New, highly efficient, simple, safe, and scalable synthesis of [(Ph 3P)3Ru(CO)(H)2]

Article abstract of DOI:10.1021/om400461w

A new method has been developed to prepare [(Ph₃P) ₃Ru(CO)(H)₂] (1), an important homogeneous catalyst, directly from RuCl₃·xH₂O. Unlike previously reported procedures to make 1, the new method does not utilize toxic and hazardous materials such as formaldehyde and benzene and requires only a small excess of PPh₃, while furnishing analytically and spectroscopically pure 1 in unprecedented >95% yield. The solvent (EtOH) is used in small quantities, thereby enabling scalability, as has been demonstrated by preparing >17 g of pure 1 in one batch.

Full text of DOI:10.1021/om400461w

Note
pubs.acs.org/Organometallics
New, Highly Efficient, Simple, Safe, and Scalable Synthesis of
[(Ph3P)3Ru(CO)(H)2]
Hamidreza Samouei and Vladimir V. Grushin*
Institute of Chemical Research of Catalonia (ICIQ), Tarragona 43007, Spain
S
* Supporting Information
ABSTRACT: A new method has been developed to prepare
[(Ph3P)3Ru(CO)(H)2] (1), an important homogeneous catalyst,
directly from RuCl3·xH2O. Unlike previously reported procedures to
make 1, the new method does not utilize toxic and hazardous
materials such as formaldehyde and benzene and requires only a
small excess of PPh3, while furnishing analytically and spectroscopi-
cally pure 1 in unprecedented >95% yield. The solvent (EtOH) is
used in small quantities, thereby enabling scalability, as has been
demonstrated by preparing >17 g of pure 1 in one batch.
he title compound, [(Ph3P)3Ru(CO)(H)2] (1), was
Table 1. Selected Reported Methods for the Synthesis of 1
T
originally reported by Hallman, McGarvey, and Wilkinson
CO
45 years ago.1 Since then, 1 has become one of the most
important and widely used homogeneous catalysts for a broad
variety of transformations, ranging from efficient C−H
activation and functionalization to the borrowing hydrogen
methodology and polymerization.2−6
Ru source
reaction conditions
source
yield of 1, % ref
a
[(Ph3P)3RuCl2] benzene−EtOH or
MeOH, NaBH4, H2,
reflux
EtOH or
MeOH
60
1
b
b
c
RuCl3·xH2O
RuCl3·xH2O
RuCl3·xH2O
RuCl3·xH2O
PPh3, EtOH, KOH,
reflux
CH2O
CH2O
CH2O
CH2O
70
8
PPh3, EtOH, KOH,
reflux
70
9
PPh3, MeOH, KOH,
reflux
68
10
11
d
PPh3, EtOH, KOH,
reflux
66
a
b
c
Analytically pure 1, as precipitated out of the reaction solution.
Crude product prior to purfication; yield of purified 1 not specified.
The reported methods to synthesize 1 are, however, far from
being on par with its excellence as a catalyst. Originally, 1 was
prepared in 60% yield by the reaction of [(Ph3P)3RuCl2] with
NaBH4 in benzene−ethanol or benzene−methanol under reflux
in a hydrogen atmosphere.1 A few years later, Robinson’s
group7 reported the synthesis of 1 from RuCl3·xH2O, PPh3,
formaldehyde, and KOH in EtOH. After additional optimiza-
tion, this procedure affording 1 in 70% yield was published in
Inorganic Syntheses in 19748 and since then has remained the
only widely used preparative method for this complex. The
synthesis employs 6 equiv of PPh3, a ca. 130-fold excess of
highly toxic formaldehyde, and large volumes of solvent. To
make 20 g of crude 1 by this method, one would have to use
over 300 mL of 40% aqueous formaldehyde and nearly 3 L of
ethanol. In our hands, Robinson’s method7,8 consistently
furnished crude 1 in ca. 65% yield.
Numerous attempts have been made to improve the
preparation of 1.9−12 Although a number of modifications of
Robinson’s method7,8 have been made, the yield of 1 has
remained in the range of 62−68%.9−11 A summary of the
reported methods to synthesize 1 is presented in Table 1.
