmercury, (C2 H 3 )2 Hg, followed by addition of pyridine, in 60% yield as shown in Scheme 5.2. Vinyl-Ir-Py Scheme 5.2. Synthesis of Vinyl-Ir-Py Vinyl-Ir-Py was fully characterized by 'H, 1 3 C NMR spectroscopy, Q elemental analysis and single crystal X-Ray crystallography. An ORTEP projection is shown in Figure 5.1 Figure 5.1. ORTEP projection of Vinyl-Ir-Py. Thermal ellipsoids are at the 50% probability level. Hydrogen atoms omitted for clarity. Bond lengths (A): Ir-C: 1.97(3); Ir-N: 2.209(14). 217 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.2.2 Catalytic Hydrovinylation Vinyl-Ir-Py is catalytically active for olefin oligomerization. Thus, heating a 5 mM solution of Vinyl-Ir-Py in hexaflourobenzene with ethylene (2.96 MPa) at 180 °C for 1 h results in the catalytic formation of 1-butene, cis and trans 2-butene in 1:2:1 ratio (TN = 32, TOF ~ 10 x 10'3 sec'1 ). Similarly, carrying out the reaction with propylene results in the formation of various hexene isomers as observed by GC/MS analysis. A proposed mechanism for this catalytic hydrovinylation is postulated to proceed through two key steps, i.e. insertion of olefin into an Ir-vinyl bond to generate an Ir-alkyl and C-H activation of ethylene by the Ir-alkyl to regenerate the Ir-vinyl intermediate as shown in Scheme 5.1. To provide evidence for these steps, both the stoichiometric C-H activation of an olefin with an Ir-alkyl complex, CH 3-Ir-Py, to generate an Ir-vinyl complex and the insertion of olefins into an Ir-vinyl complex, Vinyl-Ir-Py, were examined. The stoichiometric C-H activation of olefins by an Ir-alkyl complex to generate an Ir-vinyl complex can be readily observed by the reaction of CH3-Ir-Py with ethylene (3.5 MPa) in cyclohexane solvent at 120 °C for 15 hr. This reaction is efficient and the Vinyl-Ir-Py complex can be isolated in -60% yield after reaction. To examine the olefin insertion step, the reaction of the vinyl complex, Vinyl-Ir- Py, with propylene was carried out in C6F6 as solvent at 180 °C for 3 h. Consistent with the expected olefin insertion, analysis of the reaction mixture showed that a stoichiometric amount of pentene isomers (based on added Vinyl- 218 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ir-Py) was formed. The pentene consisted of various isomers as expected based on the reported activity of these (acac-0,0)2lr(III) complexes to catalyze the isomerization of olefins via a cascade of reversible (3-hydride eliminations.9 V in y l-Ir-P y ^Ir Scheme 5.3. Proposed Mechanism for hydrovinylation using Vinyl-Ir-Py. 219 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.2.3 DFT Calculations for Hydrovinylation Preliminary theoretical calculation, Figure 5.2 (Solvent and ZPE corrected B3LYP/LACVP**) on this hydrovinylation reaction suggests a mechanism similar to that reported for olefin hydroarylation by the (acac-0,0)2lr(III) catalysts.1 0 Thus, pyridine exchange and trans to cis isomerization generates the cis-Vinyl-Ir- olefin complex A (7.8 kcal/mol), initiating the catalytic cycle. Insertion of the olefin into the vinyl group generates a metal-butenyl species B (-4.2 kcal/mol) with a coordinated terminal double bond. This insertion is found to be the rate- determining step with a calculated AHi=30.6 kcal/mol. A series of low-energy reversible [3-hydride eliminations (TS2 - TS4) eventually yield the allyl species E (-12.7 kcal/mol), which is significantly more stable than any of the preceding metal-butyl complexes. Addition of olefin to the allyl complex (G) and C-H activation via an OHM (oxidative hydrogen migration) mechanism (TS5) yields a cis or trans 2-butene (H), with a AH* of 16.8 kcal/mol with respect to Vinyl-Ir-Py and 31.6 kcal/mol with respect to G. 220 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30.6 TS1 3 0 .2 J + J 15.8 TS6 C is/Trans isom erization 8.1 TS7 75.5 16.1 13.0 13.2 TS2 -CH3 13.1 TS4 Ir— 12.8 7.8 TS3 \ .-14.1 -12.7 0.0 V inyl-lr-Py -12.7 -3 .3 -4.2 -22 0 Figure 5.2. Calculated AH surface for the hydrovinylation of alkenes (shown only for ethylene) catalyzed by Vinyl-Ir-Py through C-H activation (solid black line) and Cossee Arlman mechanism {dotted blue line). Structures shown without acac ligands for clarity. The Cossee-Arlman mechanism was found not to be competitive on the AH surface, either for initiation or propagation. The Cossee mechanism is expected to initiate in the same manner as the C-H activation, eventually yielding intermediate C. Instead of undergoing reverse P-hydride elimination, butadiene (J) would dissociate and leave an unsaturated metal hydride (I). Addition of ethylene (K), hydride insertion (TS6) and addition of a second ethylene would yield M, which can then undergo a second olefin insertion (TS7). The linear metal-butyl species N features an agostic interaction to the P-hydrogen, and facile P-hydride elimination (TS8) yields O, which then regenerates I by dissociation of product. The catalytic cycle would thus be I O I. 221 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The highest barrier to initiation (dissociation of butadiene from C, 30.2 kcal/mol) is significantly higher in energy than any of the transition states leading to C-H activation. While entropy effects favor the dissociative Cossee-Arlman mechanism, and would thus be more competitive at higher temperatures, it is not believed to be worth more than the 17.1 kcal/mol difference between (I + J ) and TS3/TS4. Furthermore, once the C-H activation pathway reaches intermediate E, the reaction can be considered irreversible. Another possible mechanism involving reductive coupling, as shown by Morokuma and co-workers,1 1 was investigated theoretically but no stable Irv intermediate could be isolated. In summary, olefin oligomerizations are typically proposed to proceed via a Cossee-Arlman type migratory mechanism involving relative electron rich metal- hydrides. We provide experimental evidence and theoretical calculations that show, in contrast, relatively electron-poor O-donor Ir complexes can catalyze the oligomerization of olefins via a mechanism that involves olefin activation via C-H bond activation and insertion via a metal-vinyl intermediate. 5.3 Experim ental Section General Considerations: All air and water sensitive procedures were carried out either in an inert atmosphere glove box or using standard Schlenk techniques. All solvents used were reagent grade. THF was dried over 222 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sodium/benzophenone ketyl and distilled under nitrogen. All deuterated solvents (Cambridge Isotopes), Hg(vinyl) 2 (Organometallics, Inc.) and IrC^.xtkO (Pressure chemicals) were used as received. GC/MS analysis was performed on a Shimadzu GC-MS QP5000 (ver. 2) equipped with cross-linked methyl silicone gum capillary column (DB5). The retention times of the products were confirmed by comparison to authentic samples. NMR spectra were obtained on a Bruker AC- 250 spectrometer {250.13 MHz ('H) and 62.90 MHz (1 3 C)}, Bruker AM-360 spectrometer {360.14 MHz (*H) and 90.57 MHz (1 3 C)} or on a Varian Mercury 400 {400.151 MHz (!H) and 100.631 MHz (1 3 C)} spectrometer. All coupling constants are reported in units of Hz. Elemental analyses were done by Desert Analytics Laboratory; Arizona. Acac-Ir-H20 and CH3 -Ir-Py was synthesized as reported earlier. P y): To a mixture containing 100 mg (0.197 mmol) of Acac-Ir-H2 0 in 10 mL of methanol, 100 pL (-0.40 mmol) of divinylmercury, [Hg(CH=CH2 )2 ] was added. { [Hg(CH=CH2) 2] is a stench, handle with care!} The mixture was stirred at room temperature for 2 h under Argon. During this the formation of elemental mercury was observed and the color of the solution changed from orange to yellow. To this Synthesis of [CH2 =CH -Ir(0,0-acac)2 (Py)] (Vinyl-Ir- 223 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 |o.L (1.26 mmol) of pyridine was added and stirred for 10 minutes. The solution was vacuum transferred and the distillate was disposed off after treatment with concentrated nitric acid. The resulting yellow precipitate was then redissolved in methanol and cooled slowly with dry ice/acetone mixture, whereby yellow needles were formed. The solution was decanted and the solid was thoroughly washed with hexanes, followed by ether. The x-ray quality crystals were formed by the diffusion of hexanes into a concentrated solution of CH2 CI2 and obtained in 40% (40 mg) yield. ]H NMR (CDC13 ): 8 8.42 (d, 3 J = 5.3, 2H, o-/fpy), 8.20 (dd, 3 Ja b = 9 .7 ,3 Ja c =17.7, 1H, CHa-Ir), 7.80 (tt, 3 J = 8.0, 4J = 1.8, 1H, p-i/py), 7.36 (m, 2H, m-H py), 5.28 (s, 2H, acac-CH), 5.22(dd, 3 Jab = 9.7, 3 Jb c =2.7, 1H, Hb), 4.74(dd, 3 Ja c = 17.7,3 Jb c =2.7, 1H, Hc ), 1.83 (s, 12H, acac-CH3 ). (CDC13): 8 184.56 (acac C=0), 149.95(o-Py), 137.51 (p-Py), 127.13(Ir-CH=CH2 ), 125.10 (m-Py), 118.63(Ir-CH=CH2), 102.92 (acac-C3 H), 27.22 (acac-CH3 ). Anal. Calcd for Ci7H2 2N04Ir: C, 41.12; H, 4.47; N, 2.82. Found: C, 41.38; H, 4.95; N, 2.70. Catalytic hydrovinylation with Ethylene using CH3-Ir-Py or Vinyl-Ir- Py: A 3 mL stainless steel autoclave, equipped with a glass insert and a magnetic stir bar was charged with 1 mL of distilled hexaflourobenzene and 10 mg (5 mM, -0.1 mol %) of catalyst (CH3-Ir-Py or Vinyl-Ir-Py). The reactor was degassed with argon, pressurized with 2.96 MPa of ethylene. The autoclave was heated for 1 h in a well-stirred heating bath maintained at 180 °C. The liquid phase was sampled and the product yields were determined by GC-MS using methyl 224 