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CH activation and catalysis with iridium hydroxo and methoxo complexes and related chemistry
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CH activation and catalysis with iridium hydroxo and methoxo complexes and related chemistry
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Content
CH ACTIVATION AND CATALYSIS WITH
IRIDIUM HYDROXO AND METHOXO COMPLEXES
AND RELATED CHEMISTRY
by
William Joseph Tenn, III
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
August 2007
Copyright 2007 William Joseph Tenn, III
ii
DEDICATION
For my family.
iii
ACKNOWLEDGEMENTS
As this amazing California adventure draws to its end, it is my great
pleasure to thank those people who have helped me get through the last four
years and without whom much of this work would not have been possible.
First and foremost, I must thank my graduate advisor Roy Periana, for “beating
me up” routinely for the last four years, for giving me a chance to contribute to
one of the most relevant problems facing contemporary chemistry, to take part
in the quest for the “holy grail”, and always providing a great scientific role
model. You taught me how to learn and think about tough problems in
chemistry in a very constructive and creative way.
The Periana Group! Kenny, Xiang, Oleg, Gaurav, CJ, Vadim, Brian,
Steve, Somesh, Jooho, Siva, Satoshi, and Genette. You guys were my friends
and at times my enemies, but you made my life in grad school great and I truly
appreciate all of you and hope that you find fame and fortune, or whatever you
want in your own lives.
I need to thank my parents for their encouragement and limitless
support. Not to mention their important financial contributions over the years
toward my education, both institutional and social.
In addition, our collaborators who I learned much from, Bill Kaska,
Bill Goddard, Jonas Oxgaard, and Smith Nielsen; I thank you too.
iv
I of course have to thank the lunch group has met regularly since the
beginning: Carsten, Marco, Sayantan, and Sujith. Our “quarterly group
meetings” were great and I always looked forward to them.
My Ph.D. committee was great! Thank you Bill Weber, Surya Prakash,
and Mark Thompson for teaching me so much; I really learned something from
you too.
We should all do it again sometime.
v
TABLE OF CONTENTS
DEDICATION .................................................................................................. ii
ACKNOWLEDGEMENTS ............................................................................. iii
LIST OF TABLES .......................................................................................... vii
LIST OF FIGURES...........................................................................................xi
LIST OF SCHEMES .......................................................................................xiv
ABSTRACT....................................................................................................xvi
1 Introduction............................................................................................... 1
1.1 Background ........................................................................................ 1
1.2 CH Activation as a Coordination Reaction........................................ 5
1.3 CH activation in Strongly Acidic Media:
Catalyst Inhibition by Ground State Stabilization............................ 12
1.4 Strategies Towards Catalytic Systems that are not Inhibited by
Methane Oxidation Products............................................................ 21
1.5 References ........................................................................................ 25
2 CH Activation with an O-Donor Iridium Methoxo Complex................. 29
2.1 Introduction. ..................................................................................... 29
2.2 Results and Discussion..................................................................... 31
2.3 Experimental Section. ...................................................................... 37
2.4 References ........................................................................................ 64
3 CH Activation and Catalysis by an Iridium Hydroxo Complex ............. 66
3.1 Introduction. ..................................................................................... 66
3.2 Results and Discussion..................................................................... 67
3.3 Experimental Section. ...................................................................... 73
3.4 References ........................................................................................ 90
4 Mechanistic Analysis of Iridium Heteroatom CH Activation................. 92
4.1 Introduction. ..................................................................................... 92
4.2 Results and Discussion..................................................................... 94
4.3 Experimental Section. .................................................................... 101
4.4 References. ..................................................................................... 104
vi
5 Synthesis and Structural Characterization of Novel, Organometallic,
Rh(III), bis-(acetylacetonate) Complexes ............................................ 106
5.1 Introduction. ................................................................................... 106
5.2 Results and Discussion................................................................... 108
5.3 Experimental Section. .................................................................... 114
5.4 References. ..................................................................................... 118
6 Synthesis, Characterization and CH Activation Reactions of
Organometallic, O-Donor Ligated, Rh(III) Complexes....................... 119
6.1 Introduction. ................................................................................... 119
6.2 Results and Discussion................................................................... 122
6.2 Conclusion...................................................................................... 129
6.3 Experimental Section. .................................................................... 130
6.4 References. ..................................................................................... 162
7 Functionalization of a Low Valent Metal Carbon Bond with Se(IV)... 164
7.1 Introduction. ................................................................................... 164
7.2 Results and Discussion................................................................... 167
7.3 Conclusion...................................................................................... 169
7.4 Experimental Section. .................................................................... 170
7.5 References. ..................................................................................... 175
Bibliography.................................................................................................. 176
vii
LIST OF TABLES
Table 2.1. Crystal data and structure refinement for
(acac)
2
Ir(OCH
3
)(CH
3
OH). 42
Table 2.2. Atomic coordinates (x 10
4
) and equivalent isotropic
displacement parameters (Å
2
x 10
3
) for
(acac)
2
Ir(OCH
3
)(CH
3
OH). U(eq) is defined as one
third of the trace of the orthogonalized U
ij
tensor. 43
Table 2.3. Bond lengths [Å] and angles [°] for
(acac)
2
Ir(OCH
3
)(CH
3
OH). 44
Table 2.4. Anisotropic displacement parameters (Å
2
x 10
3
) for
(acac)
2
Ir(OCH
3
)(CH
3
OH). The anisotropic
displacement factor exponent takes the form: -2π
2
[
h
2
a*
2
U
11
+ ... + 2 h k a* b* U
12
]. 48
Table 2.5. Hydrogen coordinates ( x 10
4
) and isotropic
displacement parameters (Å
2
x 10
3
) for
(acac)
2
Ir(OCH
3
)(CH
3
OH). 50
Table 2.6. Crystal data and structure refinement for
(acac)
2
Ir(OCH
3
)(Py). 52
Table 2.7. Atomic coordinates ( x 10
4
) and equivalent
isotropic displacement parameters (Å
2
x 10
3
) for
(acac)
2
Ir(OCH
3
)(Py). U(eq) is defined as one third
of the trace of the orthogonalized U
ij
tensor. 53
Table 2.8. Bond lengths [Å] and angles [°] for
(acac)
2
Ir(OCH
3
)(Py). 54
viii
Table 2.9. Anisotropic displacement parameters (Å
2
x 10
3
) for
(acac)
2
Ir(OCH
3
)(Py). The anisotropic displacement
factor exponent takes the form: -2π
2
[ h
2
a*
2
U
11
+
... + 2 h k a* b* U
12
]. 56
Table 2.10. Hydrogen coordinates ( x 10
4
) and isotropic
displacement parameters (Å
2
x 10
3
) for
(acac)
2
Ir(OCH
3
)(Py). 57
Table 3.1. Crystal data and structure refinement for
(acac)
2
Ir(OH)(Py). 76
Table 3.2. Atomic coordinates ( x 10
4
) and equivalent
isotropic displacement parameters (Å
2
x 10
3
) for
(acac)
2
Ir(OH)(Py). U(eq) is defined as one third of
the trace of the orthogonalized U
ij
tensor. 77
Table 3.3. Bond lengths [Å] and angles [°] for
(acac)
2
Ir(OH)(Py). 78
Table 3.4. Anisotropic displacement parameters (Å
2
x 10
3
) for
(acac)
2
Ir(OH)(Py). The anisotropic displacement
factor exponent takes the form: -2π
2
[ h
2
a*
2
U
11
+
... + 2 h k a* b* U
12
]. 80
Table 3.5. Hydrogen coordinates ( x 10
4
) and isotropic
displacement parameters (Å
2
x 10
3
) for
(acac)
2
Ir(OH)(Py). 81
Table 6.1. Crystal data and structure refinement for
(acac)
2
Rh(Cl)(CH
3
OH). 133
Table 6.2. Atomic coordinates ( x 10
4
) and equivalent
isotropic displacement parameters (Å
2
x 10
3
) for
(acac)
2
Rh(Cl)(CH
3
OH). U(eq) is defined as one
third of the trace of the orthogonalized U
ij
tensor. 134
Table 6.3. Bond lengths [Å] and angles [°] for
(acac)
2
Rh(Cl)(CH
3
OH). 135
ix
Table 6.4. Anisotropic displacement parameters (Å
2
x 10
3
) for
(acac)
2
Rh(Cl)(CH3OH). The anisotropic
displacement factor exponent takes the form: -2π
2
[
h
2
a*
2
U
11
+ ... + 2 h k a* b* U
12
]. 138
Table 6.5. Hydrogen coordinates ( x 10
4
) and isotropic
displacement parameters (Å
2
x 10
3
) for
(acac)
2
Rh(Cl)(CH
3
OH). 139
Table 6.6. Crystal data and structure refinement for trans-
(acac)
2
Rh(CH
3
)(Py). 141
Table 6.7. Atomic coordinates ( x 10
4
) and equivalent
isotropic displacement parameters (Å
2
x 10
3
) for
trans-(acac)
2
Rh(CH
3
)(Py). U(eq) is defined as one
third of the trace of the orthogonalized U
ij
tensor. 142
Table 6.8. Bond lengths [Å] and angles [°] for trans-
(acac)
2
Rh(CH
3
)(Py). 143
Table 6.9. Anisotropic displacement parameters (Å
2
x 10
3
) for
trans-(acac)
2
Rh(CH
3
)(Py). The anisotropic
displacement factor exponent takes the form: -2π
2
[
h
2
a*
2
U
11
+ ... + 2 h k a* b* U
12
]. 146
Table 6.10. Hydrogen coordinates ( x 10
4
) and isotropic
displacement parameters (Å
2
x 10
3
) for trans-
(acac)
2
Rh(CH
3
)(Py). 148
Table 6.11. Crystal data and structure refinement for cis-
(acac)
2
Rh(CH
3
)(Py). 149
Table 6.12. Atomic coordinates ( x 10
4
) and equivalent
isotropic displacement parameters (Å
2
x 10
3
) for
cis-(acac)
2
Rh(CH
3
)(Py). U(eq) is defined as one
third of the trace of the orthogonalized U
ij
tensor. 150
Table 6.13. Bond lengths [Å] and angles [°] for cis-
(acac)
2
Rh(CH
3
)(Py). 151
x
Table 6.14. Anisotropic displacement parameters (Å
2
x 10
3
) for
cis-(acac)
2
Rh(CH
3
)(Py). The anisotropic
displacement factor exponent takes the form: -2π
2
[
h
2
a*
2
U
11
+ ... + 2 h k a* b* U
12
]. 157
Table 6.15. Hydrogen coordinates ( x 10
4
) and isotropic
displacement parameters (Å
2
x 10
3
) for cis-
(acac)
2
Rh(CH
3
)(Py). 158
xi
LIST OF FIGURES
Figure 1.1 Examples of Some of the Reported CH Activation
Systems. 4
Figure 1.2. Orbital Interaction Between the Low Lying
Compact HOMO of a CH Bond and the Low Lying,
Polarizable LUMO of a “Soft” Electrophile. 10
Figure 1.3. Comparison of the Ligand Environment of the
Pt(bpym)Cl
2
/H
2
SO
4
System with the BARF Anion. 19
Figure 1.4. Correlation of CH activation Rates (Measured by
H/D exchange rates between CH
4
and D
2
SO
4
) with
Solvent Acidity, H
0
(98 % H2SO4 = 10.4 H
0
and
85% = 8 H
0
). 21
Figure 2.1. ORTEP diagram of the (acac-
O,O)
2
Ir(OCH
3
)(CH
3
OH) complex, showing
ellipsoids at the 50% probability level. A molecule
of co-crystallized CHCl
3
has been omitted for
clarity. 40
Figure 2.2. ORTEP diagram of the (acac-O,O)
2
Ir(OCH
3
)(Py)
complex, showing ellipsoids at the 50% probability
level. A molecule of co-crystallized CHCl
3
has
been omitted for clarity. Selected bond distances
(?): Ir1-O3, 2.024(4); Ir1-N1, 2.048(5). 52
Figure 2.3. Plot of TON for H/D Exchange Between D
2
O and
C
6
H
6
Catalyzed by 1-CH
3
OH. 61
Figure 3.1. ORTEP diagram of complex 1, showing ellipsoids
at the 50% probability level. A molecule of
cocrystallized CHCl
3
has been omitted for clarity.
Selected bond distances ( ? ): Ir1-O5, 2.018(4); Ir1-
N1, 2.044(5). 68
Figure 3.2. Plot of TOF versus 1/[Py] for C
6
H
6
/D
2
O H/D
Exchange with 1 (10mM). 70
Figure 3.3. Plot of TON vs. Time for Benzene/D
2
O H/D
Exchange with 1. 84
xii
Figure 3.4. Plots of TON vs. Time for Benzene/D2O H/D
Exchange with 1 for runs with varied free pyridine
added. Where diamond = 0 Py added, x = 0.5 mol
eq, square = 1 mol eq, and triangle = 2 mol eq. 85
Figure 3.5. Plot of TOF vs. 1/[Py] for Benzene/D2O H/D
Exchange with 1. 85
Figure 4.1. Left: The CH activation transition state TS1, where
a hydrogen is transferred from a benzene to a
methoxo group. Right: Close-up of the four relevant
atoms in TS1. 93
Figure 4.2. Conceptual orbital view of Sigma-Bond Metathesis
(left) and Internal Electrophilic Substitution (right). 95
Figure 4.3. Mulliken charges (in electrons) on the reacting
moieties Ir (circles), H (diamonds), CH
3
(triangles)
and OH (squares) during the IRC of the model
reaction. 98
Figure 5.1. Thermal ellipsoid plot of I (50% probability thermal
ellipsoids), showing the [Rh(acac)
2
Cl
2
]
-
complex
anion (top); each complex is bridged to the next by
a cis-[Na(CH
3
OH)
2
]
+
in the crystal lattice (bottom). 110
Figure 5.2. Thermal ellipsoid plot of II (50% probability),
showing the s-bonded -CH
2
COCH
3
ligand and a
water ligand in axial positions. The hydrogen atoms
of the aqua ligand have not been located and were
omitted. 112
Figure 5.3. Thermal ellipsoid plot of III (50% probability).
Two molecules of cocrystallized CHCl
3
have been
omitted for clarity. The hydrogen atom of the
methanol ligand was not located and was omitted. 113
Figure 6.1. ORTEP of 1 (50% probability thermal ellipsoids).
A molecule of cocrystallized methanol has been
omitted for clarity. The hydrogen atom on the
methanol was not located and was omitted. 123
xiii
Figure 6.2. ORTEP plot of trans-2 (50% probability thermal
ellipsoids). Selected bond lengths (? ): Rh1-N1,
2.236(3); Rh1-C16, 2.031(3). 124
Figure 6.3. ORTEP plot of cis-2 (50% probability thermal
ellipsoids). Selected bond lengths (? ): Rh1-N1,
2.017(5); Rh1-C16, 2.026(5). 125
Figure 6.4. ORTEP plot of 4 (50% probability thermal
ellipsoids). Selected bond lengths (? ): Rh1-N1,
2.021(4); Rh1-C16, 2.062(4). 127
Figure 7.1. Proposed Mechanism for the Conversion of CH
3
Re
to Methanol Catalyzed by Se(IV). 167
Figure 7.2.
1
H NMR of (CO)
5
ReCH
3
in CD
3
CN/D
2
O with
cyclohexane internal standard. d -0.02(s, 3H,
(CO)
5
ReCH
3
methyl); 1.40 (s, cyclohexane I.S.);
1.97 (s, acetonitrile residual peak); 3.71 (water
residual peak). 172
Figure 7.3.
1
H NMR of mixture after heating at 100oC for 30
min. d1.40 (s, cyclohexane I.S.); 1.97 (s,
acetonitrile residual peak); 2.65 (s, CH
3
SeO
2
D,
methyl); 3.71 (water residual peak). 173
xiv
LIST OF SCHEMES
Scheme 1.1. Oxidative Conversion of Fossil Fuels is a
Foundational Technology. 2
Scheme 1.2. Examples of Products Potentially Impacted by Next
Generation, Low Temperature, Selective,
Hydrocarbon Oxidation Catalysts. 3
Scheme 1.3. General Scheme for Oxidation Catalysis Based on
CH Activation. 5
Scheme 1.4. Classification of Various Modes of CH Activation. 8
Scheme 1.5. Activation and Functionalization of Methane by
Electrophilic Systems. 9
Scheme 1.6. Proposed Electrophilic CH Activation Mechanism
for the Oxidation of Methane by the Hg(II)/H
2
SO
4
System. 11
Scheme 1.7. Generalized Energy Diagram for CH Activation via
CH Coordination followed by CH Cleavage
Showing Ground State Stabilization. 13
Scheme 1.8. Redox (A) and Non-Redox (B) Catalytic Sequences
for Functionalization of Hydrocarbons via CH
Bond Activation. 23
Scheme 2.1. Redox (A) and Non -redox (B) Catalytic Sequences
for Functionalization of Hydrocarbons via CH bond
Activation. 30
Scheme 2.2. Synthetic Procedure for the Production of 2-
CH
3
OH. 32
Scheme 2.3. CH Activation of Benzene with Ir(III) Methoxo
Complexes. 32
Scheme 2.4. Proposed mechanism for the reaction of 2 (values in
parenthesis are calculated DH in benzene). 35
xv
Scheme 2.5. Mechanism for CH Activation Proceeding via an
Intermediate Ir-H. 36
Scheme 2.6. Reaction of 2-
13
C with Benzene. 59
Scheme 3.1. CH Activation of Benzene with (acac-
O,O)
2
Ir(III)(OH)(Py), 1. 67
Scheme 3.2. Proposed mechanism for the reaction of 1 (values in
parenthesis are calculated DG). 71
Scheme 3.3. Determination of Deuterium Kinetic Isotope Effect
on CH Activation of Benzene by 1. 86
Scheme 3.4. Computational Determination of Deuterium Kinetic
Isotope Effect by DFT. 89
Scheme 4.1. Determination of Deuterium Kinetic Isotope Effect
on CH Cleavage by 1. 101
Scheme 4.2. Computational Determination of Deuterium Kinetic
Isotope Effect by DFT. 103
Scheme 5.1. Synthesis of (acac-O,O)
2
Rh(III) Complexes. 109
Scheme 6.1. Synthesis of (hfac-O,O)
2
Rh(III) Complexes. 123
Scheme 6.2. CH Activation of Hydrocarbons by cis-2. 127
Scheme 7.1. Generalized Reaction for Oxy-Functionalization of
a Metal Carbon Bond via O-Atom Transfer. 165
Scheme 7.2. Calculated Low Energy Pathways for Methanol
Formation from MTO and Periodate in Water. 165
Scheme 7.3. Observed Transformation in the Reaction Between
Methyl Rhenium(I) Pentacarbonyl and Selenious
Acid. 166
Scheme 7.4. Calculated Thermodynamics for Reactions of CH
3
-
Y (Y = H, Re(CO)
5
) with H
2
SeO
3
. 174
xvi
ABSTRACT
This dissertation describes a veritable smorgasbord of organometallic
chemistry, including the use of transition metal methoxo and hydroxo
complexes based on iridium(III) as homogeneous catalysts for the activation of
hydrocarbon CH bonds, the functionalization of a low valent rhenium methyl
complex, and the design, synthesis, and study of related systems for the
catalytic functionalization of hydrocarbons.
Chapter 1 introduces the CH activation reaction and catalytic
functionalization of hydrocarbons via electrophilic systems, and discusses the
problem of inhibition of electophilic catalysts by products such as methanol
and water. Approaches towards the development of the next generation of
catalysts that are active for CH activation in water are discussed.
Chapter Two describes a thermally and air stable iridium(III) methoxo
complex that undergoes intermolecular CH activation of benzene with co-
generation of methanol and the iridium-phenyl complex.
Chapter Three highlights a well-defined, iridium hydroxo complex that
is competent for CH activation and long-lived, H/D exchange between benzene
and water. An inverse dependence of the H/D exchange rate on added
pyridine, deuterium kinetic isotope effects, and density functional theory
calculations are consistent with CH activation proceeding via rate-determining
benzene coordination followed by fast CH cleavage.
xvii
Chapter Four discusses the mechanism responsible for CH cleavage in
(acac-O,O)
2
Ir(OCH
3
)(C
6
H
6
), which has been identified and described as an
internal electrophilic substitution (IES) mechanism, on the basis of orbital
changes and predicted reactivity. In the IES mechanism, the lone pair on a M-
X ligand forms a X-H bond, while the orbital making up the M -X bond
becomes a coordinating lone pair.
Chapter Five describes the synthesis and structural characterization, of
novel, Rh(III), bis-acetylacetonate complexes. The first rational synthesis and
characterization of the O-donor, air and water stable organometallic complex,
(acac)
2
Rh(Ph)(CH
3
OH), and related analogs are reported.
Chapter Six discusses the synthesis, characterization, and CH activation
reactions of a series of new organometallic, bis(hexafluoroacetylacetonato)
rhodium(III) complexes. These complexes were found to be active for CH
activation.
Chapter Seven summarizes the development of compatible
functionalization reactions with a methyl rhenium species, for integration with
the CH activation reaction of hydrocarbons by transition metal alkoxo
complexes.
1
1 Introduction
1.1 Background
The conversion of fossilized hydrocarbons to energy and materials is a
foundational technology of our petrochemical industry. While it is important that
we consider a switch to future alternatives, such as the proposed hydrogen -based
economy of the future, it is critical that as a bridge to this long term future, we
develop more environmentally benign, “greener technologies” for these essential
fossil fuel based processes that will continue to be important in the next decade.
As shown in Scheme 1.1, the key objectives of such greener processes must be to
minimize emissions and capital while maximizing energy and materials o utput.
Importantly, reducing dependence on petroleum and increasing use of under-
utilized, abundant natural gas would facilitate this movement to these greener
technologies while extending the life time of these limited fossilized resources.
Alkanes from natural gas and petroleum are among the world’s most
abundant and low-cost feedstocks. Current petrochemical technologies to convert
these feed stocks to energy, fuel and chemicals operate at high temperatures and
utilize multiple steps that lead to inefficient, capital intensive processes. The
development of low temperature, selective, direct alkane oxidation chemistry
could lead to a new paradigm in petrochemical technology that is environmentally
cleaner, economically superior and allow the large reserves of untapped remote
2
natural gas to be valorized as primary feedstocks for fuels and chemicals.
1
Alcohols are among the highest volume commodity chemicals and most versatile
feedstocks.
1b
A primary reason that technologies for direct, selective
hydroxylation of alkanes to alcohols remain a challenge is that the current
commercial catalysts for alkane oxidation (typically solid metal oxides) are not
sufficiently active for the functionalization of alkane CH bonds and high
temperatures and harsh conditions must be employed that lead to low reaction
selectivity.
1a
ENERGY
$$$
EMISSIONS
-$$
MATERIALS
$$$
FOSSIL FUELS
+
AIR
CAPITAL
-$$
Minimize
Maximize
Minimize
Maximize
Global warming
Lessen dependence
on oil
Currently:
Primarily oil
Future:
Natural gas
Scheme 1.1. Oxidative Conversion of Fossil Fuels is a Foundational Technology.
The development of next generation catalysts that would allow the
selective hydroxylation of methane and higher alkanes to alcohols at low
temperatures (~200 – 250
o
C) in inexpensive reactors, with fewer steps and in high
3
yields could provide a basis for this paradigm change in the petrochemical
industry. Examples of the products that could be dramatically impacted by such
low temperature, hydroxylation catalysts are shown in Scheme 1.2.
R-H R-X
Phenol
1,4-Butane Diol
Propylene Glycol
t-Butanol
1,3-Propane Diol
Ethanol
Ethylene Glycol
Methanol
(DMM)
Low Temperature
Fuel Cells
Acetic Acid
Lower
Temperatures
~200
o
C
Higher efficiencies
Lower capital
Today
High Temperatures
>600
o
C
High capital
Lower atom and
energy efficiency
Cinnamates
Linear Alkyl Benzene
MSA
Methyl Chloride
Divinyl Benzene
Cyclohexanol
Neoacids
Diphenyl Carbonates
Hydrogen peroxide
Liquid Fuels
Styrene
Isobutyl Benzene
Scheme 1.2. Examples of Products Potentially Impacted by Next Generation,
Low Temperature, Selective, Hydrocarbon Oxidation Catalysts.
Significant advances in the chemistry of the hydrocarbons have been made
since the 1970’s. Particularly relevant to the development of low temperature,
selective, heteroatom hydrocarbon functionalization catalysts has been the
discovery of homogeneous metal complexes that cleave the CH bonds of
unactivated hydrocarbons at low temperatures and with extraordinary selectivity,
Figure 1.1.
2,3
Thus, studies have shown that primary CH bonds are more reactive
than tertiary, aromatic more reactive than aliphatic and important to the challenge
4
N
N
N
N N
N
Ru
Ph
3
P H
L
B
H
Periana
Periana
Green
W
H
H
Ir CO
CO
Graham
Pt
P
H P
Whitesides
H
Os
PR
3
R3P PR 3
R
3
P
Flood
N N
Pt
CH
3
B
N
N
N
N
H
Goldberg
Watson
Lu CH
3
N N
N N
Pt
Cl
Cl
Goldman, Jensen, Kaska
Lau
Pt
N CH 3
L N
Bercaw Hartwig
P
P
Ir
H
H
Ir
Me
3
P
H
H
Bergman
Hg(II)
Ir
H
H
BPin
BPin
Sen
Pd(II)
Pt
Cl H2O
H
2
O Cl
Shilov
Me
5
Ir
Me3P
Me
Bergman
Periana
[(Por)
2
Rh
II
]
2
Wayland
NR Zr
RHN
RHN
Wolczanski Bergman
Re
Me
3
P
PMe3
PMe3
O
Ir
O O
O O
N
CH
3
Figure 1.1 Examples of Some of the Reported CH Activation Systems.
of selective oxidation of methane to methanol, the CH bonds of alcohols are less
reactive than those of the parent alkanes. Since this discovery, there has been and
continues to be intense interest in incorporating the CH activation reaction into
catalytic cycles to convert hydrocarbon to more useful functionalized products.
However, to date relatively few catalyst systems that are based on the CH
activation reaction have been developed that allow the functionalization of
hydrocarbons
4,5,6,7,8,9,10
and there are still large gaps in our fundamental knowledge
of how to design such catalysts.
2,3
In this chapter, the focus is discussion of some
of the challenges and approaches to developing the next generation of alkane
hydroxylation catalysts based on the CH activation reaction.
5
1.2 CH Activation as a Coordination Reaction
Homogeneous transition metal catalysis has had a substantial impact on
organic chemistry. From polymerizations to hydrogenations there are few aspects
of organic chemistry that have not been touched by this field of research. The
majority of these catalytic reactions take place in the inner, or first coordination
sphere of the homogeneous metal catalyst and in many cases lead to the formation
of organometallic, M-C, intermediates. The advantage of these inner sphere,
organometallic reactions is that the reactant of interest is bound to the catalyst
center during conversion to products and as a result, the catalyst can effectively
mediate both rate and selectivity in the conversion of the reactants to desired
products.
C H
MX
1/2 O
2
C-OH
+
Functionalization
CH Activation
<250
o
C
Stable
Catalyst
MX +
H
XM
C
H
XM
C
XM C XM C
Scheme 1.3. General Scheme for Oxidation Catalysis Based on CH Activation.
There are many definitions of “CH activation.” As shown in Scheme 1.3,
in this discussion we define CH activation as a facile CH cleavage reaction with an
“MX” species that proceeds by coordination of a hydrocarbon to the inner-sphere
6
of “M” (either via an intermediate “alkane or arene complex” or a transition state)
leading to a M-C intermediate. Important to this definition is the requirement that
during the CH cleavage the hydrocarbyl species remains in the inner-sphere and
under the influence of “M”. Theoretical studies as well as experimental studies
support this view that classically unreactive CH bonds can be cleaved by such
inner-sphere mechanism.
11
This emphasis on inner-sphere coordination is based
on the presumption that cleavage reactions of the CH bond that proceed in this
manner, with strong interaction between the CH bond and “M”, can be expected to
show unique high selectivity and activities.
As might be expected from the wide variety of complexes that cleave CH
bonds by such an inner-sphere reaction there are several recognized mechanistic
classifications as shown in Scheme 1.3. As can be seen, these are all related by the
requirement that the alkane coordinate to the inner-sphere of the metal center
either as an intermediate or in a transition state leading to the formation of
organometallic M -C intermediates. The specifics of the actual mode of cleavage
depend on the electronic configuration of the metal, the X group and various
variations of these classifications have been observed. Of these, the most common
modes are Electrophilic Substitution (ES), Oxidative Addition (OA) and Sigma
Bond Metathesis and in all cases unique CH cleavage selectivity patterns are
observed.
3
To utilize the unique properties of the CH activation reaction (as
defined above) the M -C species must be more easily functionalized than the CH
bond to yield a useful C-X product with regeneration of the MX species. Ideally,
7
to maintain high reaction selectivity and catalyst control it may be desirable that
this functionalization also occur within the inner sphere of “M”.
This cleavage of the CH bond mediated via formation of a M-C species can
be contrasted to other reactions of alkane CH bonds such as metal mediated
generation of alkyl free radicals, acid or base catalyzed generation of carbocations
or carbanions that are not as selective. In these processes, unlike the CH activation
reaction as defined above, the reactive alkyl fragments that are generated are not
under the influence of the catalyst (because they are not strongly bound to the
catalyst center) and consequently, can exhibit intrinsic reactivities that are
generally undesirable. This may be a reason that the commercially available
oxidation catalysts based on metal oxides and utilized at high temperatures are not
selective for the conversion of methane to methanol: such catalysts may operate by
the generation of free radical species that exhibit intrinsic reactivity that cannot be
controlled by the catalyst.
8
Scheme 1.4. Classification of Various Modes of CH Activation.
Thus, as shown in Scheme 1.5, in the CH activation by an ES pathway the
coordination of the CH of the alkane to an electrophilic center followed by loss of
a proton can also be described as attack of a nucleophile, “sol”, on the coordinated
CH bond that leads to CH cleavage and generation an intermediate E -CH
3
species.
While this is a valid comparison, it would be expected that as the CC double bond
is considerably more electron rich than that of an alkane CH bond, that more
reactive electrophilies would be required for similar coordination and cleavage of
the CH bond. Frontier orbital considerations of this interaction between the CH
M
C
H
X
+
C H
M X
Alkane
Complex
M
C
H
X
+
H X
M C
Sigma Bond Metathesis
M
C
H
X
+
H X
M C
Electrophilic Substitution
M
C
H
X
M
C
H
X
Oxidative Addition
XMC + HMX
M
C
H
X
1,2 Addition
M
C
XH
Metalloradical
C H MX XM
M
C
H
X
+
C H C H
M X M X
Alkane
Complex
M
C
H
X
+
H X
M C
+
H X H X
M C M C
Sigma Bond Metathesis
M
C
H
X
+
H X
M C
Electrophilic Substitution
M
C
H
X
+
H X
M C
+
H X H X
M C M C
Electrophilic Substitution
M
C
H
X
M
C
H
X
Oxidative Addition
XMC + HMX
M
C
H
X
1,2 Addition
M
C
XH
M
C
H
X
1,2 Addition
M
C
XH
Metalloradical
C H MX XM
9
bond and electrophiles, Figure 1.2, would indicate, given the low energy, σ-
symmetry and low polarizability of the HOMO
CH
that “soft”, electrophiles
characterized by low lying, polarizable LUMO’s with σ-symmetry would be
effective for this mode of CH activation.
CH ACTIVATION
H
+
1/2 O
2
+ 2 H
+
H
2
O
CH
3
OH + H
+
CH
3
-E
n+
CH
4 E
n+
H
2
O
FUNCTIONALIZATION
OXIDATION
E
(n-2)+
C
H
H
H
H
E
Sol
E
n+
sol
CH
4
sol
CH Cleavage
CH coordination
Scheme 1.5. Activation and Functionalization of Methane by Electrophilic
Systems.
10
C H
Low lying
Polarizable
LUMO
E+
E
Low lying
Compact HOMO
CH
E
C H
+
Figure 1.2. Orbital Interaction Between the Low Lying Compact HOMO of a CH
Bond and the Low Lying, Polarizable LUMO of a “Soft”
Electrophile.
This has been found to be the case with the “soft,” powerful electrophilic
species, [XHg]
+
, generated by dissolving HgX
2
salts in strongly acidic solvent
such as sulfuric acid or Triflic acid. These species have been found to react
readily with methane via CH activation and are among the most effective catalysts
for the conversion of methane to methanol in 96% sulfuric acid solvent.
5
Thus at
~180
o
C with a 20mM concentration of Hg(HSO
4
)
2
in sulfuric acid, methanol
concentration of ~1 M with yields of over 40% based on added methane, at
methanol selectivities >90% have been observed by the reaction shown in Scheme
1.6.
11
H
2
X
+
X
-
C-H Cleavage
Functionalization
Oxidation
XHg Sol
+
Sol
H
CH
3
+
HX
X
-
Methane
Coordination
X
-
CH
4
+ 3HX
CH
3
OH
HX
XHg
XHg CH
3
Hg
2
X
2
2 H
2
O + SO
2
+ HgX
2
HgX
2
+ H
2
O
+ HX
CH
4
X = HSO
4
Electrophilic
CH Activation
Scheme 1.6. Proposed Electrophilic CH Activation Mechanism for the Oxidation
of Methane by the Hg(II)/H
2
SO
4
System.
Most of organic chemistry, characterized by mild reaction conditions and
high reaction selectivity, can be classified as inner-sphere coordination chemistry
at carbon centers; i.e. chemistry that occurs within the first-coordination sphere of
three, four and five coordinate carbon species. While the coordination chemistry
of carbon in functionalized organic molecules is well-developed, the coordination
chemistry of alkanes is much less so and is characterized by reactions with
superacids, superbases, free-radicals or carbenes. These very reactive species are
either generated under high energy conditions, or with high energy precursors and
are generally not amenable to efficient syntheses with alkanes as starting materials.
12
The high rate of the CH activation reaction results partly from formation of
strong M -C bonds that compensate for the cleavage of the strong C-H bonds
(thermodynamics) and availability of appropriate orbitals on the central atom, M,
that ensure good overlap in the transition states (kinetics). Coupled with the
possibility for oxidative conversion of the M -C intermediate to functionalized
products with regeneration of “M”, as outlined in Scheme 1.3, the C-H activation
reaction can provide a basis for the development of the next generation catalysts
for the atom and energy efficient conversion of alkanes directly to useful products.
