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

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)_nH_8−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)₇HSi₈O₁₂can be treated with organochlorosilanes in the presence of a BiCl₃catalyst 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.