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cyclohexane as an internal standard, introduced into the reaction solution after the reaction. Catalytic hydrovinylation with Propylene using CH3 -Ir-Py or Vinyl-Ir- Py: A 3 mL stainless steel autoclave, equipped with a glass insert and a magnetic stir bar was charged with 1 mL of distilled hexaflourobenzene and 10 mg (5 mM, -0.1 mol %) of catalyst (CH3-Ir-Py or Vinyl-Ir-Py). The reactor was degassed with argon, pressurized with 0.96 MPa of propylene with an additional 2.96 MPa of argon. The autoclave was heated for 3 h in a well stirred heating bath maintained at 180 °C. The liquid phase was sampled and the product yields were determined by GC-MS using methyl cyclohexane as an internal standard, introduced into the reaction solution after the reaction. Stoichiometric reaction of Ethylene with CH3 -Ir-Py: A solution of CH3- Ir-Py in C6 D 1 2 (5 mM) was made with trimethoxybenzene (internal standard) and transferred to an oven-dried high pressure NMR tube fitted with a valve. Ethylene (4 MPa) was added to this NMR tube at room temperature and subjected to NMR studies. The formation of the vinyl-Ir-Py (verified by independent synthetic route) was standardized at different temperatures and was finally heated for 15 h at 150 °C. 225 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. X-ray Crystallography. Diffraction data for Vinyl-Ir-Py was collected at low temperature (T= 143K) on a Bruker SMART APEX CCD diffractometer with graphite-monochromated Mo K a radiation (X= 0.71073 A). The cell parameters for the Ir complex were obtained from the least-squares refinement of the spots (from 60 collected frames) using the SMART program. A hemisphere of the crystal data was collected up to a resolution of 0.75 A, and the intensity data was processed using the Saint Plus program. All calculations for structure determination were carried out using the SHELXTL package (version 5.1). Initial atomic positions were located by direct methods using XS, and the structure was refined by least-squares methods using SHELX with 3503 independent reflections and within the range of 02.71-26.36° (completeness 100 %). Absorption corrections were applied by using SADABS. Calculated hydrogen positions were input and refined in a riding manner along with the attached carbons. 226 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 5.1. Crystal data and structure refinement for C1 7 H2 2lrN04. (Vinyl-Ir- P y) Identification code Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 26.36° Transmission factors Refinement method Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I>2sigma(I)] R indices (all data) Largest diff. peak and hole irvinylm C17 H22 Ir N 04 496.56 143(2) K 0.71073 A Trigonal P3(2) a = 8.2247(8) A a= 90°. b = 8.2247(8) A p= 90°. c = 22.586(4) A y= 120°. 1323.2(3) A3 3 1.869 Mg/m3 7.586 mm'1 720 0.23 x 0.16 x 0.02 mm3 2.71 to 26.36°. -7<=h<=10, -10<=k<=8, -28<=1<=26 7624 3503 [R(int) = 0.0571] 100.0 % min/max ratio: 0.521 Full-matrix least-squares on F2 3503 /20/ 103 1.146 R1 =0.0668, wR2 = 0.1611 R1 =0.0713, wR2 = 0.1629 2.610 and -6.542 e.A'3 227 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 5.2. Atomic coordinates ( x 10^) and equivalent isotropic displacement parameters (A^x 10^) for C nt^IrN CU (Vinyl-Ir-Py). U(eq) is defined as one third of the trace of the orthogonalized UU tensor. X y z U(eq) Ir(l) 6440(1) 10206(1) 5006(3) 29(1) 0(1) 4510(30) 10070(20) 5570(7) 30(4) 0(2) 6430(40) 12220(30) 4468(10) 51(7) 0(3) 6460(20) 8230(20) 5510(7) 26(4) 0(4) 8350(30) 10330(30) 4407(9) 49(6) N(l) 4230(20) 8080(20) 4429(5) 33(6) C(l) 2550(40) 11050(40) 6005(12) 56(7) 0(2) 3860(30) 11200(30) 5525(10) 49(6) 0(3) 3980(30) 12390(30) 5046(8) 41(5) 0(4) 5340(30) 12870(30) 4583(10) 42(5) 0(5) 5490(40) 14260(30) 4124(11) 51(6) 0(6) 7620(40) 6340(30) 5894(11) 51(6) 0(7) 7630(30) 7700(30) 5442(9) 32(5) 0 ( 8 ) 8940(30) 8270(30) 4988(8) 48(6) 0(9) 9200(30) 9430(30) 4512(9) 35(5) 0(10) 10560(30) 9710(40) 4018(11) 52(6) 0(11) 2620(20) 6640(30) 4654(5) 45(5) 0(12) 1270(30) 5390(30) 4285(6) 52(6) 0(13) 1500(30) 5620(30) 3691(6) 57(6) 0(14) 3100(20) 7070(30) 3463(5) 50(6) 0(15) 4450(20) 8310(20) 3834(5) 40(5) 0(16) 8400(40) 12110(40) 5521(11) 34(7) 0(17) 8640(40) 12360(40) 6093(13) 63(7) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 5.3. Bond lengths [A] and angles [°] for CntfolrNC^ (Vinyl-Ir-Py). Ir(l)-C(16) 1.97(3) Ir(l)-0(3) 1.988(16) Ir(l)-0(1) 1.994(18) Ir(l)-0(4) 2.04(2) Ir(l)-0(2) 2.06(2) Ir(l)-N(l) 2.209(14) 0(1)-C(2) 1.29(3) 0(2)-C(4) 1.28(3) 0(3)-C(7) 1.26(2) 0(4)-C(9) 1.27(2) N(l)-C(15) 1.356(13) N (l)-C(ll) 1.358(13) C(l)-C(2) 1.49(2) C(2)-C(3) 1.43(2) C(3)-C(4) 1.43(2) C(4)-C(5) 1.50(2) C(6)-C(7) 1.51(2) C(7)-C(8) 1.39(2) C(8)-C(9) 1.38(2) C(9)-C(10) 1.51(2) C(ll)-C(12) 1.357(13) C(12)-C(13) 1.355(13) C(13)-C(14) 1.360(13) C(14)-C(15) 1.358(13) C(16)-C(17) 1.31(4) C(16)-Ir(l)-0(3) 88.4(9) C( 16)-Ir( 1 )-0( 1) 88.9(9) 0(3)-Ir(l)-0(l) 85.3(6) C(16)-Ir(l)-0(4) 92.7(11) 0(3)-Ir(l)-0(4) 95.8(8) 229 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 5.3. Continued 0(l)-Ir(l)-0(4) 178.1(9) C(16)-Ir(l)-0(2) 92.3(12) 0(3)-Ir(l)-0(2) 178.8(9) 0(l)-Ir(l)-0(2) 95.7(8) 0(4)-Ir(l)-0(2) 83.2(8) C(16)-Ir(l)-N(l) 179.6(13) 0(3)-Ir(l)-N(l) 91.8(8) 0(1)-Ir(l)-N(l) 90.9(7) 0(4)-Ir(l)-N(l) 87.5(7) 0(2)-Ir(l)-N(l) 87.4(8) C(2)-0(1)-Ir(l) 121.0(14) C(4)-0(2)-Ir(l) 120.1(18) C(7)-0(3)-Ir(l) 122.4(14) C(9)-0(4)-Ir(l) 118.9(16) C(15)-N(l)-C(ll) 119.8(6) C(15)-N(l)-Ir(l) 118.3(8) C(11)-N(l)-Ir(l) 121.7(8) 0(1)-C(2)-C(3) 130(2) 0(1)-C(2)-C(1) 115(2) C(3)-C(2)-C(l) 114(2) C(2)-C(3)-C(4) 122(2) 0(2)-C(4)-C(3) 130(2) 0(2)-C(4)-C(5) 112(2) C(3)-C(4)-C(5) 118(2) 0(3)-C(7)-C(8) 125.1(18) 0(3)-C(7)-C(6) 117.1(19) C(8)-C(7)-C(6) 117.8(19) C(9)-C(8)-C(7) 129(2) 0(4)-C(9)-C(8) 127(2) O(4)-C(9)-C(10) 111(2) C(8)-C(9)-C(10) 122(2) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 5.3. Continued C(12)-C(l l)-N(l) 120.1(6) C(13)-C(12)-C(ll) 120.0(6) C(12)-C(13)-C(14) 120.1(5) C(15)-C(14)-C(13) 119.7(6) N(l)-C(15)-C(14) 120.2(6) C(17)-C(16)-Ir(l) 135(2) Symmetry transformations used to generate equivalent atoms: Table 5.4. Anisotropic displacement parameters (A^x 10^) for C nf^IrN C ^ (V inyl-Ir-Py). The anisotropic displacement factor exponent takes the form: -2n^[ h^ a*2ul 1 + ... + 2 h k a* b* U l2 ] U1 1 u2 2 U3 3 U2 3 U1 3 u1 2 Ir(l) 26(1) 31(1) 33(1) 1(1) 0(1) 17(1) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 5.5. Hydrogen coordinates ( x 10^) and isotropic displacement parameters (A^x 10 3) for irvinylm. x y z U(eq) H(1A) 1484 9763 6020 85 H(1B) 2089 11922 5926 85 H(1C) 3212 11364 6385 85 H(3) 3148 12869 5033 49 H(5A) 6794 15288 4101 77 H(5B) 4671 14753 4232 77 H(5C) 5110 13631 3738 77 H(6A) 7965 6955 6283 77 H(6B) 8531 5961 5778 77 H(6C) 6365 5235 5915 77 H(8) 9771 7784 5007 57 H(10A) 9920 8748 3714 78 H(10B) 11619 9616 4178 78 H(10C) 11030 10958 3842 78 H(ll) 2446 6503 5070 54 H(12) 171 4356 4443 63 H(13) 537 4770 3433 69 H(14) 3274 7212 3047 60 H(15) 5555 9346 3676 47 H(16) 9410 13072 5302 41 H(17A) 7723 11479 6357 76 H(17B) 9738 13414 6245 76 232 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.4 References (1) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100, 1169. (b) RajanBabu, T. V. Chem. Rev. 2003,103, 2845. (c) Pillai, S. M.; Ravindranathan, M.; Sivaram, S. Chem. Rev. 1986, 86, 353. (2) (a) Wilke, G.; Bogdanovic, B.; Hardt, P.; Heimbach, P.; Keim, W.; Kroner, M.; Oberkirch, W.; Tanaka, K.; Steinrucke, E.; Walter, D.; Zimmermann, H. Angew. Chem., Int. Ed. Engl. 1966, 5, 151. (b) Chauvin, Y., Olivier, H. In Applied Homogeneous Catalysis with Organometallic Compound; Comils, B., Herrmann, W. A., Eds.; VCH: New York, 1996; Vol. 1, p 258. (c) Keim, W. Angew. Chem., Int. Ed. Engl. 1990, 29, 235. (3) (a) Peuckert, M.; Keim, W.; Storp, S.; Weber, R. S.; J. Mol. Catal. 1983, 20, 115. (b) Muller, U.; Keim, W.; Kruger, C.; Betz, P.; Angew. Chem. Intl. Ed. Engl. 1989, 28, 1011. (c) Hauptman, E.; Sabo-Etienne, S.; White, P. S.; Brookhart, M.; Gamer, M. J.; Fagan, P. J.; Calabrese, J. C. J. Am. Chem. Soc. 1994,116, 8038. (4) (a) McLain, S. J.; Schrock, R. R.; J. Am. Chem. Soc. 1978,100, 1315. (b) Grubbs, R. H.; Miyashita, A. J. Am. Chem. Soc., 1978, 100, 1300. (c) Briggs, J. R., J. Chem. Soc. Chem. Commun. 1989, 674. (5) (a) Stoutland, P. O.; Bergman, R. G. J. Am. Chem. Soc., 1988, 110, 5732. (b) Baker, M. V.; Field, L. D. J. Am. Chem. Soc., 1986,108, 7433. (6 ) (a) Perez, P. J.; Poveda, M. L.; Carmona, E. J. Chem. Soc., Chem. Commun., 1992, 8 . (b) Alvarado, Y.; Boutry, O.; Gutierrez, E.; Monge, A.; Nicasio, M. C.; Poveda, M. L.; Perez, P. J.; Ruiz, C.; Bianchini, C.; Carmona, E. Chem. Eur. J. 1997, 3, 860. (7) (a) Wong-Foy, A. G.; Bhalla, G.; Liu, X. Y.; Periana, R. A. J. Am. Chem. Soc. 2003, 125, 14292. (b) Periana, R. A.; Liu, X. Y.; Bhalla, G. Chem. Commun. 2002, 3000. (c) Matsumoto, T.; Periana, R. A.; Taube, D. J.; Yoshida, H. J. Mol. Cat. A-Chemical 2002, 180, 1. (d) Matsumoto, T.; Periana, R. A.; Taube, D. J.; Yoshida, H. J. Catal. 