A highly active phosphine-borane organocatalyst for the reduction of CO2 to methanol using hydroboranes

Article abstract of DOI:10.1021/ja404585p

In this work, we report that organocatalyst 1-Bcat-2-PPh₂-C ₆H₄ ((1); cat = catechol) acts as an ambiphilic metal-free system for the reduction of carbon dioxide in presence of hydroboranes (HBR₂ = HBcat (catecholborane), HBpin (pinacolborane), 9-BBN (9-borabicyclo[3.3.1]nonane), BH₃·SMe₂ and BH ₃·THF) to generate CH₃OBR₂ or (CH ₃OBO)₃, products that can be readily hydrolyzed to methanol. The yields can be as high as 99% with exclusive formation of CH ₃OBR₂ or (CH₃OBO)₃ with TON (turnover numbers) and TOF (turnover frequencies) reaching >2950 and 853 h^-1, respectively. Furthermore, the catalyst exhibits "living" behavior: once the first loading is consumed, it resumes its activity on adding another loading of reagents.

Full text of DOI:10.1021/ja404585p

Communication
pubs.acs.org/JACS
A Highly Active Phosphine−Borane Organocatalyst for the Reduction
of CO to Methanol Using Hydroboranes
2
†
†
,‡
ic-Georges Fontaine*,†
Marc-Andre
́
Courtemanche, Marc-Andre
́
Leg
́
are,
́
Laurent Maron,* and Fred
́
er
́
†
Dep
́
artement de Chimie, Centre de Catalyse et de Chimie Verte (C3V), Universite
Universite de Toulouse, INSA, UPS, LCPNO, CNRS, UMR 5215 CNRS-UPS-INSA, 135 avenue de Rangueil, Toulouse, France
S Supporting Information
́ ́
Laval, Quebec G1V 0A6, Canada
‡
́
*
using the robust TMP/B(C F ) (TMP = 2,2,6,6-tetramethyl-
6
5 3
9
ABSTRACT: In this work, we report that organocatalyst
-Bcat-2-PPh −C H ((1); cat = catechol) acts as an
piperidine) system with Et SiH, albeit with limited turnovers.
3
1
2
6
4
It has been shown that the FLP system consisting of PMes3/
AlX (Mes = mesityl, X = Cl, Br) not only binds CO but also
ambiphilic metal-free system for the reduction of carbon
dioxide in presence of hydroboranes (HBR = HBcat
3
,
2
10
2
reduces it to methanol using BH ·NH as hydrogen source.
3 3
Alternatively, O’Hare and Ashley demonstrated that CO could
be hydrogenated using TMP/B(C F ) . Unfortunately, the
(
catecholborane), HBpin (pinacolborane), 9-BBN (9-
2
11
borabicyclo[3.3.1]nonane), BH ·SMe and BH ·THF) to
generate CH OBR or (CH OBO) , products that can be
3
2
3
6 5 3
3
2
3
3
last two systems require stoichiometric amounts of FLP.
Although interesting in concept, none of the FLP or ambiphilic
systems reported to date demonstrate good catalytic activity for
carbon dioxide reduction. The only efficient organocatalytic
readily hydrolyzed to methanol. The yields can be as high
as 99% with exclusive formation of CH OBR2 or
3
(
(
CH OBO) with TON (turnover numbers) and TOF
turnover frequencies) reaching >2950 and 853 h ,
3 3
−
1
system reported to date for the reduction of CO into methanol
2
respectively. Furthermore, the catalyst exhibits “living”
behavior: once the first loading is consumed, it resumes its
activity on adding another loading of reagents.
use highly Lewis basic N-heterocyclic carbene catalysts and
diphenylsilane as hydrogen source with turnover frequencies
1
12
(
TOF) of 25 h− at 25 °C.
