Journal of the American Chemical Society
Communication
NMR and 29Si NMR) with Co(OPv)2/CNAd catalyst (195 ppm
based on Co) at 120 °C for 15 min gave an insoluble silicone gel.
Solid-state 1H quantitative and 29Si DD NMR suggested that the
degree of cross-linkage was 70−80%, which was supported by IR
spectroscopy. The Co residues were likely to cause coloring of the
silicone gel formed, which was found to be true. The brown color
of the reaction mixture due to the catalytically active Co species
was maintained even when the product was kept under an
atmosphere of inert gas. Surprisingly, the brown color of the
silicone gel faded upon exposure to air and turned slightly pale
blue to almost colorless after 12 h at room temperature,
presumably due to oxidation of the catalytically active species to
Co(III).
on Recent Advances; Marciniec, B., Ed.; Springer: New York, 2009.
(c) Speier, J. L. Adv. Organomet. Chem. 1979, 17, 407. (d) Nakajima, Y.;
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(2) Tondreau, A. M.; Atienza, C. C. H.; Weller, K. J.; Nye, S. A.; Lewis,
K. M.; Delis, J. G. P.; Chirik, P. J. Science 2012, 335, 567.
(3) Nakamura, E.; Sato, K. Nat. Mater. 2011, 10, 158.
(4) Earlier reports: (a) Mitchener, J. C.; Wrighton, M. S. J. Am. Chem.
Soc. 1981, 103, 975. (b) Harrod, J. F.; Chalk, A. J. J. Am. Chem. Soc. 1967,
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3858. (e) Seitz, F.; Wrighton, M. S. Angew. Chem., Int. Ed. Engl. 1988, 27,
289. Related references are cited in the SI.
(5) (a) Hojilla Atienza, C. C.; Tondreau, A. M.; Weller, K. J.; Lewis, K.
M.; Cruse, R. W.; Nye, S. A.; Boyer, J. L.; Delis, J. G. P.; Chirik, P. J. ACS
Catal. 2012, 2, 2169. (b) Bart, S. C.; Lobkovsky, E.; Chirik, P. J. J. Am.
Chem. Soc. 2004, 126, 13794. Related references are cited in the SI.
(6) Hydrosilylation of 1,3-dienes: Wu, J. Y.; Stanzl, B. N.; Ritter, T. J.
Am. Chem. Soc. 2010, 132, 13214.
A clue to understanding the possible intermediates may be the
well-known analogy of isocyanides (CNR) to carbon
monoxide (CO) as a π-acceptor ligand to the metal. Similar
to iron and cobalt carbonyls, isocyanide complexes of Fe(0) and
Co(I) are prepared from the Fe(II) and Co(II) precursors in the
presence of reducing agents. Earlier studies on the hydrosilylation
(7) Marciniec, B.; Kownacka, A.; Kownacki, I.; Taylor, R. Appl. Catal., A
2014, 486, 230.
(8) Atienza, C. C. H.; Diao, T.; Weller, K. J.; Nye, S. A.; Lewis, K. M.;
Delis, J. G. P.; Boyer, J. L.; Roy, A. K.; Chirik, P. J. J. Am. Chem. Soc. 2014,
136, 12108.
4a,c
of alkenes with Et3SiH proposed involvement of Fe(CO)3
R3SiCo(CO)3,4d,e and HCo(CO)3 These suggest that similar
4b
(9) Mo, Z.; Liu, Y.; Deng, L. Angew. Chem., Int. Ed. 2013, 52, 10845.
(10)Chen, C.;Hecht, M. B.;Kavara, A.;Brennessel, W.W.;Mercado, B.
Q.; Weix, D. J.; Holland, P. L. J. Am. Chem. Soc. 2015, 137, 13244.
(11) (a) Lipschutz, M.; Tilley, T. D. Chem. Commun. 2012, 48, 7146.
(b) Buslov, I.; Becouse, J.; Mazza, S.; Montandon-Clerc, M.; Hu, X.
Angew. Chem., Int. Ed. 2015, 54, 14523.
coordinatively unsaturated Fe(0) or Co(I) species stabilized by
CNR ligands generated from Fe(II) or Co(II) carboxylates
may be responsible for the present hydrosilylation. Strong affinity
of silicon to oxygen contributes to generating the active species
from the carboxylate precursor by hydrosilanes.
