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Carbon-hydrogen bond activation: Investigation into the dynamics and energetics of alkane complexes within a hard-ligated rhodium system

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Carbon-hydrogen bond activation: Investigation into the dynamics and energetics of alkane complexes within a hard-ligated rhodium system

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Content INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UM I films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. 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 bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send U M I a complete manuscript and there are missing pages, these w ill be noted. Also, if unauthorized copyright material had to be removed, a note w ill indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact U M I directly to order. ProQuest Information and Learning 300 North Zeeb Road. Ann Arbor, M l 48106-1346 USA 800-521-0600 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. C-H BOND ACTIVATION: INVESTIGATION INTO THE DYNAMICS AND ENERGETICS OF ALKANE COMPLEXES WITHIN A HARD-LIGATED RHODIUM SYSTEM Copyright 2001 by Kevin E. Janak A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (CHEMISTRY) August 2001 Kevin E. Janak Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number 3054754 _ ___ ( ft UMI UMI Microform 3054754 Copyright 2002 by ProQuest Information and Learning Company. Ail 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. UNIVERSITY OF SOUTHERN CALIFORNIA THE GRADUATE SCHOOL UNIVERSITY PARK LOS ANGELES. CALIFORNIA 9000? This dissertation, w ritten by ..JLjC under the dirf&ion of h..l$._ _ Dissertation Committee and approved by all its members* has been presented to and accepted by The Graduate School, in partial fulfillm ent of re quirements for the degree of DOCTOR OF PHILOSOPHY Dean of Graduate Stadia Date t.J.,..2001 _ [ON COMMTTTEE D IS S 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. To my father: I wish you were here, but I know you see this. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Acknowledgements I would like to start by thanking my advisor, Professor Tom Flood, for providing an intellectually rich and stimulating environment for research and graduate study. His rare blend of curiosity, intensity, and personableness made working with him exciting. I feel I have grown immensely as a chemist under his mentoring and, perhaps, I have not thanked him enough for this experience. Further, I also thank his group members, both current and past: Dr. Hongshi Zhen, Dr. Masanori Iimura (Mas), Paul Boothe, and Patrick Vagner. The group environment has always been one that includes open discussion on a variety of topics, making it an enjoyable place to work each day. Special thanks is necessary for Mas. I greatly appreciated working with him and learning from him over the years. Further, his immense enthusiasm for chemistry and overall energy was invigorating. Additional thanks goes to Dr. Jonathan Sargent. I greatly appreciate his friendship and the late night drinks after long hours in the lab. Finally, special thanks goes to my family for their continued support throughout the years and to my fiancee, Shannon, for her love and immense patience. 1 1 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table of Contents Page Acknowledgements iii List of Schemes vii List of Figures ix List of Tables xi Abstract xv Introduction 1 1 .1 Background: Alkane Activation and Functionalization 1 1.2 Alkane a-Complexes as Intermediates in Alkane Activation 6 1.3 Alkane Activation and cr-Complexes Within a Hard-Ligated Rhodium System 8 Endnotes 10 Chapter 1: Alkane Reductive Elimination in a Hard-Ligated 12 Rhodium Complex 1.1 Synthesis of Metal Alkyl Hydrides 12 1.2 Spectroscopic Characterization 17 1.3 Reactions of Metal Alkyl Hydrides 32 1.3.1 Thermolysis of Alkyl Hydrides: Alkane Reductive Elimination 32 1.3.2 Benzene Independent Alkane Elimination 34 1.3.3 Phosphite Independent Alkane Elimination 35 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.3.4 Effect of the Anion Upon Alkane Elimination 37 1.4 Discussion and Conclusion 38 Endnotes 42 Chapter 2: 2 H Migration in [CnRh(R)(D)(P(OMe)3)]+ : Evidence for the Mobility of Rhodium Along Alkanes via Alkane cr-Complexes 43 2.1 Introduction 43 2.2 Synthesis of Metal Alkyl Deuterides 44 2.3 Spectroscopic Characterization 46 2.4 Reactivity of Metal Alkyl Deuterides 46 2.4.1 Metal< - ► Alpha Deuterium Exchange: Kinetics of Equilibration 46 2.4.2 Alpha*-»Omega Migration: Deuterium Migration to the Terminal Methyl Group in Linear Alkanes 50 2.4.3 Deuterium Migration in the Cycloalkyl Derivatives 55 2.5 Discussion 57 2.5.1 Mechanism of Metal«-»Alpha Deuterium Exchange 57 2.5.2 Mechanism of Alpha+-+Omega Deuterium Exchange: Evaluation of a P-Hydride Elimination Pathway 60 2.5.3 Mechanism of Alpha«-»Omega Deuterium Exchange: Inter- vs. Intra-molecular Migration 62 2.5.4 Mechanism of Alpha«-*Omega Deuterium Exchange: Evaluation of and “End-to-End” and “Tail-to-Head” Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Mechanism 64 2.5.5 Mechanism of Alpha«->Omega Deuterium Exchange: Deuterium Exchange via Metal-Methylene o-Alkane Interactions 68 2.5.6 Mechanism of Alpha*-»Omega Deuterium Exchange: Modeling 2°<-»2° Migrations via Cycloalkyl Analogs 73 2.6 Mechanism of Alpha<-»Omega Deuterium Exchange: Final Considerations and Conclusions 77 Endnotes 81 Experimental 83 General Considerations 83 Synthetic Procedures 84 Alkyl Lithium Reagents 84 Synthesis of Decane-d6 88 Synthesis of Organometallic Rhodium Complexes 89 Kinetic Experiments 140 General Considerations and Procedures 140 Alkane Elimination Data 151 Deuterium Migration/Exchange Data 186 Endnotes 206 Bibliography 207 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. List of Schemes Paj Introduction Scheme I Cyclohexane Elmination: Cp* Ir(PMe3)(cyclohexyl)(H) 3 Scheme II Catalytic Borylation 5 Scheme III Deuterium Migration: Cp*Rh(PMe3 )(D)(1 3 CH2 CH3) 7 Chapter 1 Scheme I.I CnRhR3 Synthesis 13 Scheme I.II [CnRh(n-R)(H)(P(OMe)3 ]OTf Synthesis 14 Scheme I.III CnRh(c-Pentyl)(Cl)(OTf) Synthesis 15 Scheme I.IV Fischer Projections of [CnRh(c-Pentyl)(H)(P(OMe)3]+ 25 Scheme I.V Benzene Reaction 33 Scheme I.VI Phosphite Independence 36 Scheme I.VII Anion Dependence 38 Chapter 2 Scheme II.I Metal*-> Alpha 2 H Exchange 48 Scheme II.II Macroscopic Model for Alpha«-»Omega Deuterium Isomerization 54 Scheme II.III Alpha Elimination Mechanism 57 Scheme II.IV Alpha Elimination Mechanism: Nitrogen Dissociation 58 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Scheme II. V Metal*-*Alpha 2 H Exchange via a c-Complex Intermediate 60 Scheme II.VI Alpha*-*Omega Isomerization via P-Hydride Elimination/Insertion 61 Scheme II.VII Decane-d6 Competition Experiment: 2 H NMR 65 Scheme II. VIII “End-to-End” Mechanism for Alpha*-*Omega Isomerization: Butyl Derivative 66 Scheme II.DC Pseudo-Metallacycle Transition State 67 Scheme II.X Alpha*-*Omega Isomerization via Alkane 69 cr-Complexes Scheme II.XI Sterics in 2° Linear Alkyl Hydride vs. Cyclopentyl Hydride 76 Scheme II.XII Alpha*-*Omega Isomerization via 1,3- and 1,4-shifts 78 Scheme II.XIII Model for Determining 1,2-shifts of a-Complexes vs. 1,3-and 1,4-shifts 79 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. List of Figures Page Chapter 1 Figure I.I [CnRh(butyl)(H)(P(OMe)3 )]O T f‘ H NMR 19 Figure I.II [CnRh(butyl)(HXP(OMe)3 )]OTf HQMC 20 Figure I.III [CnRh(c-C5 H9 )(H)(P(OMe)3 )]OTf HQMC 22 Figure I.IV [CnRh(c- C5 H9 )(H)(P(OMe)3 )]OTf COSY90 23 Figure I.V [CnRh(c- C5 H9)(H)(P(OMe)3 )]OTf COSY45 26 Figure I.VI [CnRh(c- C5 H9 )(H)(P(OMe)3 )]OTf NOESY: Hydride Correlations 30 Figure I.VII [CnRh(c- C5 H9 XHXP(OMe)3)]OTf NOESY: Alkyl/N-H Correlations 31 Chapter 2 Figure II.I Macroscopic Fit of Metal« - ► Alpha 2 H Exchange: [CnRh(hexyl)(D)(P(OCD3 )3 )]+ 49 Figure II.II 2H NMR: Butyl Alpha<-»Omega Isomerization 51 Figure II.Ill 2 H NMR: Hexyl Alpha<-»Omega Isomerization 53 Figure II.IV Macroscopic Fit: Butyl Alpha<-*Omega Isomerization 55 Figure II.V Macroscopic Fit: 2 H Rearrangement in [CnRh(c-C5 H9 )(D)(P(OCH3 )3 ) f 56 Figure II.VI Microscopic Fit: Butyl Alpha«->Omega Isomerization 74 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Experimental Figure III.I Figure III.II Figure III.III Figure III.IV Figure III.V Figure III .VI Figure III.VII Figure III.VIII Apparatus for NMR Tube Used for High Temperature Kinetics in the NMR Probe 142 2 H Migration in [CnRh(butyl)D(P(OMe)3)]BAr4 f: Plot of theData Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 39.6 °C 188 2 H Migration in [CnRh(hexyl)D(P(OMe)3)]Ar4 f: Plot of theData Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 39.6 °C. 189 2 H Migration in [CnRh(hexyl)D(P(OMe)3)]BAr4f: Plot of theData Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 50.2 °C. 192 2 H Migration in [CnRh(hexyl)D(P(OMe)3)]BAr4f: Plot of theData Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 60.7 °C. 195 2 H Migration in [CnRh(decyl)D(P(OMe)3)]BAr4 f: Plot of theData Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 39.6 °C. 198 2 H Migration in [CnRh(c- CsH9)D(P(OMe)3)]BAr4 f: Plot of theData Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 39.6 °C. 201 Metal«-»Alpha 2 H Exchange in [CnRh(hexyI)D(P(OMe)3)]OT f: Plot of the Data Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 4.7 °C. 205 x Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. List of Tables Page Chapter I Table I.I Rates of Methane Reductive Elimination 32 Table I.II Activation Parameters for Alkane Loss 34 Chapter 2 Table II.I Energetic Barriers and Rate Constants for Microscopic Fit of Deuterium Migration in [CnRh(butyl)(D)(P(OMe)3 )]BAr4 f 70 Experimental Table III.I Ethane Elimination: Arrhenius Plot 151 Table III.II Ethane Elimination @ T = 89.7 °C 152 Table III.III Ethane Elimination @ T = 68.3 °C 153 Table III.IV Ethane Elimination @ T = 60.2 °C 154 Table III.V Ethane Elimination @ T = 50.1 °C 155 Table III. VI Ethane Elimination @ T = 40.2 °C 156 Table III.VII Butane Elimination: Arrhenius Plot 157 Table III.VIII Butane Elimination @ T = 80.0 °C 158 Table III.IX Butane Elimination @ T = 69.4 °C 159 Table III.X Butane Elimination @ T = 69.4 °C: 80/20 (v/v) CeDe/CeFe 160 Table III.XI Butane Elimination @ T = 69.4 °C: excess P(OCD3>3 161 xi Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XII Butane Elimination @ T = 60.5 °C 162 Table III.XIII Butane Elimination @ T = 49.5 °C 163 Table III.XIV Butane Elimination @ T = 39.5 °C 164 Table III.XV Hexane Elimination: Arrhenius Plot 165 Table III.XVI Hexane Elimination @ T = 83.0 °C 166 Table III.XVII Hexane Elimination @ T = 69.6 °C 167 Table III.XVIII Hexane Elimination @ T = 69.6 °C: 80/20 (v/v) C6F6/C6D6 168 Table III.XIX Hexane Elimination @ T = 69.6 °C: 80/20 (v/v) CelVQHs 169 Table III.XX Hexane Elimination @ T = 60.3 °C: -A = -BAr/ 170 Table III.XXI Hexane Elimination @ T = 60.3 °C: A = OTf 171 Table III.XXII Hexane Elimination @ 60.2 °C: A = O2CCF3 172 Table III.XXIII Hexane Elimination @ T = 49.4 °C 173 Table III.XXIV Hexane Elimination @ T = 37.6 °C 174 Table III.XXV Cyclopentane Elimination: Arrhenius Plot 175 Table III.XXVIA Cyclopentane Elimination @ T = 60.5 °C: Method A 176 Table III.XXVIB Cyclopentane Elimination @ T = 60.5 °C: Method B 177 Table III.XXVII Cyclopentane Elimination @ 50.2 °C 178 Table III.XXVIII Cyclopentane Elimination @ T = 39.6 °C 179 Table III.XXIX Cyclopentane Loss @ T =39.6 °C: excess P(OCD3>3 180 Table III.XXX Cyclohexane Elimination: Arrhenius Plot 181 Xll Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXXI Cyclohexane Elimination @ 68.5 °C 182 Table III.XXXII Cyclohexane Elimination @ 50.2 °C 183 Table III.XXXIII Cyclohexane Elimination @ T = 50.5 °C: 80/20 (v/v) CtFe/QDs 184 Table III.XXXTV Cyclohexane Loss @ T = 39.6 °C 185 Table III.XXXV [CnRh(butyl)(D)(P(OMe)3 )]BAr4 f 2H Data: Alpha*->Omega Migration @ T = 39.6 °C 186 Table III.XXXVI [CnRh(butylXD)(P(OMe)3 )]BAr4 f 2 H Data: Alkane Elimination @ T = 39.6 °C 187 Table III.XXXVII [CnRh(hexyl)(D)(P(OMe)3 )]BAr4 f 2 H Data: Alpha<-»Omega Migration @ T = 39.6 °C 189 Table ni.XXXVIII [CnRh(hexyl)(D)(P(OMe)3 )]BAr4 f 2 H Data: AIpha«-»Omega Migration @ T = 50.2 °C 190 Table III.XXXDC [CnRh(hexyl)(D)(P(OMe)3 )]BAr4f 2 H Data: Alkane Elimination @ T = 50.2 °C 191 Table III.XXXX [CnRh(hexyl)(D)(P(OMe)3 )]BAr4 f 2 H Data: Alpha«-»Omega Migration @ T = 60.7 °C 193 Table III.XXXXI [CnRh(hexyl)(D)(P(OMe)3 )]BAr4f 2 H Data: Alkane Elimination @ T = 60.7 °C 194 Table III.XXXXII [CnRh(decyl)(D)(P(OMe)3 )]BAr4 f 2 H Data: Alpha«-»Omega Migration @ T = 39.6 °C 196 Table IILXXXXffl [CnRh(decyl)(D)(P(OMe)3 )]BAr4 f 2 H Data: Alkane Elimination @ T = 39.6 °C 197 Table III.XXXXrVJCnRh(c-C5 H9)(D)(P(OMe)3)]BAr4f 2 H Data: Deuterium Migration @ T = 39.6 °C 199 Table III.XXXXV rCnRh(c-C5 H9)(D)(P(OMe)3 )]BAr4f H Data: Alkane Elimination @ T = 39.6 °C 200 Table III.XXXXVI [CnRh(c-C6HnXDXP(OMe)3 )]BAr4f 2 H Data: Deuterium Migration @ T = 39.6 °C 202 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXXXVII rCnRh(c-C6Hn)(D)(P(OMe)3)]BAr4f H Data: Alkane Elimination @ T = 39.6 °C 203 Table III.XXXXVIII [CnRh(hexyl)(D)(P(OMe)3 )]BAr4 f 2 H Data: Metal<-»Alpha Deuterium Exchange @ T = 4.7 °C 204 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Kevin E. Janak Dr. Thomas C. Flood ABSTRACT C-H BOND ACTIVATION: INVESTIGATION INTO THE DYNAMICS AND ENERGETICS OF ALKANE COMPLEXES WITHIN A HARD-LIGATED RHODIUM SYSTEM The alkyl hydride complexes, [CnRh(R)(H)(P(OMe)3)]A (Cn = 1,4,7- triazacyclononane; R = Et, Bu, hexyl, decyl, cyclopentyl, and cyclohexyl; A = ' O3SCF3 fOTf), *BAr4 f, and -C > 2CCF3, where *BAr4f is tetrakis(3,5-trifluoromethyl- phenyl)borate), were prepared in 21-32% overall yields from RhCl3(H2 0 )„. The complexes were fully characterized. In benzene at temperatures ranging 38-90 °C, these alkyl hydrides react with clean first-order kinetics and quantitative formation of the benzene C-H activated product, [CnRh(C6HsXH)(P(OMe)3)]BAr4f. Arrhenius plots of the benzene reaction give AH* ranging from 27.8 to 34.8 kcal/mol and AS* from 5.6 to 25.8 eu. The reaction rates of the Et, Bu, hexyl, and decyl derivatives are similar, while the cyclopentyl and cyclohexyl complexes eliminate alkane at a rate - 2 x faster. The deuterated analogues, [CnRh(R)(D)(P(OMe)3)]BAr4 f, all exhibit deuterium exchange into the (X-CH 2 (R = Et, Bu, hexyl, and decyl) and the a-CH (R = cyclopentyl, and cyclohexyl) sites significantly faster than the rate of alkane loss. The rate of migration of deuterium to the a-carbon of [CnRh(CHD(CH2 )4 CH3 )(HXP(OCD3 )3)]+ at 4.7 °C (ka = 4.3 x 10" s* 1 ) is comparable to the rate of formation of [CnRh(CH2(CH2)4 CH3)(D)(P(OCD3)3)]+ xv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (kform ['BD4] = 6.6 x 10'5 s'1 ), with the equilibrium constant, K R h H /R h D , close to 1.7. In the linear alkyls at 40 °C, deuterium was found to migrate to the terminal methyl group at rates faster than alkane elimination. The macroscopic rate constants (k < a) decrease with increasing chain length, with k < o = 5.9 x 10"6 s'1 for R = Bu, 3.8 x 10"6 s'1 for R = hexyl, and 3.0 x K T 6 s* 1 for R = decyl. In the cycloalkyls, deuterium exchanges into other methylene sites, but at rates slower than alkane loss (kp = 5.2 x N T6 s'1 vs. k io ss = 7.2 x 1 0 "6 s'1 for R = cyclopentyl). Competition experiments indicate that the process is intramolecular. The mechanism of deuterium migration is postulated to involve alkane c-complex intermediates, whereby the rhodium metal center interacts with the methyls and methylenes of the alkane to effect rearrangement. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Introduction 1.1 Background: Alkane Activation and Functionalization The activation and functionalization of alkanes is possibly one of the most significant and challenging problems within organotransition metal chemistry.1 The ever-growing human population continues to put significant demands upon the world’s energy supply. Although interest continues to grow in renewable energy sources, non-renewable fossil fuels still remain our primary source of energy. Nonetheless, there exist significant deposits of fuel sources, such as methane, that remain relatively untapped. This is due to both the cost of mining and transporting such fuels in areas of difficult terrain and, in a related sense, the limited ability to efficiently transform these abundant feedstocks into value-added fuels. For example, the present methodology for conversion of methane to methanol or higher order alkanes involves a process whereby methane is initially oxidized and the mixture of carbon monoxide and hydrogen gas generated (“syngas”) is subsequently reduced to higher order organics via Fischer-Tropsch catalysts.2 Ultimately, direct conversion of methane to methanol, or selective oxidation of higher order alkanes, would streamline these processes and significantly reduce methane waste associated with such production. However, such functionalization is inherently difficult. The strong C-H bonds of alkanes (e.g., BDE -104 kcal/mol for methane, -98 kcal/mol for ethane)3 mean that the low-lying HOMO o-orbitals and high-lying LUMO o*-orbitals make these bonds relatively difficult to functionalize. Although radical functionalization 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. methods are known, they suffer from both lack of selectivity as well as the difficulty of large scale application of such techniques. Hence, the desire for greater efficiency and selectivity in alkane functionalization, in conjunction with the overall world energy demand, has contributed to the considerable growth of research concerning alkane activation with organometallic transition metal complexes over the past 25 years.2 Beginning with the earliest example of C-H activation of naphthalene by a ruthenium complex,4 significant efforts have been made to understand the factors that affect the interactions and reactions of alkanes with transition metal centers. As early as the 1970s, alkanes were observed to complex to transition metal complexes in low temperature matrices.5 These low temperature matrix isolation methods have been used to detect the relative binding ability of different alkanes. For instance, in the photogeneration of (CO)sW in the presence of alkanes in matrix, the tungsten complex was found to bind a series of alkanes, whereby the relative metal-alkane bonding interactions were found to increase with the size of the alkane.6 Similarly, a discrete complex was also found to form between methane and Co atoms in an argon matrix.5 In spite of the fundamentally interesting and important nature of these findings, reactions with the alkanes in the metal carbonyl complexes were not observed. In the early 1980s, however, new research developed in several groups that began to provide credence for the potential development of homogeneous systems that could functionalize alkanes. Seminal work in this area was done by 2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Bergman and Graham, who were among the first to report examples in which the C-H activated product of alkane reduction, metal alkyl hydrides, were directly observed.7 In Bergman’s system, for example, photolysis of Cp*Ir(PMe3)(H) 2 resulted in dihydrogen reductive elimination, followed by oxidative addition of both linear and cyclic alkanes. Graham’s Tp*Rh(CO) 2 system (Tp* = tris(dimethyl- pyrazolyl)borate) was shown to oxidatively add cyclohexane and methane upon photolytic extrusion of carbon monoxide.8 However, this latter reaction suffered from low yield as well as unstable metal alkyl hydride products. Eventually, the discovery of thermal methane activation was made by Bergman. Oxidative addition of methane was observed following reductive elimination of cyclohexane from a Cp*Ir(PMe3)(cyclohexyl)(H) precursor under a methane atmosphere. (Scheme I) This reaction was proposed to occur via initial generation of a highly reactive intermediate, Cp*Ir(PMe3), which subsequently inserted into the C-H bonds of methane. Similar results in other systems followed. For instance, thermal C-H activation of methane was found to occur upon elimination of neopentane at 80 °C from (Me3P)4 0 s(H)(neopentyl) . 9 Generation of a highly reactive Os(0) complex, (Me3P)3 0 s, was proposed as the intermediate that oxidatively added methane. Scheme I 3 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. While the previous studies focused on the nuances of metal-alkane interactions and C-H oxidative addition, other studies have focused on alkane functionalization. In one of the earliest systems exhibiting methane functionalization, Shilov showed that Pt(II) salts catalytically covert methane to methanol and methyl chloride.1 0 Studies on Pt(II) systems designed to model the Shilov system have elucidated significant details concerning this mechanism, revealing that a Pt(IV) intermediate is generated via methane C-H activation.1 1 The design of the experiments involved the microscopic reverse of methane oxidative addition: methane reductive elimination. The existence of such Pt(IV) intermediates was confirmed via generation of (tmeda)Pt(H)(CH3)2(Cl) by protonation of (tmeda)Pt(CH3 )2 in MeOH with anhydrous HCl. It was reported that the chloride, which lies trans to the hydride, dissociates prior to methane loss. Importantly, conducting the reaction in MeOH-d4 revealed that the full range of methane isotopomers was produced upon methane eliminaton. Other examples of methane functionaliztion via soluble transition metal complexes also exist. As a recent example, catalytic conversion of methane to methyl sulfates was achieved using bipyridine-based Hg and Pt salts in fuming sulfuric acid.1 2 The high product conversions and negligible overoxidation within this system makes it one of the most efficient to date. However, isolation of the products proved too difficult to make this a useful method for catalytic methane functionalization. 4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The catalytic functionalization of higher order alkanes has also been achieved with moderate success.1 3 As shown in scheme II, borylation of the alkane by the Cp*RJi(r|4 -C6Me6) catalyst occurs regiospecifically. Decent catalytic turnovers and yields were reported, with the octylboronate ester obtained in 88% yield (determined via GC) after a period of 25 hours. Control experiments suggested that the selectivity at the terminal methyl groups arises from kinetic factors that favor the terminal positions over the internal methylenes. Hence, the terminal product is not formed from rearrangement of an initially formed internal alkylboronate ester. Cp*RK ii4 - C 6 M e 6 ) 5 mol% H2 Scheme II Although progress has been made towards achieving the goal of catalytic alkane functionalization, more efficient systems still need to be developed. This can primarily be achieved via a rational catalyst design, based upon knowledge gained about the intricacies of how alkanes interact with transition metals. In fact, the previously mentioned examples benefited greatly from earlier studies involving the 5 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. oxidative addition and reductive elimination of alkanes from soluble transition metal complexes. 1.2 Alkane o-Complexes as Intermediates in Alkane Activation As previously mentioned, alkanes have been found to act as ligands in the presence of transition metal fragments photochemically generated in low temperature matrices. Subsequent studies have indirectly revealed that such alkane cr-complex intermediates exist on the reaction coordinate of alkane C-H activation. Most of these systems involve studying the reductive elimination of alkanes, the microscopic reverse of alkane oxidative addition. For instance, Jones found that in Cp*Rh(PMe3)(Me)(D), deuterium exchanged into the methyl ligand prior to methane elimination at -20 °C.1 4 However, because exchange occurred during the synthesis of the compound, a rate for deuterium incorporation was not obtained. Similarly, deuterium incorporation into the methyl group occurred prior to methane elimination in (Cp*)2W(CH3)(D) . 15 In this system, reductive elimination of CH4 and CD4 revealed an inverse kinetic isotope effect (kn/ko = 0.70 (7) at 100 °C). Such an inverse kinetic isotope effect has been found in other systems as well.1 6 ,1 8 Although potentially explained by a concerted, single-step elimination, wherein the product possesses a very strong vibrational force constant compared to the reactant, and the transition state is late (i.e., productlike), such an effect may also arise when the reaction proceeds stepwise, via an intermediate, prior to the rate-determining step.1 7 In the latter case, the kinetic deuterium isotope effect for the entire reaction will be a 6 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. composite of the thermodynamic isotope effect for the preequilibrium and the kinetic deuterium isotope effect for the rate-determining step. An inverse thermodynamic isotope effect and a late transition state account for the net kn/ko <1. Ultimately, the existence of a methane a-complex in equilibrium with the methyl hydride complex has been postulated as the source of this effect. Studies with Cp*Rh(PMe3)(Et)(H) resulted in the postulate that alkane a- complexes may form with higher order alkanes.1 8 In the rhodium complex, Cp*Rh(PMe3)(1 3 CH2CH3)(D), deuterium exchanged with the protons on the l3 C carbon at a rate faster than elimination at -60 °C. However, upon warming to -30 °C, the l3 C label was found to exchange into the methyl position. Importantly, deuterium migrated concomitantly with t3C migration (Scheme III). The mechanism — — J. -60 °c r -30 °c T MejP^ ( D " MesP^ i " H " '» 1 3 C H 2C H 3 1 3 C H (D )C H 3 C H 21 3 C H 2(D ) CH31 3 CH2 (D) Scheme III of the observed migrations was explained involve via preequilibrium formation of a Cp*Rh(PMe3)(1 3 C-ethane-di) a-complex intermediate, which could either dissociate ethane or undergo oxidative addition of ethane at either terminus. Oxidative addition at the non-labeled methyl terminus results in the I3 C-D migration. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. U Alkane Activation and a-Complexes within a Hard-ligated Rhodium System All of the aforementioned systems involve soft ligands (i.e., polarizable, tt- acidic) such as Cp*. Tp*, CO, and PMe3 . 19 Further, the complexes studied in the thermal reactions either tend to be very unstable (e.g, Cp*Rh(PMe3)(R)(H)) or require more extreme conditions for reactivity (e.g., Cp*Ir(PMe3)(R)(H)). In an effort to enhance the stability of metal alkyl hydrides while maintaining a moderate temperature range in which to observe metal-alkane interactions, our group has developed chemistry involving the Cn/Cn*M system (Cn = 1,4,7-triazacyclononane; Cn* = l,4,7-trimethyl-l,4,7-triazacyclononane; M = Rh, Ir) . 20 Further, due to fact that amines are good a-donors and poor n-acceptors, the metal environment is “harder” , 21 allowing for systematic “tuning” of the electronic nature of the metal center via the other ancillary ligand. The [Cn*Rh(PMe3)(Me)(H)]+ 'BAr4f complex ("BAr/ = tetrakis(3,5- trifluoromethylphenyl)borate) was the first rhodium methyl hydride complex that was stable to methane loss at room temperature. 200 Methane was found to reductively eliminate with clean first-order kinetics at 75 °C and a ti/2 =91 minutes. Further, a kn/ko = 0.74 (2) was observed for the loss of CH4 vs. CD4 . More significantly, the [Cn*Rh(PMe3)(Me)(D)]+ *BAr4f complex was found to exchange deuterium into the methyl subunit at 50 °C, resulting in an equilibrium ratio of RhH/RhD = 6.59 (6 ) in less than 6 hours. Also, although reversible activation of 13CH4 was observed in the absence of benzene, no 1 3 C incorporation into the starting 8 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. methyl hydride complex was observed in a C6D6/C6F6 mixed solvent system. Taken together, these observations were rationalized by a mechanism involving a preequilibrium between the starting methyl hydride and a methane a-complex, with rate-determining dissociation of methane. The unusual stability of this methyl hydride complex led to the pursuit of higher order alkyl hydride complexes, with the hope of gaining information about the structure, bonding, energetics, and dynamical properties of alkanes within this unique organometallic coordination environment. Specifically, a series of alkyl complexes, [CnRh(R)(X)(P(OMe)3)]+ *A (R = -ethyl, -butyl, -hexyl, -decyl, -cyclopentyl, and -cyclohexyl; A = O3SCF3, H A r/, and "ChCCFs; X = H, D, when " A = O3SCF3, T3Ar4f ), have been synthesized and their reactions in benzene solvent and relative aptitudes for deuterium rearrangement studied. The ensuing chapters report on the recent progress of this pursuit, with part of the contents already having been communicated. 22 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Endnotes 1 See Chapter 2, reference lb. 2 Selected reviews: (a) Crabtree, R. H. Chem. Rev. 1995, 95, 987. (b) Arakawa, H.; Aresta, M.; Armor, J. N.; Barteau, M. A.; Beckman, E. J.; Bell, A. T.; Bercaw, J. E.; Creutz, C.; Dinjus, E.; Dixon, D. A.; Domen, K.; DuBois, D. L.; Eckert; Fujita, E.; Gibson, D. H.; Goddard, W. A.; Goodman, D. W.; Keller, J.; Kubas, G. J.; Kung, H. H.; Lyons, J. E.; Manzer, L. E.; Marks, T. J.; Morokuma, K.; Nicholas, K. M.; Periana, R.; Que, L.; Nielson, J. R.; Sachtler, W. M. H.; Schmidt, L. D.; Sen, A.; Somoijai, G. A.; Stair, P. C.; Stults, B. R.; Tumas, W. Chem. Rev. 2001,101,953, and references therein, (c) Chapter 2, reference 1. 3 Morrison, R. T.; Boyd, R. N., Organic Chemistry, 4lh Ed., Allyn and Bacon, Inc.: Boston, 1983. 4 Chatt, J.; Davidson, J. M. J. Chem. Soc. 1965, 843. 5 (a) Graham, M. A.; Perutz, R. N.; Poliakoff, M.; Turner, J. J. J. Organometal. Chem. 1972, 34, C34. (b) Perutz, R. N.; Turner, J. l.J. Am. Chem. Soc. 1975, 97,4791. 6 Brown, C. E.; Ishikawa, Y.; Hackett, P. A.; Rayner, D. M. J. Am. Chem. Soc. 1990,112,2530. 7 (a) Janowicz, A. H.; Bergman, R. G. J. Am. Chem. Soc. 1982,104,352. (b) Hoyano, J. K.; Graham, W. A. G. J. Am. Chem. Soc. 1982,104,3723. 8 Ghosh, C. K.; Graham, W. A. G. J. Am. Chem. Soc. 1987,109,4726. 9 Harper, T. G. P.; Shinomoto, R. S.; Deming, M. A.; Flood, T. C. J. Am. Chem. Soc. 1988,110, 7915. 1 0 Hill, C. L., Ed., Activation and Functionalization o f Alkanes; John Wiley & Sons, Inc.: New York, 1989. 1 1 Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 19%, 118,5961. 1 2 Periana, R. A.; Taube, D. J.; Evitt, E. R.; Loffler, D. G.; Wentrcek, P. R.; Voss, G.; Masuda, T. Science 1993,259, 340. 1 3 (a) Chen, H. Y.; Hartwig, J. F. Angew. Chemie, Int 7 Ed. 1999, 38,3391. (b) Chen, H. Y.; SchJecht, S.; Semple, T. C.; Hartwig, J. F. Science 2000,287, 1995. (c) Waltz, K. M.; Hartwig, J. F. J. Am. Chem. Soc. 2000,122, 11358. 1 4 Jones, W. D.; Feher, F. J. J. Am. Chem. Soc. 1984,106, 1650. 1 5 Parkin, G.; Bercaw, J.E. Organometallics 1989,8 , 1172. 1 6 Buchanan, J. M.; Stryker, J. M.; Bergman, R. G. J. Am. Chem. Soc. 1986,108, 1537. * ' (a) see reference 15. (b) Bigeleisen, J. Pure Appl. Chem. 1964, 8 ,217. 1 8 Periana, R. A.; Bergman, R. G.J. Am. Chem. Soc. 1986,108, 1537. 1 9 Attempts at comparison between Tp/Tp* and Cp/Cp* have been made (see following references). Although potentially “harder” than Cp/Cp*, Tp/Tp* would appear to have relatively lower lying n 10 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. molecular orbitals than Cn/Cn*, thereby making it “softer” than the Cn/Cn* ligands, (a) Rflba, E.; Simanko, W.; Mereiter, K.; Schmid, R.; Kirchner, K. Inorg. Chem. 2000,39 ,382. (b) Tellers, D. M.; Skoog, S. J.; Bergman, R. G.; Gunnoe, T. B.; Hannan, W. D. Organometallics 2000,19,2428 and references therein. 2 0 (a) Wang, L.; Flood, T. C. J. Am. Chem. Soc. 1992,114,3169. (b) Wang, L.; Lu, R. S.; Bau, R.; Flood, T. C. J. Am. Chem. Soc. 1993, 115,6999. (c) Wang, C.; Ziller, J. W.; Flood, T. C. J. Am. Chem. Soc. 1995,117, 1647. (d) Zhou, R_; Wang, C.; Hu, Y.; Flood, T. C. Organometallics 1997,16, 434. (e) Zhen, H.; Wang, C.; Hu, Y.; Flood, T. C. Organometallics 1998,17, 5397. (0 Flood, T. C.; Iimura, M.; Perotti, J. P. J. Chem. Soc. Chem. Comm. 2000, xr, xxxx. 2 1 Wang, L.; Sowa Jr., J. R.; Wang, C.; Lu, R. S.; Gassman, P. G.; Flood, T. C. Organometallics 1996, 15,4240. XPS data revealed that a triphos analog to Cn*, P3 (P3 = MeC(CH2PMe2)3 ), makes Rhm a softer metal in comparison to the Rhm in the Cn* ligated environment. 2 2 Flood, T. C.; Janak, K. E.; Iimura, M.; Zhen, H. J. Am. Chem. Soc. 2000, 122, 6783. 11 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chanter 1 Alkane Reductive Elimination in a Hard-Ligated Rhodium Complex 1.1 Synthesis of the Metal Alkyl Hydrides The synthetic methodology for obtaining the desired rhodium alkyl hydrides was developed extensively by former group members. 