Our research program targets ambiphilic systems with little
13
“
frustrated” character and/or weak Lewis acidity and basicity.
t is widely known that carbon dioxide is a green-house gas
and one of the most important contributors to global
One ambiphilic system of interest is that of aryl bridged
I
phosphine−boranes extensively studied by Bourissou and
14
warming, and several political initiatives have been put forward
collaborators. These molecules have been shown to be
quite robust, stable, and easy to synthesize. More recently, they
1
to reduce carbon dioxide emissions. Most of the current
15
systems known to catalyze the reduction of CO into valuable
have been used in the activation of singlet oxygen and as
2
2
16
products use transition metals, including notably the reverse
organocatalysts for the Michael addition reaction, but to our
water−gas shift reaction to generate carbon monoxide which in3
turn can be transformed into several useful chemicals.
Recently, some homogeneous organometallic systems have
knowledge the activity of these molecules for carbon dioxide
reduction has not been investigated. Here we report that the 1-
Bcat-2-PPh
−C H ambiphilic system is one of the most active
2
6 4
4
shown promise in generating valuable chemicals. The most
catalysts for the selective catalytic reduction of carbon dioxide
to methanol.
active systems to date for the reduction of CO into high
2
hydrogen content molecules include a ruthenium phosphine
Although several ambiphilic phosphine−boranes were
4
c
4d
14,15
prepared by Bourissou,
the synthesis of the catecholborane
complex and a nickel pincer complex, using respectively H2
and HBcat (HBcat = catecholborane), to generate MeOH from
CO , and an iridium catalyst that can reduce CO into methane
derivative 1-Bcat-2-PPh −C H (1, Scheme 1) was never
2
6
4
reported. The air-stable product is easily synthesized in 80%
yield from previously reported o-lithiated triphenylphosphine
using a known synthetic pathway (Figure S1, Supporting
2
2
using hydrosilanes as hydrogen source with turnover numbers
4e
(TON) up to 8300.
Recently, a variety of transition metal-free systems have
emerged for carbon dioxide activation and functionalization.
Scheme 1. Reduction of CO
catalyst 1
in Presence of HBcat and
2
+
Indeed, it has recently been shown that Lewis acidic Et Al
2
5
species can catalytically reduce carbon dioxide to methane.
Similarly, silyl cations can catalytically reduce CO to a mixture
2
6
of benzoic acid, formic acid, and methanol. However, both
systems greatly lack selectivity and generate undesirable
alkylation byproducts. An avenue of interest for carbon dioxide
activation is the use of “frustrated Lewis pairs” (FLP), work
7
pioneered by Stephan and Erker. Since this initial discovery,
many ambiphilic systems have been shown to be active in the
8
stoichiometric fixation CO . Piers demonstrated elegant use of
Received: May 7, 2013
2
this concept for the catalytic reduction of CO into methane
2
©
XXXX American Chemical Society
A
dx.doi.org/10.1021/ja404585p | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
1
7
Information [SI]). Multinuclear NMR characterization of
species 1 demonstrates this molecule to be monomeric in
31
1
solution having no observable P−B interaction. The P{ H}
and 11B{ H} NMR chemical shifts are respectively of −4.57
and 33.1 ppm. The solid-state structure (see SI Figure S24)
does not show any evidence of P−B interaction, the latter
distance being quite long (3.28 Å).
1
Unsurprisingly, exposing 1 to 1 atm of CO2 at room
temperature resulted in no spectroscopic change in solution
1
31
11
(
H, P, and B NMR spectroscopy). Although no adduct was
observed between CO and 1, the addition of 100 equiv of
2
HBcat to a 9 mM solution of 1 in benzene-d in a J-Young
6
NMR tube under one atmosphere of CO resulted in the
2
formation of a white precipitate after 24 h. This was
characterized as catBOBcat on the basis of spectroscopic
comparison with the independently synthesized product (see
Scheme 1). Monitoring of the solution using H NMR
spectroscopy showed the presence of a single new peak at
Figure 2. Turnover numbers (TON) for the formation of
(CH
OBO)
from a 9 mM solution of 1 in benzene-d
·SMe under one atmosphere of CO .
