Journal of the American Chemical Society
Communication
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displacement of the catalyst, within the ion pair prior to silylium
rotation, resulting in stereochemical retention. Loss of stereo-
specificity is caused by the formation of a solvent separated ion
pair or ion aggregate (C), which is favored in more polar solvents
or upon increasing salt concentration. An alternative mechanism
featuring a four-membered cyclic transition state has been
proposed for related silane additions to activated carbonyls.24
This concerted, asynchronous addition should afford complete
stereochemical retention and is inconsistent with the observed
racemization under more polar conditions. For comparison, a
catalytically competent silane−Si(catF)2 adduct should lead to
inversion in the major product,20a allowing us to exclude this
possible mechanism.
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In conclusion, bis(perfluorocatecholato)silane (1) was pre-
pared, and reactions to assess its Lewis acidity were investigated.
Coordination of fluoride, triethylphosphine oxide, and N,N′-
diisopropylbenzamide demonstrate the ability of Si(catF)2 to
bind several common classes of Lewis bases. Additionally,
hydrosilylation and silylcyanation of electron-deficient aldehydes
were catalyzed by Si(catF)2 under mild conditions. A stereogenic
silicon substrate was employed in combination with solvent and
salt effect studies to provide evidence for a carbonyl activation
mechanism involving an ionic intermediate. We hope that future
work will expand upon the use of neutral, yet potent, silicon
Lewis acids in catalytic transformations.
(8) This range represents the shortest and longest distances measured
between the least-squares mean plane defined by the catecholate ligands
of the molecule containing Si1 to individual atoms of the Si2-containing
silicate complex.
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ASSOCIATED CONTENT
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S
(b) Muther, K.; Oestreich, M. Chem. Commun. 2011, 47, 334.
(15) Hamashima, Y.; Sawada, D.; Kanai, M.; Shibasaki, M. J. Am. Chem.
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̈
* Supporting Information
Additional experimental information, characterization, X-ray
crystallographic details, and CIF files. This material is available
(16) (a) Kim, S. S.; Rajagopal, G.; Song, D. H. J. Organomet. Chem.
2004, 689, 1734. (b) Denmark, S. E.; Chung, W. J. Org. Chem. 2006, 71,
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(17) NMR kinetics experiments were attempted for the hydrosilation
of 2-trifluoromethylbenzaldehyde with a 10-fold excess of triethylsilane
at 30 °C. Unfortunately, the kinetics data were complex and could not be
fit to a standard rate law, in part due to complications from catalyst
decomposition.
AUTHOR INFORMATION
■
Corresponding Authors
Notes
(18) Koller, J.; Bergman, R. G. Organometallics 2012, 31, 2530.
(19) Blackwell, J. M.; Foster, K. L.; Beck, V. H.; Piers, W. E. J. Org.
Chem. 1999, 64, 4887.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(20) (a) Rendler, S.; Oestreich, M. Angew. Chem., Int. Ed. 2008, 47,
■
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5997. (b) Metsanen, T. T.; Hrobarik, P.; Klare, H. F. T.; Kaupp, M.;
̈
This work was supported by the Director, Office of Science,
Office of Basic Energy Sciences of the U.S. Department of Energy
under Contract No. DE-AC02-05CH11231 and the National
Science Foundation under Award No. CHE-0841786. We also
acknowledge the National Institutes of Health for funding of the
ChexRay X-ray crystallographic facility (College of Chemistry,
University of California, Berkeley) under Grant No. S10-
RR027172. We thank Michael Lipschutz for assistance with X-
ray diffraction and Jigar Patel for Chiral HPLC expertise.
Oestreich, M. J. Am. Chem. Soc. 2014, 136, 6912. (c) Shinke, S.;
Tsuchimoto, T.; Kawakami, Y. Silicon Chem. 2007, 3, 243.
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Chem. Soc. 1964, 86, 3271. (b) Ojima, Y.; Yamaguchi, K.; Mizuno, N.
Adv. Synth. Catal. 2009, 351, 1405.
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