1.3 CH activation in Strongly Acidic Media: Catalyst
Inhibition by Ground State Stabilization
Many systems that activate CH bonds are now known and it is possible
that if these systems can be made stable that some could be used as the basis for
development of catalysts for alkane oxidation. In most cases, the CH activation
rates of these systems are quite rapid when rates are extrapolated to temperatures
of ~200
o
C. Indeed, in some cases CH activation has even been observed at
temperatures below room temperature. On the basis of these observations and
assuming that stable motifs can be identified that would facilitate CH activation
and functionalization, it might be considered that acceptable catalysis rates can be
readily obtained by simply basing catalyst designs on the CH activation reaction.
Importantly, this is not the case and other considerations are important.
13
The CH activation is typically a rapid reaction only when the reaction i s
carried out by the generation of high energy species and where the reaction
system is carefully chosen such that the alkane is the most (or only) reactive
species present. Under these circumstances it is understandable that the CH
activation reactions observed are rapid. Unfortunately, under conditions where
products such as alcohols can be produced, typically in the presence of protic,
oxidizing higher temperature conditions, many of these catalysts, even if they can
be made stable, could exhibit very l ow rates.
M
L L
Sol L
M
L L
CH
4
L
E
act
M
L L
CH
3
L
+ CH
4
+ Sol
+ H-Sol Ligand
displacement
CH cleavage
M
L L
CH
3
L
H
Sol
Scheme 1.7. Generalized Energy Diagram for CH Activation via CH Coordination
followed by CH Cleavage Showing Ground State Stabilization.
One fundamental reason for this is that the alkane CH bond, unlike CC
double bonds of olefins or other functional groups, are among the poorest known
ligands and unlikely to compete well with other more ligating species for
coordination to the metal center. Indeed, this may well be the “Achilles heel” of
14
catalyst development based on the CH activation reaction. Consistent with the
poor ligating capability of alkanes, other than by spectroscopic methods and
mechanistic studies, only one experimental observation of a transient alkane
complex, and that by low temperature NMR, has been reported.
12
,
13
The
coordination of an alkane to the first coordination sphere of a metal center in the
CH activation reaction (either leading to an intermediate alkane complex or a
transition state that leads directly to CH cleavage) can be viewed as inner sphere
ligand displacement or interchange mechanism where the alkane in one of the
ligands and the other is the ligand initially occupying that coordination site. In
general this ligand to be displaced by the alkane, shown as “Sol” i n Scheme 1.7,
will be the most nucleophilic (ligating) species present in the reaction system and
can be either reactants other than the alkane, solvent or the products. There is
some debate as to whether this ligand exchange involving the alkane is
dissociative or associative.
14,3
This depends on the binding constant of the ligand
being displaced by the alkane but given the poor binding characteristics of
alkanes, it is reasonable that there is will be substantial dissociative character to
the displacement reaction in all cases except with extremely poor ligands.
These considerations point a fundamental issue that must be overcome in
developing catalyst systems based on the CH activation reactions: inner-sphere
ligand displacement mechanisms with alkanes (whether associative or
dissociative) leading to weakly bound, intermediate alkane complexes, or directly
to a transition state leading to CH cleavage, can be expected to be subject to
15
severe ground state inhibition in most media that would be useful for oxidation
catalysis. This ground state stabilization fundamentally arises from strong binding
of other possible ligands to the catalyst in the reaction system. This leads to drop
in energy of the catalyst resting state and as can be seen from Scheme 1.7, the
more stable this state the higher the expected activation barrier for CH activation.
For example, it is challenging to imagine how methane coordination could
occur to sufficient extent to allow efficient catalysis in a solvent such as liquid
water, given the excellent coordinating properties of water that would lead to
stable water complexes and extensive ground state inhibition. This is heightened
by the poor solubility of methane in most useful media and the high concentration
of the solvent. Of course, the reaction does not have to be carried out in solvents
as ligating as water. However, if the objective is the hydroxylation of methane to
methanol, then at a minimum, (if as desired, the catalyst is expected to operate at
high turn over numbers before separation of product) methanol, which can be
expected to bind more tightly to the catalyst than methane, will be present in the
system and catalyst inhibition may be observed.
As might be anticipated this issue of ground state inhibition is observed in
many catalytic hydrocarbon functionalization systems. Thus, of the systems that
are known or likely to activate and hydroxylate hydrocarbon s, such as the Shilov,
Sen and Periana systems, this issue of inhibition is present. Thus, for the Sen
Pd(II) and Periana Hg(II) and Pt(bpym)Cl
2
systems, independent of stabilities, the
16
slow rates or eventual inhibition of these catalyst systems that prevent their utility
can be traced to water (or methanol) binding that leads to ground state inhibition.
In addition to the transition metal based approaches that are described
herein, another notable approach for hydrocarbon oxy- functionalization by
electrophilic systems in strongly acidic media is the super-acid catalyzed
approach which was developed by George A. Olah.
15
Other CH activation/functionalization systems that operate by mechanisms
other than ES, such as the Kaska/Goldman/Jensen system
6
for the
dehydrogenation of alkanes to olefins that operate by an OA mechanism, this
inhibition is observed. In this case, this reaction cannot be carried in the presence
of ethylene, an ideal, inexpensive, hydrogen acceptor due to ground state
inhibition from olefin binding. The slow rates of the Shilov system that is
proposed to operate by an OA mechanism is also most likely due to strong ground
state inhibition from water binding.
To this end, this research program has focused on altering the electronics
of the metal center so as to minimize this ground state inhibition. The
fundamental idea behind the use of an acidic solvent (this can be Lewis, or
Bronsted acid) is that in principle, the strongest base that can exist in such a
solvent is the conjugate base of the acid. In the case of a strong acid, both the
acidic and the conjugate base will be weakly basic and expected to be poorly
coordinating. This will minimize ground state stabilization by the solvent and the
conjugate base. Critically, this use of a strong acid as a solvent rather than in
17
stoichiometric amounts relative to the catalyst is central to preventing catalyst
inhibition by products or reactants as these materials will also be present in large
excess over the catalyst in any useful catalyst system.
The use of Lewis or Bronsted acids to facilitate coordination of reactants
is a well-known phenomenon in coordination chemistry.
16
Indeed, some of the
most active systems reported for the stoichiometric CH activation can be seen as
complexes that have been activated by addition of a Lewis acid. Thus, one of the
most active complexes known for CH activation developed by Bergman,
17
[Cp
*
Ir(PMe)
3
Me(CH
2
Cl
2
)]
+
[MeB(C
6
F
5
)
3
]
-
, is generated by reaction of the Lewis
acid, B(C
6
F
5
)
3
, with Cp
*
Ir(PMe)
3
Me
2
in the poorly coordinating solvent, CH
2
Cl
2
.
One reason that this complex is quite reactive with methane (at -10
o
C) is that all
the possible competing ligands in the reaction system [MeB(C
6
F
5
)
3
]
-
and CH
2
Cl
2
,
are poorly coordinating species that minimize ground state stabilization and allow
methane to effectively compete for coordination to the metal center. While this
strategy of stoichiometric use of weakly coordinated complex can lead to very
active catalysts in reactions where no strongly coordinating reactants, solvents, or
products are present, such catalysts could not be expected to remain active in the
presence of stoichiometric or greater amounts of coordinating species such as
water or methanol. In the presence of these materials the weakly coordinated
groups will be readily displaced, resulting in severe ground state inhibition of the
catalyst. Consequently, this approach of stoichiometric use of weakly
18
coordinating groups would not be suitable for catalytic systems where the desired
product is methanol and many catalyst turnovers are required.
This is the essential idea behind the use of inexpensive sulfuric acid
solvent for facilitating the selective oxidation of methane.
5
Liquid sulfuric acid,
at concentrations > ~85%, is a polar, strongly Lewis acidic, poorly nucleophilic
liquid in which the strongest nucleophile (or ligand) that can exist, HSO
4
-
, is
substantially less coordinating that water or methanol. Above this concentration
of acid solvent, any water or methanol generated (or any other species more basic
than HSO
4
-
) is essentially fully protonated and not available for coordination to
the metal center, minimizing catalyst inhibition by ground state inhibition. Below
this acid concentration the solvent acidity drops rapidly
18
and water or methanol
can become available for coordination to the metal center leading to inhibition of
the CH activation reaction.
The key challenge to utilizing this strategy is the identification of
catalysts, reactants and products that are thermally stable in such a medium. Both
methane and methanol are thermally stable in sulfuric acid at temperature below
250
o
C and we have identified several catalyst systems that are stable in this media
for the selective oxidation of methane to methanol. As noted above both the
Hg(II) and Pt(bpym)Cl
2
system have been found to be an efficient catalyst for
methane oxidation to methanol at ~200
o
C in this solvent as both are very stable in
this media. Consistent with the concept of basicity leveling, theoretical studies
show that, at sulfuric acid concentrations > 90%, the ground state of these
19
catalysts, [(Hbpym)PtCl(HSO
4
)]
+
and Hg(HSO
4
)
2
, are coordinated to weakly
binding HSO
4
-
that is most likely extensively hydrogen bonded to solvent H
2
SO
4
molecules as shown in Figure 1.3 for the Pt(bpym)Cl
2
/H
2
SO
4
system. As can be
seen, this weakly coordination of HSO
4
-
in sulfuric acid leads to a highly
dispersed anion that is similar to the weakly coordinating anion, B(C
6
F
5
)
3
Me]
-
and
that can be expected to be displaced by methane more readily than water.
BARF anion
Weak coordinating
Ligands that can be
displaced by methane
Likely active Pt(II) Catalyst
N N
HN N
S
O
O
OH
OH
H
S
O
O
O
O
H
S
O
O
O
OH
H
S
O
OH
O
O
Pt
Cl
+
F
F
F
F
F
B
F
F
F F
F
F
F
F
F
F
F
F
F
F
F
-
Figure 1.3. Comparison of the Ligand Environment of the Pt(bpym)Cl
2
/H
2
SO
4
System with the BARF Anion.
Calculations show that replacement of the HSO
4
-
ligand by methane in the
Pt(bpym)Cl
2
/H
2
SO
4
system is uphill 24 kcal/mol with a barrier of ~33 kcal/mol.
This is comparable to the ~28- 30 kcal/mol barrier obtained experimentally for the
CH activation step by carrying out the reaction in D
2
SO
4
and monitoring the rate
of H/D exchange between methane and the solvent. Interestingly, the
calculations as well as experimental results indicate that in the Pt(bpym)X
2
system that operates via an ES mechanism, the formation of this methane
complex, rather than the CH cleavage step, is the rate determining step as shown
in Figure 1.3 above. Importantly, as a result of the large excess of solvent sulfuric
20
acid (the catalyst concentration is typically 5 – 50 mM), substantially more than
one equivalent of methanol can be generated in this system before catalyst
inhibition due to water or methanol binding slows reaction to impractical rates.
Thus, with a catalyst concentration of 50mM, and starting with 100% sulfuric acid
solvent, ~300 turnovers have been demonstrated with the generation of >1.5 M
methanol at ~80% conversion of methane with >90% selectivity to methanol. At
these high levels of water and methanol concentrations, Eq 2, the activity of water
and methanol are considerably higher because the sulfuric acid concentration is
reduced. Experimental studies show that at acid concentrations below 80%
sulfuric acid the reaction rates are too low to be useful (~10
-7
s
-1
) at 200
o
C. In this
acid concentration range, the CH activation step is rate limiting and is at least
1000 times slower than at 96% sulfuric acid solvent concentration. The basis for
this large difference in rate can be explained by theoretical calculations,
11
that
show that the water complex (which is expected to be formed at lower
concentrations of acid), [(Hbpym)PtCl(H
2
O)]
2+
is ~ 7-8 kcal/mol more stable than
the [(Hbpym)PtCl(HSO
4
)]
+
complex. Consistent with the expected dependence
on solvent acidity, as can be seen from Figure 1.4 the drop off in rate below 85%
sulfuric acid solvent correlates well with the solvent acidity.
21
Figure 1.4. Correlation of CH activation Rates (Measured by H/D exchange rates
between CH
4
and D
2
SO
4
) with Solvent Acidity, H
0
(98 % H
2
SO
4
=
10.4 H
0
and 85% = 8 H
0
).
Critically, while the use of sulfuric acid allows the catalytic reaction to
proceed efficiently, the rapid inhibition of the catalysts by water or methanol
below 90% sulfuric acid leads to uneconomical catalyst rates (for the Pt system)
and high separation costs for the methanol (for both the Pt and Hg systems).
Calculations show that if catalyst inhibition can be minimized to allow an ~5M
solution of methanol to be obtained, with an overall catalyst TOF of ~1 s
-1
that a
process based on the use of sulfuric acid could potentially be useful.
1.4 Strategies Towards Catalytic Systems that are not
Inhibited by Methane Oxidation Products.
An important consideration is that as the Pt(bpym)Cl
2
complex is modified
to increase the electron density of the platinum center the rate of functionalization
could decrease if the electrophilicity of the platinum center is important for this
0.0
0.5
1.0
1.5
2.0
6 7 8 9 10 11
D
2
SO
4
acidity, –H
0
k
H/D
x10
4
, s
-1
0.0
0.5
1.0
1.5
2.0
6 7 8 9 10 11
D
2
SO
4
acidity, –H
0
k
H/D
x10
4
, s
-1
N N
N N
Pt
Cl
Cl
22
step, as was shown for the Pt(bpym)Cl
2
/H
2
SO
4
system. Indeed, this is likely the
case when using metals to the left of platinum in the periodic table. Thus, while
facile CH activation is well known with more electron -rich, less oxidizing systems
based on the middle or early transition metals such as Ir, Ru, Zr, etc., to our
knowledge, these systems have not been incorporated into catalytic cycles that
generate oxy-functionalized products. This is likely because reductive heterolysis
or elimination reactions of the M-R intermediates are not facile and/or the systems
are not stable to the conditions required for oxy-functionalization. Thus, to
develop single-site oxidation catalysts based on these systems it is likely that new
systems that are stable and exhibit both new CH activation and oxy-
functionalization reactions will be needed.
To begin to develop such systems with the middle transition metals recent
research by this program has been focused on investigating the development of
catalytic cycles based on the reaction of metal -alkoxo complexes with CH bonds
as shown in Scheme 1.8. This is of interest because as shown, the reaction leads to
the simultaneous CH activation of the hydrocarbon and formation of a desired
oxy-functionalized product, ROH. As described in Chapter 1, we have reported
evidence for the first part of this conceptual catalytic cycle; facile, selective CH
activation with a metal alkoxo complex, (acac-O,O)
2
Ir(OCH
3
)(L), where
L=CH
3
OH or pyridine (Py). The observation of such a one step CH
activation/oxy-functionalization reaction is significant since, to our knowledge,
there is no precedent for this CH activation reaction and because we anticipated
23
possible complications due to: A) decomposition of the alkoxo complexes by
facile β-hydride elimination reactions or formation of inert dinculear complexes
and B) destruction of the alcohol product during the CH activation reaction of RH.
CH Activation
RH
Functionalization
HY
LM
n
-Y
LM
n
-R
LM
n+2
Y
Y
R
RY
Oxidation
2 HY + 1/2 O
2
H
2
O
Redox
Catalysis
CH Activation
RH
Functionalization
ROH
LM
n
-OR
LM
n
-R
1/2 O
2
and
Oxidation
Non-Redox
Catalysis
A
B
Reductive
Scheme 1.8. Redox (A) and Non-Redox (B) Catalytic Sequences for
Functionalization of Hydrocarbons via CH Bond Activation.
In addition to working on the CH activation reaction with these metal
alkoxide and related species, we have begun to develop reactions to oxy-
functionalize metal hydrocarbyl complexes to the corresponding alkoxides under
non free-radical conditions, a reaction that would complete the proposed catalytic
cycle. With the move to more electron -rich MX complexes to carry out the CH
activation reaction, we have found that the pathway for M-R Functionalization that
operates for the Pt(II) and Hg(II) system is not available. Consequently, in our
group we have conceived of and shown proof of principle for using an alternative
pathway involving O-atom insertion as a mean of converting electron -rich M-R to
the desired ROH. However, this was demonstrated for CH
3
ReO
3
where the
oxidation state of for rhenium is Re(VII) rather than the desired Re(I). This l ower
24
oxidation state is desired since this Re(I) is more electron -rich than Re(VII) and
likely to be active for CH activation in non -acidic media. Consequently, we have
been working to show feasibility for converting Re(I)-R intermediates to ROH
products. Significantly, we have now shown that (CO)
5
ReCH
3
(a motif that has
been reported to be active for CH activation)
19
will efficiently react with Se(IV) to
generate R-Se products in an essentially quantitative reaction and the R -Se species
can subsequently be converted to alcohols.
These are the first known examples of functionalization of electron -rich M-R
species to generate R-heteroatom products and alcohols by likely non -radical
reaction mechanisms. Coupling these reactions with the CH activation reaction
should allow new catalytic cycles to be developed for the selective conversion of
methane to methanol with catalysts that are not inhibited by methanol , or water.
25
1.5 References
1
(a) Methane Conversion by Oxidative Processes, Wolf. E. E. Ed.; Van Nostrand
Reinhold; New York, 1992. (b) Catalytic Activation and Functionalization of
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st
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2
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27
Tet. Lett. 1984, 25, 1283 (c) Burk, M. J.; Crabtree, R. H. J. Am. Chem. Soc. 1987,
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9
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10
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(a) Xu, Xin; Kua, Jeremy; Periana, Roy A.; Goddard, William A. III
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Goddard, William A. III. Organometallics 2002, 21, 511.
12
(a) Geftakis, S.; Ball, G. E. J. Am. Chem. Soc. 1998, 120, 9953. (b) Other
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16
Mechanisms of Inorganic Reactions, 2
nd
Ed. Basolo, F. and Pearson, R. G.
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17
(a) Klei, S. R.; Golden, J. T.; Burger, P.; Bergman, R. G. J. Mol. Cat. A: Chem.
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28
18
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19
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Hursthouse, M. B.; Bruce, D. W. J. Chem. Soc., Dalton Trans. 2000, 1473.
29
2 CH Activation with an O -Donor Iridium Methoxo
Complex
2.1 Introduction.
The CH activation of hydrocarbons has been the focus of significant effort
given the potential to develop new generations of “single-site” organometallic
oxidation catalysts that generate products such as alcohols at low temperatures and
with high yields and selectivities.
1
However, while there are now many well-
established examples of CH activation systems relatively few have been
successfully incorporated into a catalytic sequence.
2
The majority of
homogeneous catalytic systems that have been shown to generate oxy-
functionalized products via CH activation are based on electronegative, “soft,
redox-active cations such as Pt(II), Hg(II), iodine cations, Pd(II) and Au(III) in
poorly coordinating, oxy-acid solvents.
1b
Significantly, as a result of the high
electronegativity and oxidation potential of these cations, “functionalization” of
the M-R intermediates to generate oxy-functionalized products via reductive
heterolysis or elimination reactions is quite facile, Scheme 2.1.
30
CH Activation
RH
Functionalization
HY
LM
n
-Y
LM
n
-R
LM
n+2
Y
Y
R
RY
Oxidation
2 HY + 1/2 O
2
H
2
O
Redox
Catalysis
CH Activation
RH
Functionalization
ROH
LM
n
-OR
LM
n
-R
1/2 O
2
and
Oxidation
Non-Redox
Catalysis
A
B
Reductive
Scheme 2.1. Redox (A) and Non-redox (B) Catalytic Sequences for
Functionalization of Hydrocarbons via CH bond Activation.
Facile CH activation is also well known with more electron -rich, less
oxidizing systems based on the middle or early transition metals such as Ir, Ru, Zr,
etc.
1a
However, in these systems the oxy-functionalization of M-R intermediates
is not facile most likely because reductive heterolysis or elimination reactions are
much less facile. Thus, to develop single-site oxidation catalysts based on these
systems new oxy-functionalization reactions will have to be developed.
To begin to develop new oxy-functionalization pathways with this class of
CH activation systems we are investigating the reaction of metal -alkoxos with CH
bonds as shown in Scheme 2.1. This is of interest because as shown, the reaction
leads to the simultaneous CH activation of the hydrocarbon as well as the
formation of the desired product alcohol, ROH, in one step. The observation of
such a CH activation/oxy-functionalization reaction would be significant since, to
our knowledge, there is no precedent for this reaction
3
and because complications
may be anticipated from: A) decomposition of the alkoxo complexes by facile β-
hydride elimination reactions or formation of inert dinculear complexes and B)
31
destruction of the alcohol product during the CH activation reaction of RH.
Oxidation of the M -R intermediate to M -OR, for which there is precedent albeit
via free-radical reactions,
4
would complete the catalytic cycle. The design of
systems capable of both the CH activation and oxidative insertion could lead to
new pathways for the selective, low-temperature, oxidation of hydrocarbons to
highly desirable alcohols.
2.2 Results and Discussion.
Complex 2-CH
3
OH was synthesized from [Ir(μ-acac-O,O,C
3
)(acac-
O,O)(acac-C
3
)]
2
, 1, in moderate yields (22%) by treatment with an excess of
sodium methoxide in methanol at 130
o
C for 30 min, as in Scheme 2.2. The
compound is an air and thermally stable orange solid that has been fully
characterized by
1
H,
13
C NMR spectroscopy, elemental analysis, high-resolution
mass spectrometry, and x-ray crystallography. The exchange of the CH
3
O-Ir
groups with CD
3
OD solvent is slow on the NMR time scale and only ~20%
exchange (and generation of CH
3
OD) is observed after 24 hr at room temperature.
Addition of pyridine leads to generation of the more stable pyridine complex, 2-
Py, which has also been fully characterized (see Experimental Section ).
32
Ir
O O
O O
Ir
O O
O O
Ir
O O
O O
OMe
MeOH
2-CH
3
OH
O O
O O
8 eq NaOMe
MeOH
1
Scheme 2.2. Synthetic Procedure for the Production of 2-CH
3
OH.
Ir
O O
O O
N
3
2-CH
3
OH
+ CH
3
OH
Ir
O O
O O
CH
3
OH
O
CH
3
Ir
O O
O O
N
O
CH
3
Py
2-Py
160
o
C
10 min
180
o
C
4 hr
- CH
3
OH
Scheme 2.3. CH Activation of Benzene with Ir(III) Methoxo Complexes.
The arene CH activation with 2-L, L = CH
3
OH and pyridine was carried
out under an inert atmosphere in neat C
6
H
6
, Scheme 2.3. In the case of 2-CH
3
OH
the reaction with benzene was carried out at 160
o
C for 10 min followed by
addition of pyridine.
5
Subsequent, removal of all volatiles in vacuo and complete
dissolution with CDCl
3
containing 1,3,5-trimethoxybenzene as an internal standard
showed that 3 was produced in 75% yield based on added 2-CH
3
OH. Reaction of
33
benzene with 2-Py provided 3 in similar yields, but required longer reaction times,
4 hr, and higher reaction temperatures, 180
o
C. In both cases, 3 could be separated
from the reaction mixtures by preparative TLC and identified by comparison of the
1
H and
13
C NMR spectra and mass peaks to that of independently prepared and
fully characterized 3.
6
When the reaction is carried out in benzene-d
6
labeled
methanol, CH
3
OD, was produced in >99% yield and identified by gas
chromatography-mass spectrometry (GC-MS) analyses. No formaldehyde or other
C
1
products were detected.
It is interesting that this CH activation reaction proceeds cleanly given the
possibility for side reactions. Additionally, the observation that the reaction of this
Ir-methoxo proceeds in high yield shows this reaction is substantially different
from the corresponding reaction of Ru-NH
2
complexes with benzene, that while
not directly observed, have been calculated to be unfavorable.
3a
Possible p -type
destabilizing interactions between the O-donor ligands, the d
6
Ir(III) center and the
-OMe group along with the increased electronegativity of the Ir in an O -donor
ligand field could account for the favorable thermodynamics for this CH activation
reaction. It is also likely that these properties of the Ir center in an O-donor ligand
field could serve to minimize the expected irreversible side reactions of metal
alkoxides such as: A) β-hydride elimination reactions due to the reduced electron
density at the metal center or B) the formation of bridging alkoxo complexes by
the cis-labilization effect of pi -donor spectator O-ligands.
7
34
Theoretical calculations (B3LYP/LACVP** with ZPE and solvent
corrections) are consistent with the reaction proceeding via the pathway shown in
Scheme 2.4. The observation that 2-L, L = Py, reacts more slowly than 2-L, L =
MeOH is consistent with the requirement for reversible loss of L since pyridine is
a less labile ligand than methanol. The calculated barrier (23.4 kcal/mol) and
favorable thermodynamics ( -17.1 kcal/mol) of the reaction with the methanol
complex, 2-CH
3
OH, are consistent with the reaction proceeding at 160
o
C in ~10
min. and in good yield. The transition state for CH cleavage was initially
described as a formal s-bond metathesis based on the geometry of the reacting
atoms. This can be observed in the Ir-H distance of 1.98 Å, Scheme 2, which
corresponds to classical s -bond metathesis geometry. Pathways involving
oxidation addition, Oxidative Hydrogen Migration
8
or ionization of the methoxide
group were all found to be higher in energy. However, more detailed analysis of
the transition state indicates that the transition state is actually best described as an
internal electrophilic substitution (IES), as discussed in detail in Chapter 4.
Possible reasons for the system to favor an IES mechanism could be that the lone
pair on the methoxo oxygen facilitates the hydrogen transfer and the decreased
electron-density of an Ir with five electronegative O -donor ligands disfavors a
transition state with oxidative addition character.
35
Ir
O O
O O
O
CH3
O
Ir
O
O
OCH
3
O
N
Ir
O O
O O
Ir
O O
O O
O
CH
3
O
H H3 C
O
Ir
O
O
OCH
3
O
H
(17.5 kcal/mol)
(17.8 kcal/mol)
(15.0 kcal/mol)
(23.4 kcal/mol)
(-2.6 kcal/mol)
O
Ir
O
O
OCH
3
O
(0.0 kcal/mol)
(-17.1 kcal/mol)
H
O
Ir
O
O
O
O
CH
3
-CH3OH + C6H6
+Py
-CH3OH
Scheme 2.4. Proposed mechanism for the reaction of 2 (values in parenthesis are
calculated ΔH in benzene).
Transition metal alkoxides are well known to decompose to metal hydrides
via ß-hydride elimination reactions
9
and Ir-H’s are well documented to be highly
active for CH activation reactions.
10
For the CH activation reaction to proceed via
an Ir-H, the formation of such a species must necessarily be reversible to account
for the stoichiometric formation of MeOH. To examine this possibility we
examined the reaction of (acac-O,O)
2
Ir(O
13
CH
3
)(Py),
11
2-
13
C, with C
6
D
6
as the Ir-
H pathway would be expected to lead to generation of the D
13
CH
2
OD isotopomer,
as in whereas the proposed s-bond metathesis would lead to
13
CH
3
OH(D).
13
C
NMR spectroscopy showing that only
13
CH
3
OH(D) was formed
12
supports the
mechanism shown in Scheme 2.4.
36
Scheme 2.5. Mechanism for CH Activation Proceeding via an Intermediate Ir-H.
Having established that 2-L can stoichiometrically activate the CH bonds
of benzene we examined the catalytic CH activation of benzene with this complex
in water at 160
o
C. The reaction system is stable over the time period studied (6 h)
and turn -over-frequencies (TOF) of 2.7 x 10
-3
s
-1
were observed based on added 2-
CH
3
OH. It is anticipated that the Ir-OCH
3
group is converted to Ir-OH in water
and in ongoing efforts we are examining the extension this chemistry to the
corresponding hydroxo, phenoxo and t-butoxo complexes, CH activation of
O
Ir
O
O
OCH
3
O
O
Ir
O
O
O
H
O
CH 2
O
Ir
O
O
O
H
O CH
2
Ir
O O
O O
O
CH 3
- Py
*
*
*
*
D
6
- *CH
2
O
*
O
Ir
O
O
O
D
O
CH
2
D
5
+ *CH2O
-
*
O
Ir
O
O
OCH
2
D
O
D
6
Ir
O O
O O
+ D*CH
2
OD
D
5
+ Py
+
N
O
Ir
O
O
O
H
D
D
5
N
37
alkanes as well as developing non -free radical reactions for the oxidation of the M-
R complexes to the corresponding alkoxo complex.
In summary, it was demonstrated that the air, protic and thermally stable
O-donor alkoxo complexes, (acac-O,O)
2
Ir(OMe)(L), 2-L, L = Py and CH
3
OH,
react in a stoichiometric CH activation reaction with benzene to generate the
corresponding phenyl complex, 3, with co-generation of methanol in high yield.
This is the first example of such an intermolecular CH activation reaction with a
metal -alkoxo complex and benzene. In addition 2-CH
3
OH is a thermally stable
catalyst for H/D exchange reaction between benzene and water.
2.3 Experimental Section.
General Considerations: All air and water sensitive procedures were carried
out either in an MBraun inert atmosphere glove box, or using standard Schlenk
techniques under argon. Methanol was dried from Mg/I
2
, and benzene from
sodium/benzophenone ketal. All deuterated solvents (Cambridge Isotopes), and
NaOCH
3
(Aldrich) were used as received. Complexes 1 and 1-Cl were prepared
as described in the literature.
13
GC/MS analysis was performed on a Shimadzu
GC-MS QP5000 (ver. 2) equipped with cross-linked methyl silicone gum capillary
column (DB5). The retention times of the products were confirmed by comparison
to authentic samples. NMR spectra were obtained on a Varian Mercury -400
38
spectrometer at room temperature. All chemical shifts are reported in units of ppm
and referenced to the residual protonated solvent. All high-resolution mass spectra
were obtained by UCLA Pasarow Mass Spectrometry Laboratory on an ESI mass
spectrometer. Elemental Analysis was performed by Desert Analytics of Tucson,
Arizona.
X-ray Crystallography. Diffraction data for 2-Py and 2-CH
3
OH were
collected at low temperature ( T = 153 K ans 133 K respectively) on a Bruker
SMART APEX CCD diffractometer with graphite-monochromated Mo Kα
radiation (?= 0.71073 Å). The cell parameters for the Ir complex were obtained
from the least-squares refinement of the spots (from 60 collected frames) using the
SMART program. A hemisphere of the crystal data was collected and the intensity
data was processed using the Saint Plus program. All calculations for structure
determination were carried out using the SHELXTL package (version 5.1).
Initial
atomic positions were located by direct methods using XS, and the structure was
refined by least-squares methods using SHELX. Absorption corrections were
applied by using SADABS. Calculated hydrogen positions were input and refined
in a riding manner along with the attached carbons.
Synthesis of [CH
3
O-Ir(O,O-acac)
2
(CH
3
OH)] (2-CH
3
OH): To a 30 mL
thick-walled ampoule equipped with a high-vacuum valve at top [acac-Ir(O,O-
acac)
2
]
2
1 (370 mg, 0.38 mmol), sodium methoxide (128 mg, 2.37 mmol), and 30
mL methanol were added. The mixture was heated at 130°C with stirring for 30
min. During this time the color of the solution turned from yellow to dark red.
39
After cooling, the solution was twice filtered through a pad of basic alumina on a
medium porosity frit, and purified by centrifugal thin layer chromatography using
ethyl acetate: methanol 9:1 on alumina (the material was loaded onto the disk
using methylene chloride and washed with methylene chloride for approximately 5
minutes before eluting. The elutant was concentrated under vacuum to yield
approximately 74 mg (22%) of title complex as an orange solid.
1
H NMR
(CD
3
OD): d 5.50(s, 2H, CH), 2.83(s, 3H, Ir-OCH
3
), 2.01(s, 12H, CH
3
).
13
C{
1
H}
NMR (CD
3
OD): d 187.39(C-acac, C=O), 103.9(O-acac, CH), 55.9(OCH
3
),
27.0(O-acac, CH
3
). HRMS (ESI): Calculated for C
12
H
22
IrO
6
(M+H) 455.1046,
found 455.1035. Elemental Analysis: Calculated for C
12
H
21
IrO
6
:
C, 31.78; H,
4.67. Found: C, 31.82; H, 4.53. Single crystals were grown by slow evaporation
of a concentrated sample in chloroform.
Summarized crystal data for 2-CH
3
OH (See Figure 2.1): A yellow-orange
prisim-shaped crystal of dimensions 0.29 x 0.05 x 0.03 mm was grown from
chloroform by slow evaporation of the solvent. C
24
H
40
Ir
2
O
12
: orthorhombic, group
Pnma, a = 7.8771(16) Å, b = 11.924(2) Å, c = 16.046(3) Å, V = 1147.1(5) Å
3
, Z =
2, T = 133(2) K, D
calcd
= 2.035 Mg/m
3
, R(F) = 6.02 for 8995 observed reflections.
All non -hydrogen atoms were refined with anisotropic displacement parameters.
40
Figure 2.1. ORTEP diagram of the (acac-O,O)
2
Ir(OCH
3
)(CH
3
OH) complex,
showing ellipsoids at the 50% probability level. A molecule of co-
crystallized CHCl
3
has been omitted for clarity.
Alternative synthesis of [CH
3
O-Ir(O,O-acac)
2
(CH
3
OH)] (2): To a 30 mL
re-sealable Schlenk tube [Cl -Ir(O,O-acac)
2
]
2
1-Cl (250 mg, 0.29 mmol), sodium
methoxide (125 mg, 2.32 mmol), and 30 mL methanol were added. The mixture
was heated to gentle reflux with stirring for 32 hr. During this time the color of
the solution turned from yellow to dark red. The volatiles were removed from the
tube under vacuum, and the remaining solids were dissolved in methylene
chloride, filtered through a medium porosity frit, and purified by column
chromatography using ethyl acetate: methanol 5:1 on alumina. The elutant was
concentrated under vacuum to yield 5% of title complex as an orange solid.
41
Synthesis of [CH
3
O-Ir(O,O-acac)
2
(Py)] (2-Py): A 15 mL re-sealable
Schlenk tube was charged with 2-CH
3
OH (10 mg, 0.022 mmol) and pyridine (7
mL) was added. The Schlenk tube was then sealed, and placed in a 55°C oil bath
for 30 min. The resulting yellow-orange solution was cooled to room temperature,
and the volitiles were removed under vacuum, yielding a yellow -orange solid in
quantitative yield. The product was recrystallized from dichloromethane.
1
H NMR
(CDCl
3
): d 8.25(d, 2H, o-Py), 7.72(t, 1H, p-Py), 7.24(t, 2H, m -Py), 5.32(s, 2H,
CH), 3.16(s, 3H, Ir-OCH
3
), 1.94(s, 12H, CH
3
).
13
C{
1
H} NMR (CDCl
3
): d 185.2(C-
acac, C=O), 152.1(o-Py), 137.5(p-Py), 124.9(m -Py), 102.8(O-acac, CH),
57.9(OCH
3
), 26.9(O-acac, CH
3
). HRMS (MALDI-TOF): Calculated for
C
16
H
22
IrNO
5
Na (M+Na) 524.1025, found 524.1043. Single crystals were grown
by slow evaporation of a concentrated sample in chloroform.