1 Nonetheless, minor modifications to the overall preparation were necessary in order to maximize the yield of each specific complex. First of all, for the synthesis of the trialkyl complexes (Scheme I.I), CnRhRj, it was found that the amount of excess acid (MeOH) and the temperature of the protonation were important factors to control in order to maximize yields. For example, in a typical experiment, -3 Vz hours was allowed for alkylation of the rhodium. Then, the solution was cooled to -78 °C and excess MeOH (typically 13 equivalents) was added dropwise to the reaction mixture. The amount of MeOH used dramatically affected the yields of the desired CnRhR3. Too large an excess resulted in significantly lower yields (-10-15% vs. 38-67%). Further, after addition of methanol, stirring commenced for approximately twenty minutes at -78 °C. Then, the solution was allowed to warm only to 0 °C, with stirring continuing for another twenty minutes. Allowing the solution to reach ambient temperature resulted in significantly lower yields. Hence, removal of solvent in vacuo was also done at 0 °C. After isolation of the crude product as a powder, however, further 12 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i) 10 RLi, Et2 Oor THF; -78 °C - RT ii) 10 MeOH; -78 °C - 0 °C HNk A / /V - R R R R = -Et, -Bu, -hexyl, -decyl, -cyclopentyl, -cyclohexyl Scheme I.I work-up at ambient temperature was possible, with no noticeable decomposition of the desired products. The desired linear alkyl hydrides were synthesized using previously P(OMe>3 for use in the ensuing studies was affected primarily by the ability to obtain the corresponding [CnRh(R)(H)(P(OMe)3]+ 'A (where A = ‘OTf, UAr/, ‘ 0 2CCF3, and R = ethyl, butyl, hexyl, decyl, cyclopentyl, cyclohexyl) in consistently moderate yields. The use of other ligands, such as PMe3, resulted in inconsistent and low yields (or none at all) of the corresponding alkyl hydrides, even with numerous hydride sources (e.g., NaBH4, LiBFLj, Me4NBH4, LiB(H)Et3 , [Cp2ZrH2 ]2 , Cp2Zr(H)Cl, NaBH4/H 0 2CCF3 , NaB(H)(OMe)3 , and NaAl(H)2(OCH2CH2OCH3)2). Ultimately, this bit of serendipidity resulted in numerous exciting observations and experiments. An adaptation of the synthetic procedure was necessary in order to obtain the cycloalkyl hydride derivatives. Initial attempts at synthesizing CnRh(c-CsH9)OTf2 failed, with each attempt resulting in a complex, unidentified mixture of products. developed procedures (Scheme I.II).lc ,d The choice of the fairly soft, n-acidic 13 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 HOTf; CH2C12 -78 °C -> 0 °C •‘ R h - o i f R OTf R = -ethyl, -butyl, -hexyl, -decyl (MeO)3P N aB H j (or NaBD4),THF -78 °C — > RT, overnight * (M tO)Jp/ V R 'H (D ) Scheme I.n In order to determine whether the acid cleavage was feasible, the analogous CnRh(c- C5H9)C 1 2 complex was made using anhydrous HC1. Clean conversion to the fairly insoluble product was achieved in good yield (75%). Further transformation of this general type of complex (i.e., CnRh(R)Cl2 ) proved unsuccessful. For instance, addition of P(OMe) 3 to either a DMSO-d6 solution or THF slurry resulted in no formation of the desired [CnRh(R)(Cl)(P(OMe)3)]+ 'Cl. Additionally, heating a THF slurry of the dichloride in the presence of 5 equivalents of P(OMe) 3 at 50 °C for two weeks also resulted in no reaction. Other attempts at replacing the chloride ligand were also made. For example, two equivalents of Ag(OTf) were mixed with a dilute CD3 CN solution of the dichloride in a 5mm NMR tube. No reaction was observed, even upon heating at 60 14 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. °C for up to one week. A similar attempt in the presence of 2.5 equivalents of P(OMe)3 also yielded no reaction. Due to the overall difficulty in derivatizing the dichloride complexes, an alteration of this approach was made in order to obtain the desired [CnRh(c- CsH9)(H)(P(OMe)3)]+ 'A. To a solution of CnRhCc-CsH^, one equivalent of HC1 (via an anhydrous HCl/Et2 0 solution) was added. Immediately after addition, one equivalent of HOTf was added to the solution. This resulted in the desired CnRh(c- C5H9XCIXOTF) (Scheme I.III). Confirmation of the presence of only one triflate was made by dissolving 5.1 mg of the rhodium complex in DMSO-d6 along with 13.0 mg of NaBAr/as an internal l9 F standard. The expected ratio of'OTfTBAr/ was 1:1.4. A ratio of 1:1.41 was obtained via integration of the respective 1 9 F resonances. H C 1, HOTf i/v iu M H N -W ^ HN4h" / t ~ R .78°C->0°C / { - C l R R R OTf R = -cyclopentyl, -cyclohexyl Scheme I.III Although less soluble in THF than the linear alkyl ditriflate analogues, the CnRh(c-CsH9)(Cl)(OTf) could be dissolved. Upon addition of an equivalent of P(OMe>3 at room temperature and stirring overnight, the desired [CnRh(c- C5H9XCl)(P(OMe)3)]OTf was obtained in good yield (-85%). 15 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Further adjustments proved necessary in order to obtain the corresponding alkyl hydride. Reaction of [CnRh(c-C5H9)(Cl)(P(OMe)3)]OTf with 2.5 equivalents ofNaBK, in THF produced the alkyl hydride, [CnRh(c-CsH9)(HXP(OMe)3)]OTf, but in low to moderate yield. Significant formation of the known [CnRh(Fl)2(P(OMe)3)]OTf resulted, in addition to two unidentified products.2 The combination of the last three components comprised more than 75% of the isolated products. Various anempts at removing the unidentified products were unsuccessful. In order to circumvent the formation of these unknown species, the THF solvent was replaced with isopropyl alcohol. The synthesis of transition metal hydrides from alcoholic solutions is well precedented.3 This change proved fruitful, as the desired cyclopentyl hydride complex was isolated, with the only impurity being the previously mentioned dihydride. Although the procedure developed for the cyclopentyl hydride could be used in producing the cyclohexyl derivative, complications unique to this alkyl group arose that are worth mentioning. In the synthesis of [CnRh(c-C6Hn)(Cl)(P(OMe)3)] OTf, the known [Rh(P(OMe)3)s]+ also formed.4 Exact amounts of the [Rh(P(OMe)3)5]+ varied from one reaction to another, but it typically formed in an amount approximately equal to 5-25% of the isolated products. Confirmation of the identity of this component was obtained via independent synthesis and characterization of the [LsRhJBAr/ species (where L = P(OMe)3). Separation of this impurity from the desired product proved difficult, thus synthesis of the desired cyclohexyl hydride was commenced in the NaBftyi-PrOH 16 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. solution with the impurity present. This resulted in formation of the desired cyclohexyl hydride, the aforementioned rhodium dihydride, and the P(OMe)3 analogue of the known ((EtO)3P)4Rh(H) . 5 The latter compound was confirmed via its independent synthesis as well. Removal of the L»Rh(H) was achieved by washing the isolated mixture with 4 x 20 ml of pentane, since the compound is alkane soluble but the [CnRh(R)(H)(P(OMe)3)]+ *A salts are not. Ultimately, the isolated alkyl hydride complexes are stable at room temperature for up to approximately 3 Vz weeks in solution or the solid state without significant decomposition. However, for the purpose of accuracy, the compounds were typically used soon after synthesis for obtaining the kinetic information desired {vide infra). 1.2 Spectroscopic Characterization The most useful and convenient method for characterization of these organometallic compounds is NMR spectroscopy. It provides both significant structural information in solution, and convenient measurement of the rates of dynamic processes. All of the compounds were fully characterized by ‘H, l3C, l9F, and 3 1 P NMR (see Experimental Section), but only items of interest are discussed in detail in the ensuing section. The ‘H NMR spectrum of all of the[CnRh(R)(H)(P(OMe)3]A reveals a hydride resonance centered near -16.4 to -16.5 ppm in polar solvents such as DMSO-d6 , MeOH-d4 , or CD3CN. In C6D6, this resonance shifted upfield with the 17 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. degree of shift dependent upon the counter ion. For instance, when A = "BAr/ the chemical shift of the hydride is centered at -16.89 ppm. Yet, when A = OTf, there is a downfield shift of -0.2 ppm to -16.71 ppm, and when A = O2CCF3, the hydride resonance shifts further downfield to -16.39 ppm. For reasons that are made clear below, it was critical to make the 'H and 1 3 C NMR assignments for certain sites of the alkyl ligands of [CnRh(R)(H)(P(OMe)3] A. Specifically, it was imperative to ascertain which resonance(s) corresponded to the a-methylene (RI1-CH2), the internal methylenes, and the terminal methyl group (herein referred to as the C 0 -CH3). In MeOH-cfi, for every linear alkyl except ethyl, resonances occur at 0.88 ppm, 1.01 ppm, and at 1.25 ppm, with the resonances appearing as a triplet, a broad multiplet, and a larger, broad multiplet, respectively. Due to the chirality of the metal center, the alpha protons are diastereotopic, and are expected to exhibit different chemical shifts. In the butyl derivative, for instance, the two multiplets near 1.25 ppm overlap but appear to be in a ratio of 1:3 (Figure I.I). This initial observation seemed to indicate that the alpha protons overlapped with one of the internal methylene resonances. In the I3 C NMR, the a-carbon is clear, being a doublet of doublets due to coupling with I0 3 Rh and 31 P. Further, each carbon is unique and well separated from one another. Hence, a 'H-^C correlation experiment (HMQC) was conducted in order to assign all of the sites. MeOH-tLj was used since the greatest dispersion between the peak at 1 . 0 1 ppm and 0 . 8 8 pm was achieved in this solvent. The resonances shift in other solvents such as DMSO-cU or CD3CN, resulting in overlap of the two resonances. 18 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Alkyl Region in the spectrum o f [CnRh(butyl)(H)(P(OMe)3 ) f Figure I.I As shown in figure I.II, the broad multiplet at 1.01 ppm actually corresponds to the (X -CH 2, while the clearly diastereotopic resonances are one of the internal methylenes, either the P- or y-Cfb’s. The terminal methyl group was always clear, being a well-defined triplet at 0.88 ppm. This overall pattern was observed for the hexyl and decyl alkyl chains, with the only difference being the relative intensity of the broad peaks at 1.25, due to the increasing number of methylene units. 19 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 2 1 ppm 'H-'C Correlation: Butyl Derivative Figure I.n 20 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Similar assignments were required for the cyclopentyl and cyclohexyl derivatives. Interestingly, every carbon is unique in l3C spectrum of both of the cyclic alkyls, a consequence of the diastereotopism induced by the chiral rhodium center. In the cyclopentyl compound, the a-CH resonance in the *H spectrum was unambiguously assigned both via a ‘H-i3 C correlation experiment (Figure I.III) and the observation of deuterium in this site in the initially isolated deuteride species {vide infra). Each of the carbons in the cyclopentyl ring is assigned to a pair of protons, which show clear diasterotopic shifts in only one case (‘H shifts at 1.49 ppm and 1.58 ppm). Slight resolution can be observed on finely tuned samples for the protons located near 1.78 ppm. In the hope of further clarifying the connectivity of the cyclopentyl species, a series of COSY experiments were conducted. In the first COSY experiment (a COSY-90), a pulse sequence of 90°x —ti—90°x —FID was used.6 In the spectrum shown (Figure I.IV), there are strong coupling interactions between the a-proton and the resonance at 1.25 ppm. Further, another strong interaction is observed between the resonances at 1.78 ppm and 1.08 ppm. Interestingly, these were the only strong interactions observed. 21 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i ► lH-l3C Correlation: Cyclopentyl Derivative Figure I.III 22 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sf J T COSY-90: Cyclopentyl Derivative Figure I.IV Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Hence, another COSY experiment using a 45° pulse in the sequence (a COSY-45), corresponding to a 90°x —tj—45°x —FID pulse train, was run in order to observe any other, weaker interactions. Using such a pulse sequence reduces the overall intensity of the diagonal, enhancing the relative intensity of the crosspeaks with respect to the diagonal. 5 It was hoped that in doing so, peaks that may have overlapped with the diagonal of the COSY-90 experiment could be observed. As exhibited in figure I.V, the same two strong couplings are observed between the a-CH at 0.95 ppm and the CH2 resonance at 1.25 ppm, and between the methylene resonances at 1.07 ppm and 1.79 ppm. A less intense cross-peak reveals interactions between the resonances at 1.25 ppm and 1.58 ppm. Further, although there is overlap with the diagonal, there appear to be cross-peaks between the methylenes at 1.58 ppm and 1.79 ppm. Construction of a model, either with a ball- and-stick model or molecular mechanics simulation, reveals that different conformations that the ring can result in specific coupling interactions between vicinal protons and, in some cases, to such a small degree that none may be observed. 7 This would be due to the Karplus angle, 0, between vicinal protons, where maximum coupling is observed at 0 = 0 ° and 180°, while minimal coupling occurs at 0 = 90°. Scheme I.IV illustrates one such conformation that could account for the observed cross-peaks. As shown, the a-CH would show strong coupling with one of the protons on Cp2 . The protons on Cp2 would further be coupled with the protons on 24 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ha- 2a * ) P‘ Fischer Projection: Ca—Cpi Fischer Projection: Cp2 Cy2 Ca—Cp2 Cpi Cyl Cyl Cy2 -Asterisk (*) designates projections with stronger coupling Scheme I.IV C y 2, and the protons on Cpi and C yi would show significant coupling interactions. On the otheF hand, the a-CH would exhibit a minimal interaction with Cpi. while the protons on Cyi and C y 2 would show a slight interaction. Although it is to be noted that significant ring flipping would occur which would average different conformations, it is probable that steric interactions with the ancillary ligand(s) bound to the metal would result in a significantly favored conformation. Evaluating of the COSY-45 spectrum in light of scheme I.IV, the cross-peaks between the a-CH at 0.95 ppm and the CH2 at 1.25 ppm would correspond to the Ca—Cp 2 projection. The Cp2 —C y 2 projection would correspond to the strong interaction observed between 1.07 ppm and 1.79 ppm. The less intense cross-peaks 25 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. COSY-45: Cyclopentyl Derivative Figure I.V 26 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. between the methylenes at 1.25 ppm and 1.58 ppm would reflect the Cpi— C^l projection. Finally, the apparent interactions between the resonances at 1.58 ppm and 1.79 ppm that overlap with the diagonal would correspond to the C^l— Cy2 projection. Finally, as the Ca—Cpi projection reveals, the Karplus angle between the a-CH and the other P-CH2 would result in a small or non-observable interaction in the COSY spectrum. Although significant interactions are observed between sites, and the a- carbon and proton resonances have been unambiguously assigned, the connectivity of the [CnRh(c-CsH9)(H)(P(OMe)3]+ remains somewhat ambiguous. While one might assume that the strong cross-peak between the a-CH and the resonance at 1.25 ppm identifies the protons at this chemical shift as P-CH2’s, it is perplexing that only one p-position is identified. If the resonance at 1.25 ppm is a P-methylene, then the lack of interaction of the a-CH with the other P-methylene (pl) suggests a fairly rigid and/or dominant stereochemical conformation in solution. Although an argument was made to assign the stereochemical locations of the cyclopentyl protons, further substantiation of the assignments was sought. A NOESY spectrum was acquired in order to determine spatial relationships within the molecule. Specific interactions between distinct protons were predicted based on molecular mechanics modeling of the complex. In particular, the a-CH should show a cross-peak with the Rh-H, as would one or both of the p-methylenes (P1 and/or p2 ). Further, the P-methylenes should show cross-peaks with the N-H of the nitrogen cis to the Rh-H and with the N-H of the nitrogen atom tram to the Rh-H. 27 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In fact, such details are observed in the NOESY spectrum of the cyclopentyl hydride complex. Although the spectrum suffers from only amoderate signal-to- noise ratio, and the intense P(OMe)3 cross peaks disrupt much of the spectrum, certain areas do exhibit real, informative interactions. These are shown in figures I. VI and I. VII. In figure I. VI, the interactions between different portions of the complex with the Rh-H are shown. As expected, an intense cross-peak with the a- CH and ligand P(OMe) 3 is observed. Less intense cross-peaks exist with the resonance at 1.25 ppm (alkyl methylene) and the resonances at 4.02 and 4.72 ppm (N-H’s). The latter interactions indicate that these N-H’s are bonded to the nitrogens that are cis to the Rh-H. More significantly, the interaction with the resonance at 1.25 ppm suggests that this belongs to a P-methylene. The lack of another observable cross-peak with the other P-methylene may imply that a particular conformation/rotamer is preferred in solution. Figure I. VII reveals possible interactions between one N-H that is cis to the Rh-H and the resonance at 1.25 ppm and between the N-H that is trans to the Rh-H and the same alkyl methylene centered at 1.25 ppm. The latter interaction is perplexing in light of the absence of any other Rh-H/p-methylene interactions. Based upon the previously mentioned models, a p-methylene can exhibit interactions with the N-H cis to the Rh-H and a N-H trans to the Rh-H only if there is Rh-Ca bond rotation. Yet, this should also result in a second observable Rh-H/p-methylene interaction. However, if there is a second, minor isomer where these P-methylenes are especially close to the N-H that is trans to the Rh-H, an intense cross-peak due to 28 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. this interaction would be observed while other couplings would not. Nonetheless, the totality of the information obtained from the COSY and NOES Y experiments seems to suggest that the resonance at 1.25 ppm corresponds to a P-methylene. Overall, while the linear alkyl hydride complexes have been unambiguously characterized in solution, the connectivity in the cyclopentyl hydride complex remains less clear. However, the evidence obtained strongly suggests that the methylene resonance at 1.25 ppm in the cyclopentyl hydride compound corresponds to a P-CH2. Full characterization of the cyclohexyl derivative has not yet been achieved. The implications and importance of these characterizations are discussed in chapter 2 . 29 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. r T _ ppa -ia -17 -16 Alkyl*-*Hydride Interactions: [CnRh(c-Pentyl)(H)(P(OMe)=)f Figure I.VI Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Alkyl+-*NH Interactions: [CnRh(c-PentyljfH)(P(0\ie) •)] Figure I.VII Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13 Reactions of Metal Alkyl Hydrides 13.1 Thermolysis of Alkyl Hydrides: Alkane Reductive Elimination It was of particular interest to gain information concerning the energy barriers involved in the elimination of the series of alkanes from the rhodium complexes. Previous work in this group primarily focused on the reductive elimination of methane from the metal center. 1 The methyl hydride complex in our system cleanly eliminates methane in benzene, forming the corresponding phenyl hydride with smooth, first-order kinetics (Table I.I). Differences in the rate of methane elimination are seen with differing ancillary ligands, with the Cn and P(Me)3 derivatives being the most stable. Complex kobsd, (S ) ti/2 (min) [CnRhMe(H)(P(OMe)3 )]+ 6.81 x 1 0 * 5 170 [CnRhMe(H)(P(Me)3 )]+ 2.65 x 10' 5 436 Methane Loss at 80 °C in CeD* Table 1.1 Although initial studies in the group indicated that methane loss was slower than ethane loss, information concerning the enthalpic and entropic contribution to the barrier for elimination was not obtained. Hence, with temperatures ranging from 40-90 °C, the elimination of the corresponding alkane from each derivative (e.g., butane, cyclopentane) was followed in neat benzene (Scheme I.V). 32 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (MeO)3P QD6 (MeO)jP^ V H . Temp°C ♦ CH34 C H rfC H 3 'n n = 0 ,2 ,4 , 8 (MeO)3P Temp °C QDe (M e< 'n n = 1,2 Scheme I.V In each case, approximately 2.5 mg of [CnRh(RXH)(P(OMe)3 )] BAr/ was NMR. The phosphite resonances for the starting alkyl hydride and the product phenyl deuteride ([CnRh(C6Ds)(D)(P(OMe)3)]BAr4f) are distinct from one another in both spectra. Hence, the reaction could be conveniently followed via integration of the starting material and product P(OMe) 3 resonances. The proton resonances of the the integrations. In every case, clean first-order (in [CnRhCR^CHXPCOMe^)]*) kinetics and quantitative formation of product were observed. Arrhenius plots of the benzene reaction were constructed for every alkyl and activation parameters were determined. For the linear alkyls, the activation enthalpies (A //) ranged from 28.9 to 34.8 kcal/mol and the activation entropies (AS*) varied from 7.4 to 25.8 eu. The dissolved in 0.5 mL of and alkane elimination was followed by either *H or 3 1 P "BAr/ anion could be used as an internal standard, serving as a secondary check for 33 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cycloalkyls are similar, with a A // of 27.8 kcal/moi for the cyclopentyl derivative and 29.8 kcal/mol for the cyclohexyl derivative. The activation entropies are 5.6 and 12.0 eu, respectively. The fairly large, positive activation entropies are indicative of a dissociative process where alkane elimination is rate-determining. Table I.II lists these parameters for comparison. R = -alkvl AG* (kcal/mol) AH* (kcal/mol) AS* feu) -ethyl 26.6 28.9(1.06) 7.37 (3.26) -butyl 26.6 31.2 (1.14) 14.8 (3.51) -hexyl 26.7 34.8 (2.26) 25.8 (7.05) -C-C 5H 9 26.1 27.8 (3.27) 5.58(11.1) -c-CfiHii 26.1 29.8 (2.83) 1 2 . 0 (8.881 Activation Parameters for [CnRh(R)(H)(P(OMe)s)]+ Table 1 1 1 13.2 Benzene Indpendent Alkane Elimination In order to confirm the apparent first-order nature of the elimination, the reaction was carried out at different concentrations of benzene in a comparatively inert co-solvent, hexafluorobenzene (QFe). This was done to determine if the reaction was first order in benzene and second-order overall, since the previously described thermolyses were done under pseudo-first order conditions. At 69.6 °C in neat benzene, a rate of 1.96 (9) x lO "4 s' 1 was observed for the loss of hexane, while a k o b s of 2.03 (4) x 10-4 s*1 was measured in a 80/20 (v/v) C6F6/C6D6 solution. Similarly, for the cyclohexyl derivative a kobs of 1.61 (3) x 10*5 s' 1 was measured in neat benzene, compared to a k o b s of 1.62 ( 1 ) x 1 0 ‘ 5 s*1 in a 80/20 (v/v) solution at 50.2 °C. Hence, the lack of an observed dependence of alkane loss upon 34 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the concentration of benzene indicates that the elimination of alkane is first order in [Rh] and first order overall. Further, the rate of elimination of hexane was found to be 2.10 (4) x 10"4 s' 1 in a 80/20 (v/v) C6F6/C6H6 solution at 69.6 °C. If the oxidative addition of the benzene C-H bond were rate-determining, then not only would one expect to find a rate dependence on benzene concentration, but a primary isotope effect would also be predicted. 8 The lack of an observed isotope effect rules out rate-determining benzene C-H activation and further substantiates the first order nature of the alkane elimination. It is noted, however, that if benzene complexation were rate- determining, a significant isotope effect would not necessarily be expected. 9 1 J J Phosphite Independent Alkane Elimination The reductive elimination of various substrates from 5-coordinate, 16- electron late transition metal complexes is well-precedented. 10 In order to determine if phosphite dissociation occurs prior to alkane elimination from [CnRh(R)(H)(P(OMe)3)]+ , the reactions of different alkyls were run in the presence of excess trimethylphosphite-d9 (P(OCD3> 3). Clean first-order kinetics were observed in the elimination of butane from [CnRh(butyl)(H)(P(OMe)3)]BAr4f in 80/20 (v/v) CelVCsFfi at 69.4 °C in the presence of 12 equivalents of P(OCD3)3. A kobs for loss of alkane of 1.47 (2) x 10"4 s*1 , compared to a k o b s of 1.48 (2) x HT 4 s*1 in the absence of excess phosphite. A subsequent 2 H NMR revealed that no P(OCD3 )3 had been incorporated in the product 35 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. complex, [CnRh(phenyl-ds)(DXP(OCH3)3)]BAT 4f (Scheme I.VI). Similarly, monitoring the loss of cyclopentane from [CnRh(c-C5H9)(H)(P(OMe)3)]BAr4f via 3 1 P NMR in QHs at 39.6 °C with 41 equivalents of P(OCD3 )3 present also resulted in clean first-order kinetics with a k o b s of 4.33 (2) x 10 "6 s'1 , compared to 4.35 (1) x 10"6 s'1 . After the first and second half-lives, a 2 H NMR was taken and, again, no resonance corresponding to P(OCD3 )3 was observed in the [CnRh(phenyl- d5)(D)(P(OMe>3)]BAr4f product. VH'H t +h ^ Rh® SOS^OSCsDtCsFstv/v) / V n -----------7^ ----------* (MeO)jP *N^R H ® (M oO bP / V _ 12 eq. P(OCD3)3 d 5 No P(OCD3)3 in starting material or product Rate o f alkcme loss identical with or without added P(OCD3)3 Scheme I.VI Due to the method of following alkane elimination in the cyclopentane case (3 1 P NMR), and possibly due to the larger excess of phosphite^, a second product in addition to that of benzene activation product was observed. This product corresponded to the known [LsRh]+ . This reached a relative concentration of only -22 % after three half-lives. The reaction was run to completion and upon additional heating for another 1 l A weeks at 39.6 °C, a 3 1 P NMR spectrum showed no conversion of [CnRh(phenyl-ds)(D)(P(OMe)3)]BAr4finto [LsRh]+ . 36 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Nonetheless, the lack of dependence of the rate of alkane elimination from [CnRh(R)(HXP(OMe)3)]BAr4 f upon phosphite concentration implies that a pre- dissociation of phosphite prior to alkane loss is not on the path to product formation. This is further substantiated by the absence of any P(OCD3 )3 incorporation in the [CnRh(phenyl-d5)(D)(P(OMe)3)]BAr4f product. 13.4 Effect of the Anion on Alkane Elimination In order to test the effect of differing anions on the rate of alkane elimination, the hexyl hydride complexes [CnRh(Hexyl)(H)(P(OMe)3)]+ 'A, where A is HAr/, 'OTf, and O2CCF3, were prepared (Scheme I. VII). For each anion, alkane loss was followed via *H NMR in neat at 60.2 °C. Clean first-order kinetics and quantitative formation of the corresponding [CnRh(phenyl-d5)(D)(P(OMe)3)]A product was observed for each anion, with kobs of 3.28 (+0.15) x 10*5 s’ 1 for“BAr4f; k o b s of 7.74 (+0.25) x 10 ' 5 s' 1 for "OTf; and kobs of 13.6 (+0.18) x 10' 5 s' 1 for "0 2CCF3 . The source of this rate acceleration is not entirely clear. It is tempting to conclude that the rate differences reflect the relative nucleophilicities of the different anions and, hence, is the result of alkane displacement by the anion in solution. Further, although this is equivalent to proposing an associative mechanism for alkane loss, and in conflict with the measured AS*, the charge an n ih ilatio n in the transition state could still result in an overall positive AS^.n However, the overall effect is fairly small, and could simply be the result of an alteration in the dielectric constant or other aspect of the medium. 37 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1/ k ^ N NH ^ - R h e (MeO)3p ' V ‘H e QA> h n '^ - 2 h 60 °C (MeO)3P C H r(cH ^ c h 3 A = counteranion 3.3 (2) cf3 7.7(3) 13.6 (2) Scheme I.VII 1.4 Discussion and Conclusion Taken together, the results from the previous sections indicate that reductive elimination of alkane from this system appears to occur via a dissociative process. The fairly large, positive AS^ (8-24 eu) for each alkyl hydride is indicative of dissociative mechanisms. 10 Further, the lack of a rate dependence upon the concentration of benzene disallows an associative mechanism by which benzene displaces alkane. This is precedented within our system, 4 but such associative displacements have been proposed in other systems. 12 For instance, Jones reported that methane elimination from TpRh(Me)(HXCN-neopentyl) was dependent upon 38 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the concentration of benzene, with the loss of methane ~2 times faster in neat benzene versus a 80/20 (v/v) C6F6/C6D6 solution.1 2 In addition, alkane loss from a 5-coordinate, 16-electron intermediate generated by pre-dissociation of P(OMe)3 is further ruled out. This is deduced from the lack of rate inhibition upon alkane loss in the presence of excess trimethylphosphite. Recently, however, there has been renewed emphasis on the ability of tridentate ligands to dissociate one of the coordinating atoms prior to reaction.1 1 1 3 For instance, in the photolysis of TpRh(CO) 2 (Tp = tris(pyrazolyl)- borate) in neat alkane, the investigators proposed that one of the pendant nitrogen atoms dissociates from the intermediate formed prior to oxidative addition of an alkane C-H bond.1 2 ® In another example invoking this pre-dissociation, the platinum complex K[(K-2-)TpPt(CH3)2] was made and, upon reaction with B(C6Fs)3 in benzene, produced a tridentate, Pt(IV), benzene activated complex.1 4 Given that the present system involves a tridentate, cyclic triamine, it is possible that one of the nitrogens dissociates prior to alkane reductive elimination. Although no experiments have been conducted to directly rule out this type of mechanism, results from the analogous “Cnlr” system may apply that disfavor such a mechanism. A crystal structure was obtained of the Ir(I) species [CnIr(COD)]OTf which showed that all three nitrogen atoms remain bound to the Ir(I) center.1 5 It seems plausible, then, that the ligand maintains its facial coordination environment upon generating a highly reactive, reduced Rh(I) intermediate prior to oxidative 39 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. addition of a benzene C-H bond. However, as stated, no conclusive evidence has been obtained to directly rule out this possibility. Interestingly, there is a slight rate dependence on the couteranion present. Initially, this appears contrary to the results discussed above. In a purely dissociative mechanism, no dependence on nucleophiles present in solution should exist. Further, since the rhodium complexes are salts in a non-polar solvent such as benzene, it seems reasonable that they exist as tight ion-pairs in solution. Hence, the counteranion may be involved in associatively displacing the alkane in the rate- determining step. The annihilation of charge in this step might account for the observed positive AS^, in spite of the associative nature of the process. However, the overall dependence upon the anion is slight (a factor of 4 going from "BAr/ to ■O 2CCF3) given the considerably greater nucleophilicity of the trifluoroacetate anion versus the tetrakis((3,5-trifluoromethyI)aryl)borate anion. Thus, the nature of this rate enhancement is ambiguous and may simply be the result of a change in the medium, such as the dielectric constant, upon chan g in g the anions. Further, it is also interesting to note that upon changing the nature of the alkyl subunit, there are subsequent changes in the rates of alkane loss. Most noticeably, the cycloalkyl derivatives eliminate alkane at a rate approximately twice as fast as the linear species. This observation is not suprising given that in related Tp* Rh(CN-neopentyl)(R)(H), when R = cyclopentyl, the rate of cyclopentane loss is -8 times faster than n-pentane loss.1 6 Steric crowding due to the conformations of the secondary carbon in the cycloalkyl subunit may contribute to this enhanced rate 40 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of alkane loss. Consistently, the methyl derivative was found to eliminate methane at a rate approximately ten times slower than the rest of the alkanes.Id The possibility of interaction with the internal methylenes and further nuances of the interaction of the alkane with the rhodium metal center are discussed further in the next chapter. In summary, the reductive elimination of alkane from a series of metal alkyl hydrides was investigated. The rates of elimination were determined at different temperatures for different derivatives, providing information on the enthalpic and entropic contributions to alkane loss. Each alkyl displayed a moderate to large, positive A S^, indicating that alkane loss occurs via a dissociative (D or Id) process. The first order process is further substantiated by the lack of a rate dependence on benzene concentration. Alkane elimination is not inhibited by added P(OCD3)3, ruling out elimination via a 5-coordinate intermediate generated via phosphite loss in a pre-equilibrium step. The lack of incorporation of P(OCD3 )3 into the benzene activation product also rules out rate-determining phosphite loss. Finally, the cycloalkyl derivatives are less stable to alkane loss by -0.7 kcal/mol, as calculated from the rates of hexane and cyclohexane elimination at 39.6 °C, and assuming that there is no transition state effect on alkane dissociation as a function of alkane structure. 