Stoichiometric reduction of CO2 to CO by phosphine/AlX 3-based frustrated Lewis pairs

Article abstract of DOI:10.1021/om400619y

The reactions of the bulky phosphines Mes₃P or (otol) ₃P with AlX₃ (X = I, Br, Cl) and CO₂ are probed and shown to give complexes of the form Mes₃PC(OAlX ₃)₂ (X = I (3), Br (4), Cl (5)) and (otol) ₃PC(OAlI₃)₂ (6). The former compounds under CO₂ are further transformed to Mes₃PC(OAlX ₂)₂OAlX₃ (X = I (8), Br (10)) and [Mes ₃PX][AlX₄] (X = I (9), Br (11)). These latter reactions are thought to proceed via dissociation of alane, as evidenced by the generation of (otol)₃PC(OAl(C₆F₅)₃) from (otol)₃PC(OAl(C₆F₅)₃)₂ (7) and the isolation of (otol)₃PC(O)OAl(OC(CF₃) ₃)₃ (15). Subsequent insertion of CO₂ into the Al-X bond is evidenced by the characterization of [(C₆F ₅)C(O)OAl(C₆F₅)₂]₂ (14) from the reaction of Al(C₆F₅)₃ and CO ₂. The isolation of Al(C₆F₅) ₃·2(C₆H₅Br) (16) also suggests dissociation of Al(C₆F₅)₃ from 7 may be facilitated by interactions with solvent. Kinetics of the formation of 8/9 from 3 show the reaction is first order in 3 and CO₂ and the rate-determining step involves an associative process. A mechanism involving dissociation of alane and subsequent insertion of CO₂ into the Al-X bond is proposed.

Full text of DOI:10.1021/om400619y

Article
pubs.acs.org/Organometallics
Stoichiometric Reduction of CO2 to CO by Phosphine/AlX3‑Based
Frustrated Lewis Pairs
Gabriel Menard,† Thomas M. Gilbert,‡ Jillian A. Hatnean,† Anne Kraft,§ Ingo Krossing,§
́
and Douglas W. Stephan*,†
†Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6
‡Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115, United States
§Institut fur Anorganische und Analytische Chemie, Freiburger Materialforschungszentrum (FMF) and Freiburg Institute for
̈
Advanced Studies (FRIAS), Universitat Freiburg, Albertstraße 19, 79104 Freiburg, Germany
̈
S
* Supporting Information
ABSTRACT: The reactions of the bulky phosphines Mes3P or (otol)3P with AlX3
(X = I, Br, Cl) and CO2 are probed and shown to give complexes of the form
Mes3PC(OAlX3)2 (X = I (3), Br (4), Cl (5)) and (otol)3PC(OAlI3)2 (6). The
former compounds under CO2 are further transformed to Mes3PC(OAlX2)2OAlX3
(X = I (8), Br (10)) and [Mes3PX][AlX4] (X = I (9), Br (11)). These latter
reactions are thought to proceed via dissociation of alane, as evidenced by the
generation of (otol)3PC(OAl(C6F5)3) from (otol)3PC(OAl(C6F5)3)2 (7) and the
isolation of (otol)3PC(O)OAl(OC(CF3)3)3 (15). Subsequent insertion of CO2 into
the Al−X bond is evidenced by the characterization of [(C6F5)C(O)OAl(C6F5)2]2
(14) from the reaction of Al(C6F5)3 and CO2. The isolation of Al(C6F5)3·2-
(C6H5Br) (16) also suggests dissociation of Al(C6F5)3 from 7 may be facilitated by interactions with solvent. Kinetics of the
formation of 8/9 from 3 show the reaction is first order in 3 and CO2 and the rate-determining step involves an associative
process. A mechanism involving dissociation of alane and subsequent insertion of CO2 into the Al−X bond is proposed.
have also reported the further reaction of these systems with
CO2 to give CO.32 In this full report, we focus our attention on
the latter reactions, probing related systems and aspects of the
mechanism of CO2 reduction.
INTRODUCTION
■
Rapidly increasing levels of greenhouse gases in the
atmosphere, especially levels of CO2, require urgent action to
mitigate emissions.1 While the direct use of CO2 as a C1
feedstock for chemical transformation is attractive,2,3 the
reduction of CO2 could be far more useful. This C1 feedstock4
can be used in large-scale processes including the Cativa
(formerly Monsanto) process to produce acetic acid,5 Fischer−
Tropsch chemistry to produce liquid hydrocarbons,6,7 or
hydroformylation reactions to produce aldehydes.8 Because of
the scale of these industries, a process where CO2 is recycled
and used to generate CO could help to mitigate greenhouse gas
emissions; however, reduction of the strong CO bonds (532
kJ/mol)9 presents a significant kinetic barrier.2
The enzyme carbon monoxide dehydrogenase (CODH) is
Nature’s approach to reducing CO2 to CO and H2O.10
Heterogeneous systems have been developed to effect similar
reductions via photochemical11−15 or electrochemical16,17
methods. Alternatively, chemical reduction remains under
intense investigation.9,18−28 More recently, main group
mediated routes for CO2 reduction have also been
reported.29−38 In this vein, we have previously reported the
reversible capture of CO2 by phosphine/borane combina-
tions.39 Modification of these so-called “frustrated Lewis pairs”
(FLP) to combinations of phosphine and alane allows for
capture of CO2 and further reaction with ammonia borane to
afford methanol in a stoichiometric fashion.33 Alternatively, we
RESULTS AND DISCUSSION
■
Combinations of the bulky phosphines Mes3P or (otol)3P with
AlI3 affords the isolation of the adducts (R3P)AlI3 (R = Mes, 1;
otol, 2).32 Interestingly, while both displayed broad 31P{1H}
NMR resonances due to coupling to the quadrupolar (I = 5/2)
27Al nucleus, the spectrum for 1 displayed a second broad
resonance centered at −35 ppm, indicative of free Mes3P. This
is consistent with an equilibrium involving dissociation of the
adduct. Variable-temperature NMR spectroscopy was used to
extract the thermodynamic parameters of this equilibrium: ΔG
= 8.2 kJ/mol, ΔH = 42(1) kJ/mol, and ΔS 113(3) J/(K·mol)
with a Keq of 0.0372 at 25 °C. NMR spectra show that such
dissociation is significantly less for the analogous AlCl3 and
AlBr3 adducts.33 The adduct 2 shows no 31P NMR resonance
attributable to free (otol)3P over the same temperature range,
consistent with stronger Al−P binding as a result of the
diminished steric congestion.
It is interesting to note that mixtures of Mes3P/AlX3 yield
deep purple solutions in bromobenzene (λmax = 384, 572 nm;
Received: June 26, 2013
© XXXX American Chemical Society
A
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see the Supporting Information). This color is attributable to
the generation of the [Mes3P]•+ radical cation via electron
transfer to the alane.40 Indeed, monitoring solutions of Mes3P/
AlX3 (X = Br, I) by X-band EPR spectroscopy revealed the
presence of a doublet (g = 2.0056, aP = 239 G) consistent with
literature reports of the Mes3P•+ radical (Figure 1).41−43 The
Figure 2. POV-Ray depiction of the molecular structure of 6. C: black;
P: orange; Al: teal; I: pink; O: red. H atoms are omitted.