2002, 206, 272. (e) Matsumoto, T.; Yoshida, H. Catal.Lett. 2001, 72, 107. (f) Matsumoto, T.; Taube, D. J.; Periana, R. A.; Taube, H.; Yoshida, H. J. Am. Chem. Soc. 2000,122, 7414. (8 ) Crystal data for C17H22IrN04: A7,=496.56, trigonal, space group P3(2), a= 8.2247(8), b= 8.2247(8), c= 22.586(4)A, a= 90, 90, y=120°, V= 1323.2(3) A3, F(0 0 0 )= 720, pcaic d (Z=3) =1.869 mgm'3, g= 7.586 m m '1 , approximate crystal dimensions 0.23 x 0.16 x 0.02 mm3, 6 range= 2.71 to 26.36°, MoKa (2=0.71073 A), T=143 K, 7624 measured data (Bruker 3- circle, SMART APEX CCD with x axis fixed at 54.74°, using the SMART V 5.625 program, Bruker AXS: Madison, WI, 2001), of which 233 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3503 (Rint= 0.0571) unique. Lorentz and polarization correction (SAINT V 6.22 program, Bruker AXS: Madison, WI, 2001), absorption correction (SADABS program, Bruker AXS: Madison, WI, 2001). Structure solution by direct methods (SHELXTL 5.10, Bruker AXS: Madison, WI, 2000), full-matrix least-squares refinement on F , data to parameters ratio: 34.0:1, final R indices [I>2a(I)] : R l= 0.0668, wR2= 0.1611, R l= 0.0713, wR2= 0.1629 (all data), GOF on F2 = 1.146. CCDC 269600 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (+44)1223-336-033; ordeposit@ccdc.cam.ac.uk). (9) Bhalla, G.; Liu X. Y.; Wong-Foy, A. G.; Jones, C.; Periana, R. A. in ACS Symposium Series, Activation and Functionalization o f C-H bonds, 2004, 885, 105-115. (10) (a) Oxgaard, J.; Periana, R. A.; Goddard, W.A. Ill J. Am. Chem. Soc. 2004,126, 11658. (b) Oxgaard, J.; Muller, R. P.; Periana, R. A.; Goddard, W. A. Ill J. Am. Chem. Soc. 2004,126, 352. (11) V. P. Ananikov, D. G. Musaev, K. Morokuma J. Am. Chem. Soc. 2002, 124, 2839. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 Alkane and Arene C-H Activation Catalyzed by an O-Donor, bis-tropolonato Iridium (III) complex. 6.1 Introduction As mentioned in earlier chapters, catalysts based on the C-H activation reaction show potential for the development of new, selective, hydrocarbon oxidation chemistry. 1 One of the key challenges in this field is developing C-H activation based catalysts that yield useful functionalized products such as alcohols. 1 8 We have been interested in O-ligated, late transition metal complexes as a basis for developing new hydrocarbon oxidation catalysts based on the C-H activation reaction. While O-donor ligands have been utilized with early and late transition metals, 2 to our knowledge the only well-defined, O-ligated, late transition metal complexes that activate alkane and arene C-H bonds have been reported recently by our group.3 , 4’ 5 Compared to the N, C or P-donor ligands generally utilized for homogeneous catalysts, 6 O-donor ligated complexes may have the potential for higher thermal, protic and oxidant stability as well as significant differences in chemistry given the lower basicity and higher electronegativity of O. Another key reason for study of this class of complexes is that the electronegativity and “hardness” of O-donor ligands could allow access to higher oxidation states during catalysis that may be required to generate functionalized products in a catalytic cycle. 1 8 The use of ligands with 235 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. electronegative O-donor atoms to facilitate C-H activation reactions, especially those that proceed via transition state or intermediates with “oxidative addition” character, may seem counter to the common guiding principle that such reactions require “electron rich” metals. 7 However, since the “oxidative addition” reaction could be viewed as a concerted, “insertion” reaction a full orbital analysis would be required to fully reconcile trends for this reaction. 8 It has been shown that O- donors are good 7t-donors to late transition metals. 9 Consequently, as the d- orbitals of t2 g symmetry of late transition metal octahedral complexes (e.g. Ir(III)) are typically occupied, we anticipate that C-H activation reactions with d6, late transition metal (Mn ) octahedral, O-donor complexes that take place via “oxidative addition” or insertion pathways could benefit from: A) possible ground state destabilization from O-ptt to Mn-d7t, filled-filled repulsions or so-called “pi- conflict” 1 0 and B) stabilization as back-bonding, from the filled 0 -p7t to empty d7t orbitals on the metal center (now formally Mn+ 2, d4), becomes possible as C-H “insertion” or “oxidative addition” proceeds with the generation of seven coordinate transition states or intermediates. Earlier, it was demonstrated that the bis bidentate O-donor complex, (acac- 0 ,0 )2 lr(CH3 )Py), (acac-0,0 = r)2 -0,0-acetylacetonate, Py = pyridine), catalyzes the C-H activation of alkanes3 and functionalization of arenes via the intermolecular, anti-Markovnikov, hydroarylation of olefins to selectively generate n-alkyl benzenes 4 Experimental and theoretical5 calculations reveal that this O- donor, octahedral, d6, late transition metal complex is thermally stable to air and 236 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. protic media and activates the C-H bonds of alkanes and arenes by a transition state with “oxidative addition” or “insertion” character. As discussed above, this could be facilitated by the rr-donor properties of the O-donor ligands. This demonstrated combination of stability and C-H bond reactivity is very attractive for developing oxidation catalysts based on the C-H activation reaction and it is important to determine if this chemistry can be extended to other O-donor ligands such as aryloxides, 11 tropolones, 12 catechols, 13 hydroxyacetophenones,1 3 c etc. O- donor ligands are among the largest class of known ligands and complexes with late transition metals could lead to a broad, new class of stable, homogeneous complexes with a unique reactivity. Acac-0,0 Trop-0,0 Figure 6.1. Comparison of A cac-0,0 and T rop-0,0 Ligands The O-donor ligand, trop-0,0 (trop-0,0 = k -0,0-tropolonato) has often been speculated to be an analogue of the acac-0 , 0 ligand as they share many common features, Figure 6.1. Both ligands are bidentate, mono-anionic and bond though delocalized chelate rings formed through two oxygen atoms. Importantly, however, on the basis of the smaller “bite angle” 1 4 as well as increased 237 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. delocalization over the larger tropolonato aromatic system, significant differences in reactivity could be anticipated. Thus, for example, trop-0,0 complexes may more readily accommodate an increase in the coordination number at the metal 12 center or potentially, due to changes in the extent of ^-donation resulting from the differences in bite angle, change the reactivity of the metal center. Rate changes related to differences in ligand bite-angle have been reported.1 4 a ’ 1 5 Herein, we report the synthesis and chemistry of the bis-bidentate, O-donor, tropolonato Iridium complex, CH 3 -IrT -Py, [trop-0 ,0 )2 lr(CH 3 )(Py)], (Py = pyridine). Importantly, we find that this O-donor complex is more active for C-H activation of alkanes and arenes than the analogous bis-acac-0 , 0 iridium complex. 6.2 Results 6.2.1 Synthesis of CH3-lr(lll)(trop-0,0)2 (Py) To obtain the bis trop-0,0 complex of Iridium, the original synthesis of the tris complex, (trop-0 ,0 )3 lr, was reinvestigated in anticipation that the bis trop-0 , 0 complex could be isolated as an intermediate in this synthesis. 1 6 As reported by Griffith et. al., heating RCI3 with excess of tropolone and sodium acetate in water resulted in the formation of (trop-0,0)3Ir in 40% yield (Scheme 6.1). However, in addition to this material a red-black solid, 1 , was also isolated that was insoluble in dichloromethane. Attempts to purify 1 or obtain reproducible analytical data for 238 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. this material have been unsuccessful and we presume that the material is 17 polymeric. The solid, 1, is soluble in coordinating solvents such as THF, CH3CN, DMSO and Pyridine, but NMR spectroscopy suggests that multiple species are present. Attempted separation by chromatography was also 1 8 unsuccessful. However, addition of (CHs^Zn to a solution of 1 in THF followed by addition of pyridine, resulted in a black organometallic complex, (trop- 0 ,0 )2 lr(CH3 )(Py), CH 3 -IrT-Py, that could be obtained in 10% overall yield after column chromatography (Scheme 6.1). This material has been fully characterized by 'H, l3C NMR spectroscopy, elemental analysis and single crystal x-ray diffraction. 1 9 An ORTEP drawing of CH 3 -IrT -Py is shown in Figure 6.2. Similarly, CH 3 CH 2 -Ir -Py was synthesized using diethylzinc reagent. O OH + 6 NaOAc CH N . 2-Me Scheme 6.1. Synthesis of CH 3 -Ir -Py. 239 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. From 'H NMR spectroscopy, the methyl bound to the Iridium center in CH3 -Ir -Py (2.08ppm, Ir-CH3 ) is downfield compared to the acac-0,0 analogue, (acac-0 ,0 )2 lr(CH 3 )(Py),2° (1.65ppm, Ir-CH3 ) suggesting possible significant electronic differences at the metal centers. A similar trend is also observed in the 1 3 C NMR spectrum with the chemical shift of the Ir-CH3 at -23.3ppm for CH 3 -IrT - Py compared to -27.1ppm for the acac-0,0 analogue. However, the most significant difference between the two complexes can be seen in the crystal structures of these complexes. As anticipated, the bite angle, O l-Ir-02, in CH 3 - IrT -Py, 78.4(3)°, is much smaller than that in the acac-0,0 analogue, 95.17(16)°. The Ir-N bond length (2.180(8) A) is comparable to that in the analogous acac complex (2.181(4) A). C 20 C9 03 Figure 6.2. ORTEP drawing of CH3 -IrT -Py. Thermal ellipsoids are at the 50% probability level. Hydrogen atoms omitted for clarity. Selected bond lengths (A°): Irl- C20: 2.046(10); Irl-N l, 2.180(8). Selected bond angle (°): O l-Irl-0 2 : 78.4(3). 