Reduction of carbonyl groups by high-valent rhenium oxides

Abstract

The oxo-rhenium complexes [Re 2O 7] ( 1), [ReMeO 3] ( 2), [Re(η 5-C 5H 5)O 3] ( 3), [ReO 2Cl(DMSO) 2] ( 4), [ReO 2Me(PhC CPh)] ( 5), and [ReOCl 3(PPh 3) 2] ( 6) catalyze the hydrosilylation of aliphatic and aromatic aldehydes with dimethylphenylsilane in C 6D 6 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 °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 [ReO 2Me(PhC CPh)] and [ReO 2Cl(DMSO) 2] also catalyze the reaction of dimethylphenylsilane and aldehydes, although longer reaction times were required.