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Investigations in cooperative catalysis: synthesis, reactivity and metal-ligand bonding
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Investigations in cooperative catalysis: synthesis, reactivity and metal-ligand bonding
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Content
INVESTIGATIONS IN COOPERATIVE CATALYSIS:
SYNTHESIS, REACTIVITY AND METAL-LIGAND BONDING
by
Megan K. Pennington-Boggio
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
August 2013
Copyright 2013 Megan K. Pennington-Boggio
ii
Dedication
To Mom, Dad, Brother and John.
iii
Acknowledgments
I would like to thank my advisor, Professor Travis J. Williams, for his teaching,
support, and guidance these last five years. I am thankful to have had the opportunity to
learn from someone who truly loves chemistry and all it has to offer. He has taught me to
appreciate the joys and challenges equally and to see the opportunities in both, which is
something I will carry with me always.
A special thank you to my qualification and dissertation committee members:
Professors G. K. Surya Prakash, Mark Thompson, Barry Thompson, John Petruska and
Steven Nutt for their time, advice and support. Thank you to Professor Mike Richmond
of the University of North Texas for using his computational expertise to prove that we
actually know what we are doing. I also want to thank every teacher that encouraged me
to pursue my dreams, no matter how difficult it seemed. Specifically, I would like to
acknowledge the supervisors who gave me my first opportunities of doing wet chemistry:
Bob Sellards, Ph.D., Nikki Flores, Erika Wagner, Ph.D., and Professor Hal Van Ryswyk.
It was through them that I truly learned to love chemistry.
A big thank you to all former and current Williams’ group members for making
the lab a pleasant and often highly entertaining place to spend my days: Brian Conley,
Ph.D., Anna Dawsey, Ph.D., Vincent Li, Xinping Wu, Zhiyao Lu, Jeff Celaje, Xingyue
Zhang, Kathryn Hathaway, Christina Ratto, Ana Victoria Flores, Brock Malinoski,
Denver Guess, Christine Epperson, and Emine Boz, Ph.D. Thank you all for your support
and friendship in this endeavor.
Thanks to the excellent staff of LHI and USC Department of Chemistry: Carole
Phillips, Jessy May, David Hunter, Dr. Robert Anizfeld, Michele Dea, Marie de la Torre,
Allan Kershaw, and Katie McKissick.
iv
Thank you to my fantastic friends: Deirdre Connolly, Talia Gershon, Matt
McCabe, Matt Stern and especially John Duffner. Without you, I would not have made it
through the last five years with my sanity intact.
Finally, a heartfelt thank you to my amazing family: Mom, Dad, Brad, Geetha,
Grandpa Bob, Grandma Lila, Grandpa Glenn, Grandma Margie, and all of my aunts,
uncles, and cousins. Your love and encouragement has supported me on every step of this
journey and I could not have done it without you.
v
Table of Contents
Dedication ii
Acknowledgements iii
List of Tables ix
List of Figures x
List of Schemes xi
Table of Experimentals xiv
Abstract xix
Chapter 1. Cooperative Catalysis 1
1.1 Introduction 1
1.2 Dual-Site Catalysis 1
1.3 The Shvo System 6
1.4 Dimethyldipyridylborate as a Proposed Dual-Site Ligand 22
1.5 Overview 27
1.6 References 29
Chapter 2. Studies of the Shvo Catalyst 39
2.1 Introduction 39
2.2 Metal Catalyzed Alkylation of Amines 40
2.3 The Pictet-Spengler Reaction 43
2.4 Shvo-Catalyzed Alkylation of Amines 47
2.5 Formation of Heterocycles Using the Shvo Catalyst 49
vi
2.6 Investigations Toward Shvo-Catalyzed Pictet-Spengler Reactions 51
2.7 Conclusions 54
2.8 References 55
Chapter 3. Ruthenium Catalyzed Coupling of Alkynes and 1,3-Diketones 61
3.1 Introduction 61
3.2 Conia-Ene Reaction and Intermolecular Variants 61
3.3 Ruthenium Catalysts 66
3.4 Condition Optimization 68
3.5 Alkyne Scope 69
3.6 Diketone Scope 72
3.7 Conclusion 73
3.8 References 74
Chapter 4. Quantification of Ligand-Metal π-Bonding Using Group 9
Dimethyldipyridylborate Complexes 76
4.1 Introduction 76
4.2 Quantification Parameters for Ligand-Metal Bonding 77
4.3 Design of a System to Selectively Parameterize π-Bonding 83
4.4 Synthesis and Structure of Rhodium and Iridium Complexes 84
4.5 Kinetic Measurement of Metallocycle Ring Inversion 86
4.6 Computational Studies 90
4.7 Proposed Origin of the Barrier to Ring Flip 90
4.8 Comparison of Measured π-Bonding Parameters to Known Parameters 91
vii
4.9 Conclusions 95
4.10 References 96
Chapter 5. Synthesis and Structures of Nickel(II) Dimethyldipyridylborate
Complexes 101
5.1 Introduction 101
5.2 Selected Chemistry of Nickel Complexes 102
5.3 Fluxional Behavior of Square Planar Metal Complexes 105
5.4 Structure and Reactivity of Nickel Complexes with Anionic Bis-Nitrogen
Chelating Ligands 108
5.5 Synthesis and Structure of Nickel(II) Dimethyldipyridylborate Complexes 110
5.6 Lability of Dimethyldipyridylborate Complexes of Nickel(II) 114
5.7 Conclusions 116
5.8 References 118
Chapter 6. Experimental and Spectral Data 123
6.1 General Procedures 123
6.2 Chapter 2 experimental and spectral data 125
6.3 Chapter 3 experimental and spectral data 138
6.4 Chapter 4 experimental and spectral data 164
6.5 Chapter 5 experimental and spectral data 183
6.6 References 192
Appendix. X-ray Crystallographic Data 195
Acknowledgement 195
viii
[(py)
2
B(Me)
2
]Rh(CO)
2
(4.3a) 195
[(py)
2
B(Me)
2
]Rh(cod) (4.4a) 203
[(py)
2
B(Me)
2
]Ir(cod)
(4.4b) 210
[(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27) 219
[(py)
2
BMe
2
]Ni(acac) (5.29) 228
References 236
ix
List of Tables
Table 1.1. Scope of esterification of alcohols with diphenylacetylene and Ru
3
(CO)
12
. 10
Table 1.2. Hydrogenation reactions of Shvo’s catalyst (1.24). 13
Table 1.3. Scope of amine coupling. 17
Table 2.1. Alkylation of n-hexylamine with alcohols using Ru
3
CO
12
. 40
Table 2.2. Catalysts for the alkylation of aniline with benzyl alcohol. 41
Table 2.3. Formation of indole from 2-aminophenethyl alcohols. 42
Table 2.4. Optimization of the conditions for the alkylation of aniline with ethanol. 48
Table 2.5. Alkylation of 2.9 with alcohols. 49
Table 2.6. Heterocycle formation using 2.1. 50
Table 2.7. Cyclization of diols onto amines using 2.1. 51
Table 2.8. Reactivity of 2.1 in the presence of acid. 54
Table 3.1. Comparison of catalysts for a Conia-Ene cyclization. 62
Table 3.2. Examples of asymmetric Conia-Ene reactions. 64
Table 3.3. Comparison of catalysts for an intermolecular ene reaction. 65
Table 3.4. Catalyst Optimization. 67
Table 3.5. Condition Optimization. 68
Table 3.6. Alkyne Scope. 70
Table 3.7. Diketone Scope. 71
Table 4.1. Dihedral Angle and M-Me Distance for Complexes 4.3a and 4.4ab. 86
Table 4.2. Rates and corresponding errors measured for complexes 4.3-4.7. 88
Table 4.3. Values for ΔH
‡
(kcal/mol) and ΔS
‡
(eu) for 4.3-4.7. 89
Table 5.1. Rates and corresponding errors measured for the isomerization of 5.27. 115
x
List of Figures
Figure 1.1. Examples of bimetallic cooperative catalysts. 2
Figure 1.2. Bifunctional catalysts that utilize an N–H bond reported by Hiroi (1.10) and Zhang (1.11). 4
Figure 1.3. Iron-based transfer hydrogenation catalysts reported by Morris et al. 5
Figure 1.4. Examples of catalysts bearing ligands with Lewis-basic nitrogens. 6
Figure 1.5. ORTEP diagrams of the molecular structures of [Ph
4
(η
4
-C
4
CO)]Ru(CO)
3
(1.27, left) and
{[2,5-Ph
2
-3,4-Tol
2
(η
5
-C
4
CO)H]}Ru
2
(CO)
4
(μ-H) (1.24-Tol, right). 8
Figure 1.6. A DFT study of reversible formaldehyde reduction with a homolog of 1.24. 21
Figure 4.1. Correlation between TEP (cm
-1
) and LEP (V). 78
Figure 4.2. Correlation between CEP (cm
-1
) and TEP (cm
-1
). 79
Figure 4.3. Correlation between CEP (cm
-1
) and LEP (V). 79
Figure 4.4. Plot of LDP (kcal/mol)
12
versus LEP (V). 80
Figure 4.5. ORTEP diagrams for Complexes 4.3a and 4.4ab. 85
Figure 4.6. NMR spectra showing the boron methyl signals of 4.3a from -30 °C to +40 °C. 86
Figure 4.7. Calculated geometry of the ring flip transition state for 4.3a (left, 20° twist) and
[(py)
2
B(Me)
2
]Rh(PH
3
)
2
(right, 31° twist). 91
Figure 4.8. Correlation of
1
B
2
-
1
A
2
energy difference and ΔH
‡
(kcal/mol). 92
Figure 4.9. Correlation of AOM-calculated
e
π
L
(cm
-1
)
,
and ΔH
‡
(kcal/mol). 93
Figure 4.10. Plot of TEP (cm
-1
)
,,
versus ΔH
‡
(kcal/mol). 93
Figure 4.11. Plot of LEP (V)
,
versus ΔH
‡
(kcal/mol). 94
Figure 5.1. Dimethyldipyridylborate complexes of ruthenium. 101
Figure 5.2. Structures of nickel catalysts for ethylene polymerization (A), nitrene transfer (B) and
Kumada coupling (C) supported by anionic bis-nitrogen ligands. 109
Figure 5.3. ORTEP diagrams of 5.27 and 5.29. 113
Figure 5.4. Cross-eyed stereoview of 5.27. 114
Figure 5.5. Plot of ln[PPh
3
] versus ln[k
obs
] for the isomerization of 5.27. 116
xi
List of Schemes
Scheme 1.1. Mechanism of asymmetric hydrogenation of acetophenone with Noyori’s (S)-
TolBINAP/(S,S)-DPEN ruthenium catalyst (1.5) (Ar = 4-CH
3
C
6
H
4
). 4
Scheme 1.2. Examples of the ligand-based reactivity of some complexes reported by Milstein et al. 5
Scheme 1.3. Shvo’s catalyst (1.24): a heterodimer of oxidizing (1.25) and reducing (1.26) complexes. 7
Scheme 1.4. Aldehyde and aldimine hydroboration. 14
Scheme 1.5. Example of amine oxidation with Shvo’s catalyst 1.24. 14
Scheme 1.6. Oxidation of amines with terminal oxidants. 14
Scheme 1.7. Example of imine hydrogenation with Shvo’s catalyst 1.24. 15
Scheme 1.8. Direct coupling of an alcohol and an amine. 16
Scheme 1.9. Mechanism for N-alkylation of aryl amines with cyclic alkyl amines. 18
Scheme 1.10. Proposed catalytic cycles for alcohol oxidation. 20
Scheme 1.11. Attempt to oxidize 1-phenthylalcohol using borylated Shvo analog, 1.52. 22
Scheme 1.12. Synthesis of sodium dimethyldipyridylborate (1.55). 23
Scheme 1.13. Synthesis and ORTEP diagrams of zinc (1.56, left) and nickel (1.57, right) complexes
of dimethyldipyridylborate. 23
Scheme 1.14. Synthesis of dimethyldipyridylborate platinum complex 1.59. 24
Scheme 1.15. Reactivity of 1.59: catalyzed stoichiometric C–H activation (A) and methyl migration
from boron to platinum (B). 24
Scheme 1.16. Synthesis of dimethyldipyridylborate complexes of ruthenium. 25
Scheme 1.17. Formation of the agostic complex 1.68. 25
Scheme 1.18. Catalytic reactivity of 1.64: ammonia borane dehydrogenation (A), alcohol oxidation
(B), arene C–H activation (C), cyanation (D) and water oxidation (E). 27
Scheme 1.19. Borylation of terminal sp
3
carbons with HB(pin) catalyzed by 1.63. 27
Scheme 2.1. Synthesis of primary amines from alcohols and ammonia. 42
Scheme 2.2. Formation of N-phenylpyrrolidines from anilines and pyrrolidine. 43
xii
Scheme 2.3. Iridium-catalyzed cyclization of diols onto tryptamine. 43
Scheme 2.4. The first examples of the Pictet-Spengler reaction. 43
Scheme 2.5. Pictet-Spengler cyclization of tryptophan methyl ester hydrochloride. 44
Scheme 2.6. Biosynthetic significance of the enzymatic Pictet-Spengler reaction. STR1 =
strictosidine synthase (a Pictet-Spenglerase). 44
Scheme 2.7. Application of the Pictet-Spengler reaction in the synthesis of (–)-quinocarcin (A) and
(–)-yohimbine (B). 45
Scheme 2.8. Pictet-Spengler reactions utilizing aldehyde alternatives. 46
Scheme 2.9. Proposed 2.1 catalyzed tandem Pictet-Spengler-cyclization. 51
Scheme 2.10. Attempt to catalyze the tandem oxidation-Pictet-Spengler using 2.1. 52
Scheme 2.11. Acylation of tryptamine. 52
Scheme 2.12. Formation and attempted cyclization of the Pictet-Spengler imine intermediate 2.64. 52
Scheme 2.13. Acid-catalyzed cyclization of 2.65. 53
Scheme 3.1. Conia-Ene (top) and intermolecular-ene (bottom) reactions. 61
Scheme 3.2. Application of the Conia-Ene reaction to the synthesis of salinosporamide A (A) and
tetrahydrocarbazoles (B). 63
Scheme 3.3. Retro-Claisen decomposition of 3-substitued 1,3-diketones. 72
Scheme 3.4. Isomerization in cases where R
2
= Ph. 72
Scheme 3.5. Parent reaction on 1 g scale. 73
Scheme 4.1. Rotation of Cr-N bond in the model complex NCr(NH
2
)
2
(X) proceeds through a
transition state where nitrogen can π-donate into d
xz
/d
xy
orbitals along the nitrido vector. 80
Scheme 4.2. Interconversion of 4.1 and 4.2 does not involve a ring flip to give 4.1’. 83
Scheme 4.3. Synthesis of Complexes 4.3-4.7. 84
Scheme 4.4. Diagram of the filled-filled π-interaction that would occur in a planar transition state. 90
Scheme 5.1. Reduction of CO
2
with HBcat using Ni-POCOP 5.3.
a
102
Scheme 5.2. Insertion of CO
2
into Ni-E bonds (E = H, Me, or allyl). 103
Scheme 5.3. Addition of CO
2
to the PNP backbone of 5.6. 103
xiii
Scheme 5.4. [2 + 2 + 2] cycloaddition catalyzed by an NHC ligated Ni(0).
b
103
Scheme 5.5. Nickel-catalyzed carboxylation of benzyl chloride with CO
2
(A) and Nickel-catalyzed
hydroesterification of styrene with CO
2
(B). 104
Scheme 5.6. Reversible addition of H
2
across a nickel-borane unit. 104
Scheme 5.7. Potential mechanisms of isomerization in square planar complexes. 105
Scheme 5.8. Isomerization via Berry pseudorotation of a five-coordinate intermediate. 106
Scheme 5.9. Isomerization via pseudorotation of a complex bearing a ligand with multiple
coordination modes. 107
Scheme 5.10. Structures of Bp
2
Ni complexes: bis(bipyrazolylborate)nickel(II) (5.18) and bis(3-tert-
butylpyrazolylborate)nickel(II) (5.19). 108
Scheme 5.11. Reactivity (A) and fluxional behavior (B) of complexes of the type BpNi(PMe
3
)R. 110
Scheme 5.12. Synthesis of [(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27). 111
Scheme 5.13. Conversion of 5.27 to 5.28. 111
Scheme 5.14. Formation of 5.28 from nickel(II) acetate or nickel(II) acetylacetonate. 112
Scheme 5.15. Synthesis of [(py)
2
BMe
2
]Ni(acac) (5.29). 112
xiv
Table of Experimentals
125
126
127
128
129
130
131
132
133
134
xv
135
136
137
138
139
140
141
142
143
xvi
145
147
149
151
153
154
155
162
xvii
163
164
167
170
172
174
176
179
181
xviii
183
186
187
190
xix
Abstract
Research presented in this work describes investigations into the synthesis, structure, and
reactivity of cooperative catalysts. Cooperative catalysis, the concept of actively involving
ligands in catalytic transformations, is used extensively in enzymatic systems and has been shown
to enable organometallic catalysts to realize improved enantioselectivity, chemoselectivity, or
activation of otherwise unreactive bonds. Two types of cooperative catalysts are investigated in
this work: non-innocent ligands and ligand-based directing groups. Initial investigations detailed
in this work revolve around a catalyst of the first type: Shvo’s catalyst ({[Ph
4
( η
5
-
C
4
CO)]
2
H]}Ru
2
(CO)
4
( μ-H)) which is known for containing a non-innocent cyclopentadienone
ligand. Shvo’s catalyst is shown to be a competent catalyst for alkylation of amines with alcohols
and amines and is superior to other reported catalysts in some cases. Subsequent studies
investigated the potential of Shvo’s catalyst to mediate cascade reactions, such as Pictet-Spengler
type cyclizations without the need for a starting aldehyde.
Later explorations were directed towards the development of a catalyst with a pendant
Lewis acid, specifically boron, which could be used to direct C–H activation of substrates.
Studies of the reactivity of a proposed cooperative catalyst, {[(py)
2
BMe(μ-OH)]Ru(MeCN)
3
}
+
-
OTf (py = 2-pyridyl, cym = η
6
-p-cymene), led to the discovery that ruthenium(III) chloride
hydrate is a convenient catalyst for the addition of active methylene compounds to aryl alkynes.
These reactions are inexpensive, operationally simple, air and water tolerant, and high yielding in
cases.
Further investigations towards the synthesis of a cooperative catalyst with a Lewis acid
directing group focused on the synthesis of rhodium(I) and iridium(I) complexes of type
[(py)
2
BMe
2
]ML
2
(L
2
= (tBuNC)
2
, (CO)
2
, (C
2
H
4
)
2
, cyclooctadiene, 1,2-
bis(diphenylphosphino)ethane). These complexes were found to undergo a ring inversion of the
xx
six-membered metallocycle. Inversion recovery kinetic analysis was used to measure the rate and
enthalpic barrier (ΔH
‡
) of this transformation across the series. Whereas the ring flip is proposed
to proceed through a transition state in which a filled-filled π-interaction between the metal and
the pyridines becomes available, this ring flip barrier is used to parameterize the π-acceptor
ability of the ancillary ligands. The observed values were found not to correlate to either Tolman
or Lever parameters, indicating that the ring flip barrier selectively reports the strength of a
transient π-bond, while the other known metrics report combined π- and σ- effects.
Finally, the synthesis of cooperative catalysts based on first-row metals was also
explored. [(py)
2
BMe
2
]Ni(PPh
3
)Cl and [(py)
2
BMe
2
]Ni(acac) (acac = acetylacetonate) were
synthesized and structurally characterized. [(py)
2
BMe
2
]Ni(PPh
3
)Cl is observed to exhibit both
inter- and intramolecular substitutional lability. Early investigations of the kinetics of this
isomerization reveal that the mechanism is not straightforward.
1
Chapter 1. Cooperative Catalysis
1.1 Introduction
1
Activation of chemical bonds is a key aspect of transition metal catalyzed
reactions.
2
In conventional homogenous metal catalyzed reactions, activation generally
occurs at the metal center, with the ligands serving only to tailor the steric and electronic
properties of the metal. However, in recent years a new class of catalysts which activate
bonds through cooperation of the metal center and the ligands has gained significant
attention. This type of cooperative catalysis is used extensively by nature in enzymatic
systems
3
and has evolved as a successful principle for the design of homogeneous
transition metal catalysts.
4,5,6
Through the use of a bifunctional mechanism, many of these
catalysts have been able to realize improved enantioselectivity, chemoselectivity, or in
some cases, activation of otherwise unreactive bonds.
This chapter summarizes some of the significant developments in dual-site,
cooperative catalysis, with particular emphasis on the Shvo catalyst.
1
Also described is
the synthesis and early application of a proposed ligand for dual-site catalysis,
dimethyldipyridylborate.
7
1.2 Dual-Site Catalysis
Dual-site, cooperative catalysis involves two atoms in a single catalyst that
cooperate to effect molecular transformation of a target molecule.
8
Dual-site catalysts
primarily include bimetallic and metal-heteroatom systems. Bimetallic systems have been
applied to a number of synthetic challenges, from cooperative bond activations to
asymmetric transformations in complex molecule synthesis.
5
The metal-heteroatom
strategy is most notably exemplified by those systems reported by Noyori
6
and Shvo,
9
2
where a ligand-based acidic proton directs selectivity of a ruthenium-based catalyst,
though the contributions by Morris
10
and Milstein
11
are also significant.
1.2.1 Bimetallic Cooperative Catalysis
Multiple groups have reported bimetallic cooperative catalysts for the asymmetric
ring opening of cyclohexene oxide. This reaction has been a target for cooperative
catalysis strategies based on the success of enzymatic catalysts for this transformation. As
enzymes often possess multiple active sites, it is often proposed that bifunctional
catalysts may be more adept at duplicating enzyme-like catalysis.
12
Jacobsen et al. report
dimeric chromium salen complexes (1.1, Figure 1.1) which catalyze this transformation
with significantly lower catalyst loading as compared to a monomeric species.
5d
Nugent
and Finn report a zirconium-triisopropanolamine which exists in equilibrium between
Figure 1.1. Examples of bimetallic cooperative catalysts.
3
dimeric and trimeric species, with the dimer showing significantly improved catalytic
activity.
5c
Shibasaki and Kumagai have reported numerous examples of lanthanide metals
participating in cooperative catalysis with other metals, including lithium and silver (1.2,
Figure 1.1).
5a,13
Marks et al. demonstrated a dinickel complex (1.3, Figure 1.1) which
catalyzes the formation of highly branched polyethylenes as well as ethylene-norbornene
copolymerizations with increased activity relative to monometallic species.
5b
More
recently, Thomas reported extensive studies on metal-metal multiple bonds in
heterometallic complexes containing early and late transition metals (1.4, Figure 1.1),
some of which have been shown to catalyze Kumada couplings and to activate H
2
.
5f
1.2.2 Metal-Ligand Heteroatom Cooperative Catalysis
There are two primary types of metal-heteroatom cooperative ligands in the
literature: ligands with acidic protons and ligands with Lewis basic atoms. The first type
was pioneered by Noyori and Shvo and is often regarded as the parent “ligand-metal
bifunctional” system. In general, these catalysts feature a hydrogen bond-directed
reduction of a carbonyl group through a transition state which can also be used in the
oxidative direction. The Shvo-type systems are based on a cyclopentadienone ligand and
are discussed in detail in section 1.3.
The Noyori catalytic motif involves cooperation between ruthenium and a ligand
N–H bond and has been widely adapted by a number of groups.
6,14
The mechanism of
ketone reduction with Noyori complex 1.5 is representative of the hydrogenation
mechanism available to the (DPEN)Ru scaffold (Scheme 1.1, DPEN = 1,2-tolyl-1,2-
diaminoethane).
15
This mechanism begins with dissociation of borohydride from the
catalyst precursor to give the active species, 1.6. The stereochemistry of the product is
then determined in the reaction of acetophenone and 1.8 to give (R)-1-phenylethanol and
4
1.9. The stereochemical control is imparted as a result of the concerted metal-ligand
bifunctional transition state.
16
Other pathways are possible under different reaction
conditions and careful studies have been published in this area.
6
Other examples of
bifunctional catalysts which utilize a ligand N–H bond include those by Hiroi (1.10)
17
and Zhang (1.11).
18
While the majority of the transfer hydrogenation catalysts that utilize
a bifunctional scaffold are ruthenium based, Morris et al. have expanded the methodology
Figure 1.2. Bifunctional catalysts that utilize an N–H bond reported by Hiroi (1.10) and
Zhang (1.11).
Scheme 1.1. Mechanism of asymmetric hydrogenation of acetophenone with Noyori’s
(S)-TolBINAP/(S,S)-DPEN ruthenium catalyst (1.5) (Ar = 4-CH
3
C
6
H
4
).
5
to some iron catalysts (Figure 1.3).
10a
Another bifunctional scaffold which is gaining significant attention is based on
the pincer ligands developed by Milstein et al. While these catalysts do not technically
utilize a bifunctional metal-heteroatom strategy, they make use of acidic ligand protons
bound to carbon.
11,19
Milstein ligands include PNN, PCP, PNP, and PCN pincer
ligands
all of which contain an acidic proton in the backbone which can be deprotonated to give a
dearomatized ligand (Scheme 1.2). The drive toward rearomatization aids these
Figure 1.3. Iron-based transfer hydrogenation catalysts reported by Morris et al.
Scheme 1.2. Examples of the ligand-based reactivity of some complexes reported by
Milstein et al.
6
complexes in activating a number of different substrates. Activation of H
2
, alcohols,
amines (including ammonia), CO
2
, and others have all been achieved with Milstein-type
ligands (Scheme 1.2).
The second class of metal-ligand heteroatom bifunctional catalysis focuses on the
incorporation of Lewis basic moieties into the ligand scaffold. Most examples utilize
ligand-bound nitrogen atoms to coordinate or activate substrates.
20
Dixon et al. have
created a cinchona-derived ligand which contains a Lewis basic nitrogen which, when
bound to copper, catalyzes the Conia-Ene reaction (see Chapter 3).
20a
Lin et al. also
utilize a cinchona alkaloid (quinine) based ligand. They report a derivatized salen ligand
which was used to generate a cobalt salen with a pendant Lewis base (1.21).
20b
This
complex catalyzes the asymmetric Wynberg reaction. In addition to this case, salen
ligands are a popular target for derivatization with Lewis basic functionality; two other
examples have been reported by Liu (1.22)
20c
and Kozlowski (1.23).
20d
1.3 The Shvo System
Shvo’s catalyst
9
is an air- and water-stable cyclopentadienone-ligated ruthenium
complex, {[Ph
4
( η
5
-C
4
CO)]
2
H]}Ru
2
(CO)
4
( μ-H) (1.24, Scheme 1.3). It is a crystalline solid
that is commercially available from several sources and is a generally useful catalyst for
Figure 1.4. Examples of catalysts bearing ligands with Lewis-basic nitrogens.
7
transfer hydrogenation of alkenes, alkynes, carbonyl groups, and imines using alcohols,
amines, dihydrogen, and several dihydrogen surrogates.
1
Its discoverer, Youval Shvo,
and colleagues introduced this versatile ruthenium catalyst which utilizes noninnocent
21
cyclopentadienone ligands to stabilize the metal in low oxidation states. The mechanism
of hydrogenation and dehydrogenation reactions catalyzed by Shvo’s catalyst involves
simultaneous transfer of separate hydrogen atoms from (or to) the metal center and the
ligand. Thus, Shvo’s catalyst is an example of a ligand-metal bifunctional catalyst
wherein redox activity is distributed between the metal center and a cyclopentadienone
ligand. This complex and its analogs have been studied extensively for reactions such as
hydrogenation of aldehydes, ketones, alkynes, and alkenes, transfer hydrogenation,
disproportionation of aldehydes to esters, isomerization of allylic alcohols, dynamic
kinetic resolution (DKR), amine-amine coupling, and hydroboration reactions.
Complex 1.24 is a dimeric precatalyst that forms monomeric oxidizing unsaturated
dicarbonyl 1.25 and reducing ruthenium hydride 1.26 upon dissociation in solution
(Scheme 1.3). The concentrations of these active forms are governed by equilibrium
effects; compounds 1.25 and 1.26 are interconverted through the gain or loss of “H
2
”
Scheme 1.3. Shvo’s catalyst (1.24): a heterodimer of oxidizing (1.25) and reducing
(1.26) complexes.
a
a
1.25 and 1.26 equilibrate in the presence of a hydrogen acceptor (A) or donor (AH
2
).
☐ = vacant coordination site.
8
from donors and acceptors as shown. Although there is no crystal structure for either 1.25
or 1.26, solution NMR data, mechanistic probes, and trapping experiments have been
utilized to establish their structures. The structure of 1.26 is well characterized by NMR,
while the structure of 1.25 is proposed to be a coordinatively unsaturated intermediate,
based on the characterization of trapped derivatives. Coordinatively unsaturated complex
1.25 rapidly (and usually reversibly) adds a dative ligand to its open site.
Notably, both bridging hydrogen atoms are associated with the same monomer
upon dissociation. Thus, upon dissociation one ruthenium is in the 2+ oxidation state
(1.26) while the other is formally in the zero oxidation state (1.25). Ironically, it is the
ruthenium(0) center, the formally more reduced monomeric form, that oxidizes alcohols
by the concerted abstraction of H
+
and H
-
. The formally more oxidized monomeric form
possessing the two hydrogen atoms is the reducing complement. It is a conundrum
created by the conversion of a formally neutral cyclopentadienone ligand to a formally
anionic hydroxycyclopentadienone ligand by addition of a formal cation, H
+
. It might be
more reasonable to think of these species as two ruthenium(II) species, with the oxidizing
1.27 1.24-Tol
Figure 1.5. ORTEP diagrams of the molecular structures of [Ph
4
( η
4
-C
4
CO)]Ru(CO)
3
(1.27, left) and {[2,5-Ph
2
-3,4-Tol
2
( η
5
-C
4
CO)H]}Ru
2
(CO)
4
(μ-H) (1.24-Tol, right).
Aromatic groups are omitted for clarity.
9
form bearing a dianionic η
5
-alkoxycyclopentadiene. However, such a view is inconsistent
with the X-ray structure of [Ph
4
( η
4
-C
4
CO)]Ru(CO)
3
(1.27, Figure 1.5). In this case, the
cyclopentadienone ligand is puckered so that the Ru-C distance to C1 (2.509 Å) is larger
than C2 (2.217 Å) or C5 (2.240 Å) as seen in Figure 1.5. This structure can be understood
as an η
4
-diene with a pendant carbonyl that has little (if any) interaction with the metal.
By contrast, the Shvo homologue 1.24-Tol (bearing p-tolyl groups) has similar Ru-C
distances to C1, C2, and C5 (2.399, 2.269, and 2.250 Å, respectively).
Mechanistic studies by Casey, Bäckvall, and others have confirmed that the
catalyst transfers dihydrogen through a hydride on the transition metal (Ru-H in 1.26) and
a proton on the hydroxy cyclopentadienyl ligand (O-H in 1.26) and is thereby a ligand-
metal bifunctional catalyst.
1.3.1 Discovery of Shvo’s Catalyst
The discovery of 1.24 and its catalytic reactivity stemmed from the observation
that triruthenium dodecacarbonyl, Ru
3
(CO)
12
, catalyzes the transfer dehydrogenation of
alcohols in the presence of hydrogen acceptors such as diphenylacetylene, alkenes, and
ketones. Aldehyde products from these reactions undergo subsequent Tishchenko-style
oxidative coupling to the corresponding esters (vide infra, Table 1.1).
22
In these studies,
Shvo found that diphenylacetylene greatly enhanced the activity of the parent ruthenium
carbonyl, allowing for both increased rate and turnover number relative to a reaction in
which diphenylacetylene is absent. Also, reactions run in the presence of
diphenylacetylene maintain their homogeneity while some of those that are run with other
acceptors precipitate metallic material and lose reactivity. These observations were
initially unexplained, but a series of insightful experiments indicated that a
cyclopentadienone-ligated ruthenium complex was involved. Specifically, when
10
cyclohexanone was used alone as the hydrogen acceptor, a ruthenium mirror formed on
the side of the reactors, apparently due to loss of carbon monoxide from ruthenium and
aggregation of ruthenium metal, resulting in only 25% conversion of alcohol.
22b
When a
catalytic amount of diphenylacetylene is present, the solution maintains its yellow color
and homogeneity throughout the reaction. Further, even when a stoichiometric amount of
diphenylacetylene is present in bulk ketone, ketone is the predominant H
2
acceptor (as
opposed to the alkyne). These observations imply that diphenylacetylene forms a
derivative of Ru
3
(CO)
12
that remains soluble under the reaction conditions. At the time it
was not clear why added phosphines did not have the same stabilizing effect on the
system.
Table 1.1. Scope of esterification of alcohols with diphenylacetylene and Ru
3
(CO)
12
.
Entry Alcohol Time (h) Conversion (%) Ester (%) Aldehyde (%)
1 Propanol 4 93 91 2
2 Octanol 4 98 97 1
3 Isobutanol 4 95 94 1
4 Neopentanol 4 76 73 3
5 2-Ethoxyethanol 4 56 56 0
6 Benzyl alcohol 4 96 93 3
7 Benzyl alcohol
a
9 83 71 2
8 4-Chlorobenzyl alcohol 4 63 53 10
9 4-Methylbenzyl alcohol 4 99 86 13
10 4-Methoxybenzyl alcohol
b
4 75 52 19
11 1,4-Butanediol
c
6 95 95 -
a
Acetone (22.5 mmol) and diphenylacetylene (0.75 mmol) were used as acceptors. A small quantity
of isopropyl benzoate was detected.
b
Bis-(4-methoxybenzyl) ether was detected.
c
The product is γ-
butyrolactone. Adapted from ref. 22b.
11
It was shown in 1967 that refluxing Ru
3
(CO)
12
in aromatic solvents in the
presence of an alkyne results in the synthesis of cyclopentadienone-ligated transition
metal complexes via a [2 + 2 + 1] cycloaddition among two equivalents of
diphenylacetylene and one metal-bound CO.
23
Along these lines, [Ph
4
( η
4
-C
4
CO)]Ru(CO)
3
(1.27), {[Ph
4
( η
5
-C
4
CO)]
2
H}Ru
2
(CO)
4
(μ-H) (1.24),
24
and free tetracyclone were present in
Shvo’s reaction solutions. Shvo isolated 1.24 and 1.27, used them directly in catalysis,
22c,
25
and observed that they both have higher activity than a catalyst generated in situ.
1.3.2 Synthetic Applications of 1.24
Many applications of Shvo’s catalyst have been reported since its discovery in the
mid-1980s, and some of these were reviewed as recently as 2005,
26
so these topics are
given only cursory treatment in this presentation. Since then, a number of synthetic
applications have appeared, most notably involving the use of alcohols and amines
directly as alkylating agents via an oxidation-condensation-reduction sequence. These
recent advances are well reviewed in the Encyclopedia of Reagents for Organic
Synthesis.
27
Since those publications, significant advancements have appeared, most
notably amine coupling and hydroboration. This section will give special emphasis to
historical development and recent contributions to the area.
1.3.2.1 Oxidative Coupling of Primary Alcohols to Esters
Shvo’s catalyst, generated in situ from Ru
3
(CO)
12
and diphenylacetylene,
catalyzes the transfer dehydrogenation of alcohols in the presence of hydrogen acceptors,
such as diphenylacetylene, alkenes, and ketones.
22b
Aldehyde products from these
reactions then undergo a Tishchenko-type disproportionation
28
to give the corresponding
esters.
22a,c
When diphenylacetylene is employed as the hydrogen acceptor, the reaction is
quite broad and general, as seen in Table 1.1.
12
The next important advance with this motif was acceptorless dehydrogenation of
alcohols using 1.24 and 1.27 as catalysts with direct release of H
2
from open reactors.
23c
As above, these reactions oxidatively couple simple alcohols to form esters with the
intermediacy of an aldehyde. This was quickly extended to the reverse reaction,
hydrogenation of aldehydes, ketones, alkenes, and alkynes in the presence of pressurized
hydrogen gas.
29
1.3.2.2 Oxidation of Alcohols to Form Ketones
Shvo’s catalyst is useful for the oxidation of secondary alcohols to ketones;
examples of these reactions are reviewed elsewhere.
26
Along these lines, several effective
stoichiometric oxidants have been reported, including alkenes, alkynes, carbonyl
groups,
30
and even chloroform.
31
Notably, an intramolecular acceptor can be used; this
concept enables isomerization of allylic alcohols (and other alkene-alcohols) to the
corresponding ketones.
32
Aerobic oxidation is also possible through the use of quinone
and cobalt cofactors.
33,34
1.3.2.3 Hydrogenation of Ketones and Alkenes
Shvo used 1.24 directly in hydrogenation of alkenes, alkynes, and carbonyl
compounds (Table 1.2).
22c,35,36
Although a catalyst generated in situ from a mixture of
Ru
3
(CO)
12
and diphenylacetylene was effective in reactions of this type, 1.24 and 1.27
afforded higher activity than the in situ-generated catalyst. Remarkably, these reactions
can be conducted on large scales with reasonable catalyst loadings and minimal (if any)
solvent. Transfer hydrogenation with formic acid as the reducing agent is also known.
37
13
1.3.2.4
Aldehyde, Ketone, and Imine Hydroboration
Clark and Casey have recently introduced conditions for hydroboration of
aldehydes and aldimines with Shvo derivative 1.28-Tol (Scheme 1.4).
38
In these reactions
the H–B(pin) bond is added to a carbonyl (or imine) system by a mechanism wherein
boron apparently takes on the role played by a proton in the reduction reactions above.
Near quantitative hydroboration of benzaldehyde is observed by NMR, and high-yielding
preparative scale reduction reactions can be realized by hydrolyzing the resulting boronic
ester (or amide) upon completion of the catalysis. Importantly, crossover experiments
indicate that this reaction is not reversible. These data are significant to the mechanistic
story of the Shvo system because they provide the first example of the use of a Lewis
acid in the place of H
+
in the Shvo transition state. Moreover, they show that although
this works well for reduction reactions, it is not effective in the complementary oxidation
process; we have similarly observed the latter.
Table 1.2. Hydrogenation reactions of Shvo’s catalyst (1.24).
Entry Starting Material (mmol) Cat (μmol, mol%) Solvent (mL) Time (min) Conv (%) (TON)
1 1-Octene (17.2) 10, 0.06 bulk 10 100 (1720)
2 Cyclohexene (49.4) 25, 0.05 bulk 15 100 (1976)
3 Styrene (52.4) 19, 0.04 bulk 720 67 (2760)
4 1-Hexyne (10) 50, 0.05 toluene (10) 35 100 (200)
5 Diphenylacetylene (10) 50, 0.05 toluene (10) 135 100 (326)
6 Diethyl ketone (95) 47, 0.05 bulk 45 97 (1940)
7 Cyclohexanone (100)
a
50, 0.005 bulk 300 98 (1960)
8 Acetophenone (50) 25, 0.005 bulk 255 94 (1880)
9 Benzaldehyde (10) 50, 0.05 toluene (10) 10 81 (162)
a
At 100 °C. Adapted from ref. 22c.
14
1.3.2.5 Oxidation of Amines to Imines
Amine oxidation with Shvo’s catalyst was first reported by Bäckvall’s group in
2002 using either MnO
2
or 2,6-dimethoxybenzoquinone (1.39) as the oxidant.
39
Mild
conditions were used to afford very selective, high yielding conversion of aromatic
amines to the corresponding imines (Scheme 1.5). In 2005, Bäckvall expanded this
system to biomimetic aerobic oxidation by using a cobalt co-catalyst 1.42 to re-oxidize
the quinone (Scheme 1.6).
40
Scheme 1.4. Aldehyde and aldimine hydroboration.
Scheme 1.6. Oxidation of amines with terminal oxidants.
Scheme 1.5. Example of amine oxidation with Shvo’s catalyst 1.24.
39
15
1.3.2.6 Imine Hydrogenation
Reduction of imines by Shvo’s catalyst was first reported for comparison of the
rate of reduction; an imine is reduced approximately 26 times faster than the
corresponding aldehyde in an analogous case (compare benzaldehyde versus
benzaldehyde-N-methyl imine).
41
Shortly after the original report, a preparative transfer
hydrogenation of imines was reported with 2-propanol acting as the hydrogen donor in an
aromatic solvent (Scheme 1.7).
42
Several aromatic imines were reduced in high yields.
1.3.2.7 Alkylation of Amines with Alcohols
While Shvo’s catalyst is not known to be highly efficient for the alkylation of
amines using alcohols as alkyl donors, other catalysts have been used successfully.
Scheme 1.8 illustrates early examples of this reaction.
43,44
Further examples involving
both ruthenium and iridium
catalysts have been reported subsequently. The ruthenium
catalysts include [(PPh
3
)
3
RuCl
2
],
45
[Ru(cod)(cot)],
45
[Ru(p-cymene)Cl
2
]
2
plus dppf,
46,47
[(PPh
3
)
2
Ru(CH
3
CN)
3
Cl][BPh
4
],
48
and Ru
3
(CO)
12
with various phosphines,
49,50
while the
iridium catalysts are [Cp*IrCl
2
]
2
51
and [Ir(COD)Cl]
2
plus dppf
52
or Py
2
NP(i-Pr)
2
.
53
The
reaction can be very selective for mono-alkylation; in fact Milstein has prepared primary
amines from ammonia.
54
The oxidative process wherein an amine and alcohol are
coupled to give the corresponding amide has also been reported.
55,56
Scheme 1.7. Example of imine hydrogenation with Shvo’s catalyst 1.24.
42
16
1.3.2.8 Alkylation of Amines with Amines
Beller’s group has recently extended the utility of 1.24 to include direct coupling
of anilines and alkyl amines in high yield and selectivity. While investigating the reaction
above (Scheme 1.8), they showed 1.24 to be only moderately effective for the alcohol-
amine coupling, but observed an amine homocoupling side product, presumably resulting
from nucleophilic attack by free amine on an intermediate imine.
50
Thus, they developed
1.24 as a catalyst for the formation of N-substituted anilines using aliphatic amines as
alkylating agents (Table 1.3).
57
Initial studies showed high yields above 140 °C, which
were achieved with a variety of anilines and amino pyridines. Only 4-nitroaniline and
2,6-substituted anilines produced low yields. Further studies showed that in addition to
primary amines, secondary, and tertiary amines are effective alkylating agents.
58
In fact, a
mixture of mono-, di-, and tri- substituted amines was used selectively to produce mono-
alkylated anilines. In addition to anilines, amines bearing tertiary alkyl groups can also be
coupled with primary, secondary, and tertiary amines (Table 1.3, entry 8).
59
These
conditions can also be used with cyclic alkyl amines as the alkylating agents (Table 1.3,
entry 9).
