Hydrosilylation is a valuable method for reducing carbonyl compounds. Typically, early metals are expected to react at C=O to give Si�O bond formation. Surprisingly, ToMMgHB(C6F5)3 (ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate) catalyzes hydrosilylation of the C=C bond of a,�-unsaturated esters. The products of these reactions are a-silyl esters. The precatalyst, ToMMgHB(C6F5)3, is synthesized by the reaction of ToMMgMe, PhSiH3, and B(C6F5)3. This magnesium hydridoborate compound persists in solution and in the solid state, whereas ToMMgH decomposes to an intractable black solid. In addition, complexes such as ToMMgMe are not effective precatalysts for ester hydrosilylation. The alkyl borate, ToMMgMeB(C6F5)3, is investigated as a model intermediate in hydrosilylation. Interestingly, isolated ToMMgMeB(C6F5)3 remains unreacted in the presence of PhSiH3 and readily undergoes aryl group transfer from B(C6F5)3 to give ToMMgC6F5 and MeB(C6F5)2.

Unusual selectivity in a magnesium-catalyzed hydrosilylation of a,�-unsaturated esters

248th National Meeting (2014)

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