Regardless of whether the original or a modified procedure is
used, the precipitated crude product needs purification. The
d
Purified product. Before or after purification (not specified).
latter incurs losses while requiring large quantities of solvents
(often toxic benzene), filtration through alumina or silica, and/
or recrystallization. Wang12 has recently reported an
optimization study of the standard procedure,8 claiming higher
yields for 1 (up to 84%) in the presence of even a larger excess
of formaldehyde (160-fold). We have failed to reproduce these
high yields of 1, apparently because of lack of sufficient
experimental details in the report.12
Considering all of the above, there is a clear need for a
higher-yielding, more convenient, and safer procedure to
synthesize 1. Herein we report a new, highly efficient, safe,
simple, and easily scalable method to prepare 1 in nearly
quantitative yield directly from RuCl3·xH2O. Our method
utilizes PPh3 in a minimal excess and, unlike the previously
developed procedures, does not employ highly toxic form-
aldehyde and benzene, any complex hydrides such as NaBH4,
Received: May 24, 2013
© XXXX American Chemical Society
A
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Note
or a hydrogen atmosphere. No purification step is required,
because at the end of the reaction 1 precipitates out analytically
and spectroscopically pure.
Two key findings provided the foundation for the develop-
ment of the new synthetic method for 1:
(1) It was found that 1 was formed quantitatively after a
suspension of [(Ph3P)4Ru(H)2] (2)13 was stirred in EtOH
under reflux for several hours. This transformation was
apparently mediated by the formation of a Ru−OEt species
that underwent β-H-elimination to produce acetaldehyde that
served as the CO source.
Indeed, the final product 1, like 3, bears three PPh3 ligands on
the metal atom. We also reasoned that although intermediate 2
is a tetraphosphine species, the small amounts of extra PPh3
might be sufficient for its gradual formation and disappearance
throughout the process. That was confirmed in a series of runs,
thus allowing an approximately 1:4 RuCl3·xH2O to PPh3 molar
ratio to be maintained in subsequent studies.
Obviously, the precise stoichiometry of the formation of 1
from RuCl3·xH2O cannot be determined (see above).17 It was
clear, however, that 3 equiv of KOH per Ru would be needed
to convert all of the chlorine in the system to KCl. We found
that excellent results in terms of both yield (>95%) and purity
(>98%) of 1 could be achieved with just over 3 equiv of KOH,
so long as the amount of EtOH used for the synthesis was
approximately 85 mL per 1 g of 1 to be made. Lowering the
volume of EtOH resulted in the formation of [(Ph3P)3Ru(H)-
(OAc)]18 (4), with ethyl acetate being detected in the liquid
phase by 1H NMR and GC-MS. With 3 times less EtOH (25−
30 mL) under identical conditions, the product was heavily
contaminated with 4 (up to 30%), as was revealed by 31P NMR
analysis. Complex 4 was prepared independently and
structurally characterized (Figure 1).19,20 Evidently, the
(2) We also found that [(Ph3P)3RuCl2] (3)14 generated in
situ from RuCl3·xH2O and PPh3 in EtOH remained unchanged
after agitation under reflux was continued for 4 days. Upon
addition of KOH to this reaction mixture, however, the dark
brown color from 3 gradually changed to yellow. 31P NMR
analysis pointed to full conversion of 3 to a mixture of 2 and 1.
Evidently, the addition of alkali prompted the formation of
ethoxide, followed by its coordination to the metal center and
β-H-elimination leading to the conversion of the Ru−Cl bonds
to the Ru−H bonds.
The findings described above suggested that formaldehyde-
and NaBH4-free synthesis of 1 directly from RuCl3·xH2O,
PPh3, and KOH in EtOH (Scheme 1) should be possible. This
Scheme 1. CH2O-Free, One-Pot Synthesis of 1 from
RuCl3·xH2O
Figure 1. ORTEP drawing of 4 with thermal ellipsoids drawn at the
50% probability level and all H atoms of the AcO and PPh3 ligands
omitted for clarity.
assumption was experimentally confirmed. In order to develop
a truly practicable procedure, we then performed a series of
experiments to study the reaction sequence, minimize the
amounts of PPh3 and EtOH used, and establish an optimal
temperature regime to achieve the highest possible yield and
purity of 1.
acetaldehyde produced in the β-H-elimination step (see
above) underwent the Tishchenko reaction that is known19
to be efficiently catalyzed by 2, a key intermediate involved in
the reaction sequence (Scheme 1). Alkaline hydrolysis of the
AcOEt thus produced gave rise to the acetate anion for the
formation of the side product 4.
