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Communication

Mechanism for Reduction Catalysis by Metal Oxo: Hydrosilation of Organic Carbonyl Groups Catalyzed by a Rhenium(V) Oxo Complex

Supporting Info

Elon A. Ison, Evan R. Trivedi, Rex A. Corbin, and Mahdi M. Abu-Omar*

Brown Laboratory, Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907

J. Am. Chem. Soc., 2005, 127 (44), pp 15374–15375

DOI: 10.1021/ja055704t

Publication Date (Web): October 13, 2005

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, mabuomar@purdue.edu

Abstract

The rhenium oxo complex [Re(O)(hoz)₂][TFPB], 1 (where hoz = 2-(2‘-hydroxyphenyl)-2-oxazoline(−) and TFPB = tetrakis(pentafluorophenyl)borate) catalyzes the hydrosilation of aldehydes and ketones under ambient temperature and atmosphere. The major organic product is the protected alcohol as silyl ether. Isolated yields range from 86 to 57%. The reaction requires low catalyst loading (0.1 mol %) and proceeds smoothly in CH₂Cl₂ as well as neat without solvent. In the latter condition, the catalyst precipitates at the end of reaction, allowing easy separation and catalyst recycling. Re(O)(hoz)(H), 3, was prepared, and its involvement in an ionic hydrosilation mechanism was evaluated. Complex 3 was found to be less hydridic than Et₃SiH, refuting its participation in catalysis. A viable mechanism that is consistent with experimental findings, rate measurements, and kinetic isotope effects (Et₃SiH/Et₃SiD = 1.3 and benzaldehyde-H/benzaldehyde-D = 1.0) is proposed. Organosilane is activated via η²-coordination to rhenium, and the organic carbonyl adds across the coordinated Si−H bond [2 + 2] to afford the organic reduction product.