41 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Endnotes 1 (a) Wang, C. Ph.D Thesis, University o f Southern California, 1994. (b) Zhou, R. Ph.D Thesis, University of Southern California, 1997. (c) Zhou, R.; Wang, C.; Hu, Y.; Flood, T. C. Organometallics 1997,1 6 ,434. (d) Zhen, H. Ph.D Thesis, University of Southern California, 1999. 2 The impurities were identified by two > 0 3 Rh and 3IP coupled hydride resonances at -13.4S ppm and -16.22 ppm. J (a) Vaska, L.; Diluzio, J. W. J. Am. Chem. Soc. 1962, 8 4 ,4889. (b) Arnold, D. P.; Bennett, M. A. Inorg. Chem. 1984,23, 2110. 4 (a) Haines, L. M. Inorg. Chem. 1971, 10, 1685. (b) Couch, D. A.; Robinson, S. D. J. Chem. Soc.Dall. Trans. 1971,23, 1508. (c) Meakin, P.; Jesson, J. P. J. Am. Chem. Soc. 1973,95, 7272. (d) English, A. D.; Meakin, P.; Jesson, J. P. J. Am. Chem. Soc. 1976, 98, 7590. (e) English, A. D.; Meakin, P.; Jesson, J. P. Inorg. Chem. 1976,15, 1233. 5 Meakin, P.; Muetterties, E. L.; Jesson, J. P. J. Am. Chem. Soc. 1972,94, 5271. 6 Gunther, H., NMR Spectroscopy, 2n d Ed.; John Wiley & Sons, Inc.: Chichester, 1995. 7 PCMODEL for Windows, Version 7.50.00, CSerena Software. 8 (a) Lowry, T. H.; Richardson, K.S., Mechanism and Theory in Organic Chemistry, 3rd Ed.; Harpers & Row: New York, NY, 1987. 9 (a) Jones, W. D.; Feher, F. J. J. Am. Chem. Soc. 1986, 108,4814. (b) Jones, W. D.; Dong, L.; Simoes, J. A. Inorg. Chem. 1991, 3, 16. 1 0 See Introduction, ref. 9 and references therein. 1 1 (a) Atwood, J. D., Inorganic and Organometallic Reaction Mechanisms, 2n d Ed.; Wiley-VCH: New York, 1997. (b) Cotton, F. A.; Wilkinson, G., Advanced Inorganic Chemistry, 5® Ed.; John Wiley & Sons, Inc.: New York, 1988. 1 2 (a) Wick, D. D.; Reynolds, K. A.; Jones, W. D. J. Am. Chem. Soc. 1999,121,3974. (b) Johansson, L.; Tilset, M. J. Am. Chem. Soc. 2001, 123, 739. 1 3 (a) Bromberg, S. E.; Yang, H.; Asplund, M. C.; Lian, T.; McNamara, B. K.; Kotz, K. T.; Yeston, J. S.; Wilknes, M.; Frei, H.; Bergman, R. G.; Harris, C. B. Science 1997,278,260. (b) Jenkins, H. A.; Yap, G. P. A.; Puddephatt, R. J. Organometallics 1997,16, 1946. (c) Prokopchuk, E. M.; Jenkins, H.A.; Puddephatt, R. J. Organometallics 1999,18 ,2861. 1 4 Wick, D. D.; Goldberg, K. I. J. Am. Chem. Soc. 1997,1 1 9 ,10235. 1 3 Iimura, M. Ph.D. Thesis, University o f Southern California, 2000. 1 6 Jones, W. D.; Hessel, E. T. J. Am. Chem. Soc. 1993,115, 554. 42 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chanter 2 2H Migration in [CnRh(RXDXP(OMe)3 )]*: Evidence for the Mobility of Rhodium Along Alkanes via Metal-Alkane o-complexes 2.1 Introduction As previously mentioned, there has been considerable interest over the past several decades in the interactions of alkanes with transition metals. In particular, since the initial proposal of alkane o-complexes, discrete intermediates wherein an alkane acts as a ligand within the coordination sphere of a metal, there have been many attempts at obtaining structural and energetic information concerning such species.1 ,2 There have been several pieces of evidence that have led to the acceptance of the existence of such intermediates. For example, in the reductive elimination of ethane from Cp*Rh(PMe3)(Et)(H) and Cp*Rh(PMe3)(Et-ds)(D), an inverse kinetic deuterium isotope effect (kH/ko = 0.5 (1)) was observed.2 6 This is consistent with a concerted, one-step reductive elimination,3 however, since such one-step inverse kinetic isotope effects have not been observed, formation of an intermediate prior to dissociation of ethane was proposed. More directly related to the present system, a kn/ko = 0.74 (4) was also observed in [Cn*Rh(PMe3)(Me-do)(H)]+ and [Cn*Rh(PMe3 )(Me-d3 )(D)]+.4 43 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. More significantly, deuterium labeling studies have given evidence for the existence of alkane o-complex intermediates. For instance, with [Cn*Rh(PMe3>(Me-do)(D)]+ , deuterium was found to exchange into the methyl position at 50 °C at a rate faster than loss of methane, reaching equilibrium (K c q (R h H /R h D ) = 6.56 (6)) in less than 6 hours.4 Importantly, it was found that added methane did not compete with benzene for the generated (but unobserved) Rh(I) species, [Cn*Rh(PMe3)]+ , establishing that the exchange was intramolecular. Further, such observations of exchange have been made in other systems.2 ,5 More recently, Gefiakis has directly observed a cyclopentane a-complex of CpRe(CO)2 system.6 From a specially designed NMR experiment, a resonance observed at -2 ppm was interpreted as belonging to a coordinated, but not C-H activated, methylene. Hence, there has been increasing evidence for the existence of metal-alkane interactions (o-complexes). This has resulted in further questions concerning the energetics and dynamical properties of such species. These questions prompted the development of the current system to explore the nature of alkane interactions in a hard-ligated, soluble rhodium complex. 2.2 Synthesis of Metal Alkyl Deuterides Deuteration of the linear alkyl derivatives is effected by reduction of the appropriate [CnRh(R)(P(OMe)3XOTf)]+ precursor with NaBD4 in THF, analogous to the synthesis of the alkyl hydrides. However, initial attempts at monitoring the 44 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. incorporation of deuterium into the a-methylene site revealed that exposure to light during the synthesis significantly affected the rate of exchange from the Rh~D site to the (X-CH 2. Hence, the synthetic procedure was adapted so that all work with the alkyl deuterides was done with careful exclusion of light. Upon work-up, [CnRh(D)(RXP(OMe)3)]OTf was isolated in typically 20-30% yield. Since the cycloalkyl precursors included the chloride complex, generation of the deuteride complexes required an adaptation similar to that described for the cycloalkyl hydrides (see Experimental). Initial use of a NaBDVi-PrOH-do solution produced the desired deuteride, but the 3 1 P spectrum was anomalous, exhibiting a set of peaks with odd multiplicities, differing from the expected set of overlapping 1:1:1 triplets (Rh-D) and singlets (Rh-H, a-CH(D)). Therefore, synthesis of the deuterides was always conducted in an NMR tube using i-PrOH-dg as the solvent, circumventing complications that might arise if some of the deuterium comes from the solvent. In addition, all manipulations were done with careful exclusion of light. Upon work-up, [CnRh(D)(cycloalkyI)(P(OMe)3)]OTf was isolated in -15-25% yield. 2.3 Spectroscopic Characterization Isolation of the desired [CnRh(D)(R)(P(OMe)3)]+ 'A ('A = ’OTf or "BAr/) at r.t., followed by characterization via 2 H NMR, revealed that the deuterium was fully exchanged between the Rh-D and a-CH(D) sites and reflected both the statistical distribution and an equilibrium isotope effect of-1.7-1.8, depending upon the alkyl.7 45 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Such isotope effects are well precedented in other systems and arise from the difference in metal-D and carbon-D force constants.2,4 In the linear alkyl complexes, small, variable amounts of deuterium were present initially at 1.2 ppm as well as at 0.88 ppm, according to 2 H NMR. These chemical shifts correspond to the internal methylenes and C 0 -CH3, respectively, as determined via the 2D NMR experiments described in Chapter 1. Importantly, it was found that careful control of temperature during synthesis, such as very slow warming, reduced the amount of deuterium initially present in these sites. Similarly, 2 H NMR of the cyclopentyl and cyclhexyl derivatives revealed deuterium in the Rh- D and a-C(D) sites initially, with neglible amounts at other sites. 2.4 Reactivity of the Metal Alkyl Deuterides 2.4.1 Metal<-»Alpha Deuterium Exchange: Kinetics of Equilibration Isolation of [CnRh(D)(R)(P(OMe)3> ] A with the deuterium predominantly in the Rh-D site proved unsuccessful on the vacuum manifold. Thus, a low temperature NMR tube reaction was conducted in THF-do and monitored via 2 H NMR. The outcome of the experiment is particularly sensitive to the method of preparation and handling of the sample. Hence, a brief description of the methodology is warranted. The rhodium precursor was dissolved in THF-do and added very slowly via a microsyringe to a pre-cooled (-78 °C), nearly completely immersed, foil covered, 5mm NMR tube containing NaBD4. Addition of the precursor too quickly results in a reaction that quickly incorporates deuterium into the a-methylene. This is 46 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. probably due to insufficient temperature equilibration of the added rhodium solution prior to contact with the NaBD4. After proper addition, however, the NMR tube was quickly placed in a pre-cooled NMR probe (in the dark). It was found that at ~ -20 °C, the product could be slowly generated with deuterium being >95% Rh-D, as determined via 2 H NMR. Upon wanning, incorporation of deuterium into the a- methylene was observed. However, complete formation of product was never achieved prior to the onset of exchange. Due to the slow rate of formation of product, obtaining the rate of equilibration required additional adjustments: (1) a temperature at which the rate of formation is reasonable and, (2) a way to monitor both the rate of formation and the rate of exchange simultaneously. Hence, in order to satisfy both conditions, the hexyl precursor, [CnRh(hexyI)(OTf)(P(OCD3)3)]BAr4f , was used and the reaction followed at 4.7 °C in the NMR probe. Formation of the deuteride complex (either Rh-D or a-D) could be conveniently monitored by following the loss of starting material via integration of the P(OCD3 )3 peaks (5 = 3.86 ppm) with respect to residual deuterium in THF as an internal standard (8 = 1.73 ppm). Overlap of the product P(OCD3 )3 with the other THF peak and a small impurity prevented accurate integration of these peaks for additional confirmation of the rate of formation. Further, Rh-D (8 = -16.50 ppm) and a-D (8 = 0.98 ppm) were conveniently integrated with respect to the same internal standard. 47 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The relative concentration of each species was plotted with respect to time and the data fitted via computer modeling.8 The rate of equilibration (ka) is comparable with the rate of product formation (kfonn[NaBD 4]) with ka = 4.3 x lO "4 s'1 and kform[NaBD 4] = 6.6 x 10'5 s'1 . (Scheme II.I) H-N-R h® k form atIon[NaBP4] ttN w jyi© / V OTf ------------------- ► / V^I (CDjOfeP (CQjOfcP V J (CDjOfeP Metal<— >Alpha Deuterium Exchange Scheme II.1 Thusfar, the synthetic method of preparing the cycloalkyl hydride/deuteride derivatives has prevented measurement of the metal to alpha exchange in the secondary metal alkyls. For example, [CnRh(c-CsH9XCl)(P(OCH3)3)]BAr4fwas dissolved in i-PrOH-dg, added to NaBD4, and followed via 'H NMR at 26 °C. As in the case of the linear derivatives, the precursor P(OCH3 )3 resonance (6 = 3.87 ppm) is distinct from the product P(OCH3 ) 3 (8 = 3.66 ppm), providing a convenient way of monitoring product formation. Further, the "BAr4f proton resonances provide an internal standard. Due to the significantly slower rate of formation of the cycloalkyl hydrides and deuterides from the chloride precursors (X\a~ 12-14 hrs at ambient temperature), product formation always resulted in a species with 2 H frilly equilibrated between the Rh-D and a-CH sites. 48 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.00 • SM SM (fit) Rh-D 0.75 — Rh-D (fit) ♦ Alpha-D Alpha-D (fit) 0.50 0.25 0.00 0 5000 10000 15000 20000 25000 time (s) Macroscopic Fit o f Metal**Alpha Deuterium Exchange: Hexyl Complex Figure II.I In an attempt to circumvent this, the [CnRh(c- C5 H9XC1)(P(0 CD3)3)] BAr/ complex was treated with one equivalent of AgOTf and resulted in [CnRh(c- C5 H9)(OTfXP(OCD3)3)]BAr4f. Under reaction conditions similar to those of the linear alkyl analogues, treatment with NaBD4 at 10 °C in the NMR probe resulted in a complex mixture of products. The desired [CnRh(c-C5H9)(DXP(OCD3)3)]BAr4f component was only ~ 30% of the products formed at 35% conversion, as determined by 3IP NMR. 49 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Hence, while the rate of metal-to-alpha exchange was conveniently followed via 2 H NMR in the linear alkyl derivatives, measurement of these exchange rates in the cycloalkyl derivatives proved elusive and remain undetermined. 2.4.2 AlphaoOmega Rearrangement: Deuterium Migration to the Terminal Methyl Group in Linear Alkanes In an effort to observe any further migration(s) of deuterium within the alkyl subunit, the corresponding alkyl deuterides [CnRh(R)(D)(P(OCH3)3)]BAr4f (R = butyl, hexyl, decyl, cyclopentyl, and cyclohexyl) were dissolved in and heated at 39.6 °C (all alkyls), 50.5 °C (R = hexyl), and 60.2 °C (R = hexyl). In every experiment, the complex was heated for a discrete period of time, then cooled to r.t., the benzene removed in vacuo, and the reaction mixture washed with pentane in order to remove free alkane. The mixture was dissolved in MeOH-do (R = butyl, hexyl, decyl, cyclohexyl) or CH3CN (R = cyclopentyl), and a 2H NMR spectrum was recorded. The relative intensities of the Rh-D, a-D, and either co-D (linear alkyls) or “P-D” (cycloalkyls) were then determined via deconvolution of the peak areas, with the total 2 H amount checked against integration of all sites with respect to residual 2 H in the solvent. The percent conversion/rate of product formation was followed via 3IP NMR, taken subsequent to each 2 H spectrum. As shown for the butyl derivative (Figure II.II), deuterium cleanly migrates from the Rh-D and a-D sites to the c o site in the linear alkyls, with the site specificity determined via the previously described 2D NMR experiments. The initial amount 50 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. a-CHD internal CHD 2642, minutes 2312 1762 1327 325 150 / = 0 1.0 'H NMR: Buryi Alpha*-*Omegci Isomerization Figure D.II Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of deuterium in the internal methylenes, which varied from one sample to another, did not increase or decrease relative to the total amount of deuterium in the other sites. This was confirmed via an NMR tube experiment (monitored via 2 H NMR) heating the butyl compound in MeOH-do with a small amount of as an internal standard. In addition, in the hexyl sample heated at 50.7 °C, no deuterium was observable in the internal methylene sites in the initial (t = 0) 2 H spectrum and never appeared as the reaction progressed. (Figure Il.QI) The rates of deuterium migration were determined in the following manner. At every point, the relative intensity of deuterium content at each site (Rh-D, a-D, and o-D) was calculated and then adjusted for the extent of reaction with benzene (see Experimental). Thus, the percent deuterium content in each site represents the relative concentration of each species with respect to total [Rh]. This is then plotted with respect to time. The plots were fit with a kinetic program8 , according to the macroscopic model shown in scheme II.II. One assumption made was that the AS* for the metal/alpha exchange is nearly zero. Stated differently, the rate and reversibility of the exchange is primarily affected by the M-H(D), M-C, and C-H(D) bond strengths. Thereby, the AG* measured for this process at 4.7 °C can be used to approximate the rates of metal/alpha exchange at 39.6, 50.7, and 60.2 °C. Finally, the efficacy of this general/macroscopic model seems reasonable for it assumes nothing concerning the mechanism of exchange (discussed below). It does establish that the system is kinetically well-behaved and so warrants further scrutiny. 52 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o-CH2(D) a-CH(D) internal methylenes : s t t ~H NblR: Hexyl Alpha*-*Omega Isomerization (a..T= 50.7 °C Figure D.III Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (MeOfeP (MeOfeP (MeOfcP (MeOfcP Macroscopic Model for Alpha -XDmega Deuterium Isomerization Scheme n .n The calculated rates of rearrangement (ka) were 5.9 x 10"6 s'1 , 3.6 x 10-6 s'1 , and 3.0 x 10"6 s'1 at 39.6 °C for the butyl, hexyl, and decyl derivatives, respectively. Further, the rate for the hexyl species was 3.9 x 10'5 s'1 at 50.7 °C and 8.6 x 10'5 s'1 at 60.2 °C. For illustration, the fit for the butyl derivative is shown in figure II.III. Although migration of deuterium from a metal deuteride to a metal methylene (a-methyl) is precedented in ours and others’ system, to our knowledge only one example of a migration to another alkyl subunit via an alkane a-complex has been reported.2 b Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.800 Rh-D 0.700 Alpha-D Omega-D 0.600 Phenyl 0.500 w c U 0.400 e c 0.300 Rh-D (fit) Alpha-D (fit) Omega-D (fit) Phenyl (fit) 0.200 0.100 0.000 200000 100000 300000 0 400000 500000 time(s) Macroscopic Fit: Butyl A Ipha <-> O m ega Isomerization Figure II.IV 2.43 Deuterium Migration in the Cycloalkyl Derivatives As previously stated, deuterium exchange between the Rh-D and a-CH sites occurred prior to isolation of the final product It is likely that the rate of exchange is similar to that of the linear derivatives. Further exchange was also observed in the cyclopentyl and cyclohexyl derivatives, however. Upon heating the cyclopentyl species, deuterium was observed to appear at 8 = 1.25 ppm. According to the 2D NMR techniques described earlier, this site integrates to 2 protons in the *H spectrum and corresponds to only one carbon. The rearrangement could be fit with the model 55 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.700 0.600 0.500 e e U 0.400 £ 0.300 0.200 0.100 0.000 ♦ Phenyl ■ Alpha-D 4 Rh-D • Beta-D Alpha-D (fit) Beta-D (fit) Gamma (fit) Phenyl (fit) Rh-D (fit) 0 50000 100000 150000 200000 250000 time(s) Macroscopic Fit o f2 H Rearrangement in the Cyclopentyl Complex Figure II.V depicted in scheme II.IV. Stepwise migration from the a-isomer to the (J-isomer, followed by another rearrangement to the y-isomer (becoming p' after the first migration), implies that deuterium should be observed in other sites. However, as figure II.V shows, in order to obtain a good fit of the initial migration, the model predicts very little formation of the y-isomer. The relatively low concentrations would be inadequate for detection, as is observed. Overall, a rate of 5.2 x KT 6 s' 1 is obtained, resulting in a barrier that is ~0.5 kcal/mol higher than the barrier for alkane loss (k eiim = 4.78 x 10"6 s'1 ). Implications of this will be discussed further in the following section(s). 56 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.5 Discussion 2.5.1 Mechanism of Metal*-* Alpha Deuterium Exchange As previously stated, examples exist that show deuterium exchange of a metal-deuteride with the metal-carbon C-H bond (a-CHx ). Different mechanisms can be envisaged that could account for such exchange. First of all, it is possible that the exchange occurs via a-elimination, a process precedented in early transition metal systems.9 In the present system, one a-elimination pathway would result in the generation of a Rh(V) alkylidene hydride. (Scheme II.III) Subsequent reduction with NaBD4 would place the deuterium on the a-methylene first, contrary to what is observed. In another a-elimination pathway, after deuteration of the rhodium with NaBD4, either P(OCH3 ) 3 or a ligand nitrogen could dissociate, followed by a- elimination. Then, the deuteride could insert into the alkylidene moiety (Scheme II.IV). This pathway would account for Rh-D being observed prior to a-D. However, in light of the fact that P(OCH3 )3 does not dissociate in the reductive elimination of alkane (see Chapter 1), it seems unlikely that coordinative unsaturation would be achieved via phosphite loss. (CDjObP (CDjObP^) (CDjObP Scheme Il.m 57 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The possibility of nitrogen dissociation was addressed briefly in the previous chapter. In the present context, such a process is required to be much faster than a- elimination. It seems reasonable to assume that if nitrogen dissociation was on the same order of magnitude as, or even one order of magnitude slower than, a- elimination, build-up of an intermediate alkylidene such as [K 2-CnRh(=CHRXHXD)(P(OMe)3)]+ would be observed. 10 Undoubtedly, the Rh-D chemical shift would differ significantly from the chemical shift of the Rh-D in the alkyl species. If the ligation of the dissociated nitrogen were much slower than a- elimination, this should result in all observed Rh-D being fully equilibrated with observed a-D, which is clearly not the case. HN-'rf. (C D jO fe P ^ V / f f l \ ’ OTf NaBD4 (CDjOfeP (CDjOJjP » N-RhT (CDjOfePl*^ (CDjObP (CDjOfeP a-Elimination Mechanism via Nitrogen Dissociation Scheme II.IV 58 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Further, an a-elimination mechanism via pre-equilibrium nitrogen dissociation seems unlikely based upon observations made in the a-CH(D) to cd-CH 2(D) isomerization. Since no P-CH(D) incorporation is observed upon heating, a process involving an open coordination site seems unlikely since this should allow for a facile, competitive P-hydride elimination process {vide infra). Thus, nitrogen dissociation appears unlikely to occur. Consistent with the data and observations, is a mechanism whereby the alkane undergoes reductive elimination to form a cr-complex intermediate which then undergoes oxidative addition either to reform the Rh-D or to form the a-CH(D) (Scheme II.V). Due to the statistical distribution of sites, as well as an equilibrium isotope effect (K < R h H /C D y (R h D /c H )) resulting from the AAG° of M-H/C-H vs. M-D/C-D, the deuterium should favor the a-methylene, as is observed. The kinetic modeling yielded an alpha exchange rate (ka) of 4.3 x KT 4 s*1 and a metal exchange rate (kR h) of 1.0 x 10^ s'1 . Adjusting for the statistical distribution, this results in an equilibrium isotope effect of ~2. Based upon precedents in this group4 and others2, it seems reasonable that the pathway of exchange involves a cr-complex intermediate. Finally, although no a-equilibration rate was directly measured, the cycloalkyl derivatives are assumed to undergo the same mechanism of exchange, given that upon isolation, an equilibrated mixture of Rh-D and a-D is obtained, with K R h H /R h D = 1.9. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. N-H Metal*-*Alpha Deuterium Exchange via a a-Complex Intermediate Scheme II.V 2.5.2 Mechanism of Alpha<-*Omega Deuterium Exchange: Evaluation of a P- Hydride Elimination Pathway As previously mentioned, wanning the [CnRh(R)(DXP(OMe)3)]BAr4f species in benzene incorporates deuterium into the (D-CH 3 position of the linear alkyl. In light of the conclusion drawn for the mechanism of metal<->alpha deuterium exchange, it seems feasible that the mechanism of incorporation also involves o-complex intermediates. However, a series of control experiments were conducted in order to evaluate other mechanisms. One such mechanism would involve a series of p-hydride eliminations/insertions, allowing the metal center to rearrange to the terminal methyl 60 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. J 7 n* n h * J / ^ --D H ) p \ J — s "H 1/ N +* N-H If ryn k/ — x 1/ N « H H ’ N* ‘R h-,«D (C H jO feP ^ X lP ^ , ( C Hj Ob P , (C H jO ijP ^ 0 ® N-H i/ 1 ttN^ , u ^ steP s ^ N4 h l H D °r » N^ % (CHjOfeP / V _ x* (CH3 0>3 P/ V _ / (CHsObP V )4 — Deuterium should exchange into each site (Approximated %D): Rh-D a-CH; B-CH? Y-CH2 <n-CHi 3-Elimination Pathway 6 21 21 21 31 CT-Complex Pathway 10 36 0 0 54 (K(CD,RhHy(OiRhD)= 1-79); calc'd w/o accounting for product formation) Butyl Alpha Omega Isomerization via fi-Hydride Elimination/Insertion Scheme II. VI group. In order for this to occur, a vacant coordination site is required. As discussed earlier, phosphite loss in not observed in the current system under the conditions that the experiments are conducted. Therefore, the coordinative unsaturation would need to occur via nitrogen dissociation. Although arguments against this have already been presented, the following seems to be the most convincing: if nitrogen dissociation occurs allowing for P-hydride elimination, statistical incorporation of deuterium in each position of the alkyl moiety should be observed. (Scheme II. VI) 61 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Although there is an initial, small amount of deuterium incorporated into the internal methylenes upon synthesis of the rhodium alkyl deuterides, the deuterium content does not increase upon heating. Yet, deuterium is efficiently incorporated into the 0 3-CH3. Further, as shown in figure II.III, no significant amount of deuterium was present initially in the internal methylene site in the hexyl experiment at 50.2 °C, and no incorporation occurs upon further reaction. Thus, a P-hydride elimination/insertion mechanism does not fit the observations. 2.SJ Mechanism of Alpha<-»Omega Deuterium Exchange: Inter- vs. Intra molecular Migration Up to this point, the inter- vs. intramolecular nature of the reaction has not been discussed. One possible mechanism of exchange involves the reductive elimination and dissociation of alkane to a solvent-cage, followed by oxidative addition of the caged alkane. A persuasive argument against this has been made2 b , but a series of experiments were conducted to determine whether or not the exchange was intermolecular. First, a crossover experiment was conducted by heating [CnRh(butylXH)(P(OCD3)3)]BAr4f and [CnRh(hexylXHXP(OCH3)3)]BAr4f together in a 90/10 (v/v) C6F6/C6H6 solvent mixture to ~1 V 2 half-lives. The mixture was then analyzed by FAB-MS. Exact masses were obtained for both benzene activated products (P(OCH3 ) 3 and P(OCD3 )3) and the butyl P(OCD3) 3 species was observed, although the hexyl species was not determined, in spite of a sufficient signal 62 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. intensity. 11 Yet, ions representing possible crossover products were present in < 3% combined. However, the overall spectrum was fairly complicated, with a significant and complex number of fragments. Therefore, in order to more conclusively determine if the rearrangement is intermolecular, [CnRh(butylXH)(P(OCH3)3)]BAr4f was heated in under 11 atm of methane. At ~2 half-lives, 18% of the rhodium products was the known methyl hydride, [CnRh(CH3)(H)(P(OCH3)3)]BAr4f , as determined by ‘H NMR. 12 Yet, thermolyzing [CnRh(hexyl)(H)(P(OCH3)3)]BAr4f in a 90/10 (v/v) CdFfJC&f, solvent mixture under an atmosphere of l3CH4, both the 'H NMR and l3C NMR revealed no methane activated product. Hence, although intermolecular methane C-H activation occurs in the absence of benzene, it is not competitive with benzene, indicating that the solvent-cage mechanism is not likely. Although the competition experiment above seemed reasonably convincing, a recent report has suggested that methane does not effectively compete with other alkanes for C-H oxidative addition by highly reactive metal intermediates. 13 In light of this, another competition experiment was conducted. Heating [CnRh(hexyl)(H)(P(OCD3)3)]BAr4f in a 90/10 (mol/mol) C6lVa,<D-decane-d6 to ~ 2 half-lives of hexane reductive elimination revealed that -12% of the total [Rh] resulted from the a,o)-decane-d6 activated product, [CnRh(CD2(CH2)gCD 3XDXP(OCD3)3)]+ , as determined from 2 H NMR. However, thermolyzing the hexyl complex in a 4.3/2.0/1.0 (mol/mol/mol) CfilVCglVa,©- 63 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. decane-d* solvent mixture and analysis via 2 H NMR revealed a clean reaction with C^Dg only. (Scheme II.VII) Taken together, these results imply that the rearrangement occurs via an intramolecular process. Given the high affinity of the presumed rhodium intermediate, [CnRh(P(OMe)3]+ , for reaction with benzene, even when another alkane is in a greater amount within the solvent cage, it is highly unlikely that oxidative addition of liberated alkane even in the solvent cage is the mechanism for the observed deuterium migration to the C 0-CH3 site. In a similar vein, the previous experiment also disfavors oxidative addition of the terminal methyl group in an intact [CnRh(R-a-di)(H)(P(OMe)3)]+ by [CnRh(P(OMe>3]+ , followed by reductive elimination from the deuterated end. 2.5.4 Mechanism of Alpha<->Omega Deuterium Exchange: Evaluation of an “End-to-End” and “Tail-to-Head” Mechanism While the intermolecular nature of the migration was reasonably established, the different types of intramolecular processes can be postulated. One such mechanism could involve direct oxidative addition of the terminal methyl, via prior nitrogen dissociation to produce a vacant site, followed by C-D reductive elimination. This “tail-to-head” possibility could involve unlikely scenarios: 1) the involvement of a Rh(V) intermediate, and 2) that dissociation and oxidative addition of the terminus occurs faster than P-hydride elimination/insertion. Given the 64 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ttN^Rh® (MeOhp/Vl!L CDsCCH^CDj (0.8 M) inC ^F* Q A (l.o M ) 0 > 3 (C H 2 )tC D 3 (2-1M ) ( M e O ] C D f c C C H U tC D j ~ 10% of total [Rh] (® 2 x tj/j) only “ r -17 T T T 1 — 1 1 14 T T T T r -15 * 6 -lc Decane-eU Competition Experiment: 2 H NMR Scheme II. VII Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. $5L (CH3 0)3 P/ d > J L (CHaOfeP 7 ^ 0 H (CHsOJaP / J ^ H . ^ Rhft IM lw ft D "End-to-End" Mechanism fo r Alpha*-*Omega Isomerization: Butyl Derivative Scheme II. VIII typically fast rates of the latter process, and the relatively efficient deuterium incorporation into the 0 -CH3 in the butyl, hexyl, and decyl derivatives, this type of mechanism seems improbable. A permutation of this involves an “end-to-end” displacement. For instance, it was previously argued that the metal/alpha deuterium exchange occurs via the transient formation of an alkane cr-complex intermediate. In the present context, upon formation of the initial alkane cr-complex (a-a-CH^D), the terminal methyl group would associatively displace the cr-a-CH2D forming another cr-complex, C T - 0 -CH3. Subsequent oxidative addition would result in deuterium incorporating into the ©-CH3 (Scheme II. VIII). Although not explicitly ruled out, the similar 66 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. efficiencies of the different linear alkyls also make this mechanism seem unlikely. In essence, the transition state for associative displacement of the o-a-CH2D by the ( 0 -CH3 can be roughly modeled as pseudo-metallacyclopentanes, -heptanes, and -undecanes for the butyl, hexyl, and decyl derivatives, respectively (Scheme ILEX). Given that metallacyclopentanes are typically the most stable form of metallacycle, it is expected that the migration in the butyl would be the fastest, as observed. However, the relative rates are fairly similar, differing by only a factor of ~2 between the butyl and decyl derivatives. Yet, with the additional conformational requirements for the pseudo-metallacycloheptane, and especially the metallacycloundecane, one might expect much more siginificant rate differences between the alkyl derivatives. Thus, although a “tail-to-head” mechanism involving a Rh(V) intermediate can be reasonably repudiated, an associative displacement of an initially formed alkane o-complex by the terminus has not been conclusively ruled out. Nonetheless, (CHaOfeP^ H H X (CHsOfeP (CHsOfcP n = 1,3, or 7 pseudo-Metallacycle Transition State Scheme II.IX 67 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the relative efficiencies of migration in each alkyl might favor other alternatives, as discussed in the following section. 