A yellow-orange prisim-shaped crystal of dimensions 0.35 x 0.32 x 0.10
mm was grown from chloroform by slow evaporation of the solvent.
C
16
H
22
IrNO
5
-CHCl
3
: orthorhombic, group Pnma, a = 11.2909(8) Å, b =
13.7659(10) Å, c = 13.9240(10) Å, V = 2164.2(3) Å
3
, Z = 4, T = 133(2) K, D
calcd
=
1.903 Mg/m
3
, R(F) = 2.46 for 12680 observed reflections. All non-hydrogen
atoms were refined with anisotropic displacement parameters.
42
Table 2.1. Crystal data and structure refinement for (acac)
2
Ir(OCH
3
)(CH
3
OH).
Identification code iracacm
Empirical formula C24 H40 Ir2 O12
Formula weight 904.96
Temperature 133(2) K
Wavelength 0.71073 Å
Crystal system Triclinic
Space group P-1
Unit cell dimensions a = 7.8771(16) Å α=80.722(4)°.
b = 11.924(2) Å β=84.914(3)°.
c = 16.046(3) Å γ =84.786(3)°.
Volume 1477.1(5) Å
3
Z 2
Density (calculated) 2.035 Mg/m
3
Absorption coefficient 9.057 mm
-1
F(000) 868
Crystal size 0.29 x 0.05 x 0.03 mm
3
Theta range for data collection 1.29 to 27.51°.
Index ranges -10<=h<=10, -14<=k<=15, -8<=l<=20
Reflections collected 8995
Independent reflections 6310 [R(int) = 0.0444]
Completeness to theta = 27.51° 92.8 %
Transmission factors min/max ratio: 0.332
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 6310 / 0 / 358
Goodness-of-fit on F
2
1.001
Final R indices [I>2sigma(I)] R1 = 0.0602, wR2 = 0.1361
R indices (all data) R1 = 0.0975, wR2 = 0.1484
Largest diff. peak and hole 3.603 and -2.606 e.Å
-3
43
Table 2.2. Atomic coordinates (x 10
4
) and equivalent isotropic displacement
parameters (Å
2
x 10
3
) for (acac)
2
Ir(OCH
3
)(CH
3
OH). U(eq) is defined as one third
of the trace of the orthogonalized U
ij
tensor.
_______________________________________________________________________________
x y z U(eq)
_______________________________________________________________________________
Ir(1) 6837(1) 1612(1) 2920(1) 25(1)
Ir(2) 10000 10000 0 23(1)
Ir(3) 5000 5000 5000 24(1)
O(1) 7935(11) 161(7) 3510(5) 27(2)
O(2) 4443(10) 1215(7) 3310(6) 27(2)
O(3) 5748(10) 3063(7) 2300(6) 27(2)
O(4) 9256(11) 1992(7) 2552(6) 32(2)
O(5) 6853(11) 935(7) 1817(6) 33(2)
O(6) 6798(11) 2325(8) 3997(6) 39(2)
O(7) 7277(10) 5103(8) 4318(6) 30(2)
O(8) 3772(10) 6117(7) 4142(5) 26(2)
O(9) 4523(10) 3633(7) 4460(6) 30(2)
O(10) 7673(10) 9406(8) 14(6) 33(2)
O(11) 11230(10) 8454(7) 303(6) 25(2)
O(12) 9605(11) 10248(8) 1233(6) 32(2)
C(1) 8175(17) -1729(11) 4207(10) 40(4)
C(2) 7108(17) -661(11) 3897(8) 27(3)
C(3) 5328(15) -600(11) 4012(8) 25(3)
C(4) 4103(17) 282(12) 3756(9) 33(3)
C(5) 2254(17) 107(12) 3977(10) 44(4)
C(6) 5551(18) 4748(12) 1344(10) 45(4)
C(7) 6622(15) 3751(12) 1827(10) 37(4)
C(8) 8455(17) 3688(12) 1619(10) 42(4)
C(9) 9604(16) 2865(12) 2024(8) 28(3)
C(10) 11472(18) 2975(12) 1793(9) 44(4)
C(11) 5585(18) 203(16) 1764(10) 60(5)
C(12) 8351(16) 2435(12) 4332(9) 37(3)
44
C(13) 5627(17) 8062(13) 190(11) 50(4)
C(14) 7433(15) 8361(12) 216(10) 36(3)
C(15) 8736(17) 7490(11) 426(10) 37(4)
C(16) 10458(17) 7577(12) 427(9) 33(3)
C(17) 11603(18) 6474(12) 671(11) 44(4)
C(18) 10570(17) 9541(13) 1837(9) 41(4)
C(19) 9279(16) 5604(13) 3204(9) 41(4)
C(20) 7481(17) 5659(12) 3600(9) 34(3)
C(21) 6202(19) 6364(12) 3161(9) 40(4)
C(22) 4475(18) 6556(11) 3443(10) 36(3)
C(23) 3318(19) 7339(12) 2877(9) 42(4)
C(24) 3110(16) 3736(11) 3948(9) 34(3)
Table 2.3. Bond lengths [Å] and angles [°] for (acac)
2
Ir(OCH
3
)(CH
3
OH).
_____________________________________________________
Ir(1)-O(1) 1.996(8)
Ir(1)-O(2) 2.007(8)
Ir(1)-O(3) 2.011(8)
Ir(1)-O(4) 2.014(9)
Ir(1)-O(6) 2.042(9)
Ir(1)-O(5) 2.059(9)
Ir(2)-O(11) 2.011(8)
Ir(2)-O(11)#1 2.011(8)
Ir(2)-O(10) 2.021(8)
Ir(2)-O(10)#1 2.021(8)
Ir(2)-O(12)#1 2.040(9)
Ir(2)-O(12) 2.040(9)
Ir(3)-O(8)#2 2.004(8)
Ir(3)-O(8) 2.004(8)
Ir(3)-O(7)#2 2.020(8)
Ir(3)-O(7) 2.020(8)
Ir(3)-O(9)#2 2.043(8)
Ir(3)-O(9) 2.044(8)
45
O(1)-C(2) 1.272(15)
O(2)-C(4) 1.259(15)
O(3)-C(7) 1.238(16)
O(4)-C(9) 1.265(15)
O(5)-C(11) 1.401(17)
O(6)-C(12) 1.404(15)
O(7)-C(20) 1.238(16)
O(8)-C(22) 1.261(17)
O(9)-C(24) 1.425(15)
O(10)-C(14) 1.262(15)
O(11)-C(16) 1.238(15)
O(12)-C(18) 1.406(15)
C(1)-C(2) 1.501(17)
C(2)-C(3) 1.394(17)
C(3)-C(4) 1.397(16)
C(4)-C(5) 1.494(18)
C(6)-C(7) 1.538(18)
C(7)-C(8) 1.451(16)
C(8)-C(9) 1.394(19)
C(9)-C(10) 1.498(18)
C(13)-C(14) 1.503(17)
C(14)-C(15) 1.415(18)
C(15)-C(16) 1.370(18)
C(16)-C(17) 1.542(18)
C(19)-C(20) 1.500(17)
C(20)-C(21) 1.414(19)
C(21)-C(22) 1.405(19)
C(22)-C(23) 1.499(18)
O(1)-Ir(1)-O(2) 94.6(4)
O(1)-Ir(1)-O(3) 178.7(3)
O(2)-Ir(1)-O(3) 85.9(3)
O(1)-Ir(1)-O(4) 84.5(3)
O(2)-Ir(1)-O(4) 178.8(4)
46
O(3)-Ir(1)-O(4) 95.1(3)
O(1)-Ir(1)-O(6) 90.2(4)
O(2)-Ir(1)-O(6) 86.4(4)
O(3)-Ir(1)-O(6) 91.1(4)
O(4)-Ir(1)-O(6) 92.9(4)
O(1)-Ir(1)-O(5) 91.4(3)
O(2)-Ir(1)-O(5) 93.6(3)
O(3)-Ir(1)-O(5) 87.4(4)
O(4)-Ir(1)-O(5) 87.1(4)
O(6)-Ir(1)-O(5) 178.4(4)
O(11)-Ir(2)-O(11)#1 180.0(4)
O(11)-Ir(2)-O(10) 95.0(3)
O(11)#1-Ir(2)-O(10) 85.0(3)
O(11)-Ir(2)-O(10)#1 85.0(3)
O(11)#1-Ir(2)-O(10)#1 95.0(3)
O(10)-Ir(2)-O(10)#1 179.999(2)
O(11)-Ir(2)-O(12)#1 87.0(3)
O(11)#1-Ir(2)-O(12)#1 93.0(3)
O(10)-Ir(2)-O(12)#1 87.6(4)
O(10)#1-Ir(2)-O(12)#1 92.4(4)
O(11)-Ir(2)-O(12) 93.0(3)
O(11)#1-Ir(2)-O(12) 87.0(3)
O(10)-Ir(2)-O(12) 92.4(4)
O(10)#1-Ir(2)-O(12) 87.6(4)
O(12)#1-Ir(2)-O(12) 180.0(5)
O(8)#2 -Ir(3)-O(8) 179.998(2)
O(8)#2-Ir(3)-O(7)#2 93.5(3)
O(8)-Ir(3)-O(7)#2 86.5(3)
O(8)#2 -Ir(3)-O(7) 86.5(3)
O(8)-Ir(3)-O(7) 93.5(3)
O(7)#2 -Ir(3)-O(7) 179.998(2)
O(8)#2 -Ir(3)-O(9)#2 93.1(3)
O(8)-Ir(3)-O(9)#2 86.9(3)
47
O(7)#2 -Ir(3)-O(9)#2 90.4(3)
O(7)-Ir(3)-O(9)#2 89.6(3)
O(8)#2 -Ir(3)-O(9) 86.9(3)
O(8)-Ir(3)-O(9) 93.1(3)
O(7)#2 -Ir(3)-O(9) 89.6(3)
O(7)-Ir(3)-O(9) 90.4(3)
O(9)#2 -Ir(3)-O(9) 179.999(2)
C(2)-O(1)-Ir(1) 123.9(8)
C(4)-O(2)-Ir(1) 123.1(8)
C(7)-O(3)-Ir(1) 121.0(8)
C(9)-O(4)-Ir(1) 122.5(8)
C(11)-O(5)-Ir(1) 117.5(8)
C(12)-O(6)-Ir(1) 119.1(8)
C(20)-O(7)-Ir(3) 124.1(8)
C(22)-O(8)-Ir(3) 123.6(8)
C(24)-O(9)-Ir(3) 118.7(7)
C(14)-O(10)-Ir(2) 122.3(8)
C(16)-O(11)-Ir(2) 121.4(8)
C(18)-O(12)-Ir(2) 118.3(7)
O(1)-C(2)-C(3) 123.1(11)
O(1)-C(2)-C(1) 115.5(12)
C(3)-C(2)-C(1) 121.4(12)
C(2)-C(3)-C(4) 130.8(13)
O(2)-C(4)-C(3) 124.3(13)
O(2)-C(4)-C(5) 116.5(11)
C(3)-C(4)-C(5) 119.2(13)
O(3)-C(7)-C(8) 129.3(13)
O(3)-C(7)-C(6) 113.4(11)
C(8)-C(7)-C(6) 117.0(12)
C(9)-C(8)-C(7) 123.9(13)
O(4)-C(9)-C(8) 127.5(12)
O(4)-C(9)-C(10) 114.9(12)
C(8)-C(9)-C(10) 117.6(12)
48
O(10)-C(14)-C(15) 124.5(12)
O(10)-C(14)-C(13) 115.5(12)
C(15)-C(14)-C(13) 119.9(13)
C(16)-C(15)-C(14) 128.7(13)
O(11)-C(16)-C(15) 127.9(13)
O(11)-C(16)-C(17) 114.1(12)
C(15)-C(16)-C(17) 117.9(12)
O(7)-C(20)-C(21) 125.6(13)
O(7)-C(20)-C(19) 115.2(12)
C(21)-C(20)-C(19) 119.1(13)
C(22)-C(21)-C(20) 127.1(13)
O(8)-C(22)-C(21) 125.9(12)
O(8)-C(22)-C(23) 115.2(13)
C(21)-C(22)-C(23) 118.8(14)
_____________________________________________________________
Symmetry transformations used to generate equivalent atom s:
#1 -x+2,-y+2,-z #2 -x+1,-y+1,-z+1
Table 2.4. Anisotropic displacement parameters (Å
2
x 10
3
) for
(acac)
2
Ir(OCH
3
)(CH
3
OH). The anisotropic 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
______________________________________________________________________________
Ir(1) 16(1) 26(1) 32(1) -8(1) 0(1) 3(1)
Ir(2) 12(1) 26(1) 31(1) -7(1) 2(1) 1(1)
Ir(3) 17(1) 26(1) 30(1) -10(1) -1(1) 4(1)
O(1) 26(5) 28(5) 26(5) -5(4) -1(4) 3(4)
O(2) 16(4) 30(5) 32(5) -6(4) -1(4) 5(4)
O(3) 16(4) 25(5) 41(6) -3(4) -4(4) -2(4)
O(4) 18(4) 26(5) 52(6) -8(5) -5(4) 12(4)
O(5) 36(5) 30(5) 35(6) -16(4) 1(4) -4(4)
O(6) 24(5) 50(6) 51(6) -36(5) -8(4) 11(4)
49
O(7) 18(4) 41(6) 29(5) -7(4) -2(4) 5(4)
O(8) 28(5) 29(5) 19(5) -5(4) 5(4) -2(4)
O(9) 13(4) 37(5) 45(6) -20(5) -5(4) 7(4)
O(10) 14(4) 30(5) 54(6) -6(5) 1(4) 3(4)
O(11) 17(4) 25(5) 36(5) -7(4) -9(4) 1(4)
O(12) 26(5) 41(6) 28(5) -11(4) -3(4) 11(4)
C(1) 26(7) 34(8) 61(10) -2(7) -11(7) -5(6)
C(2) 36(7) 27(7) 21(7) -13(6) -13(6) 9(6)
C(3) 18(6) 29(7) 29(7) -5(6) -7(5) 5(5)
C(4) 33(7) 30(8) 33(8) 1(6) -11(6) 6(6)
C(5) 27(7) 41(9) 57(10) 2(8) 15(7) -7(6)
C(6) 31(8) 35(9) 65(11) 14(8) -16(7) -2(6)
C(7) 10(6) 34(8) 68(11) -15(8) 7(6) -1(5)
C(8) 25(7) 43(9) 50(10) 12(8) 10(7) -8(6)
C(9) 25(7) 36(8) 25(7) -1(6) -2(6) -11(6)
C(10) 38(8) 43(9) 41(9) 12(7) 0(7) 6(7)
C(11) 23(8) 123(16) 42(10) -29(10) 3(7) -24(9)
C(12) 29(7) 39(9) 45(9) -14(7) -8(7) 6(6)
C(13) 20(7) 55(10) 75(12) -11(9) 0(7) -13(7)
C(14) 12(6) 42(9) 54(10) -6(7) -9(6) -1(6)
C(15) 30(7) 22(7) 58(10) 2(7) -4(7) -4(6)
C(16) 31(7) 41(9) 30(8) -11(7) -4(6) -3(6)
C(17) 30(7) 30(8) 67(11) 0(8) -7(7) 6(6)
C(18) 34(8) 59(10) 28(8) -14(7) -8(6) 24(7)
C(19) 21(7) 53(10) 45(9) -1(8) 5(6) -6(6)
C(20) 30(7) 37(8) 34(8) -10(7) 4(6) 1(6)
C(21) 45(9) 40(9) 30(8) -2(7) 9(7) -3(7)
C(22) 34(8) 25(8) 51(10) -5(7) -20(7) 6(6)
C(23) 46(9) 41(9) 42(9) -5(7) -16(7) -3(7)
C(24) 29(7) 33(8) 37(8) -1(6) 0(6) 2(6)
50
Table 2.5. Hydrogen coordinates ( x 10
4
) and isotropic displacement parameters
(Å
2
x 10
3
) for (acac)
2
Ir(OCH
3
)(CH
3
OH).
_______________________________________________________________________________
x y z U(eq)
_______________________________________________________________________________
H(1A) 8474 -2168 3741 60
H(1B) 7526 -2189 4667 60
H(1C) 9222 -1529 4416 60
H(3) 4872 -1272 4315 31
H(5A) 1561 801 3763 66
H(5B) 2043 -65 4593 66
H(5C) 1945 -530 3718 66
H(6A) 4488 4478 1205 68
H(6B) 6202 5055 820 68
H(6C) 5281 5348 1698 68
H(8) 8899 4242 1179 50
H(10A) 12064 2953 2307 65
H(10B) 11630 3700 1420 65
H(10C) 11944 2344 1498 65
H(11A) 5803 -515 2146 90
H(11B) 5602 49 1182 90
H(11C) 4463 562 1928 90
H(12A) 8947 1679 4475 55
H(12B) 8124 2793 4844 55
H(12C) 9066 2910 3912 55
H(13A) 4853 8527 534 75
H(13B) 5542 7253 416 75
H(13C) 5307 8211 -396 75
H(15) 8367 6744 589 45
H(17A) 12483 6381 210 65
H(17B) 10903 5820 769 65
H(17C) 12150 6520 1188 65
51
H(18A) 10212 8763 1908 62
H(18B) 10385 9828 2379 62
H(18C) 11786 9539 1643 62
H(19A) 10044 5838 3583 61
H(19B) 9336 6116 2662 61
H(19C) 9630 4822 3110 61
H(21) 6547 6749 2615 47
H(23A) 2508 6894 2665 64
H(23B) 4001 7736 2398 64
H(23C) 2687 7898 3197 64
H(24A) 2077 4016 4263 51
H(24B) 2941 2990 3802 51
H(24C) 3340 4274 3429 51
52
Figure 2.2. ORTEP diagram of the (acac-O,O)
2
Ir(OCH
3
)(Py) complex, showing
ellipsoids at the 50% probability level. A molecule of co-crystallized
CHCl
3
has been omitted for clarity. Selected bond distances (?): Ir1-
O3, 2.024(4); Ir1-N1, 2.048(5).
Table 2.6. Crystal data and structure refinement for (acac)
2
Ir(OCH
3
)(Py).
Identification code iromepym
Empirical formula C17 H23 Cl3 Ir N O5
Formula weight 619.91
Temperature 133(2) K
Wavelength 0.71073 Å
Crystal system Orthorhombic
Space group Pnma
Unit cell dimensions a = 11.2909(8) Å α= 90°.
b = 13.7659(10) Å β= 90°.
c = 13.9240(10) Å γ = 90°.
Volume 2164.2(3) Å
3
53
Z 4
Density (calculated) 1.903 Mg/m
3
Absorption coefficient 6.566 mm
-1
F(000) 1200
Crystal size 0.35 x 0.32 x 0.10 mm
3
Theta range for data collection 2.08 to 27.48°.
Index ranges -14<=h<=13, -12<=k<=17, -18<=l<=17
Reflections collected 12680
Independent reflections 2562 [R(int) = 0.0235]
Completeness to theta = 27.48° 99.1 %
Transmission factors min/max ratio: 0.646
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 2562 / 0 / 142
Goodness-of-fit on F
2
1.060
Final R indices [I>2sigma(I)] R1 = 0.0220, wR2 = 0.0660
R indices (all data) R1 = 0.0246, wR2 = 0.0672
Largest diff. peak and hole 1.545 and -1.354 e.Å
-3
Table 2.7. Atomic coordinates ( x 10
4
) and equivalent isotropic displacement
parameters (Å
2
x 10
3
) for (acac)
2
Ir(OCH
3
)(Py). U(eq) is defined as one third of
the trace of the orthogonalized U
ij
tensor.
_______________________________________________________________________________
x y z U(eq)
_______________________________________________________________________________
Ir(1) 8856(1) 2500 6250(1) 18(1)
Cl(1) 1025(1) 1449(1) 1501(1) 37(1)
Cl(2) 2661(1) 2500 2706(1) 39(1)
O(1) 10162(2) 1510(2) 6309(2) 23(1)
O(2) 7532(2) 1529(2) 6162(2) 24(1)
O(3) 8858(3) 2500 4796(3) 27(1)
N(1) 8817(3) 2500 7720(3) 21(1)
C(1) 11015(4) -45(4) 6404(3) 36(1)
C(2) 9944(4) 595(3) 6324(2) 26(1)
54
C(3) 8826(3) 165(3) 6259(3) 30(1)
C(4) 7728(4) 618(3) 6150(2) 26(1)
C(5) 6643(4) 7(3) 5985(3) 37(1)
C(6) 9834(5) 2500 8223(4) 43(2)
C(7) 9864(5) 2500 9213(4) 44(2)
C(8) 8830(5) 2500 9715(4) 33(1)
C(9) 7786(6) 2500 9217(4) 55(2)
C(10) 7816(5) 2500 8214(4) 43(2)
C(11) 9941(5) 2500 4335(4) 27(1)
C(12) 1908(5) 2500 1591(4) 25(1)
Table 2.8. Bond lengths [Å] and angles [°] for (acac)
2
Ir(OCH
3
)(Py).
_____________________________________________________
Ir(1)-O(2) 2.010(3)
Ir(1)-O(2)#1 2.010(3)
Ir(1)-O(1) 2.010(3)
Ir(1)-O(1)#1 2.010(3)
Ir(1)-O(3) 2.024(4)
Ir(1)-N(1) 2.048(5)
Cl(1)-C(12) 1.762(3)
Cl(2)-C(12) 1.771(5)
O(1)-C(2) 1.284(5)
O(2)-C(4) 1.273(5)
O(3)-C(11) 1.382(6)
N(1)-C(10) 1.323(7)
N(1)-C(6) 1.344(7)
C(1)-C(2) 1.501(5)
C(2)-C(3) 1.397(6)
C(3)-C(4) 1.396(6)
C(4)-C(5) 1.504(5)
C(6)-C(7) 1.380(9)
C(7)-C(8) 1.360(8)
C(8)-C(9) 1.368(8)
55
C(9)-C(10) 1.397(9)
C(12)-Cl(1)#1 1.762(3)
O(2)-Ir(1)-O(2)#1 83.44(15)
O(2)-Ir(1)-O(1) 95.59(12)
O(2)#1 -Ir(1)-O(1) 178.54(9)
O(2)-Ir(1)-O(1)#1 178.54(9)
O(2)#1 -Ir(1)-O(1)#1 95.59(12)
O(1)-Ir(1)-O(1)#1 85.36(15)
O(2)-Ir(1)-O(3) 86.56(10)
O(2)#1 -Ir(1)-O(3) 86.56(10)
O(1)-Ir(1)-O(3) 92.30(9)
O(1)#1 -Ir(1)-O(3) 92.30(9)
O(2)-Ir(1)-N(1) 92.57(10)
O(2)#1 -Ir(1)-N(1) 92.57(10)
O(1)-Ir(1)-N(1) 88.55(10)
O(1)#1 -Ir(1)-N(1) 88.55(10)
O(3)-Ir(1)-N(1) 178.84(14)
C(2)-O(1)-Ir(1) 121.7(3)
C(4)-O(2)-Ir(1) 121.8(3)
C(11)-O(3)-Ir(1) 117.8(3)
C(10)-N(1)-C(6) 117.3(5)
C(10)-N(1)-Ir(1) 122.5(4)
C(6)-N(1)-Ir(1) 120.2(3)
O(1)-C(2)-C(3) 126.0(4)
O(1)-C(2)-C(1) 115.0(4)
C(3)-C(2)-C(1) 119.0(4)
C(4)-C(3)-C(2) 128.3(4)
O(2)-C(4)-C(3) 126.3(4)
O(2)-C(4)-C(5) 114.3(4)
C(3)-C(4)-C(5) 119.4(4)
N(1)-C(6)-C(7) 122.8(5)
C(8)-C(7)-C(6) 119.5(5)
C(7)-C(8)-C(9) 118.6(6)
56
C(8)-C(9)-C(10) 119.1(6)
N(1)-C(10)-C(9) 122.7(5)
Cl(1)-C(12)-Cl(1)#1 110.4(3)
Cl(1)-C(12)-Cl(2) 109.54(19)
Cl(1)#1-C(12)-Cl(2) 109.54(19)
_____________________________________________________________
Symmetry transformations use d to generate equivalent atoms:
#1 x,-y+1/2,z
Table 2.9. Anisotropic displacement parameters (Å
2
x 10
3
) for
(acac)
2
Ir(OCH
3
)(Py). The anisotropic 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
______________________________________________________________________________
Ir(1) 17(1) 16(1) 20(1) 0 -1(1) 0
Cl(1) 41(1) 32(1) 39(1) 1(1) -2(1) -10(1)
Cl(2) 40(1) 50(1) 27(1) 0 -10(1) 0
O(1) 21(1) 22(1) 24(1) 1(1) 0(1) 4(1)
O(2) 23(1) 22(1) 28(1) -1(1) -2(1) -3(1)
O(3) 28(2) 30(2) 21(2) 0 -6(1) 0
N(1) 17(2) 20(2) 24(2) 0 -1(1) 0
C(1) 41(2) 32(2) 36(2) -2(2) -7(2) 17(2)
C(2) 34(2) 24(2) 19(2) 1(1) -1(1) 7(2)
C(3) 39(2) 18(2) 33(2) 4(1) -2(2) 0(1)
C(4) 33(2) 24(2) 20(2) 2(1) 0(1) -6(2)
C(5) 42(2) 30(2) 40(2) 4(2) -4(2) -15(2)
C(6) 20(3) 82(5) 27(3) 0 3(2) 0
C(7) 22(3) 86(5) 24(3) 0 -4(2) 0
C(8) 31(3) 44(3) 23(3) 0 4(2) 0
C(9) 28(3) 113(7) 23(3) 0 3(2) 0
C(10) 19(3) 80(5) 29(3) 0 4(2) 0
C(11) 33(3) 22(2) 25(2) 0 -4(2) 0
57
C(12) 25(3) 30(3) 21(2) 0 0(2) 0
Table 2.10. Hydrogen coordinates ( x 10
4
) and isotropic displacement parameters
(Å
2
x 10
3
) for (acac)
2
Ir(OCH
3
)(Py).
_______________________________________________________________________________
x y z U(eq)
_______________________________________________________________________________
H(1A) 11181 -343 5780 55
H(1B) 10867 -554 6881 55
H(1C) 11698 346 6605 55
H(3) 8811 -524 6294 36
H(5A) 5958 316 6292 56
H(5B) 6765 -639 6262 56
H(5C) 6498 -53 5293 56
H(6) 10562 2500 7882 51
H(7) 10601 2500 9543 53
H(8) 8833 2500 10398 40
H(9) 7050 2500 9548 66
H(10) 7088 2500 7872 51
H(11A) 10419 3046 4567 40
H(11B) 9819 2565 3641 40
H(11C) 10355 1889 4469 40
H(12) 2503 2500 1059 30
58
Reaction between 2 and benzene: A re-sealable Schlenk tube was added 2
(5 mg, 0.011 mmol), and benzene (1 mL). The resulting suspension was
thoroughly degassed before being placed under an atmosphere of argon. The tube
was sealed and then heated to 160°C in an oil bath for 10 min. After a few
minutes of heating, the solid dissolved to yield a clear orange-yellow solution that
lightened over the course of the reaction to clear light yellow. After cooling to
room temperature, the solvent was removed to yield a yellow solid which was
characterized as the iridium phenyl complex which has been previously reported
by our group.
4a
1
H NMR (THF-d8): d 6.65(m, 3H, Ph), 6.57(m, 2H, Ph), 5.21(s,
2H, CH), 1.77(s, 12H, CH
3
),
13
C{1H} NMR (THF-d
8
): d 184.5(s, O-acac, C=O),
136.3(s, Ph), 125.3(s, Ph), 122.9(s, Ph), 103.0(s, O-acac, CH), 26.6(s, O-acac,
CH
3
). Further treatment of this material with pyridine yielded the pyridyl
derivative, which has been previously reported by our group.
4a
1
H NMR (CDCl
3
):
d 8.52(m, 2H, py), 7.81(m, 1H, py), 7.46(m, 2H, py), 6.99(m, 5H, Ph), 5.14(s, 2H,
CH), 1.80(s, 12H, CH
3
),
13
C{1H} NMR (THF-d
8
): d 184.5(s, O-acac, C=O),
149.7(s, py), 137.3(s, Ph), 135.7(s, py), 131.3(s, Ph), 125.2(s, py), 124.5(s, Ph),
103.2(s, O-acac, CH), 27.2(s, O-acac, CH
3
). MS (ESI): Calculated for
C
21
H
25
IrNO
4
(M+H) 548.14, found 548.20.
59
Ir
O O
O O
N
C
6
D
6
180
o
C
+
13
CH
3
OD
Ir
O O
O O
O
13
CH
3
1)
N 4 h
D
5
Scheme 2.6. Reaction of 2-
13
C with Benzene.
CH activation experiment with 2 -
13
C (As depicted in Scheme 2.6): To
prepare the
13
C labeled complex, a 5 mL screw-cap vial was charged with 2-
CH
3
OH (10 mg, 0.022 mmol) and
13
CH
3
OH (0.5 mL) was added. The vial was
then sealed, and placed in an inert atmosphere (Ar) glovebox for 4 days. The
resulting yellow-orange solution was then was evaporated under vacuum, yielding
a yellow-orange solid. The solid was then transferred to a Schlenk tube, 5 mL of
pyridine was added, and the tube was placed in an oil bath regulated at 55°C for 30
min. A yellow -orange solid was obtained after the volitiles were removed under
vacuum. The complex was estimated to be 62%
13
C enriched by comparison of
the integration of the doublet resulting form the
13
C-labeled of methoxide protons
to that of the singlet of the remaining unlabeled methoxide.
1
H NMR (C
6
D
6
): d
8.43(d, 2H, o -Py), 6.58(t, 1H, p -Py), 6.29(t, 2H, m -Py), 5.08(s, 2H, CH), 3.76(d,
3H, Ir-OCH
3,
J = 140 Hz), 1.67(s, 12H, CH
3
).
13
C{
1
H} NMR (C
6
D
6
): d 185.4(C-
acac, C=O), 102.7(O-acac, CH), 57.1(OCH
3
), 27.3(O-acac, CH
3
).
To examine the possibility of the generation of a reactive Ir-H via ß-
hydride elimination, 2-
13
C (10 mg) was heated in C
6
D
6
(1.5 mL) at 180°C for 4 h,
60
following which the
13
C NMR was obtained. Only
13
CH
3
OD was detected,
supporting the mechanism occurring via s-bond metathesis. To account for the
stoichiometric formation of CH
3
OH, the Ir-H pathway would be expected to lead
to generation of the D
13
CH
2
OD isotopomer (mechanism shown below) whereas
the proposed s -bond metathesis would lead to
13
CH
3
OH(D).
H-D exchange: Catalytic H-D exchange reactions were quantified by
monitoring the increase of deuterium into C
6
H
6
by GC/MS analyses. This was
achieved by deconvoluting the mass fragmentation pattern obtained from the MS
analysis, using a program developed with Microsoft EXCEL. An important
assumption made with this method is that there are no isotope effects on the
fragmentation pattern for the various benzene isotopologs. Fortunately, because
the parent ion of benzene is relatively stable towards fragmentation, it can be used
reliably to quantify the exchange reactions. The mass range from 78 to 84 (for
benzene) was examined for each reaction and compared to a control reaction
where no metal catalyst was added. The program was calibrated with known
mixtures of benzene isotopologs. The results obtained by this method are reliable
to within 5%. Thus, analysis of a mixture of C
6
H
6
, C
6
D
6
and C
6
H
5
D
1
prepared in a
molar ratio of 40: 50: 10 resulted in a calculated ratio of 41.2(C
6
H
6
): 47.5(C
6
D
6
):
9.9(C
6
H
5
D
1
). Catalytic H/D exchange reactions were thus run for sufficient
reaction times to be able to detect changes >5% exchange. 2 was the catalyst used
to carry out the H/D exchange between benzene and deuterium oxide.
61
In a typical experiment, a 5 mL Schlenk tube was charged with 10 mg of 2-
CH
3
OH, benzene 1 mL, and 0.2 mL of deuterium oxide under an atmosphere of
argon. The tube was then placed in a temperature controlled oil-bath maintained at
160 °C, and deuteration was then measured as described above. A representative
graph of the data from this reaction is shown below.
C6H6/D2O
0
5
10
15
20
25
30
0 20 40 60 80 100 120 140 160
Time (min)
TON
Figure 2.3. Plot of TON for H/D Exchange between D
2
O and C
6
H
6
Catalyzed by
1-CH
3
OH.
Theoretical Calculations: All calculations were performed using the hybrid
DFT functional B3LYP as implemented by the Jaguar 5.0 and Jaguar 5.5 program
packages.
14
This DFT functional utilizes the Becke three-parameter functional
15
(B3) combined with the correlation functional of Lee, Yang, and Par
16
(LYP), and
is known to produce good descriptions of reaction profiles for transition metal
containing compounds.
17,18
The metals were described by the Wadt and Hay
19
core-valence (relativistic) effective core potential (treating the valence electrons
62
explicitly) using the LACVP basis set with the valence doub le- contraction of the
basis functions, LACVP**. All electrons were used for all other elements using a
modified variant of Pople’s
20
6-31G** basis set, where the six d functions have
been reduced to five.
Implicit solvent effects of the experimental benzene medium were calculated with
the Poisson-Boltzmann (PBF) continuum approximation,
21
using the parameters e
= 2.284 and r
solv
= 2.602Å. Due to the increased cost of optimizing systems in the
solvated phase (increase in computation time by a factor of ~4) solvation effects
are calculated here as single point solvation corrections to gas phase geometries.
Our previous work on the Ir(acac)
2
system has shown that the total energies,
geometries, frequencies and zero point energies were also largely unchanged when
the systems were optimized in the solvation phase.
All energies here are reported as ?E + zero point energy corrections at 0K
+ solvation correction. Relative energies on the ?H(0K) surface are expected to be
accurate to within 3 kcal/mol for stable intermediates, and within 5 kcal/mol for
transition structures. Moreover, relative energies of iso-electronic species (such as
regio-isomers) are considerably more accurate, since the errors largely cancel.
Free energies are not included, due to the inadequacies of free energy calculations
in solutions. However, a free energy term is implicitly included in the PBF
solvation methodology.
All geometries were optimized and evaluated for the correct number of
imaginary frequencies through vibrational frequency calculations using the
63
analytic Hessian. Zero imaginary frequencies correspond to a local minimum,
while one imaginary frequency corresponds to a transition structure.
To reduce computational time the methyl groups on the acac ligands were replaced
with hydrogens. Control calculations show that relative energies of intermediates
and transition structures change less than 0.1 kcal/mol when methyl groups are
included.
