Reduction of carbonyl groups by high-valent rhenium oxides

The oxo-rhenium complexes [Re2O7] (1), [ReMeO3] (2), [Re(eta(5)-C5H5)O-3] (3), [ReO2Cl(DMSO)(2)] (4), [ReO2Me(PhC=CPh)] (5), and [ReOCl3 (PPh3)(2)] (6) catalyze the hydrosilylation of aliphatic and aromatic aldehydes with dimethylphenylsilane in C6D6 solutions. Compound 1 catalyzes the hydrosilylation of aldehydes at room temperature, affording the corresponding silyl ethers in good yield, but is ineffective as ketone hydrosilylation catalyst. The reactions of aldehydes and ketones with dimethylphenylsilane using compounds 2-6 as catalysts, require heating at 80 degrees C. The scope of rhenium oxides-mediated hydrosilylation with a variety of aldehydes and ketones has been studied. Methyltrioxorhenium(VII) (2) and oxotrichlorobis(triphenylphosphine)rhenium(V) (6) shown to be the most active and versatile catalysts for the hydrosilylation of aliphatic and aromatic aldehydes and also ketones. The dioxo-rhenium derivatives [ReO2Me(PhC=CPh)] and [ReO2Cl(DMSO)(2)] also catalyze the reaction of dimethylphenylsilane and aldehydes, although longer reaction times were required. (c) 2005 Elsevier B.V All rights reserved.