2.5.5 Mechanism of Alpha«-»Omega Deuterium Exchange: Deuterium Exchange via Metal-Methylene cr-Alkane Interactions Studies involving the preequilibrium binding energies and relative rates of oxidative addition of differing alkanes by highly reactive transition metal intermediates have shown that the rates show a dependence upon the number of methylene units present within the alkane.2 6 ,1 3 Further, photogeneration of (CO)sCr in the presence of aliphatic alcohols revealed that the complex bound to each methylene prior to migration of the metal to the hydroxy position.1 4 Given these precedents, a mechanism for the observed rearrangement in the current system can be postulated whereby the metal would migrate along the alkane chain from end-to- end, equilibrating among each isomeric species via metal coordination to either a methyl or methylene group. Oxidative addition to form the range of 2°-alkyl hydrides may occur but these have yet to be observed (Scheme II.X).1 5 In order to test the efficacy of this model, a computer simulation attempting to fit the observed 2 H data was made for the butyl derivative. The model required a few assumptions about different energy barriers, listed in Table II.I, and will be discussed presently. First, since activation parameters have not been obtained for the metal/alpha exchange process (represented by k ^ , krea, and k ^ ), the barrier for reductive elimination in this step was calculated at 39.6 °C assuming AS2 ~ 0. Given 68 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (MeO)3 P 5.1 koa 3.4koa kre. x ¥ h * k h A K nh ** Rh« - Rh* (MeO^P^ V H k» (M e° )3 p / . N l / X . H koa k i 2 » 1 1 k o ^ o not observed not observed Alpha*-+Omega Isomerization via Alkane & ■ Complexes Scheme ILX that there is a seemingly limited amount of reorganization in this step, a small A S* might be expected. Thus, setting the value to zero is not entirely unreasonable. In addition, in order to account for the isotope effect and statistical distribution, the rates of oxidative addition from the 1° cr-complex intermediate (koa) to form the Rh-D, a-D, and co-D isomers were adjusted for the observed isotope effect and the 69 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rxn Steo Enerev fkcal/mol) Enerev IJ/moh Rate fs'S krem 20.70 86567.4 2.26 E-02 koa 10.15 42447.3 5.30 E+05 3.4koa 9.38 39214.6 1.84 E+06 krea 20.70 86567.4 2.26 E-02 ki2 13.00 54366.0 5.41 E+03 h i 11.00 46002.0 1.35 E+05 koa2° 11.00 46002.0 1.35 E+05 kre2° 17.00 71094.0 8.69 E+00 k 2 2 12.35 51647.7 1.54 E+04 k 2 2 12.35 51647.7 1.54 E+04 koa2° 11.00 46002.0 1.35 E+05 k re2 o 17.00 71094.0 8.69 E+00 k/2 11.00 46002.0 1.35 E+05 k2l 13.00 54366.0 5.41 E+03 5.1koa 9.12 38148.2 2.77 E+06 kfem 20.70 86567.4 2.26 E-02 kdissl0 15.30 63984.6 1.34 E+02 kdiss20 13.30 55620.6 3.34 E+03 kdiss2° 13.30 55620.6 3.34 E+03 kdissl0 15.30 63984.6 1.34 E+02 Energy Values and Rates Used for Fitting the Alpha*-*Omega Isomerization According to Scheme IIJC Table II.I statistical differences. It is unlikely that the isotope effect arises solely from the oxidative addition step, but since conditions for obtaining this information within the current system have not been found, the assumption allows for simplification of the model and is not entirely fallacious. Further, the barrier to oxidative addition was adjusted according to values found in literature. For instance, femtosecond flash-IR studies have provided the 70 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. rates of oxidative addition of a series of alkanes to the photogenerated transient, TpRh(COXcr-RH).1 6 From this, a value o f-10 kcal/mol was set for oxidative addition to for the Rh-D isomer, and the calculated rate was subsequently adjusted according to the conditions discussed above. This resulted in values of 9.4 kcal/mol for the a-D isomer and 9.1 kcal/mol for the co-D isomer. Since no secondary C-H activated species were observed in the thermolyses of the linear alkyl derivatives, this results in a lower limit for the AAG° - 3 kcal/mol between the primary and secondary C-H activated isomers. Use of a value of 3.7 kcal/mol resulted in a better fit and was reflected in the barrier for reductive elimination (k^o) to form the 2° CT-complex intermediate. Further, a value of 1 1 kcal/mol was used for the oxidative addition step to form the secondary alkyl hydride isomer. In this system, as well as others, the primary alkyl hydride isomers predominate, hence the barriers for migration from the 1° cr-complex intermediate to the 2° a-complex intermediate (ki2, and k2 i) were adjusted to favor formation of the 1° intermediate.1 7 This difference is further reflected in the rate of alkane dissociation, as discussed below. Further, because of the degenerate nature of the migration, the barriers to migration from one secondary isomer to the other (kz2) are equal. Finally, because of the assumptions made for the reductive elimination and oxidative addition of alkane, and the AG1 values set for the migratory barriers, the barriers to dissociation could be calculated from the macroscopic barrier determined 71 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. in the experiment and the relative ground state energies of the presumed intermediate CT-complexes. An assumption made in this calculation was that the transition states for dissociation from either a 1° or a 2° a-complex intermediate were the same energy. Support for this assumption comes from the previously described photolysis of (CO)sCr in aliphatic alcohols, where entire range of possible isomers (dependent upon the number of methylenes and the terminal hydroxy and methyl subunits) were initially formed prior to rearrangement to form the hydroxy complexed product.1 4 Further, in the photolysis of Cp*Rh(PMe3)(cyclohexyl)(H) in neat alkanes, the relative rates of oxidative addition of each alkane were found to depend upon the number of methylene subunits present in the alkane, with the rate increasing with the increasing amount of methylenes.2 b This suggests that the reactive intermediate formed samples each type of site indiscriminantly. With respect to the current system, these observations imply that the relative stabilities of primary vs. secondary C-H activated products appear to be determined by the relative ground state stabilities of both the alkyl hydride and the corresponding a-complex, as well as the barriers to oxidative addition, rather than the barrier to complexation. Thus, it appears reasonable to assume that the transition states for dissociation from either the primary or secondary a-complex intermediates are the same energy and the calculation using the macroscopic barrier to elimination is warranted. Ultimately, adjustment of the relative values for the oxidative addition, migration, and dissociation steps, resulted in a reasonable fit of the data (Figure 72 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. II.VI). Although not proof of such a mechanism, the ability to obtain a good fit, given the few assumptions made based upon previous results within this system and results from other research, shows the very real possibility that such a mechanism is operating in the observed, macroscopic rearrangements. 2.5.6 Mechanism of AlphaoOmega Deuterium Exchange: Modeling 2V*2° Migrations via Cydoalkyl Analogs Due to the possibility of the aforementioned mechanism, and the considerable uncertainty in the energetic values of key reaction step, it was hoped that specific information could be obtained on the rate of migration from one 2° a-complex to another 2° a-complex. However, the synthesis of secondary isomers of linear alkyls has been prevented thusfar, evidenced by the isomerization of the 1 3 C label in the precursors of the a,©-I3 C-[CnRh(Decyl)(D)(P(OMe)3)]+ ,1 8 . This suggests that 2° alkyl precursors would rearrange to the 1° alkyl isomer. In order to circumvent this problem, it was thought that a cydoalkyl derivative would provide the desired information, yet would not be subject to isomerization to a more thermodynamically favored primary isomer. Thus, the first attempt involved the synthesis of the cyclopentyl derivative, [CnRh(c-PentylXD)(P(OMe)3)]BAr4f. As previously mentioned, deuterium exchanges between the Rh-D and a-CH sites. However, due to the method of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 0.800 Rh-D 0.700 Alpha-D Omega-D 0.600 Phenyl 0.500 Rh-D (fit) 0.400 Alpha-D (fit) Omega-D (fit) Phenyl (fit) 0.300 0.200 0.100 0.000 0 100000 200000 300000 400000 500000 tim e(s) Fit of Buty A Ipha <-*Omega Isomerization Data via the Mechanism in Scheme IIJGI and Energy Values in Table II. I Figure II. VI synthesis this rate of exchange was unable to be measured. Nonetheless, subsequent heating in benzene and following the rate via 2 H NMR was thought to be able to provide the desired information. Upon heating the complex in benzene, deuterium was observed to appear at 5 = 1.25 ppm and increase in concentration relative to the Rh-D and a-D sites. However, the resonance at 1.25 ppm corresponds to only one fi-methylene si tel Initially, because the deuterium exchange/isomerization was relatively efficient in 74 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the linear alkyl complexes, and because of the model previously described, it was expected that deuterium would exchange into each of the different methylene units of the cyclopentyl ring at a rate much faster rate what was observed. The reason for the slower observed rate is unclear. It is possible that the methylenes in the cycloalkanes are constrained away from the metal center, resulting in reduced accessibility and, hence, a slower rate for isomerization. However, the greater freedom of C-C bond rotation in the linear alkyl complexes may provide an orientation that effectively allows for the metal to migrate to the next adjacent methylene. In addition, the reason for observing isomerization to only one site is not entirely clear. Although the rate of isomerization may be sufficiently slow to allow for observation of rearrangement to either of the y-methylenes, the presence of two P-methylenes suggests that deuterium should be observed in two sites, not one. In spite of the fact that the metal center is chiral, upon reductive elimination of cyclopentane to form the initial 2° <y-complex-d|, an intermediate postulated as the source of deuterium exchange from Rh-D to a-CH, the metal complex should have a plane of symmetry. It is unclear why the migration occurs essentially in one “direction”. A possible source of such directionality may be the ancillary phosphite ligand. If it is oriented in a certain manner in either enantiomeric alkyl hydride, then this orientation may be kept in the intermediate o-complex, thereby directing the migration, possibly via some steric interaction. However, this is purely speculative and the precise reason remains ambiguous and perplexing. 75 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Further, it is interesting to note (as stated in Chapter 1) that the overall barrier to cycloalkane loss is only -0.7 kcal/mol lower than for linear alkane loss. Yet, no secondary alkyl hydride isomers, resulting from methylene C-H activation in the linear complexes, are observed while monitoring the loss of alkane. As discussed previously, this results in a AAG° of ~3 kcal/mol, which can be directly translated into an overall barrier for alkane loss (AG*) from a secondary alkyl hydride equal to AAG°. A s discussed above, the cydoalkyl methylenes are oriented away from the metal center and do not have a mode in which the other methylene will rotate toward the metal, destabilizing the complex. However, such a mode exists within the supposed secondary linear alkyl derivatives and could result in greater instability (Scheme II.XI). Yet, the nearly 2.5 kcal/mol difference in energy seems too large to be solely due to steric interactions. Scheme II.XI Finally, in order to fit the data with the computer modeling program, the rate for isomerization was slower than the rate for cyclopentane loss. This results in a to cyclopentane loss. This result is different from both the macroscopic and microscopic models for the rates of isomerization within the linear alkyl complexes. (MeO)jP' AAG* -0.4 kcal/mol, meaning the barrier for isomerization is higher than the barrier 76 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Due to these anomalies, the corresponding cyclohexyl derivative was synthesized. It was thought that the cyclopentyl moiety might be too “inaccessible” and that the cyclohexyl methylenes would be closer to the metal center and, hence, more rapid migration would occur. Further, a possible dependence upon the structure of the ring would be interesting. Ultimately, it was hoped that this would provide the k& rate in the original model.1 9 Although full analysis is still in progress, the rate of migration qualitatively appears comparable to that of the cyclopentyl complex. Incorporation of deuterium into the methylene resonances at 0.8 ppm and at 1.24 ppm was observed. Further, although the overall rate of rearrangement is slower than expected for a 1,2-shift from one 2° a-complex intermediate to another, the less constrained cyclohexyl derivative differs from the cyclopentyl complex, given the observation of another site of deuterium incorporation. 2.6 Mechanism of Alpha<-»Omega Deuterium Exchange: Final Considerations and Conclusions In light of the results from the cydoalkyl complexes, an final, alternative mechanism for the rearrangement of the linear alkyl complexes can be postulated. It is possible that while the migration may occur via discrete a-complex intermediates, the metal may not interact sequentially with every methylene (1,2-shifis). Hence, an amalgamation of the “end-to-end” mechanism and the previously discussed mechanism may be the mechanism that is operating. As shown in scheme II.XII, a 77 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3.4koa' krc20 ^ k o t2 ° » N-Rh-.H (MeObP/ V - \ koa D not observed Alpha*-*Omega Isomerization via 1,3- and 1,4-shifts Scheme I1.X1I series of 1,3- and 1,4-shifts from 1° a-complexes to 2° a-complexes would result in the same observed rearrangement in the linear derivatives. Further, unlike the “end- to-end” mechanism, each alkyl would form a series of pseudo-metallacyclobutyl (resulting from a 1,3-shift) and metallacyclopentyl (1,4-shift) transition states, possibly accounting for the similar efficiencies of rearrangement observed within each alkyl. Also, if such shifts are also operative in the cydoalkyl derivatives, the 78 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. rings might be constrained in such a manner that doesn’t allow for a 1,3 -shift and, hence, the rates observed in the cydoalkyl examples are possibly a direct measure of a 1 ,2 -shift. One possible test to determine if the migration occurs via a series of 1,2- shifts or a variety of 1,3- and 1,4-shifts would be to make a linear alkyl derivative with a quaternary center in the middle of the chain (Scheme II.XIII). If either no rearrangement or a rate of rearrangement slower than the rate for the analogous chain without the quaternary center is observed, then it would appear that a mechanism involving a series of 1 ,2 -shifts is primary mechanism for rearrangement. Conversely, an equivalent rate would suggest a series of 1,3- and 1,4-shifts. Unfortunately, attempts at making the decyl analogue with the quaternary center at C4 have proved unsuccessful, and this aspect of investigation is still in progress. In summation, novel rearrangements have been observed in a series of [CnRh(RXDXP(OMe)3)]+ complexes, where R = butyl, hexyl, decyl, cyclopentyl, (Me k eo C 12 = kOdecyl ?? HN^'Rh? (MeO)3P ' V D Scheme II.XI1I 79 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and cyclohexyl. The macroscopic rate constants for deuterium migration have been calculated by fitting the data with a computer simulation program. Deuterium migration from the metal into the (X-CH 2 occurs at a rate much faster than alkane loss. Further, for the linear derivatives, rearrangement to the C 0 -CH3 occur at rates faster than alkane loss, with the rate of isomerization dependent upon the amount of methylenes in the alkyl subunit. However, the rates of rearrangement for the cydoalkyl derivates are slower than the rates for alkane loss. Yet, in each case, the mechanism for rearrangement is consistent with the formation of discrete alkane a-complex intermediates. Although a model involving interaction with each methylene subunit in the linear alkyl can be constructed and fitted to the data, the discrepancies arising within the cydoalkyl compounds cast doubt upon the legitimacy of this model. Nonetheless, the isotopic rearrangements within a series of soluble metal alkyl deuteride complexes with alkyl chains longer than an ethyl subunit are unprecendented, and a mechanism for rearrangement involving the formation of alkane a-complexes appears to be the most reasonable for the observed rearrangements. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Endnotes 1 Recent Reviews: (a) Amdsten, B.A.; Bergman, R.G.; Mobley, T.A.; Peterson, T.H. Acc. Chem. Res. 1995,28, 154. (b) Hall, C.; Perutz, R.N. Chem. Rev. 1996,9 6 ,3125. (c) Stahl, S.S.; Labinger, J.A.; Bercaw, J.E. Angewandte Chemie-Int. 'I Ed. 1998,16,2181. 2 For references implicating alkane o-complexes as intermediates: (a) Buchanan, J.M.; Stryker, J.M.; Bergman, R.G. J. Am. Chem. Soc. 1986,108, 1537. (b) Periana, R.A.; Bergman, R.G. J. Am. Chem. Soc. 1986,108, 7332. (c) Parkin, G.; Bercaw, J.E. Organometallics 1989,8, 1172. (d) Stahl, S.S.; Labinger. J.A.; Bercaw, J.E. J. Am. Chem. Soc. 19%, 118, 5961. (e) Schafer, D.F.; Wolczanski, P.T. J. Am. Chem. Soc. 1998,120,4881. (f) Fekl, U.; Zahl, A.; van Eldik, R. Organometallics 1999,18, 4156. (g) Wick, D.D.; Reynolds, K.A.; Jones, W.D. J. Am. Chem. Soc. 1999,121,3974. 3 Abis, L.; Sen, A.; Halpem, J. J. Am. Chem. Soc. 1978,100,2915. 4 Wang, C.; Ziller, J.W.; Flood, T.C. J. Am. Chem. Soc. 1995,117, 1647. 5 (a) Bullock, R.M.; Headford, C.E.L.; Hennessy, K.M.; Kegley, S.E.; Norton, J.R. J. Am. Chem. Soc. 1989, 111, 3897. (b) Gould, G.L.; Heinekey, D.M. J. Am. Chem. Soc. 1989, 111, 5502. 6 Geftakis, S.; Ball, G.E. J. Am. Chem. Soc. 1998,120,9953. 7 Precise determination of the 2 Jd-p was precluded by overlap of the 3IP resonance of the Rh-H isomer. 8 Data fitted to kinetic models using a stochastic kinetics program: Chemical Kinetics Simulator™, Version 1.01, © IBM Corp., 1996. 9 Turner, H.W.; Schrock, R.R.; Fellmann, J.D.; Holmes, S.J. J. Am. Chem. Soc. 1983,105,4942. l0Espenson, J. H., Chemical K inetics and Reaction Mechanisms, 2n d Ed., McGraw-Hill: New York, 1995. 1 1 Although it was requested that the exact mass of each cation be calculated, the butyl complex starting material (non-crossover complex) was below the minimal level of intensity necessary for a precise mass detection. However, it was clearly observed. Further, the hexyl complex starting material was well within the range for exact mass determination, but the experimenters at UCR failed to calculate it. Nonetheless, the peaks corresponding to any potential crossover products were < 3% in intensity. 1 2 The hydride resonance of the methane activated complex, [CnRh(MeXHXP(OMe)3 )]+ , appears as a pseudo-triplet centered at 6 = -16.11 ppm. 1 3 McNamara, B.K.; Yeston, J.S.; Bergman, R.G.; Moore, C.B. J. Am. Chem. Soc. 1999,121,6437. 1 4 Xie, X : Simon, J. D. J. Am. Chem. Soc. 1990,112, 1130. 1 5 After -1 half-life for decane loss, a 1 3 C NMR spectrum was collected on the a.to-l3 C-[CnRh(decyl)(D)(P(OMe)3)]*. A Gaussian function was applied to the spectrum in order to observe any evidence of -1 3 CH3 isotopomers resulting from sec-alkyl hydrides. 1 6 Bromberg, S.E.; Yang, H.; Asplund, M.C.; Lian, T.; McNamara, B.K.; Kotz, K.T.; Yeston, J.S.; Wilkens, M.; Frei, H.; Bergman, R.G.; Harris, C.B. Science 1997,2 7 8 ,260. 81 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 7 Hessei, E.T.; Jones, W.D. J. Am. Chem. Soc. 1993,115,554. 1 8 (a) Iimura, M.; Flood, T.C. unpublished results, (b) It was found that the l3C label in the o-CH3 isomerized in the precursors leading up to the synthesis of the corresponding deuteride. Rapid (J- hydride elimination/insertion appears to occur in the precursors, although not in the final desired product Further evidence o f this is that in the synthesis of the Rh-D complexes, the impurity is [CnRh(HXDXP(OMe)3)]*. 1 9 The actual rate, k2 2 , could not be directly measured, since the alkane complex is not observed. However, by calculating the rate for reductive elimination in the Rh-D->a-D exchange and estimating the rate for oxidative addition, as described in the discussion of the model, an estimate for kz2 could be obtained. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Experimental Section General Considerations All reactions and manipulations were carried out under a nitrogen or argon atmosphere, unless otherwise noted. Nitrogen and argon were purified by passage through a glass tower containing a reduced copper catalyst (BASF R3-11) and passage through a subsequent tower containing either indicated 4 A molecular sieves or a combination of 4 A molecular sieves and indicated Drierite®. Standard vacuum and Schlenk flask line techniques were applied to carry out most reactions. Storage and manipulation of compounds was done in a Vacuum Atmospheres Model HE- 553-2 glove box equipped with a DriTrain MO40-2 inert gas purifier. The oxygen content of the glove box was monitored with Cr(acac) 2 as an indicator, with a light orange color indicating that the glove box is sufficiently air free for use. Benzene, diethyl ether, pentane, and tetrahydrofuran (THF) were dried over Na/benzophenone and distilled immediately prior to use. Acetonitrile, dichloromethane, fluorobenzene, isopropanol, methanol, and pyridine were distilled from CaH2 and stored in solvent flasks under nitrogen. Hexafluorobenzene was purified by washing with H2SO4 until the sulfuric acid solution remained colorless, then washed with H2O, NaHCOj/I^O, H2O, and dried overnight over M gSC> 4 . It was then distilled from CafE and stored in a solvent flask under nitrogen. Benzene- d6 used for kinetic experiments was dried over Na/benzophenone and distilled under reduced pressure prior to use. All other NMR solvents were used as received from Cambridge Isotopes, Inc.. 83 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. NMR spectra were recorded on Bruker AC-F250, AM-360, and AMX-500 MHz FT spectrometers. Chemical shifts are reported in par.t.s per million (5) downfield from TMS via reference to residual protons in the deuterated solvent for the 'H NMR and the solvent carbon(s) in the l3 C NMR. 3 1 P NMR are referenced to external 85% H3PO4 or trimethylphosphite (8=141 ppm), which was referenced to external 85% H3PO4. 2 H NMR are referenced to the residual deuterium in the proteo solvents, with the following chemical shifts: MeOH-do (3.30 ppm, -CH2Z)), CH3CN (1.93 ppm, CH2ZX:N), and THF-do (1-73 ppm 0 (CH2CHD)2 . Accurate integrals in all spectra were obtained by allowing 3-10s relaxation delays. For each of the linear alkyl derivatives, the 37h-h for the terminal methyl group (C 0-CH3) was typically close to 7.0 Hz and, hence, is not listed for every alkyl. Gas chromatography was conducted using a Hewlett Packard Series 6890 GC and a HP-5 (5% diphenyl/95% dimethylpolysiloxane) capillary column. Elemental analyses were performed by Deser.t. Analytics, Tuscon, AZ or Oneida Research Services, Inc., Whitesboro, NY. High resolution FAB-MS spectra were obtained from the University of California, Riverside Mass Spectrometer Facility. Synthetic Procedures Alkyl Lithium Reagents The alkyl lithium reagents were prepared as described below, adapted from literature procedures, except for butyllithium and hexyllithium. 1 The latter two were used as received from Aldrich. However, if the bottles had sat for some time, the 84 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. contents were titrated using a biphenyl methanol (4-phenyl-benzyl alcohol) indicator in THF.lb The end point was indicated by a color change from a light yellow to a fairly deep rose-red. In a typical alkyllithium reagent preparation, 15 ml of the corresponding alkyl chloride or bromide was degassed with argon and placed in an addition funnel specially designed for a slow, highly controllable drip rate. The lithium used was either purchased from Aldrich as a wire (0.5 % Na content) and stored under argon in a 2-necked, 500 mL round bottom flask, or was prepared independently. Preparation of the lithium for use in synthesizing the alkyllithium reagent was done as follows. Lithium rod, that had been standing in mineral oil, was cleaned by removing the hydroxide layer with a razor blade. The lithium was wiped free of granules and rinsed with pentane or hexane. Then, 40 g of lithium was weighed in mineral oil and subsequently pounded into flat pieces with a hammer on the bench top. It was important to ensure that enough sodium would amalgamate with the lithium, so 4 g (10%) was cut into pieces and each piece was pounded into a piece of the flattened lithium. These pieces were then folded and pounded more, until it seemed that the two metals were mixed sufficiently. The pieces were place in a 500 mL, 3-necked, round bottom flask and covered with mineral oil. The metal mixture was heated to 210 oC for 12 hr via an oil bath. During this time, the metal darkened and melted into a large disk, resembling a rice cake. After heating, the oil and metal mixture was allowed to cool and the oil was removed via cannula. The lithium was washed with 5 x 40 mL of dry pentane, with 85 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. each portion being removed via cannula. The round bottom flask containing the lithium “rice-cake” was transferred to a glove bag under an argon atmosphere, and the lithium was broken to pieces using a screwdriver and pincer clamps. Once ~lcm x lcm x 1cm lumps were obtained, the round bottom flask containing the lithium was removed from the glove bag. The lithium was subsequently washed with 4 x 35 mL portions of dry pentane, with each portion being removed via cannula. The washing was done in order to remove the black soot on the metal lumbs. After sufficient washing, the lithium was stored in the flask under an argon atmosphere for future use. Once the lithium was prepared and ready for use in the alkyllithium preparation, 4 equivalents of lithium (ranging in sodium content from 0.5-10%) were weighed, pounded into flat pieces under mineral oil, cut into thin strips, and transferred to a 250 mL, 3-necked, round bottom flask via a sidearm under an argon flush. The strips were washed with 3 x 30 mL portions of pentane, with each 30 mL portion removed via cannula. Then, 20 ml of pentane was added to the lithium turnings. The pentane was refluxed for -30-45 min and then cooled to ambient temperature. Eventually, it was further cooled to 0 °C via an ice bath. -1-2 ml of the neat alkyl halide was added to the lithium at 0 °C and allowed to stir for 15 min. The ice bath was then removed and the reaction mixture allowed to warm to ambient temperature. Typically, the reaction began to initiate, as indicated by the formation of a blue-gray to dark purple cloudiness to the reaction mixture or on the surface of the lithium. The ice bath was kept nearby in order to control the reaction 86 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. temperature. Allowing the reaction to become too vigorous leads to significantly reduced yields, primarily resulting from coupling. After reaction initiation, the alkyl halide in the addition funnel was diluted with 40-60 mL of pentane and the solution was added slowly to the reaction mixture over a period of 5-8 hr. Typically, mild heating of the reaction to -30-35 °C was done during addition in order to ensure completion of reaction. Often, it was found that the reaction stopped at different amounts of conversion if no heating was applied. Reinitiating via heating usually resulted in reduced yields due to dehydrohalogenation of the starting material by the alkyllithium already formed. Reaction progress was monitored via gas chromatography (GC) by adding 100 pL portion of the reaction mixture to a 8 ml vial containing 2 mL of pentane and 2 mL of water. After hydrolysis, a 1 pL aliquot of the pentane layer was injected into the gas chromatograph for analysis. Upon completion, the precipitate was either allowed to settle, or the mixture was transferred in portions via a cannula to a centrifuge tube equipped with a rubber septum and previously dried in an oven and cooled under an argon stream. The tube was placed in a centrifuge until nearly all of the suspended solids settled to the bottom. In either case, the solution was filtered and then the volume reduced to -25- 40 ml under reduced pressure. The filtered solution was transferred via cannula to a solvent flask for storage. The solution concentration was determined using the method of titration described above. 87 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Synthesis of Decane-d* The synthesis of this reagent for control experiments (see Kinetic Experiments section below) was done according to adaptations of standard literature procedures.1 Initially, 67.0 g of sebacic acid was esterified via the Fischer esterification method. The resulting ethyl sebacate was distilled under reduced pressure (113-117 oC; 0.6 mm Hg) and obtained in good yield (65.9 g; 77%). The ester was reduced to the corresponding diol-d4 via adding an ether solution of the ester (37 g ester in 80 mL ether) dropwise to a cooled (0 °C) suspension of 6.0 g LAD. After addition was complete, the solution was allowed to reach ambient temperature and stirred for another 2.5 hr. It was then refluxed for an hour to ensure completion. The solid, white decane-l,1 0 -diol-d4 was isolated using a basic hydrolysis method, filtration of solids, and subsequent removal of ether via rotovap.2 The diol was further dried in vacuo overnight and obtained in good yield (19.0 g; 74%). In order to prepare the ditosylate, 18.0 g of the diol was dissolved in 65 mL pyridine and added dropwise to a cold (0 °C) pyridine solution of tosyl chloride (39.0 g in 100 ml pyridine) over a period of 3.5 hr. The solution was stirred for another 1.5 hr at 0 °C and then the reaction vessel was placed in the refiidgerator overnight. The next day, the white product precipitate was collected on a glass filter frit, and the supernatant kept to the side. The precipitate was then washed with a dilute, cold 10% sulfuric acid solution, and then with 5 x 30 mL portions of diethyl ether. The pyridine solution was also washed with dilute, cold 10% sulfuric acid, resulting in 88 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the precipitation of more product ditosylate. This was filtered and washed with 4 x 20 mL portions of water and then 3 x 35 mL of ether. The white solids were combined and then dried under vacuum for 1.5 days. A total of 17.5 g of the ditosylate was obtained (38% yield). The resulting ditosylate was dissolved in 275 ml of THF and added to an addition funnel. The solution was then added dropwise over a period of 3 hr to a suspension of 0.93 g LAD in 75 ml THF at 0 °C. After addition, the reaction mixture was allowed to warm to ambient temperature and stirred for 3 hr. Then, the mixture was refluxed for an hour to ensure completion. The ensuing work-up involved the same basic hydrolysis as above, filtration, and washing of the solids with 2 x 25 ml ether. Then, the ether and THF were distilled, leaving a slightly yellow, high-boiling liquid. The liquid was mixed with 10 ml of pentane and run through a column of silica gel. The water-white pentane solution was distilled, first removing pentane at atmospheric pressure, and then collecting the desired decane-d6 under reduced pressure (90-93 °C/60 mm Hg). The yield of decane-d^ was 6.3 ml (88%), and was >98.7% pure as determined via GC. Synthesis of Organometallic Rhodium Complexes CnRhEt Derivatives. The synthesis of all CnRhEt derivatives were performed according to published procedures.3 89 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Synthesis of CnRh(Butyl)3 (la) In an experiment typifying the synthesis of the rhodium trialkyl complexes, 450 mg (1.26 mmol) of CnRhCU H2O was loaded into an oven-dried Schlenk flask flask (previously allowed to cool under vacuum), and placed under vacuum for 2-8 hr. The yellow solid was then suspended in 40 mL of dry Et20 and cooled to -78 °C. Then, 7.5 mL of a 1.7 A/ butyllithium solution (in hexanes; 10 equivalents) was added dropwise over 3 min. The reaction mixture was stirred at -78 °C for 20 min and then was allowed to warm to ambient temperature. Within 45 min, the reaction began to change color from yellow to either orange or brown. Stirring was continued for another 3.5 hr at ambient temperature. After 3.5 hr, the solution was again cooled to -78 °C and 0.475 mL of dry MeOH (13.2 mmol) was added dropwise. The reaction was stirred at this temperature for 15-25 min, usually becoming more tan and cloudier with time. The dry ice/acetone bath was replaced with an ice bath and the reaction stirred for 5-10 min at 0 °C. The solvents were removed in vacuo at 0 °C. After solvent removal, the tan solids were dried in vacuo. In order to obtain the product, 30 mL of CH2CI2 was added to the tan precipitate and the suspension was transferred via cannula to an oven-dried centrifuge tube equipped with a septum and stir bar, and under N2 atmosphere. The slurry was stirred for 30 min and then centrifuged until the solids settled. The solids then collected at the bottom or at the top level of the solvent, varying from one 90 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. synthesis to another. Another oven-dried Schlenk flask flask was equipped with a filter frit and celite and allowed to cool under vacuum. The orange solution in the centrifuge tube was transferred via cannula to the filter frit and filtered through the celite. Then, 3 x 25 mL of CH2CI2 portions were added to the centrifuge tube and the process of stirring, centrifuging, and filtering repeated. After filtration, all of the remaining CH2CI2 was removed in vacuo, yielding an orange oil. This was washed with 2 x 15 mL of pentane, with each portion of supernatant being removed via cannula after allowing the resulting tan precipitate to settle. The residual pentane was then removed in vacuo and the solids were dried under vacuum. Yield: 218 mg (43%; M. W = 403.13 g/mol) 'H NMR (dmso-d6 ; 500.14 MHz): 8 = 0.29 (br t, 6H, Rh(C//2CH2 CH2 CH3 )); 0.81 (t, 9H, Rh(CH2 CH2CH2 C//3)); 1.06 (pentet, 6H, Rh(CH2 C//2CH2 CH3 )); 1.19 (septet, 6H, Rh(CH2CH2 C/f2 CH3 )); 2.48-2.53 (br, 6H, NC//H), 2.75-2.83 (br multiplets, 6H, NCHtf); 3.16 (broad singlet, 3H, N-H). (CeDe; 360.14 MHz) 6 = 0.93 (br m, 6H, Rh(C//2 CH2 CH2 CH3 )); 1.27 (t, 9H, Rh(CH2CH2 CH2 Ctf3 )); 1.30-1.40 (m, 6H, Rh(CH2 Ci/2CH2 CH3 )); 1.49-1.59 (m, 6H, Rh(CH2 CH2C//2 CH3)); 1.80-1.90 (br multiplet, 9H, NCHtfand N -//); 2.19-2.29 (br multiplet, 6H, N.C//H). I3C NMR (CeD6 ; 90.57 MHz): 8 = 15.11 ppm (1C, Rh(CH2CH2 CH2 CH3)); 19.08 (d, J^-c = 32 Hz, 1C, Rh(CH2 CH2 CH2CH3 )); 29.51 (d, 3 Jr.hc= 3.2 Hz, 1C, Rh(CH2 CH2 CH2CH3 )); 38.89 (1C, Rh(CH2CH2CH2 CH3 )); 47.22 (NCH2 ). 