2
in the
3
3
6
1
presence of 100 equiv of BH
The TONs are based on the number of hydrogen atoms transferred to
CO . Reactions were carried out at (⧫) 23 °C and (■) 70 °C.
3
2
2
3
.37 ppm attributed to CH OBcat by comparison to the
3
independently synthesized product. Hydrolysis of the latter
product produces methanol, which was confirmed using GC-
FID. As expected, carrying out the same reaction under an
obtained. The TON numbers being greater than 100 suggests
that all hydrogen atoms from BH ·SMe are available for the
3
2
13
13
atmosphere of CO shows the formation of CH OBcat with
2
3
reduction of CO . To our knowledge, it represents the first
2
1
4d
the expected J
of 145 Hz.
C−H
time that BH is used as a hydrogen source for the catalytic
3
Monitoring the reduction of CO in presence 1 and 100
2
reduction of CO to methanol. It is interesting that the catalyst
2
1
31
1
equiv of HBcat using H and P{ H} NMR spectroscopy
showed an induction period of 30 min where no spectroscopic
change was observed in the solution. However, after the
induction period the reaction started readily, and after 2 h a
remains active even if BH is known to coordinate phosphine
3
moieties, which could inhibit catalysis; it is thus logical to
presume that the longer induction period is caused by a
competition between BH and CO for coordination to the
3
2
−1
3
4% yield (TON = 34, TOF = 17 h ) of CH OBcat was
3
catalyst. BH is of great interest since it has the highest
3
obtained (Figure 1, ⧫). The rate of the reaction diminished as
hydrogen content of any hydroborane.
A factor that dramatically increased the efficiency of the
catalytic system was temperature. Heating a solution of 1 with
1
00 equiv of HBcat to 70 °C under one atmosphere of CO2
generated CH OBcat without any observable induction period
3
(
=
Figure 1, ■). After 36 min, a TON of 86 was observed (TOF
−1
143 h ), which increased to 92 after a period of 98 min
(
Table 1, entries 1−2). After letting the solution rest for a 24-h
period, another loading of 100 equiv of HBcat was added and
the solution reheated to 70 °C. The catalytic reaction resumed,
but with a rate that seemed somewhat slower (an overall TON
of 136 after 30 min), possibly due to the presence of a large
quantity of precipitate in the solution (catBOBcat) that reduced
the homogeneity of the solution. However, 60 min after the
addition of the second loading a TON of 185 was measured
(
Table 1, entries 3−4), a yield similar to that observed in the
Figure 1. Turnover numbers (TON) for the formation of CH OBcat
3
first run. Such behavior is reminiscent of a durable and “living”
catalyst. Under similar conditions, BH ·SMe proved to be an
from a 9 mM solution of 1 in benzene-d in the presence of 100 equiv
6
3
2
of HBcat under one atmosphere of CO . The TONs are based on the
2
excellent hydrogen source, generating 90% yield of
CH OBO) in 67 min (TON = 271). A TON of 211 was
number of hydrogen atoms transferred to CO . Reactions were carried
2
(
3
n
out at (⧫) 23 °C and (■) 70 °C.
−1
obtained after only 13 min, representing a TOF of 973 h
(
Figure 2, ■). The latter result is remarkable since the highest
the reaction progressed, suggesting that conversion is depend-
ent on the concentration of HBcat in solution. Indeed, 50%
TOF reported for the reduction of CO to a methanol derivate
2
is 495 h− by a homogeneous nickel catalyst using HBcat as an
1
4d
conversion to CH OBcat was obtained in less than 5 h and a
hydrogen source. The reaction was also carried out using
3
yield of 69% of CH OBcat was observed after a period of 24 h.
other hydroborane sources. The addition of 100 equiv of
3
The reduction of CO also proceeded in the presence of 100
HBpin to a solution of 1 under one atmosphere of CO at 70
2
2
equiv of BH ·SMe to generate (CH OBO) but a longer
°C generated 60% yield of the desired product in a 3-h period
(Table 1, entry 6). The significantly lower activity of the latter
borane compared to HBcat is not surprising since it is known
3
2
3
3
induction period was observed (>2 h; Figure 2, ⧫).