(10)) and [Mes3PX][AlX4] (X = I (9), Br (11)) were formed
with the concurrent liberation of CO (Scheme 1).32 These
reactions took ca. 16 h (X = I) and 48 h (X = Br), respectively.
While similar reactivity seemed to occur with AlCl3, the
reaction was significantly slower, precluding product isolation.
This trend parallels the reactivity of AlX3 (I > Br ≫ Cl).48
Reaction times also varied with solvent with completion after
ca. 4 days in fluorobenzene and <12 h in iodobenzene. This
observation suggests solvent-induced dissociation of AlX3 from
3 or 4 may be necessary to initiate the reduction of CO2 to CO
(vide infra).49 In further support for this dissociative pathway,
[Mes3PMe][AlI4] (12) was found to enhance the rate of
reaction, yielding 8 and 9 under CO2.32 This is thought to act
by promoting dissociation of AlI3 from 3, generating the halide-
bridged species [I3Al(μ-I)AlI3]−.
Further evidence of dissociation of alane is derived from the
analogous species (otol)3PC(OAl(C6F5)3)2 (7).50 This species
does not react under CO2 (1 atm) at 25 °C, consistent with the
relatively high computed Lewis acidity of Al(C6F5)3.51
However, heating a sample of 7 to 90 °C under CO2 in
bromobenzene for 48 h led to the gradual consumption of 7
and the appearance of the new species 13 and 14 (Scheme 2).
Figure 1. X-band EPR spectrum of Mes3P/2 AlBr3 in bromobenzene
(experimental: blue, simulation: red). Analogous signals are observed
when using AlI3. Simulation was done using PIP4Win v. 1.2.46
corresponding Al-based radical anion does not generate an EPR
signal. While this may be due to signal broadening due to the
quadrupole of Al, an electron transfer equilibrium is suggested
by the presence of both 31P/27Al NMR and EPR spectra for
these solutions. While the nature of the anion in this case
remains unknown, Norton has characterized the corresponding
B-radical anion [B(C6F5)3]•−.44 In this regard it is notweworthy
that the diamagnetic dimer [X3Ga-GaX3]2− is known.45
Interestingly, solutions of AlX3 (X = Br, I) with (otol)3P are
EPR inactive, consistent with the higher oxidation potential of
this phosphine.41
We previously reported that initial exposure of the FLPs
derived from Mes3P and AlX3 to CO2 leads to the rapid
formation of the complexes Mes3PC(OAlX3)2 (X = I (3), Br
(4), Cl (5)), which can be isolated in high yields (Scheme
1).32,33
Scheme 1. Reaction of Mes3P and AlX3 with CO2
Scheme 2. Synthesis of 13−15
The synthesis of the related compound (otol)3PC(OAlI3)2
(6)32 required heating of the (otol)3P/AlI3 solution to 80 °C
for 1 h under an atmosphere of CO2. Single crystals of 6
suitable for X-ray diffraction (Figure 2) reveal that the structure
is largely analogous to 3 with the P−CO2 bond length in 6
being shorter (1.877(4) Å) than that in 3 (1.903(8) Å).33 The
O−C−O angle in 6 is also slightly larger (127.4(4)°) than in 3
(125.0(8)°).33 Both these metric parameters reflect the reduced
steric bulk around (otol)3P vs Mes3P, as reflected in the
differing Tolman cone angles of 196° and 212°, respectively.47
On prolonged exposure of Mes3P/AlX3 solutions to a CO2
atm, the compounds Mes3PC(OAlX2)2OAlX3 (X = I (8), Br
The product 13 exhibits doublets in the 31P{1H} and 13C NMR
spectra at 12 and 160 ppm (1JP−C = 121 Hz) when [13C]-7 is
used. Similar resonances in the 31P{1H}, 13C, and 19F NMR
spectra were observed when a 1:1 solution of (otol)3P/
Al(C6F5)3 was exposed to an atmosphere of 13CO2, suggesting
that 13 is the 1:1 species (otol)3PC(O)OAl(C6F5)3 (Scheme
2). While this is thought to be similar to the previously
B
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reported species tBu3PC(O)OB(C6F5)3,39 attempts to isolate
13 were unsuccessful. Nonetheless, the closely related species
(otol)3PC(O)OAl(OC(CF3)3)3 (15) was prepared by exposing
a 1:1 solution of (otol)3P and the sterically encumbered
52
Al(OC(CF3)3)3 to CO2 (Scheme 2). The formulation of 15
was confirmed both spectroscopically and by an X-ray
diffraction study (Figure 3). The metric parameters for 15
were similar to the previously reported P/B39 and P/Al2
species.32,33
Figure 5. POV-Ray depiction of the molecular structure of 16. H
atoms are omitted. C: black; Al; teal; F: pink; Br: scarlet.
While the geometry about Al remains trigonal planar as
expected, the bromine atoms of two bromobenzene molecules
occupy positions above and below the trigonal plane with
Al···Br distances of 2.80 and 3.12 Å. Such an interaction may
mimic solvation, although, π-stacking between the electron-rich
arene bromobenzene ring and the electron-deficient fluoroar-
ene ring may stabilize the interactions observed in the solid
state. It is noteworthy that computational studies by Kwon et
al.49 further suggested that such solvation of the Lewis acid by
the solvent bromobenzene favors the dissociation of the
(Mes3P)AlCl3 adduct.33
Figure 3. POV-Ray depiction of the molecular structure of 15. H
atoms are omitted. C: black; P: orange; Al; teal; F: pink; O: red.
Mechanistic Insights. While solutions of Mes3P/AlX3
generate some adduct and some radical cation, addition of
CO2 results in loss of color and disappearance of any EPR
signal. This infers that the formation of the adduct 3 precludes
an open-shell mechanism for the subsequent reduction of CO2
to 8 and 9. To further examine the generation of CO from 3,
solutions of 3 were prepared and exposed to a 50-fold excess of
CO2. This was done using 5.0 atm of CO2 pressure and using a
known volume of solvent. The concentration of CO2 in
solution was estimated to be 0.4 M, based on Raoult’s law and
the known mole fraction of 0.0079 for CO2 in bromobenzene
at 1.0 atm.54 Under these conditions, the reaction of 3 to 8 and
9 proceeds under pseudo-first-order conditions. Monitoring the
reaction by 31P{1H} NMR spectroscopy experiments over a 30
K range (303−333 K) showed a first-order dependence on 3
with the activation parameters ΔH⧧ = 85(5) kJ/mol and ΔS⧧ =
−45(15) J/(mol·K) (Figure 6).
In addition to 13, heating 7 under CO2 also yielded a second
product, 14. This species exhibited six resonances in the 19F
NMR spectrum: two sets of three peaks integrating in a 2:1
ratio. This species was independently prepared by the reaction
of CO2 and Al(C6F5)3, yielding the symmetric dimeric species
[(C6F5)C(O)OAl(C6F5)2]2 (14). This species showed a singlet
at 168 ppm in the 13C NMR spectrum attributable to the CO2
moiety. The solid-state structure of 14 (Figure 4) revealed two
Similarly reduction of CO2 pressure was also consistent with
a first-order dependence of the reaction rate with CO2. This,
together with a negative activation entropy, suggests that the
rate-determining step in the reduction of CO2 to CO and the
formation of 8/9 involves an associative process.
