Molecular-Scale Geometric Control of Organosiloxane Cage Frameworks Via Rigid Organic Bridges

Organosiloxanes represent a significant class of materials with a wide range of applications; however, achieving molecular-level framework control remains a fundamental challenge, mainly due to the intrinsic flexibility of the Si-O-Si bond angle. This study demonstrates a strategy to direct discrete cage-type organosiloxane framework geometries by utilizing rigid phenylene bridges with predefined angles between the Si-C bonds. Hydrolysis and condensation of 1,3-bis(triethoxysilyl)benzene in the presence of tetramethylammonium hydroxide facilitate the formation of cage-type organosiloxane trimers and tetramers possessing vertex SiO^-/SiOH groups. Single-crystal X-ray analysis of the tetramer stabilized via trimethylsilylation reveals a unique architecture: two tetrasiloxane rings connected by four phenylene bridges in a non-stacked configuration. Utilizing 1,4-bis(triethoxysilyl)benzene alters the fixed Si-Ph-Si bond angle, resulting in the selective formation of a cage-type hexamer. This strategy provides new insights into the molecular-level control of organosiloxane frameworks for the synthesis of novel nanobuilding blocks and will establish a versatile platform for the design of functional siloxane-based materials.