60
This apparently occurs via aminal formation and ring opening, followed by
dehydrogenation of the primary amine and ring closing as summarized in Scheme 1.9.
Scheme 1.8. Direct coupling of an alcohol and an amine.
17
The mechanism of these coupling reactions was deemed a “hydrogen borrowing
mechanism”
57
because an added hydrogen source or hydrogen transfer reagent is not
needed. In these reactions, the “borrowed” hydrogen is stored as the reduced form of the
catalyst until it is used later in the reaction. A sample mechanistic proposal is outlined in
Scheme 1.9 for a case of net arylation of pyrrolidine. Simply, pyrrolidine is
Table 1.3. Scope of amine coupling.
Entry Amine Alkyl Donor Product Yield (%)
b
1
98
2
96
4
83
5
94
6
99
7
93
8
(3 equiv)
75
(DME,
170
o
C)
9
(neat)
68
a
Adapted from references 57, 59 and 60.
b
Yields of isolated product are based on alkyl amine.
18
dehydrogenated to the dihydropyrrole and the resulting H
2
is “borrowed” and stored as
the reduced form of the catalyst until it is used later in the mechanism. The resulting
imine then undergoes nucleophilic attack and subsequent ammonia elimination to form a
new imine, which is hydrogenated by hydride 1.26.
The released ammonia forms a stable adduct with coordinatively unsaturated
intermediate 1.25 and can be displaced by equilibria with coordinating alkyl and aryl
amines.
61
The ammonia complex was isolated and characterized and can be used as a
catalyst precursor. It is only slightly soluble in organic solvents in the absence of other
coordinating amines, so it precipitates from solution when the reaction is complete. This
is a potential means of catalyst recycling.
1.3.3 Mechanism of Oxidation and Reduction
As prolific as the recent developments in applications of this catalyst are
contributions to understanding its reactivity mechanisms and designing analogous
catalytic systems based on related ligand-metal bifunctional catalysis motifs. The
mechanism of hydrogenation and dehydrogenation by Shvo’s catalyst has garnered
intense interest. The mechanism of these reactions has unfolded in many papers. Some of
the mechanistic studies were summarized in a review discussing metal-catalyzed transfer
Scheme 1.9. Mechanism for N-alkylation of aryl amines with cyclic alkyl amines.
19
hydrogenation in 2006.
62
Remarkably, detailed kinetics, isotopic labeling, and structural
characterizations have confirmed many original proposals about the catalytic cycle. This
body of work has shown the Shvo mechanism to be an example of a ligand-metal
bifunctional catalyst that has similarities to Noyori’s asymmetric transfer hydrogenation
catalysts.
63,64
Two plausible mechanisms shown in Scheme 1.10 can explain the observed
reactivity of Shvo’s catalyst. Bäckvall
65
and Shvo
22c
both argued that the mechanism
could involve a pre-equilibrium coordination of alcohol to the metal center. Bäckvall
proposed that this was followed by ( η
4
- η
3
) ring slippage and concurrent β-hydride
elimination and proton transfer, an inner-sphere mechanism as outlined in Scheme 1.10A.
Casey proposed that the transfer could occur without pre-coordination of the alcohol and
no ring slippage (Scheme 1.10B); this represents a rare example of transition metal-
catalyzed process that does not require pre-coordination to activate the substrate.
41,66
Casey
41
and Bäckvall
67,68
have both provided compelling arguments for concerted
hydrogen transfer in reactions interconverting alcohol and carbonyl compounds,
predominantly based on measured kinetic isotope effects.
41,67
A 2007 DFT study provides
further data discriminating the outer sphere and ring slippage mechanisms.
69,70
In this
systematic calculation of possible coordination and slippage events, the pre-coordination,
inner-sphere mechanism (Scheme 1.10A) was much higher in energy than the concerted
outer-sphere mechanism (Scheme 1.10B), as shown by the comparison in Figure 1.6. The
disparity in activation barriers for the two paths is large enough to strongly support the
concerted, outer-sphere path. A number of additional mechanistic experiments, which
largely support the conclusions here, are summarized in reference 1.
20
Much like the corresponding reactions of carbonyl compounds and alcohols, the
mechanism of reduction of imines and oxidation of amines has inspired debate. Inner-
sphere
71
and outer-sphere
72
mechanisms analogous to those in Scheme 1.10 have been
proposed. A number of reports have been published in support of each proposal. These
reports include studies of KIEs,
72,73,74
amine coordination and exchange
Scheme 1.10. Proposed catalytic cycles for alcohol oxidation.
21
experiments,
71,72,75,76
and computational studies.
75,77,78
Ultimately, these data indicate that
the rate-determining step is concerted hydrogen transfer in some cases but not others.
Taken together, the mechanistic details reviewed in reference 1 and outlined
above provide a clear picture of a single, rate-determining transition state through which
both the oxidation and reduction reactions pass in most cases. It differs in character from
a traditional aluminum alkoxide-catalyzed Meerwein-Ponndorf-Verley reduction (or
Oppenauer oxidation) in that there is a persistent metal hydride intermediate. Moreover,
the rates of transfer hydrogenation and dehydrogenation with 1.24 are generally
acceptable for the oxidation/reduction of a wide range of substrates. The systems can be
optimized for a desired outcome by substrate concentration, i.e. oxidizing alcohols in
acetone drives the reaction to completion. In addition, the mechanism is of fundamental
Figure 1.6. A DFT study of reversible formaldehyde reduction with a homolog of 1.24.
DFT-calculated activation parameters for hydrogen transfer to ketones using Shvo’s
catalyst is consistent with a concerted, outer-sphere mechanism. See ref. 69 for proper
geometries and other calculated pathways.
22
interest for studies of systems involving oxidative coupling of alcohols or amines and
nucleophilic substrates. Importantly, the ability of the metal hydride in 1.26 to reduce
unsaturated substrates such as alkynes, alkenes, and imines makes alcohols a practical
reducing agent in several different cascade reactions.
1.4 Dimethyldipyridylborate as a Proposed Dual-Site Ligand
Based on the success of the Shvo system, we desired to develop a more general
dual-site catalyst for directed hydride abstraction. To expand the reactivity from protic
oxidation substrates to ethers and other, less reactive substrates, we proposed to replace
the oxygen “directing group” with a boron Lewis acid. Our initial attempts focused on
functionalizing Shvo’s with a boronic acid, analogous to the hydroboration catalyst
synthesized by Clark et al. (Scheme 1.4, active catalyst 1.52-Tol).
38
1.52 proved to be
ineffective for the oxidation of phenethyl alcohol in the presence of benzoquinone.
8
We
concluded that the boron-oxygen bond in 1.52 was insufficiently robust under the
oxidative, protic conditions. A ligand containing a boron-carbon bond was proposed to be
more likely to hold up under these conditions. This led us to the explore
dimethyldipyridylborate as a ligand for dual-site directed catalysis.
Scheme 1.11. Attempt to oxidize 1-phenthylalcohol using borylated Shvo analog, 1.52.
23
1.4.1 Synthesis and Initial Complexes
Dimethyldipyridylborate was initially synthesized in 1996 as the proton salt 1.54
by Hodgkins and Powell (Scheme 1.12).
7
Both bis[dimethylbis(2-pyridyl)borato-
N,N’]zinc(II) (1.56) and bis[dimethylbis(2-pyridyl)borato- N,N’]nickel(II) (1.57) were
synthesized and studied by NMR and X-ray crystallography (Scheme 1.13). In both
complexes, the dimethyldipyridylborate ligand was observed to adopt a boat confirmation
with one of the boron methyls positioned above the metal. This conformation suggested
that if the methyl group could be removed, the resulting boron Lewis acid site would be
perfectly positioned to coordinatively direct activation by the metal.
Scheme 1.12. Synthesis of sodium dimethyldipyridylborate (1.55).
Scheme 1.13. Synthesis and ORTEP diagrams of zinc (1.56, left) and nickel (1.57, right)
complexes of dimethyldipyridylborate.
24
1.4.2 Platinum Complexes
The desired stability of the boron-carbon bonds has been confirmed by
Vedernikov et al.
79
The synthesis of dimethyldipyridylborate platinum complexes was
accomplished via generation of the sodium salt 1.55 from 1.54 (Scheme 1.12) and
reaction of 1.55 with Pt
2
Me
4
(μ-SMe
2
)
2
(Scheme 1.14). Reactions of these complexes have
shown that the ligand pyridine-boron bonds are stable to dioxygen and at elevated
temperatures. In addition to demonstrating stability, the dimethyldipyridylborate-ligated
platinum species were found to be active for the facile stoichiometric activation of arene
and alkane C–H bonds (Scheme 1.15A),
79a
suggesting that the anionic ligand might
Scheme 1.14. Synthesis of dimethyldipyridylborate platinum complex 1.59.
Scheme 1.15. Reactivity of 1.59: catalyzed stoichiometric C–H activation (A) and methyl
migration from boron to platinum (B).
25
activate a metal in addition to bearing a Lewis acid. Further studies of the platinum
complexes demonstrated methyl transfer from boron to platinum and the formation of a
bridging boron-oxygen bond Scheme 1.15B. This facile activation of the boron-methyl
bond indicated that removal of methyl to generate an open Lewis acid site is possible.
1.4.3 Ruthenium Complexes
Our group has synthesized a series of catalytically active ruthenium complexes of
1.55, as shown in Scheme 1.16.
80
The initial ligation step is a straightforward salt
metathesis to generate 1.63. Treatment of 1.63 with TlOTf in acetonitrile generates 1.67
which exhibits a unique agostic bond between a methyl group and ruthenium (Scheme
1.17). Exposing the agostic complex 1.68 to trace water results in the loss of methane and
formation of the bridging complex 1.64. Complex 1.64 can be further converted to 1.65
and 1.66 by treatment with an appropriate carboxylic anhydride.
Scheme 1.16. Synthesis of dimethyldipyridylborate complexes of ruthenium.
Scheme 1.17. Formation of the agostic complex 1.68.
26
The agostic complex 1.68 is remarkable because its formation proceeds from a
coordinatively saturated acetonitrile complex. In acetonitrile solution, 1.67 and 1.68 are
in equilibrium, indicating that the formation of the agostic complex is thermodynamically
favorable enough to overcome the entropic disadvantage of eliminating an acetonitrile
ligand. The kinetics of this equilibrium have been studied by NMR magnetization
transfer. Observation of this agostic interaction gives a glimpse into possible transition
structures for bond activation in this ruthenium, boron scaffold by demonstrating that
coordination of a substrate to the boron can position a C–H bond in proximity to
ruthenium, promoting possible hydride abstraction. Additionally, the complexes 1.65 and
1.66 demonstrate that this ruthenium, boron complex is capable of adapting to bridges of
varying size, promising the potential to activate a variety of substrates.
To date, complex 1.64 has been shown to be an active catalyst for several reactions.
Most notably, 1.64 is an excellent air and water stable catalyst for the dehydrogenation of
ammonia borane (Scheme 1.18A).
81
Additionally, 1.64 has been shown to catalyze
alcohol oxidation, arene C–H activation, cyanation, and water oxidation (Scheme 1.18).
82
1.66, bearing a bridging trifluoroacetate, is also observed to dehydrogenate ammonia
borane, with similar rates as 1.64. Furthermore, 1.63 has been shown to catalyze
borylation of terminal sp
3
carbons with HB(pin) (Scheme 1.19).
83
Our laboratory is
continuing to investigate the reactivity of 1.63 and 1.64, as well as synthesizing related
complexes bearing similar ligands.
27
1.5 Overview
Catalysts demonstrating cooperative reactivity have becomes increasingly
common in the field of homogeneous organometallic catalysis in recent years. Many of
these catalysts are transfer hydrogenation catalysts, such as Shvo’s catalyst, but catalysts
for reactions ranging from simple organic transformations such as ring opening and
coupling to the activation of H
2
and CO
2
have been reported. New cooperative catalysts
are constantly being investigated and reported, as the demonstrated advantages of this
strategy have potential application in a wide variety of areas. Particular areas of focus are
Scheme 1.19. Borylation of terminal sp
3
carbons with HB(pin) catalyzed by 1.63.
Scheme 1.18. Catalytic reactivity of 1.64: ammonia borane dehydrogenation (A), alcohol
oxidation (B), arene C–H activation (C), cyanation (D) and water oxidation (E).
28
catalysts for asymmetric transformation, directed activation of molecules lacking typical
directing groups, and the activation of challenging bonds.
The following chapter describes our efforts towards expanding the known
reactivity of Shvo’s catalyst while chapters 4 and 5 present synthetic and structural
studies of potentially bifunctional catalysts bearing the dimethyldipyridyl borate ligand. It
is hoped that subsequent investigation of these complexes will reveal aptitude as directed
catalysts or catalysts for the activation of strong bonds.
29
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38
Khaskin, E.; Zavalij, P. Y.; Vedernikov, A. N. Oxidatively Induced Methyl
Transfer from Boron to Platinum in Dimethyldi(2-pyridyl)boratoplatinum
Complexes. Angew. Chem. Int. Ed. 2007, 46, 6309-6312.
80) Conley, B. L.; Williams, T. J. Thermochemistry and Molecular Structure of a
Remarkable Agostic Interaction in a Heterobifunctional Ruthenium-Boron
Complex. J. Am. Chem. Soc. 2010, 132, 1764-1765.
81) Conley, B. L.; Williams, T. J. A Robust, Air-Stable, Reusable Ruthenium Catalyst
for Dehydrogenation of Ammonia Borane. J. Am. Chem. Soc. 2011, 133, 14212-
14215.
82) Conley, B.L.; Williams, T. J. Unpublished work.
83) Celaje, J.; Conley, B. L.; Wiliams, T. J. Unpublished work.
39
Chapter 2. Studies of the Shvo Catalyst
2.1 Introduction
The synthesis of organic small molecule targets can be an expensive and time-
consuming component of molecular scale science, as reflected by the high price of many
simple chemical building blocks. New synthetic methods that enable more economical
approaches to organic synthesis broadly impact areas of science such as chemistry,
biology, medicine, engineering, nanotechnology, agriculture, and others. To address this,
we aimed to develop catalytic reactions for hydride abstraction from general organic
substrates with the ultimate goal of enabling nucleophilic substitution reactions in which
hydride (H
-
) is activated as a leaving group.
1
In pursuit of this goal, several aspects of the reactivity of Shvo’s catalyst (2.1,
Chapter 1) were explored. The selective conversion of primary alcohols to esters was
observed, which is consistent with Shvo’s observation of an ester by-product in the
hydrogenation of pentanal
2
and report of preparatively useful disproportionation of
aldehydes to the corresponding esters.
3
As an extension of this, it was also observed that
oxidative coupling of a diol to the corresponding lactone can be realized in several cases
under the Shvo conditions.
4
Furthermore, the study of the alkylation of amines with
alcohols using 2.1 has been expanded. Finally, the
potential application of Shvo’s catalyst to complex
molecule synthesis in the form of a tandem oxidation
and Pictet-Spengler cyclization to form a tetracyclic
skeleton present in several natural products has been
investigated.
40
2.2 Metal Catalyzed Alkylation of Amines
2.2.1 Alkylation of Amines with Amines
Beller et al. have shown Shvo’s catalyst (2.1) to be effective for the alkylation of
amines with amines. Anilines, amino pyridines and amines bearing tertiary alkyl groups
are all suitable substrates. Mono-, di-, and tri-substituted amines as well as cyclic alkyl
amines were demonstrated to be effective alkylating agents. This reactivity is discussed
extensively in Chapter 1.
2.2.2 Alkylation of Amines with Alcohols
While Shvo’s has not been shown to be particularly effective for the alkylation of
amines with alcohols, many other catalysts have been successfully used. Beller has
demonstrated a ruthenium and phosphine based catalytic system that is very effective for
Table 2.1. Alkylation of n-hexylamine with alcohols using Ru
3
CO
12
.
a
Entry (compound) Alcohol Temperature (°C) Yield (%)
1 (a)
110 97
2 (b)
110 90
3 (c)
120 93
4 (d)
110 49
5 (e)
110 60
6 (f)
110 70
a
Reaction time 24-48 h. Adapted from ref. 5b.
41
the alkylation of various amines with a variety of alcohols (examples in Table 2.1).
5
Williams et al. have also successfully demonstrated this reaction using a combination of
[Ru(p-cymene)Cl
2
]
2
and 1,1'-bis(diphenylphosphino)ferrocene (Table 2.2, entry 1).
6
In
2007, Bhattacharjee et al. used [RuCl(PPh
3
)
2
(CH
3
CN)
3
]
+
[BPh
4
]
-
to selectively mono-
alkylate aniline with a variety of alcohols (Table 2.2, entry 2).
7
Watanabe found various
ruthenium complexes to be active for the mono- and di-alkylation of heteroaromatic and
aromatic amines with primary alcohols (Table 2.2, entry 3)
8
and Fujita has used
[Cp*IrCl
2
]
2
to couple a wide variety of amine and alcohol substrates (Table 2.2, entry 4).
9
Kempe demonstrated that [IrCl(COD)]
2
is effective for the alkylation of aromatic amines,
but is ineffective for alkyl amines (Table 2.2, entry 5).
10
Additionally, Pd/C with
ammonium formate and (cyanomethyl)trialkylphosphonium iodide have both been seen
Table 2.2. Catalysts for the alkylation of aniline with benzyl alcohol.
a
Entry Catalyst
Base
(mol%)
2.6
(eq.)
Solvent
Temp.
(°C)
Time
(h)
Yield (%)
b
2.10 2.11
1
[Ru(p-cymene)Cl
2
]
2
( 2.5 mol%)
dppf (5 mol%), 3 Å MS
K
2
CO
3
(10)
1 toluene 111 24 80 -
2
[RuCl(PPh
3
)
2
(CH
3
CN)
3
]
+
[BPh
4
]
-
(1 mol%)
K
2
CO
3
(100)
Solv. - 205 10 30 17
c
3 RuCl
2
(PPh
3
) (1 mol%) - Solv. - 180 5 60 22
d
4 [Cp*IrCl
2
]
2
(1 mol%)
NaHCO
3
(1)
1 toluene 110 17 94 -
5
[IrCl(cod)]
2
(1 mol%)
Py
2
NPiPr
2
(1 mol%)
KOtBu
(110)
1.1 diglyme 70 24 96
e
-
a
Adapted from references 6-10.
b
Isolated yield unless otherwise noted.
c
Yields determined by
1
H NMR,
also produced 46% bezylidinephenyl amine.
d
Determined by Gas-Liquid Chromatography.
e
Determined
by GC.
42
to N-alkylate amines with alcohols.
11
Recently, Milstein has used [RuHCl(A-iPr-
PNP)(CO)] (2.5) to synthesize primary amines from ammonia and alcohols (Scheme
2.1).
12
One useful application of the alkylation of amines with alcohols is the synthesis of
indoles from 2-aminophenethyl alcohols, which has been demonstrated by both
Watanabe
13
and Fujita (Table 2.3).
14
In contrast to the alkylation reactions, Milstein
15
and
Madsen
16
have both shown the catalytic formation of amides from amines and alcohols.
2.2.3 Cyclization of Diols onto Amines
There are only a few examples of cyclizations to form nitrogen heterocycles from
amines and diols in the literature. Beller et al. have formed N-phenylpyrrolidines from
Scheme 2.1. Synthesis of primary amines from alcohols and ammonia.
Table 2.3. Formation of indole from 2-aminophenethyl alcohols.
a
Entry Catalyst R Time (h) Yield
b
1 [Cp*IrCl
2
]
2
(5 mol%), K
2
CO
3
(10 mol%) H (a) 17 80
2 6-Cl (b) 20 77
3 5-OMe (c) 20 68
4 RuCl
2
(PPh
3
)
3
(2 mol%) H (a) 6 100
c
5 6-Cl (b) 6 92
6 5-OMe (c) 6 94
a
Adapted from references 13 and 14.
b
Isolated yield.
c
Determined by GLC.
43
aniline and pyrrolidine (Scheme 2.2) using 2.1,
17
and Williams et al. have shown the
cyclization of diols onto tryptamine (Scheme 2.3).
18
2.3 The Pictet-Spengler Reaction
In 1911, Pictet and Spengler reported the condensative cyclization of β-
phenylethylamine and formaldehyde to form 1,2,3,4-tetrahydroisoquinoline (Scheme
2.4A).
19
At present, the Pictet-Spengler reaction more often refers to the condensative
cyclization of tryptamine and an aldehyde to form tetrahydro β-carbolines, which was
reported by Tastui in 1928 (Scheme 2.4A).
20
The reaction proceeds via formation of the
imine followed by condensation onto the indole-C2. This condensation is generally acid
catalyzed, but there are a few variants which are found to cyclize under non-acidic
Scheme 2.2. Formation of N-phenylpyrrolidines from anilines and pyrrolidine.
Scheme 2.3. Iridium-catalyzed cyclization of diols onto tryptamine.
Scheme 2.4. The first examples of the Pictet-Spengler reaction.
44
Scheme 2.5. Pictet-Spengler cyclization of tryptophan methyl ester hydrochloride.
Scheme 2.6. Biosynthetic significance of the enzymatic Pictet-Spengler reaction. STR1 =
strictosidine synthase (a Pictet-Spenglerase).
45
conditions.
21
These reactions often make use of tryptophan methyl ester hydrochloride as
a starting material in place of tryptamine, which is seen to be more prone to cyclization in
the absence of acid (Scheme 2.5).
22
It is also possible that the hydrochloride carried by
the starting material is sufficient to promote the cyclization under otherwise nonacidic,
aprotic conditions. Catalytic alternatives to the traditional acidic, protic conditions
include AuCl
3
/AgOTf,
23
iodine,
24
and calcium(II) hexafluroisopropoxide.
25
Several examples of asymmetric Pictet-Spengler reactions have been reported
26
and a number of others have been developed within the context of complex molecule
synthesis. The vast number of isoquinoline and indole alkaloids with desirable medicinal
properties has driven the development of the Pictet-Spengler reaction as way to generate
molecular complexity from simple starting materials (Scheme 2.6).
27
Some examples of
the application of the Pictet-Spengler to total synthesis include the total synthesis of
tangutorine,
28
manzamine derivatives,
29
(–)-panarine,
30
(-)-quinocarcin (Scheme 2.7A),
31
Scheme 2.7. Application of the Pictet-Spengler reaction in the synthesis of
(–)-quinocarcin (A) and (–)-yohimbine (B).
46
(+)-yohimbine (Scheme 2.7B),
32
(-)-lemonomycin,
33
phalarine,
34
and countless others.
35
Further, a polymer bound tryptophan has been synthesized to allow for the application of
the Pictet-Spengler reaction in combinatorial chemistry.
36
As exemplified by its extensive use in complex molecule synthesis, the Pictet-
Spengler is an incredibly valuable transformation. One of the major failings of the Pictet-
Spengler is the requirement of an appropriately functionalized aldehyde. Aldehydes are
often difficult to prepare, reactive, and expensive. Therefore, a modified Pictet-Spengler
that does not require an aldehyde is desirable. A few such examples have been reported;
most of these strategies do not lend themselves to generality. Most examples of aldehyde
free Pictet-Spengler make use of ketone or aldehyde equivalents such as the enol form of
phenylpyruvic acid
37
or an acetal.
27b
The use of azalactones is presented as another
Scheme 2.8. Pictet-Spengler reactions utilizing aldehyde alternatives.
47
alternative. In this example, the azalactone undergoes acid hydrolysis to form an enol
followed by reaction with tryptamine (Scheme 2.8A).
38
Another example makes use of a
preformed enamine, which behaves as the imine under the reaction conditions (Scheme
2.8B).
39
The most recent example of an aldehyde equivalent for the Pictet-Spengler
reaction is a gem-dibromomethylarene (Scheme 2.8C).
40
While these examples provide
some alternatives to the use of aldehydes, most do not represent significantly cheaper or
simpler strategies. The ability to effect a Pictet-Spengler reaction using an appropriate
catalyst and an alcohol would be a desirable simplification.
2.4 Shvo-Catalyzed Alkylation of Amines
Based on the literature precedent for the Shvo-catalyzed alkylation of amines with
amines, it was proposed that our conditions might effect the less common alkylation of
amines with alcohols. Indeed, Shvo’s catalyst (2.1) was shown to catalyze the alkylation
of aniline with ethanol to form both monoethylaniline and diethylaniline. When the
reactions are stopped after a short time (< 20 h), the primary product is monoethylaniline
whereas at longer times (> 30 h), the primary product is diethylaniline. This observation
of sequential formation of 2.46 followed by 2.47 suggests that the formation of
monoethyaniline (2.46) is substantially faster than formation of diethylaniline (2.47).
To optimize the alkylation of amines with alcohols, conditions were screened for
the reaction between ethanol and aniline (Table 2.4). From these screening reactions it
was confirmed that it is not necessary to add acetone as an oxidant in order for the
reaction to proceed in reasonable time with reasonable yield, as a result of this
transformation having no net oxidation (Table 2.4, entries 6-7). The ability to exclude
acetone eliminated one cause of decreased yields: the reaction of starting amine with
acetone to form isopropyl amines.
48
Concurrent with our attempts to optimize the conditions of the alkylation of
aniline,
41
a variety of other substrates were tested. Initial substrate scope tests focused on
the reaction of a variety of alcohols with aniline. Reactivity was observed to be binary;
substrates either reacted in high yield or did not react at all. It was shown that primary
alcohols are highly reactive (with the exception of methanol, Table 2.5), while secondary
alcohols are inactive under these conditions.
Table 2.4. Optimization of the conditions for the alkylation of aniline with ethanol.
Entry
Aniline
(mmol)
Ethanol
(mmol)
2.1
(mol %)
Acetone
(eq.)
Benzene
(ml)
Temp
(°C)
Time
(h)
Conv. (%)
a
2.46:2.47
1 0.5 3 mL 2 2 - 80
10 70 1:0
30 >95 (67) 0:1
2 0.25 0.25 2 1.5 5 80 168 5 1:0
3 0.5 0.5 1 1.5 1 80 44 3 1:0
4 0.5 1.0 2 1.5 3 60
70 60 1:0
96 >95 1:0
5 1.0 2.0 0.5 1.5 - 80 22 0 -
6 0.5 3 mL 2 - - 80
20 >95 3:1
44 >95 1:8
7 0.5 5 mL 2 - - 80 30 >95 (96) 0:1
8 0.5 3 mL - - - 75 96 0 -
9 1.0 4.0 1 - - 75 96 4 1:0
10 0.5 1.0 1 - 1 75 96 20 1:0
a
Conversion determined by disappearance of starting material as measured by GC/MS. Isolated yields in
parentheses.
b
0.5 ml toluene used as solvent.
49
Following the studies focused on aniline, a wider variety of both amines and
alcohols were tested for reactivity, with minimal success. Ultimately, it was concluded
that while these reaction conditions exhibited strong reactivity towards the alkylation of
aniline, the substrate scope was limited to anilines and primary alcohols.
2.5 Formation of Heterocycles Using the Shvo Catalyst
2.5.1 Intramolecular Cyclizations
Following the observation of limited reactivity for the alkylation amines,
intramolecular reactions were investigated. 1,5-Pentanediol and 5-amino-1-pentanol were
both tested; lactone formation was observed with the diol but there was no lactam or
piperidine formation (Table 2.6, entries 1 and 2). The constrained lactonization, using
1,2-benzenedimethanol proceeded to completion after approximately 18 hours (Table 2.6,
entry 3). The reaction was also attempted with cis-1,4-butenediol which produced a high
yield of γ–butyrolactone and only a small amount of butenolide (Table 2.6, entry 4).
Table 2.5. Alkylation of 2.9 with alcohols.
Entry
(compound)
Alcohol (eq.) Solvent
Time
(h)
Conv. (%)
a
2.49:2.50
1 (a)
Solvent - 66 - -
2 (b)
Solvent - 66 >95
b
1:0
3 (c)
2 Benzene 66 >99 (>99%) 0:1
c
a
Conversion determined by disappearance of starting material as measured by GC/MS.
Isolated yields in parentheses.
b
Major product N-benzylaniline, minor product N-
isopropylaniline. Benzylbenzoate also produced.
c
N-phenylpiperidine.
50
2.5.2 Cyclization of Diols onto Amines
One of the potentitally valuable results from the initial alkylations of aniline was
the formation of N-phenylpiperidine from aniline and 1,5-pentanediol (Table 2.7,
entry 1). When run without acetone, the formation of N-phenylpiperidine proceeded in
quantitative conversion by GC/MS. However, while the reaction run in the presence of
acetone gave a high isolated yield, in the absence of acetone the isolation proved
troublesome and a 35% yield was obtained. To expand the scope of this cyclization
reaction, several amines were tested against a variety of diols. The greatest success was
achieved with tert-alkyl and aryl amines (Table 2.7). Amines attached to primary carbons
were observed to form nitriles,
42
while amines on secondary carbons preferentially self-
couple.
Table 2.6. Heterocycle formation using 2.1.
Entry Substrate(s)
Conc.
(M)
2.1
(mol %)
Acetone
(ml)
Time
(h)
Product Conv. (%)
a
1
2.51
1 2 3 114
>99% (>99%)
2
2.52
1 2 3 114 - -
3
2.53
0.1 5 10 18
>99% (94%)
4
2.54
0.1 3 10 66.5
>95
b
a
Conversion determined by disappearance of starting material as measured by GC/MS. Isolated yields in
parentheses.
b
Major product γ–butyrolactone, minor product butenolide.
51
2.6 Investigations Toward Shvo-Catalyzed Pictet-Spengler Reactions
Based on the evidence that alkylation of amines occurs via an aldimine, we
proposed that 2.1 might be able to effect the Pictet-Spengler reaction using an alcohol
instead of an aldehyde. Additionally, based on the successful formation of nitrogen
heterocycles using 2.1, we proposed that if this transformation could be conducted with a
diol, 2.1 might catalyze a second cyclization following the Pictet-Spengler (Scheme 2.9).
Table 2.7. Cyclization of diols onto amines using 2.1.
Entry Amine Diol Product Conversion (%)
a
1
2.9
2.51
2.55
>95 (35)
2
2.56
2.57
30
3
2.9
2.54
2.58
25
2.16a
25
4
2.9
2.53
2.59
20
2.60
20
a
Conversion determined by disappearance of starting material as measured by GC/MS. Isolated yields in
parentheses.
Scheme 2.9. Proposed 2.1 catalyzed tandem Pictet-Spengler-cyclization.
52
A cascade reaction of this type would generate a significant amount of molecular
complexity in a single step and generate a tetracyclic skeleton relevant to the synthesis of
reserpine, ajmaline, ajmalicine and others (Scheme 2.6). Initial attempts to demonstrate a
2.1 catalyzed Pictet-Spengler explored the reaction of several alcohols with tryptamine,
but no formation of a cyclized product was observed (Scheme 2.10). In an attempt to
promote the Pictet-Spengler cyclization, tryptamine was acylated (Scheme 2.11), and the
reactions were run again using ethanol and isopentyl alcohol; formation of cyclized
product was still not observed.
In order to understand why cyclization was not occurring, the Pictet-Spengler
aldimine intermediate 2.64 was synthesized according to literature procedures (Scheme
2.12). Comparison of GC/MS results from the attempted 2.1 catalyzed reactions with this
standard sample confirmed that formation of the imine intermediate occurred in the
presence of 2.1, but the intermediate failed to cyclize. Further support for the successful
Scheme 2.10. Attempt to catalyze the tandem oxidation-Pictet-Spengler using 2.1.
Scheme 2.11. Acylation of tryptamine.
Scheme 2.12. Formation and attempted cyclization of the Pictet-Spengler imine
intermediate 2.64.
53
formation of the imine was the observation by GC/MS of N-alkylated (mixture of mono-
and bis-) products in every case, which suggests that although the imine forms, reduction
of the imine is faster than cyclization or reduction of the oxidant (hexene or
cyclohexene). Given the demonstrated preference of 2.1 for polar bonds, this reduction of
imine over alkene is not unexpected. However, oxidants with polar bonds (acetone, for
example) are unsuitable. Oxidants with polar bonds are likely to react with tryptamine
under these conditions, as suggested by the problematic formation of N-isopropyl amines
when utilizing acetone as an oxidant.
Subjecting a pure sample of 2.64 to the reaction conditions in the absence of a
hydrogen source confirmed that 2.1 alone was not sufficient to promote cyclization
(Scheme 2.12). Based on literature results, an acid was determined to be required to
initiate the cyclization. A variety of acids were tested; HCl, acetic acid and HBF
4
·Et
2
O
were all found to cyclize 2.64 to 2.65 quantitatively. As the next step, the reactivity of 2.1
in the presence of acid was tested on the oxidation of isopentyl alcohol (Table 2.8).
Shvo’s catalyst (2.1) showed minimal activity (14% conversion) in the presence of acetic
acid but the tandem reaction does not occur when acetic acid is added. The incompatible
observations of inactivity of 2.1 in the presence of acid and the requirement of acid for
the cyclization of 2.64 resulted in the conclusion that at present it would not be possible
to catalyze a tandem oxidation-Pictet-Spengler cyclization using 2.1.
Scheme 2.13. Acid-catalyzed cyclization of 2.65.
54
2.7 Conclusions
While this search for new reactivity of 2.1 did not yield any significant
discoveries, limited cases were revealed wherein previously unreported reactivity was
obtained, some of which have since been elaborated in the literature by others. Bäckvall
et al. have reported the aerobic cyclization of diols to form lactones by using a system
which incorporates Shvo’s catalyst, 2,6-dimethoxybenzoquinone and a cobalt complex,
analogous to their previously reported aerobic oxidation of amines.
43
Perris et al. present
the only report of reactivity of 2.1 for the alkylation of amines with alcohols. In 2011,
they reported the use of 2.1 to catalyze the production of tertiary amines from primary
amines and ammonium salts.
44
These reactions require high temperatures (130 – 140 °C)
but proceed in high yields with a small scope of alcohols. Additionally, Beller and
Williams have both reported the use of 2.1 for the N-alkylation of indole with alcohols.
45
Other recent reports of successful amination of alcohols utilize other transfer
hydrogenation catalysts.
46
Finally, it was conclusively shown that the tandem oxidation-
Pictet-Spengler cyclization cascade cannot be realized under these conditions. The
inactivity of 2.1 in the presence of acid is fundamentally incompatible with the acid-
catalyzed Pictet-Spengler cyclization.
Table 2.8. Reactivity of 2.1 in the presence of acid.
Entry Acid Solvent Time (d) Conv.
a
1 - 1:1 CH
2
Cl
2
:tBuOH 3 100
2 HCl (aq.) 1:1 CH
2
Cl
2
:tBuOH 3 -
3 Acetic Acid 1:1 CH
2
Cl
2
:tBuOH 3 14
4 HBF
4
·Et
2
O CH
2
Cl
2
2 -
a
Conversion determined by GC/MS, based on ½ isopentyl alcohol.
55
2.8 References
1) Regarding hydride transfer, see (a) Deno, N. C.; Peterson, H. J.; Saines, G. S. The
Hydride-Transfer Reaction. Chem. Rev. 1960, 60, 7-14. Some examples include
(b) Li, Z.; Bohle, D. S.; Li, C.-J. Cu-Catalyzed Cross-Dehydrogenative Coupling:
a Versatile Strategy for C-C Bond Formations via the Oxidative Activation of Sp
3
C–H Bonds. Proc. Natl. Acad. Sci. 2006, 103, 8928-8933. (c) Pastine, S. J.;
McQuaid, K. M.; Sames, D. Room Temperature Hydroalkylation of Electron-
Deficient Olefins: sp3 C-H Functionalization via a Lewis Acid-Catalyzed
Intramolecular Redox Event. J. Am. Chem. Soc. 2005, 127, 12180-12181. (d)
Nijhuis, W. H. N.; Verboom, W.; El-Fadl, A. A.; Harkema, S.; Reinhoudt, D. N.
Stereochemical Aspects of the "tert-Amino Effect". 1. Regioselectivity in the
Synthesis of Pyrrolo[1,2-A]quinolines And Benzo[C]quinolizines. J. Org. Chem.
1989, 54, 199-209. Via SET: (e) Fukuzumi, S.; Ohkubo, K.; Okamoto, T. Metal
Ion-Catalyzed Diels-Alder and Hydride Transfer Reactions. Catalysis of Metal
Ions in the Electron-Transfer Step. J. Am. Chem. Soc. 2002, 124, 14147-14155. (f)
For a review: Bäckvall J.-E. Transition Metal Hydrides as Active Intermediates in
Hydrogen Transfer Reactions. J. Organomet. Chem. 2002 , 652, 105-111.
2) Blum, Y.; Czarkie, D.; Rahamim, Y.; Shvo, Y. (Cyclopentadienone)ruthenium
Carbonyl Complexes - A New Class of Homogeneous Hydrogenation Catalysts.
Organometallics 1985, 4, 1459-1461.
3) Menashe, N.; Shvo, Y. Catalytic Disproportionation of Aldehydes with
Ruthenium Complexes. Organometallics 1991, 10, 3885-3891.
4) Specifically regarding ruthenium-based conditions, see (a) Murahashi, S.-I.;
Naota, T.; Ito, K.; Maeda, Y.; Taki, H. Ruthenium-Catalyzed Oxidative
Transformation of Alcohols and Aldehydes to Esters and Lactones. J. Org. Chem.
1987, 52, 4319-4327. (b) Zhao, J.; Hartwig, J. F. Acceptorless, Neat, Ruthenium-
Catalyzed Dehydrogenative Cyclization of Diols to Lactones. Organometallics
2005, 24, 2441-2446.
5) (a) Hollmann, D.; Tillack, A.; Michalik, D.; Jackstell, R.; Beller, M. An Improved
Ruthenium Catalyst for the Environmentally Benign Amination of Primary and
Secondary Alcohols. Chem. Asian. J. 2007, 2, 403-410. (b) Tillack, A.; Hollmann,
D.; Michalik, D.; Beller, M. A Novel Ruthenium-Catalyzed Amination of Primary
and Secondary Alcohols. Tet. Lett. 2006, 47, 8881-8885.
6) (a) Hamid, M. H. S. A.; Williams, J. M. J. Ruthenium Catalysed N-Alkylation of
Amines with Alcohols. Chem. Commun. 2007, 725-727. (b) Hamid, M. H. S. A.;
Williams, J. M. J. Ruthenium-Catalysed Synthesis of Tertiary Amines from
Alcohols. Tet. Lett. 2007, 48, 8263-8265.
56
7) Naskar, S.; Bhattacharjee, M. Selective N-Monoalkylation of Anilines Catalyzed
by a Cationic Ruthenium(II) Compound. Tet. Lett. 2007, 48, 3367-3370.
8) (a) Watanabe, Y.; Morisaki, Y.; Kondo, T.; Mitsudo, T. Ruthenium Complex-
Controlled Catalytic N-Mono- or N,N-Dialkylation of Heteroaromatic Amines
with Alcohols. J. Org. Chem. 1996, 61, 4214-4218. (b) Watanabe, Y.; Tsuji, Y.;
Ige, H.; Ohsugi, Y.; Ohta, T. Ruthenium-Catalyzed N-Alkylation and N-
Benzylation of Aminoarenes with Alcohols. J. Org. Chem. 1984, 49, 3359-3363.
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Derivatives. J. Org. Chem. 2009, 74, 6895-6898. (c) Kundo, B.; Agarwal, P. K.;
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Heterocycles. Curr. Opin. Drug Discov. Develop. 2010, 13, 669-684. (e)
Czerwinski, K. M.; Cook, J. M. Stereochemical Control of the Pictet-Spengler
Reaction in the Synthesis of Natural Products. Adv. Heterocycl. Nat. Prod. Syn.
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Calcaterra, A.; Barba, M.; Macone, A.; Boffi, A.; Bonamore, A.; Botta, B.
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the Sarpagine Related Indole Alkaloids (+)-N
a
-Methyl-16-epipericyclivine, (–)-
Alkaloid Q
3
and (–)-Panarine via the Asymmetric Pictet-Spengler Reaction.
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L.; Grubisha, D.; Bennett, D.; Cook, J. M. Pictet-Spengler Reactions in Aprotic
Media. The Total Synthesis of (±) Suaveoline. Tetrahedron 1992, 48, 1805-1822.
(b) Lane, J. W.; Chen, Y.; Williams, R. M. Asymmetric Total Syntheses of (−)-
Jorumycin, (−)-Renieramycin G, 3-epi-Jorumycin, and 3-epi-Renieramycin G. J.
Am. Chem. Soc. 2005, 127, 12684–12690. (c) Schwalm, C. S.; Correia, C. R. D.
Divergent Total Synthesis of the Natural Antimalarial Marinoquinolines A, B, C,
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H.; Hiemstra, H. Total Syntheses of Mitragynine, Paynantheine and Speciogynine
via an Enantioselective Thiourea-Catalysed Pictet–Spengler Reaction. Chem.
Comm. 2012, 48, 12243-12245. (e) Zheng, H.; Zhao, C.; Fang, B.; Jing, P.; Yang,
J.; Xie, X.; She, X. Asymmetric Total Synthesis of Cladosporin and
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37) Hudlicky, T.; Kutchan, T. M.; Shen, G.; Sutliff, V. E.; Coscia, C. J. Improved
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and Biogenic Amines. J. Org. Chem. 1981, 46, 1738-1741.
38) Audia, J. E.; Droste, J. J.; Nissen, J. S.; Murdoch, G. L.; Evrard, D. A. “Pictet-
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Direct Use of Azalactones as Phenylacetaldehyde Equivalents. J. Org. Chem.
1996, 61, 7937-7939.
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39) Vohra, R.; MacLean, D. B. Enamine Precursors of 1-Substituted-1,2,3,4-
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40) Chowdappa, N.; Sherigara, B.; Augustine, J.; Areppa, K.; Mandal, A. gem-
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41) Prior to the inactive batch of catalyst.
42) Oishi, T.; Yamaguchi, K.; Mizuno, N. Catalytic Oxidative Synthesis of Nitriles
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43) (a) Endo, Y.; Bäckvall, J.-E. Aerobic Lactonization of Diols by Biomimetic
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44) Segarra, C.; Mas-Marzá, E.; Mata, J. A.; Peris, E. Shvo’s Catalyst and
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2
(amidine)] Effectively Catalyze the Formation of Tertiary Amines from
the Reaction of Primary Alcohols and Ammonium Salts. Adv. Syn. Catal. 2011,
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Catalytic Amination of Alcohols. ChemCatChem 2011, 3, 1853–1864.
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with Chelating N-Heterocyclic Carbenes: Efficient Catalysts for Transfer
Hydrogenation, β-Alkylation of Alcohols, and N-Alkylation of Amines.