240 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.2.2 Stoichiometric C-H Activation of Alkanes and Arenes To investigate the stoichiometric C-H activation chemistry of this new O- donor complex, we examined the reaction of the complex in various hydrocarbon solvents. Thus, heating CH3 -IrT -Py in neat mesitylene at 130°C for 1 hr cleanly yielded the corresponding bis trop-0,0 iridium mesityl complex, Mes-Ir -Py and methane as shown in Scheme 6.2. 'H-NMR analysis of the crude reaction mixture, after solvent removal and dissolution in CDCI3 showed that, as in the case of the acac-0 , 0 analogue, 3 the reaction was essentially quantitative and only the benzylic C-H bond of mesitylene was activated. Other hydrocarbon substrates that react by C-H activation with CH3 -IrT -Py are shown in Scheme 6.2. Thus, heating a solution of CH 3 -IrT -Py in benzene or acetone at 120 °C for 1 h results in the formation of the corresponding hydrocarbyl iridium derivatives, Ph-Ir -Py and Ace-IrT -Py, respectively, in almost quantitative yield. Similarly, heating CH3- IrT -Py in cyclohexane resulted in the corresponding cyclohexyl iridium complex, Cy-IrT -Py, which could be purified by flash chromatography and isolated in 35% yield. All these hydrocarbyl iridium derivatives, R-IrT -Py (R = Cy, Mes, Ph and Ace) were fully characterized by 'H, 1 3 C NMR spectroscopy and elemental analysis. Importantly, as was the case for the acac-0,0 analogues, these hydrocarbyl O-donor iridium derivatives are all air, water and thermally stable. Significantly, the stoichiometric C-H activation reactions of CH3 -IrT -Py are faster 241 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. than those of the acac-0,0 analogue. Thus, the X\a for reaction of CH3 -IrT -Py with benzene at 120°C is <5 min versus ~50 min for the acac-0,0 analogue. Scheme 6.2. Stoichiometric C-H Activation Reactions of CH 3- IrT Py with RH to Generate R-IrT -Py. 6.2.3 Catalytic C-H Activation and Comparison with bis Acac complex Having established that CH3 -IrT -Py can stoichiometrically activate the C- H bonds of alkanes and arenes, we examined the catalytic C-H activation of this new complex as a first step toward attempting to develop new, stable, hydrocarbon oxidation catalysts. The relative rates of the H/D exchange reaction with a CeHe/toluene-dg mixture (1:1 v/v) , 2 1 catalyzed at 120 °C by CH3 -IrT -Py (0.1 mol %) and the acac-0,0 analogue were used to compare these complexes. As can be seen in Figure 4, the trop-0,0 complex, CH3 -IrT -Py, is at least 50 times faster than the acac-0,0 analogue. Critically, both complexes are stable over the time 242 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. period studied (~5 hr, tum-over-number (TON) = -140 and TOF = 80 x 10'4 s’1 for CH3 -IrT -Py and TON = ~2 and TOF = 1 x 10~4 s’1 for the acac-0,0 analogue). This is an important result as it shows that: A) the C-H activation chemistry as well as the thermal stability to air and protic media of O-donor, late transition metal complexes are not unique to the acac-0,0 complex and B) that the chemistry of O-donor, late-transition metal complexes can be significantly changed by ligand modification. This observation of ligand dependent reactivity is an important requirement for this class of O-donor ligand-metal complexes to be most useful. This raises the expectation that further investigation of O-donor complexes of late transition metal complexes could lead to a broad, new class of homogeneous complexes with desirable stability, reactivity and ligand control properties. 243 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cat C6H6 + Tol-dg , C6H5D + Tol-d7 1 8 0 .0 150.0 - TOF = 80 x HH s" 1 120.0 Z I- 90.0 - 60.0 - 30.0 - TOF = 1 x 10"4 i 1 0 50 100 150 200 250 300 350 Time (min) Figure 6.3. Comparison of Catalytic C-H Activation o f Trop- 0 ,0 and A cac-0,0 Complexes. In conclusion, we have demonstrated a new, stable, O-donor, late-transition metal complex that activates the C-H bonds of alkanes and arenes more rapidly than does the only previously reported O-donor metal complex. 6.3 Experim ental Section General Considerations: All air and water sensitive procedures were carried out either in a Vacuum Atmospheres inert atmosphere glove box or using standard Schlenk techniques. All solvents used were reagent grade or better. THF and benzene were dried over sodium/benzophenone ketyl and distilled under nitrogen. All deuterated solvents (Cambridge Isotopes), ZnMe2 (2.0 M solution in 244 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. toluene) (Aldrich), Tropolone (Aldrich) and Iridium trichloride (Pressure chemical) were used as received. GC/MS analyses were performed on a Shimadzu GC-MS QP5000 (ver. 2) equipped with cross-linked methyl silicone gum capillary column (DB5). The retention times of the products were confirmed by comparison to authentic samples. NMR spectra were obtained on a Bruker AC-250 spectrometer (250.13 MHz for 'H and 62.90 MHz for 1 3C); Bruker AM-360 spectrometer (360.14 MHz for 'H and 90.57 MHz for 1 3C) or on a Varian Mercury 400 (400.151 MHz for ]H and 100.631 MHz for 1 3C) spectrometer. All coupling constants are reported in units of Hz. Elemental analyses were done by Desert Analytics Laboratory; Arizona. To a round-bottom flask equipped with a reflux condenser vented to an oil bubbler, IrCl3 (H 2 0 )x (1 g, 2.82 mmol, 54.11% Ir), 100 mL of water and 1.5 g of NaOAc (16 mmol) were added. The mixture was heated to gentle reflux to give a dark green color to which tropolone (2 g, 16mmol) was added. The mixture was refluxed for 20 h during which a red solid precipitated from solution. The reaction mixture was cooled to room temperature and the solid was collected. The solid was washed with water, ethanol and ether to give ~ 1.3 g of solid. This solid was Synthesis of [CH3-Ir(trop)2(Py)] (CH3-IrT -Py) : 245 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. further washed with dichloromethane to remove Ir(trop) 3 (40%) to leaving a black colored material, 1 (0.75 g) which was polymeric in nature. 1 was soluble in coordinating solvents such as DMSO, PY, CH3 CN and THF. In the glove box, a re-sealable Schlenk tube was charged with 1 (500 mg) and THF (50 mL) was added. To this was added a toluene solution o f ZnMe2 (2.0 M toluene, 1000 fiL, 2 mmol). The color of the reaction changed from reddish to black. The Schlenk tube was then sealed, removed from the glove box, and placed in a 60 °C oil bath for 3h. After cooling to room temperature, the solution was poured onto water (200 mL), extracted with CH2 CI2 (2 x 100 mL) and pyridine (lm L) was added. The solvent was removed in vacuo and the resulting black solid purified by chromatography using a silica column in the air. The column was eluted using a mixture of ethylacetate and hexanes (1:1 v/v). An intense black colored band was eluted (Rf ~ 0.3). Removal of solvent and recrystallization from dichloromethane/hexanes resulted in the title compound, CH 3 -IrT -Py (Isolated yield = 60 mg, 10% based on IrCl3 ). ’H-NMR (CDC13 ): 8 8.77(d, 3 J - 5.3, 2H, o- H Py), 7.8l(t, 3 J = 8 .0 ,5 J - 1.8, lH ,p -tf Py), 7.34-7.38(m, 3 J - 8.0, 2H, m-H Py), 7.3 l(m, 4H, 4 and 6-H-Trop), 7.06(d, 3 J = 10.7, 4H, 3 and 7-H-Trop), 6.64(t, 3 J = 9.5, 2H, 5-H-Trop), 2.08(s, 3H, CH3 -lr). ^C i'H } NMR (CDCI3 ): 8 187.8(C/,2- Trop), 150.5(o-py), 137.0(p-py), 133.5{C3 .7 or C4 .6 ), 128.2(C5 ), 128.0( C 3 . 7 or C4 m 6 ), 125.3(m-py), -23.3(CH3 -Ir). Anal. Calc, for C2 oHi8 IrN 04: C, 45.45; H, 3.43; N, 2.65. Found: C, 45.35; H, 3.82; N, 2.46. 246 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Synthesis of [CH3 CH2 -Ir(trop)2 (Py)] (CH3 CH2 - X 1 Ir -Py): The above procedure was repeated using diethylzinc as a reagent. H- NMR (CDCI3 ): 6 8.78(d, 3 J = 4.8, 2H, o-H Py), 7.71(tt, 3 J = 7 .6 ,5 J = 1.6, 1H,p -H Py), 7.39-7.3 l(m, 6 H, m-H Py & 4 and 6-H-Trop), 7.08(d, 3 J = 11, 4H, 3 and 7-H- Trop), 6 .6 6 (t, 3 J = 9.5, 2H, 5-H-Trop), 3.1 l(q, 3 J = 7.7, 2H, Ir-CH2 ), 0.61(t, 3 J = 7.7, 3H, CH3 ). ,3 C{’H} NMR (CDC13 ): 6 187.6(Cu -Trop), 150.6(o-py), 136.9(p- py), 133.3(Q,7 or C4 ,6 ), 128.2(C5 ), 127.9(C3 ,7 or C4 ,6 ), 125.2(m-py), 16.2(CH3 ), - 8 .6 (CH2 -Ir). Anal. Calc, for C2 iH2 oIrN0 4: C, 46.48; H, 3.72; N, 2.58. Found: C, 46.60; H, 4.00; N, 2.57. Synthesis of [Cy-Ir(trop)2(Py)J (Cy-IrT -Py): A re-sealable Schlenk tube was charged with CH3-IrT -Py (32.0 mg, 0.0586 mmol) and cyclohexane (3.5 mL). The resulting solution was thoroughly degassed before being placed under an atmosphere of Ar. The tube was sealed and heated to 120°C in an oil bath for 3h. After cooling to room temperature, all solvent was removed in vacuo leaving a red solid which was purified by flash chromatography on silica 247 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. using ethyl acetate as an eluent. Cy-Ir -Py was isolated as a red solid, yield ~ 12mg (-35%). 'H N M R (CDC13 ): 5 8.72(d, 3 J = 4.8, 2H, o-H Py), 7.65(t, 3 J = 7.5, 1H, p-H F y), 7.38-7.30(m, 6 H, m-H Py & 4 and 6-H-Trop), 7.06(d, 3 J = 10.9, 4H, 3 and 7-H-Trop), 6.64(t, 3 J = 9.5, 2H, 5-H-Trop), 3.28(tt, 3 J = 12.0, 5 J = 3.5, 1H, Ir-C//C 5Hn), 1.7-0.95(m, 11H, Ir-CH-C577//). N M R (CDC13): 5 \S7.2(Cu -Trop), 150.6(o-py), 136.9(p-py), 133.1(0*7 or C4 ,6 ), 128.0(C5 ), 127.8(C3 ,7 or C4 i6 ), 125.0(m-py), 36.5(Ir-CHC5 Hn), 28.4(Ir-CHC5 H n ), 28.3(Ir- CHC5H 1 1), 1 .2 (Ir-CHC5Hii). Anal. Calc, for C 25H 26lrN 04: C, 50.32; H, 4.39; N, 2.35. Found: C, 50.70; H, 4.80; N , 2.29. Synthesis of [Mes-Ir(trop)2(Py)] (Mes-IrT -Py): A re-sealable Schlenk tube was charged with CH3 -IrT -Py (32.0 mg, 0.0586 mmol) and mesitylene (5 mL). The resulting solution was thoroughly degassed before being placed under an atmosphere of Ar. The tube was sealed and heated to 120°C in an oil bath for 3h. After cooling to room temperature, all solvent was removed in vacuo leaving a red solid of Mes-IrT -Py in quantitative yields as determined by NMR. Isolated yield ~ 29mg (>95%). ‘HNMR (CD2 C12): 5 8 . 