Cubic Siloxanes with Both Si−H and Si−O t Bu 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−O t Bu groups [( t BuO) n H 8− n Si 8 O 12 ; n =1, 2 or 7] have been synthesized by the reaction of octa(hydridosilsesquioxane) (H 8 Si 8 O 12 ) and tert ‐butyl alcohol in the presence of a Et 2 NOH catalyst. The Si−H and Si−O t Bu 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 Et 2 NOH, enabling the formation of the monosilanol compound ( t BuO) 7 (HO)Si 8 O 12 . 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 ( t BuO) 7 HSi 8 O 12 can be treated with organochlorosilanes in the presence of a BiCl 3 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.