A kinetic study of the conversion of 3 to 8/9 at 50 °C in the
presence of 0.5 or 1.0 equiv of cyclohexene revealed an inverse
first-order dependence on the concentration of cyclohexene.
Figure 4. POV-Ray depiction of the molecular structure of 14. C:
black; Al; teal; F: pink; O: red.
1
This suggests competitive binding of the olefin to AlX3. H
NMR spectra for these solutions do exhibit a shifted olefinic
resonance consistent with coordination to Al. This view is also
supported by computational studies. Using the OG2R3(SCRF)
approach, the olefin adduct (η2-C6H10)AlI3 is computed to be
34 kJ/mol more stable than the (η1-CO2)AlI3 adduct in
bromobenzene solvent. It is noteworthy that we have
previously characterized the cyclohexene adduct Al-
(C6F5)3(μ2-C6H10).51
CO2 moieties, bound in an inequivalent fashion to the Al
centers with C1−O1 and C2−O2 bond lengths of 1.257(2) and
1.262(2) Å. The corresponding O−Al bond lengths are slightly
different, at 1.773(1) and 1.814(1) Å, respectively. The Al−O−
C bond angles also differ, being 135.1(1)° and 160.4(1)°,
respectively.
The dissociation of Al(C6F5)3 from 7 may also be facilitated
by interactions with solvent. This is evidenced in the
crystallization of Al(C6F5)3 from bromobenzene, which
afforded crystals of Al(C6F5)3·2(C6H5Br) (16) (Figure 5).
The consumption of 3 in the reduction of CO2 suggests that
species 3 is the initial kinetic product. Conversion of 3 to 8 and
9 requires some free phosphine and alane. Dissociation of AlX3
C
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Scheme 3. Proposed Mechanism for the Reduction of CO2
decomposition of [Mes3PC(O)I][AlI4] to [Mes3PI][AlI4] and
CO is endothermic by 46 kJ mol−1 with a reaction barrier in
excess of 150 kJ mol−1. In contrast, scans of the potential
energy surface for phosphine attack at the carbon-bound halide
of the transient cycle indicate that formation of the
halophosphonium cation/cyclic anion pair entails only a small
barrier (ca. 70 kJ mol−1; the process is barrierless with respect
to the exothermicity of the formation of the cyclic
intermediate). Subsequent liberation of CO from the cyclic
anion is barrierless and exothermic by 53 kJ mol−1 (M06-
2X(SCRF) level), clearly supporting the latter reaction
pathway. This phosphine oxidation and reduction of CO2
yields an oxo-bridged Al species ultimately incorporated into
8. Computations at the M06-2X(SCRF) level55 show that the
exchange of neutral fragment [I2AlOAlI2] for AlI3 in 3 is
exothermic by −99 kJ/mol. The overall reaction energy for the
conversion of 3 to 8/9 and CO is computed to be exothermic
by 37 kJ/mol at the OG2R3(SCRF)//ONI(M06-2x)(SCRF)
level.56,57 This is consistent with the argument that the
formation of 3 represents the kinetic product, while the
liberation of CO and formation of 8/9 are the thermodynami-
cally favored products (Scheme 3).
Figure 6. Top: Stacked plot of 31P{1H} NMR spectra at 40 °C (initial
time 5 min and then at intervals of 15 min) for the reaction of 3 (7.2
mM) with 5 atm of CO2 (ca. 0.4 M). Middle: Representative plot of
the first-order decay of [3] at 60 °C. Bottom: Eyring plot.
from 3/4 generates the analogues of 15, while further
dissociation liberates phosphine and a second equivalent of
AlX3. Further competition is provided by the equilibrium
governing phosphine-alane adduct formation. This is consistent
with the observations that addition of excess AlI3 slowed the
conversion of 3 to 8 and 9, while addition of the
[Mes3PMe][AlI4] (12) facilitates dissociation of AlI3 from 3,
presumably by an equilibrium involving the generation of the
[Al2I7]− anion. The participation of free alane in the reaction is
also consistent with the slower reduction of 4 to 10 and 11,
presumably resulting from the increased Lewis acidity of AlBr3.
Based on the formation of 13 and 14 from 7, an associative
insertion reaction of CO2 with [Al2X6] affording a transient
cyclic species of the form [XC(OAlX2)2X] is proposed
(Scheme 3, bottom left). Probing this notion computationally,
scans of the potential energy surface for insertion of CO2 into
AlI3 at the M06-2X(SCRF) level55 led to an estimated barrier of
75 kJ mol−1 (NB.: experimental barrier: 85(5) kJ mol−1). In this
case, the reaction energy, calculated at the OG2R3(SCRF)
level,56,57 was found to be essentially thermoneutral (4 kJ
mol−1). However, inclusion of the second AlI3 resulted in a
highly exothermic reaction (−145 kJ mol−1).
CONCLUSION
■
The stoichiometric reduction of CO2 to CO using R3P/AlX3
FLPs has been probed, and the kinetic product has been shown
to be species of the form R3PC(OAlX3)2. Nonetheless a further
reaction occurs under CO2 via a rate-determining associative
insertion of CO2 into the Al−X bond of AlX3. This view is
supported by kinetic data and the isolation of the insertion
product of CO2 with Al(C6F5)3, 14. Subsequent nucleophilic
attack by phosphine effects phosphine oxidation and affords the
generation of the thermodynamic product Mes3PC-
(OAlX2)2OAlX3. While this reactivity is interesting, this work
suggests that catalytic processes to effect metal-free reduction of
CO2 will require a less oxophilic Lewis acid. Efforts to uncover
such main group systems capable of catalytic chemistry are
under study.60
EXPERIMENTAL SECTION
■
Subsequent nucleophilic attack by phosphine could proceed
via formation of a phosphonium acyl halide intermediate. Such
species are known to be unstable with respect to loss of
CO53,58,59 and formation of the corresponding halo-phospho-
nium cation. Alternatively, nucleophilic attack at the halide
could yield [Mes3PI]+ directly (Scheme 3, bottom middle).
Computations at the OG2R3(SCRF) level infer that the
General Considerations. All manipulations were performed
under an atmosphere of dry, oxygen-free N2 by means of standard
Schlenk or glovebox techniques (Innovative Technology glovebox
equipped with a −38 °C freezer). Hexanes and toluene (Aldrich) were
dried using an Innovative Technologies solvent system. Fluorobenzene
and bromobenzene (-H5 and -D5) were purchased from Aldrich and
dried on P2O5 for several days and vacuum distilled onto 4 Å
D
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molecular sieves prior to use. Mes3P and (otol)3P were purchased from
Strem, (CF3)3COH was purchased from Apollo Scientific, and
B(C6F5)3 was purchased from Boulder Scientific; all of these reagents
were used without further purification. Al(C6F5)3·tol was prepared
from B(C6F5)3 and Me3Al in toluene by a known procedure.61
Al(OC(CF3)3)3·C6H5F was prepared from Et3Al and (CF3)3COH in
fluorobenzene according to a literature procedure.52 AlX3 (X = Br, I)
were purchased from Strem and sublimed three times prior to use
under vacuum using a −78 °C coldfinger and an 80 °C (X = Br) or
150 °C (X = I) bath. 13CO2 was purchased from Aldrich and used
without further purification. CO2 was purchased from Linde and
passed through a Drierite column prior to use. NMR spectra were
obtained on a Bruker Avance 400 MHz or a Varian 400 MHz, and
spectra were referenced to residual solvent of C6D5Br or externally
(27Al: Al(NO3)3, 31P: 85% H3PO4, 19F: CFCl3). Chemical shifts (δ)
listed are in ppm, and absolute values of the coupling constants are in
Hz. NMR assignments are supported by additional 2D experiments.