Organometallics 2009, 28, 321–325. (b) Wetzel, A.; Wöckel, S.; Schelwies, M.;
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Spasyuk, D.; Gusev, D. G. Osmium and Ruthenium Catalysts for
Dehydrogenation of Alcohols. Organometallics 2011, 30, 3479–3482.
61
Chapter 3. Ruthenium Catalyzed Coupling of Alkynes and
1,3-Diketones
3.1 Introduction
1
Carbon-carbon bond-forming reactions involving enolate anions are among the
most useful, fundamental transformations in organic chemistry.
2
However, the conditions
required to pre-form an enolate anion (or metal enolate) are often harsh and as such the
ability to obtain enolate-type reactivity without the need to pre-form the enolate is
desirable. The Conia-Ene reaction (Scheme 3.1, top) is one such example that will occur
thermally but requires very high temperature (200-250 °C).
3
Several examples of
catalyzed Conia-Ene reactions have been presented.
4-8
Of greater synthetic utility,
though, is the more general intermolecular-ene reaction (Scheme 3.1, bottom). Only a
few examples of systems that will catalyze the intermolecular-ene reaction have been
reported.
9-12
This chapter details the finding that commercially available ruthenium(III)
chloride is a superior catalyst for this transformation and affords uncharacteristically mild
intermolecular ene-type coupling reactions for a variety of terminal alkynes and 1,3-
dicarbonyl compounds. These conditions are operationally simple and inexpensive.
3.2 Conia-Ene Reaction and Intermolecular Variants
The Conia-Ene reaction is an electrocyclic transformation in which a β-ketoester
reacts with a pi system to form a new C–C bond. Conceptually, a Conia-Ene reaction is
Scheme 3.1. Conia-Ene (top) and intermolecular-ene (bottom) reactions.
62
similar to alkylating a ketone with an alkene or alkyne, with the latter representing a
graceful strategy to “vinylate” adjacent to a carbonyl group. These reactions occur
thermally at high temperature (c.f. 200 °C).
3
Due to their synthetic utility, several
examples of catalyzed Conia-ene reactions have been reported, including reactions
involving gold,
4
palladium/ytterbium,
5
and copper/silver,
6
systems. Additionally, some of
these methods have been demonstrated for use in complex
7
and asymmetric
8
applications.
In 2004, Toste reported a gold complex which was able to catalyze the Conia-Ene
reaction in high yield with only 1 mole percent catalyst at room temperature (Table 3.4,
entry 1).
4
In 2009, Li described a copper/silver co-catalyzed Conia-Ene reaction; this
system requires 100° C and 10 mole percent catalyst (Table 3.1, entry 3).
6
This
copper/silver co-catalyzed reaction has a broader substrate scope than Toste’s gold
complex, including 1,3-diketones and an α-cyanoketone.
The Conia-Ene cyclization has been successfully applied to the synthesis of
several complex molecule scaffolds. Hatakeyama has detailed the use of an indium-
catalyzed Conia-Ene reaction for the construction of a five-membered ring in the
Table 3.1. Comparison of catalysts for a Conia-Ene cyclization.
a
Entry Catalyst Solvent Temp. (°C) Time (h) Yield (%)
b
1
(PPh
3
)AuCl (1 mol%)
AgOTf (1 mol%)
DCM 25 18 93
2
(DTBM-SEGPHOS)Pd(OTf)
2
(10 mol%)
Yb(OTf)
3
(20 mol%)
AcOH (10 eq.)
Et
2
O 25 12 86
3
(CuOTf)
2
·C
6
H
6
(10 mol%)
AgBF
4
(10 mol%)
DCE 100 23 86
a
Adapted from references 4, 5, and 6.
b
Isolated yield.
c
All reactions are under inert atmosphere.
63
synthesis of (–)-salinosporamide A (Scheme 3.2A).
7a
A formal synthesis of (±)-
clavukerin A reported in 2010 uses a zinc-catalyzed Michael/Conia-Ene cascade to form
the bicyclic skeleton.
7b
In a reaction similar to a Pictet-Spengler reaction (Chapter 2),
Kerr et al. utilized a tandem cyclopropane ring-opening/Conia-Ene reaction to generate
tetrahydrocarbazoles (Scheme 3.2B).
7c
Another cascade reaction involving a Conia-Ene
reaction is the Prins/Conia-Ene cascade cyclization reported in the 2011 synthesis of the
tricyclic furanochroman skeleton of phomactin A.
7d
Finally, a Conia-Ene reaction was
utilized in the 2011 total synthesis of oxazolomycin A.
7e
Complimentary to its use in complex molecule synthesis, a few examples of
asymmetric Conia-Ene reactions have been reported. The initial asymmetric Conia-Ene
was described by Toste in 2005.
5
They reported a chiral, bidentate diphosphine palladium
complex that, with the addition of ytterbium(III) acetate, catalyzes the Conia-Ene
reaction in 79-95% yield with 70-94% ee (Table 3.2, entry 1). In 2009, Dixon described a
cinchona-derived precatalyst that promotes an asymmetric copper catalyzed Conia-Ene
reaction with moderate to high yields (67-99%) and good ee (73-93%, Table 3.2,
Scheme 3.2. Application of the Conia-Ene reaction to the synthesis of salinosporamide A
(A) and tetrahydrocarbazoles (B).
64
entry 2).
8a
The most recent example of an asymmetric Conia-Ene reaction was reported
by Kumagai and Shibasaki in 2011. They showed that a bifunctional lanthanum-silver
catalyst with a chiral amide-based ligand and triphenylphosphine catalyzes a Conia-Ene
reaction with high yield (86- >99%) and moderate ee (83-96%, Table 3.2, entry 3).
8b
By contrast to the success of the Conia-Ene reaction, there are fewer reports of the
analogous intermolecular ene-based coupling reaction. Only a few catalytic solutions to
this reaction are reported. These are limited to indium(III) triflate,
9
indium(III)
trifluoromethylsulfonamide,
10
a rhenium-based system,
11
and a recently reported
hydro(trispyrazolyl)borato-ruthenium(II) complex.
12
Nakamura reported in 2003 that catalytic indium(III) triflate catalyzes the ene
reaction neat, at >100° C with 5 mole percent catalyst (Table 3.3, entry 1).
9a
They
Table 3.2. Examples of asymmetric Conia-Ene reactions.
a
Entry Catalyst Solvent Temp. (°C) Time (h) Yield (%)
b
% ee
1
3.8
(10 mol%)
Yb(OTf)
3
(20 mol%)
AcOH (10 eq.)
Et
2
O 25 12 86 89
2
3.9 (20 mol%)
CuOTf·½C
6
H
6
(5 mol%)
DCM 25 36 82 91
3
La(OiPr)
2
(10 mol%)
3.10 (20 mol%)
AgOAc (10 mol%), PPh
3
(10 mol%)
AcOEt 0 118 quant. 91
a
Adapted from references 5 and 8.
b
Isolated yield.
65
propose that the reaction occurs via formation of the indium enolate complex. In 2005
they showed that in the presence of molecular sieves, indium(III) triflate would catalyze
the ene reaction with acetylene, using 20 mole percent catalyst and 1 atm welding grade
acetylene.
9b
In 2007 they expanded their substrate scope to include a variety of
substituted phenylacetylenes, alkyl alkynes, heterocycle-functionalized alkyne and a
broad spectrum of substituted 1,3-dicarbonyl compounds.
9c
Most recently, they have
shown that indium(III) trifluoromethylsulfonamide will catalyze the addition of 1-
iodoalkynes to form exclusively the E-iodoalkane, which allow for future
functionalization to form trisubstituted olefins.
10
In addition to the indium examples, in 2005, Takai reported a rhenium complex
capable of catalyzing this reaction in high yield, under moderate conditions (Table 3.3,
entry 2).
11
They presented a reasonably broad substrate scope, which includes 1,3-
diketones, β-ketoesters, alkyl alkynes and an alkynyl ether. Several of these substrates
represent examples which our conditions are not able to duplicate. Takai has also
Table 3.3. Comparison of catalysts for an intermolecular ene reaction.
a
Entry Catalyst 3.12 (eq.) Temp. (°C) Time (h) Yield (%)
b
1
In(OTf)
3
(2.5 mol%)
Et
3
N (2.5 mol%), n-BuLi (2.5 mol%)
5 100 24 97
2 [ReBr(CO)
3
(thf)]
2
(3 mol%) 1 50 24 94
3 TpRu[4-CF
3
C
6
H
4
N(PPh
2
)
2
](OTf) (0.4 mol%) 1.2 120 3.5 87
a
Adapted from references 9c, 11 and 12. All reactions are under inert atmosphere.
b
Isolated yield.
66
demonstrated that this same rhenium complex, under modified conditions (toluene, 80°
C) catalyzes insertion of an alkyne into a C-C bond, if the substrate is a β-ketoester.
13
The most recent report of a catalyst for the intermolecular reaction comes from
Lau et al. who describe a hydro(trispyrazolyl)borato-ruthenium(II) diphosphinoamino
complex which catalyzes the intermolecular addition neat at 120 °C with very low
catalyst loading (Table 3.3, entry 3).
12
This catalyst is active only for 1,3-diketones and
terminal alkynes, but tolerates halide-substituted aryl alkynes as well as aliphatic alkynes.
3.3 Ruthenium Catalysts
As several groups have reported success using bimetallic catalyst strategies for
the Conia-Ene transformation
5,6,8bc
we hoped that it might be possible to extend this
strategy to the intermolecular reaction. Whereas the solutions to the intermolecular
coupling variant of this reaction are few and the existing solutions involve forcing
conditions in many cases, it was proposed that a dual site ruthenium, boron catalyst
(Chapter 1)
14
might be a convenient solution due to its ability to simultaneously bind and
activate both reactive partners. It was found, however, that commercially-available
ruthenium(III) chloride is a superior catalyst for this transformation and affords
uncharacteristically mild intramolecular ene-type coupling reactions for a variety of
terminal alkynes and 1,3-dicarbonyl compounds.
To test the proposal that a dual-site ruthenium, boron catalyst would effect this
transformation two ruthenium complexes bearing the dimethyldipyridylborate ligand,
[(py)
2
BMe
2
]Ru(cym)Cl and {[(py)
2
BMe(μ-OH)]Ru(MeCN)
3
}
+
-
OTf
15
(py = 2-pyridyl,
cym = η
6
-p-cymene) were tested. Both complexes were found to catalyze the ene-type
coupling between phenylacetylene and acetylacetone in modest yield (Table 3.4, entries
1, 2). Further experiments revealed that a variety of ruthenium complexes also affect this
67
transformation when modified with silver hexafluorophosphate to extract the ruthenium
chlorides, including [(p-cymene)RuCl
2
]
2
, [(COD)RuCl
2
]
2
, [(CO)
3
RuCl
2
]
2
, (Ph
3
P)
3
RuCl
2
,
and [(CO)
3
RuCl
2
]
2
, but notably, RuCl
3
3H
2
O provides the highest yield (Table 3.4,
entries 4-8). In light of this observation, it was considered that a Ru(acac)
3
(acac =
acetylacetonate) species, generated in situ, might be responsible for the reactivity.
However, no coupling when a portion of Ru(acac)
3
was used as the catalyst precursor
(entry 9) was observed. This reaction resulted in the formation of 10% product with the
addition of AgOCOCF
3
(entry 10). No reaction was observed in the absence of ruthenium
(entries 11-12).
Table 3.4. Catalyst Optimization.
Entry Catalyst [Ag] (mol%) Yield (%)
a
1 [(py)
2
BMe
2
]Ru(cym)Cl AgPF
6
5 52
2 {[(py)
2
BMe(μ-OH)]Ru(MeCN)
3
}
+
-
OTf None - 10
3
b
{[(py)
2
BMe(μ-OH)]Ru(MeCN)
3
}
+
-
OTf None - 10
4 [(CO)
3
RuCl
2
]
2
AgPF
6
10 82
5 [(p-cymene) RuCl
2
]
2
AgPF
6
10 46
6 [(COD)RuCl
2
]
2
AgPF
6
10 10
7 (Ph
3
P)
3
RuCl
2
AgPF
6
10 7
8 RuCl
3
3 H
2
O AgPF
6
15 90
9 Ru(acac)
3
None - 0
10 Ru(acac)
3
AgOCOCF
3
15 10
11 None AgPF
6
15 0
12 None - - 0
a
Yield determined by NMR using nitromethane as internal standard.
b
Under N
2
atmosphere.
68
3.4 Condition Optimization
After the determination of ruthenium(III) chloride trihydrate as the best ruthenium
species, the other aspects of the reaction were optimized: silver salt, water, and solvent.
The incorporation of a silver salt proved essential (Table 3.5, entry 2) and the use of
AgOCOCF
3
instead of AgPF
6
produces similar results (entries 1 and 3). The reaction
proceeds in a variety of solvents, or with no solvent at all (entries 1, 4-6); the shortest
reaction times and highest yields are obtained using a minimal volume of diethyl ether.
Further, a small amount of water significantly accelerates the reaction rate; two
equivalents relative to diketone produces the highest yields (entries 1, 7-8).
Finally, it was observed that although three equivalents of alkyne relative to the
diketone is optimal for reaction time; the reaction proceeds to completion with only 1.5
equivalents (Table 3.5, entry 9). The need for excess alkyne arises from a side reaction in
Table 3.5. Condition Optimization.
Entry Catalyst [Ag] H
2
O (eq.) Solvent Time (h) Yield (%)
a
1 RuCl
3
3 H
2
O AgPF
6
2 Et
2
O 2 90
2 RuCl
3
3 H
2
O None 2 Et
2
O 2 9
3 RuCl
3
3 H
2
O AgOCOCF
3
2 Et
2
O 2 92
4 RuCl
3
3 H
2
O AgPF
6
2 CH
2
Cl
2
2 53
5 RuCl
3
3 H
2
O AgPF
6
2 None 2 69
6 RuCl
3
3 H
2
O AgPF
6
2 C
6
H
6
2 45
7 RuCl
3
3 H
2
O AgPF
6
0 Et
2
O 2 6
8 RuCl
3
3 H
2
O
AgPF
6
1 Et
2
O 2 84
9 RuCl
3
3 H
2
O
b
AgPF
6
2 Et
2
O 5.5 92
a
Yield determined by NMR using nitromethane as internal standard.
b
1.5 eq. Phenylacetylene.
69
which some alkyne is hydrolyzed to the corresponding methyl ketone, as is evident from
the formation of acetophenone from phenylacetylene (determined by GC/MS and
NMR).
16
Electron-rich alkynes are more susceptible to this side reaction as shown by
NMR quantification and it appears to be faster in the presence of AgPF
6
as opposed to
AgOCOCF
3
.
It is important to note that while the solvents used in this study were rigorously
anhydrous to allow for the quantification of added water, it was found that these reactions
could be run with benchtop grade solvent without the need for additional water (87%
isolated yield).
3.5 Alkyne Scope
A number of aryl alkynes afford good yield of ene-type coupling products under
our optimized conditions (Table 3.6). Our parent case, entry 1, affords coupling product
in 88% isolated yield. Electron-rich and electron-poor alkynes both participate
successfully. However, the electron-rich alkynes are more reactive towards the alkyne
hydrolysis side reaction. Entries 2 and 3 show that although these reactions are somewhat
slower than the parent, they proceed in desirable yields. For example, a reaction of 4-
ethynyltoluene (3.14) proceeds to completion to give 3.15 in 2 hours, and the analogous
1-ethynyl-4-methoxybenzene (3.16) requires 6 hours to convert to 3.17. In all cases,
reactions of electron-rich alkynes do not reach completion with only 3 equivalents of
alkyne when AgPF
6
is utilized. Even with the use of AgOCOCF
3
, the corresponding aryl
ketones are produced in quantities detectable by GC/MS. Our conditions are compatible
with ethyne-pendant heterocycles and anilines: entries 6 and 7 show the results of these
experiments.
70
Table 3.6. Alkyne Scope.
a
Entry Substrate Product Time (h) Yield (%)
b
1
2 88 (92)
3.12 3.13
2
3 77 (95)
3.14 3.15
3
6 82 (96)
3.16 3.17
4
4 92
3.18 3.19
5
2 68 (83)
3.20 3.21
6
8 36 (45)
3.22 3.23
7
24 41 (50)
3.24 3.25
a
Conditions: 0.5 mmol acetylacetone, 1.5 mmol alkyne, 150 μL diethyl ether, 1.0 mmol
H
2
O.
b
Isolated yield. NMR Yield in parentheses.
71
Table 3.7. Diketone Scope.
a
Entry Substrate Product Time (h) Yield (%)
b
1
2 78 (83)
3.26 3.27
2
c
15 44 (50)
3.28 3.29
3
c
15 50 (54)
3.30 3.31
4
3.32
3.33 +
3.34ZE
9 3.33:13 3.34Z: 4 3.34E
4 90 (95)
5
4 90 (98)
3.35 3.36
6
d
8 (37)
3.37 3.38
a
Conditions: 0.5 mmol diketone, 1.5 mmol phenylacetylene, 150 μL diethyl ether, 1.0 mmol
H
2
O.
b
Isolated yield. NMR Yield in parentheses.
c
1 eq. H
2
O.
d
1 eq. H
2
O and 10 mol% Et
3
N.
72
3.6 Diketone Scope
A number of 1,3-diketone compounds participate efficiently in coupling reactions
under our reaction conditions (Table 3.7, entries 1-5); β-ketoesters participate less
efficiently (entry 6). The products of reactions with β-ketoesters and 3-substituted 1,3-
diketones (entries 2 and 3) are susceptible to retro-Claisen type decomposition to give
deacylated products with internal alkenes (Scheme 3.3). This decomposition is promoted
by water, and the use of only one equivalent of water relative to diketone is beneficial.
In cases where R
2
= Ph (entries 4, 5), coupling is high-yielding and involves a
subsequent isomerization of the initially formed diene to an internal alkene, either
stepwise or through a [1,5] hydride shift (Scheme 3.4). Entry 4 shows all of the
possibilities available along these lines: 3.32 is converted to 3.33 under our conditions,
then 3.33 converts to isomers 3.34E and 3.34Z. By contrast, when R
1
= R
2
= Ph (3.35), a
single, isomerized product is collected in 90% yield (entry 5). Finally, these conditions
can be scaled up to 1 g with no appreciable loss of yield (Scheme 3.5). This ability to
increase the scale smoothly is indicative of homogeneous catalysis, and is an essential
part of the practicality of these conditions.
Scheme 3.4. Isomerization in cases where R
2
= Ph.
Scheme 3.3. Retro-Claisen decomposition of 3-substitued 1,3-diketones.
73
3.7 Conclusion
We have developed new catalytic conditions for the ene-type coupling reaction of
alkynes with 1,3-diketones. These reactions proceed at mild temperature under air and in
the presence of water with relatively low catalyst loading and minimal solvent waste. The
conditions reported herein have advantages over each of the previously reported catalysts.
The rhenium conditions involve significantly greater cost, and though the cost of both the
indium and hydro(trispyrazolyl)borato-ruthenium(II) conditions is similar to the
conditions reported here, all three must be prepared and conducted under inert
atmosphere with rigorously dried materials. Our system is not limited by this need and is
therefore more practically applicable. Additionally, all catalytic materials are
commercially available and the conditions are applicable to a diverse variety alkynes and
diketones. Thus, these conditions present a very convenient approach to the “vinylation”
of diketone systems.
Scheme 3.5. Parent reaction on 1 g scale.
74
3.8 References
1) This chapter reprinted with permission from Elsevier. Pennington-Boggio, M. K.;
Conley, B. L.; Williams, T. J. A Ruthenium-Catalyzed Coupling of Alkynes with
1,3-Diketones. J. Organometall. Chem. 2012, 716, 6-10.
2) Caine, D. Alkylations of Enols and Enolates. In Comprehensive Organic
Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: New York, 1991; Vol.
3, p 1-63.
3) Conia, J. M.; Le Perchec, P. The Thermal Cyclisation of Unsaturated Carbonyl
Compounds. Synthesis 1975, 1-19.
4) Kennedy-Smith, J. J.; Staben, S. T.; Toste, F. D. Gold(I)-Catalyzed Conia-Ene
Reaction of β-Ketoesters with Alkynes. J. Am. Chem. Soc. 2004, 126, 4526-4527.
5) Corkey, B. K.; Toste, F. D. Catalytic Enantioselective Conia-Ene Reaction. J. Am.
Chem. Soc. 2005, 127, 17168-17169.
6) Deng, C.-L.; Zou, T.; Wang, Z.-Q.; Song, R.-J.; Li, J.-H. Copper/Silver-
Cocatalyzed Conia-Ene Reactions of 2-Alkynic 1,3-Dicarbonyl Compounds. J.
Org. Chem. 2009, 74, 412-414.
7) (a) Takahashi, K.; Midori, M.; Kawano, K.; Ishihara, J.; Hatakeyama, S. Entry to
Heterocycle Based on Indium-Catalyzed Conia-Ene Reactions: Asymmetric
Synthesis of (–)-Salinosporamide A. Angew. Chem. Int. Ed. 2008, 47, 6244-6246.
(b) Li, W.; Liu, W.; Zhou, X.; Lee, C.-S. Amine-Induced Michael/Conia-Ene
Cascade Reaction: Application to a Formal Synthesis of (±)-Clavukerin A. Org.
Lett. 2010, 12, 548-551. (c) Grover, H. K.; Lebold, T. P.; Kerr, M. A. Tandem
Cyclopropane Ring-Opening/Conia-ene Reactions of 2-Alkynyl Indoles: A [3 +
3] Annulative Route to Tetrahydrocarbazoles. Org. Lett. 2011, 13, 220-223. (d)
Huang, S.; Du, G.; Lee, C.S. Construction of the Tricyclic Furanochroman
Skeleton of Phomactic A via the Prins/Conia-Ene Cascade Cyclization Approach.
J. Org. Chem. 2011, 76, 6534-6541. (e) Eto, K.; Yoshino, M.; Takahashi, K.;
Ishihara, J.; Hatakeyama, S. Total Synthesis of Oxazolomycin A. Org. Lett. 2011,
13, 5398-5401.
8) (a) Yang, T.; Ferrali, A.; Sladojevich, F.; Campbell, L.; Dixon, D. J. Brønsted
Base/Lewis acid Cooperative Catalysis in the Enantioselective Conia-Ene
Reaction. J. Am. Chem. Soc. 2009, 131, 9140-9141. (b) Matsuzawa, A.; Mashiko,
T.; Kumagai, N.; Shibasaki, M. La/Ag Heterobimetallic Cooperative Catalysis: A
Catalytic Asymmetric Conia-Ene Reaction. Angew. Chem. Int. Ed. 2011, 50,
7616-7619.
75
9) (a) Nakamura, M.; Endo, K.; Nakamura, E. Indium Catalyzed Addition of Active
Methylene Compounds to 1-Alkynes. J. Am. Chem. Soc. 2003, 125, 13002-13003.
(b) Nakamura, M.; Endo, K.; Nakamura, E. Indium Triflate-Catalyzed Vinylation
of β-ketoesters with Acetylene Gas. Org. Lett. 2005, 7, 3279-3281. (c) Endo, K.;
Hatakeyama, T.; Nakamura, M.; Nakamura, E. Indium Catalyzed 2-Alkenylation
of 1,3-Dicarbonyl Compounds with Unactivated Alkynes. J. Am. Chem. Soc.
2007, 129, 5264-5271.
10) Tsuji, H.; Fujimoto, T.; Endo, K.; Nakamura, M.; Nakamura, E. Stereoselective
Synthesis of Trisubstituted E-Iodoalkenes by Indium-Catalyzed syn-Addition of
1,3-Dicarbonyl Compounds to 1-Iodoalkynes. Org. Lett. 2008, 10, 1219-1221.
11) Kuninobu, Y.; Kawata, A.; Takai, K. Rhenium-Catalyzed Insertion of Terminal
Acetylenes into a C-H Bond of Active Methylene Compounds. Org. Lett. 2005, 7,
4823-4825.
12) Cheung, H. W.; So, C. M.; Pun, K. H.; Zhou, Z.; Lau, C. P.
Hydro(trispyrazolyl)borato-Ruthenium(II) Diphosphinoamino Complex-
Catalyzed Additiona of β-Diketones to 1-Alkynes and Anti-Markovnikov
Addition of Secondary Amines to Aromatic 1-Alkynes. Adv. Synth. Catal. 2011,
353, 411- 425.
13) Kuninobu, Y.; Kawata, A.; Nishi, M.; Takata, H.; Takai, K. Rhenium- and
Manganese-Catalyzed Insertion of Acetylenes into β-Ketoesters: Synthesis of 2-
Pyranones. Chem. Commun. 2008, 6360-6362.
14) Conley, B. L.; Williams, T. J. Dual Site Catalysts for Hydride Manipulation.
Comments Inorg. Chem. 2012, 32, 195-218.
15) Conley, B. L.; Williams, T. J. Thermochemistry and Molecular Structure of a
Remarkable Agostic Interaction in a Heterobifunctional Ruthenium-Boron
Complex. J. Am. Chem. Soc. 2010, 132, 1764-1765.
16) Halpern, J.; James, B. R.; Kemp, A. L. W. Catalysis of the Hydration of
Acetylenic Compounds by Ruthenium(III) Chloride. J. Am. Chem. Soc. 1961, 83,
4097-4098.
76
Chapter 4. Quantification of Ligand-Metal π-Bonding Using
Group 9 Dimethyldipyridylborate Complexes
4.1 Introduction
1
Unlike most bonds in traditional organic systems, transition metal-ligand binding
interactions range in nature across a wide diversity of strengths, sigma and pi
components, polarities, labilities, and reactivities. While one can develop a predictive
intuition for the reactivity of organic molecules, having the same command of the
reactivity of metal complexes requires a much wider knowledge base. Along these lines,
design and development of transition metal catalyzed reactions for organic synthesis
requires an effective, but simple, system to understand the stereoelectronic behavior of
non-reacting ligands that support the metal. For this reason, a number of useful systems
have been reported, including the Tolman Electronic Parameter (TEP),
2
Lever Electronic
Parameter (LEP)
3
and others.
Unfortunately, most of the current parameterization systems fail to separate σ and
π effects in a simple and broadly applicable way. π-Based binding effects can be critical
in governing the reactivity of a metal complex; in fact, this chapter will show that a
change in backbonding can skew a bond rotation barrier by 10 kcal/mol. Given the
importance of the electronic environment of the metal in designing catalysts,
4
we believe
that an easily measured, simple, energy-based parameter which allows the independent
analysis of π-effects will have utility in the organometallic community. Thus, this chapter
describes a system in which the barrier of a simple ring flip reports primarily the π
contribution to ligand-metal binding of the ancillary ligands on the metal. The tool is
simple, and because its output does not correlate with that of other ligand categorizing
systems, it offers new insight into the nature of metal binding to common ligating groups.
77
4.2 Quantification Parameters for Ligand-Metal Bonding
A large number of attempts to quantify ligand-metal bonding in meaningful ways
have been made. Described below are a few of the most prevalently used systems, as well
as those most relevant to our results. This is not a comprehensive review of quantification
experiments, but does provide a general overview of those parameters which have found
some degree of general use in the field of organometallic chemistry.
4.2.1 Tolman Electronic Parameter (TEP)
Two of the oldest and most well known ligand quantification parameters are
Chadwick Tolman’s cone angle and electronic parameter (TEP).
2
Tolman’s cone angle is
a simple way to compare steric properties, while the TEP, the energy of the symmetric
carbonyl stretch of the complex LNi(CO)
3
,
is a useful and commonly used parameter for
comparing ligand donor properties.
5
While Tolman’s work focused exclusively on
monodentate phosphines, TEPs have since been determined experimentally or
computationally for a number of other ligand types such as N-heterocyclic carbenes
(NHCs)
6
and divalent carbon(0) compounds.
7
Additionally, some groups have developed
the use of other metal carbonyls to compare to TEPs including iridium
8
and
molybdenum.
9
Finally, several attempts have been made to generate TEPs
computationally.
9,10
Despite the focus on phosphine donors and the inability to
distinguish σ and π effects, the TEP is still one of the primary methods for quantitatively
comparing ligands.
4.2.2 Lever Electronic Parameter
A second-generation approach to the quantification of the electronic effects of
ligands is the Lever electronic parameter (LEP), which measures the redox potential for
the reduction of Ru(III) to Ru(II) as a function of the ligands.
3
The LEP is defined as one-
78
sixth of the Ru(III)/Ru(II) potential in the RuL
6
complexes. LEP values have been
measured for over 200 different ligands. A important advantage of the LEP over the TEP
is the significantly broader ligand scope: the LEP is not restricted to neutral, monodentate
ligands. Where there is ligand overlap, the LEP shows good agreement with the TEP,
giving a Pearson coefficient,
11
or normalized covariance, of +0.99 (8 points, Figure 4.1)
4.2.3 Computational Electronic Parameter
Crabtree has expanded the utility of the TEP and LEP by developing a
computational method that generates a computational electronic parameter (CEP) which
shows good agreement with both TEP and LEP.
10
The CEP is based on the calculated A
1
ν(CO) vibration in (L)Ni(CO)
3
. From these calculated values, it was possible to
determine linear correlations with TEP (Pearson coefficient +0.98, Figure 4.2), LEP
(Pearson coefficient +0.96, Figure 4.3) and even σ
m
, the meta-substituted Hammet
parameter.
12
As a result of this excellent covariance, it is possible to approximate the TEP
or LEP for ligands which are not directly measurable. The ability to interconvert TEP,
Figure 4.1. Correlation between TEP (cm
-1
)
2
and LEP (V).
3
CO
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
2060 2070 2080 2090 2100 2110 2120 2130
LEP (V)
TEP (cm
-1
)
P(OMe)
3
PMePh
2
PMe
3
PEt
3
P(o-Tol)
3
PMe
2
Ph
PPh
3
79
LEP, and σ
m
through the intermediacy of the CEP demonstrates that all three parameters
essentially measure the same quantity.
4.2.4 Rotational Barrier of Diisopropylamidochromium(VI) Nitrido Complexes
More recently Odom et al. have reported a rotational barrier-based parameter
utilizing diisopropylamidochromium(VI) nitrido complexes (NCr(iPr
2
N)
2
(X), X =
monodentate, anionic ligand).
13
In these complexes, the isopropylamido groups are
Figure 4.2. Correlation between CEP (cm
-1
) and TEP (cm
-1
).
10
PF
3
PCl
3
PH
2
F
P(OMe)
3
PH
3
PMe
2
CF
3
PH
2
Me
PHMe
2
P(CH=CH
2
)
3
PMe
3
P(NMe
2
)
3
2050
2060
2070
2080
2090
2100
2110
2120
2140 2150 2160 2170 2180 2190 2200 2210
TEP (cm
-1
)
CEP (cm
-1
)
Figure 4.3. Correlation between CEP (cm
-1
) and LEP (V).
10
NO
+
CO
PHF
2
σN
2
H
2
O
C
2
H
4
P(OMe)
3
NH
3
Me
2
S
PMe
3
Cl
-
, I
-
, Br
-
CN
-
F
-
, HS
-
OH
-
-1
0
1
2
2050 2100 2150 2200 2250 2300
LEP (V)
CEP (cm
-1
)
80
observed to rotate about the chromium-amide bond. In the ground state, the nitrogen is
oriented such that it π-donates into acceptor orbitals near the xy-plane (Scheme 4.1, left
and right). As it rotates 90° around the chromium-nitrogen bond, it creates a filled-filled
π-interaction with the d
xz
/d
yz
orbitals, which are filled by the strongly donating nitrido
(Scheme 4.1, center). As the donor ability of X increases the barrier to rotation is reduced
due to destabilization of the ground-state π-donation. The rate of this rotation was
determined by measuring the exchange of the isopropyl methylenes using
1
H NMR Spin
Saturation Transfer (SST). These rates were used to determine ΔG
‡
as a function of X
Scheme 4.1. Rotation of Cr-N bond in the model complex NCr(NH
2
)
2
(X) proceeds
through a transition state where nitrogen can π-donate into d
xz
/d
xy
orbitals along the
nitrido vector. Atoms and bonds in the plane defined by N-Cr-N are shown in gray.
Figure 4.4. Plot of LDP (kcal/mol)
13
versus LEP (V).
3
SPh
F
NCO
Cl
I
Br
NO
3
NCS
CN
13
13.5
14
14.5
15
15.5
16
-0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1
LEP (cm
-1
)
LDP (kcal/mol)
81
using the Eyring equation. Odom concludes that the ΔH
‡
values can be used as a “ligand
donor parameter” (LDP) which measures the total donor ability of a given X-type ligand.
Interestingly, despite showing good covariance with other examples of measuring donor
ability
14
there is no clear correlation between LDP and LEP (Figure 4.4).
4.2.5 Classical Physical Organic Approaches
Other tools for quantification of metal-ligand bonding utilize classical quantitative
parameters used in physical organic chemistry, which enjoy some success and simplicity.
These examples range from pKa to the parameters developed by Hammett, Taft, and
others.
15
While these values may be useful predictors in cases where the ligands being
compared are all of a similar class (such as all alkoxy ligands or all ligands containing
para-substituted aryl groups), the validity of comparison decreases when comparing
ligands containing different donor atoms or the same donor atom in different
hybridization states. To supplement these methods, several examples of quantification of
ligand effects, both experimental and computational, for specific systems have been
published. These examples include substituted zirconocenes,
16
bidentate phosphines,
17
and N-heterocyclic carbenes.
18
While these studies are a useful contribution, they still do
not allow for general comparison across different ligand classes.
4.2.6 π-Orbital Axis Vector Analysis and Angular Overlap Model
In organic chemistry, one can use π-orbital axis vector (POAV) calculations to
separate σ- and π-contributions in non-planar conjugated organic molecules,
19
but this has
little relevance to organometallic complexes. The corresponding method for
organometallic species is the angular overlap model (AOM).
20
AOM is a computational
approach which allows the determination of orbital energies in transition metal
complexes. The overlap integrals include angular parameters, which allows for the
82
calculation of orbital energies even when the ligand orbital is not directed along an axis.
This inclusion of angular parameters also allows for the rotation of the coordinate system
such that it aligns with the ligand π-orbitals. This realignment of the coordinate system
enables the individual evaluation of the ligand-metal π-interaction. (See reference 20 for
a detailed explanation of the construction and evaluation of the overlap integrals.) While
AOM provides a computational approach to separating σ- and π-energies, it has not
gained widespread use.
21
4.2.7 Quantitative Analysis of Ligand Effects (QALE) Semi-Empirical Approach
QALE represents a semi-empirical attempt to quantify phosphine ligands in terms
of parameters that represent each aspect of the ligand.
9,22
Through extensive regression
and graphical analysis of available experimental data,
23
Giering developed a method
which resolves experimental data into four parameters: χ
d
, λ, E
ar
, and π
p
. χ
d
represents the
TEP, corrected to remove the π-acceptor contribution and the aromatic effect, E
ar
. The
steric parameter which corresponds to Tolman’s cone angle is represented by λ. E
ar
is an
additional electronic parameter that results from the influence exerted by aromatic groups
on phosphine and π
p
describes the π-acidic character. While QALE does successfully
separate the σ and π components of ligand binding, it is dependent on extensive
experimental data and is currently limited to phosphine ligands.
4.2.8 Limitations of Current Parameterization Systems
A limitation of all the parameterization methods mentioned thus far is their
inability to easily, independently quantify σ- and π-effects. The separation of these two
electronic effects is non-trivial, and while attempts have been made, both experimental
and computational, to generate quantitative values that separate the σ- and π-effects, no
simple, general method has yet been presented. Currently, the computational reports lack
83
experimental evidence to confirm their values
17,24
and the experimental methods require
less common technology such as EPR
25
and single-crystal electronic absorption.
26
Given
the importance of the electronic environment of the metal in designing catalysts,
4
an
easily measured parameter which allows the independent analysis of σ- and π-effects
would significantly improve the ability to tailor future catalysts with improved reactivity.
4.3 Design of a System to Selectively Parameterize π-Bonding
This problem drew our attention when it was observed that agostic bond
formation from borate complex 4.1 (chapter 1) was rapid relative to a boat-to-boat
interconversion, i.e., bond cleavage and formation (4.1 to 4.2) is more rapid than bond
rotation (4.1 to 4.1’, Scheme 4.2). This was unexpected, as it is known that most
scorpionate-style complexes with six-membered metallacycles undergo facile ring flip,
the rate of which has been measured in a variety of ways.
27
To explain the absence of the
ring flip in this complex, and suspecting a stereoelectronic effect, a series of square
planar complexes of rhodium(I) and iridium(I) bearing the dimethyldipyridylborate
ligand was designed. Analyzing the barrier to ring flip for these systematically varied
complexes showed the unexpected importance of Dewar-Chatt back-bonding
28
in
governing the flipping rate of the metallaborapyrimidine ring.
Scheme 4.2. Interconversion of 4.1 and 4.2 does not involve a ring flip to give 4.1’.
84
Due to the boat conformation of the ground state in complexes containing the
dimethyldipyridylborate ligand, the electron dense borate ligand is unable to
communicate with the pi symmetry orbitals on the metal: the dihedral angle between the
pyridine and metal planes is 49.3(4)° among all complexes. However, if the ring flip
proceeds through a planar transition state, π communication is selectively “turned on” as
the bonds rotate through the transition state, thus selectively stabilizing or destabilizing it
based on the preferences of the ancillary ligand set. We propose that the strength of this
interaction is directly correlated to the π-acceptor ability of the ancillary ligands, while
sigma bonding remains largely unaltered. Therefore, by measuring the relative barriers of
the ring flips strength of metal-ligand π-backbonding can be quantified. In sum, a
stronger π-acid in the ancillary ligand will enable a lower barrier to ring flip.
4.4 Synthesis and Structure of Rhodium and Iridium Complexes
Experimental data were collected with square planar rhodium(I) and iridium(I)
dimethyldipyridylborate complexes 4.3-4.7 of the type [(py)
2
BMe
2
]ML
2
where L
2
is
either two monodentate ligands or one bidentate ligand. These complexes are easily
prepared by simple salt metathesis between sodium dimethyldipyridylborate
([(py)
2
BMe
2
]Na)
29
and the corresponding chloro-bridged metal dimer ([L
2
MCl]
2
)
Scheme 4.3. Synthesis of Complexes 4.3-4.7.
85
(Scheme 4.3). This method was used for rhodium complexes featuring (CO)
2
(4.3a),
cyclooctadiene (4.4a), (tBuNC)
2
(4.5a), and (ethylene)
2
(4.6a) and the corresponding
iridium species 4.3b, 4.4b, and 4.5b. In cases where the precursor chloro-bridging dimer
was not commercially available (4.3b, 4.5ab), the dimers were prepared according to
literature procedures.
30
Phosphine complex 4.7a was synthesized by addition of 1,2-
bis(diphenylphosphino)ethane (dppe) to 4.6a.
Single crystal X-ray diffraction structures were obtained for complexes 4.3a, 4.4a,
and 4.4b. Figure 4.5 shows all three structures, which clearly illustrate the boat
conformation of the metallocycle. Note that in complex 4.3a a dihedral angle of 48.9(2)°
between the metal and pyridine planes and a C9-Rh distance of 3.200 Å were observed.
Table 4.1 shows these same metrics for the structures of 4.4ab: no significant difference
in structure is observed among these complexes.
4.3a
4.4a 4.4b
Figure 4.5. ORTEP diagrams for Complexes 4.3a and 4.4ab. Ellipsoids are drawn at the
50% probability level. H atoms have been omitted for clarity.
86
4.5 Kinetic Measurement of Metallocycle Ring Inversion
The NMR properties of boron-bound methyl groups in complexes 4.3-4.7 feature
two distinct, broad methyl peaks, which sharpen with reduced temperature. For example,
Figure 4.6 illustrates these peaks for complex 4.3a ([LRh(CO)
2
)]) between -30 and +40
°C. The wide separation between these signals over a very large temperature range
enables facile inversion recovery rate measurements
31
for magnetization transfer between
these two peaks, from which we obtained Eyring parameters for the ring flip. In cases
such as 1,5-cyclooctadiene complex 4.4a, the observed rate constant can be corroborated
by an analogous study of the protons on the ancillary ligand.
Table 4.1. Dihedral Angle and M-Me Distance for Complexes 4.3a and 4.4ab.
Complex Dihedral Angle (°)
a
M-Me (Å)
4.3a 48.9(2) 3.200 (C9)
4.4a 49.5(2) 3.315 (C11)
4.4b 49.7(2) 3.359 (C12)
a
Dihedral angles are calculated as an average of four measured torsion angles in the crystal structure.
Figure 4.6. NMR spectra showing the boron methyl signals of 4.3a from -30 °C to +40
°C. Referenced to toluene-d
8
. Note: complex is crystallized from diethyl ether.
87
These measurements were acquired over a broad range of temperatures (-50 °C to
95 °C), with the temperature range determined individually for each complex; for each
complex, spectra were acquired over a minimum range of 40 °C. All measured rates and
errors are shown in Table 4.2. Once the rates were known, the Eyring equation was used
to calculate ΔH
‡
and ΔS
‡
(Table 4.3). The ΔS
‡
values were expected to be zero or nearly
zero for this unimolecular process. The values obtained experimentally were quite small
and showed no consistent trend towards negative or positive. Based on the conclusion
that the ring flip is a unimolecular process, the barrier to ring flip is expected to be purely
enthalpic. Therefore, we choose to compare the values obtained for ΔH
‡
.
Experimental values for the energetic barriers for ring flips are shown in Table
4.3. Generally, those ligands that are π electron acceptors lower the barrier of the ring
flip. The effect is dramatic. For example, compare rhodium(I) complexes of tert-
butylisonitrile and the bidentate phosphine dppe (entries 1 and 5): adding π-acceptor
ability removes 9 kcal/mol from the ring flip barrier. This effect is systematic according
to π acceptor ability: cyclooctadiene and ethylene show levels of π-acidity similar to each
other.
The change in the relative barriers is not due to steric effects: the observed trend
opposes the one predicted by a steric argument. If steric crowding at the metal were
responsible, the barrier should decrease with increasing ligand size according to a ground
state destabilization argument. By contract, we observe that the bulkiest ligand (dppe,
4.7a, ΔH
‡
= 21.5 kcal/mol) has a significantly higher barrier than complexes of smaller
ligands such as CO and tert-butylisonitrile (ΔH
‡
= 15.5, 12.3 kcal/mol respectively),
therefore stereoelectronics must dominate.
88
Table 4.2. Rates and corresponding errors measured for complexes 4.3-4.7.
