Direct alkoxysilylation of alkoxysilanes for the synthesis of explicit alkoxysiloxane oligomers

Direct alkoxysilylation, which is a powerful tool to provide explicit alkoxysiloxanes, is developed and its versatility is investigated. Siloxane pentamers Si[OSiR1(OMe)2]4 having various functional groups (R1 = methyl, vinyl, phenyl, chloropropyl and n-butyl groups) were successfully obtained by direct alkoxysilylation of Si(OR)4 (R = t-Bu, CHPh2). Thus, the versatility of the reaction is confirmed on organic functional groups R1. Functional group tolerance of the reaction is discussed on the basis of electronegativity of the R1 groups. Alkoxysilylation of Si(Ot-Bu)2(OMe)2 and Si(Ot-Bu)(OMe)3 selectively gives trimer (MeO)2Si[OSiMe(OMe)2]2 and dimer (MeO)3SiOSiMe(OMe)2, respectively. Thus, the feasibility on siloxane structure is also confirmed. Various siloxane compounds are synthesized by this newly developed reaction for the first time.