91 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Synthesis of CnRhButyl(OTf)2 (lb) In a typical experiment, 300 mg (0.74 mmol) of CnRhBti3 was dissolved in 60 mL of CH2CI2. The moderately dark orange solution was cooled to -78 °C and 131 pL of triflic acid (HOTf; 1.48 mmol) was added dropwise to the cold solution. After stirring the reaction mixture for 10 min at -78 °C, the reaction was placed in an ice bath. Stirring was continued for another hour with the solution becoming cloudy with a light orange precipitate. Stirring was stopped and the precipitate was allowed to settle. The temperature was maintained at 0 °C. Once the precipitate settled, the light yellow-green solution (occasionally it was clear) was removed via cannula and the solids were washed with 2x15 mL portions of CH2CI2, with each portion removed via cannula. Residual solvent was removed under high vacuum and the very light orange solid powder dried in vacuo. Yield: 400 mg (92%;MW. = 587.18 g/moT) *H NMR (dmso-d6 ; 360.14 MHz): 5 = 0.98 (t, 3H, Rh(CH2CH2CH2C//3 )); 1.38,1.50, and 1.67 (m, 1H, m, 2H, m, 1H, respectively, Rh(CH2 C//2 C//2 CH3 )); 1.94 (br m, 1H, Rh(CH^/b CH2 CH2 CH3 )); 2.15 (brm, 1H, Rh(CHa ^ b CH2CH2 CH3 )); 2.76-3.27 (br multiplets, 12H, NCH2 ); 5.71,6.13, and 6.93 (br s, 1H each, N-H). ,3C NMR [dmso-d6 ; 90.57 MHz): 5 = 13.79 ppm (C4, Rh(CH2 CH2 CH2 CH3 )); 22.41 (d, Jrh-c = 22.6 Hz, 1C, Rh(CH2CH2CH2 CH3 )); 25.42 (1C, Rh(CH2CH2CH2 CH3 )); 33.61 (1C, Rh(CH2 CH2CH2 CH3 ); 42.48,48.81,49.53 (2C), 51.57, 56.31, (6C total, NCH2 ). Anal. Calcd. for ^ C u N sO g l^R li: %C 24.28 % H 4.37 %N 6.74 Found: %C24.54 %H4.12 %N 7.15. 92 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Synthesis of CnRhBu(P(OMe)3)OTf2 (lc) In the drybox, a Schlenk flask flask was charged with 185 mg of CnRhBuOTf2 (0.32 mmol). The Schlenk flask flask was attached to the vacuum line manifold and 35 mL of THF was added to the flask via syringe. To the clear, orange solution, 39 p.L (0.32 mmol) of purified trimethylphosphite was added to the solution at r.t.. The reaction mixture was then allowed to stir for 14 hr at r.t.. The resulting yellow solution was filtered (occasionally, a small amount of precipitate formed) and collected in another Schlenk flask flask. The THF was removed under reduced pressure. The resulting yellow/yellow-orange oil was rinsed with 3 x 20 mL portions of pentane, with each portion being removed via cannula. The residual pentane was removed in vacuo, yielding a yellow/yellow-orange precipitate. Yield: 205 mg (90%;M. W . = 711.19 g/mot). !H NMR (dmso-d6 ; 360.14 MHz): 5 = 0.96 (t, 3H, Rh(CH2CH2CH2C/f3)); 1.27, 1.43, and 1.53 (m, 1H, m, 2H, and m, 1H, respectively, Rh(CH2 C//2 C//2CH3 )); 1.84 (brm, 1H, Rh(C//a H feCH 2 CH2 CH3 )); 1.93 (brm, 1H, Rh(CHtflr 4 CH2 CH2 CH3 )); 2.60-3.40 (br multiplets, 12H, NCH2 ); 5.46, 5.63,6.43 (br s, 1H each, N-H); (MeOH-d4 ; 500.14 MHz): 6 = 0.86 (t, 3H, Rh(CH2CH2CH2 C//3 )); 1.24-1.48 (br, 8H, Rh(CH2 C//2C//2 CH3 )); 1.82 (br m, 1H, Rh(C//a HftCH2 CH2 CH3 )); 2.00 (br m, 1H, Rh(Ctf,H6 CH2CH2CH3 )); 2.62-3.20 (br multiplets, 12H, NCH2 ); 3.87 (d, 3 Jp.H = 11 Hz; 9H, P(OCtf3 )3 ); 4.93,5.27,5.51 (br s, 1H each, N-H). ,3C NMR (,dmso-d6 ; 90.57 MHz): 5 = 13.71 ppm (1C, Rh(CH2CH2 CH2 CH3)); 17.82 (dd, jRh-c = 19 Hz, 2 JP -c= 11 Hz, Rh(CH2CH2 CH2 CH3 )); 25.1,33.5 Rh(CH2 CH2CH2 CH3 ); 47.91,48.29,49.20, 52.08 (2 C’s), 53.11, (6C total, NCH2 ); 93 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 56.68 (d, 2 JP ^ = 9.8 Hz, P(OCH3 )3 ). 3IP NMR (dmso-d6; 145.79 MHz): 5 = 107.50 ppm (d, jRh.P = 213 Hz, Rh-P(OMe)3 ). Synthesis of [CnRhButyl(H)(P(OMe)3)]OTf (Id) In the drybox, a Schlenk flask flask was charged with 99 mg (0.14 mmol) of CnRhButyl(P(OMe)3 )OTf2 (lc). The solids were dissolved in 20 mL of freshly distilled, dry THF. This solution was cooled to -78 °C. Another Schlenk flask flask was charged with 13 mg of NaBFL (0.35 mmol; 2.5 equivalents) in the dry box. This Schlenk flask was covered with foil (outside of the dry box) and cooled to -78 °C. The solution of lc was transferred via cannula to the Schlenk flask flask containing theNaBFL. The reaction mixture was stirred at -78 °C for one hour, and then was allowed to warm to room temperature and stirred overnight, for a total of 14 hr. It is important to allow for sufficient time in order for the reaction to complete. The ensuing orange/brown reaction mixture was filtered through celite into another Schlenk flask, and the solvent was removed under reduced pressure. The resulting gray/tan precipitate was brought into the box, scraped down, and then 35 mL of fluorobenzene was added to the solids in the Schlenk flask. The flask was removed from the dry box, and the orange/brown slurry was stirred for 2 hr. The suspension was filtered into another flask, resulting in a pale orange solution. The fluorobenzene was removed in vacuo (and recollected), and the oily residue washed with 4x15 mL portions of pentane, with each portion of pentane being removed via 94 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. cannula. Residual pentane was removed in vacuo, yielding a light tan precipitate. The product can be further purified via dissolution in acetonitrile and flashing the solution through a small pad of neutral alumina (~ 1 cm x 1cm x 1cm), using acetonitrile as the eluent. It is important that it is neutral alumina and not acidic nor basic alumina, since it binds to these irreversibly. Further, it also binds to silica gel and, thus, this cannot be used either. The acetonitrile was then removed in vacuo and the resulting oil washed with 3x15 mL portions of pentane, with each portion removed via cannula. Residual pentane was removed in vacuo, yielding the light tan powder. This precipitate was always a mixture of the desired product and CnRh(H>2(P(OMe)3)+ OTf. Therefore, the yield was calculated from the overall weight of the collected solids and the molar ratio of the two as indicated by either 'H or 3IP NMR. (e.g. X m o te s a(M W a) + y m o ie s b(M W b) = total mass, where y m o ies b = [Ratio (B /A JK xm oies a ) ) Yield: 50 mg (64%;M. W . = 563.12 g/mol). *H NMR (MeOH-d4; 500.14 MHz): 8 = -16.34 ppm (pseudo-t, Jrji-h = 2Jp-h = 30 Hz, 1H, Rh- H); 0.88 (t, 3H, Rh(CH2 CH2 CH2 Ctf3)); 1.19-1.31 (br, 4H, Rh(CH2 C//2 C//2 CH3 )); 1.01 (m, 2H, Rh(C//2 CH2 CH2 CH3 )); 2.70-3.86 (br, 6H, NC//H) 3.0-3.2 (br, 6H) NCHtf); 3.67 (d, JP .H = 11.0 Hz, 9H, P(OCtf3 )3 ); 4.48,4.87,5.47 (br s, 1H each, but the 4.87 resonance is under residual MeOH, N-H). ,3C NMR (dmso-de: 125.77 MHz): 8 = 6.51 (dd, J^-c = 25 Hz, JP c = 15.1 Hz, 1C, Rh(CH2 CH2 CH2 CH3 »; 13.80 ppm (1C, Rh(CH2 CH2 CH2 CH3 )); 26.92, (1C, Rh(CH2 CH2 CH2 CH3 )); 37.22 (1C, Rh(CH2 CH2 CH2 CH3 )); 46.51,47.53,48.72,49.54,49.51,49.91 (6C total, NCH2 ); 51.60 (d, 2 JP -c - 6.0 Hz, P(OCH3 )3). 3,P {'H decoupled, Rh-//coupled} NMR 95 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (dmso-d6 ; 145.79 MHz): 8 = 138.82 ppm (dd, Jrh-p = 241 Hz, 2 JH -p = 27 Hz, Rh- P(OMe)3 ). I9 F NMR (dmso-d6 ; 470.57)i 8 = -77.80 ppm (O3SCF3). Synthesis of [CnRhButyl(DKP(OMe)3 ))OTf (le) In the synthesis of the deuteride compound, it was necessary to rigorously exclude light in all steps of manipulation and synthesis in order to obtain a relatively good time zero 2 H NMR for the Alpha-> Omega migration. In a typical experiment, a Schlenk flask flask was charged with 75 mg (0.11 mmol) of CnRhButyI(P(OMe)3)OTf2 (lc) and the solids dissolved in 20 mL of freshly distilled, dry THF. This solution was cooled to -78 °C. Another Schlenk flask flask was charged with 12 mg of NaBD4 (0.29 mmol; 2.6 equivalents) in the dry box. This Schlenk flask was covered with foil (outside of the dry box) and cooled to -78 °C. The lc solution was then transferred via cannula to the foil covered Schlenk flask. After transfer was complete, the reaction mixture was stirred at -78 °C for one hour. The bath was then removed and the reaction placed in an ice bath and stirred for 3 hr. This bath was removed and then the reaction was allowed to reach ambient temperature and stirred overnight, for a total of 15 hr. It is important to allow for sufficient time in order for the reaction to go to completion. The reaction mixture was filtered and solvent was removed in vacuo. The resulting precipitate was brought into the box, scraped down, and then 35 mL of fluorobenzene was added to the foil covered Schlenk flask. The slurry was stirred for 2 hr and then filtered, with the filter and receiver Schlenk flask flask also covered 96 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. in aluminum foil. The fluorobenzene was removed in vacuo (and recollected), and the oily residue was washed with 4 x 15 mL portions of pentane, with each portion removed via cannula. Residual pentane was removed in vacuo, yielding a light tan precipitate. This precipitate was always a mixture of the desired product and CnRh(H)(D) (P(OMe)3)+ OTf. Therefore, the yield was calculated from the overall weight of the collected solids and the molar ratio of the two as indicated by either 'H or 3 1 P NMR. (e.g. X m oies a(M W a ) + ym oles b(M W b) = total mass, where ym o ie s b = [Ratio (B/A)](xm o ie S a) )• The 'H, 13C, and 3IP were identical to those above, save for broadening of the a-CH 2 by deuterium in the 1 3 C spectrum and coupling to the 3 lP. The 2 Jd-p was not resolved due to broadening and overlap with the a-exchanged species. Yield: 30 mg (51%;M. W . = 588.18 g/mol). 2 H NMR (MeOH-do; 76.77 MHz): 8 = -16.40 ppm (br) Rh-D; 0.88 (br, different at t0 ; increases upon heating) Rh(CH2CH2 CH2CH2D); 1.01 (br) Rh(CHDCH2CH2 CH3). FARMS: Calcd: 415.1456 Found: 415.1438 (4.5 ppm). Synthesis of [CnRh(Butyl)(H)(P(OMe)3)]+ 'BAr4r (If) In a typical experiment, 20 mg (0.034 mmol) of Id was combined with 30 mg (0.034mmol) of NaBAr/ in a Schlenk flask flask equipped with a stir bar and then 15 mL of fluorobenzene was added. The orange solution was stirred for 3-4 hrs and became slightly cloudy with time. The solution was then filtered through celite 97 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and the fluorobenzene removed in vacuo. Despite washing with greater than 5 x 20 mL of pentane, removing each portion via cannula, the resulting oil never crystallized. Hence, an overall yield was not calculated. The 'H, l3C, and 3,P NMR of the cation are the same as Id. I9 F NMR (470.57 MHz; MeOH-d4 ): 8 = -62.00 ppm (aryl-Cfys). Synthesis of [CnRh(ButylXD)(P(OMe)3)]+ "BAr4f (Ig) The synthetic procedure is the same as for If, except everything was done with the rigorous exclusion of light. The 2 H spectrum is the same as for le. I9 F NMR 0 470.57 MHz; MeOH-d4 ): 8 = -62.00 ppm (aryl-CFj’s). Synthesis of CnRh(HexyI)j (2a) In an experiment typifying the synthesis of the rhodium trialkyl complexes, 450 mg (1.26 mmol) of CnRhCh'^O was loaded into an oven-dried Schlenk flask flask (previously allowed to cool under vacuum), and placed under vacuum for 2 - 8 hr. The yellow solid was suspended in 40 mL of dry Et2 0 and cooled to -78 °C. Upon cooling, 5.1 mL of a 2.5 M hexyl lithium solution (in hexanes; 10 equivalents) was added dropwise over 3 min. The reaction mixture was stirred at -78 °C for 20 min. The bath was removed, and the reaction was allowed to reach ambient temperature. Within 45 min, the reaction changed color from yellow to 98 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. either orange or brown. Stirring commenced for another 3.5 hr at ambient temperature. After the 3.5 hr, the solution was cooled to -78 °C and 0.475 mL of dry MeOH (13.2 mmol) was added dropwise. The reaction was stirred at this temperature for 15-25 min, usually becoming more tan and cloudier in this time. The dry ice/acetone bath was removed and replaced with an ice bath and the reaction stirred for 5-10 min at 0 °C. The reaction became dark brown in color. Then, the solvents were removed in vacuo at 0 °C. Once all of the solvents were removed, the ice bath was removed and the tan solids dried in vacuo. The product was isolated by adding 30 mL of CH2CI2 to the tan precipitate and transferring the suspension via cannula to an oven-dried centrifuge tube equipped with a septum and stir bar, and under N2 atmosphere. The slurry was stirred for 30 min and centrifuged. The solids either collected at the bottom or at the top level of the solvent, varying from one synthesis to another. The resulting orange solution was filtered through celite. Then, 3 x 25 mL of CH2CI2 portions were added to the centrifuge tube, with each portion stirred, centrifuged, and filtered. After filtration, all of the remaining CH2CI2 was removed in vacuo, yielding an orange oil. This was washed with 2x15 mL portions of pentane, with each portion removed via cannula after allowing for the tan precipitate to settle. The residual pentane was removed in vacuo and the solids dried. Yield: 412 mg (67%;M.W. = 487.20g/mot) *H NMR (dmso-d6 ; 500.14 MHz): 5 = 0.29 ppm (multiplet, 6 H, RhC//2(CH2)4CH3 )); 0.85 (t, 9H, RhCH2(CH2)4C//3 ); 0.93-1.35 (br multiplets, 99 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24H, RhCH2(Ctf2)4CH3 ; 2.49-2.54 (br, 6 H, NC//H), 2.74-2.82 (br, 6 H, NCH//); 3.15(brs,3H,N-//). ,3C NMR{dmso-d6; 125.77Aff/z): S= 14.14ppm(s, 1C, RhCH2(CH2)4CH3 ); 17.94 (d, = 35 Hz, RhCH2(CH2)4CH3 ); 22.43, 31.66, 33.80, (C2, C4, C5) RhCH2CH2CH2(CH2)2CH3 ); 35.42 (d, 3JRh-c= 2.7 Hz, C3, RhCH2CH2CH2(CH2)2CH3 ). Synthesis of CnRhHexyl(OTf)2 (2b) In a typical experiment, a Schlenk flask flask was charged with 310 mg (0.64 mmol) of 2a in the dry box, the flask attached to the vacuum line manifold, and the powder dissolved in 45 mL of CH2C 12. The moderately dark orange solution was cooled to -78 °C and 113 pL of triflic acid (HOTf; 1.28 mmol) was added dropwise to the cold solution. After stirring the reaction mixture for 10 min at -78 °C, the reaction was placed in an ice bath. Stirring was continued for another hour with the solution becoming cloudy with a light orange precipitate. Stirring was stopped and the precipitate was allowed to settle. The temperature was maintained at 0 °C. Once the precipitate settled, the light yellow-green solution (occasionally it was clear) was removed via cannula and the solids were washed with 2x15 mL portions of CH2C12 , with each portion removed via cannula. Residual solvent was removed under high vacuum and the very light orange solid powder dried in vacuo. Yield: 360 mg (92%;M. W . = 615.20 g/mol) *H NMR (CDjCN; 500.14 MHz): 6 = 0.92 ppm (t, 3Jh.h = 6.5 Hz, 3H, RhCH2(CH2)4C//3 ); 1 .37 (br multiplet, 4H), 1.47 (br multiplet, 2H),1.54 (br multiplet, 2H) RhCH2(C//2)4CH3; 2.16 (br multiplet, 1H, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RhC//a Hb (CH2)4CH3 ); 2.33 (br multiplet, 1H, RhCHa//b(CH2) 4CH3 ); 2.58-3.18 (multiplets, 8 H, NC//2 ), 3.30 (br multiplet, 3H, NC Hi), 3.48 (br multiplet, 1H, NC//2 ); 4.78 (br s, accidental overlap of 2 N-H), 5.04 (br s, 1H, N-H). I3 C NMR C CD3 CN; 125.77MHz): 5 = 14.44 ppm (C6 , RhCH2(CH2)4CH3 ); 21.16 (d, Jrm;= 20 Hz, Ca, RhCH2(CH2)4CH3 ); 23.51,32.61,33.24,33.77 (C2-C5, RhCH2(CH2)4CH3 ); 46.73,47.14,50.89,52.57,52.91,53.91 NCH2 ’s; 123.50 (q, Jf-c = 321 H z,0 3SCF3). i9F NMR (CD3CN; 420.42 MHz): -77.80 ppm (s, 0 3SCF3 ). Anal. Calcd. for H28Ci4N306F6S2Rh: %C 27.32 %H4.59 %N6.83 Found: %C 27.48 %H 4.81 %N 6.85. Synthesis of CnRhHx(P(OMe)3)OTf2 (2c) A Schlenk flask flask was charged with 165 mg of CnRhHxOTf2 (0.27 mmol) in the dry box, attached to the vacuum line manifold, and 30 mL of THF added via syringe, resulting in a clear, orange solution. Then, 32 pL (0.27 mmol) of purified trimethylphosphite was added to the solution at r.t.. The reaction mixture was allowed to stir for 14 hr at r.t. The resulting yellow solution was filtered (occasionally, a small amount of precipitate formed) and the THF was removed in vacuo. The resulting yellow/yellow-orange oil was then rinsed with 3 x 20 mL of pentane, with each portion being removed via a cannula. The residual pentane was removed in vacuo, resulting in a yellow/yellow-orange precipitate. Yield: 176 mg (8 8 %; M. W . = 739.21 g/mol). 'H NMR (MeOH-d4; 500.14 MHz): 8 = 0.86 (t, 3H, Rh(CH2(CH2)4C//3 )); 1.24-1.48 (br, 8 H, Rh(CH2(C//2)4CH3 )); 1.82 (br, 1H, 101 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rh(C//a Hb (CH2)4CH3 )); 2.00 (br, 1H, Rh(CHa//b (CH2)4CH3 )); 2.62-3.20 (br multiplets, 12H, NCH2 ) 3.87(d, 3 JP .H= 1 1 Hz,9H, P(OC//3 )3 ); 4.93,5.27,5.51 (br s, each 1H, N-H. I3 C NMR (CDjCN; 125.77 MHz): 8 = 14.38 (1C, Rh(CH2(CH2)4CH3 )); 18.05 (dd, 1 ^ = 20 Hz, 2JP ^ = 10 Hz, Rh(CH2(CH2)4CH3 )); 23.37,32.39,33.28, 33.74 (C2-C5) Rh(CH2(CH2)4CH3 ); 48.05,48.60,49.03, 51.45, 53.82, 55.09 NCH2’s; 56.07 (d, 2 JP -c= 9.6 Hz, P(OCH3 )3 ); 122.10 (q, JF -c= 321 Hz, 0 3SCF3 ). 3IP NMR (CD3CN; 202.48 MHz): 5=110.78 (d, jR h-P = 205 Hz). I9 F NMR (CDsCN; 470.57 MHz): 5 = -77.80 ppm (s, 0 3SCF3 ). Synthesis of CnRhHx(P(OMe)3-< / 9)OTf2 (2c') a) Synthesis o f trimethylphosphite-dg An oven dried, 3-necked, 500 mL RBF was equipped with an addition funnel, reflux condenser, and septa. It was cooled under vacuum and flamed twice before use. Then, 300 mL of freshly distilled, dry Et2 0 was added to the RBF and 10 mL (15.7 g; 0.12 mol) of previously purified and distilled PC1 3 was added to the ether. After this, 27.8 mL (27.2 g; 0.36 mol) of pyridine (dried over CaH2 and distilled prior to use) was added to the PC13 solution. In the dry box, 15.7 mL (14.0 g; 0.39 mol) ofMeOH-rf, was added to a Schlenk flask. The methanol was diluted with 50 mL of ether and the solution was transferred to the addition funnel via cannula. This was further diluted with 25 mL of ether. The PCl3/pyridine/ether solution was then cooled to 0 °C using an ice bath. This solution was maintained at this temperature throughout the addition of the methanol solution, which was added dropwise over a 102 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. period of 4 hr. During this course of addition, pyridinium chloride precipitated out of solution. After addition was complete, the reaction mixture was allowed to warm to r.t. and the reaction mixture was allowed to continue to stir overnight. The pyridinium chloride was allowed to settle and the supernatant ether solution was filtered through celite into a 500 mL RBF equipped with a Claisen adapter and a filter. After filtration, the filter and Claisen adapter were quickly switched with a distillation apparatus taken from the oven. The apparatus was cooled under a nitrogen purge and, after the apparatus cooled, the ether was distilled. The trimethylphosphite-(bp = 128 °C/760 mm Hg) was also distilled and collected in a Schlenk flask. The Schlenk flask was removed from the distillation apparatus, capped with a septum, and cooled to 0 °C. A small piece of sodium (approximately 2 0 0 mg) was added to the trimethylphosphite-</p (some effervescence occurred, and an off-white solid formed). The trimethylphosphite-</p was distilled again, this time under reduced pressure via bulb-to-bulb transfe r Yield: 5.2 g (4.9 mL) (34%; M. W . = 133.01 g/mol). 3IP NMR (CD3CN; 202.46 MHz): 5 =141.0 ppm (s). I3 C NMR (CD3C N 90.57 MHz)\ 8 = 47.87 ppm (septet of doublets, 2h-c= 10 Hz, Joe = 22 Hz). b) The phosphite complex was synthesized in the following manner: 150 mg of 2b (0.24 mmol) was placed in a Schlenk flask in the dry box, the Schlenk flask attached to the vacuum line manifold, and 35 mL of THF was added via syringe, resulting in a clear, orange solution. Then, 31 pL (0.24 mmol) of purified trimethylphosphite-t/p was added to the solution at r.t.. The reaction mixture was 103 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. allowed to stir for 14 hr at r.t.. The resulting yellow solution was filtered (occasionally, a small amount of precipitate formed) and the THF was removed under reduced pressure. The resulting yellow/yellow-orange oil was rinsed with 3 x 20 mL portions of pentane, with each portion being removed by cannula. The residual pentane was then removed in vacuo, resulting in a yellow/yellow-orange precipitate. Yield: 158 mg (8 8 %; M. W . = 748.21 g/mot). 'H NMR (MeOH-d4 ; 500.14 MHz): same as above, except no peak at 3.87 ppm was observed. I3 C NMR (dmso-d6 ; 125.77 MHz): 5 = 14.91 (1C, Rh(CH2(CH2)4CH3 )); 18.18 (dd, jRh-c= 20 Hz, 2JP ^ = 10 Hz, Rh(CH2(CH2)4CH3 )); 22.09, 30.88, 31.20,32.13 (C2- C5, Rh(CH2(CH2)4CH3 )); 47.97,48.34,49.09,51.90, 52.13, 52.29 (6 C, NCH2 ); 120.66 (q, J f-c =323 Hz, 0 3SCF3 ). No observable peak for P(OCD3 )3 , due to Jc-d- 3,P NMR (MeOH-d4 ; 145.79 MHz): 6 = 109.95 (d, W = 206 Hz). I9 F NMR (CDsCN; 470.57 MHz): 6 = -77.80 ppm (s, 0 3SCF3 ). Synthesis of [CnRhHexyl(H)(P(OMe)3 )]OTf (2d) In the dry box, a Schlenk flask was charged with 100 mg (0.14 mmol) of CnRhHexyl(P(OMe)3)OTf2 was dissolved in 20 mL of freshly distilled, dry THF. This solution was cooled to -78 °C. Another Schlenk flask was charged with 13.0 mg ofNaBR, (0.35 mmol; 2.4 equivalents). This Schlenk flask was covered with foil (outside of the dry box) and cooled to -78 °C. The CnRhHexyl(P(OMe)3)OTf2 solution was then transferred via cannula to the foil covered Schlenk flask. After transfer was complete, the reaction mixture was stirred at -78 °C for one hour. The 104 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. bath was then removed and the reaction was allowed to warm to room temperature and stirred overnight, for a total of 14 hr. It is important to allow for sufficient time in order for the reaction to go to completion. The reaction mixture was filtered through celite into another Schlenk flask and solvent was removed in vacuo. The resulting gray/tan precipitate was brought into the box, scraped down, and then 35 mL of fluorobenzene was added. The slurry was stirred for 2 hr and then filtered, resulting in a pale orange solution. The fluorobenzene was removed in vacuo (and recollected), and the oily residue was washed with 4x15 mL portions of pentane. Each portion was removed via cannula prior to addition of the next portion. Residual pentane was also removed in vacuo and yielded a light tan precipitate. The product can be further purified via dissolution in acetonitrile and flashing the solution through a small pad of neutral alumina (approximately 1 cm high), eluting with acetonitrile. It is important that it is neutral alumina and not acidic nor basic alumina, since it binds to these irreversibly. Further, it also binds to silica gel and, thus, this cannot be used either. The acetonitrile was removed under reduced pressure and the resulting oil washed with 3 x 15 mL portions of pentane. Each portion was removed via cannula prior to addition of the next portion. Residual pentane was removed in vacuo, yielding a light tan powder. This precipitate was always a mixture of the desired product and CnRh(H)2(P(OMe)3)+ *OTf. Therefore, the yield was calculated from the overall weight of the collected solids and the molar ratio of the two as indicated by either *H or 3IP NMR. (e.g. Xmotes a(M W a ) + y ^ ^ b(M W b) = total mass, where y ^ B = 105 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. [Ratio (B/A)](xm 0 ie s a ) ) Yield: 32 mg (calc’d; 39%; M. W . = 591.14 g/mol). *H NMR (MeOH-d4; 500.14 MHz): 8 = -16.38 ppm (pseudo-t, Jrh.h = 2 Jp-h = 30 Hz, 1H, Rh-//); 0.88 (t, 3H, Rh(CH2(CH2) 4C//3 )); 1.19-1.31 (br, 4H, Rh(CH2(C//2)4CH3 )); 1.01 (m, 2H, Rh(C//2(CH2)4CH3 )); 2.70-3.86 (br, 6 H, NC//H); 3.01-3.22 (br, 6 H, NCHH); 3.67 (d, 3JP .H = 11 Hz,9H, P(OC//3 )3 ); 4.48, 4.87, and 5.47 (br s, 1H each, but the 4.87 resonance is under residual MeO//, N-H). 'H NMR (C < jD ( 5; 500.14 MHz): 5= -16.37 ppm (pseudo-t, Jri,-h = 2 Jp-h = 28 Hz, 1H, Rh-//); 1 02 (br t, overlap with <x-CH 2 ’s, 5H, Rh(C//2(CH2)4C//3 )); 1.32-1.49 (br, 8 H, Rh(CH2(C//2)4CH3 )); 2.50-2.93 (br, 12H, NC//2 ); 3.40 (d, 3JP .H = 11 Hz, 9H, P(OC//3)3); 3.70 (br s, 1H, N-//); 3.81 (br s, 2H, accidental overlap of 2N-//). I3C NMR (dmso-d6 ; 125.77 MHz): 8 = 7.06 ppm (dd, Jrh-c = 24 Hz, 2 JP c = 14 Hz, 1C, Rh(CH2(CH2)4CH3 )); 14.00 (1C, Rh(CH2(CH2)4CH3 )); 22.18 (s, 1C, Rh(CH2(CH2)4CH3 )); 31.11 (s 1C, Rh(CH2(CH2)4CH3 )); 33.80 (d, 3JR h c = 2.1 Hz, 1C, Rh(CH2(CH2) 4CH3 )); 34.68 (s, 1C, Rh(CH2(CH2)4CH3 )); 46.47,47.45,48.70, 49.18,49.44,49.88 (6 C total, NCH2 ); 51.73 (d, 2JP -c= 5.7 Hz, P(OCH3)3 ); 120.66 (q, hc= 323 Hz, 0 3SCF3 ). 3 1 P {'H decoupled, Rh-//coupled} NMR (dmso-d6 ; 145.79 M Hz)-. 8 = 138.05 ppm (dd, W = 239 Hz, 2 JH -p= 26 Hz). I9 F NMR (dmso-d6; 470.57 MHz): 8 = -77.80 ppm (s) 0 3SCF3. TR(KBr): 2029.02 cm 1 (Rh-// stretch). FAB MS: Calcd: 442.1706 Found: 442.1721 (-3.4 ppm). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Synthesis of [CnRhHexyl(D)(P(OMe)3)]OTf (2e) For the synthesis of 2e, it was necessary to rigorously exclude light in all steps of manipulation and synthesis in order to obtain a relatively good ta (t = 0 s) 2 H NMR for the deuterium migration. In the dry box a Schlenk flask was charged with 75 mg (0.10 mmol) of CnRhHexyl(P(OMe)3)OTf2. Upon removing the flask from the dry box, it was covered with foil and the powder was dissolved in 20 mL of freshly distilled, dry THF. This solution was cooled to -78 °C. Another Schlenk flask was charged with 10.5 mg of NaBD4 (0.25 mmol; 2.5 equivalents) in the dry box. This Schlenk flask was covered with foil (outside of the dry box) and cooled to -78 °C. The CnRhHexyl(P(OMe)3)OTf2 solution was transferred via cannula to the foil covered Schlenk flask. After transfer was complete, the reaction mixture was stirred at -78 °C for one hour. The bath was removed and the reaction vessel placed in an ice bath and stirred for 3 hr. This bath was removed and the reaction mixture was stirred overnight, for a total of 15 hr. It is important to allow for sufficient time in order for the reaction to go to completion. The reaction mixture was filtered through celite into another Schlenk flask and solvent was removed in vacuo. The resulting precipitate was brought into the dry box, scraped down, and 35 mL of fluorobenzene was added to the foil covered Schlenk flask. This procedure was done with the lights off. The slurry was stirred for 2 hr and then filtered into another Schlenk flask, with the filter and flask also covered in aluminum foil. The fluorobenzene was removed in vacuo (and recollected), and the oily residue was washed with 4x15 mL portions of pentane. 107 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Each portion was removed via cannula prior to addition of the next portion. Residual pentane was removed in vacuo and yielded a light tan precipitate. This precipitate was always a mixture of the desired product and CnRh(H)(D) (P(OMe)3)+ 'OTf. Therefore, the yield was calculated from the overall weight of the collected solids and the molar ratio of the two as indicated by either lH or 3 1 P NMR. (e.g. xm o i c s a(M W a) + ym o i e s b(MWb) = total mass, where ym 0 ic s b = [Ratio (B/A)](xm o ie s a) )• The 'H, 13C, and 31P were identical to those above, except for the same differences as mentioned for le. Yield: 23 mg (39%; M. W . = 592.14 g/mol). 2 H NMR (MeOH-do; 76.77 MHz): 6 = -16.41 ppm (br t, Rh-D); 0.88 (br, different at t0\ increases upon heating, Rh(CH2(CH2) 4CH2D)); 1.01 (br,Rh(CHD(CH2)4CH3)). FAB MS: Calcd: 443.1769 Found: 443.1778 (-2.1 ppm). Synthesis of [CnRh(Hexyl)(H)(P(OMe)3)]BAr4r(2 f) In a typical experiment, 20 mg (0.034 mmol) of 2d was combined with 30 mg (0.034mmol) of NaBAr4f in a Schlenk flask equipped with a stir bar and then 15 ml of fluorobenzene was added. The orange solution was stirred for 3-4 hrs and became slightly cloudy with time. The solution was then filtered through celite and the fluorobenzene removed in vacuo. Despite washing with greater than 5 x 20 ml of pentane, the resulting oil never crystallized. Hence, an overall yield was not calculated. The ‘H, 13C, and 3 1 P NMR of the cation are the same as 2d in polar solvents. ‘H NMR (CtD6 ; 500.14 MHz): 8 = -16.96 ppm (pseudo-t, Jru-h = 2Jp-h = 108 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27 Hz, 1H, Rh-//); 1.00 (br t, overlap with a-CH2 ’s, 5H, Rh(C//2(CH2)4C//3 )); 1.29- 1.42 (br, 8 H, Rh(CH2(C//2)4CH3 )); 1.76-2.23 (br m, 12H, NCH2 ); 2.37-2.51 (br m, 3H, overlap of each N-//); 3.11 (d, 3JP .H = 11 Hz, 9H, P(OC//3 )3 ); 7.64 (br s, 4H, "BAr/), and 8.33 (br s, 8 H, "BAr/). I9 F NMR {470.57 MHz; MeOH-d4 ): 6 = -62.00 ppm (“BAr/, aryl-CF3 ). Synthesis of [CnRh(HexyI)(D)(P(OMe)3)]+BAr4 r (2g) The synthetic procedure is the same as for 2f, except everything was done with the rigorous exclusion of light. The 2 H spectrum is the same as for 2e. I9 F NMR {470.57 MHz; MeOH-d4 ): 5 = -62.00 ppm fBAr4faryl-CF3 ). Synthesis of [CnRh(HexylXHXP(0 Me)3)]0 2CCF3 (2h) In a typical experiment, 15 mg (0.026 mmol) of 2d was combined with 3.5 mg (0.026 mmol) of Na02CCF3 in a Schlenk flask equipped with a stir bar and then 15 ml of fluorobenzene was added. The orange solution was stirred for 4 hrs and became slightly cloudy with time. The solution was then filtered through celite and the fluorobenzene removed in vacuo. Washing with 3 x 20 ml of pentane, and subsequent removal of residual pentane in vacuo, yielded a light tan precipitate. Yield: 13 mg {90%; M. W . = 555.09 g/mol) The 'H, ,3C, and 3,P NMR of the cation are the same as 2d in polar solvents. *HNMR (QDg; 500.14 MHz): 8 = -16.48 ppm (pseudo-triplet, Jrh-h = 2 Jp-h = 27.5 Hz, 1H, Rh-//); 0.87 (t, overlapped with broad peak at 0.90 (a-CH2 ), 5H total, Rh(C//2(CH2)4C//3 )); 1.24-1.37 (br m, 8 H, 109 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rh(CH2(Ctf2)4CH3 )); 2.38-2.81 (br m, 12H, NCH2 ); 3.24 (d, 3JP .H = 12 Hz, 9H, P(OC//3 )3); 3.74 (br s, 3H, accidental overlap of all 3N-H); l9F NMR (C < sD tf ; 470.57 MHz): 8 = -81.23 ppm (O2CCF3 ). 