Reactions of silanes with allylic alcohols catalyzed by titanocene derivatives: an approach to catalytic cross dehydrocoupling/co-intramolecular hydrosilation

Abstract

A preliminary study of the dimethyltitanocene, 7, and rac-[ethylene-1,2-bis( η 5-4,5,6,7-tetrahydroindenyl)]TiMe 2, 8, catalyzed reactions of silanes with allylic and homoallylic alcohols is described. In the presence of catalysts 7 or 8, tertiary silanes bearing at least one phenyl group react with 2-methyl-but-1-ene-4-ol, 2a, to produce the 4-siloxy-2-methylbut-1-ene, 3a. Secondary silanes react with either 2a, or 2-methylpropen-3-ol, 2b, to give different product distributions depending on the catalyst type, concentration, and the substituents on the silicon atom. With high catalyst concentration and diphenylsilane, a redistribution reaction substantially converts the initially produced allyloxydiphenylsilane to bis(allyloxy)diphenylsilane. Low catalyst concentrations give primarily the intramolecular hydrosilation product. Under the same reaction conditions, phenylmethylsilane gives more intramolecular hydrosilation product than diphenylsilane does. Phenylsilane reacts with 2b, to give a polymeric product, 6b (R  Ph, R′  H), via intermolecular hydrosilation. Under the same conditions phenylsilane reacts with 2a to give primarily the hydrogenation product tris(3-methylbutoxy)phenylsilane, 5a (R  Ph, R′  -OCH 2Ch 2CH(CH 3) 2), together with traces of oligosilane and intermolecular hydrosilation product 6a. Some possible reaction pathways, including the observed side reactions, are discussed.