UV−vis spectra were obtained on an Agilent 8453 UV−vis
spectrophotometer using Quartz cells modified with a J-Young
NMR cap to ensure a near-perfect seal. Elemental analyses (C, H)
and X-ray crystallography were performed in-house. EPR spectra were
recorded at the University of Windsor at 25 °C or 77 K on a Bruker
EMXplus X-band spectrometer controlled using Xenon software on a
PC operating under Linux. The spectra were modeled using PIP4Win
v. 1.2.46
Synthesis of (Mes3P)AlI3 (1). A 50 mL round-bottom flask
equipped with a magnetic stir bar in the glovebox was charged with
PMes3 (250 mg, 0.64 mmol), AlI3 (262 mg, 0.64 mmol), and
bromobenzene (6−7 mL). The solution was allowed to stir for 5−10
min while a precipitate formed. The white precipitate was collected on
a glass frit, washed with bromobenzene (several drops) and hexanes
(ca. 5 mL), and dried (300 mg, 0.38 mmol, 59%). 1H NMR (C6D5Br):
6.84 (bs, 3H, m-Mes), 6.68 (bs, 3H, m-Mes), 2.71 (s, 9H, o-CH3Mes),
2.02 (s, 9H, p-CH3Mes), 1.79 (s, 9H, o-CH3Mes). 31P{1H} NMR
(C6D5Br): −19, −29 (bm). 27Al NMR (C6D5Br): 37 (bd, 1JAl−P = 193
Hz). 13C{1H} NMR (C6D5Br): 145.6 (bs), 143.3 (bs), 142.0 (bs),
132.5 (bs, m-C6H2), 131.5 (m-C6H2, signal lost in solvent peak), 120.5
(d, 1JC−P = 40.0 Hz, i-C6H2), 28.6 (bs, o-CH3Mes), 24.4 (bs, o-CH3Mes),
21.0 (s, p-CH3Mes). Anal. Calcd for C27H33AlI3P: C, 40.73; H, 4.18.
Found: C, 40.65; H, 3.81.
144.1 (bs, o-C6H2), 133.9 (s, m-C6H2), 133.8 (s, m-C6H2), 114.1 (d,
1JC−P = 76 Hz, i-C6H2), 24.9 (bs, o-CH3Mes), 23.8 (bs, o-CH3Mes), 21.3
(s, p-CH3Mes). Anal. Calcd for C28H33PO2Al2Br6: C, 34.82; H, 3.44.
Found: C, 34.78; H, 3.64. 13C-4: Yield: 83%. 31P{1H} NMR
1
(C6D5Br): 21.0 (d, JP−C = 121 Hz).
5: yield: 82%. 1H NMR (C6D5Br): 6.80 (bs, 3H, m-Mes), 6.68 (bs,
3H, m-Mes), 2.32 (bs, 9H, o-CH3Mes), 2.03 (s, 9H, p-CH3Mes), 1.85
(bs, 9H, o-CH3Mes). 31P{1H} NMR (C6D5Br): 20.1 (d, JP−C = 123
1
Hz). 27Al NMR (C6D5Br): 105 (bs, υ1/2 = 750 Hz). 13C{1H} NMR
1
4
(C6D5Br): 171.5 (d, JC−P = 123 Hz, CO2), 146.8 (d, JC−P = 3.2 Hz,
p-C6H2), 145.0 (bs, o-C6H2), 144.4 (bs, o-C6H2), 133.6 (bs, 2 × m-
C6H2), 114.6 (d, 1JC−P = 76 Hz, i-C6H2), 24.5 (bs, o-CH3Mes), 23.6 (bs,
o-CH3Mes), 21.2 (s, p-CH3Mes). Anal. Calcd for C28H33PO2Al2Cl6: C,
48.10; H, 4.76. Found: C, 48.24; H, 4.71. 13C-5: Yield: 82%. 31P{1H}
NMR (C6D5Br): 19.8.
6: Heating to 60 °C for 1 h. Yield: 72%. 1H NMR (C6D5Br): 7.57−
7.51 (m, 3H), 7.36−7.32 (m, 3H), 7.16−7.09 (m, 6H), 2.08 (bs, 9H,
o-CH3). 31P{1H} NMR (C6D5Br): 27.5. 27Al NMR (C6D5Br): 23 (bs,
1
υ1/2 = ca. 1500 Hz). 13C{1H} NMR (C6D5Br): 164.3 (d, JC−P = 123
Hz, CO2), 144.5 (d, JC−P = 9.3 Hz), 136.9 (d, JC−P = 3.0 Hz), 135.7 (d,
JC−P = 12.7 Hz), 134.5 (d, JC−P = 11.6 Hz), 128.5 (d, JC−P = 13.6 Hz),
3
111.2 (d, JC−P = 81.2 Hz, i-C6H4), 23.4 (d, JC−P = 4.9 Hz, o-CH3).
Anal. Calcd for C22H21PO2Al2I6: C, 22.71; H, 1.82. Found: C, 23.22;
H, 2.00.
1
7: Yield, 90%. H NMR (C6D5Br): 7.60−6.85 (m, 12H), 1.81 (bs,
3
9H, o-CH3), 1.27−1.13 (m, 4H, 0.5·(CH3(CH2)CH3)), 0.84 (t, JH−H
= 6.8 Hz, 3H, 0.5·(CH3(CH2)CH3)). 31P{1H} NMR (C6D5Br): 30.0.
27Al NMR (C6D5Br): not observed. 19F{1H} NMR (376 MHz,
3
3
C6D5Br): −121.8 (bd, JF−F = 19.2 Hz, 12F, o-C6F5), −152.5 (t, JF−F
= 19.9 Hz, 6F, p-C6F5), −161.4 (m, 12F, m-C6F5). 13C{1H} NMR
1
1
(C6D5Br): 167.3 (d, JC−P = 128 Hz, CO2), 149.9 (dm, JC−F = 234
2
1
Hz), 144.2 (d, JC−P = 8.4 Hz, C-Me), 141.7 (dm, JC−F = 252 Hz),
136.7 (dm, 1JC−F = 253 Hz), 136.4 (d, JC−P = 1.8 Hz), 135.2 (d, JC−P
=
11.8 Hz), 133.7 (d, JC−P = 11.4 Hz), 127.7 (d, JC−P = 13.5 Hz), 112.9
(m, i-C6F5), 112.1 (d, 1JC−P = 78 Hz, i-C6H4), 31.8 (s, C6H14), 22.9 (s,
C6H14), 22.4 (bs, o-CH3), 14.4 (s, C6H14). Anal. Calcd for
C61H28Al2F30O2P·0.5C6H14: C, 50.61; H, 1.95. Found: C, 50.36; H,
2.06.