Complex Temperature (°C) er(T) (°C) k (s
-1
) er(k) (s
-1
)
[(py)
2
B(Me)
2
]Rh(CO)
2
(4.3a) -14.48 0.2 1.7410 0.0211
-9.84 0.2 3.1094 0.0301
-5.55 0.2 5.5690 0.0348
-0.07 0.2 9.6620 0.0851
9.85 0.2 27.7620 0.4509
16.70 0.2 53.5230 0.3929
20.07 0.2 71.5260 2.6480
25.00 0.2 109.4590 2.3860
[(py)
2
B(Me)
2
]Rh(cod) (4.4a) 24.15 0.2 0.5409 0.0066
40.06 0.2 2.2590 0.0301
47.43 0.2 3.9119 0.1319
55.63 0.2 8.3124 0.0558
66.10 0.2 18.2796 0.1783
[(py)
2
B(Me)
2
]Rh(CNtBu)
2
(4.5a) -53.19 0.2 0.2170 0.0694
-43.38 0.2 0.5978 0.0445
-32.67 0.2 2.4328 0.0620
-19.29 0.2 8.8486 0.2311
-12.44 0.2 19.1226 1.0998
-10.05 0.2 25.6949 2.9421
[(py)
2
B(Me)
2
]Rh(C
2
H
4
)
2
(4.6a) 24.50 0.2 0.6403 0.0147
34.69 0.2 1.8175 0.0386
44.97 0.2 3.9649 0.0518
55.41 0.2 9.5801 0.1110
65.81 0.2 19.5536 0.3997
[(py)
2
B(Me)
2
]Ir(CO)
2
(4.3b) -14.63 0.2 3.6980 0.2008
-0.08 0.2 14.7950 0.3815
10.05 0.2 42.0620 1.4550
24.27 0.2 155.1060 31.3127
[(py)
2
B(Me)
2
]Ir(cod) (4.4b) 24.27 0.2 0.4819 0.1618
39.88 0.2 2.3600 0.3934
46.72 0.2 4.2750 0.0318
54.56 0.2 7.5310 0.4196
69.99 0.2 25.1340 0.4149
[(py)
2
B(Me)
2
]Ir(CNtBu)
2
(4.5b) -54.41 0.2 0.4050 0.0359
-43.38 0.2 1.9388 0.0387
-32.58 0.2 7.1934 0.2282
-21.77 0.2 23.6337 0.7668
-11.33 0.2 75.5290 1.1767
[(py)
2
B(Me)
2
]Rh(dppe) (4.7a) 55.22 0.2 0.0975 0.0098
65.81 0.2 0.3395 0.0142
75.98 0.2 0.9464 0.0176
86.46 0.2 2.0120 0.0163
97.10 0.2 4.7410 0.0736
89
Ligands exhibit similar ring flip barriers in both rhodium(I) and iridium(I)
complexes: the flip barriers for dimethyldipyridylborate complexes of isonitrile (4.5ab),
CO (4.3ab), and cyclooctadiene (cod, 4.4ab) ligands differ pair wise by less than 1.5
kcal/mol despite the variation of size and bond strengths
32
between the second-and third-
row metals, which is interesting because it indicates that the energetics of the π-symmetry
backbonding is independent of these factors. This observation is consistent, however,
with the high homology in bond distances and angles around the ground states: for
example the average metal-nitrogen bond length is 2.1078(26) Å in 4.4a and 2.0998(17)
Å in 4.4b and the average metal-carbon bond length to the cod ligand is 2.137(4) Å in
4.4a and 2.126(3) Å in 4.4b. The bite angle of the borate ligand in 4.4a is 85.89(7)° and
86.00(5)° in 4.4b. It is interesting that these complexes exhibit significant homology
between the second- and third-row metals despite their size differences.
Table 4.3. Values for ΔH
‡
(kcal/mol) and ΔS
‡
(eu) for 4.3-4.7.
Entry Complex Experimental Calculated
ΔH
‡
(kcal/mol) ΔS
‡
(eu) ΔH
‡
(kcal/mol)
1 4.5a LRh(tBuNC)
2
12.3(7) -5.3(21) 14.4
a
2 4.8a LRh(NCMe)
2
- - 14.9
3 4.3a LRh(CO)
2
15.5(1) 2.8(5) 15.4
4 4.6a LRh(C
2
H
4
)
2
15.9(2) -6.0(5) -
5 4.4a LRh(cod) 16.2(2) -5.3(5) 17.1
6 4.9a LRh(NH
3
)
2
- - 17.6
7 4.10a LRh(AsH
3
)
2
- - 19.2
8 4.7a LRh(dppe) 21.5(3) 2.2(8) 19.5
b
9 4.5b LIr(tBuNC)
2
13.2(3) 0.8(9) -
10 4.3b LIr(CO)
2
14.2(5) -0.9(16) -
11 4.4b LIr(cod) 16.8(8) -3.4(24) -
a
tBuNC modeled as MeNC
b
dppe modeled as (PH
3
)
2
.
90
4.6 Computational Studies
Computational analysis by Prof. Richmond
33
predicts values for ΔH
‡
that are in
good agreement with the values obtained experimentally (Table 4.3, right). This adds
value to our observation because, knowing that the calculated values are calibrated to
experiment, meaningful values for additional ligands which are not easily prepared can
be predicted. Along this line, we determined calculated ligand flip barriers for rhodium
complexes of acetonitrile, NH
3
, AsH
3
. Relating the value obtained for acetonitrile back to
the original complex (4.1, Scheme 4.2), the calculated ΔG
‡
of 15.2 kcal/mol for the ring
flip acetonitrile complex 4.8a is near the measured ΔG
‡
for the formation of agostic
complex 4.2, ca. 16 kcal/mol over the temperatures studied in scheme 4.1. This makes
sense in the context that the ring flip from 4.1 to 4.1’ was not observed in the formation
of 4.2, while showing that its barrier is probably very close. Ammonia and arsine
complexes 4.9a and 4.10a have ring flip barriers near that of phosphine complex 4.7a,
which is consistent with a view that these ligands are similarly poor π acceptors. This
seems counterintuitive as we often think of phosphines as π acceptors.
34
4.7 Proposed Origin of the Barrier to Ring Flip
The observed barrier to ring flip is proposed to arise from an unfavorable filled-
filled interaction
35
between the pyridine π-system and filled metal d
xz
and d
yz
orbitals
which can exist in the transition state (Scheme 4.4). One manifestation of this interaction
Scheme 4.4. Diagram of the filled-filled π-interaction that would occur in a planar
transition state. The pyridine π-system is represented by a single p-orbital on nitrogen.
91
is observed in the calculated transition state; these complexes exhibit a twisted
confirmation in the transition state which minimizes the orbital overlap of the pyridine π-
system with the filled metal orbitals (Figure 4.7). In complexes with poor π-accepting
ligands, such as phosphine, this filled-filled interaction is accentuated and the calculated
transition state is observed to be strongly twisted. The reduction of the filled-filled
interaction thus reduces the energy of the transition state, lowering the barrier to ring flip.
Through the measurement of the ring flip barrier the π-acceptor capability of the ligand
can be directly quantified.
4.8 Comparison of Measured π-Bonding Parameters to Known
Parameters
Scientists have been attempting to parameterize ligand properties for many years
now, and while several valuable techniques have been produced, none yet exists which
can simply measure a ligand’s π-effects separately from its σ-effects. We propose that the
ΔH
‡
values reported here can be used as a parameter which measures exclusively a
ligand’s aptitude as a π-acceptor. Support for this conclusion is gained when one
compares the values obtained here to other parameters obtained for the same ligands.
4.8.1 Polarized Electronic Spectroscopy Data
Zink et al. have reported that, through the application of AOM
20
to the transition
energies observed in single-crystal polarized electronic absorption, they were able to
Figure 4.7. Calculated geometry of the ring flip transition state for 4.3a (left, 20° twist)
and [(py)
2
B(Me)
2
]Rh(PH
3
)
2
(right, 31° twist).
92
obtain parameters representing the σ and π interactions between the metal and ligand, e
σ
L
and e
π
L
respectively.
26
The observed transition energies for (Pr
4
N)[PtCl
3
L] were treated
with AOM to identify the absorption bands which correspond to values for e
σ
L
and e
π
L
;
e
π
L
was determined to be represented by the
1
B
2
-
1
A
2
energy difference. Comparison of
measured ΔH
‡
values with the
1
B
2
-
1
A
2
energy difference produces a linear correlation
with a Pearson coefficient of -0.97 (5 points, Figure 4.8). According to this method, large
energy differences correspond to strong π-acceptor ligands, which means the observed
inverse correlation supports the proposal that both methods are able to selectively
parameterize the π-acceptor ability of ligands with a simple spectroscopic test.
Interestingly, the
1
B
2
-
1
A
2
energy difference for NMe
3
does not correlate and is omitted
from the correlation above. While the ΔH
‡
calculated for NH
3
falls within the same range
as the other barriers observed, the measured
1
B
2
-
1
A
2
energy difference for NMe
3
is -2140
cm
-1
. This dramatic inconsistency is proposed to be the result of reported ambiguity in
the assignment of the energy of the
1
A
2
band in the spectroscopy.
36c
If one instead
Figure 4.8. Correlation of
1
B
2
-
1
A
2
energy difference
26
and ΔH
‡
(kcal/mol). PPh
3
was
used to compare to dppe and AsPh
3
was used to compare to AsH
3
. Computational data
was used for the ΔH
‡
of AsH
3
. NH
3
/NMe
3
(17.6, -2140) is excluded from the linear
regression.
CO
C
2
H
4
dppe/PPh
3
tBuNC
AsH
3
/AsPh
3
1700
1900
2100
2300
2500
2700
2900
3100
3300
11 13 15 17 19 21 23
1
B
2
-
1
A
2
(cm
-1
)
ΔH
‡
(kcal/mol)
93
compares the values for ΔH
‡
with the calculated values for e
π
L
,
26,36
the calculated e
π
L
value for NH
3
is observed to be similar to what is expected based on the calculated ΔH
‡
.
For this correlation, a Pearson parameter of 0.87 (6 points) is obtained (Figure 4.9).
Figure 4.10. Plot of TEP (cm
-1
)
3,8,10
versus ΔH
‡
(kcal/mol). MePPh
2
was used to compare
to dppe. Points marked with triangles indicate that computational data was used for one
or both values (ΔH
‡
: MeCN, NH
3
, and AsH
3
; TEP: MeCN, C
2
H
4
, NH
3
, and AsH
3
).
.
CO
C
2
H
4
dppe/MePPh
2
AsH
3
MeCN
NH
3
2060
2070
2080
2090
2100
2110
2120
2130
14 16 18 20 22
TEP (cm
-1
)
ΔH
‡
(kcal/mol)
Figure 4.9. Correlation of AOM-calculated
e
π
L
(cm
-1
)
26,36
and ΔH
‡
(kcal/mol). PPh
3
was
used to compare to dppe and AsPh
3
was used to compare to AsH
3
. Triangles indicate that
computational data was used for ΔH
‡
(NH
3
and AsH
3
).
CO
C
2
H
4
dppe/PPh
3
tBuNC
AsH
3
/AsPh
3
NH
3
-2000
-1500
-1000
-500
0
500
1000
1500
2000
2500
10 12 14 16 18 20 22 24
e
π
L
(cm
-1
)
ΔH
‡
(kcal/mol)
94
4.8.2 Tolman Electronic Parameter
When the ΔH
‡
values obtained here are plotted against experimentally or
computationally obtained TEPs, there is little relation between the two (Figure 4.10).
2,10
The Pearson coefficient between our values and the Tolman parameter is -0.57 (6 points)
which indicates little correlation and, if any relationship exists, it is inverse.
4.8.3 Lever Electronic Parameter
Comparing the ΔH
‡
values presented here with the LEP also results in no clear
correlation between the values (Figure 4.11). The LEPs for both a phosphine ligand and
tert-butylisonitrile are similar, while the values reported here indicate that they exhibit
very different electronic properties. The Pearson coefficient between our values and the
Lever parameter is -0.29 (8 points) which indicates little to no correlation and, again, if
any relationship exists, it is inverse.
Figure 4.11. Plot of LEP (V)
3,10
versus ΔH
‡
(kcal/mol). Norbornadiene (nbd) was used to
compare to cod. Points marked with triangles indicate that computational data was used
for one or both values (ΔH
‡
: MeCN, NH
3
, and AsH
3
; LEP: AsH
3
).
CO
C
2
H
4
cod/nbd
dppe
tBuNC AsH
3
MeCN
NH
3
0
0.2
0.4
0.6
0.8
1
1.2
11 13 15 17 19 21 23
LEP (V)
ΔH
‡
(kcal/mol)
95
In stark contrast to the comparison of ΔH
‡
to TEP and LEP, we observe pair-wise
correlation of +0.99 (8 points) between Tolman and Lever parameter sets. The disparity
in magnitude (and sign) of this correlation parameter as compared to those with ΔH
‡
is a
remarkable testament to the separation of σ and π effects that is intrinsic to this unique
parameterization system.
4.9 Conclusions
The technique described here is a simple way to obtain basic information about a
ligand’s π-acceptor properties to aid in the intentional design of new catalyst species. To
further support the unique place of this method, its correlation and non-correlations to
several established ligand parameterization systems were examined and very little
correlation with those methods which are known to measure the combined effect of both
σ- and π-interactions was found. However, we found good agreement with spectroscopic
measurements that report exclusively the π-interactions. Thus, reported here is a system
that graduates ligands, experimentally and computationally, based solely on π effects,
which could not previously be easily isolated. The addition of this method will further aid
the organometallic community in both understanding mechanism and designing new,
tailored catalysts.
96
4.10 References
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98
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0
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24) (a) Fielder, S. S.; Osborne, M. C.; Lever, A. B. P.; Pietro, W. J. First-Principles
Interpretation of Ligand Electrochemical (EL(L)) Parameters. Factorization of the
σ and π Donor and π Acceptor Capabilities of Ligands J. Am. Chem. Soc. 1995,
117, 6990-6993. (b) Antonova, N. S.; Carbo, J. J.; Poblet, J. M. Quantifying the
Donor–Acceptor Properties of Phosphine and N-Heterocyclic Carbene Ligands in
Grubbs’ Catalysts Using a Modified EDA Procedure Based on Orbital Deletion.
Organometallics 2009, 28, 4283-4287.
25) Lukens, W. W.; Smith, M. R.; Andersen, R. A. A π-Donor Spectrochemical
Series for X in (Me
5
C
5
)
2
TiX, and β-Agostic Interactions in X = Et and N(Me)Ph.
J. Am. Chem. Soc. 1996, 118, 1719–1728.
26) Chang, T. H.; Zink, J. I. The σ and π Interactions of the Carbonyl Ligand
Determined from Single-Crystal Polarized Electronic Spectroscopy and Ligand
Field Theory. J. Am. Chem. Soc. 1987, 109, 692–698.
27) (a) Trofimenko, S. Boron-pyrazole chemistry. IV. Carbon- and Boron-Substituted
Poly[(1-pyrazolyl)borates]. J. Am. Chem. Soc. 1967, 89, 6288-6294. (b) Echols,
H. M.; Dennis, D. Crystal and Molecular Structure of Bis[diethyl bis(1-
pyrazolyl)borato]nickel(II). Evidence for Apical Positioning of the Methylene
Hydrogen in the Square Planar Nickel Complex. Acta Cryst. 1974, B30, 2173-
2176. (c) Herring, F. G.; Patmore, D. J.; Storr, A. Spectroscopic Studies on
Pyrazolylgallate and -Borate Complexes of Copper(II) and Nickel(II). J. Chem.
Soc., Dalton Trans. 1975, 711-717. (d) Keyes, M. C.; Young, V. G. Jr; Tolman,
W. B. Diastereoselective Intramolecular C-H bond Activation by Optically Active
Tris(pyrazolyl)hydroborate Complexes of Rhodium. Organometallics 1996, 15,
99
4133-4140. (e) Hikichi, S.; Fujita, K.; Manabe, Y.; Akita, M.; Nakazawa, J.;
Komatsuzaki, H. Coordination Properties of Organoborate Ligands - Steric
Hindrance Around the Distal Boron Center Directs the Conformation of the
Dialkylbis(imidazolyl)borate Scaffold. Eur. J. Inorg. Chem. 2010, 5529-5537.
28) Chatt, J.; Duncanson, L. A. Olefin Coordination Compounds. III. Infrared Spectra
and Structure: Attempted Preparation of Acetylene Compounds. J. Chem. Soc.
1953, 2939-2947.
29) a) Hodgkins, T. G.; Powell, D. R. Derivatives of the Dimethylbis(2-
pyridyl)borate(1-) Ion: Synthesis and Structure. Inorg. Chem. 1996, 35, 2140–
2148. b) Khaskin, E.; Zavalii, P. Y.; Vedernikov, A. N. Facile Arene C-H Bond
Activation and Alkane Dehydrogenation with Anionic LPt
II
Me
2
- in Hydrocarbon-
Water Systems (L = Dimethyldi(2-pyridyl)borate). J. Am. Chem. Soc. 2006, 128,
13054–13055.
30) (a) Werner, H.; Hofmann, L.; Feser, R.; Paul, W. Basic Metals. XLIX. Half-
Sandwich Type Compounds C
5
H
5
RhL
2
and C
5
H
5
RhLL' as Synthetic Synthons for
Carbenoid- and Yliderhodium(III) Complexes. J. Organomet. Chem. 1985, 281,
317-347. (b) Roberto, D.; Cariati, E.; Psaro, R.; Ugo, R. Formation of
[Ir(CO)
2
Cl]
x
(x = 2, n) Species by Mild Carbonylation of [Ir(cyclooctene)
2
Cl]
2
Supported on Silica or in Solution: A New Convenient Material for the Synthesis
of Iridium(I) Carbonyl Complexes. Organometallics 1994, 13, 4227–4231.
31) Williams, T. J.; Kershaw, A. D.; Li, V.; Wu, X. An Inversion Recovery NMR
Kinetics Experiment. J. Chem. Educ. 2011, 88, 665-669. We prefer the classical
1-D inversion recovery to 2-D EXSY because of its ease of quantification, low
statistical error, and high precision.
32) Regarding metal-methyl bonds see (a) Armentrout, P. B. Guided Ion Beam
Studies of Transition Metal-Ligand Thermochemistry. Int. J. Mass. Spectrom.
2003, 227, 289-302. (b) Uddin, J.; Morales, C. M.; Maynard, J. H.; Landis, C. R.
Computational Studies of Metal-Ligand Bond Enthalpies across the Transition
Metal Series. Organometallics 2006, 25, 5566-5581. Consistent with our
observations, a study on the bonding energy of N-heterocyclic carbenes (NHCs)
to group 10 metals reports similar π-contributions in second and third row
complexes, while first row complexes have a much larger π-contribution of 43%.
(c) Radius, U.; Bickelhaupt, F. M. Bonding Capabilities of Imidazol-2-ylidene
Ligands in Group-10 Transition-Metal Chemistry. Coord. Chem. Rev. 2009, 253,
678-686.
33) Calculations were performed by Prof. Michael Richmond at the University of
North Texas using Gaussian 09 and the hybrid functional B3LYP; the rhodium
100
was described by a the Stuttgart-Dresden effective core potential (ecp) and SDD
basis set, with the remaining atoms employing a 6-31G(d’) basis set.
34) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals; Wiley &
Sons: Hoboken, 2005; p 87-124.
35) Caulton, K. G. The Influence of π-Stabilized Unsaturation and Filled/Filled
Repulsions in Transition Metal Chemistry. New J. Chem. 1994, 18, 25-41.
36) (a) Chang, T. H.; Zink, J. I. Inorg. Chem. 1986, 25, 2736-2741. (b) Chang, T. H.;
Zink, J. I. J. Am. Chem. Soc. 1984, 106, 287-292. (c) Chang, T. H.; Zink, J. I.
Inorg. Chem. 1985, 24, 4499-4503.
101
Chapter 5. Synthesis and Structures of Nickel(II)
Dimethyldipyridylborate Complexes
5.1 Introduction
While the iridium and rhodium complexes of dimethyldipyridylborate (Chapter 4)
have not yet been tested for catalytic competency, the ruthenium analogs (5.1 and 5.2,
Chapter 1) have been shown to catalyze a number of desirable reactions including the
dehydrogenation of ammonia borane,
1
reduction of carbon dioxide, alkane borylation and
cyanation.
2
For industrial scale applications, catalysts based on first row metals are
strongly preferred, due to the decreased cost and low toxicity associated with the first
row.
3
For that reason, we desired to expand this ligand scaffold to a first-row metal for
use in further investigations of ammonia borane dehydrogenation and reduction of carbon
dioxide. Therefore, the possibilities of synthesizing a dimethyldipyridylborate complex of
a first row metal were explored in our group.
The existence of bis(dimethyldipyridylborate)nickel(II) and reports of nickel
catalyzed ammonia borane dehydrogenation
4
and carbon dioxide reduction
5
motivated
the pursuit of nickel. We concluded that the bis(dimethyldipyridylborate)nickel(II) was
unlikely to be catalytically competent due to its stability and noted insolubility
6
and that a
mono(dimethyldipyridylborate)nickel(II) would be more likely to exhibit catalytic
Figure 5.1. Dimethyldipyridylborate complexes of ruthenium.
102
activity. The strategy of salt metathesis applied to the synthesis of the rhodium and
iridium complexes in Chapter 4 was adapted to nickel and two
mono(dimethyldipyridylborate)nickel(II) complexes were obtained:
(dimethyldipyridylborate)(triphenylphosphine)nickel(II) chloride (5.27, Scheme 5.12)
and (dimethyldipyridylborate)nickel(II) acetylacetonate (5.29, Scheme 5.15). These
complexes exhibit significant substitutional lability, the mechanism of which we have
begun to study. This demonstrated lability shows promise of catalytic competency.
5.2 Selected Chemistry of Nickel Complexes
The reactivity of nickel complexes has been reviewed extensively.
7
Specifically,
nickel complexes are well known as catalysts for alkene polymerization reactions.
8
Of
interest to our group is the demonstrated activity of nickel complexes toward activation
of CO
2
. Along with the need for a greener energy source (such as hydrogen) the need to
reduce CO
2
is one of the major environmental chemistry challenges facing the world
today. In addition to reducing production of CO
2
, the ability to capture CO
2
and convert it
into a useful chemical feedstock has the potential to significantly impact the course of
global warming.
Several examples of nickel-catalyzed CO
2
activation have been described.
Regarding direct reduction of CO
2
, Guan et al. have published POCOP pincer ligated
nickel(II) complexes (such as 5.3) which catalyze the reduction of CO
2
with either
LiAlH
4
or catecholborane (HBcat) through the intermediacy of a nickel hydride
Scheme 5.1. Reduction of CO
2
with HBcat using Ni-POCOP 5.3.
9a
103
(Scheme 5.1).
9
Hazari reported the activation of CO
2
resulting in the formation of nickel
carboxylates from PCP supported nickel (Scheme 5.2)
10
and also described the insertion
of CO
2
into an allyl-nickel bond in (allyl)
2
NiL complexes, where L = phosphine or N-
heterocyclic carbene (NHC).
11
Another example of addition of CO
2
to a ligand has been
demonstrated by Milstein. Utilizing their bifunctional PNP ligand (Chapter 1), conditions
are reported wherein carbon dioxide is observed to add to the ligand backbone (Scheme
5.3).
12
Other reports of CO
2
activation by nickel regard the functionalization of organic
substrates. There are numerous examples of nickel-catalyzed [2 + 2 + 2] reactions
between diynes and CO
2
to form 2-pyrones. While most examples of this reaction require
high pressures of CO
2
(10 – 50 atm),
13
Louie et al. have reported high yielding conditions
Scheme 5.4. [2 + 2 + 2] cycloaddition catalyzed by an NHC ligated Ni(0).
14b
Scheme 5.2. Insertion of CO
2
into Ni-E bonds (E = H, Me, or allyl).
Scheme 5.3. Addition of CO
2
to the PNP backbone of 5.6.
104
that necessitate only 1 atm of CO
2
(Scheme 5.4).
14
Other examples of nickel catalyzed
addition of CO
2
to organic substrates include direct carboxylation of benzyl halides
(Scheme 5.5A)
15
and reductive hydroesterification of styrenes (Scheme 5.5B).
16
One
other instance of nickel reactivity that is of particular interest to our group is the
reversible addition of H
2
across a nickel-borane unit reported by Peters.
17
In this system,
H
2
is reversibly activated by cooperative catalysis between the nickel and the ligand
bound boron (Scheme 5.6). The combination of examples of nickel-based CO
2
activation
and the ability of a cooperative nickel-boron catalyst to activate H
2
presents a promising
platform for initiation of our investigations of a (dimethyldipyridylborate)nickel(II)
species.
Scheme 5.5. Nickel-catalyzed carboxylation of benzyl chloride with CO
2
(A)
15
and
Nickel-catalyzed hydroesterification of styrene with CO
2
(B).
16
(dippe = 1,2-bis(di-
isopropylphosphino)ethane).
Scheme 5.6. Reversible addition of H
2
across a nickel-borane unit.
17
105
5.3 Fluxional Behavior of Square Planar Metal Complexes
Square planar metal complexes are known to undergo isomerization to
interconvert between cis and trans isomers. As a result of the prevalence of square planar
platinum and palladium complexes in catalysis, mechanisms of this type of isomerization
have been studied extensively to further understand mechanisms of catalysis.
18
In cases
where the complex contains a symmetrical chelating ligand, isomerization appears as a
pseudorotation
19
as the isomerized complex is identical to the starting material. While it
is more difficult to identify and measure isomerization in complexes of this type,
isomerization is assumed to occur through the same mechanisms as other cis and trans.
The isomerization of a large number of square planar transition metal complexes has
been studied in detail, both computationally and experimentally by utilizing techniques
such as NMR spectroscopy and spectrophotometry.
20
These studies have led to the identification of two classes of isomerization:
associative and dissociative (Scheme 5.7), with associative mechanisms being
significantly more common. Associative isomerization can proceed through two
Scheme 5.7. Potential mechanisms of isomerization in square planar complexes.
106
mechanisms: Berry pseudorotation (Scheme 5.7, pathway II)
21
or consecutive
displacement (Scheme 5.7, pathways I and III). All associative isomerizations initiate by
coordination of a “catalytic” molecule to form a five-coordinate intermediate, such as that
shown in Scheme 5.8. This catalytic molecule can be an added base, excess ligand or
solvent. In the case of pseudorotation, the five coordinate intermediate isomerizes to a
trigonal bipyramid in which ligands can be exchanged via the Berry mechanism,
followed by dissociation of the catalytic ligand (Scheme 5.8). In the consecutive
displacement mechanism, coordination of the catalytic ligand is followed by either loss of
an anionic ligand to generate a cationic metal species (Scheme 5.7, pathway III) or
dissociation of a neutral ligand to generate a neutral metal species (Scheme 5.7, pathway
I). This is followed by re-coordination of the original ligand and loss of the catalytic
ligand. Some authors contend that displacement of a neutral ligand would not result in
isomerization due to the stereospecific nature of ligand substitutions,
18
while others claim
to have definitively proven the existence of the neutral intermediate.
22
There is also
debate about the existence of complexes which isomerize via the pseudorotation
mechanism and disagreement about what evidence definitively proves a pseudorotation
mechanism over a consecutive displacement mechanism.
18,23
Scheme 5.8. Isomerization via Berry pseudorotation of a five-coordinate intermediate.
107
However, supposing that all three mechanisms are accessible, it is possible that
multiple isomerization pathways are available to each compound and choice of solvent
could result in a change of mechanism.
24
Consecutive displacement of an anion (pathway
III) would be favored in polar solvents when the anionic ligand X
-
is poorly coordinating,
while displacement of a neutral ligand would be preferred in non-polar solvents when X
-
is strongly coordinating (pathway I). Pseudorotation is proposed to be favored in
nonpolar solvent when L and L’ have similar basicity and are small (pathway II).
22
Square planar complexes bearing bidentate ligands which possess the ability to become
tridentate, such as complexes where hydridotris(pyrazolyl)borate or
hydridobis(pyrazolyl)(thioxotriazolyl)borate is bidentate in the ground state are generally
accepted to isomerize via a pseudorotation mechanism (Scheme 5.9). These complexes
have been shown to isomerize via a tridentate intermediate that undergoes
pseudorotation.
25
Scheme 5.9. Isomerization via pseudorotation of a complex bearing a ligand with multiple
coordination modes.
108
While it is difficult to distinguish among the types of associative isomerization, it
is straightforward to classify an isomerization as associative: if isomerization is
accelerated by addition of a coordinating species, isomerization proceeds through an
associative mechanism. Conversely, whether the absence of acceleration is evidence of a
dissociative mechanism is disputed.
18
In theory, dissociative isomerization proceeds
through loss of a ligand, either X
-
to generate a cationic tricoordinate complex (Scheme
5.7, pathway V) or L to generate a neutral tricoordinate complex (Scheme 5.7, pathway
IV). Retardation of rate in the presence of excess ion or ligand, isomerization in the
absence of potential ligands, including coordinating solvents, and positive ΔS
‡
are often
taken as evidence of a dissociative process but definitive evidence of the existence of a
three-coordinate intermediate is required to conclusively prove a dissociative
mechanism.
20c,d
5.4 Structure and Reactivity of Nickel Complexes with Anionic Bis-
Nitrogen Chelating Ligands
There is literature precedent for the synthesis and isolation of stable nickel(II)
complexes with anionic bis-nitrogen chelating ligands, the most common being
dihydrobis(pyrazolyl)borate (Bp).
26
The structure of (Bp)Ni complexes has been studied
extensively. It has been shown that when the pyrazole ring bears small substituents (H,
Scheme 5.10. Structures of Bp
2
Ni complexes: bis(bipyrazolylborate)nickel(II) (5.18) and
bis(3-tert-butylpyrazolylborate)nickel(II) (5.19).
109
Me) the Bp
2
Ni complexes (such as 5.18) adopt a trans double boat confirmation that is
square planar at nickel (5.18, Scheme 5.10).
27
However, when the pyrazole is substituted
by a bulky group such as tert-butyl, the resulting complexes are octahedral, with Ni–H–B
agostic bonds filling the apical coordination sites (5.19, Scheme 5.10).
28
Bp nickel
complexes and other nickel species bearing anionic bis-nitrogen ligands have been shown
to be competent catalysts for a variety of transformations including ethylene
polymerization (Figure 5.2A),
29
nitrene transfer to isocyanides (Figure 5.2B)
30
and
Kumada coupling reactions (Figure 5.2C).
31
A series of Bp-ligated nickel(II) complexes of particular relevance, are the
BpNi(PMe
3
)R (R = CH
2
SiMe, CH
2
CMe
3
, C
6
H
5
) complexes synthesized by Paneque.
32
These complexes have been shown to insert CO into the Ni-R bond when R = CH
2
SiMe
3
or CH
2
CMe
3
(Scheme 5.11A). In addition, while all three complexes undergo the boat-to-
boat ring flip common among bidentate scorpionates (Chapter 4), when R = C
6
H
5
(5.24c)
the complex also exhibits isomerization to average the
1
H NMR resonances of both
pyrazolyl rings (Scheme 5.11B). The authors propose that this is occurring via an
associative mechanism (vide supra) based on the
31
P NMR indication of exchange
between bound and free PMe
3
in the presence of excess PMe
3
.
Figure 5.2. Structures of nickel catalysts for ethylene polymerization (A), nitrene transfer
(B) and Kumada coupling (C) supported by anionic bis-nitrogen ligands.
110
While the existence of complexes that isomerize via a dissociative mechanism is
debated, proposals of dissociation of a donor ligand from nickel complexes bearing
anionic bis-nitrogen chelating ligands are present in the literature. In 5.22 (Figure 5.2),
the complex exchanges bound and free lutidine at room temperature and addition of
excess lutidine decreases the catalytic activity of 5.22 for Kumada coupling. The related
complex 5.23 does not exchange bound phosphine for free phosphine at room
temperature. However, at -20 °C the addition of excess triphenylphosphine decreases the
catalytic activity.
31b
Taken together these results suggest that a key step in the catalytic
cycle is dissociation of triphenylphosphine to form a three-coordinate intermediate.
5.5 Synthesis and Structure of Nickel(II) Dimethyldipyridylborate
Complexes
Whereas the synthesis of bis(dimethyldipyridylborate)nickel(II) was already
reported, the synthesis a mono(dimethyldipyridylborate)nickel(II) species was desired.
The synthesis of such a complex was approached using a salt metathesis strategy similar
to that used for rhodium and iridium complexes (Chapter 4). The reaction of one
Scheme 5.11. Reactivity (A) and fluxional behavior (B) of complexes of the type
BpNi(PMe
3
)R.
111
equivalent of bis(triphenylphosphine)nickel(II) chloride with sodium
dimethyldipyridylborate (5.26) in dichloromethane produces
(triphenylphosphine)(dimethyldipyridylborate)nickel(II) chloride (5.27) in 71% isolated
yield (Scheme 5.12). The formation of 5.27 is plagued by the thermodynamically favored
formation of bis(dimethyldipyridylborate)nickel(II) (5.28). Even when isolated cleanly,
5.27 was found to undergo facile disproportionation in solution to form 5.28 and
bis(triphenylphosphine)nickel(II) chloride (Scheme 5.13).
Following the synthesis of 5.27, I attempted form a
(dimethyldipyridylborate)nickel(II) acetate or (dimethyldipyridylborate)nickel(II)
acetylacetonate. Initially, these attempts focused on the reaction of one equivalent of
either nickel(II) acetate tetrahydrate (Ni(OAc)
2
·H
2
O) or nickel(II) acetylacetonate
(Ni(acac)
2
) with sodium dimethyldipyridylborate (5.26). Under these conditions this
reaction resulted exclusively in the formation of bis(dimethyldipyridylborate)nickel(II)
(Scheme 5.14). To circumvent the formation of 5.28, using a large excess of nickel(II)
Scheme 5.13. Conversion of 5.27 to 5.28.
Scheme 5.12. Synthesis of [(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27).
112
acetylacetonate (2.5 equivalents) was found to result in clean formation of
(dimethyldipyridylborate)nickel(II) acetylacetonate (Scheme 5.15). This compound was
isolated in 67% yield.
Both 5.27 and 5.29 were characterized by single crystal X-ray crystallography and
the structures are displayed in Figure 5.3. In 5.29, the ligands are square planar around
nickel (sum of angles around nickel 360.03(7)°). In 5.27, the ligands exhibit a distorted
square planar confirmation (sum of angles around nickel is 361.6(2)°), with the P-Ni-Cl
plane tilted 14° relative to the N-Ni-N plane (Figure 5.4). A similar compound bearing an
anionic bis-nitrogen chelating ligand, 5.20 (Figure 5.2), adopts a fully tetrahedral
conformation.
29
While 5.20 exhibits greater steric congestion near the metal, the distorted
structure of 5.27 suggests that the tetrahedral conformation is likely the result of a
combination of electronic and steric effects. This proposal is supported by the distorted
square planar conformation of another nickel complex (5.22, Figure 5.2) bearing an
Scheme 5.14. Formation of 5.28 from nickel(II) acetate or nickel(II) acetylacetonate.
Scheme 5.15. Synthesis of [(py)
2
BMe
2
]Ni(acac) (5.29).
113
anionic bis-nitrogen chelating ligand and triphenylphosphine.
31b
As in all previous
complexes of dimethyldipyridylborate, the six-membered ring exhibits a boat
confirmation in both compounds. The dihedral angle between metal and pyridine planes
in 5.29 is 47.9(2)° which is similar to that observed in the related rhodium and iridium
complexes (Chapter 4). However, in 5.27 the angle is 53.3(4)° indicating that the
dimethyldipyridylborate ligand is titled farther out of plane in this complex. This larger
angle is similar to that reported for 5.28, 52.9(1)°.
6
In agreement with the observation of
the increased tilt is the decreased distance between nickel and the carbon in the boron-
bound methyl group in 5.27: 3.147 Å versus 3.171 Å in 5.29. Both of these metal-methyl
distances are shorter than those observed in the rhodium and iridium structures (3.200 –
3.354 Å). This decrease in the distance between the metal and the methyl group indicates
increased potential for Ni-Me interactions in these complexes. In 5.29 the Ni-N bonds are
equivalent (1.8948(9) and 1.8943(9) Å) as are the Ni-O bonds (1.8606(8) and 1.8558(8)
Å). Complex 5.27 exhibits the expected trans effect with the Ni-N bond trans to
triphenylphosphine longer than that trans to the chloride (1.947(3) and 1.898(3) Å,
5.27 5.29
Figure 5.3. ORTEP diagrams of 5.27 and 5.29. Ellipsoids are drawn at the 50% probability
level. H atoms omitted for clarity. 5.27 was observed to cocrystallize with ½ hexanes,
which was removed by Squeeze.
114
respectively). The Ni-N bond lengths in both 5.27 and 5.29 are consistent with those
observed for 5.28 (1.906(2) and 1.902(2) Å) and are shorter than those measured for the
rhodium and iridium complexes (2.082(2) - 2.108(3) Å).
5.6 Lability of Dimethyldipyridylborate Complexes of Nickel(II)
First-row metal complexes of dimethyldipyridylborate have been found to exhibit
significant inter- and intra-molecular lability. While this is consistent with the reported
behavior of related complexes, it is inconsistent with the observed robust nature of
dimethyldipyridylborate complexes of second- and third-row metals and the stability of
5.28. As mentioned above, in the case of 5.27, dissolution of the complex in
dichloromethane, benzene, or toluene results in the formation of a small amount of 5.28
(Scheme 5.13). Heating these solutions at 60 °C promotes further disproportionation,
with complete conversion after approximately 4 days. Similar lability has prevented the
isolation of dimethyldipyridylborate copper(I) complexes,
33
with the exception of
complexes bearing very bulky NHC ligands.
34
Complex 5.27 also exhibits intramolecular fluxionality, undergoing a rapid cis-
trans type isomerization at room temperature which equilibrates both sets of pyridine
Figure 5.4. Cross-eyed stereoview of 5.27, highlighting the distorted square planar
conformation at nickel.
115
resonances in
1
H NMR. Paneque et al. report similar behavior of BpNi(Ph)(PMe
3
)
(5.24c), which they conclude to occur via an associative mechanism (vide supra).
32
Several kinetics experiments have been conducted in an attempt to elucidate the
mechanism of isomerization in 5.27. First, inversion recovery kinetics analysis
35
was
used to measure the rate of isomerization of 5.27 in the absence of excess phosphine,
from which we obtained the activation parameters of ΔH
‡
= 12.6(7) kcal/mol and ΔS
‡
=
2.2(27) eu using the Eyring equation. The measured rates are shown in Table 5.1. The
observation of a ΔS
‡
that is effectively zero suggests that the rate determining step is an
intramolecular process, which is inconsistent with both associative and dissociate
mechanisms. Second, the rate of isomerization at -40 °C as a function of concentration of
triphenylphosphine (0.5 eq. – 10 eq., 7 – 126 mM) has been measured (Figure 5.5). No
clear trend is observed; the data suggests the possibility of different mechanisms at low (7
– 20 mM) and high phosphine concentration (20 – 126 mM).
We have observed circumstantial evidence that supports a dissociative
mechanism. Complex 5.27 is observed to undergo rapid isomerization in non-
coordinating solvents (dichlormethane-d
2
, benzene-d
6
and toluene-d
8
) and in the absence
of free ligand. Additionally, 5.27 is observed to be unstable in acetonitrile: upon
dissolving 5.27 in acetonitrile an unidentified green precipitate is immediately formed.
Table 5.1. Rates and corresponding errors measured for the isomerization of 5.27.
Temperature (°C) er(T) (°C) k (s
-1
) er(k) (s
-1
)
-18.93 0.2 204.533 12.4866
-32.64 0.2 60.2004 0.72787
-46.82 0.2 12.7834 0.08534
-61.63 0.2 1.09511 0.00961
116
This finding supports dissociation of triphenylphosphine to create an open coordination
site which is filled by acetonitrile, generating an unstable species. However, at this point
there are insufficient data to establish the mechanism of isomerization conclusively.
Further experiments are being conducted to explore the fluxional behavior of 5.27 in
detail. Regardless of the mechanism, the observation of rapid isomerization is promising
for future catalytic studies, as it indicates the availability of an open coordination site on
nickel which could coordinate a substrate molecule.
5.7 Conclusions
This chapter reports the synthesis and structural studies of two
mono(dimethyldipyridylborate)nickel(II) complexes. While [(py)
2
BMe
2
]Ni(acac) (5.29)
exhibits the expected square planar structure, [(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27) adopts a
distorted square planar conformation. In addition, 5.27 exhibits significant substitutional
lability, both inter- and intramolecularly. At this time, the intramolecular isomerization is
proposed to occur via a complicated mechanism and further studies will attempt to
Figure 5.5. Plot of ln[PPh
3
] versus ln[k
obs
] for the isomerization of 5.27.
2.8
3
3.2
3.4
3.6
-6 -5 -4 -3 -2 -1
ln(k
obs
)
ln[PPh
3
]
117
discover the details. Additionally, the ability of these complexes to catalyze reactions
including CO
2
activation and NH
3
BH
3
dehydrogenation will be investigated. The
observed lability of these complexes promises the potential for significant catalytic
activity.
118
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119
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. Organometallics 2013, 32, 300–308.
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/Trialkylphosphine Catalysts.
Synlett 2005, 2141–2146. (c) Tsuda, T.; Morikawa, S.; Sumiya, R.; Saegusa, T.
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Nickel-Catalyzed [2 + 2 + 2] Cycloaddition of CO
2
and Diynes. J. Am. Chem.
Soc. 2002, 124, 15188–15189.
120
15) León, T.; Correa, A.; Martin, R. Ni-Catalyzed Direct Carboxylation of Benzyl
Halides with CO
2
. J. Am. Chem. Soc. 2013, 135, 1221-1224.
16) González-Sebastián, L.; Flores-Alamo, M.; García, J. J. Nickel-Catalyzed
Reductive Hydroesterification of Styrenes Using CO
2
and MeOH.
Organometallics 2012, 31, 8200–8207.
17) Harman, W. H.; Peters, J. C. Reversible H
2
Addition across a Nickel-Borane Unit
as a Promising Strategy for Catalysis. J. Am. Chem. Soc. 2012, 134, 5080-5082.
18) Anderson, G. K.; Cross, R. J. Isomerisation Mechanisms of Square-Planar
Complexes. Chem. Soc. Rev. 1980, 9, 185-215.
19) IUPAC defines pseudorotation as a conformational change resulting in a structure
that appears to have been produced by rotation of the entire initial molecule and is
superimposable on the initial one, unless different positions are distinguished by
substitution or isotopic labeling.