In the first step of the reaction, Ru(III) (RuCl3·xH2O) is
reduced to Ru(II) (3)14 on heating with PPh3 in EtOH. In
principle, both ethanol and phosphine could act as the reducing
agent. A definitive answer to the question “which of the two (or
both) actually reduces the Ru(III)?” is still not without
controversy,15 despite the fact that the reaction has been
widely known and used for nearly 50 years.16 We therefore
analyzed by 31P NMR spectroscopy the mother liquor after the
synthesis of 3 from RuCl3·xH2O and PPh3 (4 equiv) in EtOH
under argon to find that both PPh3 and Ph3PO were present.
Clearly, some of the phosphine must have been oxidized during
the formation of 3. The PPh3 to Ph3PO ratio in the mother
liquor was found to vary in a broad range, from ca. 1:1 to 1:4,
depending on the source of RuCl3·xH2O used for the reaction.
This is hardly surprising, since RuCl3·xH2O is a non-
stoichiometric mixture of ruthenium species that is “called
the “trichloride” because the Cl:Ru ratio is about 3:1” and that
in fact can contain various quantities of Ru(IV).17 Importantly,
however, the presence of unreacted PPh3 after the formation of
3 in the reaction of RuCl3·xH2O with 4 equiv of PPh3 pointed
to the possibility of using RuCl3·xH2O and PPh3 in a 1:4 molar
ratio for the entire reaction sequence leading to 1 (Scheme 1).
We reasoned that the undesired Tishchenko reaction of the
acetaldehyde could be suppressed by dilution and/or higher
concentrations of KOH, prompting alkali-catalyzed aldol
condensation. Both methods proved to be efficient. For the
smaller scale preparation, one may use a larger quantity of
EtOH with less KOH. For the synthesis on a larger scale, it is
more convenient to keep a lower volume of EtOH at the
expense of using a 2−4-fold excess of alkali. An increased
concentration of ethoxide at a higher pH also facilitates the
formation of Ru−OEt species involved in the β-elimination,
including those originating from the side product 4.
Adding KOH to a suspension of 3 in boiling EtOH was
found to trigger side reactions leading to [(Ph3P)3Ru(CO)2]21
as a side product, which was identified by NMR and IR
spectroscopy. We were delighted to find, however, that these
side processes could be avoided altogether by adding KOH at
room temperature. Therefore, after the formation of 3 in EtOH
under reflux, the resultant mixture was first cooled to 25−30
°C. Solid KOH was then added and the reaction mixture was
stirred for 1 h at room temperature and 1−1.5 h at 50−70 °C
and finally brought back to reflux that was continued until full
B
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Note
conversion of 2 to 1 was reached after several hours (31P
NMR). Running the reaction for a longer time only may have a
beneficial effect on purity, while not affecting the yield of 1 that
is stable under the reaction conditions. Two factors are
important for shortening the time of the reaction that is mainly
controlled by the transformation of 2 to 1 (Scheme 1). First,
the amount of water in the system should be minimized by
using absolute ethanol and fresh KOH. Larger quantities of
water in the system have been found to not only slow down the
formation of 1 but also favor the side formation of 4 (see
above). Second, efficient agitation shortens the reaction time
because the intermediates and the final product are poorly
soluble in ethanol.
reaction times required in the one-pot synthesis of 1 described
above (Scheme 1). The excess of PPh3 that is needed for the
formation of 3 from RuCl3·xH2O in the first step (see above)
remains in the reaction solution, slowing down the sequential
transformations leading to 1.24
In conclusion, we have developed a new method to prepare
[(Ph3P)3Ru(CO)(H)2] (1), an important catalyst for a broad
variety of organic transformations and a useful starting material
in inorganic and organometallic synthesis. Unlike the currently
used procedure to make 1,8 our method does not utilize toxic
and hazardous materials such as formaldehyde and benzene,
uses PPh3 in the minimum possible excess, and produces 1 in
unprecedented, nearly quantitative yield.25 For most purposes,
no purification is needed for the product that precipitates out of
the reaction mixture spectroscopically (>98%) and analytically
pure. The reaction is conducted in ethanol, the “greenest”
organic solvent. Importantly, the latter can be used in small
quantities, thereby enabling scalability, as has been demon-
strated by preparing up to over 17 g of pure 1 in one batch. The
new method is likely to find use in both academic and industrial
research.