Isolation of Mes3PC(OAlX2)2OAlX3 (X = I, 8; Br, 10). Small
portions of these products were separated from reactions yielding 3
and 4, respectively, upon standing for 24 h and after slow cooling of
the fluorobenzene solutions to −38 °C.33 Crystals obtained were
suitable for X-ray crystallography. The crystals were partly soluble in
deuterated bromobenzene.
Synthesis of Mes3P(CO2)(AlX3)2 (X = I, 3; Br, 4; Cl, 5) and
(otol)3P(CO2)(AlX3)2 (X = I, 6; C6F5, 7). These compounds were
synthesized in an analogous manner. Thus, only one preparation is
detailed. A 50 mL round-bottom flask equipped with a magnetic stir
bar in the glovebox was charged with PMes3 (200 mg, 0.51 mmol) and
AlCl3 (69 mg, 0.51 mmol). Bromobenzene (10 mL) was added to this
all at once. The solution was allowed to stir for 30 min, at which point
ca. 15 mL of hexanes was added dropwise with rapid stirring. The
white precipitate 5 that forms was collected on a glass frit, washed with
hexanes (ca. 5 mL) followed by pentane (ca. 5 mL), and dried (215
mg, 0.41 mmol, 81%). Vapor diffusion of a bromobenzene solution of
the compound with pentane yielded single crystals suitable for X-ray
crystallography.
8: Small portions of 8 were isolated from reactions. 1H NMR
(C6D5Br): 7.09−6.83 (m, 7−8H, 1.5·C6H5F), 6.82 (bs, 3H, m-Mes),
6.70 (bs, 3H, m-Mes), 2.33 (bs, 9H, o-CH3Mes), 2.06 (s, 9H, p-
CH3Mes), 1.83 (bs, 9H, o-CH3Mes). 31P{1H} NMR (C6D5Br): 19.5. 27Al
NMR (C61D5Br): 31 (s, υ1/2 = ca. 170 Hz). 13C{1H} NMR (C6D5Br):
1
173.9 (d, JC−P = 118 Hz, CO2), 162.8 (d, JC−F = 244 Hz, i-C6H5F),
4
147.0 (d, JC−P = 3.0 Hz, p-C6H2), 144.7 (bs, 2C, o-C6H2), 133.5 (bs,
3
4
2C, m-C6H2), 130.0 (d, JC−F = 7.7 Hz, m-C6H5F), 124.1 (d, JC−F
=
3: yield: 87%. 1H NMR (C6D5Br): 6.83 (d, 4JH−H = 4.4 Hz, 3H, m-
3.1 Hz, p-C6H5F), 115.3 (d, 2JC−F = 20.6 Hz, o-C6H5F), 113.6 (d, 1JC−P
= 76.2 Hz, i-C6H2), 26.0 (bs, o-CH3Mes), 23.8 (bs, o-CH3Mes), 21.3 (s,
p-CH3Mes). 19F NMR (376 MHz, C6D5Br): −112.4. Anal. Calcd for
C28H33Al3I7O3P·3C6H5F (8·3C6H5F)): C, 28.45; H, 2.61. Found: C,
28.36; H, 2.60.
4
Mes), 6.70 (d, JH−H = 4.4 Hz, 3H, m-Mes), 2.48 (s, 9H, o-CH3Mes),
2.06 (s, 9H, p-CH3Mes), 1.90 (s, 9H, o-CH3Mes). 31P{1H} NMR
(C6D5Br): 22.0. 27Al NMR (C6D5Br): 20 (bs, υ1/2 = ca. 1500 Hz).
1
13C{1H} NMR (C6D5Br): 167.8 (d, JC−P = 119 Hz, CO2), 146.5 (d,
4JC−P = 3.0 Hz, p-C6H2), 144.9 (d, 2JC−P = 11.6 Hz, o-C6H2), 144.4 (d,
1
10: Small portions of 10 were isolated from reactions. H NMR
3
2JC−P = 10.3 Hz, o-C6H2), 134.5 (d, JC−P = 12.2 Hz, m-C6H2), 133.7
(CD2Cl2): 7.52−7.24 (m, 5H, C6H5Br), 7.17 (bs, 6H, m-Mes), 2.41 (s,
9H, p-CH3Mes), 2.32 (bs, 9H, o-CH3Mes), 2.11 (bs, 9H, o-CH3Mes).
31P{1H} NMR (CD2Cl2): 19.5. 27Al NMR (CD2Cl2): 88 (bs).
(d, 3JC−P = 12.5 Hz, m-C6H2), 115.0 (d, 1JC−P = 74.5 Hz, i-C6H2), 25.5
(d, 3JC−P = 5.7 Hz, o-CH3Mes), 23.9 (d, 3JC−P = 5.2 Hz, o-CH3Mes), 21.2
5
(d, JC−P = 1.5 Hz, p-CH3Mes). Anal. Calcd for C28H33PO2Al2I6: C,
1
13C{1H} NMR (CD2Cl2): 176.8 (d, JC−P = 123 Hz, CO2), 147.9 (d,
26.95; H, 2.67. Found: C, 26.91; H, 2.71. 13C-3: 31P{1H} NMR
4JC−P = 3.0 Hz, p-C6H2), 145.5 (bd, 2JC−P = 11 Hz, o-C6H2), 134.0 (bd,
1
(C6D5Br): 22.0 (d, JP−C = 119 Hz).
3JC−P = 12.4 Hz, m-C6H2), 131.9 (s, C6H5Br), 130.5 (s, C6H5Br), 127.4
4: Yield: 83%. 1H NMR (C6D5Br): 6.84 (bs, 3H, m-Mes), 6.76 (bs,
3H, m-Mes), 2.32 (bs, 9H, o-CH3Mes), 2.08 (s, 9H, p-CH3Mes), 1.90
1
(s, C6H5Br), 122.7 (s, C6H5Br), 113.7 (d, JC−P = 76.6 Hz, i-C6H2),
25.1 (bs, o-CH3Mes), 24.3 (bs, o-CH3Mes), 21.5 (d, JC−P = 1.6 Hz, p-
5
(bs, 9H, o-CH3Mes). 31P{1H} NMR (C6D5Br): 22.3. 27Al NMR
CH3Mes). Anal. Calcd for C28H33Al3Br7O3P·C6H5Br (10·C6H5Br): C,
1
(C6D5Br): not observed. 13C{1H} NMR (C6D5Br): 172.5 (d, JC−P
=
119 Hz, CO2), 147.2 (d, 4JC−P = 3.0 Hz, p-C6H2), 145.3 (bs, o-C6H2),
32.78; H, 3.07. Found: C, 32.52; H, 3.11.
E
dx.doi.org/10.1021/om400619y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Synthesis of [Mes3PX][AlX4] (X = I, 9; Br, 11). These
compounds were synthesized in an analogous manner. Thus only
one preparation is detailed. A 50 mL round-bottom Schlenk flask
equipped with a magnetic stir bar was charged with PMes3 (0.300 g,
0.77 mmol) and AlI3 (0.315 g, 0.77 mmol). Toluene (20 mL) was
added to this all at once. To this mixture was then added dropwise a
solution of I2 (0.196 g, 0.77 mmol) in ca. 5 mL of toluene. The
mixture turned to a pale yellow, oily solution and was allowed to stir
for 30 min. The solvent was removed in vacuo to obtain a pale orange
solid. The solid was stirred in hexanes (ca. 10 mL) for 10 min, and the
mixture was filtered on a glass frit, washed with hexanes (ca. 5 mL),
and dried (0.72 g, 89%).