In summary, this new catalyst system consisting of cobalt or
iron carboxylates and isocyanide ligands provides new non-
precious-metal-based catalysts for hydrosilylation of hydro-
siloxanes, which are active enough to be used in industrially
important processes to modify silicone fluids and cross-link
silicone polymers to silicone gels. An important feature of these
multi-component catalyst systems is that all of the components
(metal carboxylates, isocyanide ligands, and hydrosilanes) are
stable and easily handled.18 We are now actively investigating the
hydrosilylation and the further improvement of catalyst efficiency
and functional group compatibility19 by combinatorial methods
of catalyst screening, systematically changing the hydrosilane,
alkene, metal carboxylate, isocyanide ligand, and activator with
the aid of mechanistic studies.
(12) Greenhalgh, M. D.; Frank, D. J.; Thomas, S. J. Adv. Synth. Catal.
2014, 356, 584. Related references are cited in the SI.
(13) Dow Corning applied for patents for hydrosilylation catalyzed by
metal salts and ligands with the aid of various activators, such as
organometallic reagents. Examples include Co- and Fe-catalyzed
hydrosilylation with MD′M, which were limited to reaction of 1-hexene
by complexes containing multidentate heteroatom ligands. Automatic
screening of the metal compounds and the ligand was performed to show
whether the reaction took place. Brandstadt, K.; Cook, S.; Nguyen, B. T.;
Surgenor, A.; Taylor, R.; Tzou, M. WO Patent Appl. 2013043846, 2013.
Related patents are cited in the SI.
(14) (a) Sunada, Y.; Noda, D.; Soejima, H.; Tsutsumi, H.; Nagashima,
H. Organometallics 2015, 34, 2896. See also: (b) Sunada, Y.; Tsutsumi,
H.;Shigeta, K.;Yoshida, R.;Hashimoto, T.;Nagashima, H. Dalton. Trans.
2013, 42, 16687.
(15) (a) Nishiyama, H.; Furuta, A. Chem. Commun. 2007, 760. Related
references are cited in the SI.
́ ́
(16) Marko, I. E.; Sterin, S.; Buisine, O.; Mignani, G.; Branlard, P.;
Tinant, B.; Declercq, J.-P. Science 2002, 298, 204.
(17) Selected results using strong organometallic reagents, e.g., HBpin,
Et3Al, and EtMgBr, are described in the SI. With these co-catalysts, metal
halides can be used instead of metal carboxylates when strong alkyl and
hydride reagents are used as activators.
ASSOCIATED CONTENT
* Supporting Information
TheSupportingInformationisavailablefreeofchargeontheACS
■
S
Experimental details and spectral data (PDF)
(18) Among the catalyst component, cobalt and iron pivalates are
somewhatsensitivetowardair, andstorageunderaninertgasatmosphere
is recommended. It is notable that the iron and cobalt pivalates, after
exposure to air for 72 h, possessed catalytic activity similar to that of
samples maintained underan inert gas atmosphere, though the induction
period was observed (for details see the SI).
(19) Functional group compatibility is a recent topic in the non-
precious-metal-catalyzed hydrosilylation of alkenes. Chirik’s catalyst is
useful for alkenes having ether and amines,2 whereas several reactions
with Ph2SiH2 or PhSiH3 are tolerant to carbonyl groups.10,11b,12 At the
present stage, hydrosilylation with hydrosiloxanes is tolerant to ethers,
amines, esters, and amides, but not to aldehydes and ketones.
AUTHOR INFORMATION
Corresponding Author
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank Mr. Koji Sakuta (Shin-Etsu Chemical Co.,
Ltd.) for helpful discussion and donation of silicone compounds.
This work was supported by CREST, JST.
REFERENCES
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(1) (a) Marciniec, B.; Gulinsky, J.; Urbaniak, W.; Kornetka, Z. W. In
Comprehensive Handbook on Hydrosilylation; Marciniec, B., Ed.;
Pergamon: Oxford, 1992. (b) Hydrosilylation: A Comprehensive Review
D
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