6 6 (dt, 3 J = 4 .8 ,5 J = 1.6 2H, o-H Py), 7.71 (tt, 3 J = 7 .5 ,5 J = 1.6, IH, p -H Py), 7.37-7.30(m, 6 H, m-H Py 248 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. & 4 and 6-H-Trop), 6.95 (dt, 3 J = 10.7,5 J = 0.8, 4H, 3 and 7-H-Trop), 6.63(tt, 3 J = 9.7, 5 J = 0.8, 2H, 5-H-Trop), 6.46(s, 2H, o- Mesityl H), 6.45(1H, p-Mesityl H), 4.25(s, 2H, Ir-CH2 ), 2.05(s, 6 H, Aromatic CH3 ) . ^C l'H } NMR (CD2 C12): 6 187.8(Cu -Trop), 152.7(Mes), 151.1 (o-Py), 137.6ip-Py), 136.8 (Mes), 133.7(C?,7 or C4 ,6 ), 128.5(C5 ), 128.1(Mes), 127.1(C?,7 or C4,6 ), 125.5 (Mes), 123.l(m-Py), 21.3 (Aromatic CH3 ), 4.8 (CH2 -Ir). Anal. Calc, for C2 8 H2 6 IrN 04: C, 53.15; H, 4.14; N, 2.21. Found: C, 53.22; H, 4.52; N, 2.26. 2 3 4 Synthesis of [Ph-Ir(trop)2 (Py)] (Ph-IrT-Py): A re- sealable Schlenk tube was charged with CH 3 -IrT-Py (30 mg, 0.056 mmol) and benzene (5 mL). The resulting solution was thoroughly degassed before being placed under an atmosphere of Ar. The tube was sealed and then heated to 120°C in an oil bath for 30 min. After cooling to room temperature, the solvent was removed to yield a red black solid in quantitative yields as determined by NMR. Isolated yield = 27mg (>95%) ]HNMR (CD2 C12): 8 8.81 (dt, 3 J - 4 .9 ,5 J = 1.6 2H, o-H Py), 7.78 (tt, 3 J = 7.7 ,5 J = 1.6, lH ,/?-i/P y), 7.40-7.46(m, 2H, m-HVy), 7.32(t, 3 J = 10.7, 4H, 4 and 6-H-Trop), 7.15 (d, 2H, o-H Ph), 7.1 l(d, 3 J = 10.7, 5 J = 0.8, 4H, 3 and 7-H-Trop), 6.93(t, 2H, m-H Ph), 6.77(t, lH ,/?-//P h ), 6.69(tt, 2H, 5-H- Trop). 1 3C{'H} NMR (CD2 C12): 6 187.9(Cu -Trop), 151.1(o-Py), 138.1 (p-Py), 249 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 137.5 (Ph), UA.1(C3 ,7 or Cu \ 128.9(C5 ), 127.9(C5 ,7 or C4 ,6 ), 125.9 (Ph), 125.6(m- Py), 123.1 (Ph). Anal. Calc, for C2 5 H2 oIrN0 4: C, 50.84; H, 3.41; N, 2.37. Found: C, 50.95; H, 3.62; N, 2.46. Synthesis of [Ace-Ir(trop)2 (Py)] (Ace-IrT -Py): A re-sealable Schlenk tube was charged with CH3 -IrT -Py (30 mg, 0.056 mmol) and acetone (5 mL). The resulting solution was thoroughly degassed before being placed under an atmosphere of Ar. The tube was sealed and then heated at 120°C in an oil bath for 3 h. After cooling to room temperature, the solvent was removed to yield an orange solid in quantitative yields as determined by NMR. Isolated yield ~ 27mg (>95%) ]H NMR (CDC13 ): 5 8.76(dt, 3 J = 4 .8 ,5 J = 1.6 2H, o-H Py), 7.73(tt, 3 J = 7.5, 5 J = 1.5, 1H, p-H Py), 7.40-7.35(m, 6 H, m-H Py & 4 and 6-H- Trop), 7.18(d, 3 J = 10.8, 4H, 3 and 7-H-Trop), 6.73(t, 3 J = 9.5, 2H, 5-H-Trop), 4.1 l(s, 2H, lr-CHi), 1.95(s, 3H, CH3 ). i3 C{'H} NMR (CDCI3 ): 5 220.5(C=O), \%1.5(Cu -Trop), 151.1 (o-py), 137.6(p-py), 134.4(Q 7 or C4 .6 ), 128.9(C5 ), 128.5(C5 ,7 or C4 .6 ), 125.4(m-py), 29.8(CH3 ), 15.4(CH2-Ir). Anal. Calc, for C2 2 H2 oIrN0 5: C, 46.31; H, 3.53; N, 2.45. Found: C, 46.58; H, 3.51; N, 2.29. 250 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. H/D exchange: Catalytic H/D exchange reactions were quantified by monitoring the loss of deuterium in CgDg or by the increase of deuterium into C6 H6 by GC/MS analyses. This was achieved by deconvoluting the mass fragmentation pattern obtained from the MS analysis, using a program developed with Microsoft EXCEL. An important assumption made with this method is that there are no isotope effects on the fragmentation pattern for the various benzene isotopomers. Fortunately, because the parent ion of benzene is relatively stable towards fragmentation, it can be used reliably to quantity the exchange reactions. The mass range from 78 to 84 (for benzene) was examined for each reaction and compared to a control reaction where no metal catalyst was added. The program was calibrated with known mixtures of benzene isotopomers. The results obtained by this method are reliable to within 5%. Thus, analysis of a mixture of C6 H 6 , C6 D6 and C6 H 5D 1 prepared in a molar ratio of 40: 50: 10 resulted in a calculated ratio of 41.2(C6H6): 47.5(C6D6): 9 .9 (CeH5 Di). Catalytic H/D exchange reactions were thus run for sufficient reaction times to be able to detect changes >5% exchange. CH3- j Ir -Py was the catalyst used to carry out the H/D exchange between various substrates and deuterium sources. H/D exchange between Benzene-Toluene-dg: In a typical 5 mL Schlenk tube, 5.5 mg (5mM) of CH3-IrT -Py was added followed by equal volumes of C6 H6 and C7 D 8 (1 mL each). The Schlenk tube was sealed under an inert atmosphere of Ar, placed in a well stirred oil bath maintained at 120 °C and the liquid phase was 251 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. monitored regularly using GC-MS. Deconvolution of the benzene peak at various reactions times shows the exchange of the H and D between the arenes. The amount of deuterium incorporation is calculated from the increase in the deuterium isotopomers mol ratio. 'H NMR of the residue confirmed the Ph-IrT -Py as the main species (>90%). X-ray Crystallography. Diffraction data for CH3-IrT -Py was collected at low temperature (T = 153 K) on a Bruker SMART APEX CCD diffractometer with graphite-monochromated Mo K a radiation (k= 0.71073 A). The cell parameters for the Ir complex were obtained from the least-squares refinement of the spots (from 60 collected frames) using the SMART program. A hemisphere of the crystal data was collected and the intensity data was processed using the Saint Plus program. All calculations for structure determination were carried out using the SHELXTL package (version 5.1).2 2 Initial atomic positions were located by direct methods using XS, and the structure was refined by least-squares methods using SHELX. Absorption corrections were applied by using SADABS. Calculated hydrogen positions were input and refined in a riding manner along with the attached carbons. 252 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 6.1. Crystal data and structure refinement for C2 oHigIrN0 4 (CH 3 -IrT - P y) Identification code Empirical formula Formula weight Temperature Wavelength Crystal system Space group Unit cell dimensions Volume Z Density (calculated) Absorption coefficient F(000) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 27.50° Transmission factors Refinement method Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I>2sigma(I)] R indices (all data) Absolute structure parameter Largest diff. peak and hole irc7acam C20 H18 IrN 0 4 528.55 153(2) K 0.71073 A Monoclinic P2(l) a = 8.463(2) A <x= 90°. b = 11.060(3) A |3= 94.721(4)° c = 9.924(3) A y = 9 0 ° . 925.6(4) A3 2 1.896 Mg/m3 7.236 mm"1 508 0.28 x 0.06 x 0.01 mm3 2.06 to 27.50°. -10<=h<=10, -14<=k<= 12, -1 1<=1<=12 5610 3120 [R(int) = 0.0436] 97.3 % min/max ratio: 0.670 Full-matrix least-squares on F2 3 1 2 0 /1 /2 3 6 1.008 R1 = 0.0396, wR2 = 0.0676 R1 = 0.051 l,w R 2 = 0.0698 0.032(16) 2.256 an d -1.910 e.A" 3 253 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 6.2. Atomic coordinates (x 10^) and equivalent isotropic displacement parameters (A^x 1C )3) for C2 oH]gIrN0 4 (CH 3 -IrT-Py). U(eq) is defined as one third of the trace of the orthogonalized UU tensor. X y z U(eq) Ir(l) 1173(1) 3181(1) 6812(1) 23(1) 0 (1 ) -333(7) 2227(6) 5520(7) 25(2) 0 ( 2 ) 1171(8) 4188(6) 5103(7) 27(2) 0 (3 ) 1235(8) 2182(6) 8524(7) 29(2) 0 (4 ) 2751(8) 4136(6) 8035(7) 31(2) N (l) 3112(9) 2075(7) 6177(8) 27(2) C (l) -472(13) 2631(9) 4272(12) 25(3) 0 ( 2 ) -1355(11) 1937(9) 3308(10) 29(2) 0(3) -1676(14) 2159(10) 1919(11) 36(3) 0(4) -1296(11) 3180(30) 1173(9) 44(3) 0(5) -450(14) 4130(10) 1600(11) 40(3) 0 ( 6 ) 259(13) 4408(9) 2834(11) 31(3) 0(7) 349(13) 3746(9) 4061(12) 24(2) 0 ( 8 ) 2195(14) 2578(10) 9484(13) 32(3) 0(9) 2369(14) 1890(11) 10705(11) 41(3) 0(10) 3288(15) 2109(11) 11896(11) 46(3) 0(11) 4310(14) 3000(30) 12243(12) 48(5) 0 ( 1 2 ) 4688(15) 3994(12) 11453(13) 47(3) 0(13) 4145(13) 4285(11) 10146(12) 41(3) 0(14) 3032(14) 3676(9) 9240(12) 26(3) 0(15) 2799(12) 1007(8) 5600(10) 30(2) 0(16) 3978(13) 242(11) 5197(11) 38(3) 0(17) 5519(13) 621(10) 5380(12) 37(3) 0(18) 5856(13) 1710(11) 6002(13) 46(3) 0(19) 4621(12) 2414(9) 6367(11) 34(3) C(20) -661(12) 4181(9) 7445(11) 35(3) 254 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 6.3. Bond lengths [A] and angles [°] for C2oHigIrN0 4 (CH3-IrT -Py). Ir(l)-0(3) 2.023(6) Ir(l)-0(4) 2.026(7) Ir(l)-0(1) 2.028(6) Ir(l)-0(2) 2.029(6) Ir(l)-C(20) 2.046(10) Ir(l)-N (l) 2.180(8) 0(1)-C (1) 1.313(12) 0(2)-C (7) 1.293(12) 0(3)-C (8) 1.277(13) 0(4)-C (14) 1.303(13) N (l)-C (19) 1.329(12) N (l)-C (15) 1.330(12) C(l)-C (2) 1.394(14) C(l)-C (7) 1.439(11) C(2)-C(3) 1.405(13) C(3)-C(4) 1.40(2) C(4)-C(5) 1.32(3) C(5)-C(6) 1.354(13) C(6)-C(7) 1.417(15) C(8)-C(9) 1.428(16) C(8)-C(14) 1.436(12) C(9)-C(10) 1.382(14) C (10)-C (ll) 1.33(2) C (11 )-C (l 2) 1.41(3) C(12)-C(13) 1.379(15) C(13)-C(14) 1.417(15) C(15)-C(16) 1.392(14) C(16)-C(17) 1.368(15) C(17)-C(18) 1.372(16) C(18)-C(19) 1.376(15) 255 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 6.3. Continued 0 (3 )-Ir( 1 )-0 (4 ) 79.1(3) 0(3)-Ir( 1 )-0 ( 1) 102.6(3) 0(4)-Ir( 1 )-0 ( 1) 177.3(3) 0 (3 )-Ir(l)-0 (2 ) 178.6(3) 0(4 )-Ir(l)-0 (2 ) 99.8(3) 0 (l)-Ir (l)-0 (2 ) 78.4(3) 0 (3 )-Ir( 1 )-C(2 0) 90.3(4) O(4)-Ir(l)-C(20) 90.8(4) O (l)-Ir(l)-C (20) 91.3(4) O(2)-Ir(l)-C(20) 90.7(4) 0 (3 )-Ir(l)-N (l) 88.2(3) 0(4)-Ir( 1 )-N( 1) 