Synthesis of (otol)3PC(O)OAl(OC(CF3)3)3 (15). A 50 mL Schlenk
bomb equipped with a Teflon screw cap and a magnetic stirbar was
charged with P(otol)3 (20 mg, 66 μmol), PhF-Al(OC(CF3)3)3 (54 mg,
66 μmol), and fluorobenzene (0.7 mL). The bomb was transferred to
the Schlenk line equipped with a CO2 outlet. The bomb was degassed,
filled with CO2 (1 atm), and sealed. The solution was stirred for 10
min, after which time the CO2 atmosphere was removed. Slow cooling
of the solution to −38 °C yielded single crystals suitable for X-ray
1
crystallography (66 mg, 61 μmol, 93%). H NMR (C6H5F): 7.84 (m,
3H, o-CH), 7.59 (m, 3H, p-CH), 7.39 (m, 3H, m-CH), 7.36 (m, 3H,
m-CH), 2.29 (s, 9H, CH3). 31P{1H} NMR (C6H5F): 11.2. 27Al NMR
(C6H5F): 37 (bs). 19F{1H} NMR (376 MHz, C6H5F): −75.2 (s, 27F,
CF3). 13C{1H} NMR (C6H5F): 159.1 (d, 1JP−C = 124 Hz, CO2), 144.4
1
4
9: H NMR (C6D5Br): 6.82 (d, JH−P = 4.4 Hz, 3H, m-Mes), 6.63
(d, 4JH−P = 6.0 Hz, 3H, m-Mes), 2.17 (s, 9H, o-CH3Mes), 2.12 (s, 9H, p-
CH3Mes), 1.73 (s, 9H, o-CH3Mes). 31P{1H} NMR (C6D5Br): −14.5.
27Al NMR (C6D5Br): −25 (s). 13C{1H} NMR (C6D5Br): 146.4 (d,
4JC−P = 3.4 Hz, p-C6H2), 145.4 (d, 2JC−P = 11.8 Hz, o-C6H2), 143.4 (d,
2
(d, JP−C = 8.4 Hz, o-C6H4), 135.0 (d, 4JP−C = 2.9 Hz, p-C6H4), 134.8
2
3
(d, JP−C = 12 Hz, o-C6H4), 133.2 (d, JP−C = 11 Hz, m-C6H4), 127.4
3
1
(d, JP−C = 13 Hz, m-C6H4), 121.5 (q, JC−F = 291 Hz, OC(CF3)3),
115.5 (d, JP−C = 82 Hz, i-C6H4), 78.9 (m, OC(CF3)3), 21.5 (d, 3JP−C
1
= 5 Hz, CH3). Anal. Calcd for C34H21AlF27O5P: C, 37.80; H, 1.96.
Found: C, 37.72; H, 2.04.
3
2JC−P = 12.1 Hz, o-C6H2), 133.4 (d, JC−P = 12.3 Hz, m-C6H2), 132.9
(d, 3JC−P = 12.3 Hz, m-C6H2), 119.3 (d, 1JC−P = 65.5 Hz, i-C6H2), 26.3
(d, 3JC−P = 6.4 Hz, o-CH3Mes), 24.4 (d, 3JC−P = 4.3 Hz, o-CH3Mes), 21.4
(d, 5JC−P = 1.8 Hz, p-CH3Mes). Anal. Calcd for C27H33PAlI5: C, 30.88;
H, 3.17. Found: C, 31.22; H, 3.05.
Synthesis of Al(C6F5)3(C6H5Br)2 (16). Single crystals suitable for
X-ray diffraction of this compound were obtained by slow cooling a
bromobenzene solution of Al(C6F5)3·tol to −38 °C, over several days.
1H, 27Al, 19F, 13C{1H} NMR: as reported for the known complex
Al(C6F5)3·tol.61
Kinetic Study. All kinetic experiments were performed in thick-
walled J-Young NMR tubes (total volume of 2 mL) under CO2
pressure. Saturated solutions of 5 (7.2 mM) were prepared by
dissolving 36 mg (29 μmol) in 4.0 mL of C6D5Br, and aliquots of 0.50
mL were used. The concentration of CO2 in solution was determined
using Raoult’s law for CO2 in bromobenzene at 1 atm.54 The reactions
were monitored by 31P{1H} NMR spectroscopy, samples were placed
directly in the prewarmed spectrometer, and the spectra were acquired
after a 5 min equilibration period. Data were obtained over a 30 K
range (303−333 K).
11: Yield: 89%. 1H NMR (C6D5Br): 6.87 (d, 4JH−P = 4.4 Hz, 3H, m-
Mes), 6.71 (d, JH−P = 6.4 Hz, 3H, m-Mes), 2.14 (s, 9H, p-CH3Mes),
4
2.13 (s, 9H, o-CH3Mes), 1.76 (s, 9H, o-CH3Mes). 31P{1H} NMR
(C6D5Br): 38.5. 27Al NMR (C6D5Br): 81 (s). 13C{1H} NMR
4
2
(C6D5Br): 147.2 (d, JC−2P = 3.0 Hz, p-C6H2), 145.4 (d, JC−P = 10.3
3
Hz, o-C6H2), 143.7 (d, JC−P = 15.4 Hz, o-C6H2), 133.7 (d, JC−P
=
12.1 Hz, m-C6H2), 133.2 (d, 3JC−P = 13.5 Hz, m-C6H2), 119.0 (d, 1JC−P
= 74.4 Hz, i-C6H2), 24.9 (d, 3JC−P = 6.2 Hz, o-CH3Mes), 24.4 (d, 3JC−P
= 5.5 Hz, o-CH3Mes), 21.5 (d, JC−P = 1.5 Hz, p-CH3Mes). Anal. Calcd
5
for C27H33PAlBr5: C, 39.79; H, 4.08. Found: C, 39.87; H, 4.05.
Synthesis of [Mes3PMe][AlI4] (12). A 50 mL round-bottom
Schlenk flask equipped with a magnetic stir bar was charged with
PMes3 (1.0 g, 2.57 mmol) and AlI3 (1.1 g, 2.7 mmol). Fluorobenzene
(15 mL) was added to this all at once. To this mixture was added
dropwise a solution of MeI (0.384 g, 2.7 mmol) in fluorobenzene (5
mL). The mixture turned to a pale yellow solution and was allowed to
stir for 1 h. The solvent was removed in vacuo to obtain a beige, oily
residue. The residue was stirred in hexanes (ca. 20 mL) for 10 min. An
off-white precipitate formed, which was filtered on a glass frit, washed
with hexanes (ca. 2 × 5 mL), and dried (2.1 g, 87%). 1H NMR
Computational Studies. The Gaussian suite (G09)62 was utilized
for all calculations. Optimizations employed the ONIOM63,64
composite approach, within which the DFT model M06-2X55 was
used. The appropriateness of this approach was affirmed by
observation of good agreement between computationally and X-ray
diffraction-determined structural parameters. Single-point energy
calculations at the ONIOM-determined geometries were performed
using the ONIOM G2R3 (OG2R3)56,57 composite approach, which
approximates a CCSD(T)/6-311+G(2df, 2p) calculation, providing a
more accurate prediction at modest cost.65,66 Bromobenzene solvent
effects were examined using both explicit bromobenzene molecules
and/or a polarized continuum solvent model (indicated by the
abbreviation SCRF).67,68 Inclusion of solvent in either form had only a
small effect on predicted structures but showed a detectable effect on
the reaction energetics, presumably because all species were extremely
polar. Energies were corrected using unscaled zero-point energies from
the frequency analyses, since scaling factors for ONIOM-based
frequency determinations are undetermined.