3 1 P NMR (Q£W 202.47 MHz): 8 = 137.63 ppm (d, W = 239 Hz, Rh-/>(OMe)3 ). Synthesis of CnRh(Decyl>3 (3a) In an experiment typifying the synthesis of the rhodium trialkyl complexes, 300 mg (0.84 mmol) of CnRhCl3'H2 0 was loaded into an oven-dried Schlenk flask flask (previously allowed to cool under vacuum), and placed under vacuum for 2 - 8 hr. The yellow solid was suspended in 40 mL of dry Et2 0 and the mixture was cooled to -78 °C. Upon cooling, 10.5 mL of a 0.8 M decyllithium solution (in pentane; 10 equivalents) was added dropwise over 5 min. The reaction mixture was stirred at -78 °C for 20 min and then the bath was removed, allowing the reaction to reach ambient temperature. Within 45 min, the reaction began to change color from yellow to either orange or brown. Stirring was continued for another 3.5 hr at ambient temperature. After the 3.5 hr passed, the solution was again cooled to -78 °C and then 0.380 mL of dry MeOH (8.4 mmol) was added dropwise. The reaction was stirred at this temperature for 15-25 min, becoming more tan and cloudier with time. The dry ice/acetone bath was replaced with an ice bath and the reaction mixture stirred 110 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. for 5-10 min at 0 °C. Then, the solvents were removed under reduced pressure at 0°C. All of the liquid was not removed under these conditions, however. Therefore, the ice bath was removed and 30 mL of pentane was added, resulting in a brown-orange suspension. The precipitate was allowed to settle overnight. The solution was decanted via cannula into another Schlenk flask. The residual liquid was removed in vacuo and the solids dried. Isolation of the product was achieved by adding 30 mL of CH7CI2 to the tan precipitate and transferred via cannula to an oven-dried centrifuge tube equipped with a septum and stir bar, and under a N2 atmosphere. The slurry was stirred for 30 min and then centrifuged until the solids either collected at the bottom or at the top level of the solvent, varying from one synthesis to another. The resulting orange solution was filtered through celite. Further extraction was done by adding 3 x 25 mL of CH2CI2 portions to the centrifuge tube, stirring, centrifuging and filtering each portion. After filtration, all of the remaining CH2CI2 was removed in vacuo, yielding an orange oil. This was washed with 2x15 mL portions of pentane, with each portion being removed via cannula after allowing for the tan precipitate to settle. The residual pentane was removed in vacuo and the solids dried. More compound could be recovered if the first pentane wash (mentioned above) is kept. Upon standing in the refrigerator, precipitate formed. The cold supernatant was removed via cannula at 0 °C and the solids dried in vacuo. Addition of 20 mL of CH2CI2 to the solids dissolved most of the precipitate and this solution 111 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. was filtered through celite into another Schlenk flask. All of the remaining CH2CI2 was removed in vacuo, yielding an orange oil. Ironically, addition of IS mL pentane did not dissolve the compound. This portion was removed via cannula after the solids settled. The product was washed with an additional 15 mL of pentane, and the supernatant was removed via cannula after allowing for the tan precipitate to settle. The residual pentane was removed in vacuo and the solids dried. This portion was combined with the previously collected portion. The *H NMR of each revealed the two solid portion to be the same compound. Yield: 166 mg (30%; M. W . = 655.33 g/mol) *H NMR (QD*; 500.14 MHz): 5 = 0.88-0.98 (t overlaps with multiplet, 15H, Rh(C/f2 (CH2 )8C//3 ); 1.20- 1.61 (br multiplet, 42H, Rh(CH2 (C//2 )8CH3)); 1.63-1.74 (m, 6H, Rh(CH2 (C//2 )8CH3 )); 1.79-1.89 (m, 6H, NCT/H); 1.94 (br s, 3H, N-H); 2.22-2.38 (m, 6H, NCHfl). I3C NMR (C«Dt f ; 125.77 MHz): 8 = 14.37 (1C, Rh(CH2 (CH2 )8 CH3)); 19.39 (d, J r ^ 35 Hz, Rh(CH2 (CH2 )8CH3 )); 23.11,29.99, 30.42, 30.77 (2C), 32.39, 36.04 (C2,C4-C9, Rh(CH2 CH2 CH2(CH2)6CH3 )); 36.79 (d, 3 jRh-c = 2.7 Hz, C3, Rh(CH2 CH2 CH2(CH2)6CH3 )). Synthesis of CnRhDecylfOTfc (3b) In the dry box a Schlenk flask was charged with 150 mg (0.23 mmol) of CnRh(Decyl)3. The flask was removed from the dry box and the compound was dissolved in 35 mL of CH2CI2. The moderately dark orange solution was cooled to -78 °C and 41 (iL of triflic acid (HOTf; 0.46 mmol) was added dropwise to the cold 112 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. solution. After stirring for 10 min at -78 °C, the reaction vessel was placed in an ice bath. Stirring was continued for another hour, with the solution becoming cloudy with a light orange precipitate. Stirring was stopped and the precipitate allowed to settle. The temperature was maintained at 0 °C while the precipitate settled. Upon settling, the light yellow-green super (occasionally it was clear) was removed via cannula and the solids were washed with 2x15 mL of CH2CI2, each portion being removed in the same manner. Residual solvent was then removed under high vacuum and the very light orange solids dried. Yield: 127 mg (82%; M. W . = 671.25 g/mol) *H NMR (dmso-d6 ; 360.14 MHz): 5 = 0.86 (t, 3H, Rh(CH2(CH2)8C//3 )); 1.10-1.78 (m, 16H, Rh(CH2(C/f2)8CH3 )); 1.96 (br m, 1H, Rh(C/faHb(CH2)8CH3)); 2.18 (br m, 1H, Rh(CHa//b(CH2)8CH3 )); 2.52-3.48 (br m, 12H, NC/fc); 5.70,6.12, and 6.92 (br s, 1H each, N-H). I3 C NMR (dmso-d6 ; 90.57 MHz): 5=13.97 (1C, Rh(CH2(CH2)8CH3)); 22.79 (d, W = 2 2 Hz) Rh(CH2(CH2)8CH3 )); 22.17,28.77,28.91,29.09,29.18,31.34,31.39,32.49, (C2- C9, Rh(CH2(CH2)8CH3 )); 42.47,48.78,49.43,49.51,51.56, 56.30, (6 C total, NCH2 ); 120.66 (q, J f-c = 323 Hz, O3SCF3). I9 F NMR (dmso-d6 ; 338.68 MHz): 5 = - 77.80 ppm (s, O3SCF3). Synthesis of CnRh(Decyl)(P(OMe)3>OTf2 (3c) In the dry box, a Schlenk flask was loaded with 100 mg of 3b (0.15mmol). The flask was removed from the dry box, attached to the vacuum line manifold, and 30 mL of THF was added to the flask via syringe, resulting in a clear, orange 113 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. solution. Then, 18 pL (0.15 mmol) of purified trimethylphosphite was added to the solution at r.t.. The reaction mixture was allowed to stir for 14 hr at r.t.. The resulting yellow solution was filtered into another Schlenk flask (occasionally, a small amount of precipitate formed) and the THF was removed in vacuo. The yellow/yellow-orange oil formed was rinsed with 3 x 20 mL portions of pentane, with each portion being removed via cannula. The residual pentane was removed in vacuo, yielding a yellow/yellow-orange precipitate. Yield: 106 mg (89%; M. W = 795.26 g/mol). *H NMR (dmso-d6 ; 500.14 MHz): 6 = 0.87(t,3H, Rh(CH2 (CH2 )8 C//3 )); 1.23-1.49 (br, 16H, Rh(CH2 (C//2 )8 CH3 )); 1.84(br, 1H, Rh(CHa//b(CH2 )8 CH3 )); 2.01 (br, 1H, Rh(CH^b (CH2 )8 CH3 )); 2.64-3.22 (brm, 12H, NCH2 ); 3.86 (d, 3JP .H= 11 Hz, 9H, P(OCtf3 )3 ); 4.94, 5.26, and 5.53 (br s, 1H each, N-H). I3 C NMR (dmso-d6 ; 125.77 MHz): 5 = 14.50 (CIO, Rh(CH2(CH2)8CH3 )); 18.10 (dd, jRhc=22 Hz, 2JP ^ = 11 Hz, Rh(CH2(CH2)8CH3 )); 22.19,26.57,27.95,29.04,29.14,31.35,34.28,34.62 (C2-C9, Rh(CH2(CH2)uCH 3)); 48.15,48.55,49.08, 51.57,53.62,55.03 (6 C total, NCH2 ); 56.06 (d, 2JP ^ = 8.5 Hz, P(OCH3 )3 ); 122.10 (q, JF -c= 321 Hz, 0 3SCF3 ). 3IP NM R(dmso-d6 ; 202.48MHz): 6 = 110.74 (d, W = 207 Hz, Rh-P(OMe)3 ). I9 F NMR (dmso-d6 ; 470.57 MHz): 8 = -77.80 ppm (s, O3SCF3). Synthesis of [CnRhDecyl(HKP(OMe)3 )]OTf (3d) A Schlenk flask was loaded with 100 mg (0.13 mmol) of 3c in the dry box. The flask was removed from the dry box, attached to the vacuum line manifold, and 114 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the compound 3c was dissolved in 20 mL of freshly distilled, dry THF. This solution was cooled to -78 °C. Another Schlenk flask was charged with 12.0 mg of NaBHt (0.31 mmol; 2.5 equivalents) in the dry box. This Schlenk flask was covered with foil (outside of the dry box) and cooled to -78 °C. The 3c solution was transferred via cannula to the foil covered Schlenk flask. After transfer was complete, the reaction mixture was stirred at -78 °C for one hour. The bath was removed and the reaction allowed to warm to ambient temperature and stirred overnight, for a total of 14 hr. It is important to allow for sufficient time in order for the reaction to go to completion. The reaction mixture was filtered through celite into another Schlenk flask and solvent was removed under reduced pressure. The resulting gray/tan precipitate was brought into the box, scraped down, and 35 mL of fluorobenzene was added to the flask containing the solids. The slurry was stirred for 2 hr and then filtered, resulting in a pale orange solution. The fluorobenzene was removed in vacuo (and recollected), and the oily residue washed with 4x15 mL portions of pentane. Each portion was removed via cannula prior to addition of the next. Residual pentane was also removed in vacuo and yielded a light tan precipitate. The product can be further purified via dissolution in acetonitrile and flashing the solution through a small pad of neutral alumina (approximately 1 cm high), using acetonitrile as eluent. It is important that it is neutral alumina and not acidic nor basic alumina, since it binds to these irreversibly. Further, it also binds to silica gel and, thus, this cannot be used either. The acetonitrile was removed under reduced pressure and the resulting oil 115 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. washed with 3 x 15 mL portions of pentane, with each portion decanted via cannula. The residual pentane was also removed under vacuum, yielding a light tan powder. This precipitate was always a mixture of the desired product and [CnRh(H)2(P(OMe)3)]OTf. Therefore, the yield was calculated from the overall weight of the collected solids and the molar ratio of the two as indicated by either 'H or 3IP NMR. (e.g. x^i* a(M W a ) + y m o ie s b(M W b) = total mass, where y m o ies b = [Ratio (B/A)](xm o ie s a) ) Yield: 32 mg (38%; M. W . = 647.19 g/mol). 'H NMR (MeOH-d4 ; 500.14 MHz): 5 = -16.38 ppm (pseudo-t, Jrj,-h = 2 Jp-h = 30 Hz, 1H, Rh-//); 0.88 (t, 3H, Rh(CH2 (CH2 )8C//3 )); 1-01 (m, 2H, Rh(C//2 (CH2 )8CH3 )); 1.18- 1.34 (br, 16H, Rh(CH2 (CH2 )8 CH3 ); 2.72-2.85 (br, 6H, NC//H); 3.02-3.28 (br, 6H, NCHH); 3.67 (d, 3 JP .H = 1 1 Hz, 9H, P(OC//3 )3 ); 4.48,4.87, and 5.47 (br s, 1H each, but the 4.87 resonance is under residual MeOH, N-H). I3 C NMR (dmso-dg; 125.77 MHz): 8 = 7.11 (dd, J r ^ = 22 Hz, 2 Jp < = 15 Hz, Rh(CH2 (CH2 )8 CH3 )); 13.90 ppm (CIO, Rh(CH2 (CH2 )8 CH3 )); 22.09,28.77,28.85,29.11,29.19, 31.32,34.18, 34.74 (C2-C9, Rh(CH2 (CH2 )8 CH3 )); 46.47,47.46,48.73,49.16,49.50,49.93 (6C total, NCH2); 51.75 (d, JP < : = 4.4 Hz, P(OCH3 )3 ); 120.66 (q, JF < : = 323 Hz, 0 3 SCF3 ). 3IP NMR (dmso-d6 ; 145.79 MHz): 8 = 138.32 ppm (d, W = 234 Hz, Rh-P(OMe)3 ). FARMS: Calcd: 498.2332 Found: 499.2360 (-5.7 ppm). Synthesis of [CnRhDecyl(Z)XP(OMe)3 )]OTf (3e) In the subsequent synthesis, it was necessary to rigorously exclude light in all steps o f manipulation in order to obtain a relatively good t0 (t = 0 sec) 2 H NMR for 116 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the deuterium migration. In the dry box, a Schlenk flask was loaded with 65 mg (0.082 mmol) of 3c. The flask was attached to the vacuum line manifold and the solid was dissolved in 20 mL of freshly distilled, dry THF. This solution was cooled to -78 °C. Another Schlenk flask was charged with 8.6 mg of NaBD4 (0.20 mmol; 2.5 equivalents) in the dry box. This flask was covered with foil (outside of the dry box) and cooled to -78 °C. The 3c solution was transferred via cannula to the foil covered Schlenk flask. After transfer was complete, the reaction mixture was stirred at -78 °C for one hour. The bath was removed and the reaction placed in an ice bath and stirred for 3 hr. This bath was removed and the reaction mixture allowed to warm to ambient temperature, stirring overnight, for a total of 15 hr. It is important to allow for sufficient time in order for the reaction to go to completion. The reaction mixture was filtered into another Schlenk flask and the solvent removed in vacuo. The resulting precipitate was brought into the box, scraped down, and 35 mL of fluorobenzene was added to the solids in the foil covered Schlenk flask. The slurry was stirred for 2 hr and then filtered, with the filter also covered in aluminum foil. The fluorobenzene was removed in vacuo (and recollected), and the oily residue was washed with 4x15 mL portions of pentane. Each portion was decanted via cannula prior to addition of the subsequent portion. Residual pentane was also removed in vacuo and yielded in a light tan precipitate. This precipitate was always a mixture of the desired product and [CnRh(H)(D)(P(OMe)3]OTf. Therefore, the yield was calculated from the overall weight of the collected solids and the molar ratio of the two as indicated by either 'H 117 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o r3 1 P NMR. (e.g. X m oies a(M W a ) + y™,,* B (MWB ) = total mass, where ymoies b = [Ratio (B/A)](xnK>ies a) )• The ‘H, l3C, and 3 1 P were identical to those above, with the same differences as stated for le. Yield: 22 mg {41%; M W . = 648.19 g/mol). 2 H NMR (MeOH-do; 76.77 MHz): 8 = -16.40 ppm (br, Rh-£>); 0.88 (br, different at increases upon heating, Rh(CH2 (CH2 )gCH2 £>)); 1.01 (br,Rh(CHZXCH2 )g CH3 )). FARMS: Calcd: 499.2395 Found: 499.2394 (0.1 ppm) Synthesis of [CnRh(Decyl)(H)(P(OMe)3)]BAr4r (3f) In a typical experiment, a Schlenk flask equipped with a stir bar was charged with 20 mg (0.034 mmol) of 3d and with 30 mg (0.034mmol) of NaBAr/. Then, 15 ml of fluorobenzene was added. The orange solution was stirred for 3-4 hrs and became slightly cloudy with time. The solution was filtered through celite into another Schlenk flask and the fluorobenzene removed in vacuo. Despite washing with greater than 5 x 20 ml of pentane, the resulting oil never crystallized. Hence, an overall yield was not calculated. The ‘H, i3C, and 3IP NMR of the cation are the same as 3d. I9 FNM R {470.57 MHz; MeOH-d4 ): 5 = -62.00 ppm ("BAr/, aryl- CF3 ). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Synthesis of [CnRh(Decyl)(Z))(P(OMe)3)lBAr4 r (3g) The synthetic procedure is the same as for 3f, except everything was done with the rigorous exclusion of light. The 2 H spectrum is the same as for 3e. I9 F NMR (470.57 MHz; MeOH-d4): 5 = -62.00 ppm (*BAr4 f , aryl-C/3). Synthesis of (CnRh(a,ti)-l3C-Decyl(Z)XP(OMe)3)jBAr4r(3h) This compound was made according to the same procedures for 3f and 3g. The I3 C label exchanged between the a-methylene and ©-methyl in the synthesis of the ,3C-3b and 1 3 C-3c analogues.4 *H NMR (CDjCN; 360.14 MHz): 8 = -16.43 ppm (pseudo-t, Jri,.h = 2 Jp-h = 29 Hz, Rh-//); 0.98 (br m, 5H, Rh-C//2(CH2)gC//3> ; 2.58-2.79 (m, 6H, NC//H); 2.93-3.17 (m, 6H, NCHH); 3.61 (d, 3 JP .H = 11 Hz, P(0CHih); 3.98,4.18, and 4.64 (br s, 1H each, N-//); 7.66 (br s, 4H, -BAr4f), 7.71 (br s, 8H, 'BAr/). I3 C NMR (CD3CN'; 90.57 MHz): 8 = 7.38 ppm (br m, coupling not resolved, Ca, mixture of Rh-(CH2(CH2)sCH3)and Rh-(CH(D)(CH2)8CH3); 14.35 (s, C10/Cm , Rh-(CH2 (CH2 )8CH3 ); 23.39,30.14,30.24,30.44,30.5,32.68, 35.17, 35.99 (C2-C8, Rh-(CH2(CH2 )8CH3 » ; 47.27,48.43,49.87,50.20, 50.45,51.10 (6C total, NCH2 ); 52.97 (d, 2 JP<:= 5.9 Hz, P(OCH3 )3); 118 71 (s, -BAr/) 125.53 (q, JF -c = 274 Hz, *BAr4f ) 129.98 (q, 2 JF jC = 28 Hz, *BAr4f ), 135.71 (s, *BAr4 f), 162.67 (1:1:1:1 q, Jb-c = 51 Hz, ipso carbon, "BAr/). Upon wanning 3h in benzene, then removal of benzene in vacuo, and washing the compound(s) with pentane to remove eliminated decane-di, another l3C spectrum was acquired. Isotopic shifts were observed for both the a-methylene and 119 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. the ©-methyl, in accordance with the migration of deuterium to the co-methyl position and proteo enrichment (due to the same migration) at the a-methylene. 1 3 C Isotopic shifts: 6 = 7.?1 (dd, Jrh-c^ 24 Hz, 2 Jp-c= 12 Hz; downfield shift, overlaps some with the metal/a-D isomer(s), Rh-(CH2(CH2)8CH2(D)); 14.06 (1:1:11 , Jd-c= 20 Hz, Rh-(CH2 (CH2)8CH2 (D)). No significant shifts in the other carbons were observed, nor any methyls corresponding to secondary C-H activated species (as determined by applying an Gaussian function to the spectrum and analyzing the CH3 resonance). Synthesis of CnRh(cyclopentyl>3 (4a) The cyclopentyl experiment was modified slightly in comparison to the synthesis of the other rhodium trialkyl complexes. A Schlenk flask was cooled under vacuum and then charged with 275 mg (0.77 mmol) of CnRhCb ^ O under N2 atmosphere, and the solids placed under vacuum for 2-8 hr. The yellow solid was suspended in 25 mL of dry THF and cooled to -78 °C. Upon cooling, 15.4 mL of a 0.5 M cyclopentyllithium solution (in pentane; 10 equivalents) was added dropwise over 5 min. The reaction mixture was stirred at -78 °C for 20 min, then the bath was removed, allowing the reaction to warm to ambient temperature. Within 45 min, the reaction began to change color from yellow to either orange or brown. The reaction mixture was cooled to 0 °C, and stirring was continued for another 2.5 hr. The ice bath was removed and the 120 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reaction mixture allowed to warm to ambient temperature again. The mixture was stirred for an additional hour. The solution was again cooled to -78 °C and 0.475 mL of dry MeOH (13.2 mmol) was added dropwise. Stirring continued at this temperature for 15-25 min, usually becoming more tan and cloudier. The dry ice/acetone bath was replaced with an ice bath and the reaction stirred for 5-10 min at 0 °C. Then, the solvents were removed in vacuo at 0 °C. Once all of the solvents were removed, the ice bath was removed and the tan solids dried in vacuo. Isolation of the product was achieved by adding 30 mL of CH2CI2 to the tan precipitate and transferred via cannula to an oven-dried centrifuge tube equipped with a septum and stir bar, and under N2 atmosphere. The slurry was stirred for 30 min. Stirring was stopped and the tube centrifuged until the solids either collected at the bottom or at the top level of the solvent, varying from one synthesis to another. The resulting orange solution was filtered through celite into another Schlenk flask. More product was extracted with 3 x 25 mL portions of CH2CI2, with each portion added to the centrifuge tube, stirred, centrifuged and filtered. After filtration, all of the remaining CH2CI2 was removed in vacuo, yielding an orange oil. This was washed with 2x15 mL portions of pentane, with each portion being removed via cannula after allowing for the tan precipitate to settle. The residual pentane was removed in vacuo and the solids dried. Yield: 130 mg (38%; M. W . = 475.20 g/mol) 'H NMR (CD3CN; 500.14 MHz): 8 = 0.292 (m, 3H, Rh(C//(CH2 CH2 CH2 CH2)); 1.08 (m, 8H), and 1.42-1.61 (m, 11H), and 1.70 (m, 5H) 121 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RhCH(C//2 C//2 C//2 C//2 ); 2.56 (br m, 6H, NCWH); 2.90 (br m, 6H, NCH//); 2.78 (br s, 3H, N-H). ,3C NMR (80% CD3CN, 20% dmso-d6 (v/v); 125.77 MHz): 8 = 17.86 ppm (d, jRhc = 36 Hz, Rh-CH(CH2 CH2 CH2 CH2 )); 25.87,33.46,42.34,46.05 (C2-C5, Rh-CH(CH2 CH2 CH2 CH2)); 48.14 (NCH2 ). Synthesis of CnRh(cyclopentyl)CI(OTf) (4b) In the drybox, a Schlenk flask was charged with 125 mg (0.28 mmol) of CnRh(cyclopentyl)3 . The solids were dissolved in 30 mL of CH2 C12 and the moderately dark orange solution was cooled to -78 °C. Then, 1.27 mL of a 0.22 M HCl/Et2 0 solution (0.28 mmol HC1) was added dropwise to the solution. The HCL/Et2 0 solution was previously prepared by dissolving 141 pL (121 mg; 1.11 mmol) of TMS-C1 in 5 mL of dry Et2 0 and adding 40 pL of MeOH to generate the HC1 in situ. Immediately after addition of the HC1 solution to the reaction solution, 25 pL of HOTf (0.28 mmol) was added dropwise. After stirring the solution for 15 min at -78 °C, the bath was removed and replaced with an ice bath. Stirring was continued for another hour, during which the solution became cloudy with a light orange precipitate. Stirring was stopped and the precipitate was allowed to settle. The temperature was maintained at 0 °C during settling. Once the precipitate settled, the tight yellow-green supernatant (occasionally it was clear) was removed via cannula and the solids washed with 2x15 mL portions of CH2 C 12 , with each portion being decanted via cannula. Residual solvent was removed under high vacuum and the very tight orange solids dried. Yield: 95.0 mg (70%; M. W . = 122 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 497.64 g/mof) !H NMR (dmso-de; 500.14 MHz): 8 = 2.05 ppm (br m, 1H, Rh-Ctf(CH2CH2CH2CH2 )); 1.18 (1H), 1.38 (1H), 1.50 (1H), 1.58 (1H), 1.68 (1H), 1.83 (2H), and 1.93 (1H), all Rh-CH(Ci/2C//2C//2C//2 ); 2.58-3.31 (12H, NC//2 ); 5.53, 5.83, and 6.63 (br s, 1H each, N-H). ,3C NMR (dmso-d6 ): 8 = 19.87 ppm (d, jRhc= 21 Hz, Rh-CH(CH2CH2CH2CH2 )); 24.67,31.99,32.31, and 38.09 (C2-C5, Rh-CH(CH2CH2CH2CH2 )); 43.26,48.26,48.44,49.32, 52.59, 55.98 ( 6 C total, NCH2 ); 120.66 (q,JF c = 323 Hz, O3SCF3). I9 F NMR (dmso-d6 ; 470.57 MHz): 8 = -77.80 ppm (s, O3SCF3). Synthesis of [CnRh(cyclopentyI)CI(P(OMe)3)|OTf (4c) A Schlenk flask was charged with 85 mg of 4b (0.18 mmol) and the solids dissolved in 60 mL of THF, resulting in a clear, pale orange solution. Then, 21 pL (0.18 mmol) of purified trimethylphosphite was added to the solution at r.t.. The reaction mixture was allowed to stir for 14 hr at r.t.. The resulting yellow solution was filtered (occasionally, a small amount of precipitate formed) through celite into another Schlenk flask and the THF was removed in vacuo. The resulting yellow/yellow-orange oil was rinsed with 3 x 20 mL portions of pentane, with each portion removed via cannula. The residual pentane was removed in vacuo, yielding in a yellow/yellow-orange precipitate. Yield: 77 mg (70%; M. W . = 621.65 g/mol). *H NMR (i-PrOH-dg; 500.14 MHz): 8 = 1.15-1.45 (br m, 4H), 1.62-1.75 (br m, 2H), and 1.82-1.97 (br m, 2H) all Rh-CH(C//2Ctf2Ctf2Ctf2 ); 2.08 ppm (1H, Rh- Ctf(CH2CH2CH2CH2 )); 2.78-2.95(br m, 6 H), 3.09 (br m, 1H), 3.17 (br m, 1H), 3.25 123 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (br m, 2H), 3.45 (br m, 1H), and 3.53 (br m, 1H) (12H total, NCH2 ); 3.91 (d, 3 JP .H = 12 Hz, P(OC//3)3 ); 4.98,5.08, and 5.65 (br s, 1H each, N-H. I3 C NMR (dmso-d6 ; 125.77 MHz): 6 = 14.72 ppm (dd;JR h ^ = 22 Hz, 2 JP ^ = 13 Hz, Rh-CH(CH2CH2 CH2 CH2)); 24.77,32.09, 32.29,38.58 (C2-C5, Rh-CH(CH2 CH2 CH2 CH2 )); 43.08,47.11,47.22,47.60,49.65,52.82 (6C total, NCH2 ); 54.39 (d, 2 JP -c = 7.5 Hz, P(OCH3)3 ); 120.66 (q, JF -c * 320 Hz, 0 3 SCF3 ). I9 F NMR (dmso-de; 470.57 MHz): 8 = -77.80 ppm (s, 0 3 SCF3 ). 3 1 P NMR (dmso- d6 ; 202.46 MHz): 5 = 110.10 ppm (d, W = 204 Hz, Rh-/*(0Me)3 ). Synthesis of [CnRh(cyclopentyl)H(P(OMe)3)]OTf (4d) In a foil covered Schlenk flask, 55 mg (0.09 mmol) of 4c was combined with 10.0 mg (0.27 mmol) of NaBPLt. The vessel was placed in an ice bath. In a separate Schlenk flask, 8 mL of dry isopropyl alcohol was cooled to 0 °C. This was transferred via cannula to the Schlenk flask containing the solids. The reaction was stirred at 0 °C for 30 min, the ice bath removed, and the reaction allowed to warm to ambient temperature. The reaction was stirred for 20 hr. The reaction progress could be monitored by 3IP NMR. This was done by taking aliquots of the reaction mixture, syringing them into a 5mm NMR tube, and monitoring the relative intensities of 4c to 4d. This revealed that the synthesis of the hydride complex from the chloride compound was incomplete after 20 hr. Thus, another Schlenk flask was charged with another 10.0 mg (0.31 mmol) of NaBH4 and this was dissolved in 2 mL of isopropyl alcohol. The solution was transferred to the 124 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reaction mixture via cannula and stirred for another 20 hr. Occasionally, another portion of NaBH4 (2-3 mg) was used to complete the reaction, as dictated by 3 1 P NMR. When the reaction was complete, the solution was filtered into another foil covered Schlenk flask. The isopropanol was removed in vacuo. Next, 20 mL of fluorobenzene was added to the solids and the mixture stirred for 1 hour. The solution was filtered (in the dark via a foil covered filter and Schlenk flask) through celite into another flask and the fluorobenze removed under reduced pressure. The presumed oil was washed with 3 x 20 mL pentane, with each portion being removed by cannula. Residual pentane was removed under vacuum and the solids dried. This complex can also be further purified via dissolution in acetonitrile and flashing the solution through a small pad of neutral alumina (approximately 1 cm high), with acetonitrile as eluent. As previously noted, it is important that it is neutral alumina and neither acidic nor basic alumina, since it binds to these irreversibly. Further, it also binds to silica gel and, thus, this cannot be used either. The acetonitrile was removed in vacuo and the resulting oil washed with 3x15 mL portions of pentane. Each portion was decanted from the oil via cannula. Residual pentane was removed in vacuo, yielding a light tan powder. This precipitate was always a mixture of the desired product and [CnRh(H)2(P(OMe)3)]OTf. Therefore, the yield was calculated from the overall weight of the collected solids and the molar ratio of the two as indicated by either 'H or 3,P NMR. (e.g. X m oies a(MW a) + ym oies b(MWb) = total mass, where y m o ies b = [Ratio (B/A)](Xm oics a))- Yield: 16.6 mg 125 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (32%; M. W . = 586.15 g/mot). !H NMR (CD 3CN; 500.14 MHz)'. 8 = -16.52 ppm (pseudo-t, JR h -H = 2 Jp-h = 23 Hz, Rh-//); 0.92 ppm (m, 1 H, Rh-Ctf(CH2CH2CH2CH2 )); 1.09 (m, 2H, Rh-CH(CH2CH2CH2C//2 )); 1.25 (m, 2H, Rh-CH(C/f2CH2CH2CH2 )); 1.48 (m, 1H, Rh-CH(CH2C//,HbCH2CH2 )); 1.59 (m, 1H, Rh-CH(CH2CHa //b CH2CH2 )); 1.72 (m, 2 H, Rh-CH(CH2CH2C//2CH2 )); 2.55-2.71 (m, 6 H, NC//H), 2.90-3.20 (m, 6 H, NCH//); 3.61 (d, JP .H = 13 Hz, 9H, P(OC//3 )3 ); 3.96,4.18, and 4.65 (br s, 1H each, N-H). I3 C NMR (CD 3CN; 125.77 MHz): 8 = 6.42 ppm (dd, J r ^ 24 Hz, 2JP ^ = 13 Hz, Rh-CaH(CH2CH2CH2CH2)); 25.59 (C3yl, Rh-CH(CH2CH2CH2CH2 »; 33.12 (C4y 2 , Rh-CH(CH2CH2CH2CH2 )); 33.26 (C50 2 , Rh-CH(CH2CH2CH2CH2 )); 42.88 (C2pi, Rh-CH(CH2CH2CH2CH2 )); 48.03,48.30, 49.48,49.85,50.52,50.76 (6 C total, NCH2 ); 52.95 (br, P(OCH3 )3); 118.10 (q, JF -c = 310 Hz, 0 3SCF3 ). 3,P NMR (CD 3CN; 202.46 MHz): 8 = 137.89 ppm (d, Jri,.p= 240 Hz, Rh-/> (OMe)3 ). W F NMR (CD3 CN; 470.57 MHz): 8 = -77.80 ppm (s, 0 3SCF3 ). Synthesis of [CnRh(cyclopentyl)D(P(OMe)3)]OTf (4e) Alterations to the synthesis of the cycloalkyl deuterides required changes from the synthesis of the correspond hydride. In this case, isopropanol-^ was used and the reaction was conducted in a foil covered, 5 mm NMR tube. This also allowed for ease of checking the progress of the reaction. Thus, a foil covered 5mm NMR tube was charged with 40 mg (0.074 mmol) of 4c dissolved in 0.400 mL of isopropanol-t/s An initial 3 1 P and *H NMR were taken. A separate NMR tube was loaded with 9.3 mg (0.22 mmol) of NaBD4 , covered with foil, and placed in an ice 126 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. bath. The solution of 4c was transferred via a gas tight syringe to the NMR tube with NaBD4. The reaction was shaken periodically, each time being placed back into the 0 °C bath. The NMR tube was kept in the bath for t hour, removed from the bath, and the reaction to allowed to warm to ambient temperature. The reaction was kept at ambient temperature for 16 hr. Monitoring the course of the reaction by 3 1 P NMR is useful in order to minimize reaction time. If the reaction was incomplete, another NMR tube was charged with 10.0 mg of NaBD4, covered with foil, cooled to 0 °C. The reaction mixture was transferred via a foil covered, gas tight syringe to the new NMR tube containing the NaBD4 . This mixture was allowed to react for another 16 hr. If necessary, another portion of NaBD4 (2-3 mg) was used to complete the reaction, as indicated by 3IP NMR. When the reaction was complete, the solution was removed with the foil covered syringe and transferred to a foil covered Schlenk flask. The isopropanol-^ was removed (and recovered) in vacuo. Next, 20 mL of fluorobenzene was added to the presumed oil and the mixture stirred for 1 hour. The solution was filtered in the dark via a foil covered filter and into a foil covered Schlenk flask, and the fluorobenzene removed under reduced pressure. The presumed oil was washed with 3 x 20 mL portions of pentane, with each portion being removed via cannula. Residual pentane was removed under vacuum and the solids dried. Yield: 21 mg(48%; M.W. = 590.15g/mot) 2 H NMR(CH 3CN): 6 = -16.51 ppm (br, Rh-D); 0.92 ppm (br, Rh-CZXCfLCl^CfbCHz)); 3.96,4.18, and 4.65 (br s,N-D). 127 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Synthesis of [CnRh(cyclopentyl)(H)(P(OMe)3)]BAr4r(4f) In the dry box, a Schlenk flask was loaded with 20 mg (0.034 mmol) of 3d and 30 mg (0.034mmol) ofNaBAr/, and 15 ml of fluorobenzene was added. The orange solution was stirred for 3-4 hr and became slightly cloudy with time. The solution was filtered through celite into another flask and the fluorobenzene removed in vacuo. Despite washing with greater than 5 x 20 ml of pentane, the resulting oil never crystallized. Hence, an overall yield was not calculated. The 'H, l3C, and 3IP NMR of the cation are the same as 3d. I 9 F NMR (470.57 MHz; CD 3CN): 5 = -62.00 ppm ("BAr/, aryl-CF). Synthesis of [CnRh(cyclopentyIXf>XP(OMe>3)]BAr4r(4g) The synthetic procedure is the same as for 4f, except everything was done with the rigorous exclusion of light. The 2 H spectrum is the same as for 4e. Upon heating, a peak at 1.25 ppm begins to appear (see Kinetic Experiments for details of experimental setup). l9F NMR (470.57 MHz; CD 3CN): 5 = -62.00 ppm CBAr4 f , aryl-CF3 ). Synthesis of CnRh(cyclohexyl>3 (5a) An oven-dried Schlenk flask, previously allowed to cool under vacuum, was charged with 250 mg (0.70 mmol) of CnRhCU'^O and the solids were placed under vacuum for 2 - 8 hr. 128 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The yellow solid was suspended in 20 mL of dry THF and cooled to -78 °C. Upon cooling, 9.0 mL of a 0.8 A/cyclohexyllithium solution (in pentane; 10 equivalents) was added dropwise over 5 min. The reaction mixture was stirred at -78 °C for 20 min, then the bath was removed, allowing the reaction to warm to ambient temperature. Within 45 min, the reaction began to change color from yellow to either orange or brown. The mixture was cooled to 0 °C and stirring continued for another 2.5 hr. The bath was removed and the reaction mixture allowed to warm to ambient temperature again. The solution was stirred for an additional hour. After the hour, the solution was again cooled to -78 °C and 0.260 mL of dry MeOH (7.23 mmol) added dropwise. Stirring was continued at this temperature for 15-25 min, with the reaction mixture becoming more tan and cloudier with time. The dry ice/acetone bath was replaced with an ice bath and the reaction stirred for 5- 10 min at 0 °C. Then, the solvents were removed in vacuo at 0 °C. Once all of the solvents were removed, the ice bath was removed and the tan solids dried in vacuo. Isolation of the product was achieved by adding 30 mL of CH2CI2 to the tan precipitate and transferring the slurry via cannula to an oven-dried centrifuge tube equipped with a septum and stir bar, and under N2 atmosphere. The slurry was stirred for 30 min and then centrifuged until the solids either collected at the bottom or at the top level of the solvent, varying from one synthesis to another. The resulting orange solution was filtered through celite into another flask. More product was extracted with 3 x 25 mL portions of CH2CI2 . Each portion was stirred, 129 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. centrifuged, and filtered. After filtration, all of the remaining CH2CI2 was removed in vacuo, yielding an orange oil. This oil was washed with 2x15 mL portions of pentane, with each portion being decanted via cannula after allowing the tan precipitate to settle. The residual pentane was removed in vacuo and the solids dried. Yield: 108 mg (32%; M. W = 481.20 g/mol) *H NMR (dmso-d(/CD3 CN (5%/95%; v/v) 500.14 MHz)'. 8 = 0.26 ppm (hr multiplet, 3H, Rh(C//(CH2CH2CH2CH2CH2)); 0.89-1.25 (br m, 15H, half of the methylenes in Rh(CU(CH2 CH2 CH2 CH2 CH2)); 1.52-1.80 (br m, 15H, half of the methylenes in Rh(CH(CH2 CH2 CH2 CH2 CH2)); 2.49-2.58 (br m, 6 H, NCHH); 2.77-2.89 (brm, 9H, overlap ofNCH/fand N-H). ,3C NMR (QD&- 125.77 MHz): 8 = 15.48 ppm (d, Jr»hc= 35 Hz, RhCH(CH2CH2CH2CH2CH2 )); 27.46,27.86,34.74,43.40,44.33 (C2-C6, RhCH(CH2CH2CH2CH2CH2 )); 47.04 (NCH2 ). (dmso-df/CD^CN (5%/95%; v/v) 125.77 MHz): 8 = 15.76 ppm (d, jRh-c = 37 Hz RhCH(CH2CH2CH2CH2CH2)); 27.49,27.90,34.71,43.67,43.84 (C2 -C6 , RhCH(CH2CH2CH2CH2CH2)); 48.16 (NCH2 ). Synthesis of CnRh(cyclohexyl)Cl(OTf) (Sb) A Schlenk flask was loaded with 110 mg (0.23 mmol) of CnRh(cyclohexyl>3 in the dry box. The solids were dissolved in 30 mL of CH2CI2, and the moderately dark orange solution cooled to -78 °C. Then, 1.05 mL of a 0.22 M HCl/Et2 0 solution (0.23 mmol HC1) was added dropwise to the solution. This solution was prepared by dissolving 141 pL of TMS-C1 in 5 mL of dry Et2 0 and adding 40.0 pL 130 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of MeOH to generate the HC1 in situ. Immediately after addition of the HC1 solution, 20 fiL of HOTf (0.23 mmol) was added dropwise to the flask. After stirring for 15 min at -78 °C, the bath was removed and replaced with an ice bath. Stirring continued for another hour, with the solution becoming cloudy with a light orange precipitate. Stirring was stopped and the precipitate allowed to settle. The temperature was maintained at 0 °C during settling. Once the precipitate settled, the light yellow-green supernatant (occasionally it was clear) was removed via cannula and the solids were washed with 2x15 mL portions of CH2CI2, with each portion being decanted via cannula. Residual solvent was then removed under high vacuum and the very light orange solids dried. Yield: 73.5 mg (64%; M. W . = 499.64 g/mol) 'H NMR (dmso-d6 ; 500.14 MHz)'. 8 = 0.97 (br m, 2H), 1.09-1.35 (br m, 3H), 1.66 (br m, 2H), 1.83 (br m, 1H), 1.95 (br m, 1H), and 2.06 (br m, 1H) Rh(CH(CH2 CH2 CH2CH2CH2); 2.50-3.35 (brm, 12H, NCH2 )\ 5.53,5.89, and 6.64 (br s, 1H each, N-H). I3 C NMR (dmso-d6; 125.77 MHz)'. 8 = 18.31 (d, W = 23 Hz, RhCH(CH2CH2CH2CH2CH2)); 25.94,26.34,32.74, 33.10,40.5 (C2-C6, RhCH(CH2CH2CH2CH2CH2)); 43.20,48.18,48.36,49.26,52.50,55.92 ( 6 C total, NCH2 ); 120.66 (q, JF c = 323 Hz, O3SCF3). W F NMR (dmso-d6 ; 470.24 MHz): 8 = -77.80 ppm (s, O3 SCF3). Synthesis of CnRh(cyclohexyl)CI(P(OMe)3)OTf (Sc) In the dry box, a Schlenk flask was charged with 80 mg of CnRh(cyclohexyl)Cl(OTf) (0.16 mmol). Then, 60 mL of THF was added via 131 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. syringe, resulting in a clear, pale orange solution. After dissolution, 19 pL (0.16 mmol) of purified trimethylphosphite was added to the solution at r.t.. The reaction mixture was allowed to stir for 14 hr at r.t.. The solution lightened, but remained cloudy. The THF was removed in vacuo, and the product extracted with 3 x 30 mL portions of CH2CI2. Each portion was filtered through celite into another flask, after allowing the precipitate to settle. The CH2CI2 was removed in vacuo, yielding a yellow oil. The oil was rinsed with 3 x 20 mL portions of pentane, with each portion being decanted via cannula. The residual pentane was removed in vacuo, yielding a yellow precipitate. Analysis of the precipitate revealed the desired product as well as the known [(P(OMe)3)sRh]OTf. The ratio of product to L5 RiT was 1 :0.5. From this ratio, the mass of the precipitate, and the molecular weights of the compounds, a yield was calculated. Yield: 39 mg (40%; M. W . = 623.65g/mot). 