89.5(3) 0(1 )-Ir(l)-N (l) 88.5(3) 0(2)-Ir( 1 )-N( 1) 90.9(3) C(20)-Ir( 1 )-N( 1) 178.4(4) C (l)-0(1)-Ir(l) 115.0(6) C (7)-0(2)-Ir(l) 115.1(6) C (8)-0(3)-Ir(l) 114.2(7) C (14)-0(4)-Ir(l) 114.1(7) C (19)-N(l)-C (15) 117.8(9) C (19)-N (l)-Ir(l) 122.6(7) C (15)-N (l)-Ir(l) 119.7(6) 0(1)-C (1)-C (2) 117.4(10) 0 ( 1 )-C( 1 )-C(7) 114.9(10) C(2)-C(l)-C(7) 127.6(12) C(l)-C(2)-C(3) 128.8(10) C(4)-C(3)-C(2) 128.7(11) C(5)-C(4)-C(3) 127.8(9) C(4)-C(5)-C(6) 131.2(12) C(5)-C(6)-C(7) 130.4(10) 0(2)-C (7)-C (6) 118.6(10) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 6.3. Continued 0(2)-C (7)-C (l) 116.2(11) C(6)-C(7)-C(l) 125.1(11) 0(3)-C (8)-C (9) 117.7(11) 0(3)-C (8)-C (14) 117.2(11) C(9)-C(8)-C(14) 125.1(12) C(10)-C(9)-C(8) 130.1(12) C (11 )-C( 10)-C(9) 131.0(12) C(10)-C(l 1)-C(12) 127.3(11) C(13)-C(12)-C(l 1) 129.4(13) C(12)-C(13)-C(14) 129.6(12) 0(4)-C (14)-C (13) 117.2(11) 0(4)-C (14)-C (8) 115.4(10) C(13)-C(14)-C(8) 127.3(12) N (l)-C (15)-C (16) 122.8(10) C(17)-C(16)-C(15) 118.3(10) C( 16)-C( 17)-C( 18) 119.3(10) C( 17)-C( 18)-C( 19) 118.8(10) N (l)-C (19)-C (18) 123.0(10) Symmetry transformations used to generate equivalent atoms: 257 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 6.4. Anisotropic displacement parameters (A^x 10^) for C2 oHigIrN0 4 (CH3-IrT -Py). The anisotropic displacement factor exponent takes the form: -2n^[ h^ a*2ljl 1 + ... + 2 h k a* b* ] u 1 1 U22 U 3 3 U 2 3 U 1 3 U 1 2 Ir(l) 23(1) 22(1) 25(1) 1(1) 1(1) 0(1) 0 (1 ) 24(4) 24(4) 27(4) 3(3) -3(3) 2(3) 0 (2 ) 29(4) 23(4) 28(4) 4(3) -3(3) -8(3) 0 (3 ) 29(4) 26(4) 32(4) 8(3) -8(3) -7(3) 0 (4 ) 36(4) 36(4) 22(4) 3(3) 2(3) -4(3) N (l) 17(4) 30(5) 36(5) 6(4) 2(4) -5(4) C (l) 12(6) 23(5) 40(8) 7(5) 2(5) 0(4) 0(2) 28(6) 24(5) 35(7) -5(5) 7(5) 3(5) C(3) 39(7) 33(6) 35(7) -2(5) -9(6) -2(5) 0(4) 56(6) 44(6) 31(5) 15(13) -7(5) -12(15) 0(5) 48(8) 42(7) 32(7) 9(5) 12(6) 9(6) 0(6) 37(6) 20(5) 34(7) 0(5) -5(5) -5(5) 0(7) 19(6) 21(5) 33(7) -4(4) 10(5) 5(5) 0(8) 21(6) 38(6) 38(8) 0(5) 13(6) 14(5) 0(9) 46(7) 45(7) 32(7) 0(5) -1(6) 5(6) 0(10) 59(9) 50(8) 28(7) 17(6) -6(6) 10(7) 0(11) 52(6) 55(14) 34(6) 9(9) -15(5) -3(10) 0(12) 42(8) 54(8) 43(9) -7(6) -6(6) 3(6) 0(13) 43(7) 43(7) 38(8) -6(5) 1(6) -2(6) 0(14) 27(7) 30(6) 22(6) -8(4) 5(5) 4(5) 0(15) 26(6) 26(5) 38(6) -5(5) 7(5) -1(4) 0(16) 41(7) 37(7) 36(7) 7(5) 4(6) 5(5) 0(17) 32(7) 37(7) 44(8) 4(6) 7(5) 15(6) 0(18) 23(6) 57(8) 58(9) 16(6) 10(6) -1(6) 0(19) 26(6) 33(6) 45(7) 4(5) 12(5) 2(5) C(20) 32(6) 32(6) 43(7) -7(5) 13(5) 5(5) 258 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 6.5. Hydrogen coordinates ( x 10^) and isotropic displacement parameters (A^x K p) for C2 oHisIrN0 4 (CH3-IrT -Py). x y z U(eq) H(2) -1800 1217 3636 34 H(3) -2223 1534 1418 43 H(4) -1695 3188 250 53 H(5) -317 4721 924 48 H(6) 780 5169 2886 37 H(9) 1758 1170 10697 49 H(10) 3173 1528 12586 56 H( 11) 4842 2949 13122 57 H(12) 5425 4548 11883 56 H(13) 4581 5002 9800 50 H(15) 1725 756 5457 36 H(16) 3719 -524 4805 45 H(17) 6348 137 5079 45 H(18) 6922 1972 6179 55 H(19) 4857 3178 6772 41 H(20A) -932 4827 6791 53 H(20B) -344 4536 8330 53 H(20C) -1585 3658 7516 53 259 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.4 References (1) (a) Amdtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H. Acc. Chem. Res. 1995, 28, 154. (b) Shilov, A. E.; Shulpin, G. B. Activation and Catalytic Reactions o f Saturated Hydrocarbons in the Presence o f Metal Complexes, Kluwer Academic; Dordrecht, 2000. (c) Jia, C.; Kitamura, T.; Fujiwara, Y. Acc. Chem. Res. 2001, 38, 633. (d) Jones, W. D. Acc. Chem. Res. 2003, 36, 140. (e) Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2001, 19, 2437. (f) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507. (g) Periana, R. A.; Bhalla, G.; Tenn III, W. J.; Young, K. J. H.; Liu, X. Y.; Mironov, O.; Jones, C.; Ziatdinov, V. R. J. Mol. Cat. A- Chem. 2004, 220, 7. (2) (a) Griffith, W. P.; Coord. Chem. Rev. 1970, 5, 459. (b) Besecker, C. J.; Day, V. W.; Klemperer, W. G. Organometallics 1985, 4, 564. (c) LaPointe, R. E.; Wolczanski, P. T.; Van Duyne, G. D. Organometallics 1985, 4, 1810. (d) Grim, S. O.; Sangokoya, S. A.; Colquhoun, I. J.; McFarlane, W.; Khanna, R. K. Inorg. Chem. 1986, 25, 2699. (e) Klaeui, W.; Muller, A.; Eberspech, W.; Boese, R.; Goldberg, I. J. Am. Chem. Soc. 1987, 109, 164. (f) Burk, M. J.; Crabtree, R. H. J. Am. Chem. Soc. 1987,109, 8025. (g) Bryndza, H. E.; Tam, W. Chem.Rev. 1988, 88, 1163. (h) Burk, M. J.; Crabtree, R. H. J. Am. Chem. Soc. 1987, 109, 8025. (i) Fryzuk, M. D.; Montgomery, C. D. Coord. Chem. Rev. 1989, 95, 1. (j) Power, P. P.; Comm. Inorg. Chem. 1989, 8, 177. (k) West, B. O. Polyhedron 1989, 8, 219. (1) Tanke, R. S.; Crabtree, R. H. J. Am. Chem. Soc. 1990, 112, 7984. (m) Lunder, D. M.; Lobkovsky, E. B.; Streib, W. E.; Caulton, K. G. J. Am. Chem. Soc. 1991, 113, 1837. (n) Poulton, J. T.; Folting, K.; Streib, W. E.; Caulton, K. G. Inorg. Chem. 1992, 31, 3190. (o) Johnson, T. T.; Huffman, J. C.; Caulton, K. G. J. Am. Chem. Soc. 1992, 114, 2725. (p) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239. (q) Bergman, R. G. Polyhedron 1995, 3227. (r) Mayer, J. M. Polyhedron 1995, 3273. (s) Sharp, P. R. J. Chem. Soc., Dalton Trans. 2000, 2647. (t) Cinellu, M. A.; Minghetti, G. Gold Bull. 2002, 35, 11. (3) Wong-Foy, A. G.; Bhalla, G. ; Liu, X. L.; Periana, R. A. J. Am. Chem. Soc. 2003,125, 14292. (4) (a) Periana, R. A.; Liu, X. Y.; Bhalla, G. Chem. Commun. 2002, 3000. (b) Matsumoto, T.; Periana, R. A.; Taube, D. J.; Yoshida, H. J. Mol. Cat. A Chem 2002,180, 1. (c) Matsumoto, T.; Periana, R. A.; Taube, D. J.; Yoshida, H. J. Catal. 2002, 206, 272. (d) Matsumoto, T.; Taube, D. J.; Periana, R. A.; Taube, H.; Yoshida, H. J. Am. Chem. Soc. 2000,122, 7414. 260 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (5) (a) Oxgaard, J.; Muller, R. P.; Goddard III, W. A.; Periana, R. A. J. Am. Chem. Soc. 2004, 126, 352. (b) Oxgaard, J.; Goddard III, W. A. J. Am. Chem. Soc. 2004,126, 442. (6) (a) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem. Res. 2002, 25, 44. (b) Jones, W. D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91. (c) Harper, T. G. P.; Shinomoto, R. S.; Deming, M. A.; Flood, T. C. J. Am. Chem. Soc. 1988, 110, 7915. (d) Wang, C. M.; Ziller, J. W.; Flood, T. C. J. Am. Chem. Soc. 1995, 117, 1647. (e) Holtcamp, M. W.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 1997, 119, 848. (f) Periana, R. A.; Taube, D. J.; Gamble, S.; Taube, H.; Satoh, T.; Fujii, H. Science 1998, 280, 560. (g) Johansson, L.; Ryan, O. B.; Tilset, M. J. Am. Chem. Soc. 1999, 121, 1974. (h) Fekl, U.; Goldberg, K. I. Adv. Inorg. Chem. 2003, 5454, 259. (i) Liu, F. C.; Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S. J. Am. Chem. Soc. 1999, 121, 4086. (j) Nuckel, S.; Burger, P. Angew. Chem. Int. Ed. 2003, 42, 1632. (7) (a) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th ed.; John Wiley & Sons: New York, 1988, 1189. (b) Collman, J. P. Acc. Chem. Res. 1968, 1, 136 (a) Tellers, D. M.; Skoog, S. J.; Bergman, R. G.; Gunnoe, T. B.; Harman, W. D. Organometallics 2000, 19, 2428. (b) Tellers, D. M.; Bergman, R. G. J. Am. Chem. Soc. 2000,122, 954. (c) Tellers, D. M.; Yung, C. M.; Amdtsen, B. A.; Adamson, D. R.; Bergman, R. G. J. Am. Chem. Soc. 2002, 124, 1400. (d) Zhong, H. A.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2002,124, 1378. (e) Owen, J. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 2004,126, 8247. (8) Krogh-Jespersen, K.; Czerw, M.; Zhu, K.; Singh, B.; Kanzelberger, M.; Darji, N.; Achord, P. D.; Renkema, K. B.; Goldman, A. S. J. Am. Chem. Soc. 2002,124, 10797. (9) (a) Lunder, D. M.; Lobkovsky, E. B.; Streib, W. E.; Caulton, K. G. J . Am. Chem. Soc. 1991, 113, 1837. (b) Flood, T. C.; Lim, J. K.; Deming, M. A.; Keung, W.; Organometallics 2000,19, 1166. (10) (a) Holm, R. H. Chem. Rev. 1987, 87, 1401. (b) Bates, P. A.; Nielson, A. J.; Waters, J. M. Polyhedron 1987, 6, 163. (c) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc. 1988, 110, 8729. (d) Cummins, C. C.; Baxter, S. M.; Wolczanski, P. T. J . Am. Chem. Soc. 1988, 110, 8731. (e) Parkin, G.; Bercaw, J. E. Polyhedron 1988, 7, 2053. (f) Herrmann, W. A. Angew. Chem, Int. Ed. 1988, 27, 1297. (g) Bryndza, H. E.; Domaille, P. J.; Paciello, R. A.; Bercaw, J. E. Organometallics 1989, 8, 379. (h) Chao, Y. W.; Rodgers, P. M.; Wigley, D. E.; Alexander, S. J.; Rheingold, A. L. J. Am. 261 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chem. Soc. 1991,113, 6326. (i) Rachidi, I. E. I.; Eisenstein, O.; Jean, Y. New J. Chem. 1990,14, 671. (j) Riehl, J. F.; Jean, Y.; Eisenstein, O.; Pelissier, M. Organometallics 1992, 11, 729. (k) Caulton, K. G. New J. Chem. 1994, 18, 25. (11) Bradley, D. C.; Mehrotra, R. C.; Rothwell, I. P.; Singh, A. Alkoxo and Aryloxo Derivatives o f Metals, Academic Press, 2001. (12) (a) Muetterties, E. L.; Wright, C. M. J. Am. Chem. Soc. 1965, 86, 4706. (b) Muetterties, E. L.; Wright, C. M. J. Am. Chem. Soc. 1965, 87, 21. (c) Muetterties, E. L.; Roesky, H.; Wright, C. M. J. Am. Chem. Soc. 1966, 88, 4856. (d) Narbutt, J.; Krejzler, J. Inorg. Chim. Acta 1999, 286, 175. (13) (a) Pierpont, C. G.; Buchanan, R. M. Coordn. Chem. Rev. 1981, 38, 45. (b) Pierpont, C. G.; Lange, C. W. Prog. Inorg. Chem. 1994, 41, 331. (c) Martin, R. Handbook o f Hydroxyacetophenones, Kluwer, 1997. (14) (a) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.; Dierkes, P. Chem. Rev. 2000,100, 2741. (b) Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Reek, J. N. H. Acc. Chem. Res. 2001, 34, 895. (c) Freixa, Z.; van Leeuwen, P. W. N. M. Dalton Trans. 