(C6D5Br): 6.87 (s, 3H, m-Mes), 6.69 (s, 3H, m-Mes), 2.39 (d, 2JH−P
=
11.6 Hz, 3H, Me), 2.14 (s, 9H, p-CH3Mes), 1.99 (s, 9H, o-CH3Mes),
1.72 (s, 9H, o-CH3Mes). 31P{1H} NMR (C6D5Br): 7.0. 27Al NMR
4
(C6D5Br): −25 (s). 13C{1H} NMR (C6D5Br): 145.1 (d, JC−P = 2.9
2
2
Hz, p-C6H2), 143.6 (d, JC−P = 10.6 Hz, o-C6H2), 142.8 (d, JC−P
=
10.4 Hz, o-C6H2), 133.2 (d, 3JC−P = 11.4 Hz, m-C6H2), 133.1 (d, 3JC−P
= 11.6 Hz, m-C6H2), 119.6 (d, 1JC−P = 79.0 Hz, i-C6H2), 25.7 (d, 1JC−P
= 62.4 Hz, PMe), 24.1 (d, 3JC−P = 4.7 Hz, o-CH3Mes), 24.0 (d, 3JC−P
=
5.2 Hz, o-CH3Mes), 21.4 (s, p-CH3Mes). Anal. Calcd for C28H36PAlI4: C,
35.85; H, 3.87. Found: C, 35.88; H, 3.94.
ASSOCIATED CONTENT
* Supporting Information
■
Synthesis of [(C6F5)C(O)OAl(C6F5)2]2 (14). A 50 mL Schlenk
bomb equipped with a Teflon screw cap and a magnetic stirbar was
charged with Al(C6F5)3·tol (300 mg, 0.48 mmol) and fluorobenzene
(5 mL). The bomb was transferred to the Schlenk line equipped with a
CO2 outlet. The bomb was degassed, filled with CO2 (1 atm), and
sealed. The solution was heated to 90 °C and stirred rapidly for 24 h,
after which the CO2 atmosphere was removed. The product was
isolated by crystallization at −38 °C and filtered (220 mg, 0.38 mmol,
79%). Slow cooling of a fluorobenzene solution to −38 °C of the
compound yielded single crystals suitable for X-ray crystallography.
27Al NMR (C6D5Br): blank. 19F{1H} NMR (376 MHz, C6D5Br):
S
X-ray data (CIF) have been deposited. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: dstephan@chem.utoronto.ca.
■
Notes
The authors declare no competing financial interest.
2
−122.8 (bd, JF−F = 18.0 Hz, 4F, o-C6F5-Al), −131.5 (bs, 2F, o-C6F5-
3
CO2), −135.0 (tt, JF−F = 22.6 Hz, 4JF−F = 11.3 Hz, 1F, p-C6F5-CO2),
ACKNOWLEDGMENTS
3
■
−148.3 (t, JF−F = 19.9 Hz, 2F, p-C6F5-Al), −156.5 (m, 2F, m-C6F5-
CO2), −159.1 (m, 4F, m-C6F5-Al). 13C{1H} NMR (C6D5Br), partial:
168.0 (s, CO2). Anal. Calcd for C19AlF15O2: C, 39.88. Found: C, 39.79.
The authors would like to thank J. M. Rawson at the University
of Windsor for access to the EPR spectrometer. G.M. is grateful
F
dx.doi.org/10.1021/om400619y | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(37) Roters, S.; Hepp, A.; Slootweg, J.; Lammertsma, K.; Uhl, W.
Chem. Commun. 2012, 48, 9616.
(38) Appelt, C.; Westenberg, H.; Bertini, F.; Ehlers, A. W.; Slootweg,
for the award of a Queen Elizabeth II Scholarship. D.W.S. is
grateful for the support of NSERC of Canada and the award of
a Canada Research Chair.
J. C.; Lammertsma, K.; Uhl, W. Angew. Chem., Int. Ed. 2011, 50, 3925.
(39) Momming, C. M.; Otten, E.; Kehr, G.; Frohlich, R.; Grimme, S.;
̈
̈
REFERENCES
Stephan, D. W.; Erker, G. Angew. Chem., Int. Ed. 2009, 48, 6643.
(40) Menard, G.; Hatnean, J. A.; Cowley, H. J.; Lough, A. J.; Rawson,
J. M.; Stephan, D. W. J. Am. Chem. Soc. 2013, 135, 6446.
(41) Culcasi, M.; Berchadsky, Y.; Gronchi, G.; Tordo, P. J. Org.
Chem. 1991, 56, 3537.
(42) Tojo, S.; Yasui, S.; Fujitsuka, M.; Majima, T. J. Org. Chem. 2006,
71, 8227.
(43) Sasaki, S.; Sutoh, K.; Murakami, F.; Yoshifuji, M. J. Am. Chem.
Soc. 2002, 124, 14830.
(44) Kwaan, R. J.; Harlan, C. J.; Norton, J. R. Organometallics 2001,
20, 3818.
(45) Kloo, L.; Rosdahl, J.; Taylor, M. J. Polyhedron 2002, 21, 519.
(46) Rawson, J. M.; Nilges, M. Vol. PIP for Windows v. 1.2, 2011.
(47) Tolman, C. A. Chem. Rev. 1977, 77, 313.
(48) Timoshkin, A. Y.; Bodensteiner, M.; Sevastianova, T. N.;
Lisovenko, A. S.; Davydova, E. I.; Scheer, M.; Graβl, C.; Butlak, A. V.
Inorg. Chem. 2012, 51, 11602.
■
(1) IPCC. Climate Change 2007: Synthesis Report, IPCC, 2007.
(2) Sakakura, T.; Choi, J.-C.; Yasuda, H. Chem. Rev. 2007, 107, 2365.
(3) Cokoja, M.; Bruckmeier, C.; Rieger, B.; Herrmann, W. A.; Kuhn,
F. E. Angew. Chem., Int. Ed. 2011, 50, 8510.
(4) Arakawa, H.; Aresta, M.; Armor, J. N.; Barteau, M. A.; Beckman,
E. J.; Bell, A. T.; Bercaw, J. E.; Creutz, C.; Dinjus, E.; Dixon, D. A.;
Domen, K.; DuBois, D. L.; Eckert, J.; Fujita, E.; Gibson, D. H.;
Goddard, W. A.; Goodman, D. W.; Keller, J.; Kubas, G. J.; Kung, H.