Nevertheless, the conversion to the methoxyborane species is
rapid once catalysis starts, obtaining respectively 108 and 200
TON at 2 and 5 h after the induction period (respective TOFs
18
that HBpin is less reactive for the hydroboration reaction.
Similarly, 9-BBN only showed 34 TON in a 3-h period (entry
7).
−1
of 54 and 40 h ). After a period of 14 h, a TON of 257 was
B
dx.doi.org/10.1021/ja404585p | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
a
Table 1. Reduction of CO with Various Hydroboranes
2
b
TOF (h−1
)
entry
borane
HBcat
equiv
100
time (min)
TON
1
2
3
4
5
6
7
36
98
86
143
56
HBcat
HBcat
HBcat
100
100 + 100
100 + 100
100
92
136
185
271
60
c
c
30
72
60
85
BH ·SMe2
67
242
21
3
HBpin
9-BBN
HBcat
HBcat
100
174
174
60
d
50
34
12
e
g
g
g
g
g
8
f
300
145
664
853
>2,950
340
145
166
853
>737
340
9
1000
240
60
e
10
11
12
BH ·SMe2
300
3
f
BH ·SMe2
1000
240
60
3
e
BH ·THF
300
3
a
Reaction conditions: Unless noted otherwise, 2.0 mg (0.0053 mmol)
b
of 1 in 0.6 mL of benzene-d at 70 °C Based on mole of B−H
consumed per mole of 1, determined by H NMR integration using
6
1
Figure 3. Enthalpy profile (in kcal·mol) for the reduction of CO by 1
2
hexamethylbenzene as internal standard for entries 1−7, and
and catecholborane.
i
determined by GC-FID with PrOH as a standard for entries 8−12.
c
A second addition of 100 equiv of HBcat was added 24 h after the
d
first addition. Limited at 50 equiv because of low solubility of 9-BBN.
−1
e
kcal·mol , in line with a weak coordination of carbon dioxide
as reflected by its geometry. Indeed, despite the bending of the
molecule (indicative of CO2 activation), the C−O bonds
appear to be only slightly elongated compared to free CO2
2
.0 mg (0.0053 mmol) of 1 in 3 mL of benzene at 70 °C under ∼2
f
atm of CO . 2.0 mg (0.0053 mmol) of 1 in 9 mL of benzene at 70 °C
under ∼2 atm of CO . Quenched with excess H O and analyzed by
2
g
2
2
i
GC-FID with PrOH as a standard.
(
1.28 and 1.21 Å). Nevertheless, this adduct can undergo
addition of HBcat to yield a novel species whose formation is
favorable by 14.4 kcal·mol− compared to 1. Once the
formation of the complex IM2 is achieved, the second
reduction to generate the formaldehyde-1 adduct (IM3) and
Since diffusion problems could limit the rate of the reaction
when carried out in NMR conditions, catalytic tests were
carried out on a larger scale using Fisher-Porter bottles under
1
∼
2 atm of CO . The products obtained were hydrolyzed to
2
−1
catBOBcat is downhill by 33.3 kcal·mol . The third reduction
methanol, and the turnover numbers were calculated on the
basis of the concentration of methanol using gas chromatog-
raphy with a flame ionization detector. As can be observed in
Table 1, the activities observed at the NMR scale can be
reproduced at larger scale and lower catalyst loading. Indeed,
to regenerate the catalyst as well as CH OBcat is an even more
3
−1
exothermic process (34.0 kcal·mol ). To summarize, as soon
as the difficult coordination of CO has taken place, the
2
reduction is thermodynamically highly favorable.
