Hydrosilylation of Carbonyls Catalyzed by the Rhenium(V) Oxo Complex [Re(O)(hoz)2]+—A Non-Hydride Pathway

Abstract

Catalytic conversion of silane and carbonyls by the cationic rhenium oxo complex [Re(O)(hoz)2]+ (1; hoz = 2-(2′-hydroxyphenyl)-2-oxazoline(1−)) was examined using density functional theory. It is shown that complex 1 catalyzed the carbonyl hydrosilylation via a non-hydride pathway—the ionic hydrogenation mechanism. The complete catalytic cycle is proposed to involve three steps: the formation of cis η1-silane Re(V) adduct, the heterolytic cleavage of a Si–H bond through anti attack of carbonyls at the cis η1-silane Re(V) adduct, and transfers between the rhenium and activated silylcarbonium ion to produce the silyl ether product and regenerate catalyst 1. The σ-bond metathesis like transition state suggested by Abu-Omar, although not located, can be inferred from the ionic hydrogenation transition states (TS_3syn and TS_5syn, in which the carbonyls syn attack the η1-silane Re(V) adduct) associated with the higher energy barrier.