2003, 1890. (15) Keim, W.; Schulz, R. P. J. Mol. Catal. A Chem 1994, 92, 21. (16) Griffith, W. P.; Pumphrey, C. A.; Skapski, A. C. Polyhedron 1987, 5, 891. (17) Bennett, M. A.; Mitchell, T. R. B. Inorg. Chem., 1976,15, 2936. (18) Johri, K. H.; Mehra, H. C. Separ. Sci., 1976,11, 171. (19) Crystal data for C2oHigIrN0 4 : Mr- 528.55, monoclinic, space group P2(l), a=8.463(2), 6=11.060(3), c=9.924(3)A, a= 90, ,9=94.721 (4), y=90°, V=925.6(4) A3, F(000)=508, pc a ic d (Z=2) =1.896 mgm'3, p=0.7236 m m '1 , approximate crystal dimensions 0.28 x 0.06 x 0.01 mm3, 6 range=2.06- 27.50°, MoKa (2=0.71073 A), T=153 K, 5610 measured data (Bruker 3- circle, SMART APEX CCD with / axis fixed at 54.74°, using the SMART V 5.625 program, Bruker AXS: Madison, WI, 2001), o f which 3120 (Rj„t=0.0436) unique. Lorentz and polarization correction (SAINT V 6.22 program, Bruker AXS: Madison, WI, 2001), absorption correction (SADABS program, Bruker AXS: Madison, WI, 2001). Structure solution by direct methods (SHELXTL 5.10, Bruker AXS: Madison, WI, 2000), full- matrix least-squares refinement on F2, data to parameters ratio: 13.2:1, final R indices [I>2a(I)] : R l= 0.0396, wR2=0.0676, Rl=0.0511, wR2=0.0698 (all 262 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. data), GOF on F2 =1.008. CCDC 250327 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (+44)1223-336-033; or deposit@ccdc.cam.ac.uk). (20) Bhalla, G.; Periana, R. A. Unpublished results. (21) The H/D exchange rates were quantified by GC/MS analyses. This was achieved by deconvoluting o f the mass fragmentation pattern obtained from mass spectroscopy using a program developed with Microsoft EXCEL. (22) Sheldrick, G. M. SHELXTL, version5.1; Bruker Analytical X-ray System, Inc.: Madison, WI, 1997. (23) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38. 263 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 Anti-Markovnikov, Hydroarylation of olefins Catalyzed by a bis-tropolonato ligated Iridium (III) Complex 7.1 Introduction As described earlier, one of the oldest known organic reactions involving functionalization of unactivated arenes is the Friedel-Crafts alkylation of arenes with olefins. This important C-C bond forming reaction proceeds via well-known carbocationic mechanisms. Importantly, catalysts that can catalyze this reaction by alternative, non carbocationic mechanisms, eg. C-H activation,1 have the potential to dramatically broaden the scope of this C-C bond forming reaction. Such catalysts could lead to the hydroarylation reactions that unlike the classical Friedel-Crafts alkylation reaction have the potential to: A) eliminate corrosive Lewis acids, B) favor anti-Markovnikov regioselectivity C) be stereoselective and D) be compatible with a wide range of functional groups. Despite these important advantages and in spite of the fact that arene C-H bonds are among the easiest to activate with homogeneous transition metal catalysts, relatively few metal complexes are known which catalyze this important C-C bond forming reaction via the C-H activation.2 Indeed, to date, only two homogeneous catalysts3 ,4 have been established to catalyze the intermolecular, hydroarylation of unactivated arenes with unactivated olefins via the C-H activation reaction as shown in Scheme 7.1. 264 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Catalyst Scheme 7.1. Hydroarylation of unactivated arenes with unactivated olefins. One of these systems, reported by our group, is based on a homogeneous O-donor late transition metal complex, (acac-0,0)2lr(Ph)(Py), Ph-Ir-Py, (acac- 0 ,0 is the O-bound acetylacetonate ligand). With the exception of this complex, no other O-donor complex with late transition metals have been reported for the C- H activation reaction and given the expected differences compared to more typical N, C and P-donor ligands, there is a basis to anticipate unique properties for this class of O-donor complexes. Indeed, we have observed that Ph-Ir-Py is very long lived, thermally stable to air and protic media, is not severely inhibited by olefins or water and exhibits anti-Markovnikov selectivity in reactions of unactivated arenes with olefins such as propylene and isobutylene. Uniquely, while we have shown that the reactions with this complex involve arene C-H activation and that organometallic intermediates containing (3-CH bonds are generated, no olefmic products that are typically generated in other metal catalyzed arene/olefin coupling reactions are observed. The key disadvantage that limit the utility of this initial O- 265 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. donor catalyst system is the slow reaction rate that requires reactions to be carried out at ~200°C. Our experimental and theoretical studies5 of this initial 6-coordinate O- donor complex, Ph-Ir-Py, show that the mechanism of catalytic hydroarylation of olefins involves: A) likely dissociative loss of L, B) cis-trans isomerization, C) C- H activation via a seven coordinate transition state with oxidative addition character and C) functionalization by olefin insertion. The energies for each of the steps can contribute to the overall catalyst rate depending on the reaction conditions and theoretical studies have shown that there is an unexpectedly complex interplay between the C-H activation and olefin insertion (functionalization) steps.6 Both steps are inversely influenced by the electron donating ability of the metal d-orbitals with highly donating orbitals leading to increase in the barrier for olefin insertion but decreased C-H activation barriers. However, preliminary theoretical work also shows that modifications of various ligand properties, such as sigma-donating character, can benefit one of the two steps without overly impairing the other. Given the broad potential utility of efficient catalysts for olefin hydroarylation, the wide availability of O-donor ligands, the unique properties of this first example of an O-donor late transition metal catalyst and the limited study of O-donor ligands with late transition metals for C-H activation reactions we have begun a systematic study of this class of homogeneous complexes. The focus has been on structure-function relationships based on variations in the metal center7 266 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and the O-donor ligands. The ultimate objectives of these studies will be to: A) identify other examples of O-donor, late transition metal complexes that carry out C-H activation reaction and that also allow functionalization B) determine the fundamental requirements for and issues to integrating the CH activation with functionalization reactions with this promising class of O-donor complexes and C) to use this information to rationally design new, stable functionalization catalysts with higher rates and selectivities. The O-donor tropolonato ligand (trop-0,0) is often considered an analogue of O-donor acac-0,0 ligand since they are both bidentate, monoanionic, delocalized chelate rings bonded through two oxygen atoms. However, tropolonato ligand is also significantly different from acac-0,0 in that: A) tropolone is more o acidic that acac (pka ~ 6.4 versus ~8.9 for acetylacetone) and the tropolonato ligand may be more electron withdrawing within the sigma-framework, B) the larger aromatic delocalization could lead to greater polarizability and perhaps most Acac-0,0 Trop-0,0 Scheme 7.2. Comparison of Acac and Tropolone. 267 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. significantly, C) the smaller “bite-angle” resulting from the 5-memebered ring size of the tropolonato ligand 9 (verus 6 for acac-0,0) could lead to significant differences in sterics and electronics at the metal center. One interesting possibility is that the trop-0,0 ligand may be both a better 7i-donor as well as a-acceptor than acac-0,0 ligand. This can be possible on the basis of the smaller ring size and subsequent greater p-character of the oxygen lone pairs as well as greater s- character in the O-Ir bond, respectively. Given the differences in electron demand between the transition states for C-H activation and olefin insertion such properties may be useful. 