'H NMR (80/20 (v/v) CD3CN/MeOH-d4 ): 5 = 1.19-1.28 (br m, 4H), 1.61 - 1.72 (br m, 3H), and 1.75-1.84 (br m, 3H) RhCCHCC/fcC/fcC/fcC/fcC/fc); 2.26 (br m, 1H, Rh(C//(CH2CH2CH2CH2CH2)); 2.62-3.21 (br m, 12H, NCH2); 3.85 (d, 3JP .H = 1 1 Hz, P(0CH3 )3 y, 4.52,4.73, and 4.90 (br s, 1H each, N-//). I3C NMR (80/20 (v/v) CD3 CN/MeOH-d4 ): 8 = 14.97 ppm (dd, JRhc= 21 Hz, 2JP ^ = 12 Hz, Rh(CH(CH2CH2CH2CH2CH2 )); 27.91, 34.59,41.65,42.36,47.19 (C2 -C6 , Rh(CH(CH2CH2CH2CH2CH2)); 50.98, 52.30,53.37,53.74, 53.93, 54.34 (6 C total, NCH2 ); 55.74 (d, 2JP -c= 9.1 Hz, P(OCH3 )3 ); 122.11 (q, JF -c = 310 Hz, 0 3SCF3); 3,P NMR (80/20 (v/v) CD3 CN/MeOH-d4 ; 202.46MHz): 8 = 108.82 ppm (d, Jri,-p= 207 Hz, Rh-P(OMe)3 ). 132 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Synthesis of [CnRh(cyclohexyl)H(P(OMe)3)]OTf (5d) In a foil covered Schlenk flask, 28 mg (0.045 mmol) of Sc was combined with 5.1 mg (0.14 mmol) ofNaBU, and the vessel placed in an ice bath. In a separate Schlenk flask, 5mL of dried isopropyl alcohol was added and cooled to 0 °C. The alcohol was transferred via cannula to the Schlenk flask containing the solids. The reaction was stirred at 0 °C for 30 min, then the bath was removed and the reaction allowed to warm to ambient temperature. The solution was stirred for 2 0 hr. The reaction progress could be monitored by 3 1 P NMR. This was done by taking aliquots of the reaction mixture, syringing them into a 5mm NMR tube, and monitoring the relative intensities of 5c to 5d. This revealed that the synthesis of the hydride complex from the chloride compound was incomplete after 20 hr. Thus, another Schlenk flask was charged with another 5.0 mg (0.16 mmol) of NaBH4 and this was dissolved in 2 mL of isopropyl alcohol. The solution was transferred to the reaction mixture via cannula and stirred for another 20 hr. Occasionally, another portion of NaBfL (2-3 mg) was used to complete the reaction, as dictated by 3 1 P NMR. the solution was filtered into another foil covered Schlenk flask. The isopropanol was removed in vacuo. Next, 20 mL of fluorobenzene was added to the solids and the mixture stirred for 1 hour. The solution was filtered (in the dark via a foil covered filter and Schlenk flask) through celite into another flask and the fluorobenze removed under reduced pressure. The presumed oil was washed with 3 133 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. x 20 mL pentane, with each portion being removed by cannula. Residual pentane was removed under vacuum and the solids dried. This complex can also be further purified via dissolution in acetonitrile and flashing the solution through a small pad of neutral alumina (approximately 1 cm high), with acetonitrile as eluent. As previously noted, it is important that it is neutral alumina and neither acidic nor basic alumina, since it binds to these irreversibly. Further, it also binds to silica gel and, thus, this cannot be used either. The acetonitrile was removed in vacuo and the resulting oil washed with 3x15 mL portions of pentane. Each portion was decanted from the oil via cannula. Residual pentane was removed in vacuo, yielding a light tan powder. This precipitate was always a mixture of the desired product and [CnRh(H>2(P(OMe)3)]OTf. Therefore, the yield was calculated from the overall weight of the collected solids and the molar ratio of the two as indicated by either ‘H or 3IP NMR. (e.g. X m oies a(M W a ) + ymoies b(M W b) = total mass, where y^te B = [Ratio (B/A)](xm o i c s A ». Yield: 7.7 mg (29%; M. W . = 589.15 g/mol) 'H NMR (MeOH-d4 ; 500.14 MHz)’ . 8 = -16.39 ppm (pseudo-t, Jiu,-h = 2Jp-h = 29 Hz, Rh-fl); 0.87 (m, 1H, Rh-CH(C//a Hb CH2CH2CH2CH2)); 1.02 (m, 1H, Rh- C7/(CH2CH2CH2CH2CH2)); 1.13-1.33 (m, 5H, Rh-CH(CHa//b C//2CH2CH2C//2 ); 1.62-1.70 (br m, 2H, Rh-CHCOfeCIfcCJfeCIfcCIfe)); 1.70-1.79 (br m, 2H, Rh- CH(CH2CH2CH2C//2CH2)); 2.65-2.84 (m, 6 H, NCtfH), 2.95-3.22 (m, 6 H, NCHH); 3.67 (d, Jp.H= 10 Hz, 9H, P(OC//3 )3 ); 4.47,4.86, and 5.20 (br s, 1H each, the peak at 134 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4.86 slightly overlaps with residual MeOH, N-H). I3 C NMR (MeOH-d4 ; 125.77 MHz): 8 = 5.03 ppm (dd, Jri,-c = 24 Hz, 2Jp-c = 15 Hz, Rh-CH(CH2CH2CH2CH2CH2 )); 28.04, 32.31, 34.61,43.47,44.37 (C2-C6, Rh-CH(CH2CH2CH2CH2CH2 )); 47.31,48.57, 50.20, 51.02, 51.68 (5of 6 observed, one underneath solvent peak, NCH2 ); 52.99 (br, P(OCH3)3); 121.75 (q, Jfc = 314 Hz, O3SCF3). 3,P NMR (.MeOH-d4 ; 202.46 MHz)'. 8 = 137.38 ppm (d, W = 242 Hz, Rh-P(OMe)3 ). I9 F NMR (MeOH-d4 ; 470.57 MHz): 8 = -77.80 ppm (s, O3SCF3). Synthesis of [CnRh(cyciohexyl)Z>(P(OMe)3)]OTf (5e) The synthesis of the cycloalkyl deuterides required isopropanol-<& as solvent. A foil covered 5mm NMR tube was charged with 37 mg (0.059 mmol) of 5c the compound was dissolved in 0.400 mL of isopropanol-^. An initial 3 1 P and *H NMR were taken. Another NMR tube was charged with 10 mg (0.24 mmol) of NaBD4, covered with foil, and placed in an ice bath. The solution of 5c was transferred via a gas tight syringe to the NMR tube containing NaBD4 - The reaction was shaken periodically, each time being placed back into the 0 °C bath. The NMR tube was kept in the bath for 1 hr, then removed from the bath, and the solution allowed to warm to ambient temperature. This was allowed to sit for 16 hr. Monitoring the course of the reaction by 3IP NMR is useful in order to minimize reaction time. If necessary, another NMR tube was charged with 10.0 mg of NaBD4, covered with foil, cooled to 0 °C, and the reaction mixture transferred via a foil covered, gas tight syringe to the new NMR tube containing the NaBD4. The 135 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. reaction was continued for another 16 hr. On occasion, another portion of NaBD4 (2-3 mg) was used to complete the reaction, as dictated by 3 1 P NMR. When complete, the reaction was removed with a foil covered, gas tight syringe and transferred to a foil covered Schlenk flask. The isopropanol-ds was removed (and recovered) in vacuo. Next, 20 mL of fluorobenzene was added and the mixture stirred for 1 hr. The solution was filtered through celite in the dark via a foil covered filter and into a foil covered Schlenk flask. The fluorobenzene was removed under reduced pressure. The presumed oil was washed with 3 x 20 mL portions of pentane, and each portion decanted via cannula. Residual pentane was removed under vacuum and the solids dried. Yield: 14 mg {40%; M. W . = 593.15 g/mol) 2 H NMR (MeOH-d0 ): 8 = -16.41 ppm (br, Rh-D); 1.02 ppm (Rh-CZXC^C^C^CfbCLfe)); 4.45,4.86, and 5.19 (brs, N-D). Synthesis of [CnRh(cyclohexyl)(H)(P(OMe)3)]BAr4r(5 f) A Schlenk flask equipped with a stir bar was charged with 5 mg (0.0085 mmol) of 5d and 7.5 mg (0.0085 mmol) ofNaBAr/ in the dry box. Then, 10 ml of fluorobenzene was added. The orange solution was stirred for 4 hr and became slightly cloudy with time. The mixture was filtered through celite into another Schlenk flask and the fluorobenzene removed in vacuo. Despite washing with greater than 5 x 20 ml of pentane, the resulting oil never crystallized. Hence, an overall yield was not calculated. The *H , I 3C, and 3IP NMR of the cation are the 136 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. same as 5d. ,9FNM R (470.57 MHz; MeOH-d<): 5 = -62.00 ppm (*BAr4f , aryl- CF3 ’s). Synthesis of [CnRh(cyclohexylXDXP(OMe)3)]BAr/ (5g) The synthetic procedure is the same as for 5f, except everything was done with the rigorous exclusion of light. The 2 H spectrum is the same as for 5e. Upon heating a peak at 1.25 ppm begins to appear (see Kinetic Experiments for details of experimental setup). ,9F NMR (470.57 MHz; MeOH-d4 ): 8 = -62.00 ppm fB A r/ aryl-CFj). Synthesis of [CnRh(Ph)H(P(OMe)3»BAr4r(6 a) A Schlenk flask was charged with 10 mg of [CnRh(hexyl)H(P(OMe)3]OTf and 15 mg of NaBAr/ in the dry box. Then, 15 mL of fluorobenzene was added. The mixture was stirred for 3 hr and the pale orange solution was filtered through celite into another Schlenk flask(for further discussion concerning the ion exchange, see the experimental sections above or Kinetic Experiments). Fluorobenzene was removed in vacuo and the oil washed with 2x15 mL portions of pentane, with each portion removed by cannula. The residual pentane was removed under reduced pressure as well, and the oil kept under vacuum for 2 hr. The Schlenk flask was brought into the dry box, where it was equipped with a reflux condenser and a rubber septum. This was taken to the fume hood, charged with 15 mL of benzene, and heated to reflux overnight under N2 atmosphere. 137 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The solution was allowed to cool to r.t. and the benzene removed in vacuo, yielding an orange oil. This was washed with 3x15 mL portions of pentane, with each portion removed via cannula. Removal of residual pentane via vacuum yielded a tan solid. Yield: 128 mg (90 %; M. W . = 1297.20 g/mol) 'H NMR (CeDa, 500.14 MHz)'. 8 = -15.81 ppm (pseudo-t, Jrii-h = 2Jp-h = 30 Hz, 1H, Rh-//); 1.16 (m, 2H), 1.38-1.49 (brm, 4H), 1.74 (m, 2H), 1.93-2.04 (br m, 2H), 2.11 (m, 1H), and 2.25 (m, 1H), (total 12H, all NCH2 ); 2.38,2.59, and 2.65 (br s, 1H each, N-//);3.03 (d, 3J p.h = 11 Hz; 9H) P(OC//3 )3; 6 . 8 8 (br d, 3JH .H = 5.0 Hz, 2H, phenyl -CH); 7.02 (br m, 3H, phenyl -CH); 7.71 (s, 4H, aryl -CH, BAr/); 8.39 (s, 8 H, aryl -CH, BAr/). (MeOH-d* 360.13 MHz) 6 = -15.23 ppm (pseudo-t, Jw,.h = 2Jp .h = 26 Hz. 1H, Rh-//); 2.48-2.82 (br m, 12H, NCH2); 3.43 (d, 3JP .H = 1 1 Hz, 9H, P(OC//3 )3 ); 4.61, 5.09, and 5.27 (br s, 1H each, N-//); 6.69 (t, 3JH .H = 7.2 Hz, 1H, para proton on phenyl ring); 6.77 (pseudo-t, 3JH «tho-H m eta= 3JH P # ra -H m « a= 7.6 Hz, 2H, meta protons on phenyl ring); 7.30 (d, 3Jh-h = 7.9 Hz, 2H, ortho protons on phenyl ring); 7.46 (br s, 12H, aryl -CH on BAr4 f). I3 C NMR (CDjCN; 125.77 MHz): 8 = 47.48,49.59, 50.24 (br, 2 C), 50.52,50.89 ppm (6 C total, NCH2 ); 53.79 (d, JP c = 6.3 Hz. P(OCH3 )3 ); 118.68 (shoulder on solvent CN peak, aryl -CH on BAr/); 123.10 (para-carbon, phenyl ring); 125.47 (q, Jf- c = 272 Hz, -CF 3 on BAr/); 127.83, 140.95 (ortho-, meta-carbons, phenyl ring); 129.94 (q, 2J f - c = 31 Hz, aryl-C-CF3 on * BAr/); 135.66 (s, aryl-CH on BAr4f); 162.61 ( 1 :1 :1 : 1 q, JB -c= 51 Hz, B-Con’ BAr4 f ); Rh-C of phenyl ring not observed, possibly due to overlap with solvent CN peak. This is suggested based upon broadening of the solvent peak at the base of the 138 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. peak. 3 1 P NMR (MeOH-d4 ; 145.79 MHz): 5 = 131.25 ppm (d, W = 227 Hz, Rh- P(OMe)3 ). (CD 3CN; 145.79 MHz): 8 = 131.28 ppm (d, Jrh-p = 228 Hz, Rh- P(OMe)3 ). (CaDe; 145.79 MHz): 8 = 129.67 ppm (d, W = 231 Hz, Rh-P(OMe)3 ). FAB-MS: Calcd: 434.1057 Found: 434.1080 (5.3 ppm). 139 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Kinetic Experiments General Considerations and Procedures The details of the preparation and recording of data are described in the sections below. Unless otherwise noted or given, data for the experiments are given in the ensuing Data Tables section. Further, all thermolyses conducted in a 5mm NMR tube were degassed via three freeze-pump-thaw cycles prior to sealing. The tube was either flame-sealed, if fused to a joint, or sealed with a teflon J-Young screw cap. Thermolysis of [CnRh(R)(H)(P(OMe)3)]BArr 4: Alkane Elimination Due to the fact that for R = Butyl, Hexyl, Decyl, Cyclopentyl, and Cyclohexyl the "B Arf4 salts are oils, the following procedure was adapted from those described above and applied for preparing the samples for the kinetic experiments: typically 10 mg of [CnRh(R)(H)(P(OMe)3)]OTf and the appropriate amount of NaBArf4 were mixed in a Schlenk flask and 5 mL of fluorobenzene was added. The mixture was stirred for a minimum of 2 hr (typically 3 hr) and then filtered through celite. The fluorobenzene was removed in vacuo, yielding an orange oil that never solidified, even upon extensive washing with pentane. 1 9 F NMR of the sample confirmed the absence of "OTf (-77.8 ppm, with respect to external CFCb) and only ■BA rf4 (-62.0 ppm). To the oil, 1.5 mL of dry C$D6 was added, but not all of the oil dissolved. 3 x 0.5 mL NMR tube samples were then made, with each portion being transferred either to a 5mm J-Young tube equipped with a teflon stop cock for 140 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. degassing or to an apparatus with a 5mm NMR tube fused to a joint that was attached to a Kontes adapter. The solution was then degassed via 3 freeze-pump- thaw cycles and then sealed. The remaining oil was then dried in vacuo and kept for further use. In order to determine the typical concentration of the benzene solution, one of the 0.5 mL portions was added to a 5mm NMR tube equipped with a NMR tube septum. As an internal standard, 1 pi of CH2CI2 was added and the P(OCH3 )3 proton resonance of the [CnRh(R)(H)(P(OMe)3)]BArf4 compound was integrated with respect to the dichloromethane protons. The typical amount of [CnRh(RXHXP(OMe)3)]BArf4 in 0.5 mL was determined to be 2.5 mg (0.4 mM). The kinetics of alkane elimination were followed by either ‘H or 3 1 P NMR, with a spectrum being collected after heating the sealed NMR tube in a temperature bath or in the NMR probe itself. For those conducted in the probe, the NMR sample was prepared in a special manner in order to prevent any refluxing of solvent that would skew the spectra and/or cause a loss of lock signal (see Figure III.I). The latter problem results in the Bruker kinetic program to cease. In the 'H spectra, integration of the starting material P(OMe)3 protons (5 = 3.11 for all linear alkyls) with respect to the* BArf4 resonances or integration of both the starting material and product P(OMe) 3 resonances ( 8 = 2.95 ppm) with respect to the' BArf4 resonances. This was done in order to determine At/Ao for each data 141 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 14/20 joint/5 mm NMR tube adapter from Wilmad 5 mm tube fiised- to 4mm insert solvent levd- "Flared" glass— par of 4mm tube insert 4mm tube insert — sealed at bottom 5mm NMR tube NMR Tube Apparatus for Preparing the Sample in the NMR Probe Figure III.I point. In the first method, Ao is the value for the P(OMe)3 protons at time = 0. In the second method, Ao is the sum of the starting material and product proton integration values while At is the integration value for the starting material P(OMe>3 resonances. Both methods were applied on designated samples as a secondary check for accurate rate information. Similarly, for the 3IP spectra, integration of both the starting material and product 3 1 P peaks ( 8 = 135.1 (± 0.01 ppm for each alkyl) and 129.67 ppm, in C6D & respectively) allowed for determination of A/Ao, where At = starting material value and Ao = (starting material value + product value). 142 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Special consideration was needed for evaluating the integration of the cycloalkyls. In the ‘H spectra in C ^ , the P(OMe) 3 resonance for the [CnRh(H)2(P(OMe)3)]+ overlaps with that for [CnRh(cycloallcyl)(H)(P(OMe)3)]+at 5 = 3.06 ppm. First, an initial 3,P was taken in order to determine the t 0 ratio of dihydride to alkyl hydride. Then, the total integration of the *H P(OMe)3 (vs." BArf 4) was multiplied by the calculated % of alkyl hydride {alkyl hydride % = [alkyl]re i/([alkyl]rei + [dihydridejrei)). The contribution of the dihydride was then substracted from the total integration in order to determine A,. The legitimacy of this was checked two ways: first, in the cyclopentyl case, the rate elimination was confirmed via 3 1 P NMR in two separate experiments (elimination during 2 H migration and elimination in the presence of excess phosphite. Second, plotting time vs. ln[l- (Pt/Ao)], where Pt is the integration value of the phenyl hydride P(OMe) 3 'H resonances at each time interval, and Ao is the initial calculated value for the alkyl hydride P(OMe)3 resonances, yielded the same rate constant for cycloalkane elimination. Thermolysis of [CnRh(R)(H)(P(OMe)3 )]BArr 4 : Benzene Dependence a)[CnRh(Hexyl)(H)(P(OMe)3 )]BArf4 The same method was applied for preparing the *BArf4 salt of the hexyl compound, except a 80% C^E(J2Q% C$D 6(v/v) solution was prepared and the compound dissolved in this solution. Alkane elimination was followed via ]H NMR, 143 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. integrating the P(0 Me)3 resonances of both the starting material and product with respect to the BArf4 resonances as an internal standard. b)[CnRh(Cyclohexyl)(H)(P(OMe) 3)]BA/4 The same procedure as above was applied in preparing the cyclohexyl sample for determining the effect of varying the bezene concentration on alkane elimination. Thermolysis of [CnRh(R)(H)(P(OMe)3)]BArr 4 : Detecting for Phosphite Exchange/Inhibition a)[CnRh(Butyl)(H)(P(OMe) 3)]B A /4 Preparation of the butyl complex was the same as above, but the oil was dissolved in a 80% C^D(J 2 Q% solution containing P(OMe)3-d9. An initial 3IP NMR spectrum was acquired, revealing the ratio of P(OMe)3-d9 :[Rh(R)(P(OMe)3] to be 12:1. Butane elimination was followed via *H NMR in the same method as previously described. A 2 H NMR (76 MHz) was taken in order to determine the existence of P(OMe>3-d9 in the phenyl hydride product. The dynamic range of the instrument was sufficient such that there wasn’t significant disruption of the baseline from the C6D6. No product P(OMe)3-d9 resonance was observed. b)[CnRh(Cyclopentyl)(H)(P(OMe) 3)]BAii4 A solution of the cyclopentyl complex was made, containing 41 equivalents of P(OMe)3-d9 and sealed in a 5 mm NMR tube. Cyclopentane elimination was followed via 3 1 P NMR. The sample was run unlocked and shimmed via the 'H FID. Upon completion of the data set, a 2 H NMR was taken in order to 144 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. determine the existence of P(OMe)3-d9 in the phenyl hydride product. No product P(OMe)3-d9 resonance was observed. Thermolysis of [CnRh(Hexyl)(H)(P(OMe)3)]BArr 4 : Decane-dc/Benzene-d* Competition Experiment a) Thermolysis in presence o f decane-d 6 and absence ofbenzene-de 25 mg of [CnRh(HexylXHXP(OCD3)3)]BAr4 was dissolved in 15 ml of a 90/10 (mol/mol) solvent mixture of C6F6/decane-d6 (0.8 M in decane-d6) and placed in a reaction vessel sealable via a fused Kontes joint adapter. The reaction was heated at 60.2 °C to ~2 half-lives (~2 x tif) and, subsequent to heating, the solvents removed in vacuo. The resulting oil was washed with 3 x 10 ml of pentane and then was taken up in CH3CN. A 2 H NMR spectrum was acquired and indicated that ~ 1 0 % of the [Rh] was [CnRh(CD2(CH2)8CD3)(D)(P(OCD3)3)]+ (5 = -16.42 ppm; br pseudo-triplet, J ri,-d = 2J p-d =5.4 Hz). This was determined by integrating the Rh-D peak vs. all P(OC£> 3 )3 resonances, after adjustment for initial [CnRh(H)2(P(OCD3 )3)]+ . b) Thermolysis in the presence o f decane-d 6 and benzene-d 6 29 mg of [CnRhfHexylXHXPfOCHsjsjjBAr^ dissolved in 20 ml of a 59 mol% C6F6/27.3 mol% decane-cU/13.7 mol% solvent mixture (1.0 M in CeD6 ; 2.1 Min decane-d6) and placed in a reaction vessel sealable via a fused Kontes joint adapter. The reaction was heated at 60.2 °C to ~2 half-lives (~2 x tjf). Subsequent to heating, the solvents were removed in vacuo. The resulting oil was washed with 4 145 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. x 12 ml pentane, each portion being removed via cannula. Residual pentane was removed in vacuo and the resulting oil was dissolved in CH3CN. A 2 H NMR was taken and showed only [CnRh(Phenyl-d5)(D)(P(OCH3)3)]BArf 4. ( 8 = -15.12 ppm; br pseudo-triplet, jRh.D=2Jp-D= 4.6 Hz); Rh-£>; 6.93 (br, 3D), 7.37 (br, 2D) phenyl- D’s. Thermolysis of [CnRh(Butyl)(H)(P(OMe)3)]BArr 4 : Methane/Benzene^ Competition Experiment a) Thermolysis in the presence o f CH4 and absence o f 2.8 mg of [CnRh(ButylXH)(P(OCH3)3]BArf4 was dissolved in 0.400 ml of C6F6 and transferred to a 4mm NMR tube fused to a 14/20 joint equipped with a Kontes adapter. The solution was degassed via 3 freeze-pump-thaw cycles. Then, methane was condensed into the tube and the tube was flame-sealed (be careful!!), resulting in a calculated 13 atm of methane. An initial 'H NMR was taken by inser.t.ing the 4mm tube into an empty 5mm tube. The sealed tube was them immersed in a 50 °C temperature bath and taken to approximately 2 half-lives (2 x tm). The 4mm tube was cooled and sheathed with a 5mm NMR tube. A [H NMR was taken and a pseudo-triplet (I0 3 Rh and 3,P coupled) at -16.13 ppm was observed. Confirmation of this as the corresponding methyl hydride species was obtained by taking a *H NMR spectrum of an independently made sample. The [CnRh(Me)(H)(P(OCH3)3)]+ was -18% of [Rh]to w j, integrating 146 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. with respect to the "B Arf4 protons as an internal standard. The nature of the other products were undetermined. b) Thermolysis in the presence o fI 3CH 4 and o f C ^ > 6 3.0 mg of [CnRh(Hexyl)(HXP(OCH3)3]BArf4 was dissolved in 0.500 ml of 6%/94% C^D g/CgFfi (v/v) and transferred to a high-pressure, thick walled 5mm NMR tube fused to a 14/20 joint equipped with a Kontes adapter. The solution was degassed via 3 freeze-pump-thaw cycles. Then, methane was condensed into the tube and the tube was flame-sealed (be careful!!), resulting in a calculated 1 1 atm of methane. An initial 'H NMR and 1 3 C NMR were taken. The sealed tube was then immersed in a 50 °C temperature bath and taken to approximately 2 half-lives (2 x ti/i). A 'H NMR was taken, showing formation of the benzene activated product (via the product P(OMe) 3 resonance) but no pseudo triplet corresponding to the methane activated product at -16.13 ppm was observed. Further confirmation of the lack of methane activation was done via a 1 3 C NMR spectrum, which revealed no I0 3 Rh or3 1 P coupled a-carbon corresponding to the methyl hydride complex. Metal<-+Alpha 2 H Exchange in [CnRh(Hexyl)(D)(P(OMe)3-d9)]OTf: In order to determine the rate for 2 H migration from the metal (Rh-D) to the alpha-methylene (Rh-CH(D)), the experiment was conducted in the following manner: 20 mg (0.027 mmol) of CnRh(Hexyl)(P(OMe)3-d9(OTf) 2 was dissolved in 0.450 mL of THF-do and placed in a 5mm NMR tube equipped with a NMR tube 147 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. septum. An initial 2 H spectrum was taken with the probe pre-cooled to 4.7 °C. In another 5mm tube equipped with a screw cap septum, 2.8 mg (0.068 mmol) of NaBD4 was placed. The tube was wrapped in a thin covering of aluminum foil (Important!!! 2 H migration is significantly affected by light!!) and the tube was immersed in a -78 °C bath. After the initial 2 H spectrum was taken, the THF solution of the hexyl complex was transferred via a gas tight syringe to the NMR tube containing the NaBD4- The 0.450 mL was added very slowly, over an approximate 5 minute period. Upon addition, the NMR tube was briefly removed from the bath (lights out!!), shaken, and immediately replaced. This was repeated and then the sample was quickly placed into the pre-cooled, pre-shimmed probe. Data was collected using the kinetic program on the Bruker 500 NMR machine. The data was evaluated by integrating and deconvoluting the starting material P(OMe)3-d9 resonance (3.81 ppm), the [CnRh(DXCH2(CH2)4CH3)(L)]+ resonance (-16.50 ppm), and the [CnRh(HXCDH(CH2)4CH3)(L)]+ resonance (0.98 ppm) with respect to the residual 2 H in THF resonance at 1.73 ppm. Thermolysis of [CnRh(R)(D)(P(OMe)3)]BArr 4: Alpha«-*Omega 2 H Migration The general procedure for preparing the samples was similar to that for the hydride compounds, except special care was taken in order to fully exclude light. It is useful to practice the technique of filtrating the crude THF solution of the deuteride, the initial fluorobenzene extraction, and the ion exchange solution (all 148 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. covered with foil in order to exclude light) on the hydride complexes. This allows for knowing when everything is finished filtering and all solvents are removed. Further, when setting up the ion exchange reaction, everything was weighed out in the dark in the dry box. In addition, the filtered fluorobenzene solution after ion exchange was transferred via cannula to a reaction vessel equipped with a Kontes joint for sealing. The fluorobenzene solution was removed in vacuo and then 30 mL of C6FL was added to the resulting oil. In a typical experiment, there would be 30 mg of the [CnRh(R)(D)(P(OMe)3)]BAr 4 compound dissolved in the C ^ . In a pre-calibrated temperature bath, the benzene solution would be heated for a designated period of time and then rapidly cooled in an ice bath. Benzene was removed in vacuo and the compound washed with 3 x 25 mL of pentane in order to ensure that no alkane-dl remained to give a false result in the 2 H NMR. For R = butyl, hexyl, decyl, and cyclohexyl, 0.500 mL of MeOH-do was added via a gas tight syringe covered with foil. Acetonitrile-do was used for R = cyclopentyl. After allowing for full dissolution of the complex, the solution was transferred via the syringe to a 5mm NMR tube equipped with a NMR tube septum and covered with foil. The 2 H spectrum was recorded at room temperature, typically between 5-12 hrs. Then, a 3IP spectrum was taken, in order to obtain information on the rate of alkane elimination. After data collection, the solution was removed from the NMR tube via syringe and the MeOH-do (or CH3CN) removed in vacuo and the compound 149 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. sufficiently dried. Then, 30 mL of would be added and the process repeated. Further, the bath temperature was checked every time in order to check for and correct any fluctuations. Analysis of the 3 1 P data was done as previously stated in order to obtain the rate of alkane loss. In addition, the ratio of [CnRh(H)(D)(P(OMe)3)]+ : [CnRh(Alkyl)(D)(P(OMe)3)]+ was measured at every point (the ratio of the dihydride to the sum of the alkyl hydride and the phenyl hydride product remained constant throughout the experiments). This was done in order to subtract the contribution of the [CnRh(H)(/))(P(OMe)3)]+ to the deuteride integral and, thus, determine the value of [CnRh(Alkyl)(/))(P(OMe)3 ) ] + .5 The relative integrals were determined via deconvolution of the Rh-/), Alpha-/) (Rh-CH/)(CH2)xCH 3), and Omega-/) (Rh-(CH2)X CH2/)), and setting the Alpha-/) integral to a constant, relative value for each spectrum (4.00 in the linear alkyl cases; 2.00 in the cycloalkyl cases.) The data for each alkyl and temperature are given in the ensuing section. 150 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Alkane Elimination Data Table III.I: Reductive Elimination of Ethane: Arrhenius Plot IT h h ^ h H-N-Rh© (MeO)3P ' V _ Temp (TO 1/T (T O 313.40 323.30 333.40 341.50 362.90 QD6 Temp°C Slope Rsq intercept 3.19E-03 3.09E-03 3.00E-03 2.93E-03 2.76E-03 -14862.03 0.9960 34.21 b in 1.53E-06 9.39E-06 3.65E-05 8.24E-05 1.13E-03 Std Error in Y values 0.18 H-N'Rh® (MeO)3P" V I? * HjCCHj i ) / ds Ln(kr«te) Lntk^u-d) -13.39 1.84E-06 -13.21 -11.58 7.84E-06 -11.76 -10.22 3.16E-05 -10.36 -9.40 9.08E-05 -9.31 -6.79 1.18E-03 -6.74 AG: = 26.62 kcal/mol @ 39.6 C AH: = 28.93 kcal/mol @ 39.6 C AS: = 7.37 eu @ 39.6 C Arrhenius Plot -6.55 -7.55 ♦ Ln(k) v. 1/T -8.55 Linear (Ln(k) v. 1/T) -9.55 y = -14862x+ 34214 R2= 0.996 -10.55 -11.55 -12.55 -13.55 0.0027 0.0029 0.0030 0.0031 0.0032 1/T (Kelvin) 151 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ln(At/Ao) Table III.II: Ethane Elimination @ T = 89.7 °C 0.000 -0.450 -0.900 -1.350 -1.800 -2.250 -2.700 Time (s) At/A« LnfAt/A.) 0 0.794 -0.231 150 0.611 -0.493 300 0.574 -0.555 390 0.456 -0.785 480 0.432 -0.840 600 0.382 -0.962 750 0.305 -1.188 900 0.274 -1.296 1050 0.191 -1.653 1 2 0 0 0.187 -1.679 1290 0.165 -1.799 1410 0.167 -1.792 1530 0.138 -1.983 1650 0.115 -2.159 1800 0.097 -2.335 1950 0.077 -2.565 kotad 1.13E-03 Rsq 0.9914 ♦ Alkane Loss Linear (Alkane Loss) y = -1.13E-03x - 3.03E-01 R2 = 9.91E-01 500 1000 2000 0 1500 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.III: Ethane Elimination @ T = 683 °C Time fs) At/A„ LnfAt/An) 0 0.801 -0.221 600 0.755 -0.281 1200 0.728 -0.317 1800 0.652 -0.427 2400 0.614 -0.488 3000 0.595 -0.519 3600 0.557 -0.585 4200 0.547 -0.603 5100 0.485 -0.724 6000 0.446 -0.808 7800 0.394 -0.932 9300 0.344 -1.069 10800 0.314 -1.157 12300 0.250 -1.386 14400 0.244 -1.411 15900 0.195 -1.634 17700 0.172 -1.758 20400 0.161 -1.827 22200 0.123 -2.092 kobsd 8.24 E-05 Rsq 0.9926 0.000 ♦ Alkane Loss -0.500 Liner (Alkane Loss) o ' -1.000 y=-8E-05x-0.2808 R2 = 0.9926 J -1.500 - 2.000 -2.500 5000 10000 15000 20000 25000 0 tune(s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.IV: Ethane Elimination @T = 60.2 °C Time fsl Af/An 0 1 . 0 0 0 0 . 0 0 0 7200 0.755 -0.281 10800 0.687 -0.377 14400 0.571 -0.560 18000 0.504 -0 . 6 8 6 23400 0.420 -0 . 8 6 8 28800 0.357 -1.031 34200 0.314 -1.159 41400 0.207 -1.573 kobsd - 3.65 E-05 Rsq = 0.9922 < < 0 . 0 0 0 - 0.200 -0.400 -0.600 -0.800 - 1 . 0 0 0 - 1.200 -1.400 -1.600 -1.800 ♦ Alkane Linear (Alkane y = -3.60E-05x R2 = 9.89E-01 0 9000 18000 27000 36000 45000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.V: Ethane Elimination @ T = 50.1 °C Time (s) Ai/A„ Ln(Ai/A«) 0 1 . 0 0 0 0 . 0 0 0 72480 0.488 -0.718 96780 0.473 -0.748 115380 0.380 -0.967 147780 0.244 -1.410 171420 0.197 -1.626 kotad 9.39E-06 Rsq 0.9790 0 . 0 0 0 - 0.200 -0.400 ♦ Alkane Loss -0.600 Linear (Alkane Loss) ^ -0.800 - < ¥ - 1 . 0 0 0 ■ - 1.200 - -1.400 - -1.600 -1.800 0 45000 90000 135000 180000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.VI: Ethane Elimination @ T = 40.2 °C Time (s)____A./A«_____ Ln(A»/A«) 0 1 . 0 0 0 0 . 0 0 0 33840 0.904 -0.101 116640 0.800 -0.223 206640 0.724 -0.323 ko*d 1.53E-06 448980 0.487 -0.720 Rsq 0.9989 649340 0.357 -1.031 773760 0.294 -1.224 0.00 ♦ Alkane Loss -0.25 Linear (Alkane Loss) -0.50 o < < y = -1.53E-06x R2 = 9.99E-01 c -J -0.75 - 1.00 -1.25 0 193750 387500 581250 775000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.VII: Butane Reductive Elimination: Arrhenius Plot H 'N^Rh® (MeO)3 P v Temp°C Temn (K) 1/T (K) 312.70 3.20E-03 322.70 3.10E-03 333.70 3.00E-03 342.60 2.92E-03 353.20 2.83E-03 Slope -15993.61 Rsq 0.9960 intercept 37.93 Std Error in Y values 0.17 k r» te 1.80E-06 1.05E-05 3.74E-05 1.48E-04 7.24E-04 V/t^N +i ✓ v * * » r > (MeO)3 P v u LsIKcus) -13.23 -11.46 -10.19 -8.82 -7.23 AG: = A H * = AS1 = d5 f e fc a lc d l 1.83E-06 8.91 E-06 4.57E-05 1.59E-04 6.44E-04 L n jk ^g ) -13.212 -11.632 -9.99 -8.754 -7.35 26.56 kcal/mol @ 39.6 C 31.18 kcal/mol @ 39.6 C 14.77 eu @39.6 C Arrhenius Plot -7.0 -7.8 - -8 . 6 -9.4 - ♦ Ln(k)vs. 1/T 2 'W ' B -i - 10.2 - Linear (Ln(k) vs. 1/T) - 11.0 - y = -15994x+37.934 R2 = 0.996 - 12.6 - -13.4 2.80E-03 2.91E-03 3.02E-03 3.13E-03 3.24E-03 1/T (Kelvin) 157 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.VIII: Butane Elimination @ T = 80.0 °C Time (s') AJA^ LnfAt/4 0 1 . 0 0 0 0 . 0 0 0 150 0.842 -0.172 300 0.758 -0.277 420 0.702 -0.354 540 0.662 -0.412 690 0.574 -0.555 840 0.500 -0.693 990 0.493 -0.707 1140 0.457 -0.783 1500 0.333 - 1 . 1 0 0 1680 0.279 -1.277 1860 0 . 2 2 0 -1.514 2040 0.214 -1.542 2280 0.196 -1.630 slope 7.24E-04 Rsq 0.9890 0.00 -0.25 -0.50 ♦ Alkane Loss ® -0.75 Linear (Alkane Loss) J - 1 . 0 0 -1.25 -1.50 -1.75 500 1000 1500 2000 2500 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table II1.IX: Butane Elimination @ T = 69.4 °C Time (s) At/A„ LnfAi/An) 0 1.000 0.000 2100 0.680 -0.385 4200 0.515 -0.663 5700 0.418 -0.871 7200 0.345 -1.065 8700 0.284 -1.258 10200 0.207 -1.575 11700 0.165 -1.803 13200 0.142 -1.949 15600 0.111 -2.194 kobsd Rsq = o s < 0 . 0 0 0 -0.375 -0.750 -1.125 -1.500 -1.875 -2.250 4000 8000 12000 time (s) y = 16000 1.48 E-04 0.9934 ► Alkane Loss — Linear (Alkane Loss) -1.48E-04x = 9.93&01 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table IU.X: Butane Elimination @T = 69.4 °C: 80/20 (v/v) CdVCcFfi Time Is) Ln(At/Ao) 0 1 . 0 0 0 0 . 0 0 0 1500 0.779 -0.250 3000 0.620 -0.477 4500 0.498 -0.697 6000 0.400 -0.915 7500 0.327 -1.118 9000 0.268 -1.316 10500 0.196 -1.629 1 2 0 0 0 0.167 -1.791 13500 0.134 -2 . 0 1 0 k o i M d Rsq 1.47E-04 0.9984 0.00 -0.30 - -0.60 - ♦ Alkane Loss Linear (Alkane Loss) q -0.90 - -1.50 - -1.80 - - 2.10 5000 0 10000 15000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XI: Butane Elimination @ T = 69.4 °C: Excess P(OMe)3 -d9 Time fs) A t/A <, Ln(At/A«) 0 1 . 0 0 0 0 . 0 0 0 2 1 0 0 0.709 -0.344 4200 0.526 -0.642 5700 0.424 -0.859 7200 0.344 -1.068 8700 0.264 -1.332 1 0 2 0 0 0.204 -1.591 11700 0.168 -1.785 13200 0.143 -1.947 15600 0 . 1 0 1 -2.292 lo o te d Rsq 1.47E-04 0.9977 1 2 eq. P(OCD3 ) 3 0.00 -0.50 - ♦ Alkane Loss Linear (Alkane Loss) - 1.00 - e < < B m i -1.50 - -2 . 