At the end of the reaction, the precipitated 1 was isolated by
filtration as a microcrystalline solid in over 95% yield. Although
1 is intrinsically white, the isolated off-white product was
spectroscopically (>98%) and analytically pure (Figures 2 and
EXPERIMENTAL SECTION
■
Ruthenium trichloride hydrate, ca. 40% Ru (Precious Metals Online,
PMO Pty Ltd., Australia), PPh3 (Alfa Aesar), KOH (85% min; Carlo
Erba), and absolute ethanol (Panreac) were used as received.
Deuterated solvents were purchased from Aldrich. NMR spectra
were recorded on Bruker Avance Ultrashield 400 and 500 MHz
spectrometers. An Agilent Technologies 7890A chromatograph
equipped with a 5975C MSD unit was used for GC-MS analysis.
Single-crystal X-ray diffraction studies were performed using a Bruker-
Nonius diffractometer equipped with an APEX II 4K CCD area
detector. Elemental analyses were carried out by the Microanalysis
Center at the Complutense University of Madrid. An inert atmosphere
was maintained throughout the synthesis of 1. Isolation of 1 was
performed in air.
1
Figure 2. H NMR spectrum of 1 in benzene-d6 (hydride region).
Preparation of [(Ph3P)3Ru(CO)(H)2] (1). Large Scale. A 1 L two-
neck round-bottom flask equipped with a gas inlet, a reflux condenser,
and a Teflon-coated magnetic stir bar was charged with absolute
ethanol (600 mL) and RuCl3·xH2O (5.0 g). The mixture was stirred at
reflux under an argon atmosphere for 10 min for deaeration, then PPh3
(20.0 g, 76.2 mmol) was added, and vigorous agitation at reflux under
argon was continued for 1 h. The resultant dark brown suspension of
[(Ph3P)3RuCl2] was cooled to room temperature and treated with
KOH (pellets; 13.58 g; 205.7 mmol). The mixture was agitated first at
room temperature for 1 h and then at 50−60 °C for 1 h. The resultant
dark green suspension was then vigorously stirred at reflux for 24 h,
during which time the reaction mixture turned light yellow. 31P NMR
analysis of a representative sample diluted with benzene under argon
indicated full conversion to the final product. After the mixture was
cooled to room temperature, the precipitate was separated by filtration
in air, washed with ethanol (2 × 50 mL), deionized water (3 × 50
mL), and ethanol (3 × 50 mL), and dried under vacuum. The yield of
[(Ph3P)3Ru(CO)(H)2] (1) as a pale yellowish microcrystalline solid
was 17.54 g (97%). No NMR-detectable impurities were present.
NMR (benzene-d6, 25 °C): 1H, δ 7.6−6.8 (m, 45H, PPh3), −6.5 (tdd,
1H, J = 31, 15, and 6 Hz, Ru−H trans to C), −8.3 (dtd, 1H, J = 74, 29,
and 6 Hz, Ru−H trans to P); 31P{1H}, δ 60.7 (d, 2P, J = 17 Hz), 48.6
(t, 1P, J = 17 Hz). Anal. Calcd for C55H47OP3Ru: C, 71.9; H, 5.2.
Found: C, 71.7; H, 5.1.
Figure 3. 31P{1H} NMR spectrum of 1 in benzene-d6.
3). We have also confirmed the solid-state structure of 1 by
single-crystal X-ray diffraction (Figure 4)22 and demonstrated
the facile scalability of the method by preparing over 17.5 g of 1
in one batch using only 400−600 mL of EtOH.
Figure 4. ORTEP drawing of 1 with thermal ellipsoids drawn at the
50% probability level and all H atoms of the PPh3 ligands omitted for
clarity.