7.2 Results 7.2.1 Synthesis of Ph-lr(trop-0,0)2 (Py) In previous chapter, the synthesis of the bis-tropolonato methyl iridium analogue of Ph-Ir-Py, the O-donor complex, (trop-0,0)2lr(CH3)(Py), CH 3 -IrT - Py, which activates the C-H bond of alkanes and arenas was reported. Importantly, CH3-IrT -Py, was 50 times faster for catalytic C-H activation than the bis-acetylacetonate O-donor Iridium (III) analogue.1 0 Herein, we find that this complex is the third example of a well-defined, thermally stable complex that is an active catalyst for both C-H activation of arenes and functionalization by olefin hydroarylation. Attesting to the thermal stability of these tropolonato complexes, Ph-Ir -Py was synthesized in quantitative yields by thermal CH activation of 268 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. benzene with the bis-tropolonato methyl iridium complex, CH3 -IrT -Py at 120 °C for lh according to the stoichiometry shown in Scheme 7.3. The red powder obtained after benzene removal was fully characterized by *H, 1 3 C NMR spectroscopy and elemental analysis. The complex is both air and water stable and both the solid and solutions can be handled in the air. Consistently, treatment of Ph-Ir -Py with benzene-d6 shows the expected C-H activation reaction and quantitative formation of Ph-ds-IrT -Py. h6) 1 0 0 ° c c h 3 • O , , CH3-lrT-Py Ph-lrT-Py Scheme 7.3. Synthesis of Ph-IrT -Py from CH3-IrT -Py. 7.2.2 Hydroarylation and Comparison with bis Acac Complex Having shown that Ph-Ir -Py is capable of stoichiometric and catalytic C- H activation of arenes, we examined the functionalization activity of Ph-IrT -Py by reaction with a mixture of arenes and olefin. As can be seen in Table 7.1 (entry 1), Ph-Ir -Py is active for hydroarylation of olefins. In reactions of benzene with 269 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. propylene, only two products are observed, n-propyl benzene and iso-propyl benzene in a ~61:39 ratio and no traces of olefinic products are observed. Table 7.1. Hydroarylation of olefins by Ir Complexes3 . Entry Olefin Complex lim e (min) TyN TOFxlQ' * (sec ) L:B ratiod 1. Ethylene Ph-Ir(trop)2-Py (3) 30 27 150 - 2. Propylene Ph-Ir(trop)2-Py (3) 15 4 44 61:39 3. Propylene Ph-Ir(trop)2-Py (3) 30 8 43 61:39 4. Propylene Ph-Ir(acac)2-Py 30 9 51 61:39 5. Styrene Ph-Ir(trop)2-Py (3) 30 11 62 98:2 3 All reactions were carried out at 0.96 MPa of nitrogen in neat benzene at 200 °C. bTOF = [mols of product]/([mols of added 3] x Reaction time). c Mole ratio of linear to branched products.d Mole ratio of linear to branched products. The catalyst is long lived and as seen in Table 7.1, the TOF remains constant with time (entry 2 and 3). Interestingly, however, in spite o f the higher CH activation activity compared to the analogous acac-0,0 complex, Ph-Ir-Py, the tropolonato complex, Ph-IrT -Py is slightly less active (or comparable) for olefin hydroarylation than the acac-0,0 analogue, Ph-Ir-Py, Table 7.1 (entry 4). Significantly, both complexes show the same anti-Markovnikov regioselectivity for linear alkyl benzene with propylene and styrene, Table 7.1. 270 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.2.3 DFT Calculations Comparing Acac and Trop Complexes. In order to provide a basis for the increased reactivity for C-H activation but comparable reactivity for hydroarylation of olefins we examined the energy profile for proposed reaction mechanism for the hydroarylation assuming a mechanism related to the acac-0,0 complex Ph-Ir-Py using DFT calculations. Consistent with the experimental observations, the results presented in Figure 7.1 show that the energy profiles for Ph-IrT -Py and Ph-IrT -Py are very similar, with comparable barriers for rate determining olefin insertion, TS2, and slight lower barriers for CH activation with the tropolonato complex, TS3. To access the transition state for cis-trans isomerization (TS1) the pyridine ligand must be dissociated, and the calculations show a 2.6 kcal/mol difference in pyridine binding energy. The ground state inhibition is also evident in intermediate 4, the olefin complex, which is 3.7 kcal/mol less stable than 3, while for Ir(acac) 2 the olefin complex is 6.3 kcal/mol less stable than the pyridine complex. The cis trans isomerization occurs via slipping of one of the O-ligands from the cis to the vacant trans position. The resulting five coordinate cis intermediate is very short lived, and coordination o f olefin leads to intermediate 4. The energy of TS1 is very close to the energy o f TS2, although entropic effects are expected to favor TS1. 271 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. — lr (tr o p )2 - - l r ( a c a c ) 2 40 i Ph 30 / j s v 29.8 3 0 . 9 frs2> 30.4 3 1 . 5 25 20 Ph T S 3 v 153 1 8 . 8 \ , 8 . 9 , 10 .6.3,1 ■ 4 .6 3.9 5 . 0 0.0 0.0 Figure 7.1. Calculated (B3LYP/LACVP**) energy profile of Ir(trop) 2 and Ir(acac) 2 catalyzed hydroarylation. The transition state for the insertion, TS2, has a calculated activation energy of 30.4 kcal/mol. TS2 is formally a 1,2-insertion transition state, with the three carbons and the iridium in the plane. It is predicted to be slightly faster for Ir(Trop) 2 than for Ir(acac) 2 (AAH = 1.1 kcal/mol), which does not correspond to experiment, where Ir(Trop) 2 was found to be slightly slower. Further examination of the insertion mechanism shows that the predicted acceleration is caused by a ground state effect, as pyridine is bound less tightly by the Ir(Trop) 2 complex. If only the direct insertion steps are compared, i.e. 4 -> TS2 -> 5, the barrier is 26.7 kcal/mol for Ir(Trop) 2 and 25.2 kcal/mol for Ir(acac)2 , 1.5 kcal/mol faster for Ir(acac)2 . It could thus be an error in our treatment of the pyridine concentration effects which causes the difference, rather than an error in the description o f the 272 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. transition state. Nevertheless, the experimental ratio 66:77 corresponds to a AAG = -0.2 kcal/mol, so the error, 1.3 kcal/mol, is well within the expected accuracy. The result of the insertion is the chelating Ir-CH2 -CH 2 -Ph species 5, 2.9 kcal/mol higher in energy than 4. Rotation around the CH2 -CH2 bond generates the five coordinate species 6, which enables the coordination of benzene to give 7. 7 is 3.4 kcal/mol less stable than 3, and 0.3 kcal/mol more stable than 4, although on the AG surface it is most likely a few kcal/mol higher in energy. C-H activation occurs through the Oxidative Hydrogen Migration (OHM) transition state TS3, a concerted mechanism where the hydride is covalently bonded to the iridium (Ir-H = 1.56 A) while forming partial bonds to the arene and aliphatic carbons (2.00 A and 1.66 A, respectively), as illustrated in Figure 7.2. The energy of TS3 is only 11.9 kcal/mol higher than 7. This is significantly faster than C-H activation with Ir(acac)2, where TS3 is calculated to 14.2 kcal/mol higher than 7. The reason for this enhancement is currently not clear. The electron donating ability of the two ligands are very similar, and the calculated Mulliken charge on the metal center of Ir(Trop) 2 and Ir(acac) 2 is 0.23 e' and 0.27 e' in the transition state, respectively. Furthermore, the lower bite angle in tropolone does not have a perceptible steric effect. The two oxygens in the plane of the reacting C-H-C fragment have an O-Ir-O angle of 80.6° for Ir(Trop)2 , which should be compared to 79.8 0 for Ir(acac)2 . The lower bite angle was expected to alleviate steric crowding around the metal center in the OHM transition state, but this is clearly not the case. 273 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 7.2. TS3 However, even though sterics did not change perceptibly, it is possible that the lower bite angle could change the electronic properties of the oxygen ligands. There are several possibilities here: A) increased ground state destabilization by O- p7i to Mn-d7t filled-fllled repulsions or so-called “pi-conflict”1 1 B) increased bonding from the filled 0-p7t to empty Mn + 2 -d7t orbitals on the metal center in the oxidized transition state and/or C) decreased ground state back-bonding from filled Mn-d7t orbitals to conjugated ligand n* orbitals. Computational work is currently underway to determine the extent of these contributions and whether this is the cause of the rate increase. In conclusion, we have shown that another group of oxygenated Ir(III) complexes, bis-tropolanoto Ir(III) compounds with the same structure and 274 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. composition as that of acac-Ir catalysts are active catalysts for the hydroarylation of olefins. 7.3 Experimen tal Section Reaction Procedure for the Olefin Hydroarylation: A 3 mL stainless steel autoclave, equipped with a glass insert and a magnetic stir bar was charged with lm L of distilled benzene and 4 mg (5 mmol, ~0.1 mol %) of catalyst. The reactor was degassed with nitrogen, pressurized with 1.96 MPa of ethylene (0.90 MPa of propylene or 0.2 mL of styrene) with an extra 2.96 MPa of nitrogen. The autoclave was heated for 30 min in a well-stirred heating bath maintained at 200 °C. The liquid phase was sampled and the product yields were determined by GC- MS using methyl cyclohexane as an internal standard that was introduced into the reaction solution after the reaction. Computational section: All calculations were carried out using the hybrid DFT functional B3LYP,1 2 ’ 1 3 as implemented by the Jaguar 5.5 program package.1 4 Atoms were described with the LACVP** basis set and effective core potential treatment of Ir (17 explicit electrons).1 5 We optimized the geometry for all intermediates and transition states and calculated Zero Point Energies and solvation corrections for benzene [using the Poisson-Boltzman continuum solvent method (e = 2.284 and solvent radius = 2.60219 A)]. All reported energies are solvent corrected enthalpies at 0 K (including ZPE). 275 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7.4 References (1) (a) Jones, W. D. Acc. Chem. Res. 2003, 36, 140. (c) Shilov, A. E.; Shul’pin, G. B. Activation and Catalytic Reactions o f Saturated Hydrocarbons in the Presence o f Metal Complexes Kluwer Academic; Dordrecht, 2000. (d) Crabtree, R. H. J. Chem. 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Creator Bhalla, Gaurav (author)

Core Title Activation and functionalization of carbon-hydrogen bonds catalysed by oxygen ligated iridium metal complexes

School Graduate School

Degree Doctor of Philosophy

Degree Program Chemistry

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag chemistry, inorganic,chemistry, organic,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Periana, Roy A. (committee chair), Olah, George A. (committee member), Prakash, G.K. Surya (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-603440

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