64
2.4 References
1
We define the CH Activation reaction as a reaction between a reactive species
“M” that proceeds without the involvement of free-radicals, carbocations or
carbanions to generate discrete M -C intermediates. (a) Arndtsen, B. A.; Bergman,
R. G.; Mobley, T. A.; Peterson, T. H. Acc. Chem. Res. 1995, 28, 154 and citations
therin. (b) Periana, R. A.; Bhalla, G.; Tenn III, W.J.; Young, K. J. H.; Liu, X. Y.;
Mironov, O.; Jones, CJ; Ziatdinov, V. R. J. Mol. Cat A. Chem. 2004, 220, 7 and
citations therein.
2
Crabtree, R. H. J. Organomet. Chem. 2004, 689, 4083 and references therein.
3
The related reactions of metal alkoxo and amidos with H
2
and acidic
hydrocarbons have been reported (a) Conner, D.; Jayaprakash, K. N.; Cundari, T.
R.; Gunnoe, T. B. Organometallics, 2004, 23, 2724. For a review of late transition
metal alkoxo chemistry see: ( b) Fulton, J. R.; Holland, A. W.; Fox, D. J.;
Bergman, R. G. Acc. Chem. Res. 2002, 35, 44.
4
(a) Mayer, J. M. Polyhedron, 1995, 14, 3273 and references therein. (b) Kim, S.;
Choi, D.; Lee, Y.; Chae, B.; Ko, J.; Kang, S. Organometallics 2004, 23, 559.
5
Pyrdine is added to convert any dinuclear [(acac-O,O)
2
Ir(Ph)]
2
to mononuclear
complex, 3.
6
Periana, R. A.; Liu, X. Y.; Bhalla, G. Chem. Commun. 2002, 3000.
7
(a) Caulton, K. G. New J. Chem. 1994, 18, 25 and references therein. (b) Zhou,
R.; Wang, C.; Hu, Y.; Flood, T.C. Organometallics 1997, 16, 434.
8
(a) Oxgaard, J.; Muller, R. P.; Goddard III, W. A.; Periana, R. A. J. Am. Chem.
Soc. 2004, 126, 352. (b) Oxgaard, J.; Periana, R. A.; Goddard III, W. A. J. Am.
Chem. Soc. 2004, 126, 11658.
9
(a) Vaska, L.; Di Luzio, J. W. J. Am. Chem. Soc. 1962, 84, 4989. (b) Bryndza, H.
E.; Tam, W. Chem.Rev. 1988, 88, 1163. (c) Bernard, K. A.; Rees, W. M.; Atwood,
J. D. Organometallics 1986, 5, 390.
10
(a) Yung, C. M.; Skaddan, M. B.; Bergman, R. G. J. Am. Chem. Soc. 2004,
126,13033. (b) Haenel, M. W.; Oevers, S.; Angermund, K.; Kaska, W. C.; Fan, H -
J.; Hall, M. B. Angew. Chem. Int. Ed. 2001, 40, 3596 (c). Bernskoetter, W. H.;
Lobkovsky, E.; Chirik, P. J. Chem. Comm. 2004, 764.
65
11
This
13
C labeled complex is readily prepared by exchange of the methoxide and
methanol groups of 2-CH
3
OH with
13
CH
3
OH by reaction at room temperature for
4 days.
12
This is readily evident from the distinctive singlet resonance for
13
CH
3
OH(D)
13
Matsumoto, T.; Periana, R. A.; Taube, D. J.; Yoshida, H. J. Mol. Cat. A-
Chemical 2002, 180, 1.
14
Jaguar 5.0, Schrodinger, Inc., Portland, Oregon, 2000, Jaguar 5.5, Schrodinger,
Inc., Portland, Oregon, 2002
15
Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
16
Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
17
Baker, J.; Muir, M.; Andzelm, J.; Scheiner, A. In Chemical Applications of
Density-Functional Theory; Laird, B. B., Ross, R. B., Ziegler, T., Eds.; ACS
Symposium Series 629; American Chemical Society: Washington, DC, 1996.
18
Niu, S.; Hall, B. M. Chem. Rev. 2000, 100, 353.
19
(a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299. (b) Goddard, W. A.,
III Phys. Rev. 1968, 174, 659. (c) Melius, C. F.; Olafson, B. O.; Goddard, W. A.,
III Chem. Phys. Lett. 1974, 28, 457.
20
(a) Hariharan, P. C.; Pople, J. A. Chem. Phys. Lett. 1972, 16, 217. (b) Francl, M.
M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.;
Pople, J. A. J. Chem. Phys. 1982, 77, 3654.
21
(a) Tannor, D. J.; Marten, B.; Murphy, R.; Friesner, R. A.; Sitkoff, D.; Nicholls,
A.; Ringnalda, M.; Goddard, W. A., III; Honig, B. J. Am. Chem. Soc. 1994, 116,
11875. (b) Marten, B.; Kim, K.; Cortis, C.; Friesner, R. A.; Murphy, R. B.;
Ringnalda, M. N.; Sitkoff, D.; Honig, B. J. Phys. Chem. 1996, 100, 11775.
66
3 CH Activation and Catalysis by an Iridium
Hydroxo Complex
3.1 Introduction.
The CH activation reaction has been the focus of significant effort given
the potential for designing catalysts that can selectively functionalize hydrocarbons
at low temperatures.
1
Heterolytic CH activation with M -X complexes, Eq 3.1,
where X is a heteroatom, has been incorporated into catalytic cycles for the oxy-
functonalization of hydrocarbons and is relatively common with the electrophilic
cations Pt(II), Pd(II), Hg(II), Au(III)/(I).
2
C-H + M-X à M-C + H-X (3.1)
However, heteolytic CH activation is not common with more electron -rich
cations such as Ir(III) and to our knowledge, catalytic oxy-functionalization has
not been reported with electron -rich complexes.
3
Recently, we reported the first
well-defined Ir(III) alkoxo complex that exhibited both stoichiometric and
catalytic heterolytic CH activation.
4
We and others
5
have been working to
establish the generality of this type of CH activation reaction by extension to metal
hydroxo complexes. We now report the first example of stoichiometric and
catalytic heterolytic CH activation, M = Ir(III), X = OH, Eq 1, with an air, protic
67
and thermally stable Ir(III) hydroxo complex that cleanly generates the CH
activation product Ir-R and H
2
O.
Specifically, we report on the preparation of the O-donor Iridium(III)
hydroxide complex (acac-O,O)
2
Ir(III)(OH)(Py) (acac-O,O = κ
2
-O,O-
acetylacetonate), (Py = pyridine), 1, and show that this complex undergoes
stoichiometric, heterolytic CH activation with benzene to quantitatively generate
the CH activation product, (acac-O,O)
2
Ir(III)(Ph)(Py), 2, and water, Scheme 3.1.
Combined theoretical and experimental evidence is presented in support of a
mechanism involving pre-equilibrium, dissociative loss of Py, followed by rate
determining benzene coordination and fast CH cleavage via a sigma-bond
metathesis transition state. Complex 1 is stable and is competent for the catalytic
H/D exchange reaction between benzene and water.
3.2 Results and Discussion.
Scheme 3.1. CH Activation of Benzene with (acac-O,O)
2
Ir(III)(OH)(Py), 1.
Ir
O O
O O
O
H
C
6
H
6
180
o
C
10 h
+ H
2
O
N
Ir
O O
O O
N
1 2
68
Complex 1 was synthesized from the methoxo complex, (acac-
O,O)
2
Ir(III)(OCH
3
)(CH
3
OH), 3, in quantitative yield by reaction with water at
70
o
C, followed by treatment with pyridine. The com pound is an air and water-
stable, hygroscopic yellow solid that has been fully characterized by
1
H,
13
C NMR
spectroscopy, elemental analysis, high-resolution mass spectrometry, and x-ray
crystallography. The –OH resonance in the
1
H NMR is significantly broadened,
but sharpens at low temperature, and is visible at -50 °C at -0.96 ppm. An ORTEP
diagram of this complex is shown in Figure 1, and details of the structure
determination are provided as supplementary material.
Figure 3.1. ORTEP diagram of complex 1, showing ellipsoids at the 50%
probability level. A molecule of cocrystallized CHCl
3
has been
omitted for clarity. Selected bond distances (? ): Ir1-O5, 2.018(4);
Ir1-N1, 2.044(5).
69
The benzene CH activation with 1, Scheme 3.1, was carried out in neat
C
6
H
6
at 160°C for 10 h. Removal of all volatiles in vacuo and dissolution with
CDCl
3
solvent containing 1,3,5-trimethoxybenzene as an internal standard showed
that 2 was produced in 71% yield based on added 1. Complex 2 was separated
from the reaction mixture by preparative TLC and identified by comparison of the
1
H and
13
C NMR spectra and mass peaks to that of independently prepared and
fully characterized 2.
4
Reactions with toluene are typical of other well-defined CH
activation reactions
1
and only the meta and para aromatic CH bonds are activated
in a ~2:1 ratio. A free-radical mechanism is unlikely as the both the CH activation
rate and selectivity is insensitive to added oxygen.
Having established that 1 can stoichiometrically activate the CH bonds of
benzene, we examined the complex for catalytic CH activation of benzene.
Examples of metal -catalyzed H/D exchange with water are relatively rare.
6
The
rates of H/D exchange of mixtures of C
6
H
6
and D
2
O catalyzed by 1 (0.1 mol %) at
190 °C were measured. The reaction mixture is stable over the time period studied
(~86 h) and turn-over-numbers (TON) of 329 and turn -over-frequencies (TOF) of
1.1 x 10
-3
s
-1
were observed based on added 1. We propose that the CH activation
proceeds via a mechanism involving substrate coordination and CH cleavage by
hydrogen transfer to the hydroxo group. Since 1 is a 6-coordinate, 18-electron
complex it is likely that the benzene coordination proceeds via a five-coordinate
intermediate generated by dissociative loss of pyridine in a pre-equilibrium step.
As shown in Figure 3.2, the observed linear dependence of the TOF for H/D
70
exchange versus 1/[Py] is consistent with this proposal. This result would predict
that the aquo complex (acac-O,O)
2
Ir(OH)(H
2
O) would be a more effective catalyst
and preliminary results on the synthesis and testing of this complex show this to be
the case.
Figure 3.2. Plot of TOF versus 1/[Py] for C
6
H
6
/D
2
O H/D Exchange with 1
(10mM).
To further probe the mechanism of the CH activation reaction, we
compared the deuterium kinetic isotope effect (KIE) for reaction of 1 with a
mixture of C
6
H
6
/C
6
D
6
with that for 1,3,5-trideuterobenzene. This comparison can
allow the distinction between rate determining benzene coordination and rate
determining CH cleavage
7
(assuming negligible secondary isotope effects). The
ratio of CH to CD activation by 1 was obtained from analysis of the H to D ratio,
respectively, in the water produced. The H to D ratio in the water produced was
0
0.1
0.2
0.3
0.4
0.5
0.6
0 50 100 150 200 250 300
1/[Py added] (M
-1
)
TOF x 10
-3
(s
-1
)
71
obtained by post reaction with CH
3
Li and quantification of the molar ratio of
gaseous methane isotopologs by GC/MS (see supplemental for details). The KIE
for 1,3,5-trideuterobenzene is normal with k
H
/k
D
= 2.65 ±0.56. DFT calculations
(B3LYP/LACVP** with ZPE and solvent corrections)
8
of the KIE ( k
H
/k
D
= 2.9)
compares well with this experimental value. In the case of the mixture of
C
6
H
6
/C
6
D
6
no KIE was observed ( k
H
/k
D
= 1.07 ±0.24). Taken together these
results would suggest that the CH activation of benzene occurs via rate
determining benzene coordination followed by faster CH cleavage.
.
Scheme 3.2. Proposed mechanism for the reaction of 1 (values in parenthesis are
calculated ΔG).
DFT calculations of the CH activation mechanism, summarized in Scheme
3.2, show that the lowest energy pathway involves pre-equilibrium, dissociative
loss of pyridine to generate a trans-5-coordinate intermediate, followed by rate
Ir
O O
O O
O
H
O
Ir
O
O
OH
O
N
Ir
O O
O O
Ir
O O
O O
O
Py
H
O
Ir
O
O
OH2
O
(32.8 kcal/mol)
(29.2 kcal/mol)
(30.1 kcal/mol)
(37.8 kcal/mol)
(11.2 kcal/mol)
O
Ir
O
O
OH
O
(0.0 kcal/mol)
(-6.8 kcal/mol)
H
O
Ir
O
O
O
O
H
-Py + C
6
H
6
+Py
-H
2
O
+ C6H6 - H
2
O
Isomerization
TS (42.9 kcal/mol)
72
determining trans-cis isomerization to generate the cis-benzene complex and fast
CH bond cleavage by an internal electrophilic substitution transition state.
Significantly, the calculations, unlike those reported recently for a Ru(II)
hydroxo,
5
show that the CH activation reaction, Eq 3.1, is energetically favorable
and is in accord with the generation of 2 from 1 in good yield. The calculated
overall barrier for reaction of 1 with benzene of 42.9 kcal/mol and lower barrier
for Py loss are also consistent with the reaction proceeding at 190
o
C with a t
1/2
~
4.8 h and the observed inverse rate dependence on Py, respectively. The
calculations also supports the interpretation of the KIE experiments that benzene
coordination rather than CH cleavage is rate determining.
It is interesting that 1 exhibits stable catalysis (TON of >300 observed) and
is not deactivated by the irreversible formation of bridging hydroxo species
(assuming thermodynamic control)
9
that is common for coordinatively unsaturated
metal hydroxo complexes. Our attempts at synthesis of these bridging hydroxo
complexes have thus far been unsuccessful. Calculations show that the formation
of a µ-hydroxo bridged complex from two molecules of 1 is not very favorable
(ΔG
rxn
= -2 kcal/mol) and may serve to explain the catalytic stability of 1.
In summary, we demonstrate that the discrete O-donor, air, and thermally
stable hydroxo complex, 1, reacts with benzene to generate the corresponding
phenyl complex, 2, with co-generation of water. 1 is an efficient catalyst for H/D
exchange reaction between benzene and water. Experimental and theoretical
studies suggest that the reaction proceeds via rate-determining formation of an
73
arene complex followed by faster CH cleavage by a sigma bond metathesis
reaction.
3.3 Experimental Section.
General Considerations: All air and water sensitive procedures were carried
out either in an MBraun inert atmosphere glove box (under nitrogen), or using
standard Schlenk techniques under argon. All deuterated solvents (Cambridge
Isotopes), and pyridine (Aldrich) were used as received. Methyl lithium (1.6 M
solution in diethyl ether) was degassed and filled with argon prior to use. The
methoxide complex from which 1 was prepared was synthesized as described in
the literature.
10
GC/MS analysis was performed on a Shimadzu GC-MS QP5000
(ver. 2) equipped with cross-linked methyl silicone gum capillary column (DB5)
and a Gas-pro column. The retention times of the products were confirmed by
comparison to authentic samples. NMR spectra were obtained on a Varian
Mercury -400 spectrometer at room temperature. All chemical shifts are reported
in units of ppm and referenced to the residual proteated solvent. All high-
resolution mass spectra were obtained by UCLA Pasarow Mass Spectrometry
Laboratory on either an ESI, or a MALDI-TOF mass spectrometer. Elemental
Analysis was performed by Desert Analytics of Tucson, Arizona.
74
X-ray Crystallography. Diffraction data for 1 was collected at low
temperature (T = 128 K) on a Bruker SMART APEX CCD diffractometer with
graphite-monochromated Mo Kα radiation (?= 0.71073 Å). The cell parameters
for the Ir complex were obtained from the least-squares refinement of the spots
(from 60 collected frames) using the SMART program. A hemisphere of the
crystal data was collected and the intensity data was processed using the Saint Plus
program. All calculations for structure determination were carried out using the
SHELXTL package (version 5.1).
11
Initial atomic positions were located by direct
methods using XS, and the structure was refined by least-squares methods using
SHELX. Absorption corrections were applied by using SADABS.
12
Calculated
hydrogen positions were input and refined in a riding manner along with the
attached carbons.
Synthesis of [HO-Ir(O,O-acac)
2
(H
2
O)] (1-H
2
O): A 30 mL re-sealable
Schlenk tube was charged with the previously reported methoxide analog CH
3
O-
Ir(O,O-acac)
2
(CH
3
OH) (55 mg, 0.11 mmol) and water (20 mL) was added. The
Schlenk tube was then sealed, and placed in a 60°C oil bath for 4 h. The resulting
yellow solution was cooled to room temperature, and the volatiles were removed
in vacuo, yielding a yellow solid in quantitative yield.
1
H NMR (D
2
O): d 5.56(s,
2H, CH), 2.46(s, 1H, Ir-OH), 1.89(s, 12H, CH
3
).
13
C{
1
H} NMR (D
2
O): d
186.68(C-acac, C=O), 102.40(O-acac, CH), 25.60(O-acac, CH
3
). HRMS (ESI):
Calculated for C
10
H
18
IrO
6
(M+H) 4627.0727, found 427.0712.
75
Synthesis of [HO-Ir(O,O-acac)
2
(Py)] (1): A 15 mL re-sealable Schlenk
tube was charged with 1-H
2
O (30 mg, 0.11 mmol) and pyridine (10 mL) was
added. The Schlenk tube was then sealed, and placed in a 60°C oil bath for 30
min. The resulting dark-orange solution was cooled to room temperature, and the
volatiles were removed in vacuo, yielding an orange solid in quantitative yield.
The complex is hygroscopic.
1
H NMR (CDCl
3
): d 8.32(d, 2H, o-Py), 7.79(t, 1H,
p-Py), 7.33(t, 2H, m -Py), 5.42(s, 2H, CH), 2.63(s, 1H, OH), 2.03(s, 12H, CH
3
).
13
C{
1
H} NMR (CDCl
3
): d 185.6(C-acac, C=O), 152.1(o-Py), 137.4(p-Py),
125.2(m-Py), 102.7(O-acac, CH), 26.9(O-acac, CH
3
). HRMS (MALDI-TOF):
Calculated for C
13
H
20
IrNO
5
Na (M+Na) 510.0863, found 510.0876. Elemental
Analysis: Calculated for C
12
H
21
IrO
6
:
C, 37.03; H, 4.14; N, 2.88. Found: C, 36.63;
H, 4.17; N, 2.64. Single crystals were grown by slow evaporation of a
concentrated sample in chloroform.
Summary of crystal data for 1: a yellow -orange prism -shaped crystal of
dimensions 0.24 x 0.18 x 0.10 mm
3
was grown from chloroform by slow
evaporation of the solvent. C
16
H
21
Cl
3
IrNO
5
: monoclinic, group P2(1)/n, a = 7.
7108(5) Å, b = 18.4718(12) Å, c = 14.8523(10) Å, V = 2111.8(2) Å
3
, Z = 4, T =
128(2) K, D
calcd
= 1.906 Mg/m
3
, R(F) = 2.42 for 12793 observed reflections. All
non-hydrogen atoms were refined with anisotropic displacement parameters.
76
Table 3.1. Crystal data and structure refinement for (acac)
2
Ir(OH)(Py).
Identification code irohpym
Empirical formula C16 H21 Cl3 Ir N O5
Formula weight 605.89
Temperature 128(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/n
Unit cell dimensions a = 7.7108(5) Å α= 90°.
b = 18.4718(12) Å
β=93.3430(10)°.
c = 14.8523(10) Å γ = 90°.
Volume 2111.8(2) Å
3
Z 4
Density (calculated) 1.906 Mg/m
3
Absorption coefficient 6.726 mm
-1
F(000) 1168
Crystal size 0.24 x 0.18 x 0.10 mm
3
Theta range for data collection 1.76 to 27.50°.
Index ranges -9<=h<=9, -24<=k<=19, -17<=l<=19
Reflections collected 12793
Independent reflections 4724 [R(int) = 0.0305]
Completeness to theta = 27.50° 97.6 %
Transmission factors min/max ratio: 0.736
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 4724 / 0 / 240
Goodness-of-fit on F
2
1.035
Final R indices [I>2sigma(I)] R1 = 0.0207, wR2 = 0.0502
R indices (all data) R1 = 0.0242, wR2 = 0.0512
Largest diff. peak and hole 1.116 and -0.537 e.Å
-3
77
Table 3.2. Atomic coordinates ( x 10
4
) and equivalent isotropic displacement
parameters (Å
2
x 10
3
) for (acac)
2
Ir(OH)(Py). U(eq) is defined as one third of the
trace of the orthogonalized U
ij
tensor.
_______________________________________________________________________________
x y z U(eq)
_______________________________________________________________________________
Ir(1) 2892(1) 1584(1) 1029(1) 16(1)
Cl(1) 1963(2) 10421(1) 4320(1) 61(1)
Cl(2) 4766(1) 9618(1) 3605(1) 53(1)
Cl(3) 1214(1) 9248(1) 3084(1) 55(1)
O(1) 4781(2) 2320(1) 1262(1) 19(1)
O(2) 4085(2) 1045(1) 60(1) 20(1)
O(3) 1784(2) 2107(1) 2032(1) 20(1)
O(4) 987(2) 844(1) 841(1) 19(1)
O(5) 3978(2) 938(1) 1999(1) 23(1)
N(1) 1754(3) 2238(1) 51(1) 17(1)
C(1) 7420(4) 2907(2) 1090(2) 31(1)
C(2) 6183(3) 2306(2) 845(2) 21(1)
C(3) 6597(4) 1807(2) 185(2) 25(1)
C(4) 5594(4) 1234(2) -172(2) 23(1)
C(5) 6286(4) 774(2) -909(2) 31(1)
C(6) 500(4) 1833(2) 2420(2) 23(1)
C(7) -201(3) 780(2) 1401(2) 22(1)
C(8) -432(4) 1218(2) 2154(2) 26(1)
C(9) 1024(4) 3409(2) -525(2) 28(1)
C(10) 1034(3) 1947(2) -718(2) 22(1)
C(11) 293(4) 3115(2) -1316(2) 29(1)
C(12) 1738(3) 2961(2) 138(2) 22(1)
C(13) 286(3) 2369(2) -1401(2) 26(1)
C(14) 2663(4) 9961(2) 3370(2) 38(1)
C(15) -1427(4) 161(2) 1208(2) 30(1)
C(16) 36(4) 2240(2) 3246(2) 34(1)
78
Table 3.3. Bond lengths [Å] and angles [°] for (acac)
2
Ir(OH)(Py).
_____________________________________________________
Ir(1)-O(1) 2.0075(17)
Ir(1)-O(3) 2.0081(18)
Ir(1)-O(4) 2.0138(18)
Ir(1)-O(5) 2.0148(18)
Ir(1)-O(2) 2.0153(18)
Ir(1)-N(1) 2.047(2)
Cl(1)-C(14) 1.759(4)
Cl(2)-C(14) 1.757(4)
Cl(3)-C(14) 1.763(3)
O(1)-C(2) 1.277(3)
O(2)-C(4) 1.281(3)
O(3)-C(6) 1.278(3)
O(4)-C(7) 1.278(3)
N(1)-C(12) 1.341(3)
N(1)-C(10) 1.352(3)
C(1)-C(2) 1.495(4)
C(2)-C(3) 1.397(4)
C(3)-C(4) 1.397(4)
C(4)-C(5) 1.506(4)
C(6)-C(8) 1.390(4)
C(6)-C(16) 1.500(4)
C(7)-C(8) 1.400(4)
C(7)-C(15) 1.500(4)
C(9)-C(12) 1.377(4)
C(9)-C(11) 1.384(4)
C(10)-C(13) 1.377(4)
C(11)-C(13) 1.385(4)
O(1)-Ir(1)-O(3) 83.24(8)
O(1)-Ir(1)-O(4) 178.05(7)
O(3)-Ir(1)-O(4) 95.21(7)
O(1)-Ir(1)-O(5) 90.64(7)
79
O(3)-Ir(1)-O(5) 86.09(8)
O(4)-Ir(1)-O(5) 88.07(7)
O(1)-Ir(1)-O(2) 95.79(7)
O(3)-Ir(1)-O(2) 177.58(7)
O(4)-Ir(1)-O(2) 85.71(7)
O(5)-Ir(1)-O(2) 91.71(7)
O(1)-Ir(1)-N(1) 89.95(8)
O(3)-Ir(1)-N(1) 93.39(8)
O(4)-Ir(1)-N(1) 91.32(8)
O(5)-Ir(1)-N(1) 179.16(8)
O(2)-Ir(1)-N(1) 88.82(8)
C(2)-O(1)-Ir(1) 121.92(18)
C(4)-O(2)-Ir(1) 121.19(18)
C(6)-O(3)-Ir(1) 121.20(18)
C(7)-O(4)-Ir(1) 121.20(17)
C(12)-N(1)-C(10) 118.1(2)
C(12)-N(1)-Ir(1) 121.65(18)
C(10)-N(1)-Ir(1) 120.22(18)
O(1)-C(2)-C(3) 126.1(3)
O(1)-C(2)-C(1) 114.4(3)
C(3)-C(2)-C(1) 119.5(3)
C(2)-C(3)-C(4) 128.5(3)
O(2)-C(4)-C(3) 126.5(3)
O(2)-C(4)-C(5) 114.1(3)
C(3)-C(4)-C(5) 119.4(3)
O(3)-C(6)-C(8) 126.6(3)
O(3)-C(6)-C(16) 113.5(3)
C(8)-C(6)-C(16) 119.9(3)
O(4)-C(7)-C(8) 126.5(3)
O(4)-C(7)-C(15) 114.5(2)
C(8)-C(7)-C(15) 119.0(3)
C(6)-C(8)-C(7) 127.8(3)
C(12)-C(9)-C(11) 119.9(3)
80
N(1)-C(10)-C(13) 122.1(3)
C(9)-C(11)-C(13) 117.8(3)
N(1)-C(12)-C(9) 122.3(3)
C(10)-C(13)-C(11) 119.8(3)
Cl(2)-C(14)-Cl(1) 109.77(18)
Cl(2)-C(14)-Cl(3) 110.0(2)
Cl(1)-C(14)-Cl(3) 109.55(19)
_____________________________________________________________
Symmetry transformations used to generate equivalent atoms:
Table 3.4. Anisotropic displacement parameters (Å
2
x 10
3
) for (acac)
2
Ir(OH)(Py).
The anisotropic 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
______________________________________________________________________________
Ir(1) 18(1) 15(1) 14(1) -1(1) 1(1) -1(1)
Cl(1) 71(1) 68(1) 44(1) -7(1) 6(1) -9(1)
Cl(2) 50(1) 54(1) 55(1) 22(1) -7(1) -1(1)
Cl(3) 66(1) 45(1) 51(1) 11(1) -18(1) -23(1)
O(1) 20(1) 19(1) 19(1) 0(1) 3(1) -2(1)
O(2) 23(1) 20(1) 18(1) -2(1) 4(1) 1(1)
O(3) 21(1) 22(1) 18(1) -3(1) 3(1) -2(1)
O(4) 22(1) 18(1) 19(1) -1(1) 3(1) -3(1)
O(5) 27(1) 21(1) 20(1) 2(1) 0(1) 3(1)
N(1) 17(1) 19(1) 16(1) -1(1) 4(1) 0(1)
C(1) 25(1) 30(2) 39(2) -2(1) 1(1) -7(1)
C(2) 19(1) 21(1) 23(2) 7(1) 1(1) 0(1)
C(3) 21(1) 25(2) 28(2) 1(1) 5(1) 1(1)
C(4) 28(2) 24(2) 16(1) 6(1) 2(1) 7(1)
C(5) 34(2) 30(2) 30(2) -6(1) 11(1) 4(1)
C(6) 20(1) 28(2) 22(2) -3(1) 2(1) 4(1)
C(7) 21(1) 22(2) 21(1) 4(1) -2(1) -2(1)
81
C(8) 25(1) 30(2) 24(2) -3(1) 6(1) -6(1)
C(9) 36(2) 18(2) 30(2) 3(1) 1(1) 7(1)
C(10) 22(1) 22(2) 22(2) -1(1) 3(1) -5(1)
C(11) 30(2) 32(2) 26(2) 8(1) 1(1) 5(1)
C(12) 26(1) 19(1) 21(1) -3(1) 3(1) 0(1)
C(13) 25(1) 36(2) 18(2) -1(1) -2(1) -3(1)
C(14) 46(2) 35(2) 33(2) 10(2) -3(2) -9(2)
C(15) 29(2) 29(2) 31(2) -1(1) 1(1) -8(1)
C(16) 31(2) 44(2) 30(2) -16(2) 12(1) -8(2)
Table 3.5. Hydrogen coordinates ( x 10
4
) and isotropic displacement parameters
(Å
2
x 10
3
) for (acac)
2
Ir(OH)(Py).
_______________________________________________________________________________
_ x y z U(eq)
_______________________________________________________________________________
H(5) 4818 713 1796 34
H(1A) 7149 3327 703 47
H(1B) 8611 2746 1004 47
H(1C) 7312 3042 1722 47
H(3) 7706 1865 -53 30
H(5A) 6373 270 -706 46
H(5B) 7438 950 -1050 46
H(5C) 5496 804 -1449 46
H(8) -1334 1078 2527 31
H(9) 1032 3919 -440 33
H(10) 1044 1436 -791 26
H(11) -188 3416 -1786 35
H(12) 2238 3171 676 26
H(13) -232 2148 -1928 32
H(14) 2682 10306 2852 46
H(15A) -1165 -67 636 45
H(15B) -2624 341 1167 45
H(15C) -1292 -196 1696 45
82
H(16A) 955 2176 3723 52
H(16B) -1064 2055 3453 52
H(16C) -88 2756 3102 52
Reaction between 1 and benzene: To a re-sealable Schlenk tube was added
1 (5 mg, 0.011 mmol), and benzene (1 mL). The resulting suspension was
thoroughly degassed before being placed under an atmosphere of argon. The tube
was sealed and then heated to 160°C in an oil bath for 10 min. After a few
minutes of heating, the solid dissolved to yield a clear orange- yellow solution that
lightened over the course of the reaction to clear light yellow. After cooling to
room temperature, the solvent was removed to yield a yellow solid which was
characterized as the iridium phenyl complex which has been previously reported
by our group.
4a
Pure 2 was isolated by preparative TLC (alumina, 1000 microns,
Analtech, Inc.) using CHCl
3
as the elutant.
1
H NMR (THF-d8): d 6.65(m, 3H, Ph),
6.57(m, 2H, Ph), 5.21(s, 2H, CH), 1.77(s, 12H, CH
3
),
13
C{1H} NMR (THF-d
8
): d
184.5(s, O-acac, C=O), 136.3(s, Ph), 125.3(s, Ph), 122.9(s, Ph), 103.0(s, O-acac,
CH), 26.6(s, O-acac, CH
3
). Further treatment of this material with pyridine
yielded the pyridyl derivative, which has been previously reported by our group.
1
H NMR (CDCl
3
): d 8.52(m, 2H, py), 7.81(m, 1H, py), 7.46(m, 2H, py), 6.99(m,
5H, Ph), 5.14(s, 2H, CH), 1.80(s, 12H, CH
3
),
13
C{1H} NMR (THF-d
8
): d 184.5(s,
O-acac, C=O), 149.7(s, py), 137.3(s, Ph), 135.7(s, py), 131.3(s, Ph), 125.2(s, py),
83
124.5(s, Ph), 103.2(s, O-acac, CH), 27.2(s, O-acac, CH
3
). MS (ESI): Calculated
for C
21
H
25
IrNO
4
(M+H) 548.14, found 548.20.
H/D exchange: Catalytic H-D exchange reactions were quantified by
monitoring the increase of deuterium into C
6
H
6
by GC/MS analyses. This was
achieved by deconvoluting the mass fragmentation pattern obtained from the MS
analysis, using a program developed with Microsoft EXCEL. An important
assumption made with this method is that there are no isotope effects on the
fragmentation pattern for the various benzene isotopologs. Fortunately, because
the parent ion of benzene is relatively stable towards fragmentation, it can be used
reliably to quantify the exchange reactions. The mass range from 78 to 84 (for
benzene) was examined for each reaction and compared to a control reaction
where no metal catalyst was added. The program was calibrated with known
mixtures of benzene isotopologs. The results obtained by this method are reliable
to within 5%. Thus, analysis of a mixture of C
6
H
6
, C
6
D
6
and C
6
H
5
D
1
prepared in a
molar ratio of 40: 50: 10 resulted in a calculated ratio of 41.2(C
6
H
6
): 47.5(C
6
D
6
):
9.9(C
6
H
5
D
1
). Catalytic H/D exchange reactions were thus run for sufficient
reaction times to be able to detect changes >5% exchange. 2 was the catalyst used
to carry out the H/D exchange between benzene and deuterium oxide.
In a typical experiment, a 5 mL Schlenk tube was charged with 10 mg of 1,
benzene 1 mL, and 1 mL of deuterium oxide under an atmosphere of argon. The
tube was then placed in a temperature controlled oil-bath maintained at 190 °C,
84
and deuterium incorporation was then measured as described above. A
representative graph of the data from this reaction is shown below.
R
2
= 0.9325
0
50
100
150
200
250
300
350
400
0 1000 2000 3000 4000 5000 6000
Time (min)
TON
Figure 3.3. Plot of TON vs. Time for Benzene/D
2
O H/D Exchange with 1.
Dependence of H/D exchange rate on pyridine concentration: A stock
solution of 1 (10 mM) in 1 mL C
6
H
6
and 1mL D
2
O was added to 5 mL thick-
walled ampoules equipped with high-vacuum valves. Pyridine was added (0.5 to 2
molar equivalents) and the ampoule was heated in a well-stirred oil bath
maintained at 190
o
C. The mixtures were then sampled at regular intervals and the
extent of deuterium incorporation was determined as described above. A
representative graph of this data is shown below.
85
0
50
100
150
200
250
300
350
400
0 1000 2000 3000 4000 5000 6000
Time (min)
TON
Figure 3.4. Plots of TON vs. Time for Benzene/D
2
O H/D Exchange with 1 for
runs with varied free pyridine added. Where diamond = 0 Py added,
x = 0.5 mol eq, square = 1 mol eq, and triangle = 2 mol eq.
0
0.1
0.2
0.3
0.4
0.5
0.6
0 50 100 150 200 250 300
1/[Py added] (M-1)
TOF x 10-3 (s-1)
Figure 3.5. Plot of TOF vs. 1/[Py] for Benzene/D
2
O H/D Exchange with 1.
86
Deuterium kinetic isotope effect on benzene CH activation by 1: Three 5
mL Schlenk tubes were charged with 10 mg of 1, and 0.5 mL of a 1:1 molar
mixture of C
6
H
6
/C
6
D
6
, or 1,3,5-trideuterobenzene under an atmosphere of argon.