In order to confirm these computational results, 1 was
reacted with methylformate in an attempt to generate an
analogous compound to IM2, namely species IM2mf (see
Figure S22, SI). In line with the DFT results, where the adduct
is predicted to be 3.9 kcal·mol− higher in energy than 1, no
product could be observed by NMR spectroscopy. However,
upon the addition of 3 equiv of catecholborane without the
the reduction of CO using 300 equivalents of HBcat and
2
BH ·SMe gave in one hour methanol in 48% and 95% yield,
3
2
−1
giving respectively TOF of 145 and 853 h (Table 1, entries 8
and 10). It is notable that the TOF observed under large
loading of hydroboranes are consistent with those observed at
the NMR scale at low conversion that were 143 and 973 h− for
HBcat and BH ·SMe , respectively. Catalysis using a 0.1%
1
1
3
2
presence of CO , a 90% conversion to CH OBCat was observed
catalyst loading (1000 equiv of substrate) in a 4-h period also
gave impressive results. In the presence of HBcat, a TON of
2
3
after 20 h at room temperature. These latter results suggest
that, although the formation of the adduct IM2mf is
thermodynamically slightly disfavored, the reduction occurs in
presence of a hydroborane. It is also interesting to note that the
intermediate IM3 is proposed to be formed in both reduction
pathways. A similar formaldehyde intermediate was identified as
6
64 was observed, which indicates that the rate of reaction
remains the same during the 4-h period even with a lower
catalyst loading and a lower catalyst concentration (Table 1,
entry 9, TOF = 166 h ). In the presence of BH ·SMe , all of
−1
3
2
the substrate was consumed since the conversion to methanol
was quantitative (Table 1, entry 11), once more suggesting that
the TOF observed after one hour is conserved over a longer
4
d,12
a key intermediate in previous systems,
but could not be
observed experimentally. While monitoring the reduction of
CO in the presence of hydroboranes and catalyst 1, only one
reaction time. The reaction works also with BH ·THF, albeit
2
3
1
−1
resonance in the H NMR spectra, a broad singlet at 5.20 ppm,
less efficiently (Table 1, entry 12, TOF = 340 h ).
could not be assigned to the starting materials or products.
Density functional theory studies at the B3PW91 6-31G**
level of theory were performed to obtain further insight at the
mechanistic pathway, using HBcat as the hydrogen source. It
should be noted that only potential intermediates were
considered in the following, and the results are summarized
in Figure 3. Also, we did not account for the fact that HBCat is
known to degrade in presence of Lewis bases since control
experiments have shown this process to be marginal in our
1
3
Running the experiment in the presence of CO allowed the
2
1
observation of a J
of 151 Hz, suggesting that this species
C−H
arise from the reduction of CO . In the latter experiment, a
2
1
3
13
1
JP−C of 52 Hz was also observed both in the C{ H} and
P{ H} NMR spectra. The latter species could not be isolated
1
1
from the catalytic mixture, being in too small concentration in
solution. However, when a solution of 1 was reacted with
paraformaldehyde and heated at 70 °C for 15 min, the same
product was observed to be formed with 74% conversion, as
1
9
system. As observed experimentally, the coordination of CO2
to 1 to generate intermediate IM1 is disfavored by 9.9
C
dx.doi.org/10.1021/ja404585p | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
characterized by multinuclear NMR spectroscopy as IM3 (see
Figure S19, SI).
von Stein, T.; Klankermayer, J.; Leitner, W. Angew. Chem., Int. Ed.
2
012, 51, 7499−7502. (d) Chakraborty, S.; Zhang, J.; Krause, J. A.;
Guan, H. J. Am. Chem. Soc. 2010, 132, 8872−8873. (e) Park, S.; Bezier,
D.; Brookhart, M. J. Am. Chem. Soc. 2012, 134, 11404−11407.