0 0 - -2.50 0 8000 1 2 0 0 0 16000 4000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XII: Butane Elimination @ T = 60.5 °C 0 . 0 0 -0 . 2 0 -0.40 "o' < -0.60 'e m i -0.80 - 1 . 0 0 - 1 . 2 0 Time (s) A./A« LnfAi/A,,) 0 1 . 0 0 0 0 . 0 0 0 2700 0.893 -0.113 5400 0.817 -0 . 2 0 2 8100 0.694 -0.365 14400 0.552 -0.595 21840 0.452 -0.793 29100 0.324 -1.128 3.740E-05 Rsq 0.9938 « Alkane Loss Linear (Alkane Loss) 20000 0 30000 10000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ln(At/Ao) Table III.XIII: Butane Elimination @ T = 49.S °C Time (s) Ai/Ao LnfAi/Ao) 0 1 . 0 0 0 0 . 0 0 0 7200 0.862 -0.148 14400 0.833 -0.182 31200 0.758 -0.278 49200 0.629 -0.464 68100 0.448 -0.802 86100 0.403 -0.908 124100 0.254 -1.369 162100 0.178 -1.725 2 0 0 1 0 0 0 . 1 2 1 -2 . 1 1 1 kobid 1.05E-05 Rsq 0.9950 0 . 0 0 -0.50 ♦ Butane Loss Linear (Butane Loss) - 1.00 y = -1.05E-05x R2 = 0.9950 -1.50 - 2 . 0 0 -2.50 30000 60000 90000 120000 150000 180000 210000 0 time (s) 163 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XIV: Butane Elimination @T = 39.5 °C Time Is) LnfAi/Afl) 0 1 . 0 0 0 0 . 0 0 0 29100 0.926 -0.077 95220 0.847 -0.166 178140 0.714 -0.336 343800 0.552 -0.593 433500 0.465 -0.765 606900 0.369 -0.997 783900 0.226 -1.486 koted 1.796E-06 Rsq 0.9890 0 . 0 0 0 - 0.200 -0.400 ♦ Alkane Loss -0.600 Linear (Alkane Loss) e < < -0.800 e J - 1 . 0 0 0 - 1.200 -1.400 -1.600 200000 400000 600000 800000 0 tune (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table II1.XV: Hexane Reductive Elimination V S L H - N-Rh.® (MeO)3P ' v Temp (K) 1/T flO 310.8 3.22E-03 322.6 3.10E-03 333.4 3.00E-03 342.7 2.92E-03 356.2 2.81E-03 Slope Rsq intercept Std Error in Y values Q A Temple jjnlt 1.23E-06 6.87E-06 3.28E-05 2.03E-04 1.77E-03 •17823.81 0.9919 43.49 0.30 (M eO)jP' V "D -13.61 -11.89 -10.33 -8.52 -6.34 AG* = A H * = A S* = CH3-fCHrj-CH3 1.08E-06 -13.74 7.71E-06 -11.77 4.16E-05 -10.09 1.61E-04 -8.74 1.37E-03 -6.56 26.74 kcal/mol @ 39.6 C 34.81 kcal/mol @ 39.6 C 25.82 eu @ 39.6 C Arrhenius Plot -6 . 8 - -7.6 ♦ Ln(k) -8.4 Linear (Ln(k» -9.2 - - 1 0 - y = -17824x + 43.49 R2 = 0.9919 - 10.8 -12.4 - -13.2 - -14 0.0028 0.0029 0.0030 0.0031 0.0033 1/T (Kelvin) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XVI: Hexane EUminatlon @ T = 83.0 °C Time (s) AJA« LnfAi/A^l 0 1 . 0 0 0 0 . 0 0 0 251 0.735 -0.307 1 ^ 1.77E-03 570 0.413 -0.884 Rsq 0.9973 930 0.221 -1.511 1290 0.116 -2.153 0 . 0 0 0 -0.500 - ♦ Alkane Loss - 1 . 0 0 0 - Linear (Alkane Loss) -3 -1.500 - y = -1.77E-03x R2= 1.00E+00 - 2.000 - -2.500 500 1500 1000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XVII: Hexane Loss @T = 69.6 °C Time fs) V A . 0 1 . 0 0 0 0 . 0 0 0 900 0.788 -0.238 1800 0.720 -0.329 2700 0.592 -0.524 3600 0.488 -0.718 4500 0.394 -0.932 5400 0.358 -1.028 6300 0.278 -1.281 k o b s d 1.96E-04 Rsq 0.9904 0 . 0 0 0 - 0.200 - ♦ Alkane Loss -0.400 - Linear (Alkane Loss) -0.800 - y = -1.96E-04x R2 = 0.9904 - 1 . 0 0 0 - - 1.200 - -1.400 0 800 1600 2400 3200 4000 4800 5600 6400 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XVIII: Hexane Elimination @T = 69.6°C in80/20 (v/v)C«FJC & t, Time (s) A,/A„ L n(A ^ 0 1 . 0 0 0 0 . 0 0 0 900 0.714 -0.337 1800 0.595 -0.519 2700 0.476 -0.742 3600 0.405 -0.904 4500 0.333 - 1 . 1 0 0 5400 0.286 -1.252 6300 0.238 -1.435 kotad 2.03E-04 Rsq 0.9980 0 . 0 0 0 - 0.200 ♦ Alkane Loss -0.400 - Linear (Alkane Loss) -0.600 - S -0.800 - y = -2.03E-04x R2 = 9.98E-01 J - 1 . 0 0 0 - - 1.200 - -1.400 - -1.600 0 1200 2400 3600 4800 6000 7200 time (s) 168 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table UI.XIX: Hexane Elimination @ T = 69.6 °C in 80/20 (v/v) Time Is) A »/A « Ln(A t/A<>) 0 1 . 0 0 0 0 . 0 0 0 1200 0.786 -0.241 2400 0.622 -0.475 3600 0.447 -0.805 6000 0.289 -1.241 7200 0.218 -1.523 8400 0.169 -1.778 9600 0.136 -1.995 koM Rsq 2.10E-04 0.9983 < sf m i - 0.200 -0.600 - 1 . 0 0 0 -1.400 -1.800 - 2.200 ♦ H enne Linear (Herane y = -2.!OE-O4x RJ = 9.99E-01 0 2500 5000 7500 10000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XX: Hexane Elimination @ T = 603 °C: -A = -B A r/ Time is) At/A« LnfAt/Ao) 0 1 . 0 0 0 0 . 0 0 0 1800 0.917 -0.086 5220 0.826 -0.191 10620 0.658 -0.419 14220 0.562 -0.577 44880 0.256 -1.361 50280 0.173 -1.754 55680 0.149 -1.901 kotad 3.28E-05 Rsq 0.9900 0 . 0 0 0 - 0.200 - -0.400 - ♦ Alkane Loss -0.600 - -0.800 - Linear (Alkan e Loss) c < - 1 . 0 0 0 - e m i - 1.200 - -1.400 - -1.600 - -1.800 - - 2.000 0 10000 20000 30000 40000 50000 60000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXI: Hexane Elimination @ T = 603 °C: 'Anion = '02jf Time (s) A «/A « LniAt/Ao) 0 1 . 0 0 0 0 . 0 0 0 1800 0.851 -0.161 4500 0.731 -0.313 8100 0.493 -0.707 12600 0.388 -0.947 18000 0.239 -1.431 23100 0.179 -1.720 28500 0.104 -2.263 kobtd 7.74E-05 Rsq 0.9950 ♦ Alkane loss -0.5 - Linear (Alkane loss) o < < e -2.5 0 5000 10000 15000 20000 25000 30000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table IU.XXU: Hexane Elimination @ 60.2 °C: Anion = O2CCF3 Time (s) A./An Ln(At/A<,) 0 1 . 0 0 0 0 . 0 0 0 1500 0.810 -0 . 2 1 1 3000 0.672 -0.397 4500 0.546 -0.605 6000 0.454 -0.790 7500 0.366 -1.005 9000 0.284 -1.259 10500 0.236 -1.444 1 2 0 0 0 0.192 -1.650 13500 0.166 -1.796 15000 0.132 -2.025 k o b * d 1.36E-04 Rsq 0.9987 0 . 0 0 0 -0.300 ♦ Alkane Loss -0.600 - Linear (Alkane Loss) 9 < < -0.900 - y = -1.36E-04x R2 = 9.99E-01 e m i - 1.200 -1.500 -1.800 - - 2.100 16000 4000 8000 12000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXII1: Hexane Elimination @ T = 49.4 °C Time Is) A i/A «, Ln(Ai/A«) 0 1 . 0 0 0 0 . 0 0 0 10800 0.957 -0.044 23700 0.889 -0.118 39060 0.762 -0.272 59520 0.704 -0.350 89700 0.580 -0.544 106980 0.507 -0.680 128220 0.416 -0.876 153960 0.373 -0.985 218700 0.224 -1.496 290700 0.142 -1.952 k o b sd 6.87E-06 Rsq 0.9979 0.00 - 0.20 -0.40 ♦ Alkane Loss -0.60 -0.80 Linear (ADcane Loss) o < < - 1.00 - 1.20 -1.40 -1.60 -1.80 - 2.00 0 50000 100000 150000 200000 250000 300000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table IU.XXIV: Hexane Elimination @ T = 37.6 °C Time (s) Ai/A« L n{A i/A «,)_ 0 1 . 0 0 0 0 . 0 0 0 57360 0.926 -0.077 143760 0.787 -0.239 230160 0.746 -0.293 507360 0.559 -0.582 763740 0.417 -0.875 1011960 0.313 -1.163 1154100 0.254 -1.371 1251300 0.217 -1.526 1400760 0.167 -1.792 1642920 0.128 -2.057 kohd Rsq 1.23E-06 0.9943 - 0.200 - ♦ Alkane Loss -0.600 - Linear (Alkane Loss) 1 . 0 0 0 • y = -1.23E-06x R2 = 9.94E-0I -1.400 - -1.800 - - 2.200 0.E+00 3.E+05 5.E+05 8.E+05 l.E+06 l.E+06 2.E-K)6 2.E+06 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXV: Cyclopentane Elimination H N ^ ® (MeO)jP 6 C s D e Temp °C H H ^n h “ Rh® -► (MeO)jP' V E Temp IQ 60.5 50.2 39.6 Temp m 333.62 323.32 312.72 1/T (K) 0.0029974 0.0030929 0.0031977 Slope Rsq intercept Std Error in Y values AG* = AH* = AS* = k (cyclopentane loss) 7.61E-05 Ln(k) kfcalcd) Lnfltkalcd ■9.48 6.82E-05 1.41E-05 -11.17 1.74E-05 4.27E-06 -12.37 3.86E-06 -14336.0738 0.9845 33.3789 0.2549 26.1 kcal/mol @ 39.6 C 27.8 kcal/mol @ 39.6 C 5.58 eu @ 39.6 C -9.59 -10.96 -12.46 Arrhenius Plot -9.00 -9.50 - Linear (ln(k)) - 1 0 . 0 0 - -10.50 - y = -14336x + 33.379 RJ = 0.9845 c m l - 12.00 - -12.50 - -13.00 0.00295 0.00305 0.00325 0.00315 1/T (K) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ln(At/Ao) Table III.XXVI: Cydopentane Elimination @ T = 60.5 °C Method A: Starting Material Loss Time fs> At/Ao LnlAtM 0 1 . 0 0 0 0 . 0 0 0 1 2 0 0 0.918 -0.086 2400 0.858 -0.153 3300 0.782 -0.246 4500 0.700 -0.356 8100 0.575 -0.553 1 1 1 0 0 0.459 -0.779 15900 0.313 -1.162 24900 0.147 -1.917 ko b sd 7.60E-05 Rsq 0.9972 0 . 0 0 0 - 0.700 - 1.400 - 2.100 ♦ Cydopentane Loss ■Linear (Cydopentane Loss) y = -7.47E-05x R 2 = 9.97E-0I 0 7000 14000 21000 28000 time(s) 176 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Method B: Product Formation Time fs) P. 1-fPi/Ao) Ln[l-(Pt/A<i)l 1 2 0 0 0.490 5.990 0.082 0.918 -0.085 2400 0.870 6.160 0.141 0.859 -0.152 3300 1.330 6.090 0.218 0.782 -0.246 4500 1.730 5.770 0.300 0.700 -0.356 8100 2.620 6.160 0.425 0.575 -0.554 1 1 1 0 0 3.270 6.040 0.541 0.459 -0.780 15900 4.260 6 . 2 0 0 0.687 0.313 -1.162 24900 5.260 6.170 0.853 0.147 -1.914 kotad 7.63E-05 Ave. Ao 6.073 Rsq 0.9971 StdDev 0.142 0 . 0 0 0 ♦ Alkane Loss -0.700 Linear (Alkane Loss) e < £ i y = -7.47E-05x R2 = 9.96E-01 -1.400 - 2.100 0 7000 14000 21000 28000 tim e (s) 177 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXVII: Cydopentane Elimination @ 50.2 °C Time Is) At/An LnlAt/Ao) 0 1 . 0 0 0 0 . 0 0 0 7200 0.845 -0.168 14400 0.773 -0.258 25320 0.676 -0.392 32520 0.586 -0.535 42180 0.520 -0.654 52980 0.438 -0.824 63180 0.412 -0.887 74880 0.351 -1.047 83280 0.300 -1.203 97080 0.240 -1.425 111480 0.190 -1.661 128280 0.156 -1.861 141900 0.128 -2.056 kotad 1.41E-05 Rsq 0.9977 -0 . 2 -0 . 6 ♦ Alkane Loss Linear (Alkane Loss) e < m o < e -3 -1.4 y = -1.46E-05x R2 = 9.96E-01 - 1 . 8 -2 . 2 50000 150000 100000 0 tim e (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ln(At/Ao) Table III.XXVIII: Cydopentane Elimination @ T = 39.6 °C Time (s) Ln(Ai/Ao) 0 1 . 0 0 0 0 . 0 0 0 36000 0.821 -0.197 69000 0.737 -0.305 123000 0.608 -0.498 kobfd 4.35E-06 206300 0.428 -0.849 Rsq 0.9972 275300 0.302 -1.197 343800 0.217 -1.528 415800 0.164 -1.808 -0 . 2 - -0.4 - ♦ Alkane Loss -0 . 6 - -0 . 8 - Linear (Alkane Loss) y = -4.34E-06x R2 = 9.97E-01 0 100000 200000 300000 400000 500000 time (s) 179 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXIX: Cydopentane Loss @ T =39.6 °C: Excess P(OMe)rd9 Time (s) At 0 2.410 45600 2.090 88800 1.890 157200 1.020 204900 0.860 261000 0.690 335160 0.560 393060 0.480 470460 0.280 Phenvl %Phenvl 0 . 0 0 0 0 . 0 0 0 0.410 0.155 0.750 0.261 0.850 0.378 0.940 0.417 1 . 0 1 0 0.467 1 . 1 2 0 0.517 1.480 0.589 1.560 0.627 P2 %P2 0 . 0 0 0 0 . 0 0 0 0.760 0.057 1.170 0.081 1.890 0.168 2.260 0 . 2 0 1 2.320 0.214 2.440 0.225 2.760 0.220 3.240 0.260 A./An Ln(A>/An) 1 . 0 0 0 0 . 0 0 0 0.788 -0.238 0.658 -0.419 0.454 -0.790 0.382 -0.963 0.319 -1.143 0.258 -1.354 0.191 -1.655 0.113 -2.184 Reaction Conditions k ^ it 4.33E-06 41 equivalents of P(OCD3 )3 Rsq 0.9884 P2 is the [Rh(P(OCD3 ))5 ]+ cation Ao is calcd'd from At + Phenyl + P2/5 3.4 mM in [Rh] 0.14 M in P(OCD3) 3 (followed via 3IP NMR) 0 . 0 0 0 ♦ Alkane Loss * 0 -1 . 0 0 0 Linear (Alkane Loss) J -1.500 y = -4.33E-06x R2 = 9.88E-01 - 2.000 -2.500 100000 0 200000 300000 500000 400000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ln(k) Table III.XXX: Cydohexane Reductive Elimination: Arrhenius Plot (MeO)3 p ' V 'H C f iD e Temp°C r / s HNw Rh® ✓ Temp IQ 68.5 50.2 39.6 Temp m 341.62 323.32 312.72 1/T (T O k < fv fin h > M p e io«) Ln(k) k < « ie d Ln(kf«ifd) 0.002927 2.79E-04 -8.18 2.56E-04 -8.27 0.003093 1.61E-05 -11.04 2.01 E-05 -10.81 0.003198 4.66E-06 -12.28 4.06E-06 -12.42 Slope -15315.82 Rsq 0.9915 intercept 36.56 Std Error in Y 0.28 values □AG* = 26.1 kcal/mol @ 39.6 C □AH* = 29.8 kcal/mol @ 39.6 C □AS* = 12.04 eu @ 39.6 C A rrh e n iu s Plot - 8.00 ♦ Cyclohexyl -9.00 - Linear (Cyclohexyl) - 1 0 . 0 0 - y = -15359x + 36.69 R2 = 0.9915 - 12.00 - -13.00 0.002850 0 .0 0 3 0 5 0 0.003250 1/T (Kelvin) 181 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ln(At/Ao) Table III.XXXI: Cyclohexane Elimination @ 68.5 °C Time (s) At/A« LnfAi/Ao) 0 1 . 0 0 0 0 . 0 0 0 840 0.840 -0.174 1680 0.670 -0.401 2520 0.491 -0.712 3360 0.363 -1.014 4200 0.302 -1.198 5040 0.259 -1.351 5880 0.204 -1.592 kobid 2.79E-04 Rsq 0.9921 - 0.2 -0.4 ♦ Alkane Loss - 0.6 Linear (Alkane Loss) - 0.8 - 1.2 -1.4 - 1.6 - 1.8 1000 2000 3000 4000 5000 6000 0 time (s) 182 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ln(At/Ao) Table III.XXXII Cyclohexane Elimination @ 50.2 °C Time fs) A r / A n LnfAt// 0 1 . 0 0 0 0 . 0 0 0 10800 0.805 -0.217 25200 0.645 -0.439 36000 0.579 -0.546 46800 0.450 -0.799 59400 0.402 -0.911 70200 0.321 -1.136 84600 0.246 -1.402 96300 0.209 -1.565 123300 0.135 -2 . 0 0 2 kotad 1.61E-05 Rsq 0.9976 o.ooo ♦ Alkane Loss -0.750 Linear (Alkane Loss) y = -1.61E-05x R2 = 0.9976 -1.500 -2.250 125000 100000 75000 25000 50000 0 time(s) 183 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ln(At/Ao) Table III.XXXIII: Cydohexane Elimination @ T = 50.5 °C: 80/20 (v/v) CtFe/CfiDfi Time fs) LnfAt/A 0 1.000 0.000 11100 0.853 -0.159 23700 0.678 -0.389 34500 0.577 -0.550 46200 0.489 -0.715 60600 0.386 -0.952 75000 0.301 -1.201 86700 0.248 -1.394 113700 0.160 -1.833 k o b sd 1.62E-05 Rsq 0.9995 0.000 - 0.200 -0.400 ♦ Alkane Loss -0.600 -0.800 Linear (Alkane Loss) -1.000 - 1.200 -1.400 -1.600 -1.800 - 2.000 20000 40000 60000 80000 100000 120000 time (s) 184 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ln(At/Ao) Table III.XXXIV: Cydohexane Loss @ T = 39.6 °C Time (s) A./An LnlAt/AnI 0 1.000 0.000 10800 0.944 -0.058 44100 0.843 -0.170 80160 0.722 -0.326 103560 0.645 -0.439 124560 0.572 -0.559 149760 0.495 -0.703 185760 0.434 -0.834 207360 0.388 -0.947 236160 0.345 -1.064 266760 0.312 -1.165 299160 0.276 -1.287 408960 0.177 -1.732 k o b * d Rsq 4.30E-06 0.9963 0.000 -0.400 ♦ Alkane Loss -0.800 Linear (Alkane Loss) -1.600 - 2.000 70000 140000 210000 280000 350000 420000 0 time (s) 18S Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Deuterium Migration/Exchange Data Table IH.XXXV: 2 H Migration in [CnRh(ButylKDXP(OMe)3)lBAr4 r @ T = 39.6 °C: Raw Data Time (s): 0 9000 19500 79620 105720 Alkyl (rel): 1.000 0.979 0.954 0.827 0.777 Alpha-D: 4.000 4.000 4.000 4.000 4.000 Rh-D: 1.150 1.150 1.150 1.150 1.150 Omega-D: 0.100 0.360 0.800 1.670 2.520 Phenyl (rel): 0.000 0.021 0.046 0.173 0.223 Alpha-D(rel): 0.762 0.711 0.642 0.485 0.405 Rh-D (rel): 0.219 0.204 0.184 0.139 0.116 Omega-D (rel): 0.019 0.064 0.128 0.202 0.255 Time (s): 124320 138720 158520 183720 Alkyl (rel): 0.743 0.718 0.685 0.645 Alpha-D: 4.000 4.000 4.000 4.000 Rh-D: 1.150 1.150 1.150 1.150 Omega-D: 2.950 3.390 3.810 3.990 Phenyl (rel): 0.257 0.282 0.315 0355 Alpha-D(rel): 0.367 0336 0306 0.282 Rh-D (rel): 0.105 0.097 0.088 0.081 Omega-D (rel): 0.271 0.285 0.291 0.281 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ln(At/Ao) Table III.XXXVI: 2 H Migration in [CnRh(Butyl)D(P(OMe)3)]BAr4r : Alkane Elimination Data Time fs) A»/A« LnfA JA J 0 1.000 0.000 79620 0.826 -0.191 105720 0.786 -0.241 124320 0.749 -0.290 k o b sd 2.39E-06 138720 0.711 -0.341 Rsq 0.9979 158520 0.687 -0.375 183720 0.646 -0.437 0.000 ♦ Alkane Loss -0.090 Linear (Alkane Loss) -0.180 -0.270 -0.360 -0.450 0 50000 100000 150000 200000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. R el. Cone. Figure III.II: 2 H Migration in [CnRh(Butyl)D(P(OMe)3)]BAr4r : Plot of the Data Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 39.6 °C. kia(adjd) =0.075 s '1 kadiss = 3.3xl0"6s'1 k-IRh (adj.’d) = 0.022 s ' kediss = 2.2 x 1 0 "6 s * 1 k.2a = 3.9 x 10- 6 s’1 k* = 5.9 x 1 0 "6 s'1 0.800 Rh-D 0.700 Alpha-D 0.600 Phenyl 0.500 Rh-D (fit) 0.400 Alpha-D (fit) Omega-D (fit) Phenyl (fit) 0.300 0.200 0.100 0.000 0 100000 200000 300000 400000 500000 time (s) 188 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXXVII: 2 H Migration in [CnRh(HexylXDXP(OMe)3)]BAr4 r @ T = 39.6 °C: Raw Data Time (s): 0 176880 265680 344640 433440 Alkyl (rel): 1.000 0.678 0.557 0.469 0.385 Alpha-D: 4.000 4.000 4.000 4.000 4.000 Rh-D: 1.180 1.180 1.180 1.180 1.180 Omega-D: 0.083 3.570 4.400 4.890 6.160 Phenyl (rel): 0.000 0.322 0.443 0.531 0.615 Alpha-D(rel): 0.666 0J10 0.233 0.186 0.136 Rh-D (rel): 0.196 0.091 0.068 0.055 0.040 Omega-D (rel): 0.138 0.277 0.256 0.228 0.209 Figure I1I.III: 2 H Migration in [CnRh(Hexyl)D(P(OMe)3 )]BAr4 r: Plot of the Data Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 39.6 °C. k l a ( * J j d ) =0.075 s'1 k a d i s s = 3 .0 x 1 0 " 6 s'1 k -lR h (a d j ’d) = 0.022 s'1 k m diss = 2.0 x 10- 6 s* 1 k . 2 a = 2.5x10^ s'1 k m = 3.8 x 1 0 -6 s'1 0.700 Rh-D 0.600 Alpha-D Omega-D 0.500 Phenyl u e o U 0.400 Rh-D (fit) £ 0.300 Alpha-D (fit) Omega (fit) Phenyl ( f it) 0.200 0.100 0.000 75000 150000 225000 300000 375000 450000 0 time (s) 189 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table fn.XXXVUI: 2 H Migration in [CnRh(HexylXDXP(OMe)3 )]BAr/ @ T = 50.2°C: Raw Data Time (s): 0 5400 8100 10500 13200 Alkyl (rel): 1.000 0.910 0.868 0.833 0.794 Alpha-D: 4.000 4.000 4.000 4.000 4.000 Rh-D: 1.070 1.110 1.080 1.160 1.130 Omega-D: 0.33 0.990 1.300 1.890 2.250 Phenyl (rel): 0.000 0.090 0.132 0.167 0.206 Alpha-D(rel): 0.734 0.596 0.541 0.475 0.431 Rh-D (rel): 0.204 0.165 0.150 0.132 0.120 Omega-D (rel): 0.062 0.149 0.177 0.226 0343 Time (s): 16500 20100 24300 28800 33300 Alkyl (rel): 0.750 0.704 0.654 0.605 0.559 Alpha-D: 4.000 4.000 4.000 4.000 4.000 Rh-D: 1.210 1.020 1.160 1.090 1.150 Omega-D: 2.570 3.140 3.980 4.280 4.920 Phenyl (rel): 0.250 0.296 0346 0395 0.441 Alpha-D(rel): 0.390 0341 0.288 0.257 0323 Rh-D (rel): 0.108 0.095 0.080 0.071 0.062 Omega-D (rel): 0.251 0.268 0.287 0.276 0.275 Time (s): 42300 54000 Alkyl (rel): 0.478 0.390 Alpha-D: 4.000 4.000 Rh-D: 1.130 1.120 Omega-D: 5.060 5.250 Phenyl (rel): 0.522 0.610 Alpha-D(rel): 0.188 0.150 Rh-D (rel): 0.052 0.042 Omega-D (rel): 0.238 0.198 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXXIX: 2 H Migration in [CnRh(Hexyl)D(P(OMe>3)]BAr4r : Alkane Elimination Data Time (s) At/An LnfAi/An) 0 1.000 0.000 5400 0.915 -0.089 8100 0.900 -0.105 10500 0.858 -0.153 13200 0.831 -0.185 16500 0.782 -0.245 20100 0.740 -0.301 24300 0.689 -0.372 28800 0.632 -0.459 33300 0.557 -0.586 42300 0.517 -0.659 54000 0.392 -0.936 k o b sd 1.745E-05 Rsq 0.9916 0.000 ♦ Hexane Loss Linear (Hexane Loss) -0.250 y = -1.75E-05x R2 = 0.9916 < -0.500 -0.750 -1.000 0 40000 60000 20000 time (s) 191 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rel. Cone. Figure IU.IV: 2 H Migration in [CnRh(Hexyl)D(P(OMe)3)]BAr4r : Plot of the Data Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 50.2 °C. k l a ( a d j ’d) =0.19 S' 1 k a d is s = 2.4xlO ’ 6 S ‘I k -iR h ( a d j.’d) = 0.052 s'1 k a d i s s = 1.6 x 10 " 6 s'1 k - 2 a = 2.6 x 10'5 s*1 k o , = 3 .9 x 10'5 s'1 0.750 Rh-Ph Rh-D 0.600 Alpha-D Oroega-D Rh-D (fit) 0.450 Alpha-D (fit) Omega-D (fit) Pheny(fit) 0.300 0.150 0.000 0 19000 38000 57000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXXX: *H Migration in [CnRh(HexylKDKP(OMe)3)]BAr4 r @ T = 60.7 °C: Raw Data Time (s): 0 2400 5100 6660 8160 Alkyl (rel): 1.000 0.881 0.765 0.704 0.651 Alpha-D: 4.000 4.000 4.000 4.000 4.000 Rh-D: 1.110 1.290 1.150 1.210 1.020 Omega-D: 0.860 1.740 2.420 3.190 3.430 Phenyl (rel): 0.000 0.119 0.235 0.296 0.349 Alpha-D(rel): 0.670 0.515 0.406 0.340 0.305 Rh-D (rel): 0.186 0.143 0.113 0.094 0.085 Omega-D (rel): 0.144 0.224 0.246 0.271 0.262 Time (s): 9960 17160 Alkyl (rel): 0.592 0.406 Alpha-D: 4.000 4.000 Rh-D: 0.930 1.050 Rh-D (crve) = 1.11 Omega-D: 4.130 5.220 Phenyl (rel): 0.408 0.594 Alpha-D(rel): 0.256 0.157 Rh-D (rel): 0.071 0.044 Omega-D (rel): 0.265 0.205 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXXXI: 2 H Migration in [CnRh(Hexyl)D(P(OMe>3)|BAr4 r : Alkane Elimination Data Time fs) At/A„ Ln(Ai/Ao) 0 1.000 0.000 2400 0.894 -0.112 5100 0.761 -0.273 k o b sd 5.264E-05 6660 0.719 -0.330 Rsq 0.9898 8160 0.632 -0.459 9960 0.559 -0.582 17160 0.416 -0.877 0.000 -0.250 -0.750 -1.000 5000 20000 0 10000 15000 ♦ Hexane Linear (Hexane y = -5.264E -05x R 2 = 0.9898 tim e(s) 194 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rel. Cone. Figure III.V: 2 H Migration in [CnRh(Hexyl)D(P(OMe)3)]BAr4 r : Plot of the Data Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @T = 60.7 °C. k lc t(a d j.’d) = 0.45 s‘* k a d i s s = 6.9 x 10'5 s'1 k -lR h (adj.’d) 0.12 S ko Hi« 4.6 X 10 s k-2a =5.7 x 10'5 s * 1 k to = 8.6 x 1 0 * 5 s’1 0.8 ♦ Omega-D ■ Alpha-D A Rh-D 0.6 - • Phenyl 0.5 - Rh-D (fit) Alpha-D (fit) Omega-D (fit) Phenyl (fit) 0.2 - 3600 7200 18000 0 14400 10800 time (s) 195 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXXXH: 2 H Migration in [CnRh(DecylXD)(P(OMe)3 )]BAr4 r @ T = 39.6 °C: Raw Data Time (s): 0 49800 82200 125400 158160 Alkyl (rel): 1.000 0.901 0.841 0.768 0.717 Alpha-D: 4.000 4.000 4.000 4.000 4.000 Rh-D: 1.230 1.000 1.010 1.120 0.980 Omega-D: 0.060 0.390 1.070 1.930 2.150 Phenyl (rel): 0.000 0.099 0.159 0.232 0.283 Alpha-D(rel): 0.783 0.735 0.654 0373 0.556 Rh-D (rel): 0.205 0.193 0.172 0.150 0.146 Omega-D (rel): 0.012 0.072 0.175 0.277 0.299 Time (s): 206400 250560 376560 498960 Alkyl (rel): 0.648 0.591 0.453 0.351 Alpha-D: 4.000 4.000 4.000 4.000 Rh-D: 1.030 1.010 1.040 1.060 Omega-D: 2.460 3.020 4.010 6.050 Phenyl (rel): 0352 0.409 0.547 0.649 Alpha-D(rel): 0.533 0.496 0.442 0360 Rh-D (rel): 0.140 0.130 0.116 0.095 Omega-D (rel): 0328 0374 0.443 0.545 Rh-D (ave): 1.05 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXXXIII: 2 H Migration in [CnRh(Decyl)D(P(OMe)3)]BAr4 r : Alkane Elimination Data Time (si A »/A o LnfAt/A.) 0 1.000 0.000 49800 0.910 -0.095 82200 0.863 -0.147 125400 0.785 -0.242 158160 0.729 -0.316 206400 0.659 -0.417 250560 0.559 -0.581 376560 0.459 -0.779 498960 0.359 -1.024 kobsd Rsq 2.10E-06 0.9946 o < e m i 0.000 - 0.200 -0.400 -0.600 -0.800 -1.000 - 1.200 y = -2.l0E-06x R2 = 0.9946 0 100000 200000 300000 400000 500000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rel. Cone. Figure III.VI: 2 H Migration in [CnRh(Decyl)D(P(OMe)3 )]BAr4r : Plot of the Data Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 39.6 °C. k l a ( a d j d) =0.075 S*1 k a d i s s = 2.8 x 1 0 "6 s '1 k-iR h (a d j.d ) = 0.020 s‘l k o j d is s = 1.9 x 1 0 "6 s * 1 k-2 a =2.0x1 O '6 s'1 kc = 3.0 x 10- 6 s'1 0.800 0.700 0.600 0.500 0.400 0.300 0.200 0.100 0.000 0 100000 200000 300000 400000 500000 time (s) ♦ Rh-D n Alpha-D Omega-D • Phenyl Rh-D (fit) Alpha-D (fit) Omega-D (fit) Phenyl (fit) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXXXIV: 2 H Migration in [CnRh(c-CsH9 )D(P(OMe)3)IBAr4f: Raw Data Time (s): 0 11400 33000 51000 69720 Alkyl (rel): 1.000 0.950 0.850 0.780 0.720 Alpha-D: 2.000 2.000 2.000 2.000 2.000 Rh-D: 1.060 1.060 1.060 1.060 1.060 Beta-D: 0.100 0.240 0.520 0.620 0.670 Phenyl (rel): 0.000 0.053 0.146 0.216 0.283 Alpha-D(rel): 0.632 0.574 0.476 0.426 0384 Rh-D (rel): 0.336 0305 0.253 0.226 0.204 Beta-D (rel): 0.032 0.068 0.125 0.132 0.129 Time (s): 152700 240900 Alkyl (rel): 0.480 0.320 Alpha-D: 2.000 2.000 Rh-D: 1.060 1.060 Beta-D: 1.330 2.660 Phenyl (rel): 0.518 0.684 Alpha-D(rel): 0.220 0.110 Rh-D (rel): 0.117 0.059 Beta-D (rel): 0.146 0.147 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ln(At/Ao) Table IH.XXXXV: 2 H Migration in [CnRh(c-C5H9 )D(P(OMe)3)lBAr4f: Alkane Elimination Data 0.000 - 0.200 -0.400 -0.600 -0.800 -1.000 - 1.200 -1.400 Time (si A^/A- Ln(At/A«) 0 1.000 0.000 11400 0.964 -0.037 33000 0.833 -0.183 koM 4.78E-06 51000 0.810 -0.211 Rsq 0.9949 69720 0.695 -0.364 152700 0.505 -0.683 240900 0.311 -1.168 ♦ Alkane Loss Linear (Alkane Loss) y = -4.78E-06x R2 = 0.9949 50000 100000 150000 200000 250000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Rel. Cone. Figure III.VII: Z H Migration in [CnRh(c-CsH9 )D(P(OMe)3)]BAr4r : Plot of the Data Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) kla(adj.’d) — 0.070 S * k-iRh(adj.’d) = 0.037 S ' k -2a = 2.6 X 10-6 s * 1 k p = 5.2 x 10-6 s'1 kadiss kp diss k y kydiss = 7.6 x 10- 6 s * 1 = 3.8x l O V = 2.6 x 10- 6 s'1 = 3.8 x 10- 6 s’1 0.700 0.600 - 0.500 - 0.400 - 0.300 - 0.200 0 . 1 0 0 - 0.000 ♦ Phenyl Alpha-D • Beta-D Alpha-D (fit) Beta-D (fit) Gamma (fit) Phenyl (fit) Rh-D (fit) V 0 50000 100000 150000 200000 250000 time(s) 201 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table IH.XXXXVI: 2 H Migration in [CnRh(c-QHu)D(P(OMe)3)lBAr4r : Raw Data Time Is) Rh-D g-D 1.24 nnm 0.83 nnm 0 1.47 2.00 0.47 0.10 10800 1.18 2.00 0.32 0.17 22500 1.12 2.00 0.40 0.16 44100 1.02 2.00 0.51 0.28 80160 1.11 2.00 1.03 0.33 103560 1.06 2.00 1.41 0.38 124560 1.02 2.00 1.51 0.43 149760 1.02 2.00 1.77 0.46 185760 1.00 2.00 2.23 0.58 207360 1.01 2.00 2.56 0.64 202 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table HI.XXXXVII: 2 H Migration in [CnRh(c-C6Hu)D(P(OMe)3)]BAr4r : Alkane Elimination Data Time (si At/A* Ln(A,/. 0 1.000 0.000 10800 0.944 -0.058 44100 0.843 -0.170 80160 0.722 -0.326 103560 0.645 -0.439 124560 0.572 -0.559 149760 0.495 -0.703 185760 0.434 -0.834 207360 0.388 -0.947 236160 0.340 -1.079 266760 0.291 -1.234 299160 0.253 -1.374 408960 0.152 -1.884 k o b sd 4.67E-06 Rsq 0.9990 0.000 -0.400 ♦ Alkane Loss -0.800 e < < Linear (Alkane Loss) e -J - 1.200 -1.600 - 2.000 70000 140000 210000 280000 350000 420000 time (s) 203 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table III.XXXXVIII: Metal*-*Alpha 2 H Exchange in [CnRh(HexylXD)(P(OMe)3 )l+OTf @ T = 4.7 °C: Raw Data Time (s): 0 2374 5032 7690 SM (Hx-OTf) (int/9): 8.04 6.47 5.58 4.88 Rh-D: 0.00 0.42 0.86 1.11 Alpha-D: 0.00 0.44 0.76 1.68 SM (Hx-OTf) (rel): 1.000 0.883 0.775 0.636 Rh-D (rel): 0.000 0.057 0.119 0.145 Alpha-D (rel): 0.000 0.060 0.106 0.219 Time (s): 9019 10348 11677 13006 SM (Hx-OTf) (int/9): 4.53 4.29 3.96 3.71 Rh-D: 1.02 1.06 1.23 1.20 Alpha-D: 2.15 2.67 3.08 3.47 SM (Hx-OTf) (rel): 0.588 0.535 0.479 0.443 Rh-D (rel): 0.132 0.132 0.149 0.143 Alpha-D (rel): 0.279 0.333 0.372 0.414 Time (s): 15664 18322 20980 23638 SM (Hx-OTf) (int/9): 3.28 2.99 2.68 2.37 Rh-D: 1.26 1.25 1.29 1.12 Alpha-D: 4.03 4.35 4.51 4.81 SM (Hx-OTf) (rel): 0.383 0.348 0.316 0.286 Rh-D (rel): 0.147 0.146 0.152 0.135 Alpha-D (rel): 0.470 0.506 0.532 0.580 -Starting material integrals = (integral with respect to THF = 1.00)/9 -fB D *] = 3[SM] = 0.20 M Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. R el. Cone. Figure ID.VIII: Metal<-> Alpha 2 H Exchange in [CnRh(Hexyl)D(P(OMe)3)rO T f: Plot of the Data Points, Kinetic Fit, and Derived Rate Constants (Macroscopic) @ T = 4.7 °C. k,a =4.3 X 10"4 s '1 kfonn['BD4] = 6.6 X 10*5 s ' 1 k-iRh = 1.0 x 10"4 s ' 1 kform = 2.2 X 10'5 S‘‘ 1.00 • SM SM (fit) Rh-D 0.75 - Rh-D (fit) ♦ Alpha-D Alpha-D (fit) 0.50 0 2 5 — — i ' A A 0.00 0 5000 10000 20000 25000 15000 time (s) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Endnotes 1 (a) Fieser, L.F.; Fieser, M., Reagents for Organic Synthesis, Vol. 1, John Wiley & Sons, Inc.: New York, NY, 1967. (b) Vogel, Handbook for Preparative Organic Chemistry... 2 After completion of reaction 5.0 ml of H2O was added dropwise to the reaction mixture, followed by 5.0 ml of a 15% NaOH solution and, finally, 15 ml of H2O. The etber/sluny was then filtered. 3 (a) Zhou, R.; Wang, C.; Hu, Y.; Flood, T. C. Organometallics 1997,16,434. (b) Zhou, R. Ph.D. Thesis, University of Southern California, 1997. (c) Zhen, H. Ph.D. Thesis, University of Southern California, 1999. 4 Special thanks to Dr. Mas limura and Prof. Tom C. Rood for the synthesis of the I3C labeled precursors. s Calculated according to the following equation: iRh-DmKo - [((Iu+ImVS) + IutouxaKt)]* [l]ipuiW(l3iPRMH)2a.)+ Isihuxhxrxl))]= Irkdxrxu = Rh*D value, where I® = integration value due to deconvolution at time /, I* = integration value due to deconvolution at time t, Irh-duuko = integration value due to deconvolution at time t, and (IsinMHXD/QsinihiifiDid)+ biPsuixMu)] = the % of dihydride contribution to total deuterium, with the individual integration values corresponding to the relative intensities o f3 1 P resonances of each component. 206 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Bibliography Abis, L.; Sen, A.; Halpern, J. J. Am. Chem. Soc. 1978, 100,2915. Arakawa, H.; Aiesta, M.; Armor, J. N.; Barteau, M. A.; Beckman, E. J.; Bell, A. T.; Bercaw, J. E.; Creutz, C.; Dinjus, E.; Dixon, D. A.; Domen, K.; DuBois, D. L.; Eckert; Fujita, E.; Gibson, D. H.; Goddard, W. A.; Goodman, D. W.; Keller, J.; Kubas, G. J.; Kung, H. H.; Lyons, J. E.; Manzer, L. E.; Marks, T. J.; Morokuma, K.; Nicholas, K. M.; Periana, R.; Que, L.; Nielson, J. R.; Sachtler, W. M. H.; Schmidt, L. D.; Sen, A.; Somoijai, G. A.; Stair, P. C.; Stults, B. R.; Tumas, W. Chem. Rev. 2001,101,953. Amdsten, B.A.; Bergman, R.G.; Mobley, T.A.; Peterson, T.H. Acc. Chem. Res. 1995,2 8 ,154. Arnold, D. P.; Bennett, M. A. Inorg. Chem. 1984, 23, 2110. Atwood, J. D., Inorganic and Organometallic Reaction Mechanisms, 2"d Ed.; Wiley-VCH: New York, 1997. Bigeleisen, J. Pure AppL Chem. 1964,8, 217. Bromberg, S. E.; Yang, H.; Asplund, M. C.; Lian, T.; McNamara, B. K.; Kotz, K. T.; Yeston, J. S.; Wilknes, M.; Frei, H.; Bergman, R. G.; Harris, C. B. Science 1997,278, 260. Brown, C. E.; Ishikawa, Y.; Hackett, P. A.; Rayner, D. M. J. Am. Chem. Soc. 1990,112,2530. Buchanan, J. M.; Stryker, J. M.; Bergman, R. G. J. Am. Chem. Soc. 1986,108, 1537. Bullock, R.M.; Headford, C.E.L.; Hennessy, K.M.; Kegley, S.E.; Norton, J.R. J. Am. Chem. Soc. 1989, 111, 3897. Chatt, J.; Davidson, J. M. J. Chem. Soc. 1965, 843. Chemical Kinetics Simulator™, Version 1.01, © IBM Corp., 1996. Chen, H. Y.; Hartwig, J. F.Angew. Chemie, Int’ l Ed. 1999,38, 3391. Chen, H. Y.; Schlecht, S.; Semple, T. C.; Hartwig, J. F. Science 2000,287,1995. Cotton, F. A.; Wilkinson, G., Advanced Inorganic Chemistry, 5* Ed.; John Wiley & Sons, Inc.: New York, 1988. Couch, D. A.; Robinson, S. D. J. Chem. Soc.Dalt. Trans. 1971,23,1508. Crabtree, R. H. Chem. Rev. 1995,95 ,987. English, A. D.; Meakin, P.; Jesson, J. P. Inorg. Chem. 1976,15, 1233. English, A. D.; Meakin, P.; Jesson, J. P. J. Am. Chem. Soc. 1976,9 8 ,7590. Espenson, J. H., Chemical Kinetics and Reaction Mechanisms, 2"d Ed., McGraw-Hill: New York, 1995. Fekl, U.; Zahl, A.; van Eldik, R. Organometallics 1999,18,4156. 207 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fieser, L.F.; Fieser, M., Reagents for Organic Synthesis, Vol. 1, John Wiley & Sons, Inc.: New York, NY, 1967. Rood, T. C.; Iimura, M.; Perotti, J. P. J. Chem. Soc. Chem. Comm. 2000, jc c, xxxx. Flood, T. C.; Janak, K. E.; Iimura, M.; Zhen, H. J. Am. Chem. Soc. 2000,122,6783. Geftakis, S.; Ball, G.E. J. Am. Chem. Soc. 1998,120,9953. Ghosh, C. K.; Graham, W. A. G. J. Am. Chem. Soc. 1987,109,4726. Gould, G.L.; Heinekey, D.M. J. Am. Chem. Soc. 1989, 111, 5502. Graham, M. A.; Perutz, R. N.; Poliakoff, M.; Turner, J. J. J. Organometai Chem. 1972,34, C34. Gunther, H., NMR Spectroscopy, 2n d Ed.; John Wiley & Sons, Inc.: Chichester, 1995. Haines, L. M. Inorg. Chem. 1971,1 0 ,1685. Hall, C.; Perutz, R.N. Chem. Rev. 1996,96,3125. Harper, T. G. P.; Shinomoto, R. S.; Deming, M. A.; Flood, T. C. J. Am. Chem. Soc. 1988,110,7915. Hessel, E.T.; Jones, W.D. J. Am. Chem. Soc. 1993,115,554. Hill, C. L., Ed., Activation and Functionalization o f Alkanes; John Wiley & Sons, Inc.: New York, 1989. Hoyano, J. K.; Graham, W. A. G. J. Am. Chem. Soc. 1982,104, 3723. Iimura, M. Ph.D. Thesis, University of Southern California, 2000. Janowicz, A. H.; Bergman, R. G. J. Am. Chem. Soc. 1982,104, 352. Jenkins, H. A.; Yap, G. P. A.; Puddephatt, R. J. Organometallics 1997,16, 1946. Johansson, L.; Tilset, M. J. Am. Chem. Soc. 2001,123,739. Jones, W. D.; Dong, L.; Simoes, J. A. Inorg. Chem. 1991,3 , 16. Jones, W. D.; Feher, F. J. J. Am. Chem. Soc. 1984,106, 1650. Jones, W. D.; Feher, F. J. J. Am. Chem. Soc. 1986,108,4814. Jones, W. D.; Hessel, E. T. J. Am. Chem. Soc. 1993,115,554. Lowry, T. H.; Richardson, K.S., Mechanism and Theory in Organic Chemistry, Ed.; Harpers & Row: New York, NY, 1987. McNamara, B.K.; Yeston, J.S.; Bergman, R.G.; Moore, C.B. J. Am. Chem. Soc. 1999,121,6437. Meakin, P.; Jesson, J. P. J. Am. Chem. Soc. 1973,9 5 ,7272. 208 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Meakin, P.; Muetterties, E. L.; Jesson, J. P. J. A m Chem. Soc. 1972,94,5271. Morrison, R. T.; Boyd, R. N., Organic Chemistry, 4* Ed., Allyn and Bacon, Inc.: Boston, 1983. Parkin, G.; Bercaw, J.E. Organometallics 1989,8, 1172. PCMODEL for Windows, Version 7.50.00, ©Serena Software. Periana, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1986,108, 1537. Periana, R.A.; Bergman, R.G. J. Am. Chem. Soc. 1986,108,7332. Periana, R. A.; Taube, D. J.; Evitt, E. R.; Loftier, D. G.; Wentrcek, P. R.; Voss, G.; Masuda, T. Science 1993,259, 340. Perutz, R. N.; Turner, J. J. J. Am. Chem. Soc. 1975,9 7 ,4791. Prokopchuk, E. M.; Jenkins, H.A.; Puddephatt, R. J. Organometallics 1999,18,2861. Ruba, E.; Simanko, W.; Mereiter, K.; Schmid, R.; Kirchner, K. Inorg. Chem. 2000,39, 382. Schafer, D.F.; Wolczanski, P.T. J. Am. Chem. Soc. 1998,120,4881. Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 1996, 118,5961. Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. Angewandte Chemie-lnt. 'I Ed. 1998,16,2181. Tellers, D. M.; Skoog, S. J.; Bergman, R. G.; Gunnoe, T. B.; Hannan, W. D. Organometallics 2000, 19,2428. Turner, H. W.; Schrock, R.R.; Fellmann, J.D.; Holmes, S.J. J. Am. Chem. Soc. 1983,105,4942. Vaska, L.; Diluzio, J. W. J. Am. Chem Soc. 1962,8 4 ,4889. Vogel, A. I., Vogel's Textbook o f Practical Organic Chemistry, 5* Ed.; Longman: London, 1999. Waltz, K. M.; Hartwig, J. F. J. Am Chem Soc. 2000,122, 11358. Wang, C. Ph.D Thesis, University of Southern California, 1994. Wang, C.; Ziller, J. W.; Flood, T. C. J. A m Chem Soc. 1995,117, 1647. Wang, L.; Flood, T. C. / A m Chem Soc. 1992,114, 3169. Wang, L.; Lu, R. S.; Bau, R.; Flood, T. C. J. A m Chem Soc. 1993,115,6999. Wang, L.; Sowa Jr., J. R.; Wang, C.; Lu, R. S.; Gassman, P. 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Creator Janak, Kevin Edward (author)

Core Title Carbon-hydrogen bond activation: Investigation into the dynamics and energetics of alkane complexes within a hard-ligated rhodium system

School Graduate School

Degree Doctor of Philosophy

Degree Program Chemistry

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

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