The tubes were then placed in a temperature controlled oil-bath maintained at 180
°C until the reaction had reached 10 % completion. The tubes were then cooled
and methyl lithium was added. The gas phase was then analyzed via GCMS. The
molar ratio of the liberated methane isotopologs was determined using a
deconvolution spreadsheet calibrated with known mixtures of methane
isotopologs. The liquid phase was analyzed to ensure that deuterium scrambling
was minimized in the starting materials. Control experiments without added 1,
and with 1 but without heating were also carried-out, each in triplicate, to account
for background generation of methane from reactions with methyl lithium.
Ir
O O
O O
O
H
N
D
D D
+
N
Ir
O O
O O
D D
D
+
N
Ir
O O
O O
D D
+ H
2
O + HOD
180
o
C
2.65 : 1
Ir
O O
O O
O
H
N
+
N
Ir
O O
O O
+
N
Ir
O O
O O
+ H 2O + HOD
180
o
C
C 6 H 6 / C 6 D 6
H 5 D 5
1 : 1
Scheme 3.3. Deuterium Kinetic Isotope Effect on CH Activation of Benzene by 1.
87
Theoretical Calculations: All calculations were performed using the hybrid
DFT functional B3LYP as implemented by the Jaguar 6.0 and Jaguar 6.5 program
packages.
13
This DFT functional utilizes the Becke three-parameter functional
14
(B3) combined with the correlation functional of Lee, Yang, and Par
15
(LYP), and
is known to produce good descriptions of reaction profiles for transition metal
containing compounds.
16,17
The metals were described by the Wadt and Hay
18
core-valence (relativistic) effective core potential (treating the valence electrons
explicitly) using the LACVP basis set with the valence double- contraction of the
basis functions, LACVP**. All electrons were used for all other elements using a
modified variant of Pople’s
19
6-31G** basis set, where the six d functions have
been reduced to five.
Implicit solvent effects of the experimental benzene medium were
calculated with the Poisson -Boltzmann (PBF) continuum approximation,
20
using
the parameters e = 2.284 and r
solv
= 2.602Å. Due to the increased cost of
optimizing systems in the solvated phase (increase in computation time by a factor
of ~4) solvation effects are calculated here as single point solvation corrections to
gas phase geometries. Our previous work on the Ir(acac)
2
system has shown that
the total energies, geometries, frequencies and zero point energies were also
largely unchanged when the systems were optimized in the solvation phase.
All energies here are reported as ?E + zero point energy corrections at 0K
+ solvation correction. Relative energies on the ?H(0K) surface are expected to be
accurate to within 3 kcal/mol for stable intermediates, and within 5 kcal/mol for
88
transition structures. Moreover, relative energies of iso-electronic species (such as
regio-isomers) are considerably more accurate, since the errors largely cancel.
Free energies are not included, due to the inadequacies of free energy calculations
in solutions. However, a free energy term is implicitly included in the PBF
solvation methodology.
All geometries were optimized and evaluated for the correct number of
imaginary frequencies through vibrational frequency calculations using the
analytic Hessian. Zero imaginary frequencies correspond to a local minimum,
while one imaginary frequency corresponds to a transition structure.
To reduce computational time the methyl groups on the acac ligands were
replaced with hydrogens. Control calculations show that relative energies of
intermediates and transition structures change less than 0.1 kcal/mol when methyl
groups are included.
The deuterium kinetic isotope effect calculated for the reaction of 1,3,5-
trideuterobenzene with (acac-O,O)
2
Ir(III)(OH)(Py) assumes that generation of
HOH and HOD involve the same intermediates up until the arene complex (acac-
O,O)
2
Ir(III)(OH)(C
6
H
3
D
3
) (below, 1). Using transition state theory, the kinetic
isotope effect is then determined as in Scheme 3.4, where G
TS-H
and G
TS-D
contain
the mass dependent quantities (zero point energy and vibrational enthalpy and
entropy at 473K) evaluated using the appropriately mass-weighted Hessians.
89
Ir
C
6
H
3
D
3
OH
Ir
C
6
H
2
D
3
HO
H
k
H
1
rate
H
k
H
rate
D
k
D
= = exp( )
-((G
TS-H
- G
1
)- (G
TS-D
-G
1
))
kT
KIE =
Ir
C
6
H
3
D
2
HO
D
k
D
TS-D
= exp( )
-(G
TS-H
- G
TS-D
)
kT
= 2.9
TS-H
Scheme 3.4. Computational Determination of Deuterium Kinetic Isotope Effect by
DFT.
90
3.4 References
1
We define the CH Activation reaction as a reaction between a reactive species
“M” that proceeds without the involvement of free-radicals, carbocations or
carbanions to generate discrete M-C intermediates. (a) Arndtsen, B. A.; Bergman,
R. G.; Mobley, T. A.; Peterson, T. H. Acc. Chem. Res. 1995, 28, 154. (b) Shilov,
A. E.; Shul’pin, G. B. Activation and Catalytic Reactions of Saturated
Hydrocarbons in the Presence of Metal Complexes Kluwer Academic; Dordrecht,
2000 (c) Jia, C.G.; Kitamura, T.; Fujiwara, Y. Acc. Chem. Res. 2001, 38, 633. (d)
Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2001, 19, 2437. (e) Labinger, J. A.;
Bercaw, J. E. Nature 2002, 417, 507. (f) Periana, R. A.; Bhalla, G.; Tenn III, W.J.;
Young, K. J. H.; Liu, X. Y.; Mironov, O.; Jones, CJ; Ziatdinov, V. R. J. Mol. Cat
A. Chem. 2004, 220, 7.
2
Dick, A. R.; Sanford, M. S. Tetrahedron 2006, 62, 2439 and citations therein.
3
(a) Arndtsen, B. A.; Bergman, R. G. Science 1995, 270, 1970. (b) Wong-Foy, A.
G.; Bhalla, G.; Liu, X. L.; Periana, R. A. J. Am. Chem. Soc. 2003, 125, 14292. (c)
Ben-Ari, E.; Gandelman, M.; Rozenberg, H.; Shimon, L. J. W.; Milstein, D. J. Am.
Chem. Soc. 2003, 125, 4714.
4
Tenn, W. J., III; Young, K. J. H.; Bhalla, G.; Oxgaard, J.; Goddard, W. A., III;
Periana, R. A. J. Am. Chem. Soc. 2005, 127, 14172.
5
Feng, Y.; Lail, M.; Barakat, K. A.; Cundari, T. R.; Gunnoe, T. B.; Petersen, J. L.
J. Am. Chem. Soc. 2005, 127, 14174.
6
Klei, S. R.; Golden, J. T.; Tilley, T. D.; Bergman, R. G. J. Am. Chem. Soc. 2002,
124, 2092 and citations therein.
7
(a) Jones, W. D. Acc. Chem. Res. 2003, 36, 140. (b) Jones, W. D.; Feher, F. J. J.
Am. Chem. Soc. 1986, 108, 4814. (c) Bhalla, G.; Liu, X. Y.; Oxgaard, J.; Goddard,
W. A., III; Periana, R. A. J. Am. Chem. Soc. 2005, 127, 11372.
8
For further computational details, see Experimental Section.
9
We are examining higher TON and reaction times to ensure that the system in
under thermodynamic control.
10
Tenn, W. J., III; Young, K. J. H.; Bhalla, G.; Oxgaard, J.; Goddard, W. A., III;
Periana, R. A. J. Am. Chem. Soc. 2005, 127, 14172.
91
11
Sheldrick, G. M. SHELXTL, version5.1; Bruker Analytical X-ray System, Inc.:
Madison, WI, 1997.
12
Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38.
13
Jaguar 6.0, Schrodinger, Inc., Portland, Oregon, 2004, Jaguar 6.5, Schrodinger,
Inc., Portland, Oregon, 2005.
14
Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
15
Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
16
Baker, J.; Muir, M.; Andzelm, J.; Scheiner, A. In Chemical Applications of
Density-Functional Theory; Laird, B. B., Ross, R. B., Ziegler, T., Eds.; ACS
Symposium Series 629; American Chemical Society: Washington, DC, 1996.
17
Niu, S.; Hall, B. M. Chem. Rev. 2000, 100, 353.
18
(a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299. b) Goddard, W. A., III
Phys. Rev. 1968, 174, 659. (b) Melius, C. F.; Olafson, B. O.; Goddard, W. A., III
Chem. Phys. Lett. 1974, 28, 457.
19
(a) Hariharan, P. C.; Pople, J. A. Chem. Phys. Lett. 1972, 16, 217. (b) Francl, M.
M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon, M. S.; DeFrees, D. J.;
Pople, J. A. J. Chem. Phys. 1982, 77, 3654.
20
(a) Tannor, D. J.; Marten, B.; Murphy, R.; Friesner, R. A.; Sitkoff, D.; Nicholls,
A.; Ringnalda, M.; Goddard, W. A., III; Honig, B. J. Am. Chem. Soc. 1994, 116,
11875. (b) Marten, B.; Kim, K.; Cortis, C.; Friesner, R. A.; Murphy, R. B.;
Ringnalda, M. N.; Sitkoff, D.; Honig, B. J. Phys. Chem. 1996, 100, 11775.
92
4 Mechanistic Analysis of Iridium Heteroatom CH
Activation
4.1 Introduction.
There has been great progress in the development of new alkane activation
catalysts based on mechanisms ranging from Oxidative Addition (OA) to Sigma-
Bond Metathesis (SBM) and Electrophilic Substitution (ES). However, a
commercially viable catalyst has yet to be announced. We analyze here the
mechanism responsible for CH activation in a recent system published by us, and
identify it as an Internal Electrophilic Substitution (IES). Based on this IES
mechanism we suggest guidelines for choices in metals and ligands expected to
have lower activation barriers than currently known catalysts.
Recently, we published a joint experimental/theoretical account of the first
intermolecular CH activation reaction with a metal -alkoxo complex (acac-
O,O)
2
Ir(III)(OMe)(Py) (1).
1
The mechanism for the CH activation step was
tentatively described as a SBM, based on the geometry of the reacting atoms in the
transition state ( TS1, see Figure 4.1). Gunnoe and Cundari studied the H/D
exchange for a similar reaction catalyzed by TpRu(PMe
3
)(OH) ( 2),
2
and also
proposed that the operative mechanism resembles SBM.
2a
93
Figure 4.1. Left: The CH activation transition state TS1, where a hydrogen is
transferred from a benzene to a methoxo group. Right: Close-up of
the four relevant atoms in TS1.
However, a more detailed analysis of TS1 shows that this earlier
assignment was incorrect. We report here the computational analysis of TS1 plus a
more detailed study of a simplified model system. This shows that the mechanism
is not traditional SBM; rather it reacts through a mechanism we denote as Internal
Electrophilic Substitution (IES). This is most likely analogous to the mechanism
for metal -catalyzed dihydrogen cleavage,
3
as postulated by Gunnoe et al.
4
In
addition, Gunnoe et al. pointed out the possibility that the lone pair could be
important for this type of transformation,
4
although, to the best of our knowledge,
no orbital analysis of either H -H or C-H cleavage under these conditions has been
conducted. Also, it might be related to the well known early metal M=NR
2
type
CH activation, which reacts through a [1,2] insertion mechanism.
5
1.41 Å 1.29 Å
2.08 Å 2.22 Å
1.98 Å
94
4.2 Results and Discussion.
The calculations were performed using the B3LYP functional with the
LACVP** basis and effective core potential treatment of the Ir (17 explicit
electrons), as implemented by the Jaguar 6.5 program package.
6
Orbital analysis
was performed by localizing orbitals using the Pipek-Mezey (PM) methodology as
well as single-point GVB calculations. Although only the PM orbitals are shown
in this report, both sets of orbitals agree.
To ensure that the calculated mechanism is not a computational artifact, we
compared calculated and experimental deuterium kinetic isotope effects (KIE).
The computationally predicted KIE (k
H
/k
D
) for TS1 was calculated to 3.2.
7
The
experimental KIE was determined to 3.04 ±0.20 by reaction of 1 with neat 1,3,5-
trideuterobenzene (see supplemental material for details), in very good agreement
with the theoretical KIE. It should be noted that we do not expect to be able to
differentiate between, for example, SBM and IES based solely on the predicted
KIE. However, the convergence between experimental and theoretical KIE’s
strongly indicates that the theoretical description of the transition state is correct.
The impetus for this investigation was the question of whether the lone pair
of the alkoxo group participates in the reaction, as illustrated in Figure 2. In this
conceptual view, we expect that the M-O bond is transformed into an oxygen lone
pair (which eventually coordinates to an empty d-orbital on the metal) while the O-
H bond is formed from one of the lone pairs. This is unlike SBM, where the X -H
95
bond is based on the same orbital as the X-M bond (Figure 2, left).
8
The formerly
bonding C-H orbital, on the other hand, should in the transition state be
delocalized over both the breaking C-H bond and the forming M-C bond, as would
be expected from a traditional SBM TS. Finally, in the IES mechanism, the
migrating hydrogen must cross an orbital's nodal plane during the reaction, while
in SBM it does not.
Figure 4.2. Conceptual orbital view of Sigma-Bond Metathesis (left) and Internal
Electrophilic Substitution (right).
Orbital analysis of the transition state shows that the forming O-H bond is
not based on the same orbital as the breaking O-Ir bond. To illustrate the orbital
interactions more clearly, calculations on a model compound were carried out.
The complex Ir(CH
3
)
2
(NH
3
)
2
(OH)(CH
4
), where the two NH
3
ligands are in the
equatorial position with regard to OH and CH
4
, was chosen to minimize
interference from lone pairs on the spectator ligands. The energetics from the
M
C
H
3
H
3
C
M
CH
3
H
3
C
H
H M
O
H
H
3
C
M
OH
H
3
C
H
H M
CH
3
H
3
C
H
M
O
H
CH
3
H
96
model transformation are reasonably similar (?H = -8.6 kcal/mol, ?H
‡
= 14.5
kcal/mol, as compared to -16.7 and 8.4 for the Ir(acac)
2
(OMe)(C
6
H
6
) system). A
model compound with an even closer energetic profile could most likely be found,
but we do not expect this to make any difference to our conclusion, especially
since our calculations on TS1 exhibits a similar orbital picture, albeit with
significant interference from the p orbitals on the acac.
These DFT investigations have shown that the reacting localized orbitals
correspond well to the conceptual orbitals shown in Figure 4.2. Particularly
interesting is the lack of sign change in the reacting orbitals, which is contrary to
the SBM mechanism (see Figure 4.2, left).
In the IES m echanism, the bonding CH
3
-H orbital donates to an empty d-
orbital on the metal in the form of a s -complex. During the reaction coordinate
this orbital swells out to allow for a bonding interaction with both the metal and
the H, and eventually shrinks back to form a bonding M-CH
3
orbital. Even though
the orbital is chiefly centered on the ligand, it is clear that some electron density
has been donated to the metal d-orbital.
The changes in the other two orbitals are less obvious. The oxygen lone
pair changes spatial direction due to the changes in geometry during the reaction,
but retains its overall shape. The same is true for the bonding M-O orbital,
although there appears to be some bonding character to the H in the transition
state.
97
By following the charges on the four reacting atoms during the
transformation (Mulliken charges on select IRC points shown in Figure 4.3), it can
be seen that some charge reorganization occurs, particularly in the hydrogen,
which goes from 0.21 e
-
in the starting material, through 0.37 e
-
in the TS and
ending at 0.38 e
-
in the product. Intriguingly, the charge on H is actually greater
just after the TS, peaking at ~0.41 e
-
. The charge on the iridium, on the other hand,
changes very little, from -0.06 e
-
through -0.10 e
-
to -0.05 e
-
. The methyl group
develops more negative character in the TS, from 0.06 e
-
to -0.06 e
-
, and reaches -
0.14 e
-
in the product. The OH group changes little before the TS (from -0.35 e
-
to
-0.29 e
-
) but becomes significantly more positive after the TS, ending up at -0.16 e
-
in the product. The balance of charge is donated to the spectator ligands, with no
particular concentration. Overall, electron density is thus transferred mainly from
the hydrogen and the OH group to the methyl group and the spectator ligands, the
latter presumably through the iridium.
98
Figure 4.3. Mulliken charges (in electrons) on the reacting moieties Ir (circles), H
(diamonds), CH
3
(triangles) and OH (squares) during the IRC of the
model reaction.
Based on this analysis, it appears that an electrophilic metal activates the
C-H bond by generating a positively charged hydrogen. This type of mechanism
is well known in related mechanisms involving platinum,
9
palladium,
10
, and
gold,
11
and is normally referred to as “Electrophilic Substitution”.
12
None of the
previously known systems are directly bonding to the base which abstracts the
hydrogen, however, which is a marked distinction, and we thus label this variant of
the mechanism “Internal Electrophilic Substitution”, or IES.
It should be noted that an analogue of the IES mechanism has been known
for quite some time in the field of metal -catalyzed dihydrogen activation, where it
is referred to as “heterolytic cleavage”.
3
This appears to be an overly broad term,
however, as there does not appear to be a consensus regarding the details of this
mechanism. Indeed, while the possibility that the lone pair does play a major role
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
Ir
OH
H
CH3
M
OH
H
3
C
H
M
O
H
CH
3
H
M
O
H
H
3
C
H
Mulliken charges (in e
-
) on reacting atoms
99
has been pointed out,
4
the transition state has also been described as a quadropolar
ionic transition state or as a SBM.
2a,3a
It is anticipated that the mechanistic
analysis presented for the CH
4
case is equally valid for H
2
(which would rule out
SBM) and we are currently investigating suitable systems for a detailed analysis.
Furthermore, despite the small peak in charge reorganization in the latter part of
the IES, it is more reminiscent of an asymmetric sigmatropic rearrangement than a
quadropolar transition state (which, in our view, implies a mainly ionic transition
state) and we thus do not believe this term is fitting for the current mechanism.
While the definition of precise language regarding mechanisms is
worthwhile in its own right, the ultimate utility is whether it provides sufficient
insight into the chemistry to suggest improved catalysts. It is expected that the
internal aspect of the IES would not benefit from changes due to substitutions in
the M-XR moiety, as a change affecting the energy of the lone pair would equally
affect the energy of the M-X bond. Indeed, preliminary calculations on
Ir(acac)
2
(X)(C
6
H
6
) where X = OCH
3
, OCF
3
, NH
2
indicates that this assumption is
correct, as the barriers change less than 2 kcal/mol.
Conversely, making the metal more electrophilic by removing electron
density should promote the transfer of the hydrogen, thereby reducing the barrier.
Preliminary calculations on the fluorinated analogue model complex
Ir(CH
3
)
2
(NF
3
)
2
(OH)(CH
4
) show that replacing the NH
3
groups with NF
3
groups
reduces the barrier by 6.8 kcal/mol.
100
Furthermore, the use of the lone pair might require a d
6
(or higher) metal,
since a lower d occupation on the metal could stabilize the lone pair through the
formation of an oxo species. Indeed, preliminary calculations on a singlet d
4
Re(acac)
2
system shows that the barrier for CH activation increases by up to 20
kcal/mol. (However, we have not yet established that the higher barrier is caused
by stabilization of the lone pair.)
Based on the IES mechanism we can now suggest strategies for the design
of more reactive M-X type CH activation catalysts. The first suggestion is
focusing on d
6
and higher metals, preferably with highly donating d -orbitals that
are expected to repulse the M -X lone pair. Second, low electron density on the
metal is advantageous, which would suggest Pt
II
and Pd
II
centers. However, since
the d-orbitals on these systems are not particularly donating, it is possible that a
compromise must be found between electrophilic center and the energy of the d-
orbital. Thus, in addition to the reported systems featuring Ir
III
and Ru
II
, we
suggest Os
II
and possibly Re
I
as likely candidates. Finally, regardless of which
metal is used, it is clear that ligands with low electron donating character are
beneficial. Thus, we predict that replacing the acacs in 1 with the electron
withdrawing analog ( 1,1,1,5,5,5-hexafluoropentane-2,4-dionate) or replacing the
PMe
3
group in 2 with PF
3
or OH
2
would improve the barriers by 3-4 kcal/mol.
101
4.3 Experimental Section.
Deuterium kinetic isotope effect on benzene CH activation by (acac-
O,O)
2
Ir(OCH
3
)(Py) 1: Three 5 mL Schlenk tubes were charged with 10 mg of 1,
and 0.5 mL of 1,3,5-trideuterobenzene under an atmosphere of argon. The tubes
were then placed in a temperature controlled oil-bath maintained at 180 °C until
the reaction had reached 5 % completion. The tubes were then cooled and methyl
lithium was added. The gas phase was then analyzed via GCMS. The molar ratio
of the liberated methane isotopologues was determined using a deconvolution
spreadsheet calibrated with known mixtures of methane isotopologues. The liquid
phase was analyzed to ensure that deuterium scrambling was minimized in the
starting materials. Control experiments without added 1, and with 1 but without
heating were also carried out, each in triplicate, to account for background
generation of methane from reactions with methyl lithium.
Ir
O O
O O
O
CH 3
N
D
D D
+
N
Ir
O O
O O
D D
D
+
N
Ir
O O
O O
D D
+ CH 3 OH + CH 3 OD
180
o
C
3.04 : 1
Scheme 4.1. Determination of Deuterium Kinetic Isotope Effect on CH Cleavage
by 1.
Theoretical Calculations: All calculations were performed using the hybrid
DFT functional B3LYP as implemented by the Jaguar 6.0 and Jaguar 6.5 program
102
packages. This DFT functional utilizes the Becke three-parameter functional (B3)
combined with the correlation functional of Lee, Yang, and Par
(LYP), and is
known to produce good descriptions of reaction profiles for transition metal
containing compounds.
The metals were described by the Wadt and Hay
core-
valence (relativistic) effective core potential (treating the valence electrons
explicitly) using the LACVP basis set with the valence double- contraction of the
basis functions, LACVP**. All electrons were used for all other elements using a
modified variant of Pople’s
6-31G** basis set, where the six d functions have been
reduced to five.
All geometries were optimized and evaluated for the correct number of
imaginary frequencies through vibrational frequency calculations using the
analytic Hessian. Zero imaginary frequencies correspond to a local minimum,
while one imaginary frequency corresponds to a transition structure.
To reduce computational time the methyl groups on the acac ligands were
replaced with hydrogens. Control calculations show that relative energies of
intermediates and transition structures change less than 0.1 kcal/mol when methyl
groups are included.
The deuterium kinetic isotope effect calculated for the reaction of 1,3,5-
trideuterobenzene with (acac-O,O)
2
Ir(III)(OCH3)(Pyr) assumes that generation of
MeOH and MeOD involve the same intermediates up until the arene complex
(acac-O,O)
2
Ir(III)(OCH
3
)(C
6
H
3
D
3
) (below, 1). Using transition state theory, the
kinetic isotope effect is then where G
TS-H
and G
TS-D
contain the mass dependent
103
quantities (zero point energy and vibrational enthalpy and entropy at 473K)
evaluated using the appropriately mass-weighted Hessians.
Ir
C 6H 3D 3
OCH 3
Ir
C 6H 2D 3
H 3CO
H
k
H
1
rate
H
k
H
rate
D
k
D
= = exp( )
-((GTS-H - G
1
)- (GTS-D-G
1
))
kT
KIE =
Ir
C 6H 3D 2
H 3CO
D
k
D
TS-D
= exp( )
-(GTS-H - G TS-D)
kT
= 3.0
TS-H
Classical:
Scheme 4.2. Computational Determination of Deuterium Kinetic Isotope Effect by
DFT.
The tunneling was evaluated to 1.05 according to the m ethod by Skodje
and Thrular
1
(imaginary frequency of TS-H = -822.00 cm
-1
, TS-D = -646.32 cm
-1
.
Multiplying the classical KIE of 3.0 with the tunneling correction of 1.05 yields a
total KIE of 3.2.
104
4.4 References.
1
(a) Tenn, W. J. III ; Young, K. J. H.; Bhalla, G.; Oxgaard, J.; Goddard, W. A. III;
Periana, R. A.; J. Am. Chem. Soc. 2005, 127, 14172. (b) Tenn, W. J. III ; Young,
K. J. H.; Nielsen, R.J.; Oxgaard, J.; Periana, R. A.; Goddard, W. A. III
Organometallics 2006, 25, 5173.
2
(a) Feng, Y.; Lail, M.; Foley, N. A.; Gunnoe, B.; Barakat, K. A.; Cundari, T.A.
Petersen, J. L. J. Am. Chem. Soc. 2006, 128, 7982. (b) Feng, Y.; Lail, M.; Barakat,
K. A.; Cundari, T. R.; Gunnoe, T. B.; Petersen, J. L. J. Am. Chem. Soc. 2005, 127,
14174.
3
(a) Kubas, G. J. Catalysis Letters 2005, 104, 79. (b) Hedberg, C.; Kallstrom, K.;
Arvidsson, P. I.; Brandt, P.; Andersson, P. G. J. Am. Chem. Soc. 2005, 127, 15083.
(c) Yamakawa, M.; Ito, H.; Noyori, R. J. Am. Chem. Soc. 2000, 122, 1466. (d)
Fryzuk, M. D.; Montgomery, C. D.; Rettig, S. J. Organometallics 1991, 10, 467.
(e) Fryzuk, M. D.; Bhangu, K. J. Am. Chem. Soc. 1988, 110, 961. f) Joubert, J.;
Delbecq, F. Organometallics 2006, 25, 854.
4
Conner, D.; Jayaprakash, K.N.; Cundari, T. R.; Gunnoe, T. B. Organometallics
2004, 23, 2724.
5
(a) Hoyt, H. M.; Michael, F. E.; Bergman, R. G. J. Am. Chem. Soc. 2004, 126,
1018. (b) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem.
Res. 2002, 35, 44. (c) Cundari, T. R.; Klinckman, T. R.; Wolczanski, P. T. J. Am.
Chem. Soc. 2002, 124, 1481. (d) Bennett, J. L.; Wolczanski, P. T. J. Am. Chem.
Soc. 1997, 119, 10696. (e) Bennett, J. L.; Wolczanski, P. T. J. Am. Chem. Soc.
1994, 116, 2179. (f) Cummins, C. C.; Baxter, S. M.; Wolczanski, P. T. J. Am.
Chem. Soc. 1988, 110, 8731. (g) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J.
Am. Chem. Soc. 1988, 110, 8729.
6
Jaguar 6.5, Schrodinger, Inc., Portland, Oregon, 2005.
7
For further computational details, see supporting information.
8
Ziegler, T.; Folga, E.; Berces, A. J. Am. Chem. Soc. 1993, 115, 636.
9
(a) Shilov, A. E. Activation of Saturated Hydrocarbons by Transition Metal
Complexes (Reidel, Dordrecht, Netherlands, 1984). (b) Periana, R. A.; Taube, D.
J.; Gamble, S.; Taube, H.; Satoh, T.; Fujii, H. Science 1998, 280, 560.
105
10
Periana, R. A.; Mironov, O.; Taube, D.; Bhalla, G.; Jones, C. J. Science 2003,
301, 814.
11
Jones, C; Taube, D.; Ziatdinov, V. R.; Periana, R. A.; Nielsen, R. J.; Oxgaard,
J.; Goddard, W. A. III Angew. Chem. Intl. Ed. 2004, 43, 4626.
12
Shilov, A. E.; Shul'pin, G. B. Chem. Rev. 1997, 97, 2879.
106
5 Synthesis and Structural Characterization of
Novel, Organometallic, Rh(III), bis-
(acetylacetonate) Complexes
5.1 Introduction.
Recently, we reported the first catalytic, intermolecular, anti-Markovnikov,
hydroarylation of unactivated olefins with unactivated arenes, by a homogeneous,
bis-chelating, O -donor Ir(III) complex,
1
(acac)
2
Ir(R)(L), based on the simplest ß-
diketonate, acetylacetonate, acac. Experimental and theoretical studies
2
suggest
that: A) the trans-O-donor, bis-bidentate Ir(III) motifs are remarkably thermally
stable to air and acids; B) the bis-acac ligand motif can provide access via trans to
cis isomerization to coordinatively unsaturated, 5-coordinate, square pyramidal
geometries that can be useful for catalysis; C) the active species is the
organometallic complex, (acac)
2
Ir(Ph)(L); D) catalysis occurs by arene CH
activation that involves an Ir(V) intermediate or transition state and E) the rate
determining step is olefin insertion. Intriguingly, while formation of olefins could
be expected from facile ß-hydride eliminations reactions, no olefinic products are
observed in stoichiometric or catalytic reactions with these O-donor Ir(III)
systems. Calculations and experimental results suggest that this could be due a
combination of the high barrier for ligand dissociation from the cis-octahedral
intermediates and the electron -withdrawing characteristics of the O-donor ligands
that, while allowing olefin insertion and CH activation, destabilize the Ir(III)
107
center to formation of stable olefinic complexes.
2
Both experimental and
theoretical studies suggest that the trans to cis isomerization of the O-donor, bis-
bidentate motif is required for reactivity and that this step may contribute to the
overall reaction rate. Given the broad potential utility of efficient catalysts for
olefin hydroarylation (such as heteroatom tolerance and regio and stereo control)
we have begun a systematic study of the structure-function relationships in this
class of complexes by exploring variations in the metal center as well as the bis-
bidentate, O-donor ligands.
The ultimate objectives of these studies will be to determine the
fundamental requirements for effective catalysis with this promising class of
complexes and to use this information to synthesize new, stable catalysts with
higher rates and selectivities. On the basis of the general expectation that the steps
contributing to the hydroarylation reaction, ligand loss, trans to cis-isomerization,
CH activation and olefin insertion, could be expected to be faster on replacement
of Ir(III) with Rh(III), we sought to synthesize the Rh(III) organometallic
analogue, (acac)
2
Rh(Ph)(L), of the active Ir(III) catalyst. While some steps could
be expected to be more facile with Rh(III) compared to Ir(III), given the possible
involvement of Ir(V) in the (acac)
2
Ir(Ph)(L) catalyst
1,2
and the expected difficulty
of accessing this oxidation state for Rh, the relative efficiencies of these catalysts
is not obvious. Unfortunately, in spite of the ubiquity of these long-known ß-
diketonate ligands and while many late transition metal, tris-acac complexes have
been reported, no rational syntheses of late transition metal, organometallic
108
complexes with bis-acac ligands have been reported. We now report the first
rational synthesis of the Rh(III) bis-acac, organometallic complex, III and
analogues of this material.
5.2 Results and Discussion.
The syntheses of new, trans-bis-diketonate complexes of Rh(III) with the
simplest ß-diketonate, acetylacetonate, acac, are summarized in Scheme 5.1. To
our knowledge this is the first rational route for the direct syntheses of bis-acac
Rh(III) complexes. It is noted that the products of the reaction of RhCl
3
·XH
2
O
with β-diketonate ligands strongly depend on the reaction temperature and solvent.
Well defined products include Rh(acac)
3
4
and Rh(acac)(H-acac)Cl
2
5
(where H-
acac is the acetylacetone) when different reaction conditions are used. Previous
attempts to synthesize trans bis-acac Rh(III) complexes have failed.
6
However,
we note that complex I is the same compound that has been reported earlier as a
trace product from the synthesis of Rh(acac)
3
. The only characterization reported
was an X-ray diffraction structure.
6
109
O
CH
3
H
Rh
O O
O O
O
H H
Rh
O O
O O
O
Cl
Rh
O O
O O
Cl
Na
RhCl
3
.xH
2
O
acacH / NaHCO3
Acetone / H
2
O
acacH / NaHCO3
CH
3
OH
Ph
2
Hg
CH3OH/CHCl3
I II
III
70
o
C 140
o
C
70
o
C
Scheme 5.1. Synthesis of (acac-O,O)
2
Rh(III) Complexes.
Heating RhCl
3
·XH
2
O with two equivalents of H -acac and two equivalents
of NaHCO
3
in a mixture of H
2
O/CH
3
COCH
3
at 70
o
C for 16 hr led to a mixture of
the Na[trans-(acac)
2
RhCl
2
], I. Complex I is an orange-yellow, air and water stable
microcrystalline compound. Complex I was precipitated from a concentrated
methanol solution of the reaction mixture at -30
o
C. The
1
H NMR spectrum of I
shows single resonance signals for the methyl and methine proton of the acac
ligand at their usual chemical shifts that implies a symmetric environment for the
two acac ligands as expected for the trans geometry. It was not anticipated that
this could be a mono-acac Rh complex as these typically show rather complicated
1
H NMR spectra due to the existence of isomers in solution. This assignment was
confirmed by a low temperature, single crystal X -ray diffraction study of I.
8
The
molecular structure of I is shown in Figure 5.1. Each Rh atom adopts octahedral
coordination geometry, with four O atoms of the two acac ligands in the same
plane. Two O atoms from adjacent octahedral are simultaneously in contact with
110
Na
+
ions, together with two CH
3
OH molecules at cis positions, to form a distorted
Na octahedron with a --Rh--Na--Rh-- polymeric chain structure, in which
neighboring Rh(acac)
2
equatorial planes are inclined to each other at an angle of
77
o
. It is noted that although the geometry of the Rh core is the same as that
reported by others,
6
the cell composition is different because of the different
number and types of solvent molecules in the unit cell.
Figure 5.1. Thermal ellipsoid plot of I (50% probability thermal ellipsoids),
showing the [Rh(acac)
2
Cl
2
]
-
complex anion (top); each complex is
bridged to the next by a cis-[Na(CH
3
OH)
2
]
+
in the crystal lattice
(bottom).
111
Interestingly, when the reaction of RhCl
3
(H
2
O)
3
with two equivalents of H-
acac and two equivalents of NaHCO
3
in a H
2
O/CH
3
COCH
3
mixture was carried
out at 140
o
C for 2 hr, a new organometallic species Rh(acac)
2
(CH
2
COCH
3
)(H
2
O)
(II) separated as a yellow and air and water stable microcrystalline solid with 59%
yield. The X -ray structure of II is shown in Figure 5.2. The analogous acetonyl Ir
analogue can be obtained by CH Activation of acetone
1a
and if a similar CH
activation reaction is responsible for the formation of this Rh analogue this
suggests that the Rh analogues could be active for CH activation. This is being
investigated. The molecular structure of this complex is also octahedral , with two
acac ligands in a trans relationship. The average Rh-O distance (1.993(3)Å) is
slightly shorter than that in complex I (2.009(2)Å). The Rh-C distance (2.042(5)Å)
is similar to those in other Rh(III) complexes having different ligands.
7
The
1
H
NMR spectrum of II is consistent with its solid state structure. The resonances of
the acac ligands are very similar to those in complex I but shifted to higher field
because of replacement of the Cl with the more electron rich acetonyl ligand in II.
The most diagnostic feature in the spectrum is the doublet resonance of the Rh-
bonded CH
2
group at 3.63 ppm, with a coupling of 3Hz (
2
J
Rh-H
, Rh-C-H coupling).
