Cubic Siloxanes with Both Si-H and Si-OtBu Groups for Site-Selective Siloxane Bond Formation

摘要

Cage-type siloxanes have attracted increasing attention as building blocks for silica-based nanomaterials as their corners can be modified with various functional groups. Cubic octasiloxanes incorporating both Si-H and Si-OtBu groups [(tBuO)(n)H8-nSi8O12; n=1, 2 or 7] have been synthesized by the reaction of octa(hydridosilsesquioxane) (H8Si8O12) and tert-butyl alcohol in the presence of a Et2NOH catalyst. The Si-H and Si-OtBu groups are useful for site-selective formation of Si-O-Si linkages without cage structure deterioration. The Si-H group can be selectively hydrolyzed to form a Si-OH group in the presence of Et2NOH, enabling the formation of the monosilanol compound (tBuO)(7)(HO)Si8O12. The Si-OH group can be used for either intermolecular condensation to form a dimeric cage compound or silylation to introduce new reaction sites. Additionally, the alkoxy groups of (tBuO)(7)HSi8O12 can be treated with organochlorosilanes in the presence of a BiCl3 catalyst to form Si-O-Si linkages, while the Si-H group remains intact. These results indicate that such bifunctional cage siloxanes allow for stepwise Si-O-Si bond formation to design new siloxane-based nanomaterials.