Alternatively, the synthesis of 1 can be carried out in two
steps. First, RuCl3·xH2O was reacted with PPh3 in EtOH under
reflux for 1 h to give 314 quantitatively. The dark brown
product was isolated by filtration and treated with KOH (2
equiv) in ethanol under reflux to produce white 1 in 95% yield
after only 2 h.23 We found that extra PPh3 slows down the
formation of 1 from 3. This observation accounts for the longer
Medium Scale. A 100 mL two-neck round-bottom flask equipped
with a gas inlet, reflux condenser, and a Teflon-coated magnetic stir
bar was charged with absolute ethanol (50 mL) and RuCl3·xH2O (0.50
g). The mixture was stirred at reflux under an argon atmosphere for 10
min for deaeration, then PPh3 (2.00 g, 7.62 mmol) was added, and
vigorous agitation at reflux under argon was continued for 1 h. The
resultant dark suspension of [(Ph3P)3RuCl2] was cooled to room
C
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Note
temperature and treated with KOH (pellets; 1.07 g; 16.2 mmol). The
mixture was agitated first at room temperature for 1 h and then at 50−
60 °C for 1 h, during which time the originally dark brown reaction
mixture first turned dark green and then yellow. The mixture was then
vigorously stirred at reflux for 10 h, at which point 31P NMR analysis
of a representative sample diluted with benzene under argon indicated
full conversion to the final product. After the mixture was cooled to
room temperature, the precipitate was separated by filtration in air,
washed with ethanol (2 × 20 mL), deionized water (3 × 20 mL), and
ethanol (3 × 20 mL), and dried under vacuum. The yield of
[(Ph3P)3Ru(CO)(H)2] (1) as a pale yellowish microcrystalline solid
was 1.77 g (98%). NMR data are as described above. Anal. Calcd for
C55H47OP3Ru: C, 71.9; H, 5.2. Found: C, 71.4; H, 5.1.
Small Scale. A 100 mL two-neck round-bottom flask equipped with
a gas inlet, a reflux condenser, and a Teflon-coated magnetic stir bar
was charged with EtOH (75 mL) and RuCl3·xH2O (0.25 g). This
solution was stirred at reflux under an argon atmosphere for 10 min for
deaeration. Triphenylphosphine (1.00 g, 3.81 mmol) was added, and
the mixture was stirred at reflux under an argon atmosphere for 1 h to
produce [(Ph3P)3RuCl2] as a dark brown solid and cooled to room
temperature. KOH (pellets; 0.21 g; 3.2 mmol) was added, and the
mixture was agitated at room temperature for 1 h to give a greenish
precipitate and then at 60 °C for 1 h to produce a yellow solid. The
mixture was then stirred at reflux for 5 h to reach full conversion to
[(Ph3P)3Ru(CO)(H)2] (31P NMR). After the mixture was cooled to
room temperature, the slightly yellowish precipitate was separated by
filtration, washed with ethanol (2 × 10 mL), deionized water (2 × 10
mL), and ethanol (2 × 10 mL), and then dried under vacuum. The
yield was 0.89 g (98%). NMR data are as described above. Anal. Calcd
for C55H47OP3Ru: C, 71.9; H, 5.2. Found: C, 71.5; H, 5.1.
Huang, D.; Gupta, S.; Londergan, T. M.; Sargent, J. R.; Mabry, J. M.
ACS Symp. Ser. 2000, 760, 24.
(7) (a) Robinson, S. D.; Levison, J. J. J. Chem. Soc. A 1970, 2947.
(b) Ahmad, N.; Robinson, S. D.; Uttley, M. F. J. Chem. Soc., Dalton
Trans. 1972, 843.
(8) Ahmad, N.; Levison, J. J.; Robinson, S. D.; Uttley, M. F. Inorg.
Synth. 1974, 15, 45.
(9) (a) Kakiuchi, F.; Sekine, S.; Tanaka, Y.; Kamatani, A.; Sonoda,
M.; Chatani, N.; Murai, S. Bull. Chem. Soc. Jpn. 1995, 68, 62.
(b) Kakiuchi, F.; Kochi, T.; Mizushima, E.; Murai, S. J. Am. Chem. Soc.
2010, 132, 17741.
(10) (a) Owston, N. A.; Parker, A. J.; Williams, J. M. J. Org. Lett.
2007, 9, 3599. (b) Maytum, H. C.; Tavassoli, B.; Williams, J. M. J. Org.
Let. 2007, 9, 4387. (c) Owston, N. A.; Parker, A. J.; Williams, J. M. J.
Chem. Commun. 2008, 624. (d) Blacker, A. J.; Farah, M. M.; Hall, M.
I.; Marsden, S. P.; Saidi, O.; Williams, J. M. J. Org. Lett. 2009, 11, 2039.
(11) Grounds, H.; Anderson, J. C.; Hayter, B.; Blake, A. J.
Organometallics 2009, 28, 5289.
(12) Zhang, C.; Wang, B.; Wang, Y. Jingxi Shiyou Huagong 2007, 24,
1.
(13) (a) Young, R.; Wilkinson, G. Inorg. Synth. 1977, 17, 75.