The
13
C{
1
H} NMR resonance of this Rh bonded CH
2
group appears at 31 ppm as a
doublet.
112
Figure 5.2. Thermal ellipsoid plot of II (50% probability), showing the σ-bonded
-CH
2
COCH
3
ligand and a water ligand in axial positions. The
hydrogen atoms of the aqua ligand have not been located and were
omitted.
113
Figure 5.3. Thermal ellipsoid plot of III (50% probability). Two molecules of
cocrystallized CHCl
3
have been omitted for clarity. The hydrogen
atom of the methanol ligand was not located and was omitted.
Treatment of I with Ph
2
Hg in CHCl
3
/CH
3
OH at 70
o
C gave the air and
water stable organometallic complex (acac)
2
Rh(Ph)(CH
3
OH), III. The structure of
III was confirmed by X -ray diffraction as shown in Figure 5.3. The geometry of
the Rh atom in III is very similar to that in I and the Ir analogue. The Rh---C(of
Ph) distance, 1.970(3)Å in III is slightly shorter than the Rh--C(of CH
2
COMe)
distance, 2.042(5)Å in II, presumably due to the difference in covalent radii
between C(sp
2
) and C(sp
3
) atoms. The
1
H NMR spectrum of III is consistent with
114
this structure and shows simple singlets for both the methyl and the methine
groups of the acac ligands. The resonance of the Ph group appears at about 6.8
ppm, which is comparable to that in its Ir analogue.
1a
Encouragingly, preliminary studies show that these complexes are both
thermally stable and are active for CH activation of arenes in reactions with acetic
acids. Complex III, (acac)
2
Rh(Ph)(CH
3
OH), was found to be an active catalyst for
H/D exchange between benzene and acetic acid-d
1
, with and average TOF of 0.2 s
-
1
for the catalytic reaction. The TOF of the analogous reaction with trifluoroacetic
acid-d
1
was determined to be 0.4 s
-1
.
In conclusion, we have prepared several novel bis-acetylacetonate Rh(III)
compounds with the same structure and composition as the Ir catalysts we
previously reported for the hydroarylation of olefins.
1
With the development of a
general, rational synthesis to the class of O -donor Rh(III) arylated and alkylated
complexes in hand, efforts are now underway to explore the scope of catalytic and
reaction chemistry of these O-donor, bis-bidentate, Rh(III) complexes.
5.3 Experimental Section.
Reagent-grade chemicals and solvents were used as purchased from
Aldrich or Strem. NMR spectra were obtained on a Bruker AM-360 spectrometer,
measured at 360.138 MHz for
1
H and 90.566 MHz for
13
C or on a Bruker AC-250
spectrometer, measured at 250.134 MHz for
1
H and 62.902 MHz for
13
C.
Chemical shifts are given in ppm. High-resolution mass spectra were obtained by
115
UCLA Pasarow Mass Spectrometry Laboratory on a MALDI-TOF mass
spectrometer.
Synthesis of Na[Rh(acac)
2
Cl
2
] (I). To a 50mL Shlenk flask containing a
solution of 5 mL of methanol containing 128.8mg of RhCl
3
•3H
2
O (40% Rh, 0.5
mmol), 200 mg (1 mmol) of acacH (2,4-pentanedione) and 168 mg (1 mmol) of
NaHCO
3
was added. The mixture was heated to 70
o
C for 16 hrs. The solution was
filtered through a plug of celite and solvent was removed in vacuo. The residue
was recrystallized in methanol at -20
o
C to yield 230 mg Na[Rh(acac)
2
Cl
2
] (58%)
as a yellow-orange crystalline solid.
1
H NMR (CD
3
OD): d 5.55(s, 2H, O -acac-
CH), 2.15(s, 12H, O-acac-CH
3
).
13
C{
1
H}NMR(CD
3
OD): d ? 190.4(s, O-acac,
C=O), 100.2(s, O-acac, CH), 26.5(s, O-acac, CH
3
).
Synthesis of Rh(CH
2
COCH
3
)(acac)
2
(H
2
O) (II). In a 100 mL Schlenk flask,
100 mg of RhCl
3
•3H
2
O (40% of Rh, 0.388 mmol), 78 mg (0.776mmol) of acacH
(2,4-pentanedione), and 65 mg of NaHCO
3
(0.776mmol) were mixed in a solution
of 10 mL of acetone and 5 mL of H
2
O. The mixture was heated to 140
o
C with
stirring for 2hrs. The yellow solution was filtered through a plug of celite, and the
solvent was removed in vacuo. The solid obtained was recrystallized from
methanol/diethyl ether at -20
o
C to yield 89 mg (59%) of the complex as a light
orange solid.
1
H NMR (CDCl
3
): d 5.37(br, s, 2H, acac-CH), 3.63(d, J
RhH
= 3 Hz,
2H, CH
2
CO), 2.08(s, 12H, acac-CH
3
), 1.96(s, 3H, COCH
3
).
13
C{
1
H}NMR(CD
3
OD): d 220.7? ? s, CH
2
COCH
3
, C=O??? 189.2(s, O-acac, C=O),
116
100.9(s, O-acac, CH), 31.0(d, CH
2
COCH
3
, CH
2
), 26.9(s, O-acac, CH
3
), 20.1(s,
CH
2
COCH
3
, CH
3
), 19.6(s, CH
3
OH, CH
3
). m/z 359.0393
{[Rh(acac)
2
(CH
2
COCH
3
)H]
+
}, 342.0231 {[Rh(acac)
2
(CH
2
CO)]
+
}, 300.9966
{[Rh(acac)
2
]
+
}.
Synthesis of Rh(acac)
2
(Ph)(CH
3
OH) (III). To a Schlenk flask containing a
solution of CH
3
OH and CHCl
3
(2:1) 50 mg (0.127 mmol) of Na[Rh(acac)
2
Cl
2
]
and 45 mg (0.127 mmol) of diphenyl mercury was added. The mixture was heated
at 70
o
C for 1 hr to get a pale yellow solution containing a white precipitate. The
solution was filtered through a plug of celite and evaporated to dryness in vacuo.
The residue was recrystallized from CH
3
OH/CH
2
Cl
2
at -20
o
C to yield 23 mg
(yield: ~50%) of a pale yellow solid.
1
H NMR (CD
3
OD): d 7.09(m, 5H, Ph),
5.39(s, 2H, acac-CH), 2.01(s, 12H, acac-CH
3
),
13
C{1H}NMR(CD
3
OD): d 189.9(s,
O-acac, C=O), 147.7(s, Ph), 133.4(s, Ph), 127.9(s, Ph), 125.4(s, Ph), 97.4(s, O-
acac- CH), 26.6(s, O-acac- CH
3
). m/z 401.0227 {[Rh(acac)
2
(Ph)Na]
+
}, 300.9950
{[Rh(acac)
2
]
+
}.
X-ray Crystal Structure Determinations of [Rh(acac)
2
Cl
2
]Na (I),
[Rh(acac)
2
(CH
2
COCH
3
)(H
2
O)] (II), and [Rh(acac)
2
(Ph)(CH
3
OH)] (III).
X-ray data were collected at 85K for complexes I and II and at 149K for
complex III, on a SMART APEX CCD diffractometer with graphite-
monochromated Mo-Ka radiation (λ = 0.71073 Å). The cell parameters for each
compound were obtained from the least-squares refinement of the spots (from 60
117
collected frames) using the SMART program. In each case, a hemisphere of data
was collected up to a resolution of 0.75Å, and intensity data were processed using
the SAINT PLUS program. Empirical absorption corrections were applied using
SADABS, and all calculations for the structural analyses were carried out using
the SHELXTL package. Initial positions of the Rh atoms were located by direct
methods, and the rest of the atoms found using conventional heavy atom
techniques. The structures were refined by least-squares methods using data in the
range of 2θ = 3.5 to 55.0º. All non -hydrogen atoms in the three complexes were
anisotropically refined, and calculated hydrogen positions were varied in a riding
manner along with their attached carbons.
In complex I, the rhodium atom is situated on a center of inversion, so each
of the two halves of the molecule is related to the other half by this symmetry
operation.
118
5.4 References.
1
(a) Periana, R. A.; Liu, X. Y.; and Bhalla, G. Chem. Commun., 2002, 3000. (b)
Matsumoto, T.; Taube, D. J.; Periana, R. A .; Taube, H.; Yoshida, H. J. Am.
Chem. Soc., 2000, 122, 7414.
2
Oxgaard, J.; Muller, R. P.; Goddard, W. A. III; Periana., R. A.; J. Am. Chem.
Soc., 2003, 126, 352.
3
(a) Suzuki, H.; Matsuura, S.; Moro-Oka, Y.; Ikawa, T. J. Organomet. Chem.
1985, 286, 247. (b) Kaneda, K.; Azuma, H.; Wayaku, H.; Teranishi, S. Chem.
Lett., 1974, 3, 215.
4
Belyaev, A. V.; Venediktov, A. B.; Fedotov, M. A.; Khranenko, S. P.
Koordinats. Khim., 1985, 11, 794.
5
Sarkhel, P.; Paul, B. C.; Poddar, R. J. Indian J. Chem., 1999, 38A, 150.
6
Podberezskaya, N. V.; Romanenko, G. V.; Khranenko, S. P.; Belyaev, A.V. J.
Struc. Chem., 1997, 38, 620.
7
Gerisch, M.; Krumper, J. R.; Bergman, R. G.; Tilley, T. D. Organometallics
2003, 22, 47.
8
Crystal data for I: a orange prisim-shaped crystal of dimensions 0.295 x 0.045 x
0.045 mm was grown from methanol at –30
o
C. C
12
Cl
2
NaO
6
Rh-H
2
O: monoclinic,
group C2/c, a = 19.476(4) Å, b = 8.9430(14) Å, c = 13.154(3) Å, V = 1812.1(6)
Å
3
, Z = 4, T = 85(2) K, D
calcd
= 1.675 Mg/m
3
, R(F) = 2.61 for 5334 observed
reflections. All non -hydrogen atoms were refined with anisotropic displacement
parameters. Full crystallographic information is given in the Supporting
Information. Crystal data for II: a yellow prisim-shaped crystal of dimensions
0.082 x 0.08 x 0.06 mm was grown from diethyl ether at -30
o
C. C
13
H
19
O
6
Rh:
monoclinic, group P2(1)/n, a = 8.7436(12) Å, b = 14.715(2) Å, c = 11.9556(16)
Å, V = 1456.1(3) Å
3
, Z = 3, T = 85(2) K, D
calcd
= 1.695 Mg/m
3
, R(F) = 5.49 for
8814 observed reflections. Full crystallographic information is given in the
Supporting Information. Crystal data for complex III•2CHCl
3
: a yellow prisim-
shaped crystal of dimensions 0.474 x 0.248 x 0.092 mm was grown from a 50/50
mixture of methanol/chloroform at –30
o
C. C
19
H
24
C
l6
O
5
Rh: triclinic, group P-1, a
= 10.2645(5) Å, b = 11.0621(6) Å, c = 11.7027(7) Å, V = 1307.84(12) Å
3
, Z = 2, T
= 149(2) K, D
calcd
= 1.645 Mg/m
3
, R(F) = 4.21 for 7846 observed reflections. Full
crystallographic information is given in the Supporting Information.
119
6 Synthesis, Characterization and CH Activation
Reactions of Organometallic, O-Donor Ligated,
Rh(III) Complexes
6.1 Introduction.
Highly efficient and selective transition metal mediated methods for the
functionalization of parent hydrocarbons are still largely unsolved problems that
pose significant challenges to homogeneous and heterogeneous catalysis chemists
alike. One of the key reasons for this is that the C-H bonds of saturated alkanes
are thermodynamically and kinetically difficult to break. However, significant
advances have been made in our understanding of how C-H bonds are broken and
formed by the use of well defined, homogeneous complexes.
2
These complexes
generally contain either high oxidation state early transition metals or low
oxidation state late transition metals. The ligands used in these systems range
from C-donor, e.g. cyclopentadienyl ligands, to mono and multi -dentate P- or N-
donor ligands, to chelating NC or PC type ligands.
3
O-donor ligands have been
used to a minor extent with early transition metals and much less so with late
transition metals.
We recently showed that O -donor, ligated, late transition metal catalysts
can be active for the CH activation reaction. We propose that the electron
withdrawing, “hard” characteristics of O-donor ligands may impart unique
120
stability and facilitate access to higher oxidation states needed for oxidative
functionalization. Theoretical calculations also suggest that unfavorable ligand-pp
metal -dp interactions (the “p conflict”) could destabilize the ground state while
ligand p-donation stabilizes the transition state for insertion reaction pathway.
4
A
key requirement to developing useful homogeneous catalysts is that, in addition to
reducing the reaction barrier, that the catalysts be stable to the reaction conditions.
This may be particularly important in the case of developing hydrocarbon
functionalization catalysts based on the CH activation reactions, since many of the
known CH activation systems are known to be unstable to the likely elevated
temperatures and protic, oxidizing conditions required for functionalziation. We
believe that O-donor ligated, late transition metal complexes could be a promising
new class of catalysts since, in addition to being active for the CH activation
reaction, somewhat contrary to common expectation, we find that these complexes
can be thermally stable to protic, oxidizing media.
There are a wide variety of simple, readily available, fully characterized O-
donor ligands that have been extensively utilized in traditional coordination
chemistry. This could suggest that, as for the growing new field of carbene ligated
metal complexes, that O-donor ligands with late transition metals could lead to a
broad, novel, class of homogeneous complexes with desirable stability, reactivity
and ligand control properties. Indeed, it could be considered that O-donor ligated,
homogeneous complex may be related to heterogeneous catalysts where
interactions between the metal catalysts and metal oxides support, the so-called
121
“Strong Metal -Support Interactions, SMSI”, are invoked to explain modified
reactivity of the metal center due to interactions with the support (REF). These
types of discrete, well-defined, O-donor metal complexes could ultimately lead to
significant new contributions to the fields of chemistry and contemporary catalytic
science.
Recently, we demonstrated that the O-donor ligated Ir(III) complexes, (L-
O,O)
2
Ir(CH
3
)(Py), (L-O,O = κ
2
-O,O-acetylacetonate, and ?
2
-O,O-tropolonato, Py
= pyridine), are efficient for both the stoichiometric and catalytic CH activation of
alkanes and functionalization of arenes via anti -Markovnikov hydroarylation of
olefins to selectively generate n -alkyl benzenes.
5
Our investigations have revealed
that these octahedral, d
6
,
O-donor, late transition metal complexes are thermally
stable to air and protic media. This combination of catalyst stability and CH bond
activation chemistry is very attractive for developing oxidation systems based on
the CH activation reaction. Theoretical studies suggest substituting the
acetylacetonate ligands with strongly withdrawing trifluoromethyl groups could
facilitate insertion of the olefin into the M -Ph bond, potentially reducing the
barrier to hydroarylation leading to more efficient catalysts.
6
Here, we report the
synthesis and characterization of several related cis-(hfac-O,O)
2
Rh(R)(py)
complexes and report on the reactivity with respect to CH activation and
hydroarylation. Specifically, we report on the synthesis and reactivity of trans-
(hfac-O,O)
2
Rh(CH
3
)(py), trans-2, cis-(hfac-O,O)
2
Rh(CH
3
)(py), cis-2, cis-(hfac-
O,O)
2
Rh(Ph)(py), cis-3 and cis-(hfac-O,O)
2
Rh(Mes)(py) cis-4. Complex 3 is a
122
fluorinated Rh analogue of a (acac-O,O)
2
Rh(Ph)(CH
3
OH) complex which we
recently reported,
7
and our Ir-based hydroarylation catalyst.
6.2 Results and Discussion
Synthesis of Complexes: The syntheses of new, complexes of Rh(III) with
the ß-diketonate ?
2
-O,O-1,1,1,5,5,5-hexafluoroacetylacetonate, hfac-O,O, are
summarized in Scheme 6.1. The synthesis of 1 has been previously reported.
8
Treatment of rhodium(III) trichloride hydrate with hexafluoroacetylacetone in
refluxing anhydrous ethanol for 4 hours, followed by recrystallization from
methanol yields the complex trans-(hfac-O,O)
2
Rh(CH
3
OH)(Cl), 1. Complex 1 is
an air and water stable mustard-yellow microcrystalline compound. The
1
H NMR
spectrum of 1 shows a single resonance signal for the methine proton of the hfac
ligands, and coordinated methanol at their usual chemical shifts that implies a
symmetric environment for the two hfac ligands as expected for the trans
geometry. This assignment was confirmed by a low temperature, single crystal X -
ray diffraction study of 1. The molecular structure of 1 is shown in Figure 6.1.
Although the aquo analog of 1 was previously reported, no structure of the
complex had been reported.
123
Rh
O O
O O
CF
3
CF 3
F 3 C
F 3 C
Rh
O O
O O
CF
3
CF 3
F 3 C
F 3 C CH 3
O
CH 3 H
Rh
O O
O O
CF 3
CF 3
F 3 C
F 3 C
N
N
O
Rh
O
O N
CH 3
O
F 3 C
CF 3
F 3 C
CF 3
1
trans-3
trans-2
cis-2
C l
1) Hg(CH 3 ) 2
1) Hg(Ph)
2
CH
3
OH
75
o
C
12 h
CHCl 3 /CH 3OH
100
o
C
12 h
C
6
H
1 2
130
o
C
12 h
2) pyridine
2) pyridine
RhCl3 xH2O
Hhfac
CH
3
CH
2
OH
reflux
4h
1)
2) CH
3
OH
Scheme 6.1. Synthesis of (hfac-O,O)
2
Rh(III) Complexes.
Figure 6.1. ORTEP of 1 (50% probability thermal ellipsoids). A molecule of
cocrystallized methanol has been omitted for clarity. The hydrogen
atom on the methanol was not located and was omitted.
Complex 1 was heated with (CH
3
)
2
Hg in methanol at 75
o
C for 12 hours,
followed by treatment with pyridine. This afforded the methyl complex trans-
124
(hfac-O,O)
2
Rh(CH
3
)(Py), trans-2 which has also been fully characterized by
1
H,
13
C NMR spectroscopy, elemental analysis, and x -ray crystallography (Figure 6.2).
Figure 6.2. ORTEP plot of trans-2 (50% probability thermal ellipsoids).
Selected bond lengths (? ): Rh1-N1, 2.236(3); Rh1-C16, 2.031(3).
Heating complex trans-2 in cyclohexane at 130
o
C for 12 hours induced
trans to cis isomerization of the complex to yield the cis-(hfac-O,O)
2
Rh(CH
3
)(Py)
isomer, complex cis-2. Significantly, unlike the chemistry of the non -fluorinated,
Ir, analogue CH activation of the cyclohexane solvent does not occur up to
temperatures of ~200
o
C. The isomerization process was determined to be
quantitative by use
1
H NMR spectroscopy using 1,3,5-trimethoxybenzene as an
external standard. An x -ray crystal structure is depicted in Figure 6.3.
125
Figure 6.3. ORTEP plot of cis-2 (50% probability thermal ellipsoids). Selected
bond lengths (? ): Rh1-N1, 2.017(5); Rh1-C16, 2.026(5).
Treatment of 1 with Ph
2
Hg in CHCl
3
/CH
3
OH at 100
o
C for 12 h, followed
by treatment with pyridine, gave the air and water stable organometallic complex
trans-(hfac-O,O)
2
Rh(Ph)(py), trans-3. Initial investigations of the chemistry of
this molecule revealed a decomposition pathway. Upon heating in arene solutions
or methanol, trans-3 was found to decompose to biphenyl (identified by GC-MS
and NMR analysis) and a new (hfac-O,O)
2
Rh complex which has not been fully
characterized.
126
Unlike the reactions in cyclohexane, where no CH activation is observed,
heating cis-2 in benzene at 190°C for 14 hours does result in CH activation of the
benzene solvent to generate cis-(hfac-O,O)
2
Rh(Ph)(py), cis-3 in 78% isolated yield
as shown in Scheme 2. The
1
H NMR spectrum revealed the disappearance of the
distinctive doublet of the Rh-CH
3
resonance at 2.48 ppm, which is accompanied
by appearance of two new multiplets at 7.10 and 7.36 ppm corresponding to the
new phenyl protons. The reaction in C
6
D
6
reveals an upfield 1:1:1 triplet at 0.18
ppm resulting from the formation of CH
3
D. Some decomposition of the starting
material is observed, especially when the reactions were carried out at
temperatures greater than 190
o
C. Complex cis-3 has also been fully characterized
by
1
H,
13
C NMR spectroscopy, and elemental analysis.
In a closely related reaction, when cis-2 is heated in mesitylene at 195°C
for 14 hours it is converted to cis-(hfac-O,O)
2
Rh(Mes)(Py), 4, which has also been
fully characterized by
1
H,
13
C NMR spectroscopy, elemental analysis, high-
resolution mass spectrometry, and X-ray crystallography ( Figure 6.4). 4 was
isolated from the reaction mixture in 51% yield.
127
O
Rh
O
O N
CH
3
O
F 3C
CF 3
F
3
C
CF 3
O
Rh
O
O N
R
O
F
3
C
CF
3
F
3
C
CF
3
RH
190
o
C
+ CH
4
RH =
H
H
Scheme 6.2. CH activation of hydrocarbons by cis-2.
Figure 6.4. ORTEP plot of 4 (50% probability thermal ellipsoids). Selected bond
lengths (? ): Rh1-N1, 2.021(4); Rh1-C16, 2.062(4).
128
Having established that cis-2 can stoichiometrically activate the C-H bonds
of benzene, and mesitylene we examined whether the complex was sufficiently
stable to catalyze H/D exchange between C
6
H
6
and toluene-d
8
.
To examine this, the rates of H/D exchange reaction of a mixture of C
6
H
6
and toluene-d8 (1:1 v/v),
at 190°C catalyzed by the methanol analog of trans-2,
trans-(hfac-O,O)
2
Rh(CH
3
)(CH
3
OH), trans-2-CH
3
OH, were measured. The
reaction mixture is stable over the time period studied (11.5 hr) and turn -over-
numbers (TON) of 114 and turn -over-frequencies (TOF) of 2.8 x 10
-3
s
-1
were
observed based on added catalyst. In addition, when the reaction was carried out
using the pyridyl complex, trans-2, a TOF of 2.0 x 10
-3
s
-1
was observed.
The observation that trans-2, catalyzes the reaction more slowly than 2-
CH
3
OH is consistent with the requirement for reversible loss of L and supports a
metal -mediated mechanism involving hydrocarbon coordination prior to CH
cleavage since pyridine is expected to be less labile ligand than methanol.
Having demonstrated the stoichiometric and catalytic capability of cis-2 for
the CH activation of benzene we examined competency of cis-3 for catalyzing the
hydroarylation reaction by CH activation and functionalization by olefin insertion
with a mixture of benzene and styrene. The complex was found to be inactive for
hydroarylation of styrene with benzene. However, significant quantities of
polystyrene were generated based on
1
H NMR and GC/MS analyses. No olefinic
products, such as stilbenes, which could result from ß–hydride elimination of the
products form the metal center were detected in the analysis of the reaction
129
mixture, as was also the case with the Ir analogs.
2
Attempts at reaction with
propylene in place of styrene generated no hydroarylation products. These
observations are in agreement with DFT studies which have been reported
previously that show that changing the metal center from Ir to Rh led to an
increase in the barrier for CH activation by approximately 10 kcal/mol, and a
reduction in the barrier for olefin insertion by nearly as much.
5b
Thus, it is likely
that these Rh catalysts, consistent with the observations of slower CH activation
than the Ir analogues, are inactive for hydroarylation.
6.2 Conclusion.
In conclusion, we have prepared several well-defined, novel bis-
hexafluoroacetylacetonate ligated Rh(III) compounds with the same structure and
composition as the Ir catalysts we previously reported for the hydroarylation of
olefins. The cis-(hfac-O,O)
2
Rh(CH
3
)(py) is produced quantitatively from
isomerization of the trans- analog. When cis-2 was heated at high temperature
(190
o
C) in benzene or mesitylene the corresponding phenyl- or mesityl- complexes
were generated. The phenyl analog, cis-3, was found to promote the
stoichiometric, anti -Markovnikov hydroarylation of styrene with benzene, but
catalytic hydroarylation was not accomplished. We are now working on the
extension of this research in the preparation of the discreet (hfac-O,O)
2
Ir(III)
130
analog of these systems, and in ongoing efforts we are developing non -free radical
reactions for the oxidative functionalization of M-R bonds.
6.3 Experimental Section.
Warning! Organomercury compounds are highly toxic! There is a danger
of cumulative effects. These compounds may cause serious and irreversible
effects on skin contact. These compounds may be fatal if absorbed through the
skin - even small amounts, such as a single drop, may cause serious injury or
potentially be fatal. They may cause m etal fume fever if inhaled or swallowed.
Chronic exposure may cause irreversible CNS damage, sensitization, weight loss,
immunological disease and other serious effects. Dimethylmercury is volatile and
dangerous concentrations can readily build up in poorly ventilated areas. Work
with these dangerously toxic compounds must not begin before a full assessment
of the risks has been made and suitable protocols established.
General Methods. All air and water sensitive procedures were carried out
either in an MBraun inert atmosphere glove box, or using standard Schlenk
techniques under argon. The glovebox atmosphere was maintained by periodic
nitrogen purges and monitored by an oxygen analyzer {O
2(g)
< 15 ppm}. Methanol
was dried from Mg/I
2
, and benzene from sodium/benzophenone ketal. All
deuterated solvents (Cambridge Isotopes) were used as received. 1,1,1,5,5,5-
hexafluoroacetylacetone (Synquest) was stored under argon. GC/MS analysis was
131
performed on a Shimadzu GC-MS QP5000 (ver. 2) equipped with cross-linked
methyl silicone gum capillary column (DB5). The retention times of the products
were confirmed by comparison to authentic samples. NMR spectra were obtained
on a Bruker AM-360 spectrometer, measured at 360.138 MHz for
1
H and 90.566
MHz for
13
C or on a Bruker AC-250 spectrometer, measured at 250.134 MHz for
1
H and 62.902 MHz for
13
C, or Varian Mercury-400 spectrometer, measured at
399.96 MHz for
1
H, 100.57 MHz for
13
C, and 376.34 MHz for
19
F at room
temperature. All chemical shifts are reported in units of ppm and referenced to the
residual protonated solvent. High-resolution mass spectra were obtained by
UCLA Pasarow Mass Spectrometry Laboratory on an ESI mass spectrometer.
Elemental Analysis was performed by Desert Analytics of Tucson, Arizona.
X-ray Crystallography. Table 1 summarizes the crystallographic data for
all structurally characterized compounds. X -ray data were collected at 85K for
complexes 1 and 2 and at 149K for complex 3, on a SMART APEX CCD
diffractometer with graphite-monochromated Mo-Ka radiation (λ = 0.71073 Å).
The cell parameters for each compound were obtained from the least-squares
refinement of the spots (from 60 collected frames) using the SMART program [1].
In each case, a hemisphere of data was collected up to a resolution of 0.75Å, and
intensity data were processed using the SAINT PLUS program [2]. Empirical
absorption corrections were applied using SADABS [3], and all calculations for
the structural analyses were carried out using the SHELXTL package [4]. Initial
positions of the Rh atoms were located by direct methods, and the rest of the atoms
132
found using conventional heavy atom techniques. The structures were refined by
least-squares methods using data in the range of 2 θ = 3.5 to 55.0º. All non -
hydrogen atoms in the three complexes were anisotropically refined, and
calculated hydrogen positions were varied in a riding manner along with their
attached carbons.
Synthesis of trans-(hfac-O,O)
2
Rh(Cl)(CH
3
OH). This synthesis can be
followed as reported by Chattoraj and Sievers heating 4.0 g RhCl
3
(H
2
O)
x
and 11
mL 1,1,1,5,5,5-hexafluoropentanedione (Hhfac) in 50mL absolute ethanol under
argon or dinitrogen. This makes the workup rather difficult though. The original
paper does not stress the extent to which the reaction must be dried. In practice, it
must either be pumped on in excess of 24 hours on a vacuum line (30 millitorr) or
gently heated at 40-50°C on a high vacuum line (2 millitorr). Alternatively, heat
can be applied by a heat gun on a low setting, although this can lead to inadvertent
charring of the reaction products. Upon removal of all excess ethanol, DI water
was added. A large amount was added as the desired product is very insoluble in
water. The complex precipitated from solution as mustard-yellow microcrystals.
The microcrystalline product is then washed on a medium porosity frit with
copious amounts of water. A second crop of crystals was also recovered from the
mother-liquor as they precipitated over the next four days. During 1.0 g syntheses
this “second yield” neared 0.2g. Smaller scale reactions were run using 1.0 g
RhCl
3
(H
2
O)
x
and 3.0 mL Hhfac in 15mL absolute ethanol. These reactions are
easier to dry. The yield obtained for these smaller syntheses was found to average
133
48 %. A common impurity seems to be free hfac ligand, whose methine proton
comes slightly upfield from the bound ligand. Recrystallization from methanol
gives trans-(hfac-O,O)
2
Rh(Cl)(CH
3
OH).
1
H NMR (CD
3
OD) 400 MHz: d 6.60 (s,
2H, hfac C
3
H).
19
F NMR (CD3OD) ref. to CFCl
3
360 MHz: d 71.87 (s, 12F, hfac-
CF3’s).
13
C{
1
H} NMR (C
6
D
6
): d 179.07 (q, J
CF
= 146.75 Hz, hfac C=O), 116.78
(q, J
CF
= 1132.75 Hz, hfac CF
3
), 93.34 (s, hfac CH). Single crystals structure
suitable for diffraction were obtained from a concentrated solution in methanol
stored at -30
o
C overnight.
Table 6.1. Crystal data and structure refinement for (acac)
2
Rh(Cl)(CH
3
OH).
Identification code rhf6acam
Empirical formula C12 H9 Cl F12 O6 Rh
Formula weight 615.55
Temperature 123(2) K
Wavelength 0.71073 Å
Crystal system Orthorhombic
Space group Pca2(1)
Unit cell dimensions a = 8.6144(10) Å α= 90°.
b = 19.986(2) Å β= 90°.
c = 11.7027(13) Å γ = 90°.
Volume 2014.8(4) Å
3
Z 4
Density (calculated) 2.029 Mg/m
3
Absorption coefficient 1.117 mm
-1
F(000) 1196
Crystal size 0.50 x 0.29 x 0.10 mm
3
Theta range for data collection 1.02 to 27.52°.
Index ranges -6<=h<=11, -25<=k<=25, -14<=l<=15
Reflections collected 11495
134
Independent reflections 4341 [R(int) = 0.0298]
Completeness to theta = 27.52° 99.3 %
Transmission factors min/max ratio: 0.711
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 4341 / 1 / 292
Goodness-of-fit on F
2
1.042
Final R indices [I>2sigma(I)] R1 = 0.0346, wR2 = 0.0775
R indices (all data) R1 = 0.0494, wR2 = 0.0842
Absolute structure parameter 0.06(5)
Largest diff. peak and hole 0.942 and -0.400 e.Å
-3
Table 6.2. Atomic coordinates ( x 10
4
) and equivalent isotropic displacement
parameters (Å
2
x 10
3
) for (acac)
2
Rh(Cl)(CH
3
OH). U(eq) is defined as one third of
the trace of the orthogonalized U
ij
tensor.
_______________________________________________________________________________
x y z U(eq)
_______________________________________________________________________________
Rh(1) 4978(1) 2472(1) 1140(1) 23(1)
Cl(1) 3482(1) 2646(1) 2714(1) 37(1)
F(1) 9079(4) 4025(2) 1695(3) 69(1)
F(2) 7478(4) 4772(1) 2234(3) 59(1)
F(3) 7877(4) 3924(1) 3278(3) 65(1)
F(4) 3233(4) 4066(1) -1449(3) 61(1)
F(5) 3418(4) 4871(1) -264(3) 71(1)
F(6) 1638(4) 4149(2) -80(4) 93(2)
F(7) 8199(3) 742(1) 2429(3) 54(1)
F(8) 6804(3) 1023(1) 3858(2) 45(1)
F(9) 6278(3) 134(1) 2922(3) 58(1)
F(10) 1848(3) 995(1) -796(3) 53(1)
F(11) 808(3) 936(1) 871(3) 56(1)
F(12) 2326(3) 165(1) 290(3) 47(1)
O(1) 6559(3) 3103(1) 1749(2) 29(1)
O(2) 3805(3) 3174(1) 292(3) 29(1)
135
O(3) 6179(3) 1779(1) 1985(3) 28(1)
O(4) 3425(3) 1824(1) 523(2) 27(1)
O(5) 6324(3) 2282(2) -282(3) 32(1)
O(6) 8961(3) 2841(2) -312(3) 49(1)
C(1) 7742(7) 4118(2) 2217(5) 42(1)
C(2) 6427(5) 3733(2) 1609(4) 30(1)
C(3) 5340(5) 4086(2) 985(5) 37(1)
C(4) 4146(5) 3790(2) 372(4) 30(1)
C(5) 3081(6) 4229(3) -356(5) 46(1)
C(6) 6748(5) 763(2) 2834(5) 35(1)
C(7) 5711(5) 1186(2) 2035(4) 27(1)
C(8) 4474(6) 878(2) 1519(4) 30(1)
C(9) 3436(5) 1221(2) 804(4) 28(1)
C(10) 2095(6) 823(2) 282(4) 36(1)
C(11) 5617(6) 2308(3) -1407(4) 43(1)
C(12) 9938(5) 2578(2) 522(6) 51(2)
Table 6.3. Bond lengths [Å] and angles [°] for (acac)
2
Rh(Cl)(CH
3
OH).
_____________________________________________________
Rh(1)-O(1) 1.989(3)
Rh(1)-O(3) 1.992(3)
Rh(1)-O(2) 1.992(3)
Rh(1)-O(4) 1.997(3)
Rh(1)-O(5) 2.064(3)
Rh(1)-Cl(1) 2.2747(16)
F(1)-C(1) 1.317(7)
F(2)-C(1) 1.327(5)
F(3)-C(1) 1.306(6)
F(4)-C(5) 1.327(6)
F(5)-C(5) 1.319(6)
F(6)-C(5) 1.294(6)
F(7)-C(6) 1.338(5)
F(8)-C(6) 1.308(6)
136
F(9)-C(6) 1.325(5)
F(10)-C(10) 1.325(6)
F(11)-C(10) 1.325(6)
F(12)-C(10) 1.330(5)
O(1)-C(2) 1.275(5)
O(2)-C(4) 1.270(5)
O(3)-C(7) 1.255(5)
O(4)-C(9) 1.250(5)
O(5)-C(11) 1.451(5)
O(6)-C(12) 1.392(6)
C(1)-C(2) 1.542(7)
C(2)-C(3) 1.380(6)
C(3)-C(4) 1.386(6)
C(4)-C(5) 1.529(6)
C(6)-C(7) 1.544(6)
C(7)-C(8) 1.371(6)
C(8)-C(9) 1.403(6)
C(9)-C(10) 1.530(6)
O(1)-Rh(1)-O(3) 84.66(12)
O(1)-Rh(1)-O(2) 94.55(11)
O(3)-Rh(1)-O(2) 179.10(14)
O(1)-Rh(1)-O(4) 178.81(13)
O(3)-Rh(1)-O(4) 94.43(11)
O(2)-Rh(1)-O(4) 86.36(13)
O(1)-Rh(1)-O(5) 91.19(11)
O(3)-Rh(1)-O(5) 88.87(12)
O(2)-Rh(1)-O(5) 90.73(13)
O(4)-Rh(1)-O(5) 88.03(13)
O(1)-Rh(1)-Cl(1) 90.03(10)
O(3)-Rh(1)-Cl(1) 89.91(11)
O(2)-Rh(1)-Cl(1) 90.50(10)
O(4)-Rh(1)-Cl(1) 90.73(9)
O(5)-Rh(1)-Cl(1) 178.19(10)
137
C(2)-O(1)-Rh(1) 121.3(3)
C(4)-O(2)-Rh(1) 121.9(3)
C(7)-O(3)-Rh(1) 120.9(3)
C(9)-O(4)-Rh(1) 121.7(3)
C(11)-O(5)-Rh(1) 119.3(3)
F(3)-C(1)-F(1) 108.7(5)
F(3)-C(1)-F(2) 107.1(4)
F(1)-C(1)-F(2) 107.2(4)
F(3)-C(1)-C(2) 110.8(4)
F(1)-C(1)-C(2) 111.0(4)
F(2)-C(1)-C(2) 111.8(4)
O(1)-C(2)-C(3) 129.2(4)
O(1)-C(2)-C(1) 111.6(4)
C(3)-C(2)-C(1) 119.2(4)
C(2)-C(3)-C(4) 124.0(4)
O(2)-C(4)-C(3) 128.6(4)
O(2)-C(4)-C(5) 112.1(4)
C(3)-C(4)-C(5) 119.3(4)
F(6)-C(5)-F(5) 108.1(4)
F(6)-C(5)-F(4) 107.8(5)
F(5)-C(5)-F(4) 107.2(4)
F(6)-C(5)-C(4) 111.5(4)
F(5)-C(5)-C(4) 112.4(4)
F(4)-C(5)-C(4) 109.7(4)
F(8)-C(6)-F(9) 108.5(4)
F(8)-C(6)-F(7) 107.6(4)
F(9)-C(6)-F(7) 106.5(4)
F(8)-C(6)-C(7) 111.0(4)
F(9)-C(6)-C(7) 112.9(4)
F(7)-C(6)-C(7) 110.1(4)
O(3)-C(7)-C(8) 130.8(4)
O(3)-C(7)-C(6) 111.1(4)
C(8)-C(7)-C(6) 118.2(4)
138
C(7)-C(8)-C(9) 122.7(4)
O(4)-C(9)-C(8) 129.3(4)
O(4)-C(9)-C(10) 113.0(4)
C(8)-C(9)-C(10) 117.7(4)
F(10)-C(10)-F(11) 108.4(4)
F(10)-C(10)-F(12) 106.7(4)
F(11)-C(10)-F(12) 106.8(4)
F(10)-C(10)-C(9) 111.5(4)
F(11)-C(10)-C(9) 109.6(4)
F(12)-C(10)-C(9) 113.5(4)
_____________________________________________________________
Symmetry transformations used to generate equivalent atoms:
Table 6.4. Anisotropic displacement parameters (Å
2
x 10
3
) for
(acac)
2
Rh(Cl)(CH
3
OH). The anisotropic 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
______________________________________________________________________________
Rh(1) 20(1) 25(1) 25(1) 1(1) -1(1) 1(1)
Cl(1) 29(1) 53(1) 29(1) -3(1) 5(1) 4(1)
F(1) 40(2) 79(2) 88(3) -33(2) 7(2) -16(2)
F(2) 74(2) 35(1) 68(2) -14(2) -14(2) -9(1)
F(3) 88(3) 60(2) 46(2) 6(2) -25(2) -31(2)
F(4) 91(2) 50(2) 42(2) 0(1) -18(2) 19(2)
F(5) 109(3) 29(2) 76(2) 2(2) -39(2) 14(2)
F(6) 41(2) 109(3) 130(4) 59(3) 7(2) 35(2)
F(7) 38(2) 57(2) 67(2) 6(2) -1(2) 17(1)
F(8) 54(2) 47(2) 36(2) 3(1) -14(2) 5(1)
F(9) 71(2) 31(1) 72(2) 16(1) -32(2) -7(1)
F(10) 59(2) 57(2) 44(2) 5(1) -21(2) -18(1)
F(11) 25(1) 71(2) 71(2) -18(2) 10(2) -10(1)
F(12) 51(2) 37(1) 53(2) -6(1) -12(1) -10(1)
139
O(1) 29(2) 27(2) 30(2) -2(1) -2(1) -1(1)
O(2) 28(2) 30(2) 31(2) 1(1) -5(1) 6(1)
O(3) 24(2) 25(2) 35(2) 3(1) -4(1) 1(1)
O(4) 23(2) 30(2) 28(2) 0(1) -4(1) -3(1)
O(5) 27(2) 40(2) 28(2) -3(2) -3(1) 6(1)
O(6) 31(2) 78(3) 37(2) -2(2) 2(2) -6(2)
C(1) 46(3) 39(3) 42(3) -3(2) -4(2) -9(2)
C(2) 33(3) 30(2) 26(2) -5(2) 6(2) 1(2)
C(3) 46(3) 28(2) 36(3) 1(2) 4(3) 4(2)
C(4) 28(2) 32(2) 31(2) -1(2) 6(2) 9(2)
C(5) 48(3) 45(3) 44(3) 8(3) -5(3) 12(2)
C(6) 35(3) 26(2) 43(3) 5(2) -9(2) 3(2)
C(7) 24(2) 31(2) 26(2) 0(2) 4(2) 5(2)
C(8) 28(2) 27(2) 34(3) -3(2) 1(2) -3(2)
C(9) 27(2) 30(2) 26(2) -2(2) 4(2) -1(2)
C(10) 37(3) 36(3) 35(3) -6(2) 2(2) -5(2)
C(11) 38(3) 57(3) 32(3) -6(2) 1(2) 5(3)
C(12) 34(3) 76(4) 43(3) 7(3) 2(2) 15(3)
Table 6.5. Hydrogen coordinates ( x 10
4
) and isotropic displacement parameters
(Å
2
x 10
3
) for (acac)
2
Rh(Cl)(CH
3
OH).
_______________________________________________________________________________
x y z U(eq)
_______________________________________________________________________________
H(6) 9277 2724 -961 73
H(3) 5415 4560 975 44
H(8) 4312 415 1650 36
H(11A) 4926 1923 -1505 64
H(11B) 6430 2297 -1992 64
H(11C) 5017 2723 -1482 64
H(12A) 10289 2938 1028 77
H(12B) 10839 2368 156 77
140
H(12C) 9374 2242 969 77
Synthesis of trans-(hfac-O,O)
2
Rh(CH
3
)(Py). Approximately 1.0 g of 1 was
dissolved in 15 mL of methanol in a 30 mL Schlenk tube fitted with a resealable
Teflon valve. This compound is highly soluble so not much methanol is required
to dissolve large quantities of the compound. Dimethylmercury was added in a 2:1
molar ratio with respect to the compound. Excess dimethylmercury was pumped
off with the methanol after the reaction was complete and converted to
(CH
3
)Hg(NO
3
) with HNO
3
for disposal with mercury waste. The reaction mixture
was then heated for 14 hours at 75°C under argon after 5 successive freeze-pump-
thaw cycles removed air. The products were redissolved in a minimal amount of
methanol and kept at -30
o
C overnight to precipitate methylmercuric chloride
(grayish black color).
1
H NMR (CDCl
3
) 400 MHz: d 6.4 (s, 2H, hfac CH), 3.0 (d,
3H, CH
3
split by Rh), 3.5 (s, 3H, CH
3
bound CH
3
OH). Neat pyridine was added to
the methanol adduct and the solution immediately turned red. Heating was found
to be necessary to convert the methanol adduct to the pyridyl complex, as
indicated when the process was followed by
1
H NMR. Thus, the solution was
heated for approximately 30 minutes at 65°C. Analytical TLC at this point in
every synthesis showed an impurity that stuck to neutral alumina when run in
CH
2
Cl
2
. Prep TLC or an alumina plug was employed at this point to remove the
unwanted impurity. Excess pyridine was removed in vacuuo. When nearly all
pyridine was removed, a small amount of chloroform was added to dissolve the
141
solid formed in the flask and the remaining traces of pyridine. This solution was
then fully evaporated. Crystals suitable for X -ray diffraction were grown from
methanol at low temperature (-30°C).
1
H NMR (CDCl
3
) 400 MHz: d 8.49 (d, 2H,
py-o-H’s), 7.93 (t, 1H, py -p-H), 7.54 (t, 2H, py -m-H’s), 6.14 (s, 2H, hfac-CH),
2.43 (s, 3H, CH3).
19
F NMR (CD
3
OD) ref. to CFCl
3
360 MHz: d 72.17 (s, 12F,
hfac-CF3’s).
13
C{
1
H} NMR (C
6
D
6
): d 175.15 (s, J
FC
= 141.6 Hz, hfac C=O),
148.91 (s, py), 138.75 (s, py), 125.76 (s, py), 115.29 (q, J
FC
= 1118 Hz, hfac CF
3
),
92.23 (q, J
CF
= 84 Hz, hfac CH), 5.87 (d, J
RhC
= 14 Hz, CH
3
). Analysis Calculated
for C
16
H
10
F
12
NO
4
Rh: C, 31.44; H, 1.65; N, 2.29. Found: C, 31.58; H, 1.58; N,
2.24.
Table 6.6. Crystal data and structure refinement for trans-(acac)
2
Rh(CH
3
)(Py).
Identification code rhmetf6m
Empirical formula C16 H10 F12 N O4 Rh
Formula weight 611.16
Temperature 143(2) K
Wavelength 0.71073 Å
Crystal system Triclinic
Space group P-1
Unit cell dimensions a = 10.8849(12) Å
α=117.822(2)°.
b = 10.9005(12) Å
β=108.698(2)°.
c = 10.9681(12) Å γ =99.217(2)°.
Volume 1012.91(19) Å
3
Z 2
Density (calculated) 2.004 Mg/m
3
Absorption coefficient 0.977 mm
-1
F(000) 596
142
Crystal size 0.19 x 0.09 x 0.02 mm
3
Theta range for data collection 2.13 to 27.48°.
Index ranges -13<=h<=13, -14<=k<=11, -11<=l<=14
Reflections collected 6284
Independent reflections 4373 [R(int) = 0.0225]
Completeness to theta = 27.48° 94.1 %
Transm ission factors min/max ratio: 0.681
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 4373 / 0 / 308
Goodness-of-fit on F
2
1.056
Final R indices [I>2sigma(I)] R1 = 0.0380, wR2 = 0.0890
R indices (all data) R1 = 0.0448, wR2 = 0.0921
Largest diff. peak and hole 0.882 and -0.526 e.Å
-3
Table 6.7. Atomic coordinates ( x 10
4
) and equivalent isotropic displacement
parameters (Å
2
x 10
3
) for trans-(acac)
2
Rh(CH
3
)(Py). U(eq) is defined as one third
of the trace of the orthogonalized U
ij
tensor.
_______________________________________________________________________________
x y z U(eq)
_______________________________________________________________________________
Rh(1) 4418(1) 3002(1) 1277(1) 19(1)
F(1) 1953(2) -2122(2) -1340(3) 40(1)
F(2) 1207(2) -1047(2) 301(3) 43(1)
F(3) -41(2) -1920(2) -2088(3) 49(1)
F(4) 114(3) 3536(4) -777(4) 70(1)
F(5) -374(3) 1750(3) -3043(3) 70(1)
F(6) 1255(2) 3833(3) -1933(3) 47(1)
F(7) 7955(3) 1973(3) 3877(3) 52(1)
F(8) 7361(3) 3149(3) 5601(3) 62(1)
F(9) 9196(3) 4248(3) 5651(4) 76(1)
F(10) 8692(3) 8102(2) 5135(3) 58(1)
F(11) 7091(2) 7836(2) 3190(2) 35(1)
F(12) 6720(3) 8175(2) 5100(3) 61(1)
O(1) 3267(2) 880(2) 331(2) 22(1)
143
O(2) 2916(2) 3333(2) -20(2) 23(1)
O(3) 5890(2) 2685(2) 2634(2) 23(1)
O(4) 5551(2) 5158(2) 2318(2) 23(1)
N(1) 5240(3) 2315(3) -468(3) 21(1)
C(1) 1266(3) -1222(4) -961(4) 29(1)
C(2) 1994(3) 314(3) -616(3) 22(1)
C(3) 1199(3) 897(4) -1297(4) 26(1)
C(4) 1709(3) 2329(4) -956(4) 24(1)
C(5) 663(4) 2861(4) -1701(5) 37(1)
C(6) 7909(4) 3288(4) 4735(4) 32(1)
C(7) 7008(3) 3751(4) 3759(4) 23(1)
C(8) 7468(3) 5223(4) 4224(4) 25(1)
C(9) 6717(3) 5814(3) 3499(3) 23(1)
C(10) 7318(4) 7492(4) 4234(4) 32(1)
C(11) 5060(3) 889(4) -1397(4) 25(1)
C(12) 5526(4) 419(4) -2509(4) 31(1)
C(13) 6218(4) 1464(4) -2676(4) 31(1)
C(14) 6412(4) 2939(4) -1727(4) 31(1)
C(15) 5902(3) 3316(4) -655(4) 26(1)
C(16) 3635(4) 3617(4) 2830(4) 28(1)
Table 6.8. Bond lengths [Å] and angles [°] for trans-(acac)
2
Rh(CH
3
)(Py).
_____________________________________________________
Rh(1)-O(1) 1.998(2)
Rh(1)-O(2) 2.001(2)
Rh(1)-O(4) 2.003(2)
Rh(1)-O(3) 2.007(2)
Rh(1)-C(16) 2.031(3)
Rh(1)-N(1) 2.236(3)
F(1)-C(1) 1.322(4)
F(2)-C(1) 1.331(4)
F(3)-C(1) 1.334(4)
F(4)-C(5) 1.326(5)
144
F(5)-C(5) 1.319(4)
F(6)-C(5) 1.319(4)
F(7)-C(6) 1.319(4)
F(8)-C(6) 1.322(4)
F(9)-C(6) 1.309(4)
F(10)-C(10) 1.333(4)
F(11)-C(10) 1.328(4)
F(12)-C(10) 1.331(4)
O(1)-C(2) 1.259(4)
O(2)-C(4) 1.266(4)
O(3)-C(7) 1.264(4)
O(4)-C(9) 1.262(4)
N(1)-C(11) 1.337(4)
N(1)-C(15) 1.343(4)
C(1)-C(2) 1.538(4)
C(2)-C(3) 1.384(4)
C(3)-C(4) 1.389(4)
C(4)-C(5) 1.536(5)
C(6)-C(7) 1.533(4)
C(7)-C(8) 1.380(4)
C(8)-C(9) 1.393(4)
C(9)-C(10) 1.525(4)
C(11)-C(12) 1.381(5)
C(12)-C(13) 1.381(5)
C(13)-C(14) 1.379(5)
C(14)-C(15) 1.378(5)
O(1)-Rh(1)-O(2) 94.58(9)
O(1)-Rh(1)-O(4) 177.05(8)
O(2)-Rh(1)-O(4) 85.98(9)
O(1)-Rh(1)-O(3) 85.12(9)
O(2)-Rh(1)-O(3) 177.75(9)
O(4)-Rh(1)-O(3) 94.22(9)
O(1)-Rh(1)-C(16) 88.11(12)
145
O(2)-Rh(1)-C(16) 88.60(12)
O(4)-Rh(1)-C(16) 89.01(12)
O(3)-Rh(1)-C(16) 89.16(12)
O(1)-Rh(1)-N(1) 91.57(9)
O(2)-Rh(1)-N(1) 90.35(9)
O(4)-Rh(1)-N(1) 91.32(9)
O(3)-Rh(1)-N(1) 91.88(9)
C(16)-Rh(1)-N(1) 178.88(11)
C(2)-O(1)-Rh(1) 121.3(2)
C(4)-O(2)-Rh(1) 121.2(2)
C(7)-O(3)-Rh(1) 121.6(2)
C(9)-O(4)-Rh(1) 121.7(2)
C(11)-N(1)-C(15) 117.3(3)
C(11)-N(1)-Rh(1) 121.5(2)
C(15)-N(1)-Rh(1) 121.2(2)
F(1)-C(1)-F(2) 106.9(3)
F(1)-C(1)-F(3) 108.0(3)
F(2)-C(1)-F(3) 107.1(3)
F(1)-C(1)-C(2) 112.3(3)
F(2)-C(1)-C(2) 109.2(3)
F(3)-C(1)-C(2) 113.1(3)
O(1)-C(2)-C(3) 129.6(3)
O(1)-C(2)-C(1) 111.9(3)
C(3)-C(2)-C(1) 118.4(3)
C(2)-C(3)-C(4) 123.5(3)
O(2)-C(4)-C(3) 129.4(3)
O(2)-C(4)-C(5) 113.1(3)
C(3)-C(4)-C(5) 117.2(3)
F(6)-C(5)-F(5) 107.5(3)
F(6)-C(5)-F(4) 106.9(3)
F(5)-C(5)-F(4) 107.6(3)
F(6)-C(5)-C(4) 112.4(3)
F(5)-C(5)-C(4) 112.4(3)
146
F(4)-C(5)-C(4) 109.8(3)
F(9)-C(6)-F(7) 107.6(3)
F(9)-C(6)-F(8) 107.9(3)
F(7)-C(6)-F(8) 105.6(3)
F(9)-C(6)-C(7) 113.1(3)
F(7)-C(6)-C(7) 112.3(3)
F(8)-C(6)-C(7) 109.9(3)
O(3)-C(7)-C(8) 129.0(3)
O(3)-C(7)-C(6) 112.7(3)
C(8)-C(7)-C(6) 118.2(3)
C(7)-C(8)-C(9) 124.2(3)
O(4)-C(9)-C(8) 129.0(3)
O(4)-C(9)-C(10) 113.3(3)
C(8)-C(9)-C(10) 117.7(3)
F(11)-C(10)-F(12) 106.8(3)
F(11)-C(10)-F(10) 106.6(3)
F(12)-C(10)-F(10) 107.6(3)
F(11)-C(10)-C(9) 112.5(3)
F(12)-C(10)-C(9) 110.0(3)
F(10)-C(10)-C(9) 113.0(3)
N(1)-C(11)-C(12) 123.2(3)
C(13)-C(12)-C(11) 118.9(3)
C(12)-C(13)-C(14) 118.6(3)
C(13)-C(14)-C(15) 119.0(3)
N(1)-C(15)-C(14) 123.1(3)
_____________________________________________________________
Symmetry transformations used to generate equivalent atoms:
Table 6.9. Anisotropic displacement parameters (Å
2
x 10
3
) for trans-
(acac)
2
Rh(CH
3
)(Py). The anisotropic 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
147
______________________________________________________________________________
Rh(1) 19(1) 16(1) 19(1) 10(1) 7(1) 5(1)
F(1) 43(1) 25(1) 55(1) 21(1) 26(1) 14(1)
F(2) 53(1) 41(1) 47(1) 29(1) 31(1) 11(1)
F(3) 29(1) 34(1) 58(2) 27(1) -3(1) -5(1)
F(4) 75(2) 94(2) 107(2) 75(2) 64(2) 69(2)
F(5) 46(2) 40(2) 70(2) 29(1) -23(1) 3(1)
F(6) 39(1) 47(1) 63(2) 43(1) 11(1) 15(1)
F(7) 67(2) 51(2) 43(1) 29(1) 18(1) 40(1)
F(8) 87(2) 95(2) 57(2) 63(2) 46(2) 61(2)
F(9) 36(1) 61(2) 93(2) 55(2) -22(1) -6(1)
F(10) 48(1) 28(1) 51(1) 22(1) -16(1) -11(1)
F(11) 41(1) 27(1) 33(1) 20(1) 10(1) 5(1)
F(12) 115(2) 27(1) 60(2) 21(1) 61(2) 32(1)
O(1) 21(1) 18(1) 24(1) 12(1) 9(1) 5(1)
O(2) 25(1) 21(1) 26(1) 14(1) 10(1) 10(1)
O(3) 23(1) 19(1) 25(1) 14(1) 9(1) 7(1)
O(4) 26(1) 16(1) 23(1) 11(1) 8(1) 6(1)
N(1) 21(1) 18(1) 23(1) 13(1) 8(1) 7(1)
C(1) 24(2) 26(2) 30(2) 16(2) 7(2) 5(1)
C(2) 23(2) 21(2) 19(1) 10(1) 9(1) 5(1)
C(3) 23(2) 23(2) 26(2) 12(1) 9(1) 6(1)
C(4) 23(2) 26(2) 23(2) 14(1) 9(1) 10(1)
C(5) 30(2) 33(2) 47(2) 25(2) 10(2) 11(2)
C(6) 32(2) 31(2) 29(2) 19(2) 7(2) 10(2)
C(7) 23(2) 26(2) 21(2) 15(1) 10(1) 10(1)
C(8) 23(2) 24(2) 22(2) 12(1) 6(1) 5(1)
C(9) 29(2) 20(2) 20(2) 10(1) 12(1) 8(1)
C(10) 38(2) 20(2) 21(2) 8(1) 5(2) 3(2)
C(11) 27(2) 23(2) 32(2) 19(1) 14(1) 11(1)
C(12) 39(2) 24(2) 33(2) 14(2) 18(2) 16(2)
C(13) 39(2) 33(2) 31(2) 18(2) 22(2) 18(2)
C(14) 38(2) 29(2) 40(2) 24(2) 24(2) 14(2)
148
C(15) 29(2) 24(2) 30(2) 16(1) 14(2) 11(1)
C(16) 30(2) 28(2) 26(2) 14(1) 15(2) 10(2)
Table 6.10. Hydrogen coordinates ( x 10
4
) and isotropic displacement parameters
(Å
2
x 10
3
) for trans-(acac)
2
Rh(CH
3
)(Py).
_______________________________________________________________________________
x y z U(eq)
_______________________________________________________________________________
H(3) 253 284 -2038 31
H(8) 8353 5877 5094 30
H(11) 4588 164 -1286 30
H(12) 5373 -606 -3150 38
H(13) 6554 1172 -3430 38
H(14) 6890 3684 -1810 37
H(15) 6024 4331 -19 32
H(16A) 2613 3200 2278 42
H(16B) 3963 4708 3480 42
H(16C) 3952 3238 3481 42
Synthesis of cis-(hfac-O,O)
2
Rh(CH
3
)(py). Quantitative isomerization of
the trans-complex, 2, to the cis-analog, 3, occurs upon heating 2 in cyclohexane
under argon. Complex 2 (45 mg) was dissolved upon heating in cyclohexane (6
mL) at 95
o
C and after 14 h was completely converted to the cis-isomer, 3, as
evidenced by NMR. The yield of the reaction was measured by comparison with
an internal standard, 1,3,5-trimethoxybenzene. Decomposition may occur if the
solution is not fully degassed prior to carrying out the isomerization procedure.
1
H
NMR (CDCl
3
) 400 MHz: d 2.48 (d, 3H, CH
3
, J
RhC
= 2.50 Hz), 5.99 (s, 2H, hfac
CH), 6.22 (s, 2H, hfac C
3
H), 7.43 (t, 2H, m -CH pyridine), 7.88 (t, 1H, p -CH
149
pyridine), 8.26 (d, 2H, o-CH pyridine).
19
F NMR (CDCl
3
) ref. to CFCl
3
400 MHz:
d 74.37 (s, 3F, hfac-CF3), 74.70 (s, 3F, hfac-CF3), 74.79 (s, 3F, hfac-CF3), 76.32
(s, 3F, hfac-CF3).
13
C {
1
H} NMR (CDCl
3
) 400 MHz: d 7.23 (d, CH
3
, J
RhC
=
26.1), 88.98 (s, hfac CH), 92.08 (s, hfac CH), 115.7 (q, CF
3
, J
CF
= 284 Hz), 115.9
(q, CF
3
, J
CF
= 284 Hz), 116.4 (m, CF
3
, J
CF
= 284 Hz), 117.4 (m, CF
3
, J
CF
= 284
Hz), 125.62(s, m-CH pyridine), 138.70(s, p-CH pyridine), 151.70 (s,o- CH
pyridine), 174.9 (hfac C=O
2
J
CF
= 34.9), 175.1 (hfac C=O
2
J
CF
= 33.7), 175.1 (hfac
C=O
2
J
CF
= 36.2), 177.3 (hfac C=O
2
J
CF
= 35.0).
Table 6.11. Crystal data and structure refinement for cis-(acac)
2
Rh(CH
3
)(Py).
Identification code mrhcism
Empirical formula C16 H10 F12 N O4 Rh
Formula weight 611.16
Temperature 153(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/c
Unit cell dimensions a = 8.0941(15) Å α= 90°.
b = 29.962(6) Å β= 97.310(3)°.
c = 8.7770(17) Å γ = 90°.
Volume 2111.2(7) Å
3
Z 4
Density (calculated) 1.923 Mg/m
3
Absorption coefficient 0.937 mm
-1
F(000) 1192
Crystal size 0.20 x 0.18 x 0.01 mm
3
Theta range for data collection 1.36 to 27.53°.
Index ranges -10<=h<=10, -38<=k<=36, -8<=l<=11
150
Reflections collected 12955
Independent reflections 4737 [R(int) = 0.0511]
Completeness to theta = 27.53° 97.0 %
Transmission factors min/max ratio: 0.653
Refinement method Full-matrix least-squares on F
2
Data / restraints / parameters 4737 / 21 / 329
Goodness-of-fit on F
2
1.043
Final R indices [I>2sigma(I)] R1 = 0.0556, wR2 = 0.1262
R indices (all data) R1 = 0.0849, wR2 = 0.1387
Largest diff. peak and hole 0.987 and -0.697 e.Å
-3
Table 6.12. Atomic coordinates ( x 10
4
) and equivalent isotropic displacement
parameters (Å
2
x 10
3
) for cis-(acac)
2
Rh(CH
3
)(Py). U(eq) is defined as one third of
the trace of the orthogonalized U
ij
tensor.
_______________________________________________________________________________
x y z U(eq)
_______________________________________________________________________________
Rh(1) 6023(1) 8894(1) 3231(1) 30(1)
F(1) 2537(16) 9783(4) 23(14) 80(4)
F(1A) 1717(15) 9631(3) 107(10) 67(3)
F(2) 1033(12) 9985(3) 1744(9) 57(3)
F(2A) 1644(12) 10167(3) 1880(10) 60(3)
F(3) 3586(13) 10247(4) 1494(15) 86(4)
F(3A) 3496(13) 10096(4) 552(15) 86(4)
F(4) 1411(10) 8761(3) 6046(9) 77(3)
F(4A) 2873(14) 8803(4) 7251(13) 77(4)
F(5) 1594(19) 9488(4) 6540(20) 70(5)
F(5A) 1334(19) 9350(6) 6640(20) 55(4)
F(6) 3511(11) 9002(4) 7632(10) 74(3)
F(6A) 3763(13) 9400(5) 7617(10) 98(5)
F(7) 2965(5) 7780(1) 188(4) 61(1)
F(8) 1826(4) 7727(1) 2259(4) 57(1)
F(9) 3660(5) 7244(1) 1763(5) 70(1)
151
F(10) 9965(5) 7831(2) 4832(5) 81(2)
F(11) 8252(6) 7320(1) 5258(5) 77(1)
F(12) 8619(5) 7873(1) 6746(4) 57(1)
O(1) 4646(5) 9351(1) 1997(4) 35(1)
O(2) 4704(5) 8928(1) 5029(4) 37(1)
O(3) 4301(4) 8387(1) 2225(4) 37(1)
O(4) 7445(4) 8438(1) 4437(4) 34(1)
N(1) 7400(6) 8822(1) 1486(6) 35(1)
C(1) 2558(9) 9882(3) 1372(9) 61(2)
C(2) 3414(7) 9538(2) 2490(7) 39(1)
C(3) 2794(7) 9474(2) 3866(7) 38(1)
C(4) 3430(6) 9176(2) 5031(6) 36(1)
C(5) 2556(9) 9121(3) 6386(8) 76(3)
C(6) 3253(8) 7677(2) 1679(7) 45(2)
C(7) 4581(6) 7988(2) 2507(6) 31(1)
C(8) 5915(7) 7788(2) 3454(6) 34(1)
C(9) 7170(6) 8022(2) 4305(6) 32(1)
C(10) 8515(7) 7758(2) 5286(7) 41(1)
C(11) 9065(7) 8763(2) 1750(8) 45(2)
C(12) 9988(8) 8691(2) 588(10) 56(2)
C(13) 9222(9) 8680(2) -909(9) 56(2)
C(14) 7522(9) 8741(2) -1192(8) 52(2)
C(15) 6661(8) 8814(2) 31(7) 41(1)
C(16) 7532(7) 9386(2) 4181(7) 44(2)
Table 6.13. Bond lengths [Å] and angles [°] for cis-(acac)
2
Rh(CH
3
)(Py).
_____________________________________________________
Rh(1)-O(1) 1.996(4)
Rh(1)-O(4) 2.000(3)
Rh(1)-O(2) 2.017(4)
Rh(1)-N(1) 2.017(5)
Rh(1)-C(16) 2.026(5)
Rh(1)-O(3) 2.171(4)
152
F(1)-F(1A) 0.817(11)
F(1)-C(1) 1.219(13)
F(1)-F(3A) 1.266(14)
F(1A)-C(1) 1.439(11)
F(2)-F(2A) 0.737(9)
F(2)-C(1) 1.352(10)
F(2A)-C(1) 1.248(10)
F(2A)-F(3) 1.667(14)
F(3)-F(3A) 0.937(12)
F(3)-C(1) 1.369(13)
F(3A)-C(1) 1.281(12)
F(4)-C(5) 1.429(10)
F(4)-F(4A) 1.488(13)
F(4A)-F(6) 0.830(12)
F(4A)-C(5) 1.226(12)
F(5)-C(5) 1.363(12)
F(5A)-C(5) 1.245(17)
F(6)-F(6A) 1.211(14)
F(6)-C(5) 1.307(9)
F(6A)-C(5) 1.597(14)
F(7)-C(6) 1.336(7)
F(8)-C(6) 1.328(7)
F(9)-C(6) 1.337(7)
F(10)-C(10) 1.305(7)
F(11)-C(10) 1.330(7)
F(12)-C(10) 1.319(7)
O(1)-C(2) 1.267(7)
O(2)-C(4) 1.272(6)
O(3)-C(7) 1.236(6)
O(4)-C(9) 1.270(6)
N(1)-C(15) 1.340(7)
N(1)-C(11) 1.350(7)
C(1)-C(2) 1.529(9)
153
C(2)-C(3) 1.379(8)
C(3)-C(4) 1.404(8)
C(4)-C(5) 1.468(8)
C(6)-C(7) 1.535(8)
C(7)-C(8) 1.410(7)
C(8)-C(9) 1.374(7)
C(9)-C(10) 1.521(7)
C(11)-C(12) 1.356(9)
C(12)-C(13) 1.380(10)
C(13)-C(14) 1.379(10)
C(14)-C(15) 1.370(8)
O(1)-Rh(1)-O(4) 178.66(15)
O(1)-Rh(1)-O(2) 94.34(15)
O(4)-Rh(1)-O(2) 86.94(15)
O(1)-Rh(1)-N(1) 89.15(17)
O(4)-Rh(1)-N(1) 89.59(17)
O(2)-Rh(1)-N(1) 176.34(16)
O(1)-Rh(1)-C(16) 89.4(2)
O(4)-Rh(1)-C(16) 90.2(2)
O(2)-Rh(1)-C(16) 89.6(2)
N(1)-Rh(1)-C(16) 91.6(2)
O(1)-Rh(1)-O(3) 88.47(15)
O(4)-Rh(1)-O(3) 91.98(14)
O(2)-Rh(1)-O(3) 88.67(15)
N(1)-Rh(1)-O(3) 90.29(16)
C(16)-Rh(1)-O(3) 177.18(19)
F(1A)-F(1)-C(1) 87.7(13)
F(1A)-F(1)-F(3A) 148.0(18)
C(1)-F(1)-F(3A) 62.0(8)
F(1)-F(1A)-C(1) 57.8(10)
F(2A)-F(2)-C(1) 65.9(10)
F(2)-F(2A)-C(1) 81.4(12)
F(2)-F(2A)-F(3) 134.8(13)
154
C(1)-F(2A)-F(3) 53.7(6)
F(3A)-F(3)-C(1) 64.4(10)
F(3A)-F(3)-F(2A) 98.1(12)
C(1)-F(3)-F(2A) 47.3(5)
F(3)-F(3A)-F(1) 131.0(15)
F(3)-F(3A)-C(1) 74.4(11)
F(1)-F(3A)-C(1) 57.2(8)
C(5)-F(4)-F(4A) 49.6(5)
F(6)-F(4A)-C(5) 76.2(11)
F(6)-F(4A)-F(4) 138.1(14)
C(5)-F(4A)-F(4) 62.7(7)
F(4A)-F(6)-F(6A) 143.1(14)
F(4A)-F(6)-C(5) 65.7(10)
F(6A)-F(6)-C(5) 78.6(8)
F(6)-F(6A)-C(5) 53.3(7)
C(2)-O(1)-Rh(1) 121.8(4)
C(4)-O(2)-Rh(1) 122.7(3)
C(7)-O(3)-Rh(1) 120.2(3)
C(9)-O(4)-Rh(1) 122.7(3)
C(15)-N(1)-C(11) 118.4(5)
C(15)-N(1)-Rh(1) 120.2(4)
C(11)-N(1)-Rh(1) 121.3(4)
F(1)-C(1)-F(2A) 125.3(9)
F(1)-C(1)-F(3A) 60.8(7)
F(2A)-C(1)-F(3A) 106.3(9)
F(1)-C(1)-F(2) 113.0(9)
F(2A)-C(1)-F(2) 32.6(5)
F(3A)-C(1)-F(2) 130.3(8)
F(1)-C(1)-F(3) 101.7(9)
F(2A)-C(1)-F(3) 79.0(8)
F(3A)-C(1)-F(3) 41.2(6)
F(2)-C(1)-F(3) 111.4(8)
F(1)-C(1)-F(1A) 34.6(6)
155
F(2A)-C(1)-F(1A) 113.0(8)
F(3A)-C(1)-F(1A) 94.8(8)
F(2)-C(1)-F(1A) 87.1(7)
F(3)-C(1)-F(1A) 134.6(9)
F(1)-C(1)-C(2) 114.1(8)
F(2A)-C(1)-C(2) 118.2(7)
F(3A)-C(1)-C(2) 116.4(7)
F(2)-C(1)-C(2) 110.6(7)
F(3)-C(1)-C(2) 105.5(7)
F(1A)-C(1)-C(2) 105.8(6)
O(1)-C(2)-C(3) 128.9(5)
O(1)-C(2)-C(1) 113.1(5)
C(3)-C(2)-C(1) 118.0(5)
C(2)-C(3)-C(4) 125.8(5)
O(2)-C(4)-C(3) 126.3(5)
O(2)-C(4)-C(5) 114.2(5)
C(3)-C(4)-C(5) 119.4(5)
F(4A)-C(5)-F(5A) 115.1(11)
F(4A)-C(5)-F(6) 38.1(6)
F(5A)-C(5)-F(6) 113.6(12)
F(4A)-C(5)-F(5) 129.8(10)
F(5A)-C(5)-F(5) 20.4(11)
F(6)-C(5)-F(5) 114.9(9)
F(4A)-C(5)-F(4) 67.7(8)
F(5A)-C(5)-F(4) 86.8(11)
F(6)-C(5)-F(4) 105.4(7)
F(5)-C(5)-F(4) 105.5(8)
F(4A)-C(5)-C(4) 120.3(7)
F(5A)-C(5)-C(4) 124.0(10)
F(6)-C(5)-C(4) 114.4(6)
F(5)-C(5)-C(4) 109.4(8)
F(4)-C(5)-C(4) 106.4(6)
F(4A)-C(5)-F(6A) 85.7(8)
156
F(5A)-C(5)-F(6A) 91.3(12)
F(6)-C(5)-F(6A) 48.0(6)
F(5)-C(5)-F(6A) 79.5(9)
F(4)-C(5)-F(6A) 149.4(7)
C(4)-C(5)-F(6A) 100.0(6)
F(8)-C(6)-F(7) 107.3(5)
F(8)-C(6)-F(9) 108.0(5)
F(7)-C(6)-F(9) 106.8(5)
F(8)-C(6)-C(7) 109.9(5)
F(7)-C(6)-C(7) 110.3(5)
F(9)-C(6)-C(7) 114.2(5)
O(3)-C(7)-C(8) 129.5(5)
O(3)-C(7)-C(6) 113.2(5)
C(8)-C(7)-C(6) 117.3(5)
C(9)-C(8)-C(7) 124.2(5)
O(4)-C(9)-C(8) 131.2(5)
O(4)-C(9)-C(10) 110.8(5)
C(8)-C(9)-C(10) 118.0(5)
F(10)-C(10)-F(12) 107.8(5)
F(10)-C(10)-F(11) 107.9(5)
F(12)-C(10)-F(11) 105.4(5)
F(10)-C(10)-C(9) 110.3(5)
F(12)-C(10)-C(9) 111.5(5)
F(11)-C(10)-C(9) 113.7(5)
N(1)-C(11)-C(12) 121.7(7)
C(11)-C(12)-C(13) 119.8(6)
C(14)-C(13)-C(12) 119.0(6)
C(15)-C(14)-C(13) 118.4(7)
N(1)-C(15)-C(14) 122.7(6)
_____________________________________________________________
Symmetry transformations used to generate equivalent atoms:
157
Table 6.14. Anisotropic displacement parameters (Å
2
x 10
3
) for cis-
(acac)
2
Rh(CH
3
)(Py). The anisotropic 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
______________________________________________________________________________
Rh(1) 28(1) 29(1) 32(1) 0(1) 0(1) 3(1)
F(1A) 91(7) 46(5) 51(5) 14(4) -44(5) -6(5)
F(4) 87(6) 77(6) 79(6) -14(4) 57(5) -44(5)
F(5) 97(10) 55(8) 68(8) 8(6) 53(6) 6(6)
F(5A) 50(6) 65(9) 58(7) 31(7) 32(5) 17(7)
F(6A) 92(8) 172(14) 30(5) -28(6) 3(5) 31(8)
F(7) 69(2) 80(3) 32(2) -13(2) 1(2) -23(2)
F(8) 41(2) 75(3) 58(2) -12(2) 9(2) -20(2)
F(9) 75(3) 42(2) 90(3) -14(2) -6(2) -14(2)
F(10) 41(2) 122(4) 83(3) 46(3) 16(2) 37(2)
F(11) 110(3) 39(2) 72(3) 0(2) -27(3) 28(2)
F(12) 73(2) 60(2) 34(2) -2(2) -7(2) 21(2)
O(1) 37(2) 33(2) 36(2) 3(2) 5(2) 12(2)
O(2) 37(2) 42(2) 30(2) 1(2) 2(2) 6(2)
O(3) 30(2) 41(2) 38(2) 1(2) -1(2) -1(2)
O(4) 28(2) 34(2) 37(2) -2(2) -4(2) 3(2)
N(1) 38(2) 24(2) 44(3) 1(2) 10(2) 3(2)
C(1) 64(4) 68(5) 54(5) 6(4) 21(4) 31(4)
C(2) 38(3) 35(3) 41(4) -3(3) -3(3) 5(2)
C(3) 37(3) 42(3) 35(3) -3(3) 1(2) 8(2)
C(4) 34(3) 43(3) 31(3) -7(2) 2(2) -2(2)
C(5) 68(5) 117(7) 45(4) 24(5) 19(4) 51(5)
C(6) 41(3) 52(4) 41(4) -8(3) 7(3) -8(3)
C(7) 27(3) 36(3) 33(3) -1(2) 10(2) -1(2)
C(8) 39(3) 30(3) 35(3) -1(2) 8(2) 4(2)
C(9) 34(3) 37(3) 25(3) 0(2) 8(2) 12(2)
C(10) 48(3) 41(3) 33(3) 4(3) -1(3) 14(3)
158
C(11) 37(3) 38(3) 62(4) -2(3) 12(3) -1(3)
C(12) 41(3) 41(4) 91(6) -5(4) 32(4) 0(3)
C(13) 71(5) 39(4) 69(5) -5(3) 46(4) -10(3)
C(14) 70(5) 45(4) 43(4) 3(3) 18(3) 10(3)
C(15) 49(3) 36(3) 39(3) 5(3) 8(3) 4(3)
C(16) 43(3) 33(3) 54(4) -9(3) 4(3) -2(3)
Table 6.15. Hydrogen coordinates ( x 10
4
) and isotropic displacement parameters
(Å
2
x 10
3
) for cis-(acac)
2
Rh(CH
3
)(Py).
_______________________________________________________________________________
x y z U(eq)
_______________________________________________________________________________
H(3) 1853 9647 4041 46
H(8) 5947 7472 3508 41
H(11) 9604 8771 2777 54
H(12) 11158 8649 803 67
H(13) 9857 8630 -1733 67
H(14) 6962 8734 -2211 62
H(15) 5492 8861 -160 49
H(16A) 8073 9533 3379 65
H(16B) 8383 9258 4952 65
H(16C) 6871 9605 4672 65
Synthesis of trans-(hfac-O,O)2Rh(Ph)(py). 1 (0.1 g) was heated with
diphenyl mercury (0.1 g, ~1.2 mol eq) in 1:1 CHCl
3
/CH
3
OH (15 mL) at 100°C for
12 h in a Schlenk tube fitted with a resealable Teflon valve, after 5 freeze-pump-
thaw cycles, and filled with argon. The solution became dark orange. The solvent
was then removed by vacuum, then 7 mL of dry pyridine was added and the
159
solution was heated at 50 °C for 15 min. The pyridine was mostly removed by
vacuum, then 1 mL of water was added and a yellow/orange compound
precipitated. The solid was filtered, and washed with two 5 mL portions of cold
water, then dried on the vacuum line and stored under argon until the compound
was found to be air and water stable.
1
H NMR (CDCl
3
) 250MHz: d 8.62 (d, 2H,
py-o-H’s), 7.96 (t, 1H, py -p-H), 7.57 (t, 2H, py-m-H’s), 7.14 (m, 3H, Ph-H’s),
7.05 (d, 2H, Ph-H’s), 5.91 (s, 2H, hfac-CH).
19
F NMR (CD
3
OD) ref. to CFCl
3
360
MHz: d 74.98 (s, 12F, hfac-CF3’s).
13
C{
1
H} NMR (C
6
D
6
) 360 MHz: d 92.72 (s,
hfac CH), 175.86 (q, J
CF
= 143.75 Hz, hfac C=O), 149.46 (s, py), 139.41 (s, py),
133.93 (s, Ph), 127.96 (s, Ph), 126.24 (s, Ph), 125.12 (s, py), 115.43 (q, J
CF
=
1132.25 Hz). Anal. Calcd: C, 37.47; H, 1.80; N, 2.08. Found: C, 35.73; H, 1.80;
N, 2.02.
Synthesis of cis-(hfac-O,O)
2
Rh(Ph)(py). Complex 3 was heated in neat
benzene under argon at 190°C for 24 hours. This produced cis-(hfac)
2
Rh(Ph)(py).
The reaction was done with approximately 25mg of starting material in 15mL neat
benzene. Sublimation of this compound left behind Rh metal precipitated from the
reaction.
1
H NMR (CDCl
3
) 400 MHz: d 6.06 (s, 2H, hfac C
3
H), d 6.09 (s, 2H,
hfac C
3
H), d 6.86 (d, o -CH phenyl), d 7.10 (m, m/p-CH phenyl overlapping), d
7.36 (t, 2H, m -CH pyridine), d 7.87 (t, 1H, p-CH pyridine), d 8.17 (d, 2H, o-CH
pyridine).
13
C NMR {
1
H} (CDCl
3
) 400 MHz: d 89.53 (s, hfac CH), 92.32 (s, hfac
CH), 118ppm (m, CF
3
overlapping resonances), 147.70 (d, i-C J
RhC
= 28.6),
177.10 (m, hfac C=O J
2
CF
= 36.2 Hz). Phenyl and pyridine carbons: d 125.18,
160
125.52, 127.66, 134.40, 138.98, 52.43. Analysis Calculated for C
21
H
18
F
12
NO
4
Rh:
C, 37.13; H, 2.67; N, 2.06. Found: C, 37.80; H, 2.00; N, 2.08.
Synthesis of cis-(hfac-O,O)
2
Rh(Mes)(py). Complex 3 was heated in neat
mesitylene under argon at 190°C for 28 hours. The synthesis was divided up into
5 batches of about 25 mg apiece. Larger batches took more time for complete
conversion to the mesityl product.
1
H NMR (CDCl
3
) 400 MHz: d 2.15 (s, CH
3
,
mesityl), doublet of doublets at d 4.46 (d/d, CH
2
, mesityl) and d 5.05 (d/d, 1H, CH
2
mesityl), d 5.68 (s, 1H, hfac C
3
H), d 5.96 (s, 1H, hfac C
3
H), d 6.69 (s, 1H, o-CH,
mesityl), d 6.79 (s, 1H, p-CH, mesityl), d 7.45 (t, 2H, m -CH pyridine), d 7.90 (t,
1H, p-CH pyridine), d 8.26 (d, 2H, o -CH pyridine). Single crystals suitable for
diffraction were grown from evaporation of a concentrated solution in methanol.
H-D exchange: Catalytic H-D exchange reactions were quantified by
monitoring the increase of deuterium into C
6
H
6
by GC/MS analyses. This was
achieved by deconvoluting the mass fragmentation pattern obtained from the MS
analysis, using a program developed with Microsoft EXCEL. An important
assumption made with this method is that there are no isotope effects on the
fragmentation pattern for the various benzene isotopologs. Fortunately, because
the parent ion of benzene is relatively stable towards fragmentation, it can be used
reliably to quantify the exchange reactions. The mass range from 78 to 84 (for
benzene) was examined for each reaction and compared to a control reaction
where no metal catalyst was added. The program was calibrated with known
mixtures of benzene isotopologs. The results obtained by this method are reliable
161
to within 5%. Thus, analysis of a mixture of C
6
H
6
, C
6
D
6
and C
6
H
5
D
1
prepared in a
molar ratio of 40: 50: 10 resulted in a calculated ratio of 41.2(C
6
H
6
): 47.5(C
6
D
6
):
9.9(C
6
H
5
D
1
). Catalytic H/D exchange reactions were thus run for sufficient
reaction times to be able to detect changes >5% exchange. The methanol analog
of complex 2, trans-(hfac-O,O)
2
Rh(CH
3
)(CH
3
OH), was the catalyst used to carry
out the H/D exchange between benzene and deuterium oxide.
In a typical experiment, a 2 mL Schlenk tube fitted with a resealable Teflon
valve was charged with 5 mg of methanol analog of 2, benzene 1.0 mL, and 1.0
mL of toluene-d8 under an atmosphere of argon. The tube was then placed in a
temperature controlled oil-bath maintained at 190 °C, and deuteration was then
measured as described above.
162
6.4 References.
1
Skodje, R. T.; Truhlar, D. G. J. Phys. Chem. 1981, 85, 624.
2
(a) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H. Acc. Chem.
Res. 1995, 28, 154. (b) Shilov, A. E.; Shul’pin, G. B. Activation and Catalytic
Reactions of Saturated Hydrocarbons in the Presence of Metal Complexes Kluwer
Academic; Dordrecht, 2000 (c) Jia, C.G.; Kitamura, T.; Fujiwara, Y. Acc. Chem.
Res. 2001, 38, 633. (d) Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2001, 19,
2437. (e) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507. (f) Periana, R. A.;
Bhalla, G.; Tenn III, W.J.; Young, K. J. H.; Liu, X. Y.; Mironov, O.; Jones, CJ;
Ziatdinov, V. R. J. Mol. Cat A. Chem. 2004, 220, 7.
3
For example see: (a) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G.
Acc. Chem. Res. 2002, 35, 44. (b) Jones, W. D.; Feher, F. J. Acc. Chem. Res.
1989, 22, 91. (c) Wang, C. M.; Ziller, J. W.; Flood, T. C. J. Am. Chem. Soc. 1995,
117, 1647. (e) Zhong, H. A.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc.
2002, 124, 1378-1399. (f) Johansson, L.; Ryan, O. B.; Tilset, M. J. Am. Chem.
Soc. 1999, 121, 1974. (g) Fekl, U.; Goldberg, K. I. Adv. Inorg. Chem. 2003, 5454,
259. (h) Liu, F. C.; Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S. J. Am.
Chem. Soc. 1999, 121, 4086. (i) Nuckel, S.; Burger, P. Angew. Chem. Int. Ed.
2003, 42, 1632.
4
(a) Bryndza, H. E.; Tam, W. Chem. Rev. 1988, 88, 1163. (b) Bergman, R. G.
Polyhedon, 1995, 3221-3237. (c) Mayer, J. M. Polyhedron, 1995, 3273.
5
(a) Periana, R. A.; Liu, X. Y.; and Bhalla, G. Chem. Commun., 2002, 3000. (b)
Matsumoto, T.; Taube, D. J.; Periana, R. A.; Taube, H.; Yoshida, H. J. Am.
Chem. Soc., 2000, 122, 7414.
6
Oxgaard, J.; Muller, R. P.; Goddard, W. A. III; Periana., R. A.; J. Am. Chem.
Soc., 2003, 126, 352.
7
Chattoraj, S. C.; Sievers, R. E. Inorg. Chem., 1967, 6, 408.
8
SMART V 5.625 Software System for the CCD Detector System; Bruker
AXS:Madison, WI, 2001.
9
SAINT V 6.22 Software System for the CCD Detector System; Bruker
AXS:Madison, WI, 2001.
163
10
Blessing, R.H. Acta Crystallogr. 1995, A51, 33.
11
Sheldrick, G .M. SHELXTL, version 5.1; Bruker Analytical X -ray System, Inc.:
Madison, WI, 1997.
164
7 Functionalization of a Low Valent Metal Carbon
Bond with Se(IV)
7.1 Introduction.
One of the key challenges to developing selective, low temperature
hydrocarbon oxidation catalysts based on the CH activation reaction is integration
with a compatible functionalization reaction.
1,2
As was described earlier in this
dissertation, recently a CH activation reaction with an alkoxo complex, M-OR,
that simultaneously generates a functionalized product, ROH, and a metal alkyl,
M-R, where M is Ir(III), was found.
3
A catalytic cycle for the conversion of RH to
ROH could be possible by regeneration of M -OR from M-R. Pt(IV) or Hg(II)
alkyls are M -C
s+
polarized and readily undergo reductive functionalization with
O-nucleophiles.
1b,4
With the move to more electron -rich MX complexes to carry
out the CH Activation reaction, we have found that the pathway for M-R
functionalization that operates for the Pt(II) and Hg(II) system is not available.
Such functionalizations with M-Rs of more electropositive metals such as Ir or Re
are not facile likely due to the opposite M -C
s -
polarization in the low oxidation
states. Consequently, functionalization of these M-Rs may be more facile in non -
redox, insertion reactions with electrophilic O-atom donors, YO, such as that
shown in Eq 1, if free-radical pathways or formal oxidation of the metal centers
165
could be minimized.
5
Conversion of Y to YO with O
2
could complete the overall
catalytic cycle.
M-R + YO à M-OR + Y
Scheme 7.1. Generalized Reaction for Oxy-Functionalization of a Metal Carbon
Bond via O-Atom Transfer.
The conversion of M-R to M-OR is not well known and the few reported
examples proceed with O
2
by free-radicals pathways
6
or by slow redox reactions
involving alkyl to metal oxo migration.
7
Consequently, identification of a facile
pathway for Eq 1, especially with non peroxo
8
YOs that could potentially be
recycled with O
2
, could be useful.
Consequently, we recently conceived of and reported proof of principle for
using an alternative pathway involving O-atom insertion as a mean of converting
electron-rich M -R to the desired ROH that proceeds via a low energy, Baeyer-
Villiger (BV) type, electrophilic O-atom insertion as depicted in Scheme 7.2.
9
H
3
C Re
O
IO
3
O
O
O
H
3
C
O
Re
O
O
O
CH
3
OH
H
3
C Re
O
O
O
O
H
3
C Re
O
O
O
17 kcal/mol
25 kcal/mol
+ H
2
O
MTO
+ IO
4
-
Overall Barriers
- HOReO
3
- IO
3
-
- IO
3
-
BV-type Path
h
2
-peroxo Path
Scheme 7.2. Calculated Low Energy Pathways for Methanol Formation from
MTO and Periodate in Water.
166
However, this was demonstrated for CH
3
ReO
3
where the oxidation state of
for rhenium is Re(VII) rather than the desired Re(I). This lower oxidation state is
desired since this Re(I) is more electron -rich than Re(VII) and likely to be active
for CH activation in non -acidic or basic media. Consequently, we have been
working to show feasibility for converting Re(I)-R intermediates to ROH products.
Significantly, we have now shown that RRe(CO)
5
(a motif that has been reported
to be generated from CH activation) will efficiently react with Se(IV) to generate
R-Se products in an essentially quantitative reaction.
CH
3
Re(CO)
5
+ HOSe(O)(OH) à CH
3
Se(O)OH 100 % yield
Scheme 7.3. Observed Transformation in the Reaction Between Methyl
Pentacarbonyl Rhenium(I) and Selenious Acid.
Importantly, we have also shown that by use of an oxidant, IO
4
-
and
catalytic amounts of Se(IV), CH
3
Re(CO)
5
can be converted to CH
3
OH in 80 %
yield, likely by the mechanism shown below (Figure 7.1). It is likely that these
results are related to the somewhat empirical observations that have been made on
the use of Se oxides are utilized in recent heterogeneous selective oxidation
systems,
10
and the selenium dioxide oxidation of ketones and aldehydes which has
been studied extensively.
11
167
Figure 7.1. Proposed Mechanism for the Conversion of CH
3
Re to Methanol
Catalyzed by Se(IV).
7.2 Results and Discussion.
To begin to explore whether the CH
3
Re(CO)
5
to methanol reaction could
be facile, the direct reaction of CH
3
Re(CO)
5
with three YOs was explored: PhIO,
PyO and IO
4
-
in water/acetonitrile solution. Both PhIO and IO
4
-
are efficient for
generation of methanol, however not particularly selective (30 ± 6 % yield in
methanol with PhIO and 20 ± 2 % using KIO
4
). In contrast, reaction of
CH
3
Re(CO)
5
with pyridine N-oxide yielded no methanol under the same
conditions, and at higher temperature (> 120
o
C) protonolysis of CH
3
Re(CO)
5
to
yield methane was observed. Controls show that the reaction rates and
selectivities are independent of added O
2
and free-radicals are likely not involved.
In addition to the direct oxygen -atom insertion chemistry described in this
section thus far, in the course of this investigation functionalization of the Re-CH
3
with other heteroatom agents was also determined to be facile. Carrying out the
reaction of CH
3
Re(CO)
5
with D
2
SeO
3
(generated in situ from SeO
2
and D
2
O) in a
CH Activation Functionalization
LM
n
-OH
LM
n
-CH
3
CH
4
H
2
O
Y
YO
+ H
2
O
+ CH
3
OH
Net Reaction: CH
4
+ 1/2 O
2 CH
3
OH
Oxidation
1/2 O
2
Se
O
OH H 3C
Se
O
OH HO
168
solution of acetonitrile and water produced CH
3
SeO
2
D in quantitative yield and
identified by comparison of the
1
H and
13
C NMR spectra and mass peaks to that of
the commercially available authentic sample. No carbon dioxide was identified in
gas chromatography-mass spectrometry (GC-MS) analyses of the headspace of the
reaction mixture.
It is interesting that this heteroatom functionalization reaction proceeds
cleanly given the possibility for side reactions. Additionally, the observation that
the reaction of this Se(IV) proceeds in high yield shows this reaction is
substantially different from the corresponding direct reactions with O-atom
transfer agents. Possibly the reaction may be favored by the sterically
undemanding carbonyl ligand set of the Re-CH
3
complex, along with the increased
polarizability of the Se(IV) center could account for the high selectivity observed
for this functionalization reaction.
Having established that H
2
SeO
3
can stoichiometrically react with the Re-
CH
3
bond of CH
3
Re(CO)
5
the catalytic oxy-functionalization of this complex via
use of a catalytic amount of Se(IV) (0.1 equivalent) and a terminal oxidant (excess
KIO
4
) in aqueous media at 100
o
C was examined. The CH
3
Re(CO)
5
system is
stable over the time period studied (12 h) and although production of methane in
the absence of Se(IV) or the oxidant was noted, especially at higher temperatures
or longer reaction times, no methane was observed in the catalytic system. In the
reaction system, CH
3
SeO
2
D is observed to be formed before the production of
methanol. Although periodate was found to convert CH
3
Re(CO)
5
to methanol
169
without the use of Se(IV), when a catalytic amount of H
2
SeO
3
is used the
selectivity of the overall reaction increases from approximately 20 % to 80 % yield
in methanol.
Extension of this chemistry to other electron-rich M-R complexes is being
examined along with the extension of use of other transalkyation reagents based on
S, Te, Sn, or B.
In addition, CD
3
OSeO
2
D (produced from CD
3
OD and SeO
2
) was also
found to produce CH
3
Se(O)CD
3
in high yield (79.3 %). Elemental sulfur was
found to react with CH
3
Re(CO)
5
to yield S-CH
3
products. Conversion of
Sn(CH
3
)
4
to CH
3
SeO
2
H and HOSn(CH
3
)
3
with H
2
SeO
3
in acetonitrile/water at
100
o
C for 30 minutes was also found to be facile.
7.3 Conclusion.
These are the first known examples of functionalization of electron -rich M-
R species to generate R -heteroatom products and alcohols by likely non -radical
reaction mechanisms. Coupling these reactions with the CH Activation reaction
should allow new catalytic cycles to be developed for the selective conversion of
methane to methanol with catalysts that are not inhibited by methanol or water.
These results are encouraging and may point to a mild and highly selective
pathway for heteroatom functionalization of M -R intermediates of more electron
rich metals via a pathway with catalytic transalkylation agents and a terminal
oxidant. However, there are some key considerations that must be addressed
170
before we can determine if this pathway will be broadly applicable for M -R
functionalizations. Thus, a key question to investigate is whether this type of
Se(IV) catalyzed oxy-functionalization can be extended to a range of air-
recyclable YOs and M-Rs with other ligand sets and electronic configurations and
if so, whether the Se(IV) catalyzed oxy- functionalization will continue to be facile.
In conclusion, herein is reported evidence for the facile conversion of Re-
CH
3
to methanol by reaction with Se(IV), and an O-atom donor. Currently
investigations are under way to determine the breadth of this reaction pathway and
the feasibility of incorporation into catalytic cycles of the type shown in Figure
7.1.
7.4 Experimental Section.
General Considerations: All air and water sensitive procedures were carried
out either in a Vacuum Atmospheres inert atmosphere glove box under argon, or
using standard Schlenk techniques under argon. Methyl iodide (Aldrich) was used
as purchased. The l abeled methyl iodide,
13
CH
3
I, (Cambridge Isotopes) was used
as purchased. Rhenium carbonyl (Re
2
CO
10
) was purchased from Strem.
Selenium(IV) oxide (Research Organic/Inorganic Chemical Corp.) was used as
purchased. GC/MS analysis was performed on a Shimadzu GC-MS QP5000 (ver.
2) equipped with cross-linked methyl silicone gum capillary column (DB5). The
retention times of the products were confirmed by comparison to authentic
171
samples. All NMR spectra were obtained on a Varian Mercury-400 spectrometer
at room temperature. All chemical shifts are reported in units of ppm and
referenced to the residual protic solvent.
(CO)
5
ReCH
3
+ PhIO: All reactions were carried out in 9:1 CD
3
CN/D
2
O in
8” NMR tubes equipped with a resealable J -Young Teflon valve. Approximately
30 mg (0.088 mmol) of methyl rhenium(I) pentacarbonyl was charged to the NMR
tube, followed by 3 equivalents of PhIO (58.08 mg, 0.264 mmol), followed by
acetone-d6 (0.7 mL added), along with 0.6 µL of cyclohexane for use as an
internal standard. All appropriate blanks were taken to assign solvent peaks,
starting material peaks, and product (methanol) formation. Reactions were
typically carried out under air at 100
o
C for 4 h.
(CO)
5
ReCH
3
+ KIO
4
: All reactions were carried out in 9:1 CD
3
CN/D
2
O in
8” NMR tubes equipped with a resealable J -Young Teflon valve. Approximately
10 mg (0.088 mmol) of methyl rhenium(I) pentacarbonyl was charged to the NMR
tube, followed by 3 equivalents of KIO
4
(60.24 mg, 0.262 mmol), followed by
CD
3
CN and D
2
O (9:1, 0.7 mL added), along with 0.6 µL of cyclohexane for use as
an internal standard. All appropriate blanks were taken to assign solvent peaks,
starting material peaks, and product (methanol) formation. Reactions were
typically carried out under air at 100
o
C for 12h.
(CO)
5
ReCH
3
+ H
2
SeO
3
: All reactions were carried out in 9:1 CD
3
CN/D
2
O
in 8” NMR tubes equipped with a resealable J-Young Teflon valve.
Approximately 30 mg (0.088 mmol) methyl rhenium(I) pentacarbonyl was
172
charged to the NMR tube, followed by 1 equivalent of SeO
2
(9.76 mg, 0.088
mmol), followed by CD
3
CN and D
2
O (9:1, 0.7 mL added), along with 0.6 µL of
cyclohexane for use as an internal standard. All appropriate blanks were taken to
assign solvent peaks, starting material peaks, and product (methanol) formation.
Reactions were typically carried out under air at 100
o
C for 30 minutes.
CH
3
SeO
2
H(D)
1
H NMR (9:1 CD
3
CN/D
2
O): d 2.65(s, 3H, Se-CH
3
,
2
J
Se-H
13.2 Hz).
13
C{
1
H} NMR (9:1 CD
3
CN/D
2
O): d 42.2(Se-CH
3
,
1
J
Se-H
90.2 Hz).
Figure 7.2.
1
H NMR of (CO)
5
ReCH
3
in CD
3
CN/D
2
O with cyclohexane internal
standard. d -0.02(s, 3H, (CO)
5
ReCH
3
methyl); 1.40 (s, cyclohexane
I.S.); 1.97 (s, acetonitrile residual peak); 3.71 (water residual peak).
173
Figure 7.3.
1
H NMR of mixture after heating at 100
o
C for 30 min. d1.40 (s,
cyclohexane I.S.); 1.97 (s, acetonitrile residual peak); 2.65 (s,
CH
3
SeO
2
D, methyl); 3.71 (water residual peak).
(CO)
5
ReCH
3
+ 0.1 H
2
SeO
3
+ 3 KIO
4
: All reactions were carried out in 9:1
CD
3
CN/D
2
O in 8” NMR tubes equipped with a resealable J-Young Teflon valve.
Approximately 30 mg (0.088 mmol) methyl rhenium(I) pentacarbonyl was
charged to the NMR tube, followed by approximately 0.1 equivalent of SeO
2
(1.0
mg, 0.009 mmol), KIO
4
(60.72 mg, 0.264 mmol), and finally CD
3
CN and D
2
O
(9:1, 0.7 mL added), along with 0.6 µL of cyclohexane for use as an internal
standard were added. All appropriate blanks were taken to assign solvent peaks,
starting material peaks, and product (methanol) formation. Reactions were
typically carried out under air at 100
o
C for 30 minutes.
174
Scheme 7.4. Calculated Thermodynamics for Reactions of CH
3
-Y (Y = H,
Re(CO)
5
) with H
2
SeO
3
.
Theoretical Considerations: All theoretical calculations were performed with
the B3LYP density functional, in combination with the Jaguar 6.0 computational
package. Rhenium and osmium were described with the effective core potential of
Hay and Wadt, iodine with the effective core potentials of Ermler and colleagues
while all other atoms used the 6 -31G** all electron basis set. The effects of
diffuse functions (namely 6-31G**++) were included with single point
calculations. Solvation effects, in water, (computed via single point corrections)
were modeled implicitly with the PCM model (ε = 80.37, r
solv
= 1.4).
CH
4
+ H
2
SeO
3
CH
3
SeO
2
H + H
2
O DH = 2.8 kcal/mol
(CO)
5
ReCH
3
+ H
2
SeO
3
CH
3
SeO
2
H + (CO)
5
ReOH DH = -5.9 kcal/mol
DFT (solvent is water)
175
7.5 References.
1
We define the CH activation reaction as a coordination reaction that proceeds
without the involvement of free-radicals, carbocations or carbanions, to generate
discrete M-R intermediates. (a) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.;
Peterson, T. H. Acc. Chem. Res. 1995, 28, 154 and citations therein. (b) Periana, R.
A.; Bhalla, G.; Tenn III, W. J.; Young, K. J. H.; Liu, X. Y.; Mironov, O.; Jones,
C; Ziatdinov, V. R. J. Mol. Cat A. Chem. 2004, 220, 7 and citations therein.
2
Crabtree, R. H. J. Organomet. Chem. 2004, 689, 4083.
3
Tenn, W. J., III; Young, K. J. H.; Bhalla, G.; Oxgaard, J.; Goddard, W. A., III;
Periana, R. A. J. Am. Chem. Soc. 2005, 127, 14172.
4
Lersch, M.; Tilset, M. Chem. Rev. 2005, 105, 2471.
5
Formal oxidation of electropositive metals are likely to inhibit the CH activation
reaction and free-radicals would react with the alcohol product.
6
Kim, S.; Choi, D.; Lee, Y.; Chae, B.; Ko, J.; Kang, S. Organometallics 2004, 23,
559 and references therein.
7
Matano, Y.; Northcutt, T. O.; Brugmann, J.; Bennett, S. L.; Mayer, J. M.
Organometallics 2000, 19, 2781 and references therein.
8
A peroxo bond is a weak O-O high energy bond, DH = 33 kcal/mo l
9
Conley, B. L.; Gonzales, J. M.; Ganesh, S. K.; Tenn, W. J., III; Young, K. J. H.;
Oxgaard, J.; Goddard, W. A., III; Periana R. A. J. Am. Chem. Soc., 2006, 128,
9018.
10
(a) Patel, B. M.; Price, G. L. Ind. Eng. Chem. Res. 1990, 29, 730. (b) Mann, R.
S.; Lao, K. C. Ind. Eng. Chem. Res. 1967, 6, 263.
11
(a) Sharpless, K. B.; Gordon, K. M. J. Am. Chem. Soc. 1976, 98, 300. (b) Corey,
E. J.; Schaefer, J. P. J. Am. Chem. Soc. 1960, 82, 918. (c) Waitkins, G. R.; Clark,
C. W. Chem. Rev. 1945, 36, 235. (d) Selenium in Natural Products Synthesis,
Nicolaou, K. C.; Petasis, N. A.; CIS; Philadelphia, 1984.
176
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Abstract (if available)
Abstract
This dissertation describes a veritable smorgasbord of organometallic chemistry, including the use of transition metal methoxo and hydroxo complexes based on iridium(III) as homogeneous catalysts for the activation of hydrocarbon C-H bonds, the functionalization of a low valent rhenium methyl complex, and the design, synthesis, and study of related systems for the catalytic functionalization of hydrocarbons.
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University of Southern California Dissertations and Theses
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Asset Metadata
Creator
Tenn, William Joseph, III
(author)
Core Title
CH activation and catalysis with iridium hydroxo and methoxo complexes and related chemistry
School
College of Letters, Arts and Sciences
Degree
Doctor of Philosophy
Degree Program
Chemistry
Publication Date
06/06/2007
Defense Date
05/15/2007
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
catalysis,C-H activation,hydrocarbon,OAI-PMH Harvest
Language
English
Advisor
Periana, Roy A. (
committee chair
), Bickers, Nelson E. (
committee member
), Prakash, G.K. Surya (
committee member
)
Creator Email
wjtenn@usc.edu
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-m516
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UC1338382
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etd-Tenn-20070606 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-504363 (legacy record id),usctheses-m516 (legacy record id)
Legacy Identifier
etd-Tenn-20070606.pdf
Dmrecord
504363
Document Type
Dissertation
Rights
Tenn, William Joseph, III
Type
texts
Source
University of Southern California
(contributing entity),
University of Southern California Dissertations and Theses
(collection)
Repository Name
Libraries, University of Southern California
Repository Location
Los Angeles, California
Repository Email
cisadmin@lib.usc.edu
Tags
catalysis
C-H activation
hydrocarbon