H.; Lyons, J. E.; Manzer, L. E.; Marks, T. J.; Morokuma, K.; Nicholas,
K. M.; Periana, R.; Que, L.; Rostrup-Nielson, J.; Sachtler, W. M. H.;
Schmidt, L. D.; Sen, A.; Somorjai, G. A.; Stair, P. C.; Stults, B. R.;
Tumas, W. Chem. Rev. 2001, 101, 953.
(5) Sunley, G. J.; Watson, D. J. Catal. Today 2000, 58, 293.
(6) Olah, G. A.; Prakash, G. K. S.; Goeppert, A. J. Org. Chem. 2009,
74, 487.
(7) Olah, G. A. C&E News 2003, 81, 5.
(49) Kwon, H. J.; Kim, H. W.; Rhee, Y. M. Chem.Eur. J. 2011, 17,
(8) Hebrard, F. d. r.; Kalck, P. Chem. Rev. 2009, 109, 4272.
(9) Laitar, D. S.; Muller, P.; Sadighi, J. P. J. Am. Chem. Soc. 2005, 127,
17196.
(10) Hegg, E. L. Acc. Chem. Res. 2004, 37, 775.
(11) Ettedgui, J.; Diskin-Posner, Y.; Weiner, L.; Neumann, R. J. Am.
6501.
(50) Menard, G.; Stephan, D. W. Dalton Trans. 2013, 42, 5447.
(51) Timoshkin, A. Y.; Frenking, G. Organometallics 2008, 27, 371−
380.
(52) Muller, Lutz O.; Himmel, D.; Stauffer, J.; Steinfeld, G.; Slattery,
̈
Chem. Soc. 2010, 133, 188.
J.; Santiso-Quinones, G.; Brecht, V.; Krossing, I. Angew. Chem., Int. Ed.
̃
(12) Lin, W.; Frei, H. J. Am. Chem. Soc. 2005, 127, 1610.
(13) Morris, A. J.; Meyer, G. J.; Fujita, E. Acc. Chem. Res. 2009, 42,
1983.
2008, 47, 7659.
(53) Plack, V.; Goerlich, J. R.; Fischer, A.; Schmutzler, R. Z. Anorg.
Allg. Chem. 1999, 625, 1979.
(54) Perisanu, S. T. J. Soln. Chem. 2001, 30, 183.
(55) Zhao, Y.; Truhlar, D. Theor. Chem. Acc. 2008, 120, 215.
(56) Vreven, T.; Morokuma, K. J. Chem. Phys. 1999, 111, 8799.
(57) Vreven, T.; Morokuma, K. J. Phys. Chem. A 2002, 106, 6167.
(58) Kolesinska, B. Cent. Eur. J. Chem. 2010, 8, 1147.
(59) Wells, A. Syn. Commun. 1994, 24, 1715.
(60) Dobrovetsky, R.; Stephan, D. W. Angew. Chem., Int. Ed. 2013,
52, 2516.
(61) Hair, G. S.; Cowley, A. H.; Jones, R. A.; McBurnett, B. G.; Voigt,
A. J. Am. Chem. Soc. 1999, 121, 4922.
(62) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, H. P. H.;
Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. M.,
Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.;
Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.;
Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi,
J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J.
B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador,
P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian09;
Gaussian, Inc.: Wallingford, CT, 2009.
(63) Dapprich, S.; Komaromi, I.; Byun, K. S.; Morokuma, K.; Frisch,
M. J. J. Mol. Stuct. (THEOCHEM) 1999, 461−462, 1.
(64) Vreven, T.; Morokuma, K. J. Comput. Chem. 2000, 21, 1419.
(65) Dutmer, B. C.; Gilbert, T. M. Organometallics 2011, 30, 778.
(66) Gilbert, T. M. J. Comput. Chem. 2011, 32, 1493.
(67) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105,
2999.
(14) Takeda, H.; Ishitani, O. Coord. Chem. Rev. 2010, 254, 346.
(15) Woolerton, T. W.; Sheard, S.; Reisner, E.; Pierce, E.; Ragsdale,
S. W.; Armstrong, F. A. J. Am. Chem. Soc. 2010, 132, 2132.
(16) Rosen, B. A.; Salehi-Khojin, A.; Thorson, M. R.; Zhu, W.;
Whipple, D. T.; Kenis, P. J. A.; Masel, R. I. Science 2011, 334, 643.
(17) Simon-Manso, E.; Kubiak, C. P. Organometallics 2004, 24, 96.
(18) Castro-Rodriguez, I.; Meyer, K. J. Am. Chem. Soc. 2005, 127,
11242.
(19) Silvia, J. S.; Cummins, C. C. J. Am. Chem. Soc. 2010, 132, 2169.
(20) Huff, C. A.; Sanford, M. S. J. Am. Chem. Soc. 2011, 133, 18122.
(21) Jessop, P. G.; Ikariya, T.; Noyori, R. Chem. Rev. 1995, 95, 259.
(22) Balaraman, E.; Gunanathan, C.; Zhang, J.; Shimon, L. J. W.;
Milstein, D. Nat. Chem. 2011, 3, 609.
(23) Leitner, W. Angew. Chem., Int. Ed. 1995, 34, 2207.
(24) Tanaka, R.; Yamashita, M.; Nozaki, K. J. Am. Chem. Soc. 2009,
131, 14168.
(25) Langer, R.; Diskin-Posner, Y.; Leitus, G.; Shimon, L. J. W.; Ben-
David, Y.; Milstein, D. Angew. Chem., Int. Ed. 2011, 50, 9948.
(26) Federsel, C.; Boddien, A.; Jackstell, R.; Jennerjahn, R.; Dyson, P.
J.; Scopelliti, R.; Laurenczy, G.; Beller, M. Angew. Chem., Int. Ed. 2010,
49, 9777.
(27) Sgro, M. J.; Stephan, D. W. Chem. Commun. 2013, 49, 2610.
(28) Sgro, M. J.; Stephan, D. W. Angew. Chem., Int. Ed. 2012, 51,
11343.
(29) Sgro, M. J.; Domer, J.; Stephan, D. W. Chem. Commun. 2012,
48, 7253.
(30) Neu, R. C.; Men
9016.
(31) Li, J.; Hermann, M.; Frenking, G.; Jones, C. Angew. Chem., Int.
Ed. 2012, 51, 8611.
̈
́
ard, G.; Stephan, D. W. Dalton Trans. 2012, 41,
(32) Men
8396.
(33) Men
́
ard, G.; Stephan, D. W. Angew. Chem., Int. Ed. 2011, 50,
́
ard, G.; Stephan, D. W. J. Am. Chem. Soc. 2010, 132, 1796.
(34) Berkefeld, A.; Piers, W. E.; Parvez, M. J. Am. Chem. Soc. 2010,
132, 10660.
(68) Vreven, T.; Mennucci, B.; da Silva, C. O.; Morokuma, K.;
Tomasi, J. J. Chem. Phys. 2001, 115, 62.
(35) Gu, L.; Zhang, Y. J. Am. Chem. Soc. 2009, 132, 914.
(36) Ashley, A. E.; Thompson, A. L.; O’Hare, D. Angew. Chem., Int.
Ed. 2009, 48, 9839.
G
dx.doi.org/10.1021/om400619y | Organometallics XXXX, XXX, XXX−XXX