́
In summary, we have reported a metal-free system for the
reduction of carbon dioxide to methanol using a borane as
reducing agent. The system is a robust, living catalytic system
(
1
1
f) Matsuo, T.; Kawaguchi, H. J. Am. Chem. Soc. 2006, 128, 12362−
2363. (g) Mitton, S. J.; Turculet, L. Chem.Eur. J. 2012, 48, 15258−
−
1
and generates TOFs up to 973 h and TONs up to 2950 at 70
C under 1 atm of CO , although larger TONs can be expected
5262. (h) Berkefeld, A.; Piers, W. E.; Parvez, M.; Castro, L.; Maron,
°
2
L.; Eisenstein, O. Chem. Sci. 2013, 4, 2152−2162. (i) Schmeier, T. J.;
Dobereiner, G. E.; Crabtree, R. H.; Hazari, N. J. Am. Chem. Soc. 2011,
133, 9274−9277. (j) Zhang, L.; Cheng, J.; Hou, Z. Chem. Commun.
2013, 49, 4782−4784. (k) Bontemps, S.; Vendier, L.; Sabo-Etienne, S.
Angew. Chem., Int. Ed. 2012, 51, 1671−1674. (l) Cleeberg, C.; Cheung,
M. S.; Lin, Z.; Marder, T. B. J. Am. Chem. Soc. 2011, 133, 19060−
by additional loadings of hydroboranes. The key aspect of this
reported system compared to the other metal-free systems for
the activation of CO is the weak interaction between the
2
catalyst and carbon dioxide. Indeed, contrary to most
ambiphilic and FLP systems reported to date, no adduct
formation is observed between 1 and CO . Nevertheless, CO ,
1
9063. (m) Lalrempuia, R.; Iglesias, M.; Polo, V.; Miguel, P. J. S.;
2
2
Fernandez-Alvarez, F. J.; Perez-Torrente, J. J.; Oro, L. A. Angew. Chem.
́
being an ambiphilic molecule with its electrophilic carbon atom
and nucleophilic oxygen atoms available, does not require
significant bonding interaction with an ambiphilic catalyst to
undergo reduction with hydroboranes. Once the first reduction
has occurred, following reductions occur readily to generate
CH OBR . Preliminary results demonstrate that the BPin
Int. Ed. 2012, 51, 12824−12827. (n) Tominaga, K.; Sasaki, Y.; Kawai,
M.; Watanabe, T.; Saito, M. J. Chem. Soc. Chem. Commun. 2013, 629−
6
31.
(
5) Khandelwal, M.; Wehmschulte, R. J. Angew. Chem., Int. Ed. 2012,
1, 7323−7326.
(6) Schafer, A.; Saak, W.; Haase, D.; Mu
2012, 51, 2981−2984.
(7) Momming, C.; Otten, M.; Kehr, E. G.; Fro
Stephan, D. W.; Erker, G. Angew. Chem., Int. Ed. 2009, 48, 6643−6646.
8) (a) Boudreau, J.; Courtemanche, M.-A.; Fontaine, F.-G. Chem.
5
3
2
̈
̈
ller, T. Angew. Chem., Int. Ed.
1
5
analogue 1-Bpin-2-PPh −C H is an active catalyst for the
2
6
4
CO reduction using BH ·SMe , albeit working less efficiently
̈
̈
hlich, R.; Grimme, S.;
2
3
2
−1
than 1 (TOF of 24 h in conditions similar to those of entry 2
of Table 1). Current work focuses on optimizing the steric and
electronic properties at boron and phosphorus centers to
obtain optimal catalytic activity. Computational studies to
unveil the full reaction mechanism are also well underway.
(
Commun. 2011, 47, 11131−11133. (b) Appelt, C.; Westenberg, H.;
Bertini, F.; Ehlers, A. W.; Slootweg, J. C.; Lammertsma, K.; Uhl, W.
Angew. Chem., Int. Ed. 2011, 50, 3925−3928.
(9) Berkefeld, A.; Piers, W. E.; Parvez, M. J. Am. Chem. Soc. 2010,
1
32, 10660−10661.
10) Menard, G.; Stephan, D. W. J. Am. Chem. Soc. 2010, 132, 1796−
1797.
11) Ashley, A. E.; Thompson, A. L.; O’Hare, D. Angew. Chem., Int.
Ed. 2009, 48, 9839−9843.
12) Riduan, S. N.; Zhang, Y.; Ying, J. Y. Angew. Chem., Int. Ed. 2009,
8, 3322−3325.