20) For a few examples see (a) Albright, T. A.; Hoffmann, R.; Thibeault, J. C.; Thorn,
D. L. Ethylene Complexes. Bonding, Rotational Barriers, and Conformational
Preferences. J. Am. Chem. Soc. 1979, 101, 3801–3812. (b) Redfield, D. A.;
Nelson, J. H. Equilibrium Energetics of Cis-Trans Isomerization for Two Square-
Planar Palladium(II)-Phosphine Complexes. Inorg. Chem. 1973, 12, 15–19. (c)
Romeo, R.; Plutino, M. R.; Elding, L. I. Protonolysis of Dialkyl- and
Alkylarylplatinum(II) Complexes and Geometrical Isomerization of the Derived
Monoorgano−Solvento Complexes: Clear-Cut Examples of Associative and
Dissociative Pathways in Platinum(II) Chemistry. Inorg. Chem. 1997, 36, 5909–
5916. (d) Bartolomé, C.; Espinet, P.; Martín-Álvarez, J. M.; Villafañe, F.
Bis(fluoromesityl) Palladium Complexes, Archetypes of Steric Crowding and
Axial Protection byortho Effect − Evidence for Dissociative Substitution
Processes − Observation of
19
F−
19
F Through-Space Couplings. Eur. J. Inorg.
Chem. 2004, 2326–2337. (e) Yang, F.-Z.; Wang, Y.-H.; Chang, M.-C.; Yu, K.-H.;
Huang, S.-L.; Liu, Y.-H.; Wang, Y.; Liu, S.-T.; Chen, J.-T. Kinetic and
Mechanistic Studies of Geometrical Isomerism in Neutral Square-Planar
Methylpalladium Complexes Bearing Unsymmetrical Bidentate Ligands of α-
Aminoaldimines. Inorg. Chem. 2009, 48, 7639–7644.
21) Berry, R. S. Correlation of Rates of Intramolecular Tunneling Processes, with
Application to Some Group V Compounds. J. Chem. Phys. 1960, 32, 933-938.
22) Redfield, D. A.; Nelson, J. H. Mechanism of cis-trans Isomerization for Square
Planar Complexes of the Type ML
2
X
2
. J. Am. Chem. Soc. 1974, 96, 6219–6220.
121
23) Louw, W. J. Preparative and Kinetic Study on the Mechanisms of Isomerization
of Square-Planar Complexes. Kinetic Evidence for Pseudorotation of a Five-
Coordinate Intermediate. Inorg. Chem. 1977, 16, 2147-2160.
24) (a) Romeo, R.; Minniti, D.; Lanza, S. Solvent Effect on the Rates of Uncatalyzed
Isomerization and Ligand Substitution at a Square-Planar Platinum(II) Complex.
Inorg. Chem. 1980, 19, 3663–3668. (b) Linert, W.; Taha, A. Co-Ordination of
Solvent Molecules to Square-Planar Mixed-Ligand Nickel(II) Complexes: A
Thermodynamic and Quantum-Mechanical Study. J. Chem. Soc., Dalton Trans.
1994, 1091-1095.
25) (a) Blagg, R. J.; Connelly, N. G.; Haddow, M. F.; Hamilton, A.; Lusi, M.; Orpen,
A. G.; Ridgway, B. M. Isomerism in Rhodium(I) N,S-Donor Heteroscorpionates:
Ring Substituent and Ancillary Ligand Effects. Dalton Trans. 2010, 39, 11616-
11627. (b) Webster, C. E.; Hall, M. B. Factors Affecting the Structure of
Substituted Tris(Pyrazolyl)Borate Rhodium Dicarbonyl Complexes. Inorg. Chim.
Acta 2002, 330, 268-282.
26) Crossley, I. R. The Organometallic Chemistry of Group 10 Poly(pyrazolyl)borate
Complexes. Adv. Organomet. Chem. 2010, 58, 109-207.
27) Echols, H. M.; Dennis, D. The Crystal and Molecular Structure of Bis[dihydrobis-
(1-pyrazolyl)borato]nickel(II): Evidence for the Absence of Ni-H Interaction in
Polypryazolyl Borates of Nickel. Acta Cryst. 1976, B32, 1627-1630.
28) Nieto, I.; Bontchev, R. P.; Smith, J. M. Synthesis of a Bulky Bis(carbene)borate
Ligand – Contrasting Structures of Homoleptic Nickel(II) Bis(pyrazolyl)borate
and Bis(carbene)borate Complexes. Eur. J. Inorg. Chem. 2008, 2476–2480.
29) Zhang, J.; Ke, Z.; Bao, F.; Long, J.; Gao, H.; Zhu, F.; Wu, Q. Ethylene
Polymerization and Oligomerization Catalyzed by Bulky β-Diketiminato Ni(II)
and β-Diimine Ni(II) Complexes/Methylaluminoxane Systems. J. Mol. Catal. A:
Chem. 2006, 249, 31–39.
30) Wiese, S.; Aguila, M. J. B.; Kogut, E.; Warren, T. H. β-Diketiminato Nickel
Imides in Catalytic Nitrene Transfer to Isocyanides. Organometallics 2013, 32,
2300-2308.
31) (a) Lin, S.; Agapie, T. Cross-Coupling Chemistry at Mononuclear and Dinuclear
Nickel Complexes. Synlett 2010, 1–5. (b) Ren, P.; Vechorkin, O.; Allmen, K. von;
Scopelliti, R.; Hu, X. A Structure–Activity Study of Ni-Catalyzed Alkyl–Alkyl
Kumada Coupling. Improved Catalysts for Coupling of Secondary Alkyl Halides.
J. Am. Chem. Soc. 2011, 133, 7084–7095.
122
32) Gutiérrez, E.; Hudson, S. A.; Monge, A.; Nicasio, M. C.;Paneque, M.; Ruiz, C.
Organometallic Derivatives of Ni(II) with Poly(Pyrazolyl)Borate Ligands. J.
Organomet. Chem. 1998, 551, 215-227.
33) [(py)
2
BMe
2
]Cu(NCCD
3
) and [(py)
2
BMe
2
]Cu(CNtBu) have been synthesized in
situ and are observed to exchange bound dimethyldipyridylborate rapidly with
free ligand in solution. Both complexes proved insufficiently stable for successful
isolation. See page 190 for NMR characterization of these species.
34) Thompson, M.; Djurovich, P.; Krylova, V. 3-Coordinate Copper(I)-Carbene
Complexes. U.S. Pat. Appl. Publ., US 20120056529, Mar 8, 2012.
35) Williams, T. J.; Kershaw, A. D.; Li, V.; Wu, X. An Inversion Recovery NMR
Kinetics Experiment. J. Chem. Educ. 2011, 88, 665-669.
123
Chapter 6. Experimental and Spectral Data
6.1 General Procedures
All air and water sensitive procedures were carried out either in a Vacuum
Atmosphere glove box under nitrogen (2-10 ppm O
2
for all manipulations) or using
standard Schlenk techniques under nitrogen. Deuterated NMR solvents were purchased
from Cambridge Isotopes Laboratories. Acetone, dichloromethane, toluene, molecular
sieves, and sodium bicarbonate were purchased from Mallinckrodt and used as received.
All other organic solvents and bulk inorganic reagents were purchased from EMD
science and were used as received. When indicated, benzene, toluene, toluene-d
8
, and
tetrahydrofuran-d
8
were dried over sodium benzophenone ketyl and distilled prior to use.
Dichlormethane-d
2
was dried over calcium hydride and distilled prior to use. Dry hexane,
diethyl ether, dichloromethane and tetrahydrofuran were obtained from a J. C. Meyer
solvent purification system with alumina/copper(II) oxide columns and used without
further purification. Silica gel (230-400 mesh) was purchased as pre-packed columns
from Teledyne. Organic reagents were purchased from Sigma-Aldrich Co., Alfa-Aesar,
Combi-Blocks, Inc., Maybridge, Lancaster Chemicals and TCI America and used as
received. Organometallic precursors were purchased from Strem Chemicals, except
where indicated, and were used as received.
NMR spectra were recorded on a Varian Mercury 400, 400MR (outfitted with an
AS7600 autosampler), VNMRS 500, or VNMRS 600 spectrometer. All chemical shifts
are reported in units of ppm and referenced to the residual
1
H or
13
C in the solvent and
line-listed according to (s) singlet, (bs) broad singlet, (d) doublet, (t) triplet, (dd) double
doublet, etc.
13
C spectra are delimited by carbon peaks, not carbon count.
11
B and
31
P
chemical shifts are unreferenced. Air-sensitive NMR spectra were taken in 8” J-Young
tubes (Wilmad or Norell) with Teflon valve plugs. The NMR tubes were shaken
vigorously for several minutes with chlorotrimethylsilane then dried in vacuo on a
Schlenk line prior to use. Melting points were obtained on a mel-temp apparatus and are
uncorrected. MALDI mass spectra were obtained on an Applied Biosystems Voyager
spectrometer using the evaporated drop method on a coated 96 well plate. The matrix was
anthracene. In a standard preparation, ca. 1 mg analyte and ca. 10 mg matrix were
dissolved in dry benzene and spotted on the plate with a glass capillary. Infrared spectra
were acquired on a Bruker OPUS FTIR spectrometer. High-resolution ESI mass spectra
were recorded at the University of California, Riverside. CHN elemental analyses were
collected at the University of Illinois at Urbana Champaign at the School of Chemical
Sciences Microanalysis Laboratory. Column chromatography was done in automation
using the Teledyne CombiFlash Rf 200 system using hexane and ethyl acetate.
Inversion recovery data was acquired on a VNMRS 500 or VNMRS 600
spectrometer according to the procedure previously published by our group.
1
Standard
124
error values for the activation parameters, σ(ΔH
‡
) and σ(ΔS
‡
), were calculated according
to the equations derived by Girolami et al.
2
125
6.2 Chapter 2 experimental and spectral data
6.2.1 Alkylation of Amines
Alkylation of aniline (2.9) with ethanol (2.45):
In a vial containing a teflon stir bar, Shvo’s catalyst (2.1, 10.9 mg, 0.01 mmol, 2 mol%),
freshly distilled aniline
3
(2.9, 46.6 mg, 45.6 μL, 0.5 mmol) were combined in ethanol
4
(3
mL). Acetone (58.1 mg, 73.5 μL, 1.0 mmol) was added, the vial was capped and heated
at 80 °C for 30 hours. Diethylaniline, 2.47, was isolated by column chromatography with
5:1 hexane:ethyl acetate to yield 49.8 mg (0.334 mmol, 67%).
Data are consistent with a commercial sample (Alfa Aesar).
This reaction was also varied as shown in Table 2.5 and the reactions were monitored by
GC/MS.
GC/MS method: 40 °C for 5 minutes, 15 °C/min to 250 °C, 250 °C for 5 minutes.
2.46 retention time: 7.02 min, 120.88 g/mol (calc’d 121.09 g/mol)
2.47 retention time: 8.03 min, 148.83 g/mol (calc’d 149.12 g/mol)
Alternatively:
In a vial containing a teflon stir bar, Shvo’s catalyst (2.1, 10.9 mg, 0.01 mmol, 2 mol%),
freshly distilled aniline
3
(2.9, 46.6 mg, 45.6 μL, 0.5 mmol) were combined in ethanol
4
(3
mL). The vial was capped and heated at 80 °C for 30 hours. Diethylaniline, 2.47, was
isolated by column chromatography with 5:1 hexane:ethyl acetate to yield 71.9 mg (0.48
mmol, 96%).
Data are consistent with a commercial sample (Alfa Aesar).
126
Alkylation of Aniline (2.9):
In a vial containing a teflon stir bar, Shvo’s catalyst (2.1, 5.4 mg, 0.005 mmol, 2 mol%)
and freshly distilled aniline
3
(2.9, 23.3 mg, 22.8 μL, 0.25 mmol) were combined in
benzyl alcohol
3
(3 mL). Acetone (29.0 mg, 36.8 μL, 0.5 mmol) was added, the vial was
capped and heated at 80 °C for 66 hours. 95% conversion to 2.48b was observed by
GC/MS.
GC/MS method: 40 °C for 5 minutes, 15 °C/min to 250 °C, 250 °C for 5 minutes.
Retention time: 12.17 min, 182.80 g/mol (calc’d 183.10 g/mol).
Tentative structural assignment based on agreement of mass spectrum with a known
compound.
5
127
N-phenylpiperidine (2.55):
In a vial containing a teflon stir bar, Shvo’s catalyst (2.1, 5.4 mg, 0.005 mmol, 2 mol%)
and freshly distilled aniline
3
(2.9, 23.3 mg, 22.8 μL, 0.25 mmol) were combined with 1,5-
pentanediol
6
(2.51, 52.1 mg, 54.9 μL, 0.5 mmol) in benzene (3 mL). Acetone (29.0 mg,
36.8 μL, 0.5 mmol) was added, the vial was capped and heated at 80 °C for 66 hours. The
product was isolated by column chromatography with 5:1 hexane:ethyl acetate to yield
48.5 mg (0.25 mmol, >99%).
Alternatively:
In a vial containing a teflon stir bar, Shvo’s catalyst
7
(2.1, 21.7 mg, 0.02 mmol, 2 mol%)
and freshly distilled aniline
3
(2.9, 93.1 mg, 91.2 μL, 1.0 mmol) were combined with 1,5-
pentanediol
6
(2.51, 208.3 mg, 209.6 μL, 2.0 mmol) in benzene (1 mL). The vial was
capped and heated at 80 °C for 168 hours. The product was isolated by column
chromatography with 5:1 hexane:ethyl acetate to yield 56.8 mg (0.35 mmol, 35%).
Data are consistent with a known compound.
8
128
6.2.2 Formation of Heterocycles
δ-Valerolactone (6.1):
In a test tube containing a teflon stir bar, Shvo’s catalyst (2.1, 6.5 mg, 0.006 mmol, 2
mol%) and 1,5-pentanediol
6
(2.51, 31.2 mg, 31.4 μL, 0.3 mmol) were combined in
acetone (3 mL). The tube was sealed with a septum and heated at 60 °C for 114 hours.
Product was isolated by column chromatography with 5:1 hexane:ethyl acetate to yield
30.0 mg (0.3 mmol, >99%).
Data are consistent with a known compound.
9
129
Phthalide (2.60):
In a round bottom flask containing a teflon stir bar, Shvo’s catalyst (2.1, 5.4 mg, 0.005
mmol, 5 mol%) and 1,2-dimethoxybenzene
10
(2.53, 13.8 mg, 0.1 mmol) were dissolved
in acetone (10 mL). The flask was sealed with a septum and heated at 60 °C for 18 hours.
Product was isolated by column chromatography with 1:1 hexane:ethyl acetate to yield
12.6 mg (0.094 mmol, 94%).
Data are consistent with a known compound.
11
130
γ-Butyrolactone (6.2):
In a round bottom flask containing a teflon stir bar, Shvo’s catalyst (2.1, 3.3 mg, 0.003
mmol, 3 mol%) and cis-butene-1,4-diol
12
(2.54, 8.8 mg, 8.2 μL, 0.1 mmol) were
combined in acetone (10 mL). The flask was sealed with a septum and heated at 60 °C for
66.5 hours. The reaction was analyzed by GC/MS and showed 95% conversion.
GC/MS method: 40 °C for 5 minutes, 15 °C/min to 250 °C, 250 °C for 5 minutes.
Retention time: 4.18 min, 85.84 g/mol (calc’d 86.04 g/mol)
Tentative structural assignment based on agreement of mass spectrum with a known
compound.
13
131
1-(tert-butyl)piperidine (2.57):
In a vial containing a teflon stir bar, Shvo’s catalyst
14
(2.1, 8.1 mg, 0.0075 mmol, 3
mol%), 1,5-pentanediol
6
(2.51, 26.0 mg, 26.2 μL, 0.25 mmol) and tert-butylamine
6
(2.56,
18.3 mg, 26.4 μL, 0.25 mmol) were combined in benzene (0.25 mL). The vial was
capped and heated at 80 °C for 120 hours. The reaction was analyzed by GC/MS and
showed 30% conversion.
GC/MS method: 60 °C for 3 minutes, 30 °C/min to 250 °C, 250 °C for 15 minutes.
Retention time: 7.62 min, 141.16 g/mol (calc’d 141.15 g/mol)
1
H NMR is consistent with known compound.
15
132
Formation of 2.58 and 2.16a:
In a vial containing a teflon stir bar, Shvo’s catalyst (2.1, 8.1 mg, 0.0075 mmol, 3 mol%),
cis-1,4-butenediol
12
(2.54, 22.0 mg, 20.6 μL, 0.25 mmol) and aniline
3
(2.9, 46.6 mg,
45.6μL, 0.50 mmol) were combined in benzene (0.25 mL). The vial was capped and
heated at 80 °C for 120 hours. The reaction was analyzed by GC/MS: 25% conversion to
2.58 and 25% conversion to 2.16a was observed.
GC/MS method: 40 °C for 5 minutes, 15 °C/min to 250 °C, 250 °C for 5 minutes.
2.58 retention time: 8.50 min, 143.10 g/mol (calc’d 143.07 g/mol)
2.16a retention time: 9.57 min, 147.12 g/mol (calc’d 147.10 g/mol)
1
H NMR is consistent with known compounds: 2.58
16
and 2.16a.
17
133
Formation of 2.59 and 2.60:
In a vial containing a teflon stir bar, Shvo’s catalyst (2.1, 8.1 mg, 0.0075 mmol, 3 mol%),
1,2-dimethoxybenzene
3
(2.53, 34.5 mg, 0.25 mmol) and aniline
3
(2.9, 46.6 mg, 45.6 μL,
0.50 mmol) were combined in benzene (0.25 mL). The vial was capped and heated at 80
°C for 120 hours. The reaction was analyzed by GC/MS: 20% conversion to 2.59 and
20% conversion to 2.60 was observed.
GC/MS method: 40 °C for 5 minutes, 15 °C/min to 250 °C, 250 °C for 5 minutes.
2.59 retention time: 13.57 min, 195.13 g/mol (calc’d 195.10 g/mol)
2.60 retention time: 9.40 min, 134.04 g/mol (calc’d 134.04 g/mol)
1
H NMR is consistent with known compounds: 2.59
18
and 2.60.
11
134
6.2.3 Studies of the Pictet-Spengler Cyclization
N-acyltryptamine (2.63):
To a vial containing a teflon stir bar, dimethylaminopyridine
6
(6.1 mg, 0.05 mmol, 10
mol%), pyridine (39.6 mg, 40.4 μL, 0.5 mmol), and tryptamine
12
(2.17, 80.1 mg, 0.5
mmol) were added. Dichloromethane (2 mL) and acetic anhydride
10
(2.62, 51.0 mg, 47.3
μL, 0.5 mmol) were added to the vial, the vial was capped and stirred at room
temperature for 30 minutes. Reaction was extracted with water (3 x 1 mL) and saturated
sodium bicarbonate solution (1 x 1 mL). Organic portion was dried with MgSO
4
and
solvent was removed in vacuo to yield 102 mg (0.50 mmol, >99%).
Data are consistent with a known compound.
19
135
Imine 2.64:
To a vial containing a teflon stir bar was added tryptamine
12
(2.17, 160.22 mg, 1.0 mmol)
dichloromethane (5 mL) and 4Å molecular sieves (480 mg). Benzaldehyde
6
(2.26, 111.4
mg, 106.1 μL, 1.0 mmol) the vial was capped and stirred at room temperature for 18
hours. Reaction was filtered through Celite and solvent was removed in vacuo to yield
207.4 mg (0.829 mmol, 83%).
Data are consistent with a known compound.
20
136
Cyclization product 2.65-HCl:
In a vial containing a teflon stir bar, 2.64 (69.8 mg, 0.28 mmol) was dissolved in
methanol (1.0 mL) and tert-butanol
6
(1.0 mL). Aqueous hydrochloric acid (4 M, 75 μL,
0.3 mmol) was added and the vial was capped and stirred at room temperature overnight.
Product 2.65-HCl precipitates and is isolated by filtration to yield 79.7 mg (0.28 mmol,
>99%).
Data are consistent with a known compound.
21
137
Reactivity of 2.1 in the presence of acid:
In a vial containing a teflon stir bar, Shvo’s catalyst
14
(2.1, 3.2 mg, 0.003 mmol, 2 mol%),
isopentyl alcohol
3
(2.66, 13.2 mg, 16.3 μL, 0.15 mmol) and cyclohexene
6
(37.0 mg, 45.6
μL, 0.45 mmol) were combined in dichloromethane (55 μL) and tert-butanol (55 μL).
Acid (see below) was added and vial was capped and heated at 60 °C for 72 hours. The
reactions were analyzed by GC/MS.
GC/MS method: 60 °C for 3 minutes, 30 °C/min to 250 °C, 250 °C for 10 minutes.
Retention time: 6.66 min, 172.19 g/mol (calc’d 172.15 g/mol)
1
H NMR is consistent with commercial sample (Sigma-Aldrich).
No Acid:
Product formation was observed in 100% conversion.
HCl:
Aqueous hydrochloric acid (4 M, 37.5 μL, 0.15 mmol). No product formation was
observed.
Acetic Acid:
Glacial acetic acid (9.0 μL, 0.16 mmol). Product formation was observed in 14%
conversion.
HBF
4
·Et
2
O:
HBF
4
·Et
2
O
10
(26.3 mg, 22.1 μL, 0.15 mmol). No product formation was observed.
138
6.3 Chapter 3 experimental and spectral data
6.3.1 Catalyst Screen
Several ruthenium catalysts were screened for the formation of 3.13 from 3.11 and 3.12.
Representative procedure :
To a vial containing a magnetic stir bar, ruthenium (0.25 mmol, 5 mol%) and silver
(0.25 - 0.75 mmol, 5 - 15 mol%) was added was added diethyl ether (150 μL) and water
(18 μL, 1.0 mmol). Acetylacetone
6
(3.11, 50.0 mg, 51.1 μL, 0.50 mmol and
phenylacetylene
10
(3.12, 153.2 mg, 164.7 μL, 1.50 mmol) were added to the vial. The
reaction was then stirred at 75° C for 2 hours. Results, as determined by NMR
spectroscopy with nitromethane internal standard, are shown in Table 3.4.
139
6.3.2 Condition Optimization
Representative procedure:
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg,
25 mol, 5 mol%) and silver (0.75 mmol, 15 mol%) was added was added solvent (150
μL) and water
23
(0 - 18 μL, 0 - 1.0 mmol). Acetylacetone
6
(3.11, 50.0 mg, 51.1 μL, 0.50
mmol and phenylacetylene
10
(3.12, 153.2 mg, 164.7 μL, 1.50 mmol) were added to the
vial. The reaction was then stirred at 75° C for 2 hours. Results, as determined by NMR
spectroscopy with nitromethane
10
internal standard, are shown in Table 3.5.
Conditions were varied as described in Table 3.5.
140
6.3.3 Products of the Coupling of Alkynes and 1,3-Diketones
4-hydroxy-3-(1-phenylvinyl)pent-3-en-2-one (3.13):
To a round bottom flask containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(65.4 mg, 0.25 mmol, 5 mol%) and silver(I) trifluoroacetate
6
(165.7 mg, 0.75 mmol, 15
mol%) was added diethyl ether (2 mL) and water
23
(180 μL, 10 mmol). Acetylacetone
6
(3.11, 500.7 mg, 510.9 μL, 5.0 mmol) and phenylacetylene
10
(3.12, 1.53 g, 1.65 mL, 15.0
mmol) were added to the vial. The reaction was then stirred at 75° C for 8 hours. 3.13
was isolated by automatic column chromatography using a hexane/ethyl acetate gradient
as a yellow oil, 886.7 mg (4.4 mmol, 88%yield).
This reaction can also be run at 1/10 scale to give 89.3 mg (0.44 mmol, 88%) of 3.13 in 2
hours.
Data are consistent with a known compound.
24
141
4-hydroxy-3-(1-(p-tolyl)vinyl)pent-3-en-2-one (3.15):
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL) and water
23
(18 μL, 1.0 mmol). Acetylacetone
6
(3.11, 50.0 mg,
51.1 μL, 0.50 mmol and p-tolylacetylene
10
(3.14, 174.2 mg, 190.2 μL, 1.50 mmol) were
added to the vial. The reaction was then stirred at 75° C for 3 hours. 3.15 was isolated by
automatic column chromatography using a hexane/ethyl acetate gradient as a yellow oil,
83.7 mg (0.385 mmol, 77%).
Data are consistent with a known compound.
25
142
4-hydroxy-3-(1-(4-methoxyphenyl)vinyl)pent-3-en-2-one (3.17):
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL) and water
23
(18 μL, 1.0 mmol). Acetylacetone
6
(3.11, 50.0 mg,
51.1 μL, 0.50 mmol and 1-ethynyl-4-methoxybenzene
26
(3.16, 198.2 mg, 194.5 μL, 1.50
mmol) were added to the vial. The reaction was then stirred at 75° C for 6 hours. 3.17
was isolated by automatic column chromatography using a hexane/ethyl acetate gradient
as a pale yellow solid, 95.6 mg (0.41 mmol, 82%).
Data are consistent with a known compound.
25
143
3-(1-([1,1'-biphenyl]-4-yl)vinyl)-4-hydroxypent-3-en-2-one (3.19):
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL) and water
23
(18 μL, 1.0 mmol). Acetylacetone
6
(3.11, 50.0 mg,
51.1 μL, 0.50 mmol) and 4-ethynyl-1,1’-biphenyl
27
(3.18, 267.3 mg, 1.50 mmol) were
added to the vial. The reaction was then stirred at 75° C for 4 hours. 3.19 was isolated by
automatic column chromatography using a hexane/ethyl acetate gradient as a yellow
solid, 128.1 mg (0.46 mmol, 92%).
M.P. = 75-78
°
C.
1
H NMR (CDCl
3
, 400 MHz) δ: 2.024 (s, 6H), 5.264 (s, 1H), 5.966 (s, 1H), 7.362 (tt, J =
1.2 Hz, 7.4 Hz, 1H), 7.429-7.468 (m, 2H), 7.498-7.524 (m, 2H), 7.577-7.615 (m, 4H),
16.659 (s, 1H).
13
C NMR (CDCl
3
, 100 MHz) δ: 23.8, 118.5, 126.498, 127.1, 127.6, 127.7, 129.0, 138.7,
140.5, 143.2, 191.5.
FT-IR (KBr / cm
-1
) v = 3032, 1598, 1487, 1246, 909, 774, 743, 729.
HR-MS (+ESI): m/z = 279.1380 g/mol, calc’d. for C
19
H
19
O
2
+
[MH]
+
: 279.1380 g/mol.
144
145
4-hydroxy-3-(1-(4-(trifluoromethyl)phenyl)vinyl)pent-3-en-2-one (3.21):
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL) and water
23
(18 μL, 1.0 mmol). Acetylacetone
6
(3.11, 50.0 mg,
51.1 μL, 0.50 mmol) and 1-ethynyl-4-(trifluoromethyl)benzene
6
(3.20, 255.2 mg, 244.7
μL, 1.50 mmol) were added to the vial. The reaction was then stirred at 75° C for 2 hours.
3.21 was isolated by automatic column chromatography using a hexane/ethyl acetate
gradient as a yellow semi-solid, 82.4 mg (0.34 mmol, 68%).
1
H NMR (CDCl
3
, 500 MHz) δ: 1.979 (s, 1H), 5.373 (s, 1H), 6.004 (s, 1H), 7.543 (d, J =
8.2 Hz, 2H), 7.613 (d, J = 8.2 Hz, 2H), 16.668 (s, 1H).
13
C NMR (CDCl
3
, 125 MHz) δ: 23.8, 113.4, 120.8, 124.2 (q, J
CF
= 272 Hz), 125.9 (q, J
CF
= 4 Hz), 126.3, 130.3 (q, J
CF
= 32 Hz), 142.7, 143.3, 191.5.
19
F NMR (CDCl
3
, 500 MHz, ref. CFCl
3
) δ: -63.12.
FT-IR (KBr / cm
-1
) v = 3094, 2928, 1617, 1326, 1122, 1068, 1015, 853.
HR-MS (+ESI): m/z = 271.0946 g/mol, calc’d. for C
14
H
14
F
3
O
2
+
[MH]
+
: 271.0940 g/mol.
146
147
4-hydroxy-3-(1-(thiophen-2-yl)vinyl)pent-3-en-2-one (3.23):
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL) and water
23
(18 μL, 1.0 mmol). Acetylacetone
6
(3.11, 50.0 mg,
51.1 μL, 0.50 mmol) and 2-ethynylthiophene
28
(3.22, 162.2 mg, 146.2 μL, 1.50 mmol)
were added to the vial. The reaction was then stirred at 75° C for 8 hours. 3.23 was
isolated by automatic column chromatography using a hexane/ethyl acetate gradient as an
orange-brown oil, 37.2 mg (0.18 mmol, 36%).
1
H NMR (CDCl
3
, 500 MHz) δ: 2.051 (s, 6H), 5.086 (s, 1H), 5.820 (s, 1H), 6.944 (d, J =
3.4 Hz, 1H), 6.976 (m, 1H), 7.227 (d, J = 4.9 Hz, 1H), 16.604 (s, 1H).
13
C NMR (CDCl
3
, 125 MHz) δ: 23.5, 113.9, 116.8, 125.3, 125.9, 128.0, 137.8, 145.5,
191.5.
FT-IR (Neat / cm
-1
) v = 3105, 2925, 1609, 1395, 1247, 993, 915, 702.
HR-MS (+ESI): m/z = 209.0637 g/mol, calc’d. for C
11
H
13
O
2
S
+
[MH]
+
: 209.0631 g/mol.
148
149
3-(1-(4-(dimethylamino)phenyl)vinyl)-4-hydroxypent-3-en-2-one (3.25):
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL) and water
23
(18 μL, 1.0 mmol). Acetylacetone
6
(3.11, 50.0 mg,
51.1 μL, 0.50 mmol) and 4-ethynyl-N,N-dimethylaniline
6
(3.24, 213.3mg, 1.50 mmol)
were added to the vial. The reaction was then stirred at 75° C for 24 hours. 3.25 was
isolated by automatic column chromatography using a hexane/ethyl acetate gradient as a
yellow solid, 50.4 mg (0.205 mmol, 41%).
M.P. = 38-41
°
C.
1
H NMR (CDCl
3
, 500 MHz) δ: 1.995 (s, 6H), 2.976 (s, 6H), 5.009 (s, 1H), 5.729 (s, 1H),
6.680 (d, J = 9.1 Hz, 2H), 7.319 (d, J = 9.1 Hz, 2H), 16.596 (s, 1H).
13
C NMR (CDCl
3
, 125 MHz) δ: 23.6, 40.51, 112.3, 114.2, 114.4, 127.0, 127.7, 143.1,
150.5, 191.5.
FT-IR (KBr / cm
-1
) v = 2919, 2808, 1757, 1606, 1552, 1364, 1171, 897, 820.
HR-MS (+ESI): m/z = 246.1492 g/mol, calc’d. for C
15
H
20
NO
2
+
[MH]
+
: 246.1489 g/mol.
150
151
5-hydroxy-4-(1-phenylvinyl)hept-4-en-3-one (3.27):
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL) and water
23
(18 μL, 1.0 mmol). Heptane-3,5-dione
10
(3.26, 64.1
mg, 67.8 μL, 0.50 mmol) and phenylacetylene
10
(3.12, 153.2 mg, 164.7 μL, 1.50 mmol)
were added to the vial. The reaction was then stirred at 75° C for 2 hours. 3.27 was
isolated by automatic column chromatography using a hexane/ethyl acetate gradient as a
yellow oil, 90.1 mg (0.39 mmol, 78%).
1
H NMR (CDCl
3
, 400 MHz) δ: 1.036 (t, J = 7.29 Hz, 6 H), 2.196 (b, 2H), 2.379 (b, 2H),
5.235 (s, 1H), 5.913 (s, 1H), 7.270-7.460 (m, 5H), 16.710 (s, 1H).
13
C NMR (CDCl
3
, 100 MHz) δ: 9.9, 29.5, 118.4, 126.1, 128.3, 128.8, 140.0, 143.1, 194.6.
FT-IR (Neat / cm
-1
) v = 3084, 2978, 1598, 1492, 1199, 1065, 912, 781.
HR-MS (+ESI): m/z = 231.1384 g/mol, calc’d. for C
15
H
19
O
2
+
[MH]
+
: 231.1380 g/mol.
152
153
3-methyl-3-(1-phenylvinyl)pentane-2,4-dione (3.29):
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL) and water
23
(9 μL, 0.5 mmol). 3-Methylpentane-2,4-dione
10
(3.28,
57.0 mg, 58.1 μL, 0.50 mmol) and phenylacetylene
10
(3.12, 153.2 mg, 164.7 μL, 1.50
mmol) were added to the vial. The reaction was then stirred at 75° C for 15 hours. 3.29
was isolated by automatic column chromatography using a hexane/ethyl acetate gradient
as an orange-brown solid, 47.9 mg (0.22 mmol, 44%).
Data are consistent with a known compound.
24
154
2-acetyl-2-(1-phenylvinyl)cyclohexanone (3.31):
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL) and water
23
(9 μL, 0.5 mmol). 2-Acetylcyclohexanone
10
(3.30,
70.1 mg, 65.0 μL, 0.50 mmol) and phenylacetylene
10
(3.12, 153.2 mg, 164.7 μL, 1.50
mmol) were added to the vial. The reaction was then stirred at 75° C for 15 hours. 3.31
was isolated by automatic column chromatography using a hexane/ethyl acetate gradient
as a yellow oil, 60.4 mg (0.25 mmol, 50%).
Data are consistent with a known compound.
25
155
Ene Adducts 3.33, 3.34Z, and 3.34E:
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL) and water
23
(18 μL, 1.0 mmol). Benzoylacetone
10
(3.32, 81.1 mg,
0.50 mmol) and phenylacetylene
10
(3.12, 153.2 mg, 164.7 μL, 1.50 mmol) were added to
the vial. The reaction was then stirred at 75° C for 4 hours. The products were isolated as
yellow oils (3.33, 3.34E) and a yellow solid (3.34Z). Products were collected in a
combined yield of 124 mg (0.45 mmol, 90%) with the ratio 3.33:3.34Z:3.34E = 9:13:4.
Each compound is separately characterized below. Olefin geometry assignments for
3.34E and Z were made on the basis on 1D-NOE NMR experiments.
Characterization of Compounds 3.34EZ
E and Z assignments for adducts 3.34 are proposed on the basis of 1D NOE experiments
acquired at 500 MHz with the Varian noedif pulse sequence (Table 6.1). The resulting
difference spectra did not give usable signals among the acetyl methyl groups, but the
alkyl-to-aryl NOE correlations are highly diagnostic of the reported diastereomeric
assignments as quantified below.
Table 6.1.
1
H NOE Data for 3.34Z and 3.34E.
3.34Z 3.34E
156
3-hydroxy-1-phenyl-2-(1-phenylvinyl)but-2-en-1-one (3.33):
1
H NMR (CDCl
3
, 400 MHz) δ: 2.046 (s, 3H), 5.130 (s, 1H), 5.786 (s, 1H), 7.221 (t, J = 8
Hz, 2 H), 7.279-7.350 (m, 4 H), 7.480 (d, J = 8 Hz, 2 H), 7.579 (d, J = 8 Hz, 2 H), 17.351
(s, 1H).
13
C NMR (CDCl
3
, 100 MHz) δ: 25.553, 113.333, 119.613, 126.351, 127.884, 128.194,
128.395, 128.891, 130.649, 140.422, 143.705, 183.487.
FT-IR (Neat / cm
-1
) v = 3027, 1658, 1492, 1355, 1212, 1027, 913, 697.
HR-MS (+ESI): m/z = 265.1227 g/mol, calc’d. for C
18
H
17
O
2
+
[MH]
+
: 265.1223 g/mol.
157
158
(Z)-1-phenyl-2-(1-phenylethylidene)butane-1,3-dione (3.34Z):
M.P. = 44-47
°
C.
1
H NMR (CDCl
3
, 400 MHz) δ: 2.274 (s, 3H), 2.476 (s, 3H), 7.089 (s, 5H), 7.242-7.279
(m, 2H), 7.389 (t, J = 6.8 Hz, 1H), 7.704 (d, J = 8.4 Hz, 2 H).
13
C NMR (CDCl
3
, 100 MHz) δ: 22.727, 31.059, 127.822, 128.310, 128.488, 128.550,
129.363, 133.313, 137.355, 139.841, 141.366, 151.449, 197.496, 198.781.
FT-IR (KBr / cm
-1
) v = 3058, 1654, 1595, 1449, 1315, 1211, 865, 704.
HR-MS (+ESI): m/z = 265.1227 g/mol, calc’d. for C
18
H
17
O
2
+
[MH]
+
: 265.1223 g/mol.
159
160
(E)-1-phenyl-2-(1-phenylethylidene)butane-1,3-dione (3.34E):
(Isolated as a mixture with 3.34Z)
1
H NMR (CDCl
3
, 400 MHz) δ: 1.868 (s, 3H), 2.049 (s, 3H), 7.331-7.353 (m, 2 H), 7.409-
7.434 (m, 3H), 7.507 (t, J = 8 Hz, 2 H), 7.610 (apparent t, J = 8 Hz, 1 H), 8.009 (d, J =
6.8 Hz, 2H).
13
C NMR (CDCl
3
, 100 MHz) δ: 23.486, 31.005, 127.605, 128.991, 129.061, 129.162,
129.611, 133.955, 136.960, 140.987, 141.274, 148.266, 196.396, 200.624.
FT-IR (Neat / cm
-1
) v = 2923, 1656, 1491, 1449, 1355, 1257, 1026, 700.
GC/MS: calc’d.: 264.12 g/mol, found: 264.14 g/mol.
161
162
1,3-diphenyl-2-(1-phenylethylidene)propane-1,3-dione (3.36):
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL) and water
23
(18 μL, 1.0 mmol). Dibenzoylmethane
10
(3.35, 112.1
mg, 0.50 mmol) and phenylacetylene
10
(3.12, 153.2 mg, 164.7 μL, 1.50 mmol) were
added to the vial. The reaction was then stirred at 75° C for 4 hours. 3.36 was isolated by
automatic column chromatography using a hexane/ethyl acetate gradient as a yellow
solid, 146.7 mg (0.45 mmol, 90%).
Data are consistent with a known compound.
29
163
3-(hydroxy(methoxy)methylene)-4-phenylpent-4-en-2-one (3.38):
To a vial containing a magnetic stir bar, ruthenium(III) chloride hydrate
22
(6.5 mg, 25
mol, 5 mol%) and silver(I) trifluoroacetate
6
(16.6 mg, 75 mol, 15 mol%) was added
diethyl ether (150 μL), water
23
(9 μL, 0.5 mmol) and triethylamine
3
(5.1 mg, 7 μL, 50
mol, 10 mol%). Methyl 3-oxobutanoate
6
(3.37, 58.1 mg, 54.0 μL, 0.50 mmol) and
phenylacetylene
10
(3.12, 153.2 mg, 164.7 μL, 1.50 mmol) were added to the vial. The
reaction was then stirred at 75° C for 8 hours. 3.38 was detected in 37% yield by
1
H
NMR with a nitromethane standard.
Data are consistent with a known compound.
30
164
6.4 Chapter 4 experimental and spectral data
6.4.1 Rhodium(I) and Iridium(I) complexes of dimethyldipyridylborate
[(py)
2
B(Me)
2
]Rh(CO)
2
(4.3a):
Under N
2
in a dry vial, [(CO)
2
RhCl]
2
10
(58.3 mg, 0.15 mmol) was dissolved in 5 ml of
dry diethyl ether. [(py)
2
B(Me)
2
]Na
31
(66.0 mg, 0.30 mmol) was added and the reaction
was stirred at room temperature for 4 hours. After stirring, the precipitate was allowed to
settle and the reaction mixture was filtered through Celite. Ether was removed in vacuo to
give product as a yellow solid, 108.8 mg (0.30 mmol, > 99%). Crystallization from
diethyl ether produced crystals suitable for X-ray crystallographic analysis.
MP: 125-129 °C with decomposition.
1
H NMR (toluene-d
8
, 400 MHz) δ: 8.157 (d, J = 5.6 Hz), 7.736 (d, J = 7.9 Hz), 6.886 (td,
J = 7.6, 1.6 Hz), 6.212 (td, J = 6.4, 1.6 Hz), 1.129 (br s), 0.727 (br s).
13
C NMR (toluene-d
8
, 100 MHz) δ: 186.889 (d, J = 66.9 Hz), 152.323, 136.154, 129.904,
119.349.
13
C NMR (from
1
H-
13
C HMBC, toluene-d
8
, 125 MHz, 0 °C) δ: 198.57, 152.62, 136.50,
130.17, 119.72, 23.20, 11.63.
11
B NMR (toluene-d
8
, 128 MHz) δ: -8.45.
MALDI: m/z = 358.9513 g/mol, calc’d. for C
14
H
16
BN
2
O
2
Rh
+
[M]
+
: 358.0360.
FT-IR (thin film / cm
-1
) v = 2917.62, 2828.39, 2074.01, 2003.35, 1597.04, 1420.68,
1290.11, 1012.52, 755.46.
Anal. Calc. for C
14
H
16
BN
2
O
2
Rh: C, 46.97; H, 4.5; N, 7.82. Found: C, 47.17; H, 3.98; N,
7.66.
X-ray crystallographic analysis of 4.3a: See page 195.
165
Figure 6.1. ORTEP diagram of [(py)
2
B(Me)
2
]Rh(CO)
2
. Ellipsoids drawn at the 50%
probability level.
166
167
[(py)
2
B(Me)
2
]Rh(cod) (4.4a):
Under N
2
in a dry vial, 3.5 mL dry hexane was added to [(py)
2
B(Me)
2
]Na
31
(30.8 mg,
0.14 mmol) and [(cod)RhCl]
2
(34.5 mg, 0.07 mmol). The reaction was briefly (~3 min)
sonicated and then stirred at room temperature for 2 hours or until all rhodium was
dissolved. After stirring, the precipitate was allowed to settle and the reaction mixture
was filtered through Celite. Hexane was removed in vacuo to give product as a yellow
solid, 56.6 mg (0.139 mmol, 99%). Crystallization from hexane produced crystals
suitable for X-ray crystallographic analysis.
MP: 147-149 °C.
1
H NMR (toluene-d
8
, 400 MHz) δ: 8.101 (d, J = 5.9 Hz), 7.703 (d, J = 7.8), 6.919 (td, J =
7.6, 1.6 Hz), 6.296 (td, J = 6.4, 1.6 Hz), 3.843-3.764 (m), 2.439-2.346 (m), 1.737 (q, J =
7.7 Hz), 1.671 (br s), 1.497 (q, J = 7.7 Hz), 0.867 (br s).
13
C NMR (toluene-d
8
, 100 MHz) δ: 148.216, 134.284, 128.515, 119.036, 84.397 (d, J =
14.9 Hz), 79.635 (d, J = 10.6 Hz), 30.824, 30.630.
13
C NMR (from
1
H-
13
C HSQC, toluene-d
8
, 100 MHz) δ: 148.50, 134.79, 129.23, 119.59,
84.48, 79.85, 30.81, 30.62, 21.18, 15.00.