(b) Young, R.; Wilkinson, G. Inorg. Synth. 1990, 28, 337.
(14) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth.
1970, 12, 237.
́
(15) (a) Linn, D. E., Jr. J. Chem. Educ. 1999, 76, 70. (b) Arnaiz, F. J. J.
Chem. Educ. 1999, 76, 1484. (c) Linn, D. E., Jr. J. Chem. Educ. 1999,
76, 1485.
(16) Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966, 28,
1945.
(17) Rard, J. A. Chem. Rev. 1985, 85, 1.
(18) Rose, D.; Gilbert, J. D.; Richardson, R. P.; Wilkinson, G. J.
Chem. Soc. A 1969, 2610.
(19) Ito, T.; Horino, H.; Koshiro, Y.; Yamamoto, A. Bull. Chem. Soc.
Jpn. 1982, 55, 504.
(20) A lower quality crystal structure of 4 has been reported: Skapski,
A. C.; Stephens, F. A. Chem. Commun. 1969, 1008.
(21) [(Ph3P)3Ru(CO)2] has been reported to form from 1 upon
treatment with PhCOOMe in the presence of an olefin at elevated
temperatures: Hiraki, K.; Kira, S.-i.; Kawano, H. Bull. Chem. Soc. Jpn.
1997, 70, 1583.
(22) The structure is a solvate with 0.8 molecule of toluene and 0.2
molecule of hexane, modeled with disorder over three positions with a
40:40:20 occupancy ratio. An X-ray structure of 1·CH2Cl2 has been
reported: Junk, P. C.; Steed, J. W. J. Organomet. Chem. 1999, 587, 191.
(23) The formation of 1 from [(Ph3P)3Ru(CO)(H)(Cl)] and NaOH
in boiling methyl cellosolve has been reported: Boniface, S. M.; Clark,
G. R.; Collins, T. J.; Roper, W. R. J. Organomet. Chem. 1981, 206, 109.
(24) Attempts were made to shorten the reaction time to full
conversion to 1 by performing the synthesis at a higher temperature, in
boiling n-BuOH (bp 118 °C) in place of EtOH. Under these
conditions, however, the reaction was poorly selective, giving rise to a
complex mixture of products. In MeOH, the reaction gave large
quantities of [(Ph3P)3Ru(CO)2] as a side product.21
(25) The formation of 1 in the reaction of premade 3 with KOH in
toluene−glycerol−water at 80 °C has recently been reported. The
yield of 1, the conversion of 3, and reaction selectivity are not specified
in this article. See: Dibenedetto, A.; Stufano, P.; Nocito, F.; Aresta, M.
ChemSusChem 2011, 4, 1311.
ASSOCIATED CONTENT
■
S
* Supporting Information
Text, figures, and CIF files giving full details of synthetic and
crystallographic studies. This material is available free of charge
via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail for V.V.G.: vgrushin@iciq.es.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENTS
■
́
We thank Drs. Marta Martınez Belmonte, Eddy Martin, and
Eduardo C. Escudero-Adan
́
for crystallographic studies, Fedor
M. Miloserdov for checking the procedure, and Prof. Michael
K. Whittlesey for valuable comments. The ICIQ Foundation,
Consolider Ingenio 2010 (Grant CSD2006-0003), and the
Spanish Government (Grant CTQ2011-25418) are thankfully
acknowledged for support of this research.
REFERENCES
■
(1) Hallman, P. S.; McGarvey, B. R.; Wilkinson, G. J. Chem. Soc. A
1968, 3143.
(2) (a) Kakiuchi, F.; Murai, S. Acc. Chem. Res. 2002, 35, 826.
(b) Kakiuchi, F.; Murai, S. Top. Organomet. Chem. 1999, 3, 47.
(3) Arockiam, P. B.; Bruneau, C.; Dixneuf, P. H. Chem. Rev. 2012,
112, 5879.
(4) Naota, T.; Takaya, H.; Murahashi, S.-I. Chem. Rev. 1998, 98,
2599.
(5) Nixon, T. D.; Whittlesey, M. K.; Williams, J. M. J. Dalton Trans.
2009, 753.
(6) (a) Mabry, J. M.; Runyon, M. K.; Paulasaari, J. K.; Weber, W. P.
ACS Symp. Ser. 2003, 838, 50. (b) Weber, W. P.; Paulasaari, J. K.;
D
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