13) (a) Fontaine, F.-G.; Boudreau, J.; Thibault, M.-H. Eur. J. Inorg.
Chem. 2008, 5439−5454. (b) Boudreau, J.; Fontaine, F.-G. Organo-
metallics 2011, 30, 511−519. (c) Fontaine, F.-G.; Zargarian, D. J. Am.
Chem. Soc. 2004, 126, 8786−8794. (d) Boudreau, J.; Courtemanche,
M.-A.; Marx, V. M.; Burnell, D. J.; Fontaine, F.-G. Chem. Commun.
ASSOCIATED CONTENT
(
́
■
*
S
Supporting Information
(
Synthesis and characterization of 1, catalytic procedures, and
DFT details. This material is available free of charge via the
Internet at http://pubs.acs.org.
(
4
(
AUTHOR INFORMATION
■
Corresponding Author
frederic.fontaine@chm.ulaval.ca
Notes
2
012, 48, 11250−11252.
14) (a) Bontemps, S.; Bouhadir, G. D.; Apperley, C.; Dyer, P. W.;
Miqueu, K.; Bourissou, D. Chem.Asian J. 2009, 428−435.
b) Bontemps, S.; Bouhadir, G.; Miqueu, K.; Bourissou, D. J. Am.
Chem. Soc. 2006, 128, 12056−12057.
15) Porcel, S.; Bouhadir, G.; Saffon, N.; Maron, L.; Bourissou, D.
Angew. Chem., Int. Ed. 2010, 49, 6186−6189.
16) Basle, O.; Porcel, S.; Ladeira, S.; Bouhadir, G.; Bourissou, D.
Chem. Commun. 2012, 48, 4495−4497.
17) Harder, S.; Brandsma, L.; Kanters, J. A.; Duisenberg, A.; van
Lenthe, J. H. J. Organomet. Chem. 1991, 420, 143.
The authors declare no competing financial interest.
(
ACKNOWLEDGMENTS
(
■
This work was supported by the National Sciences and
Engineering Research Council of Canada (NSERC, Canada)
and the Centre de Catalyse et Chimie Verte (Quebec). M.-A.C.
and M.-A.L. thank NSERC and FQRNT for scholarships. We
acknowledge W. Bi for the X-ray structure of 1 and R. Lafleur-
Lambert with his help setting some catalytic experiments. L.M.
is member of the Institut Universitaire de France. Cines and
CALMIP are acknowledged for a generous grant of computing
time. The Humboldt foundation is also acknowledged for
financial support.
(
(
́
(
(
18) Pereira, S.; Srebnik, M. Organometallics 1995, 14, 3127−3128.
(19) Westcott, S. A.; Blom, H. P.; Marder, T. B.; Baker, R. T.;
Calabrese, J. C. Inorg. Chem. 1993, 32, 2175−2182.
REFERENCES
■
(
2
1) D’Alessandro, D. M.; Smit, B.; Long, J. R. Angew. Chem., Int. Ed.
010, 49, 6058−6082.
2) (a) Huang, K.; Sun, C.-L.; Shi, Z.-J. Chem. Soc. Rev. 2011, 40,
(
2
1
2
435−2452. (b) Sakakura, T.; Choi, J.-C.; Yasuda, H. Chem. Rev. 2007,
07, 2365−2387. (c) Aresta, M.; Dibenedetto, A. Dalton Trans. 2007,
975−2992.
(
3) Olah, G. A.; Goeppert, A.; Surya Prakash, G. K J. Org. Chem.
2
(
009, 74, 487−498.
4) (a) Balaraman, E.; Gunanathan, C.; Zhang, J.; Shimon, L. J. W.;
Milstein, D. Nat. Chem. 2011, 3, 609−614. (b) Huff, C. A.; Sanford,
M. S J. Am. Chem. Soc. 2011, 133, 18122−18125. (c) Wesselbaum, S.;
D
dx.doi.org/10.1021/ja404585p | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX