Synthesis,Characterization and Reactivity of cis-cis-cis [ (C 6 H 5 ) 4 Si 4 O 4 (OH) 4 ]

Abstract

The hydrolytic condensation of PhSiCl₃ (H₂O/acetone, 0–5°C, 18 h) precipitates cis-cis-cis-[(C₆H₅)₄Si₄O₄(OH)₄] (5a) as the sole crystalline product in approximately 40% yield. The all-cis structure, which was originally assigned by J. F. Brown on the basis of IR spectroscopy and derivatization studies, was confirmed by a single-crystal X-ray diffraction study. The ether solvate of 5a crystallizes from Et₂O/C₆H₆ as a hydrogen-bonded, dimeric structure, which kinetically stabilizes the molecule toward self-condensation reactions. In solution, particularly in the presence of weak amine bases, 5a rapidly self-condenses to form “T-resins”; self-condensation also occurs in the solid-state (25° C) over several months. Tetrasilanol 5a can be exhaustively silylated with Me₃SiCl to afford excellent yields of cis-cis-cis-[(C₆H₅)₄Si₄O₄(OSiMe₃)₄], but all attempts to effect clean partial silylation produced complex mixtures of partially silylated T-resins. Attempts to effect catalytic hydrogenation of 5a to cis-cis-cis[(c-C₆H₁₁)₄Si₄O₄(OH)₄] (16) produced several products, including completely-condensed frameworks [(c-C₆H₁₁)₈Si₈O₁₂] (6b) and [(c-C₆H₁₁)₆Si₆O₉] (16).