13
C NMR (from
1
H-
13
C HMBC, toluene-d
8
, 100 MHz) δ: 191.10, 148.19, 134.71, 129.81,
119.39, 84.68, 81.18, 32.22, 31.92, 21.18, 14.56.
11
B NMR (toluene-d
8
, 128 MHz) δ: -8.31.
MALDI: m/z = 408.0378 g/mol, calc’d. for C
20
H
26
BN
2
Rh
+
[M]
+
: 408.1244.
FT-IR (thin film / cm
-1
) v = 3017.05, 2912.4, 1590.55, 1453.29, 1287.45, 1003.31,
753.47.
Anal. Calc. for C
20
H
26
BN
2
Rh: C, 58.85; H, 6.42; N, 6.86. Found: C, 58.92; H, 6.38; N,
6.96.
X-ray crystallographic analysis of 4.4a: See page 203.
168
Figure 6.2. ORTEP diagram of [(py)
2
B(Me)
2
]Rh(cod). Ellipsoids drawn at the 50%
probability level.
169
170
[(py)
2
B(Me)
2
]Rh(CNtBu)
2
(4.5a):
First synthetic step adapted from literature procedure.
32
Under N
2
in a dry flask, [(cod)
2
RhCl]
2
(49.3 mg, 0.10 mmol) was dissolved in 3 ml of dry
tetrahydrofuran. t-Butylisonitrile
10
(34.9 mg, 47.5 μL, 0.42 mmol) was added by syringe,
producing a dark brown solution. The reaction was stirred for 2 hours at room
temperature. Tetrahydrofuran was then removed in vacuo to give a red residue. 3 mL dry
tetrahydrofuran and [(py)
2
B(Me)
2
]Na
31
(44.0 mg, 0.20 mmol) were added to the flask and
the reaction was stirred for 2 hours at room temperature to produce an orange solution.
Filtration of the reaction mixture through Celite and evaporation of the filtrate produced a
yellow residue. The residue was triturated with 5 ml dry hexane, sonicated for 20 minutes
and filtered to give product as a bright yellow solid, 75.2 mg (0.162 mmol, 81%). This
compound is also highly air and water sensitive preventing the acquisition of accurate
ESI-MS and elemental analysis.
MP: 192-194 °C with decomposition.
1
H NMR (tetrahydrofuran-d
8
, 600 MHz, -40 °C) δ: 8.698 (d, J = 5.7 Hz), 7.472 (d, J =
7.9 Hz), 7.376 (tt, J = 7.7, 1.3 Hz), 6.796 (tt, J = 6.5, 1.3 Hz), 1.487 (s), 0.659 (s), 0.156
(s).
13
C NMR (toluene-d
8
, 150 MHz, -40 °C) δ: 152.747, 134.214, 118.210, 55.622, 30.152.
13
C NMR (from
1
H-
13
C HMBC, tetrahydrofuran-d
8
, 150 MHz, -40 °C) δ: 192.49, 156.72,
154.03, 135.01, 128.88, 119.67, 58.65, 32.15, 20.57, 12.05.
11
B NMR (toluene-d
8
, 128 MHz) δ: -8.46.
MALDI: Although the major adducts in MALDI appear to be oxygenated products, we
are able to detect [M-H]
+
(m/z = 465.0280 g/mol, calcd. for C
22
H
31
BN
4
Rh
+
[M]
+
:
465.1702) and [M-Me]
+
(m/z = 451.0582 g/mol, calcd. for C
21
H
29
BN
4
Rh
+
[M]
+
:
451.1540).
FT-IR (thin film / cm
-1
) v = 2981.55, 2913.02, 2143.56, 2097.07, 1591.48, 1456.85,
1209.06, 755.69.
171
172
[(py)
2
B(Me)
2
]Rh(C
2
H
4
)
2
(4.6a):
Under N
2
in a dry J. Young tube, [(C
2
H
4
)
2
RhCl]
2
(7.8 mg, 0.02 mmol) was dissolved in
750 μL dry toluene-d
8
. [(py)
2
B(Me)
2
]Na
31
(8.8 mg, 0.04 mmol) was added and the tube
was shaken and allowed to sit at room temperature. The reaction mixture was filtered
through Celite to give a solution containing [(py)
2
BMe
2
]Rh(C
2
H
4
)
2
with a small amount
of free [(py)
2
B(Me)
2
]Na. Toluene-d
8
was removed in vacuo to give a solid sample for
MALDI and IR.
1
H NMR (toluene-d
8
, 400 MHz) δ: 8.014 (d, J = 5.6), 7.740 (d, J = 7.5 Hz), 6.868 (td, J =
7.5, 1.6 Hz), 6.262 (td, J = 6.4, 1.7 Hz), 2.745-2.695 (m), 1.693 (br s), 0.839 (br s).
13
C NMR (toluene-d
8
, 100 MHz) δ: 146.961, 134.424, 119.455, 65.498 (d, J = 11.5 Hz).
13
C NMR (from
1
H-
13
C HSQC, toluene-d
8
, 100 MHz) δ: 147.01, 134.48, 129.04, 119.85,
65.44, 19.36, 12.82.
13
C NMR (from
1
H-
13
C HMBC, toluene-d
8
, 100 MHz) δ: 191.65, 147.77, 135.93, 130.36,
120.61, 65.73, 19.27, 12.81.
11
B NMR (toluene-d
8
, 128 MHz) δ: -13.10.
FT-IR (thin film / cm
-1
) v = 3074.98, 2972.72, 2912.42, 2820.57, 1593.12, 1455.91,
1418.81, 1286.51, 1156.79, 1003.95, 752.84.
MALDI: This complex proved insufficiently stable to obtain a direct mass by MALDI,
however we were able to detect several ions which we propose to correspond to the
complexes formed by exchange of ethylene for solvent, air or water, specifically
[(py)
2
B(Me)
2
]Rh(toluene-d
8
) (399.2000 g/mol, calc’d. for C
19
H
14
D
8
BN
2
Rh
+
[M]
+
:
400.1433),
[(py)
2
B(Me)
2
]Rh(O
2
)
2
(363.2081 g/mol, calc’d. for C
12
H
14
BN
2
O
4
Rh
+
[M]
+
:
364.0102), and
[(py)
2
B(Me)
2
]Rh(O
2
)(H
2
O) (349.1966 g/mol, calc’d. for
C
12
H
16
BN
2
O
3
Rh
+
[M]
+
: 350.0309).
173
174
[(py)
2
B(Me)
2
]Ir(CO)
2
(4.3b):
First synthetic step adapted from literature procedure.
33
Under N
2
in a dry flask, [(coe)
2
IrCl]
2
(44.8 mg, 0.05 mmol) was dissolved in 5 ml of dry
benzene. The flask was then evacuated, filled with CO (1 atm) and stirred for 2 hours.
The CO was removed and replaced by N
2
and [(py)
2
B(Me)
2
]Na
31
(22.0 mg, 0.10 mmol)
was added. The reaction was stirred overnight at room temperature. Filtration of the
reaction mixture and evaporation of the filtrate produced a brown residue. This residue
was extracted with dry hexane and filtered. The hexane solution was concentrated and
cooled to give yellow crystals. The supernatant was further concentrated and cooled to
give a second crop of yellow crystals with a combined yield of 22.2 mg (0.050 mmol,
50%).
This reaction can also be done in dry acetonitrile (10 mL), with addition of ligand
followed by CO or simultaneous addition of ligand and CO. All methods produce similar
yields.
MP: Begins to darken at 85 °C fully decomposed by 100 °C.
1
H NMR (toluene-d
8
, 400 MHz) δ: 8.266 (d, J = 5.7 Hz), 7.753 (d, J = 7.9 Hz), 6.840 (td,
J = 7.6, 1.6 Hz), 6.165 (td, J = 6.6, 1.6 Hz), 1.194 (br s), 0.669 (br s).
13
C NMR (toluene-d
8
, 100 MHz) δ: 174.956, 152.870, 136.770, 130.110, 120.105.
13
C NMR (from
1
H-
13
C HMBC, toluene-d
8
, 150 MHz, -20 °C) δ: 194.81, 153.08, 136.98,
130.29, 120.58, 30.09, 11.67.
11
B NMR (toluene-d
8
, 128 MHz) δ: -8.75.
MALDI: m/z = 448.9489 g/mol, calc’d. for C
14
H
16
BIrN
2
O
2
+
[M]
+
: 448.0934.
FT-IR (thin film / cm
-1
) v = 2921.05, 2830.29, 2064.18, 1984.51, 1599.61, 1460.61,
1460.50, 1266.04, 1113.15, 1033.64, 759.93.
Anal. Calc. for C
14
H
16
BIrN
2
O
2
: C, 37.59; H, 3.61; N, 6.26. Found: C, 36.77; H, 2.97; N,
5.98.
HR-MS (+ESI): m/z = 447.0848 g/mol, calc’d. for C
19
H
19
O
2
+
[MH]
+
: 447.0851 g/mol.
175
176
[(py)
2
B(Me)
2
]Ir(cod) (4.4b):
Under N
2
in a dry vial, 3.5 mL dry hexane was added to [(py)
2
B(Me)
2
]Na
31
(30.8 mg,
0.14 mmol) and [(cod)IrCl]
2
(47.0 mg, 0.07 mmol). The reaction was briefly (~3 min)
sonicated and then stirred at room temperature for 2 hours or until all iridium was
dissolved. After stirring, the precipitate was allowed to settle and the reaction mixture
was filtered through Celite. Hexane was removed in vacuo to give product as an orange
solid, 63.8 mg (0.128 mmol, 91%). Crystallization from hexane produced crystals
suitable for X-ray crystallographic analysis.
MP: 146-151 °C.
1
H NMR (toluene-d
8
, 400 MHz) δ: 8.153 (d, J = 5.9 Hz), 7.848 (d, J = 8.0 Hz), 6.897 (td,
J = 7.5, 1.5 Hz), 6.292 (td, J = 6.2, 1.6 Hz), 3.614-3.554 (m), 2.388-2.351 (m), 2.262-
2.224 (m), 1.682 (q, J = 8.2 Hz), 1.417 (br s),1.340 (q, J = 8.2), 0.808 (br s).
13
C NMR (toluene-d
8
, 100 MHz) δ: 148.125, 134.674, 129.625, 119.728, 68.501, 64.087,
31.577, 31.337.
13
C NMR (from
1
H-
13
C HSQC, toluene-d
8
, 100 MHz) δ: 148.14, 134.58, 129.44, 119.54,
68.38, 64.28, 31.06, 30.76, 19.86, 12.65.
13
C NMR (from
1
H-
13
C HMBC, toluene-d
8
, 100 MHz) δ: 190.47, 148.00, 134.49, 129.99,
119.69, 68.32, 64.41, 31.88, 31.64, 20.81, 13.66.
11
B NMR (toluene-d
8
, 160 MHz) δ: -8.84.
MALDI: m/z = 497.9647 g/mol, calc’d. for C
20
H
26
BIrN
2
+
[M]
+
: 498.1818.
FT-IR (thin film / cm
-1
) v = 2913.20, 2833.79, 1593.69, 1454.11, 1288.45, 1002.32,
754.50.
Anal. Calc. for C
20
H
26
BIrN
2
: C, 48.29; H, 5.27; N, 5.63. Found: C, 48.08; H, 5.08; N,
5.53.
X-ray crystallographic analysis of 4.4b: See page 210.
177
Figure 6.3. ORTEP Diagram of [(py)
2
B(Me)
2
]Ir(cod). Ellipsoids drawn at the 50%
probability level.
178
179
[(py)
2
B(Me)
2
]Ir(CNtBu)
2
(4.5b):
First synthetic step adapted from literature procedure.
32
Under N
2
in a dry flask, [(cod)
2
IrCl]
2
(47.0 mg, 0.07 mmol) was dissolved in 2.1 mL of
dry tetrahydrofuran. t-Butylisonitrile
10
(24.4 mg, 33.3 μL, 0.294 mmol) was added by
syringe, producing a dark brown solution. The reaction was stirred for 2 hours at room
temperature. Tetrahydrofuran was then removed in vacuo to give a purple or green
residue. 2.1 mL dry tetrahydrofuran and [(py)
2
B(Me)
2
]Na
31
(30.8 mg, 0.14 mmol) were
added to the flask and the reaction was stirred for 2 hours at room temperature to produce
a yellow-orange solution. Filtration of the reaction mixture through Celite and
evaporation of the filtrate produced a yellow-brown residue. 5 mL dry hexane was added
to the flask which was then sonicated for 1 hour in an ice bath and filtered to give product
as a yellow solid, 51.5 mg (0.093 mmol, 66%). It is important to note that this complex is
highly unstable in most solvents, with the exception of tetrahydrofuran. This compound is
also highly air and water sensitive preventing the acquisition of melting point, ESI-MS
and elemental analysis.
1
H NMR (tetrahydrofuran-d
8
, 600 MHz, -50 °C) δ: 8.801 (d, J = 5.5 Hz), 7.567 (d, J =
8.1 Hz), 7.478 (tt, J = 7.4, 1.5 Hz), 6.881 (tt, J = 6.7, 1.4 Hz), 1.484 (s), 0.593 (s), 0.147
(s).
13
C NMR (tetrahydrofuran-d
8
, 100 MHz) δ: 154.344, 135.293, 129.214, 119.844, 56.660,
31.546.
13
C NMR (from
1
H-
13
C HMBC, tetrahydrofuran-d
8
, 150 MHz, -50 °C) δ: 197.73, 163.16,
152.65, 133.63, 127.45, 118.42, 55.78, 32.08, 20.67, 10.40.
11
B NMR (toluene-d
8
, 128 MHz) δ: -13.462.
MALDI: We observe the hydrated product [M+H
2
0]
+
m/z = 573.0531 g/mol, calcd. for
C
22
H
34
BIrN
4
O
+
[M]
+
: 574.2455.
FT-IR (thin film / cm
-1
) v = 3281.53, 2978.65, 2921.33, 2155.90, 1600.68, 1411.36,
1269.98, 1235.61, 948.06, 764.53.
This compound is highly air sensitive and as a result we were not able to obtain accurate
HR-MS or elemental analysis.
180
181
[(py)
2
B(Me)
2
]Rh(dppe) (4.7a):
Under N
2
in a dry flask, [(C
2
H
4
)
2
RhCl]
2
(38.9 mg, 0.10 mmol) was dissolved in 4 mL of
dry toluene. [(py)
2
B(Me)
2
]Na
31
(44.0 mg, 0.20 mmol) was added to the flask and the
reaction was stirred for 1 hour at room temperature. A solution of 1,2-
bis(diphenylphosphino)ethane
6
(79.7 mg, 0.2 mmol) in 3 mL dry toluene was added
dropwise. The reaction was stirred for another hour at room temperature and then filtered
through Celite. Toluene was removed in vacuo to give a yellow oil. The residue was
triturated with 5 mL dry hexane, sonicated in a bench-top sonicator for 20 minutes and
the hexane was removed in vacuo to give product as a yellow solid, 137.4 mg (0.197
mmol, 98%).
MP: Decomposes from 85-100 °C with most rapid darkening from 173-177 °C.
1
H NMR (toluene-d
8
, 400 MHz) δ: 8.524, (d, J = 5.0 Hz), 7.963 (t, J = 8.2 Hz), 7.834 (d,
J = 7.6 Hz), 7.420-7.382 (m), 7.208-7.138 (m), 6.979-6.920 (m), 6.898 (td, J = 7.5, 1.7
Hz), 6.035 (td, J = 6.6, 1.7 Hz), 2.017-1.937 (m), 1.739-1.641 (m), 1.337 (s), 0.855 (s).
13
C NMR (toluene-d
8
, 100 MHz) δ: 152.483, 136.561 (t, J
CP
= 16.0 Hz), 134.339 (t, J
CP
=
5.8 Hz), 133.487, 133.131 (t, J
CP
= 5.3 Hz), 129.847, 129.530, 128.476 (t, J
CP
= 4.5 Hz),
128.105 (t, J
CP
= 4.5 Hz), 117.735, 30.104 (td, J
CP
= 24.9 Hz, 3.0 Hz).
13
C NMR (from
1
H-
13
C HSQC, toluene-d
8
, 100 MHz) δ: 152.50, 134.35, 133.46, 133.17,
129.95, 129.56, 129.09, 128.49, 128.10, 117.84, 30.10, 21.18, 12.74.
13
C NMR (from
1
H-
13
C HMBC, toluene-d
8
, 100 MHz) δ: 193.02, 152.81, 137.12, 134.81,
133.89, 133.32, 130.66, 129.74, 129.18, 128.81, 128.21, 118.20, 30.50, 21.49, 12.74.
11
B NMR (toluene-d
8
, 128 MHz) δ: -13.29.
31
P NMR (toluene-d
8
, 162 MHz) δ: 70.63 (d, J
PRh
= 174 Hz).
MALDI: m/z = 697.8750 g/mol, calc’d. for C
38
H
38
BN
2
P
2
Rh
+
[M]
+
: 698.1658.
FT-IR (thin film / cm
-1
) v = 3055.19, 2913.38, 1589.24, 1435.63, 1197.12, 1096.85,
1000.09, 743.11, 695.60.
182
Anal. Calc. for C
38
H
38
BN
2
P
2
Rh: C, 65.35; H, 5.48; N, 4.01. Found: C, 65.14; H, 5.79; N,
3.80.
183
6.5 Chapter 5 experimental and spectral data
6.5.1 Nickel(II) complexes of dimethyldipyridylborate
[(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27):
Under N
2
in a dry vial containing a teflon stir bar, (PPh
3
)
2
NiCl
2
10
(65.4 mg, 0.10 mmol)
was dissolved in 10 mL of dry dichloromethane. In another dry vial, [(py)
2
B(Me)
2
]Na
31
(22.0 mg, 0.10 mmol) was dissolved in 5 mL of dry dichloromethane and added slowly to
the solution of. Another 5 mL of dichloromethane was used to rinse the vial and added
slowly to the solution of (PPh
3
)
2
NiCl
2
. The dark green solution turned brown and then
orange on addition of [(py)
2
B(Me)
2
]Na. The reaction was stirred for 2 hours at room
temperature and then filtered through Celite. The solvent was removed in vacuo. Dry
diethyl ether (10 mL) was added to the residue and the vial was sonicated briefly. The
suspension was then cooled using a cold well and cold, dry hexanes (10 mL) was added.
The suspension was filtered and washed with cold, dry hexanes. The solid was then
dissolved with cold, dry benzene, chilled again and filtered. The filtrate was then
lyophilized to yield 39.5 mg (0.071 mmol, 71%) of 5.27 as an orange-red solid.
Crystallization from dichloromethane and hexanes produced crystals suitable for X-ray
crystallographic analysis.
Even when isolated cleanly, this complex was found to undergo facile disproportionation
in solution to form 5.28 and bis(triphenylphosphine)nickel(II) chloride. As a result, it has
been impossible to acquire a
1
H NMR spectrum that does not contain a few percent of
bis(dimethyldipyridylborate)nickel(II).
MP: Decomposes from 141-146 °C with most rapid darkening from 143-145 °C.
1
H NMR (benzene-d
6
, 500 MHz) δ: 8.721 (br, 2H), 7.824 (br, 5 H), 7.599 (br d, J = 9 Hz,
2H), 6.945-6.893 (m, 10H), 6.642 (br t, J = 8.8 Hz, 2H), 5.897 (br, 2 H), 2.877 (br s, 3H),
0.966 (br s, 3H).
13
C NMR (CD
2
Cl
2
, 150 MHz, -30 °C) δ: 189.448 (br), 187.96 (br), 152.237, 150.788,
134.524 (br), 133.89, 133.765, 130.784, 129.059 (d, J
CP
= 38 Hz), 128.560 (d, J
CP
= 7.6
Hz), 126.813 (br), 126.177 (br), 119.432, 19.218 (br), 9.063 (br).
184
11
B NMR (benzene-d
6
, 128 MHz) δ: -11.387.
31
P NMR (CD
2
Cl
2
, 243 MHz, -30 °C) δ: 12.419.
MALDI: m/z = 552.8941 g/mol, calc’d. for C
30
H
29
BClNiN
2
P
+
[M]
+
: 552.1203 g/mol.
FT-IR (thin film / cm
-1
) v = 3067.76, 2912.82, 2823.99, 1963.28, 1896.13, 1817.39,
1592.78, 1553.13, 149.62, 1435.29, 1290.62, 1217.84, 1093.77, 1012.64, 744.01.
Anal. Calc. for C
30
H
29
BClNiN
2
P: C, 65.1; H, 5.28; N, 5.06. Found: C, 65.04; H, 5.47; N,
5.28.
X-ray crystallographic analysis of 5.27: See page 219.
Figure 6.4. ORTEP diagram of [(py)
2
BMe
2
]Ni(PPh
3
)Cl. Ellipsoids drawn at the 50%
probability level. 5.27 cocrystallized with disordered ½ hexane, which was removed by
Squeeze.
185
186
[(py)
2
BMe
2
]
2
Ni (5.28):
Under N
2
in a dry vial containing a teflon stir bar, Ni(OAc)
2
·4 H
2
O
6
(62.2 mg, 0.25
mmol) and [(py)
2
B(Me)
2
]Na
31
(55.0 mg, 0.25 mmol) were dissolved in dry toluene (5
mL). The reaction was stirred at 50 °C until no blue starting material remained (15 h).
The product precipitates as a yellow solid and was filtered under air and washed with
H
2
O, MeOH and Et
2
O. The solid was then dried under vacuum to yield 41.4 mg (0.09
mmol, 73% based on ½ 5.26) of 5.28. Data are consistent with the compound reported in
the literature (IR, melting point).
31a
A
1
H NMR is not reported in the literature and is
therefore included here.
MP: Begins to darken at 240 °C but does not melt by 280 °C.
1
H NMR (CD
2
Cl
2
, 400 MHz) δ: 7.726 (d, J = 4.8 Hz, 2H), 7.569 (d, J = 6.8 Hz, 2H),
7.352 (t, J = 7.6 Hz, 2H), 6.579 (t, J = 6.8 Hz, 2H), 2.603 (s, 3H), 0.435 (s, 3H).
H
2
O
187
[(py)
2
BMe
2
]Ni(acac) (5.29):
Under N
2
in a dry vial containing a teflon stir bar, Ni(acac)
2
(64.2 mg, 0.25 mmol) was
suspended in 10 mL of dry dichloromethane. In another dry vial, [(py)
2
B(Me)
2
]Na
31
(22.0
mg, 0.10 mmol) was dissolved in 5 mL of dry dichloromethane and added slowly to the
solution of Ni(acac)
2
. Another 5 mL of dichloromethane was used to rinse the vial and
added slowly to the solution of Ni(acac)
2
. The green solution turned orange on addition
of [(py)
2
B(Me)
2
]Na. The reaction was stirred for 2 hours at room temperature and then
filtered through Celite. The solvent was removed in vacuo. Dry hexanes (10 mL) was
added to the residue and the vial was sonicated briefly. The suspension was then cooled
using a cold well, filtered and washed with cold, dry hexanes. The solid was dried under
vacuum to yield 23.7 mg (0.067 mmol, 67%) of 5.29 as an orange solid. Crystallization
from dichloromethane and hexanes produced crystals suitable for X-ray crystallographic
analysis.
MP: Decomposes from 212-230 °C with most rapid darkening from 225-228 °C.
1
H NMR (CD
2
Cl
2
, 400 MHz) δ: 8.296 (d, J = 5.6 Hz, 2H), 7.395 (d, J = 6.8 Hz, 2H),
7.336 (t, J = 7.4 Hz, 2H), 6.823 (t, J = 6 Hz, 2H), 5.546 (s, 1H), 2.267 (br s, 3H), 1.873
(s, 6 H), 0.265 (br s, 3 H).
13
C NMR (CD
2
Cl
2
, 150 MHz, -30 °C) δ: 189.011 (br), 187.670, 149.654, 135.045,
125.572, 119.609, 101.704, 25.909, 18.728 (br), 8.810 (br).
11
B NMR (CD
2
Cl
2
, 128 MHz) δ: -12.676.
MALDI: m/z = 354.2477 g/mol, calc’d. for C
17
H
22
BN
2
O
2
Ni
+
[M]
+
: 354.1050.
FT-IR (thin film / cm
-1
) v = 2891.92, 2821.81, 1586.41, 1532.39, 1388.63, 1289.47,
1222.57, 1159.73, 1015.71, 934.76, 788.67, 753.86, 738.46.
Anal. Calc. for C
17
H
22
BN
2
O
2
Ni: C, 57.54; H, 5.96; N, 7.89. Found: C, 56.23; H, 5.7; N,
7.49.
HR-MS (+ESI): m/z = 355.1129 g/mol, calc’d. for C
17
H
22
BN
2
O
2
Ni
+
[MH]
+
: 355.1122
g/mol.
188
X-ray crystallographic analysis of 5.29: See page 228.
Figure 6.5. ORTEP diagram of [(py)
2
BMe
2
]Ni(acac). Ellipsoids drawn at the 50%
probability level.
189
190
[(py)
2
BMe
2
]Cu(NCCD
3
) (6.3) and [(py)
2
BMe
2
]Cu(CNtBu) (6.4):
In a dry J. Young NMR tube under N
2
, CuI
6
(5.7 mg, 0.03 mmol) was suspended in
CD
3
CN (750 μL) and [(py)
2
B(Me)
2
]Na
31
(6.6 mg, 0.03 mmol) was added to the solution.
Upon addition of [(py)
2
B(Me)
2
]Na, an orange solution was generated.
1
H NMR revealed
a fluxional species, tentatively identified as 6.3. Under cover of N
2
, tert-butylisonitrile
10
(3.4 μL, 0.03 mmol) was added. The solution remained orange.
1
H NMR revealed a
complex with a slower rate of exchange, tentatively identified as 6.4.
1
H and
11
B NMR of dynamic complex 6.3:
Observed signals are the average of 6.3 and free [(py)
2
B(Me)
2
]Na.
191
1
H and
11
B NMR of dynamic complex 6.4:
192
6.6 References
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2
(CH
2
SiMe
3
)
6
]
2-
and Its Conversion to the Unusual
"Windowpane" Bis(metallacycle) Complex [Cr(κ
2
-C,C'-CH
2
SiMe
2
CH
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)
2
]
2-
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195
Appendix. X-ray Crystallographic Data
Acknowledgement
X-ray data collection for 4.3a was done at the University of Southern California
by Prof. Ralf Haiges. X-ray data collection for 4.4a, and 4.4b was done at the University
of Southern California with assistance from Prof. Ralf Haiges. Structure solution for 4.3a
was done by Prof. Ralf Haiges. Structure solution for 4.4a, 4.4b, 5.27 and 5.29 was done
with assistance from Prof. Ralf Haiges. The author gratefully acknowledges this
contribution to the collection and interpretation of this data.
[(py)
2
B(Me)
2
]Rh(CO)
2
(4.3a)
Figure A.1. ORTEP diagram of [(py)
2
B(Me)
2
]Rh(CO)
2
.
1
Ellipsoids drawn at the 50%
probability level.
A clear yellow prism-like specimen of C
14
H
14
BN
2
O
2
Rh, approximate dimensions
0.350 mm x 0.470 mm x 0.500 mm, was used for the X-ray crystallographic analysis. The
X-ray intensity data were measured on a Bruker APEX II CCD system equipped with a
TRIUMPH curved-crystal monochromator and a MoKα fine-focus tube (λ = 0.71073 Å).
A total of 2520 frames were collected. The total exposure time was 0.70 hours. The
frames were integrated with the Bruker SAINT software package using a SAINT V8.18C
algorithm. The integration of the data using a monoclinic unit cell yielded a total of
26000 reflections to a maximum θ angle of 30.70° (0.70 Å resolution), of which 4407
were independent (average redundancy 5.900, completeness = 97.7%, R
int
= 4.45%, R
sig
=
2.59%) and 4086 (92.72%) were greater than 2σ(F
2
). The final cell constants of a =
9.343(2) Å, b = 11.129(3) Å, c = 14.519(3) Å, β = 106.030(3)°, volume = 1451.0(6) Å
3
,
are based upon the refinement of the XYZ-centroids of 9898 reflections above 20 σ(I)
with 4.536° < 2θ < 61.30°. Data were corrected for absorption effects using the multi-
scan method (SADABS). The ratio of minimum to maximum apparent transmission was
0.612. The calculated minimum and maximum transmission coefficients (based on crystal
size) are 0.5911 and 0.6848.
196
The structure was solved and refined using the Bruker SHELXTL Software
Package, using the space group P 1 21/c 1, with Z = 4 for the formula unit,
C
14
H
14
BN
2
O
2
Rh. The final anisotropic full-matrix least-squares refinement on F
2
with
183 variables converged at R1 = 2.47%, for the observed data and wR2 = 6.76% for all
data. The goodness-of-fit was 1.018. The largest peak in the final difference electron
density synthesis was 0.634 e
-
/Å
3
and the largest hole was -1.248 e
-
/Å
3
with an RMS
deviation of 0.090 e
-
/Å
3
. On the basis of the final model, the calculated density was 1.630
g/cm
3
and F(000), 712 e
-
.
Table A.2. Crystal data and structure refinement for [(py)
2
B(Me)
2
]Rh(CO)
2
(4.3a).
Chemical formula C
14
H
14
BN
2
O
2
Rh
Formula weight 355.99
Temperature 100(2) K
Wavelength 0.71073 Å
Crystal size 0.350 x 0.470 x 0.500 mm
Crystal habit clear yellow prism
Crystal system monoclinic
Space group P 1 21/c 1
Unit cell dimensions
a = 9.343(2)
Å
α = 90°
b = 11.129(3)
Å
β = 106.030(3)°
c = 14.519(3)
Å
γ = 90°
Volume 1451.0(6) Å
3
Z 4
Density (calculated) 1.630 g/cm
3
Absorption coefficient 1.177 mm
-1
F(000) 712
Theta range for data collection 2.27 to 30.70°
Index ranges -13<=h<=12, -15<=k<=15, -20<=l<=20
Reflections collected 26000
Independent reflections 4407 [R(int) = 0.0445]
Coverage of independent reflections 97.7%
Absorption correction multi-scan
Max. and min. transmission 0.6848 and 0.5911
Structure solution technique direct methods
Structure solution program SHELXS-97 (Sheldrick, 2008)
Refinement method Full-matrix least-squares on F2
Refinement program SHELXL 2012-4 (Sheldrick, 2012)
197
Function minimized Σ w(Fo
2
- Fc
2
)
2
Data / restraints / parameters 4407 / 0 / 183
Goodness-of-fit on F2 1.018
Δ/σmax 0.011
Final R indices 4086 data; I>2σ(I) R1 = 0.0247, wR2 = 0.0644
all data R1 = 0.0272, wR2 = 0.0676
Weighting scheme
w=1/[σ
2
(F
o
2
)+(0.0366P)
2
+1.2011P]
where P=(F
o
2
+2F
c
2
)/3
Largest diff. peak and hole 0.634 and -1.248 eÅ
-3
R.M.S. deviation from mean 0.090 eÅ
-3
Table A.3. Atomic coordinates and equivalent isotropic atomic displacement parameters
(Å
2
) for [(py)
2
B(Me)
2
]Rh(CO)
2
(4.3a).
U(eq) is defined as one third of the trace of the orthogonalized U
ij
tensor.
x/a y/b z/c U(eq)
B1 0.12903(18) 0.27742(14) 0.11097(11) 0.0145(3)
C1 0.62868(19) 0.20832(16) 0.20151(12) 0.0216(3)
C2 0.54356(18) 0.21100(16) 0.00980(12) 0.0215(3)
C3 0.12192(17) 0.19111(12) 0.01784(11) 0.0133(2)
C4 0.20786(17) 0.19382(12) 0.20386(11) 0.0140(3)
C5 0.40594(18) 0.06648(14) 0.28437(12) 0.0202(3)
C6 0.34175(19) 0.04226(15) 0.35702(11) 0.0221(3)
C7 0.20741(19) 0.09780(14) 0.35486(11) 0.0202(3)
C8 0.14163(19) 0.17262(13) 0.27859(11) 0.0165(3)
C9 0.23007(18) 0.39915(13) 0.11333(11) 0.0184(3)
C10 0.96138(18) 0.31698(14) 0.11219(11) 0.0189(3)
C11 0.98704(17) 0.15988(13) 0.95079(11) 0.0150(2)
C12 0.98254(17) 0.08058(13) 0.87684(11) 0.0170(3)
C13 0.11555(18) 0.03216(13) 0.86765(11) 0.0179(3)
C14 0.24590(17) 0.06597(13) 0.93293(11) 0.0172(3)
N1 0.24942(14) 0.14228(11) 0.00634(9) 0.0141(2)
N2 0.34192(14) 0.14108(12) 0.21035(9) 0.0156(2)
O1 0.73456(14) 0.22238(15) 0.26089(10) 0.0310(3)
O2 0.59810(15) 0.22635(15) 0.95044(10) 0.0335(3)
Rh1 0.450477(12) 0.181329(10) 0.106372(8) 0.01496(5)
198
Table A.4. Bond lengths (Å) for [(py)
2
B(Me)
2
]Rh(CO)
2
(4.3a).
B1-C10 1.632(2) B1-C4 1.637(2)
B1-C9 1.646(2) B1-C3 1.645(2)
C1-O1 1.129(2) C1-Rh1 1.8709(17)
C2-O2 1.129(2) C2-Rh1 1.8721(17)
C3-N1 1.3609(19) C3-C11 1.407(2)
C4-N2 1.363(2) C4-C8 1.409(2)
C5-N2 1.3590(19) C5-C6 1.376(2)
C5-H4 0.95 C6-C7 1.392(2)
C6-H1 0.95 C7-C8 1.386(2)
C7-H3 0.95 C8-H2 0.95
C9-H5 0.98 C9-H7 0.98
C9-H6 0.98 C10-H9 0.98
C10-H10 0.98 C10-H8 0.98
C11-C12 1.381(2) C11-H11 0.95
C12-C13 1.394(2) C12-H12 0.95
C13-C14 1.373(2) C13-H13 0.95
C14-N1 1.3560(19) C14-H14 0.95
N1-Rh1 2.0785(13) N2-Rh1 2.0866(13)
199
Table A.5. Bond angles (°) for [(py)
2
B(Me)
2
]Rh(CO)
2
(4.3a).
C10-B1-C4 111.06(12) C10-B1-C9 108.93(12)
C4-B1-C9 109.01(12) C10-B1-C3 110.21(12)
C4-B1-C3 104.61(11) C9-B1-C3 112.98(12)
O1-C1-Rh1 177.78(16) O2-C2-Rh1 178.28(17)
N1-C3-C11 117.62(13) N1-C3-B1 119.74(13)
C11-C3-B1 122.56(13) N2-C4-C8 117.72(14)
N2-C4-B1 119.85(13) C8-C4-B1 122.42(13)
N2-C5-C6 122.41(15) N2-C5-H4 118.8
C6-C5-H4 118.8 C5-C6-C7 118.49(14)
C5-C6-H1 120.8 C7-C6-H1 120.8
C8-C7-C6 118.87(15) C8-C7-H3 120.6
C6-C7-H3 120.6 C7-C8-C4 121.57(15)
C7-C8-H2 119.2 C4-C8-H2 119.2
B1-C9-H5 109.5 B1-C9-H7 109.5
H5-C9-H7 109.5 B1-C9-H6 109.5
H5-C9-H6 109.5 H7-C9-H6 109.5
B1-C10-H9 109.5 B1-C10-H10 109.5
H9-C10-H10 109.5 B1-C10-H8 109.5
H9-C10-H8 109.5 H10-C10-H8 109.5
C12-C11-C3 121.66(14) C12-C11-H11 119.2
C3-C11-H11 119.2 C11-C12-C13 118.99(14)
C11-C12-H12 120.5 C13-C12-H12 120.5
C14-C13-C12 118.17(14) C14-C13-H13 120.9
C12-C13-H13 120.9 N1-C14-C13 122.58(14)
N1-C14-H14 118.7 C13-C14-H14 118.7
C14-N1-C3 120.96(13) C14-N1-Rh1 120.08(10)
C3-N1-Rh1 118.92(10) C5-N2-C4 120.88(13)
C5-N2-Rh1 120.50(11) C4-N2-Rh1 118.60(10)
C2-Rh1-C1 91.25(7) C2-Rh1-N1 91.76(6)
C1-Rh1-N1 176.20(6) C2-Rh1-N2 177.26(6)
C1-Rh1-N2 90.66(6) N1-Rh1-N2 86.25(5)
200
Table A.6. Torsion angles (°) for [(py)
2
B(Me)
2
]Rh(CO)
2
(4.3a).
C10-B1-C3-N1 -176.18(12) C4-B1-C3-N1 -56.73(16)
C9-B1-C3-N1 61.70(17) C10-B1-C3-C11 0.52(19)
C4-B1-C3-C11 119.96(14) C9-B1-C3-C11 -121.60(15)
C10-B1-C4-N2 172.95(12) C9-B1-C4-N2 -67.03(16)
C3-B1-C4-N2 54.07(16) C10-B1-C4-C8 -6.52(19)
C9-B1-C4-C8 113.50(15) C3-B1-C4-C8 -125.40(14)
N2-C5-C6-C7 -0.9(2) C5-C6-C7-C8 1.7(2)
C6-C7-C8-C4 -0.2(2) N2-C4-C8-C7 -2.0(2)
B1-C4-C8-C7 177.48(14) N1-C3-C11-C12 1.4(2)
B1-C3-C11-C12 -175.40(14) C3-C11-C12-C13 -1.2(2)
C11-C12-C13-C14 -0.1(2) C12-C13-C14-N1 1.3(2)
C13-C14-N1-C3 -1.1(2) C13-C14-N1-Rh1 176.58(11)
C11-C3-N1-C14 -0.2(2) B1-C3-N1-C14 176.63(13)
C11-C3-N1-Rh1 -177.93(10) B1-C3-N1-Rh1 -1.08(17)
C6-C5-N2-C4 -1.4(2) C6-C5-N2-Rh1 176.69(12)
C8-C4-N2-C5 2.8(2) B1-C4-N2-C5 -176.69(13)
C8-C4-N2-Rh1 -175.33(10) B1-C4-N2-Rh1 5.18(17)
O2-C2-Rh1-C1 132.(5) O2-C2-Rh1-N1 -46.(5)
O2-C2-Rh1-N2 -2.(6) O1-C1-Rh1-C2 -155.(4)
O1-C1-Rh1-N1 -13.(5) O1-C1-Rh1-N2 23.(4)
C14-N1-Rh1-C2 48.06(12) C3-N1-Rh1-C2 -134.21(12)
C14-N1-Rh1-C1 -94.2(9) C3-N1-Rh1-C1 83.5(9)
C14-N1-Rh1-N2 -130.06(12) C3-N1-Rh1-N2 47.66(11)
C5-N2-Rh1-C2 88.6(13) C4-N2-Rh1-C2 -93.2(13)
C5-N2-Rh1-C1 -45.93(13) C4-N2-Rh1-C1 132.22(12)
C5-N2-Rh1-N1 131.85(12) C4-N2-Rh1-N1 -50.01(11)
201
Table A.7. Anisotropic atomic displacement parameters (Å
2
) for [(py)
2
B(Me)
2
]Rh(CO)
2
(4.3a).
The anisotropic atomic displacement factor exponent takes the form: -2π
2
[ h
2
a
*2
U
11
+ ...
+ 2 h k a
*
b
*
U
12
]
U
11
U
22
U
33
U
23
U
13
U
12
B1 0.0161(7) 0.0140(7) 0.0135(7) -0.0001(5) 0.0041(5) 0.0007(5)
C1 0.0177(7) 0.0260(7) 0.0226(8) -0.0014(6) 0.0082(6) -0.0011(6)
C2 0.0162(7) 0.0260(7) 0.0226(7) 0.0020(6) 0.0056(6) 0.0011(6)
C3 0.0152(6) 0.0122(6) 0.0129(6) 0.0016(4) 0.0046(5) 0.0006(4)
C4 0.0149(6) 0.0133(6) 0.0132(6) -0.0022(4) 0.0031(5) -0.0023(5)
C5 0.0187(7) 0.0204(7) 0.0192(7) 0.0023(5) 0.0013(5) 0.0022(5)
C6 0.0276(8) 0.0191(7) 0.0169(7) 0.0039(5) 0.0014(6) -0.0010(6)
C7 0.0290(8) 0.0177(7) 0.0148(6) -0.0006(5) 0.0075(6) -0.0042(6)
C8 0.0211(7) 0.0144(6) 0.0149(6) -0.0017(5) 0.0065(6) -0.0019(5)
C9 0.0238(7) 0.0146(6) 0.0178(7) -0.0008(5) 0.0074(6) -0.0005(5)
C10 0.0195(8) 0.0211(8) 0.0164(7) -0.0011(5) 0.0056(6) 0.0044(5)
C11 0.0152(6) 0.0151(6) 0.0143(6) 0.0011(5) 0.0036(5) 0.0000(5)
C12 0.0190(7) 0.0167(6) 0.0138(6) -0.0002(5) 0.0018(5) -0.0031(5)
C13 0.0241(7) 0.0146(6) 0.0152(6) -0.0016(5) 0.0056(5) 0.0007(5)
C14 0.0202(7) 0.0155(6) 0.0169(6) -0.0014(5) 0.0067(5) 0.0028(5)
N1 0.0152(5) 0.0137(5) 0.0131(5) -0.0006(4) 0.0036(4) 0.0010(4)
N2 0.0152(5) 0.0163(6) 0.0141(5) 0.0010(4) 0.0022(4) -0.0006(4)
O1 0.0189(6) 0.0461(8) 0.0255(6) -0.0028(6) 0.0018(5) -0.0066(6)
O2 0.0245(6) 0.0503(9) 0.0287(7) 0.0080(6) 0.0124(5) 0.0027(6)
Rh1 0.01207(7) 0.01718(7) 0.01554(7) -0.00031(3) 0.00370(5) 0.00012(3)
202
Table A.8. Hydrogen atomic coordinates and isotropic atomic displacement parameters
(Å
2
) for [(py)
2
B(Me)
2
]Rh(CO)
2
(4.3a).
x/a y/b z/c U(eq)
H4 0.4984 0.0297 0.2860 0.024
H1 0.3881 -0.0112 0.4075 0.027
H3 0.1616 0.0847 0.4048 0.024
H2 0.0497 0.2105 0.2766 0.02
H5 0.1759 0.4554 0.0640 0.028
H7 0.3246 0.3773 0.1009 0.028
H6 0.2498 0.4371 0.1765 0.028
H9 -0.0980 0.2450 0.1143 0.028
H10 -0.0854 0.3631 0.0542 0.028
H8 -0.0332 0.3666 0.1688 0.028
H11 -0.1032 0.1942 -0.0435 0.018
H12 -0.1098 0.0594 -0.1671 0.02
H13 0.1160 -0.0227 -0.1824 0.021
H14 0.3372 0.0347 -0.0736 0.021
203
[(py)
2
B(Me)
2
]Rh(cod) (4.4a)
Figure A.2. ORTEP diagram of [(py)
2
B(Me)
2
]Rh(cod).
