Synthesis, characterization and reactivity of cis-cis-cis [(C6H5)4Si4O4(OH)4]

The hydrolytic condensation of PhSiCl3 (H2O/acetone, 0-5 degrees C, 18 h) precipitates cis-cis-cis[(C6H5)(4)Si4O4 (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 degrees C) over several months. Tetrasilanol 5a can be exhaustively silylated with Me3SiCl to afford excellent yields of cis-cis-cis[(C6H5)(4)Si4O4(OSiMe3)(4)] (10), 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)(4)Si4O4 (OH)(4)] (16) produced several products, including completely-condensed frameworks [(c-C6H11)(8)Si8O12] (6b) and [(c-C6H11)(6)Si6O9] (16).