2
Ellipsoids drawn at the 50%
probability level.
A specimen of C
20
H
26
BN
2
Rh, approximate dimensions 0.240 mm x 0.250 mm x
0.380 mm, was used for the X-ray crystallographic analysis. The X-ray intensity data
were measured on a Bruker APEX CCD system equipped with a graphite monochromator
and a MoKα fine-focus tube (λ = 0.71073 Å).
A total of 1315 frames were collected. The total exposure time was 3.65 hours.
The frames were integrated with the Bruker SAINT software package using a SAINT
V8.27B algorithm. The integration of the data using a monoclinic unit cell yielded a total
of 10620 reflections to a maximum θ angle of 27.51° (0.77 Å resolution), of which 4036
were independent (average redundancy 2.631, completeness = 97.4%, R
int
= 4.96%, R
sig
=
4.77%) and 3571 (88.48%) were greater than 2σ(F
2
). The final cell constants of a =
10.3908(5) Å, b = 11.3411(6) Å, c = 15.4163(8) Å, β = 96.5490(10)°, volume =
1804.85(16) Å
3
, are based upon the refinement of the XYZ-centroids of reflections above
20 σ(I). Data were corrected for absorption effects using the multi-scan method
(SADABS). The ratio of minimum to maximum apparent transmission was 0.802.
The structure was solved and refined using the Bruker SHELXTL Software
Package, using the space group P 1 21/n 1, with Z = 4 for the formula unit,
C
20
H
26
BN
2
Rh. The final anisotropic full-matrix least-squares refinement on F
2
with 219
variables converged at R1 = 3.61%, for the observed data and wR2 = 8.89% for all data.
The goodness-of-fit was 1.080. The largest peak in the final difference electron density
synthesis was 1.112 e
-
/Å
3
and the largest hole was -0.859 e
-
/Å
3
with an RMS deviation of
0.100 e
-
/Å
3
. On the basis of the final model, the calculated density was 1.502 g/cm
3
and
F(000), 840 e
-
.
204
Table A.9. Crystal data and structure refinement for [(py)
2
B(Me)
2
]Rh(cod)
(4.4a).
Chemical formula C
20
H
26
BN
2
Rh
Formula weight 408.15
Temperature 143(2) K
Wavelength 0.71073 Å
Crystal size 0.240 x 0.250 x 0.380 mm
Crystal system monoclinic
Space group P 1 21/n 1
Unit cell dimensions a = 10.3908(5) Å α = 90°
b = 11.3411(6) Å β = 96.5490(10)°
c = 15.4163(8) Å γ = 90°
Volume 1804.85(16) Å
3
Z 4
Density (calculated) 1.502 g/cm
3
Absorption coefficient 0.949 mm
-1
F(000) 840
Theta range for data collection 2.23 to 27.51°
Index ranges -13<=h<=13, -14<=k<=13, -15<=l<=20
Reflections collected 10620
Independent reflections 4036 [R(int) = 0.0496]
Absorption correction multi-scan
Structure solution technique direct methods
Structure solution program SHELXS-97 (Sheldrick, 2008)
Refinement method Full-matrix least-squares on F2
Refinement program SHELXL 2012/9 (Sheldrick, 2012)
Function minimized Σ w(Fo
2
- Fc
2
)
2
Data / restraints / parameters 4036 / 0 / 219
Goodness-of-fit on F2 1.080
Δ/σmax 0.003
Final R indices 3571 data; I>2σ(I) R1 = 0.0361, wR2 = 0.0859
all data R1 = 0.0400, wR2 = 0.0889
Weighting scheme
w=1/[σ
2
(F
o
2
)+(0.0481P)
2
+0.4245P]
where P=(F
o
2
+2F
c
2
)/3
Largest diff. peak and hole 1.112 and -0.859 eÅ
-3
R.M.S. deviation from mean 0.100 eÅ
-3
205
Table A.10. Atomic coordinates and equivalent isotropic atomic displacement
parameters (Å
2
) for [(py)
2
B(Me)
2
]Rh(cod)
(4.4a).
U(eq) is defined as one third of the trace of the orthogonalized U
ij
tensor.
x/a y/b z/c U(eq)
B1 0.8944(2) 0.7315(2) 0.15821(17) 0.0283(5)
C1 0.6626(2) 0.9931(2) 0.09598(15) 0.0308(5)
C2 0.7030(2) 0.0401(2) 0.02187(15) 0.0346(5)
C3 0.8077(2) 0.9888(2) 0.98863(16) 0.0357(5)
C4 0.8676(2) 0.8949(2) 0.03269(15) 0.0326(5)
C5 0.8244(2) 0.8470(2) 0.10861(15) 0.0260(5)
C6 0.9214(2) 0.7624(2) 0.26267(15) 0.0272(5)
C7 0.0426(2) 0.7413(2) 0.31075(16) 0.0352(5)
C8 0.0711(2) 0.7785(3) 0.39602(17) 0.0428(6)
C9 0.9786(3) 0.8399(2) 0.43422(17) 0.0379(6)
C10 0.8577(2) 0.8532(2) 0.38779(16) 0.0327(5)
C11 0.7995(2) 0.6177(2) 0.14084(17) 0.0334(5)
C12 0.0321(3) 0.7036(2) 0.11991(18) 0.0385(6)
C13 0.5667(3) 0.6751(2) 0.31525(18) 0.0370(6)
C14 0.5558(2) 0.7789(3) 0.36052(16) 0.0387(6)
C15 0.4354(3) 0.8502(3) 0.3671(2) 0.0529(8)
C16 0.3585(2) 0.8739(3) 0.27743(18) 0.0404(6)
C17 0.4426(2) 0.8738(2) 0.20346(16) 0.0319(5)
C18 0.4698(2) 0.7729(2) 0.15660(16) 0.0320(5)
C19 0.4224(3) 0.6505(3) 0.17364(19) 0.0423(6)
C20 0.4511(3) 0.6121(3) 0.2673(2) 0.0549(8)
N1 0.71811(17) 0.89821(17) 0.13778(12) 0.0266(4)
N2 0.8280(2) 0.81288(16) 0.30544(14) 0.0279(4)
Rh1 0.63729(2) 0.81712(2) 0.24202(2) 0.02566(9)
206
Table A.11. Bond lengths (Å) for [(py)
2
B(Me)
2
]Rh(cod)
(4.4a).
B1-C11 1.628(4) B1-C12 1.639(4)
B1-C6 1.641(3) B1-C5 1.644(4)
C1-N1 1.349(3) C1-C2 1.370(3)
C2-C3 1.383(4) C3-C4 1.374(4)
C4-C5 1.410(3) C5-N1 1.368(3)
C6-N2 1.360(3) C6-C7 1.407(3)
C7-C8 1.380(4) C8-C9 1.373(4)
C9-C10 1.382(3) C10-N2 1.351(3)
C13-C14 1.380(4) C13-C20 1.515(4)
C13-Rh1 2.144(2) C14-C15 1.502(4)
C14-Rh1 2.144(2) C15-C16 1.539(4)
C16-C17 1.513(3) C17-C18 1.399(4)
C17-Rh1 2.141(2) C18-C19 1.506(4)
C18-Rh1 2.120(2) C19-C20 1.505(4)
N1-Rh1 2.1075(19) N2-Rh1 2.108(2)
207
Table A.12. Bond angles (°) for [(py)
2
B(Me)
2
]Rh(cod)
(4.4a).
C11-B1-C12 109.0(2) C11-B1-C6 111.30(19)
C12-B1-C6 109.66(19) C11-B1-C5 109.11(19)
C12-B1-C5 110.1(2) C6-B1-C5 107.67(19)
N1-C1-C2 123.6(2) C1-C2-C3 118.3(2)
C4-C3-C2 118.3(2) C3-C4-C5 122.7(2)
N1-C5-C4 117.0(2) N1-C5-B1 121.1(2)
C4-C5-B1 121.8(2) N2-C6-C7 117.5(2)
N2-C6-B1 120.95(19) C7-C6-B1 121.5(2)
C8-C7-C6 122.1(2) C9-C8-C7 118.6(2)
C8-C9-C10 118.2(2) N2-C10-C9 123.1(3)
C14-C13-C20 122.9(3) C14-C13-Rh1 71.24(15)
C20-C13-Rh1 113.38(18) C13-C14-C15 127.6(3)
C13-C14-Rh1 71.21(15) C15-C14-Rh1 111.21(18)
C14-C15-C16 112.6(2) C17-C16-C15 113.1(2)
C18-C17-C16 123.9(2) C18-C17-Rh1 69.99(13)
C16-C17-Rh1 113.53(16) C17-C18-C19 125.1(2)
C17-C18-Rh1 71.67(13) C19-C18-Rh1 111.81(16)
C20-C19-C18 113.6(2) C19-C20-C13 113.0(2)
C1-N1-C5 119.9(2) C1-N1-Rh1 121.75(16)
C5-N1-Rh1 118.15(15) C10-N2-C6 119.9(2)
C10-N2-Rh1 121.99(17) C6-N2-Rh1 118.01(15)
N1-Rh1-N2 85.89(7) N1-Rh1-C18 90.00(8)
N2-Rh1-C18 160.86(9) N1-Rh1-C17 95.94(8)
N2-Rh1-C17 160.75(9) C18-Rh1-C17 38.34(10)
N1-Rh1-C13 156.85(9) N2-Rh1-C13 95.66(9)
C18-Rh1-C13 80.99(10) C17-Rh1-C13 90.14(10)
N1-Rh1-C14 165.59(10) N2-Rh1-C14 92.41(9)
C18-Rh1-C14 96.04(10) C17-Rh1-C14 81.06(10)
C13-Rh1-C14 37.55(11)
208
Table A.13. Anisotropic atomic displacement parameters (Å
2
) for [(py)
2
B(Me)
2
]Rh(cod)
(4.4a).
The anisotropic atomic displacement factor exponent takes the form: -2π
2
[ h
2
a
*2
U
11
+ ...
+ 2 h k a
*
b
*
U
12
]
U
11
U
22
U
33
U
23
U
13
U
12
B1 0.0246(12) 0.0271(13) 0.0336(13) 0.0009(11) 0.0048(10) 0.0014(10)
C1 0.0266(11) 0.0318(12) 0.0326(12) 0.0058(10) -0.0024(9) 0.0005(9)
C2 0.0373(13) 0.0342(13) 0.0306(12) 0.0080(10) -0.0033(9) -0.0030(10)
C3 0.0418(14) 0.0387(14) 0.0264(11) 0.0038(11) 0.0034(10) -0.0115(11)
C4 0.0337(12) 0.0342(13) 0.0307(11) -0.0025(10) 0.0075(9) -0.0049(10)
C5 0.0218(11) 0.0287(11) 0.0273(11) -0.0025(10) 0.0018(8) -0.0048(9)
C6 0.0227(11) 0.0265(12) 0.0328(11) 0.0072(10) 0.0049(8) -0.0042(9)
C7 0.0216(11) 0.0416(15) 0.0426(14) 0.0070(12) 0.0046(9) -0.0018(10)
C8 0.0255(12) 0.0604(17) 0.0404(14) 0.0143(14) -0.0058(10) -0.0069(12)
C9 0.0385(14) 0.0441(14) 0.0294(12) 0.0083(11) -0.0030(10) -0.0088(11)
C10 0.0353(13) 0.0334(12) 0.0290(12) 0.0050(11) 0.0019(10) 0.0004(11)
C11 0.0297(12) 0.0296(13) 0.0407(13) -0.0013(11) 0.0037(10) 0.0006(9)
C12 0.0306(13) 0.0448(15) 0.0412(14) 0.0014(12) 0.0091(11) 0.0042(11)
C13 0.0318(13) 0.0428(16) 0.0368(14) 0.0196(11) 0.0050(10) 0.0006(10)
C14 0.0300(12) 0.0575(17) 0.0301(12) 0.0120(13) 0.0099(10) 0.0033(12)
C15 0.0466(17) 0.071(2) 0.0448(16) 0.0105(16) 0.0192(13) 0.0106(16)
C16 0.0251(12) 0.0480(17) 0.0488(15) -0.0027(13) 0.0069(10) 0.0049(10)
C17 0.0217(11) 0.0354(14) 0.0377(12) 0.0083(11) -0.0006(9) 0.0034(9)
C18 0.0245(11) 0.0409(14) 0.0296(11) 0.0038(11) -0.0011(9) 0.0015(10)
C19 0.0386(15) 0.0404(14) 0.0469(15) -0.0053(13) 0.0015(11) -0.0015(12)
C20 0.0561(18) 0.0488(18) 0.0588(18) 0.0141(15) 0.0024(14) -0.0155(14)
N1 0.0249(9) 0.0284(10) 0.0262(9) 0.0017(8) 0.0020(7) -0.0012(7)
N2 0.0275(10) 0.0286(11) 0.0271(10) 0.0042(8) 0.0008(8) 0.0015(7)
Rh1 0.02037(12) 0.03182(14) 0.02489(12) 0.00534(7) 0.00305(7) 0.00228(6)
209
Table A.14. Hydrogen atomic coordinates and isotropic atomic displacement parameters
(Å
2
) for [(py)
2
B(Me)
2
]Rh(cod)
(4.4a).
x/a y/b z/c U(eq)
H1 0.5915 1.0292 0.1192 0.037
H2 0.6603 1.1064 -0.0060 0.042
H3 0.8374 1.0177 -0.0634 0.043
H4 0.9412 0.8608 0.0111 0.039
H7 1.1069 0.7001 0.2836 0.042
H8 1.1531 0.7620 0.4276 0.051
H9 0.9973 0.8724 0.4911 0.045
H10 0.7923 0.8925 0.4151 0.039
H11A 0.8390 0.5494 0.1724 0.05
H11B 0.7866 0.6003 0.0782 0.05
H11C 0.7157 0.6348 0.1615 0.05
H12A 1.0712 0.6328 0.1482 0.058
H12B 1.0909 0.7706 0.1319 0.058
H12C 1.0163 0.6907 0.0567 0.058
H13 0.6360 0.6211 0.3424 0.044
H14 0.6202 0.7854 0.4137 0.046
H15A 0.4598 0.9264 0.3956 0.064
H15B 0.3793 0.8076 0.4044 0.064
H16A 0.2906 0.8129 0.2659 0.049
H16B 0.3149 0.9514 0.2790 0.049
H17 0.4362 0.9476 0.1678 0.038
H18 0.4785 0.7886 0.0937 0.038
H19A 0.3276 0.6474 0.1569 0.051
H19B 0.4632 0.5941 0.1361 0.051
H20A 0.4678 0.5262 0.2690 0.066
H20B 0.3741 0.6272 0.2979 0.066
210
[(py)
2
B(Me)
2
]Ir(cod)
(4.4b)
Figure A.3. ORTEP Diagram of [(py)
2
B(Me)
2
]Ir(cod).
3
Ellipsoids drawn at the 50%
probability level.
A specimen of C
20
H
26
BIrN
2
, approximate dimensions 0.143 mm x 0.222 mm x
0.250 mm, was used for the X-ray crystallographic analysis. The X-ray intensity data
were measured on a Bruker APEX DUO system equipped with a TRIUMPH curved-
crystal monochromator and a MoKα fine-focus tube (λ = 0.71073 Å).
A total of 2520 frames were collected. The total exposure time was 3.50 hours.
The frames were integrated with the Bruker SAINT software package using a narrow-
frame algorithm. The integration of the data using a monoclinic unit cell yielded a total of
43335 reflections to a maximum θ angle of 30.52° (0.70 Å resolution), of which 5450
were independent (average redundancy 7.951, completeness = 99.7%, R
int
= 2.29%) and
5146 (94.42%) were greater than 2σ(F
2
). The final cell constants of a = 10.3674(3) Å, b =
11.3096(3) Å, c = 15.3893(5) Å, volume = 1793.31(9) Å
3
, are based upon the refinement
of the XYZ-centroids of 9774 reflections above 20 σ(I) with 5.327° < 2θ < 61.01°. Data
were corrected for absorption effects using the multi-scan method (SADABS). The ratio
of minimum to maximum apparent transmission was 0.774. The calculated minimum and
maximum transmission coefficients (based on crystal size) are 0.2570 and 0.4160.
The structure was solved and refined using the Bruker SHELXTL Software
Package, using the space group P 1 21/n 1, with Z = 4 for the formula unit, C
20
H
26
BIrN
2
.
The final anisotropic full-matrix least-squares refinement on F
2
with 219 variables
converged at R1 = 1.26%, for the observed data and wR2 = 2.85% for all data. The
goodness-of-fit was 1.077. The largest peak in the final difference electron density
synthesis was 0.682 e
-
/Å
3
and the largest hole was -0.596 e
-
/Å
3
with an RMS deviation of
0.079 e
-
/Å
3
. On the basis of the final model, the calculated density was 1.842 g/cm
3
and
F(000), 968 e
-
.
211
Table A.15. Crystal data and structure refinement for [(py)
2
B(Me)
2
]Ir(cod) (4.4b).
Chemical formula C
20
H
26
BIrN
2
Formula weight 497.44
Temperature 100(2) K
Wavelength 0.71073 Å
Crystal size 0.143 x 0.220 x 0.250 mm
Crystal habit clear yellow Prism
Crystal system monoclinic
Space group P 1 21/n 1
Unit cell dimensions a = 10.3674(3) Å α = 90°
b = 11.3096 (3) Å β = 96°
c = 15.3893 (5) Å γ = 90°
Volume 1793.31(9) Å
3
Z 4
Density (calculated) 1.842 g/cm
3
Absorption coefficient 7.447 mm
-1
F(000) 968
Radiation source fine-focus tube, MoKα
Theta range for data collection 2.24 to 30.54°
Index ranges -14<=h<=14, -16<=k<=16, -21<=l<=21
Reflections collected 43335
Independent reflections 5450 [R(int) = 0.0229]
Coverage of independent reflections 99.7%
Absorption correction multi-scan
Max. and min. transmission 0.4160 and 0.2570
Structure solution technique direct methods
Structure solution program SHELXTL XT 2013/1 (Bruker AXS)
Refinement method Full-matrix least-squares on F2
Refinement program SHELXTL XL 2013/2 (Bruker AXS)
Function minimized Σ w(Fo
2
- Fc
2
)
2
Data / restraints / parameters 5450 / 0 / 219
Goodness-of-fit on F2 1.077
Δ/σmax 0.002
Final R indices 5146 data; I>2σ(I) R1 = 0.0126, wR2 = 0.0282
all data R1 = 0.0141, wR2 = 0.0285
Weighting scheme
w=1/[σ
2
(F
o
2
)+(0.0101P)
2
+1.3986P]
where P=(F
o
2
+2F
c
2
)/3
Largest diff. peak and hole 0.682 and -0.596 eÅ
-3
R.M.S. deviation from mean 0.079 eÅ
-3
212
Table A.16. Atomic coordinates and equivalent isotropic atomic displacement
parameters (Å
2
) for [(py)
2
B(Me)
2
]Ir(cod) (4.4b).
U(eq) is defined as one third of the trace of the orthogonalized U
ij
tensor.
x/a y/b z/c U(eq)
B1 0.10439(16) 0.27091(15) 0.34568(11) 0.0149(3)
C1 0.33548(15) 0.00621(14) 0.40473(10) 0.0166(3)
C2 0.29445(15) 0.95803(14) 0.47921(10) 0.0188(3)
C3 0.19013(16) 0.01031(14) 0.51355(10) 0.0190(3)
C4 0.13025(15) 0.10605(14) 0.47038(10) 0.0173(3)
C5 0.17370(14) 0.15430(13) 0.39447(10) 0.0137(3)
C6 0.14144(16) 0.14887(14) 0.11475(10) 0.0173(3)
C7 0.02053(16) 0.16306(15) 0.06859(11) 0.0212(3)
C8 0.92786(16) 0.22688(17) 0.10691(11) 0.0232(3)
C9 0.95707(15) 0.26462(15) 0.19239(11) 0.0197(3)
C10 0.07766(14) 0.24224(13) 0.24065(10) 0.0139(3)
C11 0.96543(16) 0.29789(15) 0.38375(11) 0.0206(3)
C12 0.19930(15) 0.38595(14) 0.36508(11) 0.0186(3)
C13 0.44251(16) 0.21862(16) 0.14112(10) 0.0199(3)
C14 0.43425(16) 0.32483(14) 0.18790(11) 0.0196(3)
C15 0.55344(17) 0.38625(16) 0.23453(12) 0.0256(4)
C16 0.57759(17) 0.35014(15) 0.33060(12) 0.0221(3)
C17 0.52770(14) 0.22698(14) 0.34647(10) 0.0162(3)
C18 0.55523(14) 0.12557(14) 0.29818(10) 0.0165(3)
C19 0.64229(15) 0.12688(16) 0.22467(11) 0.0214(3)
C20 0.56521(17) 0.14764(17) 0.13471(12) 0.0248(3)
Ir1 0.36144(2) 0.18325(2) 0.26026(2) 0.01228(2)
N1 0.27979(12) 0.10270(11) 0.36426(8) 0.0134(2)
N2 0.17126(12) 0.19008(11) 0.19733(8) 0.0142(2)
213
Table A.17. Bond lengths (Å) for [(py)
2
B(Me)
2
]Ir(cod) (4.4b).
B1-C12 1.639(2) B1-C10 1.642(2)
B1-C11 1.643(2) B1-C5 1.643(2)
C1-N1 1.3537(19) C1-C2 1.378(2)
C1-H1 0.95 C2-C3 1.388(2)
C2-H2 0.95 C3-C4 1.381(2)
C3-H3 0.95 C4-C5 1.408(2)
C4-H4 0.95 C5-N1 1.3710(19)
C6-N2 1.357(2) C6-C7 1.380(2)
C6-H6 0.95 C7-C8 1.385(3)
C7-H7 0.95 C8-C9 1.384(2)
C8-H8 0.95 C9-C10 1.405(2)
C9-H9 0.95 C10-N2 1.3702(19)
C11-H11A 0.98 C11-H11B 0.98
C11-H11C 0.98 C12-H12A 0.98
C12-H12B 0.98 C12-H12C 0.98
C13-C14 1.408(2) C13-C20 1.517(2)
C13-Ir1 2.1377(15) C13-H13 1.0
C14-C15 1.526(2) C14-Ir1 2.1354(15)
C14-H14 1.0 C15-C16 1.528(2)
C15-H15A 0.99 C15-H15B 0.99
C16-C17 1.515(2) C16-H16A 0.99
C16-H16B 0.99 C17-C18 1.413(2)
C17-Ir1 2.1141(15) C17-H17 1.0
C18-C19 1.523(2) C18-Ir1 2.1314(14)
C18-H18 1.0 C19-C20 1.538(2)
C19-H19A 0.99 C19-H19B 0.99
C20-H20A 0.99 C20-H20B 0.99
Ir1-N1 2.0996(12) Ir1-N2 2.0996(13)
214
Table A.18. Bond angles (°) for [(py)
2
B(Me)
2
]Ir(cod) (4.4b).
C12-B1-C10 111.64(12) C12-B1-C11 108.67(13)
C10-B1-C11 109.19(12) C12-B1-C5 109.31(12)
C10-B1-C5 108.00(12) C11-B1-C5 110.03(12)
N1-C1-C2 123.10(15) N1-C1-H1 118.5
C2-C1-H1 118.5 C1-C2-C3 118.28(14)
C1-C2-H2 120.9 C3-C2-H2 120.9
C4-C3-C2 118.59(14) C4-C3-H3 120.7
C2-C3-H3 120.7 C3-C4-C5 122.34(15)
C3-C4-H4 118.8 C5-C4-H4 118.8
N1-C5-C4 117.31(14) N1-C5-B1 120.89(13)
C4-C5-B1 121.76(13) N2-C6-C7 122.82(15)
N2-C6-H6 118.6 C7-C6-H6 118.6
C6-C7-C8 118.36(16) C6-C7-H7 120.8
C8-C7-H7 120.8 C9-C8-C7 118.45(15)
C9-C8-H8 120.8 C7-C8-H8 120.8
C8-C9-C10 122.35(15) C8-C9-H9 118.8
C10-C9-H9 118.8 N2-C10-C9 117.20(14)
N2-C10-B1 120.84(12) C9-C10-B1 121.89(13)
B1-C11-H11A 109.5 B1-C11-H11B 109.5
H11A-C11-H11B 109.5 B1-C11-H11C 109.5
H11A-C11-H11C 109.5 H11B-C11-H11C 109.5
B1-C12-H12A 109.5 B1-C12-H12B 109.5
H12A-C12-H12B 109.5 B1-C12-H12C 109.5
H12A-C12-H12C 109.5 H12B-C12-H12C 109.5
C14-C13-C20 125.72(16) C14-C13-Ir1 70.68(9)
C20-C13-Ir1 111.66(11) C14-C13-H13 113.6
C20-C13-H13 113.6 Ir1-C13-H13 113.6
C13-C14-C15 122.48(15) C13-C14-Ir1 70.85(9)
C15-C14-Ir1 114.25(11) C13-C14-H14 114.0
C15-C14-H14 114.0 Ir1-C14-H14 114.0
C14-C15-C16 111.77(14) C14-C15-H15A 109.3
C16-C15-H15A 109.3 C14-C15-H15B 109.3
C16-C15-H15B 109.3 H15A-C15-H15B 107.9
C17-C16-C15 112.30(14) C17-C16-H16A 109.1
C15-C16-H16A 109.1 C17-C16-H16B 109.1
C15-C16-H16B 109.1 H16A-C16-H16B 107.9
C18-C17-C16 124.69(14) C18-C17-Ir1 71.23(8)
C16-C17-Ir1 112.53(10) C18-C17-H17 113.7
215
C16-C17-H17 113.7 Ir1-C17-H17 113.7
C17-C18-C19 123.60(14) C17-C18-Ir1 69.90(8)
C19-C18-Ir1 114.32(10) C17-C18-H18 113.8
C19-C18-H18 113.8 Ir1-C18-H18 113.8
C18-C19-C20 112.23(13) C18-C19-H19A 109.2
C20-C19-H19A 109.2 C18-C19-H19B 109.2
C20-C19-H19B 109.2 H19A-C19-H19B 107.9
C13-C20-C19 112.22(14) C13-C20-H20A 109.2
C19-C20-H20A 109.2 C13-C20-H20B 109.2
C19-C20-H20B 109.2 H20A-C20-H20B 107.9
N1-Ir1-N2 86.00(5) N1-Ir1-C17 89.58(5)
N2-Ir1-C17 159.99(6) N1-Ir1-C18 96.08(5)
N2-Ir1-C18 161.10(6) C17-Ir1-C18 38.87(6)
N1-Ir1-C14 156.71(6) N2-Ir1-C14 95.74(6)
C17-Ir1-C14 80.85(6) C18-Ir1-C14 89.73(6)
N1-Ir1-C13 164.81(6) N2-Ir1-C13 92.05(6)
C17-Ir1-C13 97.11(6) C18-Ir1-C13 81.02(6)
C14-Ir1-C13 38.47(7) C1-N1-C5 120.30(13)
C1-N1-Ir1 120.86(10) C5-N1-Ir1 118.69(10)
C6-N2-C10 120.23(13) C6-N2-Ir1 121.63(10)
C10-N2-Ir1 118.09(10)
Table A.19. Torsion angles (°) for [(py)
2
B(Me)
2
]Ir(cod) (4.4b).
N1-C1-C2-C3 -3.0(2) C1-C2-C3-C4 5.5(2)
C2-C3-C4-C5 -1.2(2) C3-C4-C5-N1 -5.7(2)
C3-C4-C5-B1 171.40(15) C12-B1-C5-N1 -75.34(17)
C11-B1-C5-N1 164.46(13) C6-B1-C5-N1 44.85(17)
C12-B1-C5-C4 107.69(16) C11-B1-C5-C4 -12.51(19)
C6-B1-C5-C4 -132.11(14) C12-B1-C6-N2 71.42(17)
C5-B1-C6-N2 -50.23(17) C11-B1-C6-N2 -169.31(13)
C12-B1-C6-C7 -106.15(16) C5-B1-C6-C7 132.19(14)
C11-B1-C6-C7 13.11(19) N2-C6-C7-C8 0.3(2)
B1-C6-C7-C8 177.94(14) C6-C7-C8-C9 1.9(2)
C7-C8-C9-C10 -1.7(2) C8-C9-C10-N2 -0.7(2)
C20-C13-C14-C15 -3.9(2) Ir1-C13-C14-C15 103.27(16)
C20-C13-C14-Ir1 -107.13(15) C13-C14-C15-C16 -48.7(2)
Ir1-C14-C15-C16 32.54(18) C14-C15-C16-C17 -28.0(2)
C15-C16-C17-C18 91.82(19) C15-C16-C17-Ir1 10.55(18)
216
C16-C17-C18-C19 -1.6(2) Ir1-C17-C18-C19 104.82(14)
C16-C17-C18-Ir1 -106.44(14) C17-C18-C19-C20 -50.1(2)
Ir1-C18-C19-C20 32.04(17) C14-C13-C20-C19 93.96(19)
Ir1-C13-C20-C19 11.92(19) C18-C19-C20-C13 -28.3(2)
C17-C18-Ir1-N1 -177.38(13) C19-C18-Ir1-N1 61.9(2)
C17-C18-Ir1-N2 -100.22(9) C19-C18-Ir1-N2 139.04(12)
C19-C18-Ir1-C17 -120.74(15) C17-C18-Ir1-C13 101.06(10)
C19-C18-Ir1-C13 -19.68(12) C17-C18-Ir1-C14 66.11(10)
C19-C18-Ir1-C14 -54.63(12) C18-C17-Ir1-N1 177.23(14)
C16-C17-Ir1-N1 -64.0(2) C18-C17-Ir1-N2 81.76(9)
C16-C17-Ir1-N2 -159.42(11) C16-C17-Ir1-C18 118.81(16)
C18-C17-Ir1-C13 -75.67(10) C16-C17-Ir1-C13 43.14(12)
C18-C17-Ir1-C14 -113.26(10) C16-C17-Ir1-C14 5.55(12)
C14-C13-Ir1-N1 86.06(10) C20-C13-Ir1-N1 -156.01(12)
C14-C13-Ir1-N2 179.34(12) C20-C13-Ir1-N2 -62.7(2)
C14-C13-Ir1-C18 -113.79(10) C20-C13-Ir1-C18 4.14(12)
C14-C13-Ir1-C17 -75.84(10) C20-C13-Ir1-C17 42.10(13)
C20-C13-Ir1-C14 117.93(16) C13-C14-Ir1-N1 -96.66(10)
C15-C14-Ir1-N1 141.53(12) C13-C14-Ir1-N2 -179.00(18)
C15-C14-Ir1-N2 59.2(3) C13-C14-Ir1-C18 65.53(10)
C15-C14-Ir1-C18 -56.28(13) C13-C14-Ir1-C17 100.99(10)
C15-C14-Ir1-C17 -20.82(12) C15-C14-Ir1-C13 -121.81(17)
C2-C1-N1-C5 -4.1(2) C2-C1-N1-Ir1 173.18(12)
C4-C5-N1-C1 8.2(2) B1-C5-N1-C1 -168.92(13)
C4-C5-N1-Ir1 -169.16(11) B1-C5-N1-Ir1 13.73(17)
N2-Ir1-N1-C1 128.77(12) C18-Ir1-N1-C1 -153.45(15)
C17-Ir1-N1-C1 31.6(2) C13-Ir1-N1-C1 -74.49(12)
C14-Ir1-N1-C1 -36.15(12) N2-Ir1-N1-C5 -53.91(11)
C18-Ir1-N1-C5 23.9(2) C17-Ir1-N1-C5 -151.05(15)
C13-Ir1-N1-C5 102.82(11) C14-Ir1-N1-C5 141.16(11)
C9-C10-N2-C6 3.0(2) C9-C10-N2-Ir1 -172.51(12)
C7-C6-N2-C10 -2.7(2) B1-C6-N2-C10 179.61(13)
C7-C6-N2-Ir1 172.93(10) B1-C6-N2-Ir1 -4.76(17)
N1-Ir1-N2-C10 -135.31(12) C18-Ir1-N2-C10 64.19(12)
C17-Ir1-N2-C10 25.86(12) C13-Ir1-N2-C10 129.41(15)
C14-Ir1-N2-C10 -52.2(3) N1-Ir1-N2-C6 49.08(11)
C18-Ir1-N2-C6 -111.42(11) C17-Ir1-N2-C6 -149.75(11)
C13-Ir1-N2-C6 -46.21(19) C14-Ir1-N2-C6 132.2(2)
217
Table A.20. Anisotropic atomic displacement parameters (Å
2
) for [(py)
2
B(Me)
2
]Ir(cod)
(4.4b).
The anisotropic atomic displacement factor exponent takes the form: -2π
2
[ h
2
a
*2
U
11
+ ...
+ 2 h k a
*
b
*
U
12
]
U
11
U
22
U
33
U
23
U
13
U
12
B1 0.0127(7) 0.0145(7) 0.0178(8) 0.0016(6) 0.0029(6) 0.0008(6)
C1 0.0149(7) 0.0172(7) 0.0172(7) 0.0023(5) -0.0011(5) 0.0007(5)
C2 0.0206(7) 0.0176(7) 0.0170(7) 0.0054(6) -0.0028(6) -0.0023(6)
C3 0.0235(8) 0.0197(7) 0.0138(7) 0.0023(5) 0.0018(6) -0.0058(6)
C4 0.0183(7) 0.0183(7) 0.0160(7) -0.0004(5) 0.0043(5) -0.0032(5)
C5 0.0124(6) 0.0147(6) 0.0138(6) -0.0007(5) 0.0003(5) -0.0027(5)
C6 0.0193(7) 0.0179(7) 0.0145(7) 0.0025(5) 0.0010(6) -0.0008(6)
C7 0.0213(8) 0.0248(8) 0.0162(7) 0.0044(6) -0.0032(6) -0.0048(6)
C8 0.0141(7) 0.0310(9) 0.0232(8) 0.0091(7) -0.0043(6) -0.0028(6)
C9 0.0120(7) 0.0232(8) 0.0238(8) 0.0055(6) 0.0015(6) 0.0003(6)
C10 0.0106(6) 0.0132(6) 0.0181(7) 0.0039(5) 0.0019(5) -0.0014(5)
C11 0.0161(7) 0.0233(8) 0.0231(8) 0.0015(6) 0.0052(6) 0.0023(6)
C12 0.0173(7) 0.0155(7) 0.0231(8) -0.0004(6) 0.0023(6) 0.0004(5)
C13 0.0172(7) 0.0278(8) 0.0152(7) 0.0067(6) 0.0040(6) 0.0009(6)
C14 0.0175(7) 0.0218(8) 0.0198(7) 0.0094(6) 0.0029(6) -0.0002(6)
C15 0.0241(8) 0.0232(8) 0.0295(9) 0.0062(7) 0.0026(7) -0.0044(6)
C16 0.0202(8) 0.0201(7) 0.0252(8) -0.0015(6) -0.0007(6) -0.0021(6)
C17 0.0118(6) 0.0199(7) 0.0159(7) 0.0022(6) -0.0025(5) 0.0003(5)
C18 0.0108(6) 0.0190(7) 0.0191(7) 0.0027(6) -0.0007(5) 0.0020(5)
C19 0.0139(7) 0.0259(8) 0.0247(8) -0.0013(6) 0.0045(6) 0.0025(6)
C20 0.0218(8) 0.0316(9) 0.0224(8) 0.0025(7) 0.0082(6) 0.0014(7)
Ir1 0.00986(3) 0.01506(3) 0.01188(3) 0.00262(2) 0.00097(2) 0.00126(2)
N1 0.0121(5) 0.0144(6) 0.0134(6) 0.0011(4) 0.0006(4) -0.0011(4)
N2 0.0128(6) 0.0150(6) 0.0147(6) 0.0031(5) 0.0002(4) 0.0000(4)
218
Table A.21. Hydrogen atomic coordinates and isotropic atomic displacement parameters
(Å
2
) for [(py)
2
B(Me)
2
]Ir(cod) (4.4b).
x/a y/b z/c U(eq)
H1 0.4062 -0.0300 0.3807 0.02
H2 0.3365 -0.1092 0.5063 0.023
H3 0.1605 -0.0191 0.5657 0.023
H4 0.0572 0.1406 0.4927 0.021
H6 0.2066 0.1085 0.0875 0.021
H7 0.0014 0.1299 0.0119 0.025
H8 -0.1539 0.2444 0.0753 0.028
H9 -0.1067 0.3072 0.2194 0.024
H11A -0.0912 0.2287 0.3742 0.031
H11B -0.0763 0.3663 0.3532 0.031
H11C -0.0191 0.3148 0.4465 0.031
H12A 0.1602 0.4547 0.3336 0.028
H12B 0.2841 0.3695 0.3452 0.028
H12C 0.2103 0.4025 0.4280 0.028
H13 0.3782 0.2129 0.0879 0.024
H14 0.3658 0.3803 0.1614 0.024
H15A 0.5411 0.4730 0.2306 0.031
H15B 0.6305 0.3659 0.2049 0.031
H16A 0.6719 0.3532 0.3497 0.027
H16B 0.5342 0.4074 0.3664 0.027
H17 0.5182 0.2102 0.4093 0.019
H18 0.5610 0.0510 0.3333 0.02
H19A 0.6887 0.0504 0.2240 0.026
H19B 0.7080 0.1901 0.2361 0.026
H20A 0.6207 0.1902 0.0967 0.03
H20B 0.5419 0.0703 0.1072 0.03
219
[(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27)
Figure A.4. ORTEP diagram of [(py)
2
BMe
2
]Ni(PPh
3
)Cl. Ellipsoids drawn at the 50%
probability level. 5.27 cocrystallized with disordered ½ hexane, which was removed by
Squeeze.
A clear red prism-like specimen of C
30
H
29
BClN
2
NiP, approximate dimensions
0.202 mm x 0.320 mm x 0.320 mm, was used for the X-ray crystallographic analysis. The
X-ray intensity data were measured on a Bruker APEX II CCD system equipped with a
TRIUMPH curved-crystal monochromator and a MoKα fine-focus tube (λ = 0.71073 Å).
A total of 2520 frames were collected. The total exposure time was 14.00 hours.
The frames were integrated with the Bruker SAINT software package using a SAINT
V8.30C (Bruker AXS, 2013) algorithm. The integration of the data using a triclinic unit
cell yielded a total of 27402 reflections to a maximum θ angle of 29.84° (0.71 Å
resolution), of which 8705 were independent (average redundancy 3.148, completeness =
98.1%, R
int
= 4.66%) and 6109 (70.18%) were greater than 2σ(F
2
). The final cell
constants of a = 10.0238(17) Å, b = 12.956(2) Å, c = 13.061(2) Å, α = 75.115(3)°, β =
77.501(3)°, γ = 72.426(2)°, volume = 1544.9(5) Å
3
, are based upon the refinement of the
XYZ-centroids of reflections above 20 σ(I). Data were corrected for absorption effects
using the multi-scan method (SADABS).
The structure was solved and refined using the Bruker SHELXTL Software
Package, using the space group P -1, with Z = 2 for the formula unit, C
30
H
29
BClN
2
NiP.
The final anisotropic full-matrix least-squares refinement on F
2
with 327 variables
converged at R1 = 6.30%, for the observed data and wR2 = 16.92% for all data. The
goodness-of-fit was 1.070. The largest peak in the final difference electron density
synthesis was 2.781 e
-
/Å
3
and the largest hole was -1.051 e
-
/Å
3
with an RMS deviation of
0.121 e
-
/Å
3
. On the basis of the final model, the calculated density was 1.190 g/cm
3
and
F(000), 576 e
-
.
220
Table A.22. Crystal data and structure refinement for [(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27).
Chemical formula C
30
H
29
BClN
2
NiP
Formula weight 553.49
Temperature 100(2) K
Wavelength 0.71073 Å
Crystal size 0.202 x 0.320 x 0.320 mm
Crystal habit clear red prism
Crystal system triclinic
Space group P -1
Unit cell dimensions a = 10.0238(17) Å α = 75.115(3)°
b = 12.956(2) Å β = 77.501(3)°
c = 13.061(2) Å γ = 72.426(2)°
Volume 1544.9(5) Å
3
Z 2
Density (calculated) 1.190 g/cm
3
Absorption coefficient 0.785 mm
-1
F(000) 576
Radiation source fine-focus tube, MoKα
Theta range for data collection 1.63 to 29.84°
Index ranges -13<=h<=14, -18<=k<=18, -18<=l<=18
Reflections collected 27402
Independent reflections 8705 [R(int) = 0.0466]
Absorption correction multi-scan
Structure solution technique direct methods
Structure solution program SHELXTL XT 2013/1 (Sheldrick, 2013)
Refinement method Full-matrix least-squares on F
2
Refinement program SHELXTL XL 2013/2 (Bruker AXS, 2013)
Diffractometer Bruker APEX II CCD
Radiation source fine-focus tube, MoKα
Function minimized Σ w(Fo
2
- Fc
2
)
2
Data / restraints / parameters 8705 / 0 / 327
Goodness-of-fit on F
2
1.070
Δ/σ
max
0.001
Final R indices 6109 data; I>2σ(I) R1 = 0.0630, wR2 = 0.1427
all data R1 = 0.0994, wR2 = 0.1692
Weighting scheme
w=1/[σ
2
(F
o
2
)+(0.0637P)
2
+4.3840P]
where P=(F
o
2
+2F
c
2
)/3
Largest diff. peak and hole 2.781 and -1.051 eÅ
-3
R.M.S. deviation from mean 0.121 eÅ
-3
221
Table A.23. Atomic coordinates and equivalent isotropic atomic displacement
parameters (Å
2
) for [(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27).
U(eq) is defined as one third of the trace of the orthogonalized U
ij
tensor.
x/a y/b z/c U(eq)
C1 0.3435(3) 0.0454(2) 0.3914(3) 0.0193(6)
C2 0.4166(3) 0.1263(3) 0.3529(3) 0.0220(6)
C3 0.4513(4) 0.1582(3) 0.2427(3) 0.0240(7)
C4 0.4101(4) 0.1113(3) 0.1752(3) 0.0227(7)
C5 0.3313(3) 0.0313(2) 0.2170(3) 0.0197(6)
C6 0.2892(4) 0.0475(3) 0.0161(3) 0.0281(7)
C7 0.3541(4) 0.8473(3) 0.1475(3) 0.0260(7)
C8 0.1042(3) 0.9961(2) 0.1883(3) 0.0192(6)
C9 0.9927(4) 0.0514(3) 0.1290(3) 0.0251(7)
C10 0.8517(4) 0.0727(3) 0.1775(3) 0.0296(8)
C11 0.8211(4) 0.0395(3) 0.2873(3) 0.0259(7)
C12 0.9311(3) 0.9828(3) 0.3443(3) 0.0208(6)
C13 0.9815(3) 0.7362(2) 0.3682(3) 0.0185(6)
C14 0.9942(4) 0.7560(3) 0.2566(3) 0.0235(7)
C15 0.8764(4) 0.7720(3) 0.2089(3) 0.0291(8)
C16 0.7456(4) 0.7695(3) 0.2713(4) 0.0352(9)
C17 0.7330(4) 0.7473(3) 0.3822(4) 0.0332(9)
C18 0.8514(4) 0.7314(3) 0.4307(3) 0.0244(7)
C19 0.2668(3) 0.6064(2) 0.3811(3) 0.0191(6)
C20 0.2205(4) 0.5263(3) 0.3549(3) 0.0251(7)
C21 0.3169(4) 0.4333(3) 0.3236(3) 0.0289(8)
C22 0.4600(4) 0.4189(3) 0.3185(3) 0.0289(8)
C23 0.5078(4) 0.4977(3) 0.3443(4) 0.0321(8)
C24 0.4124(4) 0.5915(3) 0.3748(3) 0.0258(7)
C25 0.0862(3) 0.6815(3) 0.5687(3) 0.0193(6)
C26 0.0168(4) 0.7612(3) 0.6307(3) 0.0223(7)
C27 0.9708(4) 0.7309(3) 0.7390(3) 0.0272(7)
C28 0.9957(4) 0.6195(3) 0.7882(3) 0.0305(8)
C29 0.0654(4) 0.5394(3) 0.7279(3) 0.0286(7)
C30 0.1100(3) 0.5696(3) 0.6193(3) 0.0221(6)
N1 0.0687(3) 0.9595(2) 0.2944(2) 0.0191(5)
N2 0.3021(3) 0.0003(2) 0.3258(2) 0.0180(5)
B1 0.2721(4) 0.9792(3) 0.1394(3) 0.0214(7)
Ni1 0.21169(4) 0.87934(3) 0.38076(3) 0.01664(11)
Cl1 0.35036(8) 0.80077(6) 0.50165(7) 0.01995(16)
222
x/a y/b z/c U(eq)
P1 0.13695(8) 0.72592(6) 0.42570(7) 0.01614(17)
Table A.24. Bond lengths (Å) for [(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27).
C1-N2 1.344(4) C1-C2 1.387(4)
C1-H1 0.95 C2-C3 1.388(5)
C2-H2 0.95 C3-C4 1.379(5)
C3-H3 0.95 C4-C5 1.419(5)
C4-H4 0.95 C5-N2 1.366(4)
C5-B1 1.640(5) C6-B1 1.627(5)
C6-H6A 0.98 C6-H6B 0.98
C6-H6C 0.98 C7-B1 1.644(5)
C7-H7A 0.98 C7-H7B 0.98
C7-H7C 0.98 C8-N1 1.351(4)
C8-C9 1.403(5) C8-B1 1.634(5)
C9-C10 1.394(5) C9-H9 0.95
C10-C11 1.381(6) C10-H10 0.95
C11-C12 1.377(5) C11-H11 0.95
C12-N1 1.370(4) C12-H12 0.95
C13-C18 1.391(5) C13-C14 1.397(5)
C13-P1 1.828(3) C14-C15 1.389(5)
C14-H14 0.95 C15-C16 1.391(6)
C15-H15 0.95 C16-C17 1.388(6)
C16-H16 0.95 C17-C18 1.401(5)
C17-H17 0.95 C18-H18 0.95
C19-C20 1.398(4) C19-C24 1.400(4)
C19-P1 1.830(3) C20-C21 1.389(5)
C20-H20 0.95 C21-C22 1.378(5)
C21-H21 0.95 C22-C23 1.388(5)
C22-H22 0.95 C23-C24 1.389(5)
C23-H23 0.95 C24-H24 0.95
C25-C26 1.399(4) C25-C30 1.401(4)
C25-P1 1.815(4) C26-C27 1.382(5)
C26-H26 0.95 C27-C28 1.391(5)
C27-H27 0.95 C28-C29 1.388(5)
C28-H28 0.95 C29-C30 1.382(5)
C29-H29 0.95 C30-H30 0.95
N1-Ni1 1.898(3) N2-Ni1 1.947(3)
Ni1-Cl1 2.1751(9) Ni1-P1 2.2286(9)
223
Table A.25. Bond angles (°) for [(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27).
N2-C1-C2 122.1(3) N2-C1-H1 118.9
C2-C1-H1 118.9 C1-C2-C3 118.2(3)
C1-C2-H2 120.9 C3-C2-H2 120.9
C4-C3-C2 119.8(3) C4-C3-H3 120.1
C2-C3-H3 120.1 C3-C4-C5 120.8(3)
C3-C4-H4 119.6 C5-C4-H4 119.6
N2-C5-C4 117.6(3) N2-C5-B1 120.1(3)
C4-C5-B1 122.3(3) B1-C6-H6A 109.5
B1-C6-H6B 109.5 H6A-C6-H6B 109.5
B1-C6-H6C 109.5 H6A-C6-H6C 109.5
H6B-C6-H6C 109.5 B1-C7-H7A 109.5
B1-C7-H7B 109.5 H7A-C7-H7B 109.5
B1-C7-H7C 109.5 H7A-C7-H7C 109.5
H7B-C7-H7C 109.5 N1-C8-C9 116.9(3)
N1-C8-B1 118.2(3) C9-C8-B1 124.7(3)
C10-C9-C8 121.9(3) C10-C9-H9 119.0
C8-C9-H9 119.0 C11-C10-C9 119.0(3)
C11-C10-H10 120.5 C9-C10-H10 120.5
C12-C11-C10 118.6(3) C12-C11-H11 120.7
C10-C11-H11 120.7 N1-C12-C11 121.4(3)
N1-C12-H12 119.3 C11-C12-H12 119.3
C18-C13-C14 119.8(3) C18-C13-P1 122.4(3)
C14-C13-P1 117.7(2) C15-C14-C13 119.8(3)
C15-C14-H14 120.1 C13-C14-H14 120.1
C14-C15-C16 120.5(4) C14-C15-H15 119.8
C16-C15-H15 119.8 C17-C16-C15 120.0(3)
C17-C16-H16 120.0 C15-C16-H16 120.0
C16-C17-C18 119.7(4) C16-C17-H17 120.2
C18-C17-H17 120.2 C13-C18-C17 120.2(4)
C13-C18-H18 119.9 C17-C18-H18 119.9
C20-C19-C24 118.7(3) C20-C19-P1 119.7(2)
C24-C19-P1 121.6(2) C21-C20-C19 120.7(3)
C21-C20-H20 119.6 C19-C20-H20 119.6
C22-C21-C20 120.1(3) C22-C21-H21 119.9
C20-C21-H21 119.9 C21-C22-C23 119.9(3)
C21-C22-H22 120.1 C23-C22-H22 120.1
C22-C23-C24 120.5(3) C22-C23-H23 119.7
C24-C23-H23 119.7 C23-C24-C19 120.1(3)
224
C23-C24-H24 120.0 C19-C24-H24 120.0
C26-C25-C30 118.5(3) C26-C25-P1 119.2(2)
C30-C25-P1 122.3(3) C27-C26-C25 121.1(3)
C27-C26-H26 119.4 C25-C26-H26 119.4
C26-C27-C28 119.7(3) C26-C27-H27 120.1
C28-C27-H27 120.1 C29-C28-C27 119.8(4)
C29-C28-H28 120.1 C27-C28-H28 120.1
C30-C29-C28 120.5(3) C30-C29-H29 119.7
C28-C29-H29 119.7 C29-C30-C25 120.3(3)
C29-C30-H30 119.8 C25-C30-H30 119.8
C8-N1-C12 121.9(3) C8-N1-Ni1 120.2(2)
C12-N1-Ni1 117.8(2) C1-N2-C5 121.5(3)
C1-N2-Ni1 121.6(2) C5-N2-Ni1 116.6(2)
C6-B1-C8 109.7(3) C6-B1-C5 111.1(3)
C8-B1-C5 103.5(3) C6-B1-C7 111.1(3)
C8-B1-C7 111.1(3) C5-B1-C7 110.2(3)
N1-Ni1-N2 88.43(11) N1-Ni1-Cl1 170.02(9)
N2-Ni1-Cl1 92.35(8) N1-Ni1-P1 93.99(8)
N2-Ni1-P1 170.51(8) Cl1-Ni1-P1 86.86(3)
C25-P1-C13 104.14(15) C25-P1-C19 105.98(15)
C13-P1-C19 102.99(14) C25-P1-Ni1 114.07(10)
C13-P1-Ni1 114.59(10) C19-P1-Ni1 113.91(11)
Table A.26. Torsion angles (°) for [(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27).
N2-C1-C2-C3 -2.1(5) C1-C2-C3-C4 1.4(5)
C2-C3-C4-C5 0.7(5) C3-C4-C5-N2 -2.1(5)
C3-C4-C5-B1 176.2(3) N1-C8-C9-C10 3.0(5)
B1-C8-C9-C10 -173.5(3) C8-C9-C10-C11 0.8(5)
C9-C10-C11-C12 -2.5(5) C10-C11-C12-N1 0.3(5)
C18-C13-C14-C15 0.7(5) P1-C13-C14-C15 -175.6(2)
C13-C14-C15-C16 0.7(5) C14-C15-C16-C17 -2.2(6)
C15-C16-C17-C18 2.3(6) C14-C13-C18-C17 -0.5(5)
P1-C13-C18-C17 175.6(3) C16-C17-C18-C13 -1.0(5)
C24-C19-C20-C21 0.2(6) P1-C19-C20-C21 -178.3(3)
C19-C20-C21-C22 0.3(6) C20-C21-C22-C23 -0.3(6)
C21-C22-C23-C24 -0.3(6) C22-C23-C24-C19 0.8(6)
C20-C19-C24-C23 -0.8(6) P1-C19-C24-C23 177.6(3)
C30-C25-C26-C27 -0.8(5) P1-C25-C26-C27 177.2(3)
225
C25-C26-C27-C28 1.1(5) C26-C27-C28-C29 -0.6(6)
C27-C28-C29-C30 -0.2(6) C28-C29-C30-C25 0.4(5)
C26-C25-C30-C29 0.0(5) P1-C25-C30-C29 -177.9(3)
C9-C8-N1-C12 -5.3(4) B1-C8-N1-C12 171.5(3)
C9-C8-N1-Ni1 177.9(2) B1-C8-N1-Ni1 -5.4(4)
C11-C12-N1-C8 3.8(5) C11-C12-N1-Ni1 -179.3(2)
C2-C1-N2-C5 0.6(5) C2-C1-N2-Ni1 175.4(2)
C4-C5-N2-C1 1.4(4) B1-C5-N2-C1 -176.9(3)
C4-C5-N2-Ni1 -173.6(2) B1-C5-N2-Ni1 8.1(4)
N1-C8-B1-C6 -170.2(3) C9-C8-B1-C6 6.2(4)
N1-C8-B1-C5 -51.7(3) C9-C8-B1-C5 124.8(3)
N1-C8-B1-C7 66.5(4) C9-C8-B1-C7 -117.0(3)
N2-C5-B1-C6 167.3(3) C4-C5-B1-C6 -10.9(4)
N2-C5-B1-C8 49.7(4) C4-C5-B1-C8 -128.6(3)
N2-C5-B1-C7 -69.2(4) C4-C5-B1-C7 112.6(3)
C8-N1-Ni1-N2 53.5(2) C12-N1-Ni1-N2 -123.4(2)
C8-N1-Ni1-P1 -117.3(2) C12-N1-Ni1-P1 65.7(2)
C26-C25-P1-C13 -88.1(3) C30-C25-P1-C13 89.8(3)
C26-C25-P1-C19 163.7(3) C30-C25-P1-C19 -18.4(3)
C26-C25-P1-Ni1 37.6(3) C30-C25-P1-Ni1 -144.6(2)
C18-C13-P1-C25 11.5(3) C14-C13-P1-C25 -172.3(2)
C18-C13-P1-C19 121.9(3) C14-C13-P1-C19 -61.9(3)
C18-C13-P1-Ni1 -113.8(3) C14-C13-P1-Ni1 62.4(3)
C20-C19-P1-C25 85.0(3) C24-C19-P1-C25 -93.4(3)
C20-C19-P1-C13 -24.0(3) C24-C19-P1-C13 157.5(3)
C20-C19-P1-Ni1 -148.7(3) C24-C19-P1-Ni1 32.8(3)
Table A.27. Anisotropic atomic displacement parameters (Å
2
) for
[(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27).
The anisotropic atomic displacement factor exponent takes the form: -2π
2
[ h
2
a
*2
U
11
+ ...
+ 2 h k a
*
b
*
U
12
]
U
11
U
22
U
33
U
23
U
13
U
12
C1 0.0174(14) 0.0171(13) 0.0278(17) -0.0090(12) -0.0077(12) -0.0044(11)
C2 0.0192(15) 0.0201(14) 0.0305(18) -0.0115(13) -0.0041(13) -0.0052(11)
C3 0.0219(15) 0.0188(14) 0.0334(19) -0.0056(13) -0.0059(14) -0.0069(12)
C4 0.0224(15) 0.0211(14) 0.0242(17) -0.0064(13) -0.0020(13) -0.0047(12)
C5 0.0187(14) 0.0160(13) 0.0254(17) -0.0060(12) -0.0056(12) -0.0027(11)
C6 0.0340(19) 0.0278(17) 0.0248(18) -0.0042(14) -0.0069(15) -0.0109(14)
226
C7 0.0272(17) 0.0205(15) 0.0313(19) -0.0111(14) 0.0017(14) -0.0072(13)
C8 0.0265(16) 0.0155(13) 0.0182(15) -0.0020(11) -0.0074(12) -0.0078(11)
C9 0.0269(17) 0.0222(15) 0.0278(18) -0.0035(13) -0.0102(14) -0.0059(13)
C10 0.0249(17) 0.0257(16) 0.040(2) -0.0089(16) -0.0166(16) 0.0010(13)
C11 0.0197(15) 0.0226(15) 0.036(2) -0.0099(14) -0.0088(14) 0.0003(12)
C12 0.0181(14) 0.0191(14) 0.0274(17) -0.0095(13) -0.0046(13) -0.0035(11)
C13 0.0182(14) 0.0109(12) 0.0277(17) -0.0039(12) -0.0080(12) -0.0028(10)
C14 0.0264(16) 0.0177(14) 0.0288(18) -0.0056(13) -0.0089(14) -0.0049(12)
C15 0.0357(19) 0.0210(15) 0.032(2) -0.0008(14) -0.0176(16) -0.0039(14)
C16 0.0243(18) 0.0316(19) 0.054(3) -0.0134(18) -0.0201(18) -0.0006(14)
C17 0.0184(16) 0.0330(19) 0.051(3) -0.0121(18) -0.0086(16) -0.0055(14)
C18 0.0196(15) 0.0252(16) 0.0307(19) -0.0100(14) -0.0047(13) -0.0050(12)
C19 0.0175(14) 0.0154(13) 0.0238(16) -0.0037(12) -0.0049(12) -0.0023(11)
C20 0.0210(15) 0.0178(14) 0.039(2) -0.0103(14) -0.0051(14) -0.0041(12)
C21 0.0314(18) 0.0175(15) 0.040(2) -0.0116(15) -0.0065(16) -0.0047(13)
C22 0.0298(18) 0.0192(15) 0.034(2) -0.0080(14) -0.0071(15) 0.0033(13)
C23 0.0183(16) 0.0314(18) 0.049(2) -0.0194(17) -0.0077(16) 0.0016(13)
C24 0.0191(15) 0.0223(15) 0.039(2) -0.0143(15) -0.0093(14) 0.0004(12)
C25 0.0152(13) 0.0175(13) 0.0281(17) -0.0077(12) -0.0058(12) -0.0040(11)
C26 0.0243(16) 0.0166(13) 0.0271(18) -0.0065(13) -0.0056(13) -0.0040(12)
C27 0.0321(18) 0.0267(16) 0.0245(18) -0.0099(14) -0.0018(14) -0.0078(14)
C28 0.035(2) 0.0326(18) 0.0246(18) -0.0039(15) -0.0040(15) -0.0120(15)
C29 0.0357(19) 0.0219(15) 0.0293(19) -0.0003(14) -0.0075(15) -0.0115(14)
C30 0.0214(15) 0.0205(14) 0.0253(17) -0.0054(13) -0.0048(13) -0.0053(12)
N1 0.0152(12) 0.0092(10) 0.0336(16) -0.0036(10) -0.0060(11) -0.0032(9)
N2 0.0132(11) 0.0198(12) 0.0204(14) -0.0008(10) -0.0048(10) -0.0048(9)
B1 0.0223(17) 0.0181(15) 0.0256(19) -0.0065(14) -0.0050(14) -0.0055(13)
Ni1 0.01438(19) 0.01338(18) 0.0234(2) -0.00386(15) -0.00583(15) -0.00331(13)
Cl1 0.0187(3) 0.0170(3) 0.0260(4) -0.0037(3) -0.0089(3) -0.0039(3)
P1 0.0142(3) 0.0131(3) 0.0223(4) -0.0042(3) -0.0047(3) -0.0035(3)
227
Table A.28. Hydrogen atomic coordinates and isotropic atomic displacement parameters
(Å
2
) for [(py)
2
BMe
2
]Ni(PPh
3
)Cl (5.27).
x/a y/b z/c U(eq)
H1 0.3219 1.0210 0.4667 0.023
H2 0.4423 1.1589 0.4005 0.026
H3 0.5032 1.2123 0.2139 0.029
H4 0.4349 1.1327 0.0999 0.027
H6A 0.2431 1.1262 0.0138 0.042
H6B 0.2448 1.0195 -0.0272 0.042
H6C 0.3899 1.0379 -0.0127 0.042
H7A 0.3150 0.8163 0.1034 0.039
H7B 0.3408 0.8079 0.2223 0.039
H7C 0.4553 0.8392 0.1218 0.039
H9 0.0140 1.0751 0.0536 0.03
H10 -0.2222 1.1094 0.1357 0.036
H11 -0.2738 1.0555 0.3227 0.031
H12 -0.0888 0.9593 0.4198 0.025
H14 0.0831 0.7586 0.2136 0.028
H15 -0.1147 0.7847 0.1331 0.035
H16 -0.3351 0.7830 0.2380 0.042
H17 -0.3555 0.7428 0.4251 0.04
H18 -0.1572 0.7172 0.5066 0.029
H20 0.1220 0.5354 0.3586 0.03
H21 0.2841 0.3796 0.3056 0.035
H22 0.5258 0.3552 0.2974 0.035
H23 0.6064 0.4875 0.3411 0.038
H24 0.4461 0.6455 0.3913 0.031
H26 0.0010 0.8374 0.5977 0.027
H27 -0.0776 0.7860 0.7798 0.033
H28 -0.0349 0.5982 0.8627 0.037
H29 0.0826 0.4633 0.7615 0.034
H30 0.1570 0.5141 0.5787 0.027
228
[(py)
2
BMe
2
]Ni(acac) (5.29)
Figure A.5. ORTEP diagram of [(py)
2
BMe
2
]Ni(acac). Ellipsoids drawn at the
50% probability level.
A clear intense orange specimen of C
17
H
21
BN
2
NiO
2
, approximate dimensions
0.270 mm x 0.400 mm x 0.730 mm, was used for the X-ray crystallographic analysis. The
X-ray intensity data were measured on a Bruker APEX II CCD system equipped with a
TRIUMPH curved-crystal monochromator and a MoKα fine-focus tube (λ = 0.71073 Å).
A total of 2520 frames were collected. The total exposure time was 3.50 hours.
The frames were integrated with the Bruker SAINT software package using a SAINT
V8.27B algorithm. The integration of the data using a triclinic unit cell yielded a total of
20280 reflections to a maximum θ angle of 31.27° (0.68 Å resolution), of which 5063
were independent (average redundancy 4.006, completeness = 93.8%, R
int
= 1.81%, R
sig
=
1.25%) and 4926 (97.29%) were greater than 2σ(F
2
). The final cell constants of a =
7.3097(3) Å, b = 8.1424(4) Å, c = 14.9208(7) Å, α = 96.4140(10)°, β = 92.5660(10)°, γ =
109.8230(10)°, volume = 826.96(7) Å
3
, are based upon the refinement of the XYZ-
centroids of 9154 reflections above 20 σ(I) with 5.367° < 2θ < 62.54°. Data were
corrected for absorption effects using the multi-scan method (SADABS). The ratio of
minimum to maximum apparent transmission was 0.861. The calculated minimum and
maximum transmission coefficients (based on crystal size) are 0.4802 and 0.7376.
The structure was solved and refined using the Bruker SHELXTL Software
Package, using the space group P -1, with Z = 2 for the formula unit, C
17
H
21
BN
2
NiO
2
.
The final anisotropic full-matrix least-squares refinement on F
2
with 212 variables
converged at R1 = 2.40%, for the observed data and wR2 = 7.08% for all data. The
goodness-of-fit was 4.915. The largest peak in the final difference electron density
synthesis was 0.439 e
-
/Å
3
and the largest hole was -0.530 e
-
/Å
3
with an RMS deviation of
0.062 e
-
/Å
3
. On the basis of the final model, the calculated density was 1.425 g/cm
3
and
F(000), 372 e
-
.
229
Table A.29. Crystal data and structure refinement for [(py)
2
BMe
2
]Ni(acac) (5.29).
Chemical formula C
17
H
21
BN
2
NiO
2
Formula weight 354.88
Temperature 293(2) K
Wavelength 0.71073 Å
Crystal size 0.270 x 0.400 x 0.730 mm
Crystal system triclinic
Space group P -1
Identification code mpb2270
Unit cell dimensions a = 7.3097(3) Å α = 96.4140(10)°
b = 8.1424(4) Å β = 92.5660(10)°
c = 14.9208(7) Å γ = 109.8230(10)°
Volume 826.96(7) Å
3
Volume
Z 2
Density (calculated) 1.425 g/cm
3
Absorption coefficient 1.183 mm
-1
F(000) 372
Radiation source fine-focus tube, MoKα
Theta range for data collection 1.38 to 31.27°
Index ranges -10<=h<=10, -11<=k<=11, -21<=l<=21
Reflections collected 20280
Independent reflections 5063 [R(int) = 0.0181]
Coverage of independent reflections 93.8%
Absorption correction multi-scan
Max. and min. transmission 0.7376 and 0.4802
Structure solution technique direct methods
Structure solution program SHELXS-97 (Sheldrick, 2008)
Refinement method Full-matrix least-squares on F
2
Refinement program SHELXL-97 (Sheldrick, 2008)
Function minimized Σ w(F
o
2
- F
c
2
)
2
Data / restraints / parameters 5063 / 0 / 212
Goodness-of-fit on F
2
4.915
Δ/σ
max
0.081
Final R indices 4926 data; I>2σ(I) R1 = 0.0240, wR2 = 0.0706
all data R1 = 0.0247, wR2 = 0.0708
Weighting scheme
w=1/[σ
2
(F
o
2
)+(0.0000P)
2
+0.0000P]
where P=(F
o
2
+2F
c
2
)/3
Largest diff. peak and hole 0.439 and -0.530 eÅ
-3
R.M.S. deviation from mean 0.062 eÅ
-3
230
Table A.30. Atomic coordinates and equivalent isotropic atomic displacement
parameters (Å
2
) for [(py)
2
BMe
2
]Ni(acac) (5.29).
U(eq) is defined as one third of the trace of the orthogonalized U
ij
tensor.
x/a y/b z/c U(eq)
Ni1 0.04185(2) 0.431279(17) 0.217198(9) 0.01017(5)
O1 0.07261(12) 0.30579(10) 0.11072(5) 0.01360(16)
O2 0.17255(12) 0.65168(10) 0.18378(5) 0.01423(16)
N1 0.90411(13) 0.21194(12) 0.25544(6) 0.01024(17)
N2 0.01571(14) 0.55072(12) 0.32970(6) 0.01029(17)
C1 0.97825(17) 0.08057(14) 0.24216(7) 0.0128(2)
C2 0.88685(17) 0.91651(15) 0.26766(7) 0.0149(2)
C3 0.71056(17) 0.88569(15) 0.30655(8) 0.0154(2)
C4 0.63528(16) 0.02016(14) 0.31885(7) 0.0133(2)
C5 0.73293(16) 0.18749(14) 0.29408(7) 0.0104(2)
C7 0.83893(16) 0.51223(14) 0.36389(7) 0.0106(2)
C8 0.17609(16) 0.67828(14) 0.37281(7) 0.0130(2)
C9 0.16956(18) 0.77779(15) 0.45303(7) 0.0166(2)
C10 0.99136(18) 0.74399(15) 0.49037(7) 0.0164(2)
C11 0.82914(17) 0.61204(15) 0.44584(7) 0.0138(2)
C12 0.46424(17) 0.30596(16) 0.36814(8) 0.0161(2)
C13 0.59728(17) 0.40106(15) 0.20987(7) 0.0151(2)
C14 0.17130(16) 0.37197(15) 0.04628(7) 0.0129(2)
C15 0.26080(17) 0.55113(15) 0.04252(7) 0.0150(2)
C16 0.25476(16) 0.68084(15) 0.11014(7) 0.0131(2)
C17 0.35300(19) 0.87252(15) 0.09983(8) 0.0196(2)
C18 0.18754(19) 0.23955(16) 0.97143(8) 0.0198(2)
B2 0.65303(18) 0.35189(16) 0.30943(8) 0.0112(2)
Ni1 0.04185(2) 0.431279(17) 0.217198(9) 0.01017(5)
231
Table A.31. Bond lengths (Å) for [(py)
2
BMe
2
]Ni(acac) (5.29).
Ni1-O1 1.8558(8) Ni1-O2 1.8606(8)
Ni1-N2 1.8948(9) Ni1-N1 1.8943(9)
O1-C14 1.2842(13) O2-C16 1.2827(13)
N1-C1 1.3537(13) N1-C5 1.3635(14)
N2-C8 1.3506(14) N2-C7 1.3595(14)
C1-C2 1.3808(16) C1-H1 0.93
C2-C3 1.3930(17) C2-H14 0.93
C3-C4 1.3813(16) C3-H13 0.93
C4-C5 1.4067(15) C4-H12 0.93
C5-B2 1.6307(16) C7-C11 1.4093(14)
C7-B2 1.6347(16) C8-C9 1.3806(15)
C8-H5 0.93 C9-C10 1.3925(17)
C9-H4 0.93 C10-C11 1.3813(16)
C10-H3 0.93 C11-H2 0.93
C12-B2 1.6257(17) C12-H6 0.96
C12-H7 0.96 C12-H8 0.96
C13-B2 1.6500(16) C13-H9 0.96
C13-H10 0.96 C13-H11 0.96
C14-C15 1.3905(16) C14-C18 1.5012(15)
C15-C16 1.3902(15) C15-H18 0.93
C16-C17 1.5095(15) C17-H15 0.96
C17-H16 0.96 C17-H17 0.96
C18-H19 0.96 C18-H20 0.96
C18-H21 0.96
Table A.32. Bond angles (°) for [(py)
2
BMe
2
]Ni(acac) (5.29).
O1-Ni1-O2 94.95(3) O1-Ni1-N2 176.66(3)
O2-Ni1-N2 87.26(4) O1-Ni1-N1 87.55(4)
O2-Ni1-N1 177.40(3) N2-Ni1-N1 90.27(4)
C14-O1-Ni1 125.82(7) C16-O2-Ni1 125.90(7)
C1-N1-C5 121.24(9) C1-N1-Ni1 118.42(7)
C5-N1-Ni1 120.33(7) C8-N2-C7 121.48(9)
C8-N2-Ni1 117.94(8) C7-N2-Ni1 120.54(7)
N1-C1-C2 122.18(10) N1-C1-H1 118.9
C2-C1-H1 118.9 C1-C2-C3 118.33(10)
C1-C2-H14 120.8 C3-C2-H14 120.8
232
C4-C3-C2 118.95(10) C4-C3-H13 120.5
C2-C3-H13 120.5 C3-C4-C5 121.76(10)
C3-C4-H12 119.1 C5-C4-H12 119.1
N1-C5-C4 117.52(10) N1-C5-B2 118.82(9)
C4-C5-B2 123.66(9) N2-C7-C11 117.31(10)
N2-C7-B2 118.61(9) C11-C7-B2 124.07(9)
N2-C8-C9 122.13(10) N2-C8-H5 118.9
C9-C8-H5 118.9 C8-C9-C10 118.48(10)
C8-C9-H4 120.8 C10-C9-H4 120.8
C11-C10-C9 118.65(10) C11-C10-H3 120.7
C9-C10-H3 120.7 C10-C11-C7 121.95(10)
C10-C11-H2 119.0 C7-C11-H2 119.0
B2-C12-H6 109.5 B2-C12-H7 109.5
H6-C12-H7 109.5 B2-C12-H8 109.5
H6-C12-H8 109.5 H7-C12-H8 109.5
B2-C13-H9 109.5 B2-C13-H10 109.5
H9-C13-H10 109.5 B2-C13-H11 109.5
H9-C13-H11 109.5 H10-C13-H11 109.5
O1-C14-C15 125.05(10) O1-C14-C18 114.94(10)
C15-C14-C18 120.01(10) C16-C15-C14 123.09(10)
C16-C15-H18 118.5 C14-C15-H18 118.5
O2-C16-C15 124.98(10) O2-C16-C17 115.39(10)
C15-C16-C17 119.62(10) C16-C17-H15 109.5
C16-C17-H16 109.5 H15-C17-H16 109.5
C16-C17-H17 109.5 H15-C17-H17 109.5
H16-C17-H17 109.5 C14-C18-H19 109.5
C14-C18-H20 109.5 H19-C18-H20 109.5
C14-C18-H21 109.5 H19-C18-H21 109.5
H20-C18-H21 109.5 C12-B2-C5 111.56(9)
C12-B2-C7 111.30(9) C5-B2-C7 103.76(9)
C12-B2-C13 110.29(9) C5-B2-C13 108.98(9)
C7-B2-C13 110.78(9)
233
Table A.33. Torsion angles (°) for [(py)
2
BMe
2
]Ni(acac) (5.29).
O2-Ni1-O1-C14 5.08(9) N2-Ni1-O1-C14 -126.2(6)
N1-Ni1-O1-C14 -175.63(9) O1-Ni1-O2-C16 -2.54(10)
N2-Ni1-O2-C16 174.95(9) N1-Ni1-O2-C16 -166.8(8)
O1-Ni1-N1-C1 44.45(8) O2-Ni1-N1-C1 -151.3(8)
N2-Ni1-N1-C1 -133.02(8) O1-Ni1-N1-C5 -134.57(8)
O2-Ni1-N1-C5 29.7(8) N2-Ni1-N1-C5 47.97(8)
O1-Ni1-N2-C8 83.5(6) O2-Ni1-N2-C8 -47.98(8)
N1-Ni1-N2-C8 132.84(8) O1-Ni1-N2-C7 -98.6(6)
O2-Ni1-N2-C7 129.88(8) N1-Ni1-N2-C7 -49.31(8)
C5-N1-C1-C2 -0.73(16) Ni1-N1-C1-C2 -179.74(8)
N1-C1-C2-C3 1.35(16) C1-C2-C3-C4 -0.61(16)
C2-C3-C4-C5 -0.71(17) C1-N1-C5-C4 -0.60(15)
Ni1-N1-C5-C4 178.39(7) C1-N1-C5-B2 179.18(9)
Ni1-N1-C5-B2 -1.83(13) C3-C4-C5-N1 1.31(16)
C3-C4-C5-B2 -178.45(10) C8-N2-C7-C11 0.60(15)
Ni1-N2-C7-C11 -177.18(7) C8-N2-C7-B2 -178.10(9)
Ni1-N2-C7-B2 4.12(13) C7-N2-C8-C9 -0.77(16)
Ni1-N2-C8-C9 177.07(8) N2-C8-C9-C10 0.30(17)
C8-C9-C10-C11 0.28(17) C9-C10-C11-C7 -0.43(17)
N2-C7-C11-C10 -0.01(16) B2-C7-C11-C10 178.62(10)
Ni1-O1-C14-C15 -4.90(16) Ni1-O1-C14-C18 174.67(8)
O1-C14-C15-C16 0.75(18) C18-C14-C15-C16 -178.80(11)
Ni1-O2-C16-C15 -0.36(16) Ni1-O2-C16-C17 -179.40(8)
C14-C15-C16-O2 2.07(18) C14-C15-C16-C17 -178.92(11)
N1-C5-B2-C12 -172.33(9) C4-C5-B2-C12 7.43(14)
N1-C5-B2-C7 -52.40(12) C4-C5-B2-C7 127.36(10)
N1-C5-B2-C13 65.66(12) C4-C5-B2-C13 -114.58(11)
N2-C7-B2-C12 171.19(9) C11-C7-B2-C12 -7.42(14)
N2-C7-B2-C5 51.09(12) C11-C7-B2-C5 -127.52(10)
N2-C7-B2-C13 -65.72(12) C11-C7-B2-C13 115.67(11)
234
Table A.34. Anisotropic atomic displacement parameters (Å
2
) for [(py)
2
BMe
2
]Ni(acac)
(5.29).
The anisotropic atomic displacement factor exponent takes the form: -2π
2
[ h
2
a
*2
U
11
+ ...
+ 2 h k a
*
b
*
U
12
]
U
11
U
22
U
33
U
23
U
13
U
12
Ni1 0.01204(8) 0.00895(8) 0.00953(8) 0.00150(5) 0.00423(5) 0.00318(6)
O1 0.0154(4) 0.0130(4) 0.0119(4) 0.0012(3) 0.0050(3) 0.0039(3)
O2 0.0174(4) 0.0115(4) 0.0137(4) 0.0030(3) 0.0064(3) 0.0038(3)
N1 0.0115(4) 0.0100(4) 0.0095(4) 0.0008(3) 0.0007(3) 0.0042(3)
N2 0.0122(4) 0.0091(4) 0.0094(4) 0.0014(3) 0.0011(3) 0.0034(3)
C1 0.0142(5) 0.0134(5) 0.0119(5) -0.0003(4) 0.0016(4) 0.0067(4)
C2 0.0195(6) 0.0120(5) 0.0145(5) 0.0008(4) -0.0007(4) 0.0078(4)
C3 0.0182(6) 0.0097(5) 0.0165(5) 0.0038(4) -0.0017(4) 0.0021(4)
C4 0.0120(5) 0.0125(5) 0.0139(5) 0.0027(4) 0.0015(4) 0.0019(4)
C5 0.0106(5) 0.0116(5) 0.0078(4) 0.0011(4) -0.0005(4) 0.0024(4)
C7 0.0140(5) 0.0102(5) 0.0097(5) 0.0036(4) 0.0026(4) 0.0062(4)
C8 0.0126(5) 0.0117(5) 0.0136(5) 0.0031(4) 0.0015(4) 0.0023(4)
C9 0.0187(6) 0.0136(5) 0.0138(5) 0.0000(4) -0.0018(4) 0.0020(4)
C10 0.0245(6) 0.0144(5) 0.0100(5) -0.0006(4) 0.0002(4) 0.0074(5)
C11 0.0169(5) 0.0152(5) 0.0117(5) 0.0027(4) 0.0047(4) 0.0080(4)
C12 0.0129(5) 0.0190(6) 0.0176(5) 0.0026(4) 0.0036(4) 0.0065(4)
C13 0.0170(5) 0.0139(5) 0.0146(5) 0.0014(4) -0.0009(4) 0.0061(4)
C14 0.0123(5) 0.0184(5) 0.0090(5) 0.0014(4) 0.0015(4) 0.0066(4)
C15 0.0150(5) 0.0193(6) 0.0110(5) 0.0042(4) 0.0048(4) 0.0052(4)
C16 0.0115(5) 0.0152(5) 0.0131(5) 0.0051(4) 0.0023(4) 0.0041(4)
C17 0.0236(6) 0.0149(6) 0.0203(6) 0.0062(4) 0.0081(5) 0.0045(5)
C18 0.0245(6) 0.0188(6) 0.0140(5) -0.0008(4) 0.0061(5) 0.0054(5)
B2 0.0110(5) 0.0118(5) 0.0117(5) 0.0017(4) 0.0018(4) 0.0049(4)
235
Table A.35. Hydrogen atomic coordinates and isotropic atomic displacement parameters
(Å
2
) for [(py)
2
BMe
2
]Ni(acac) (5.29).
x/a y/b z/c U(eq)
H1 1.0946 0.1015 0.2150 0.015
H14 0.9416 -0.1712 0.2591 0.018
H13 0.6446 -0.2237 0.3240 0.019
H12 0.5169 -0.0005 0.3442 0.016
H5 1.2948 0.6998 0.3476 0.016
H4 1.2816 0.8654 0.4815 0.02
H3 0.9818 0.8089 0.5442 0.02
H2 0.7099 0.5884 0.4707 0.017
H6 0.3629 0.2026 0.3380 0.024
H7 0.4176 0.4033 0.3738 0.024
H8 0.5007 0.2849 0.4272 0.024
H9 0.5446 0.4943 0.2183 0.023
H10 0.5022 0.2990 0.1752 0.023
H11 0.7127 0.4385 0.1782 0.023
H18 1.3278 0.5858 -0.0076 0.018
H15 1.4877 0.9105 0.1227 0.029
H16 1.2893 0.9419 0.1333 0.029
H17 1.3445 0.8870 0.0370 0.029
H19 1.0594 0.1605 -0.0514 0.03
H20 1.2622 0.1739 -0.0057 0.03
H21 1.2515 0.2996 -0.0765 0.03
236
References
1) CCDC-937914 contains additional supplementary crystallographic data for this
compound. This information can obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax
(+44) 1223-336-033; or deposit@ccdc.cam.ac.uk).
2) CCDC-937915 contains additional supplementary crystallographic data for this
compound. This information can obtained as in note 1.
3) CCDC-937913 contains additional supplementary crystallographic data for this
compound. This information can obtained as in note 1.
Abstract (if available)
Abstract
Research presented in this work describes investigations into the synthesis, structure, and reactivity of cooperative catalysts. Cooperative catalysis, the concept of actively involving ligands in catalytic transformations, is used extensively in enzymatic systems and has been shown to enable organometallic catalysts to realize improved enantioselectivity, chemoselectivity, or activation of otherwise unreactive bonds. Two types of cooperative catalysts are investigated in this work: non-innocent ligands and ligand-based directing groups. Initial investigations detailed in this work revolve around a catalyst of the first type: Shvo’s catalyst ({[Ph₄(η⁵-C₄CO)]₂H]}Ru₂(CO)₄(μ-H)) which is known for containing a non-innocent cyclopentadienone ligand. Shvo’s catalyst is shown to be a competent catalyst for alkylation of amines with alcohols and amines and is superior to other reported catalysts in some cases. Subsequent studies investigated the potential of Shvo’s catalyst to mediate cascade reactions, such as Pictet-Spengler type cyclizations without the need for a starting aldehyde. ❧ Later explorations were directed towards the development of a catalyst with a pendant Lewis acid, specifically boron, which could be used to direct C–H activation of substrates. Studies of the reactivity of a proposed cooperative catalyst, {[(py)₂BMe(μ-OH)]Ru(MeCN)₃}+ -OTf (py = 2-pyridyl, cym = η⁶-p-cymene), led to the discovery that ruthenium(III) chloride hydrate is a convenient catalyst for the addition of active methylene compounds to aryl alkynes. These reactions are inexpensive, operationally simple, air and water tolerant, and high yielding in cases. ❧ Further investigations towards the synthesis of a cooperative catalyst with a Lewis acid directing group focused on the synthesis of rhodium(I) and iridium(I) complexes of type [(py)₂BMe₂]ML₂ (L₂ = (tBuNC)₂, (CO)₂, (C2H₄)₂, cyclooctadiene, 1,2- bis(diphenylphosphino)ethane). These complexes were found to undergo a ring inversion of the six-membered metallocycle. Inversion recovery kinetic analysis was used to measure the rate and enthalpic barrier (ΔH,) of this transformation across the series. Whereas the ring flip is proposed to proceed through a transition state in which a filled-filled π-interaction between the metal and the pyridines becomes available, this ring flip barrier is used to parameterize the π-acceptor ability of the ancillary ligands. The observed values were found not to correlate to either Tolman or Lever parameters, indicating that the ring flip barrier selectively reports the strength of a transient π-bond, while the other known metrics report combined π- and σ- effects. ❧ Finally, the synthesis of cooperative catalysts based on first-row metals was also explored. [(py)₂BMe₂]Ni(PPh₃)Cl and [(py)₂ BMe₂]Ni(acac) (acac = acetylacetonate) were synthesized and structurally characterized. [(py)₂BMe₂]Ni(PPh₃)Cl is observed to exhibit both inter- and intramolecular substitutional lability. Early investigations of the kinetics of this isomerization reveal that the mechanism is not straightforward.
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Asset Metadata
Creator
Pennington-Boggio, Megan K.
(author)
Core Title
Investigations in cooperative catalysis: synthesis, reactivity and metal-ligand bonding
School
College of Letters, Arts and Sciences
Degree
Doctor of Philosophy
Degree Program
Chemistry
Publication Date
07/06/2013
Defense Date
06/07/2013
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
cooperative catalysis,metal-ligand bonding,OAI-PMH Harvest,organometallics
Format
application/pdf
(imt)
Language
English
Contributor
Electronically uploaded by the author
(provenance)
Advisor
Williams, Travis J. (
committee chair
), Nutt, Steven R. (
committee member
), Prakash, G. K. Surya (
committee member
)
Creator Email
meganpen@usc.edu,mkpenningtonboggio@gmail.com
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c3-285301
Unique identifier
UC11294010
Identifier
etd-Pennington-1741.pdf (filename),usctheses-c3-285301 (legacy record id)
Legacy Identifier
etd-Pennington-1741.pdf
Dmrecord
285301
Document Type
Dissertation
Format
application/pdf (imt)
Rights
Pennington-Boggio, Megan K.
Type
texts
Source
University of Southern California
(contributing entity),
University of Southern California Dissertations and Theses
(collection)
Access Conditions
The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...
Repository Name
University of Southern California Digital Library
Repository Location
USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA
Tags
cooperative catalysis
metal-ligand bonding
organometallics