Geminal di(hypersilyl) compounds - The synthesis and structure of bis [tris(trimethylsilyl)silyl]methanol

Tris(trimethylsilyl)silyllithium (1) reacts with methyl formate in diethyl ether (molar ratio 2:1) to give 1,2-di(hypersilyl)ethylene 13. The formation of 13 proceeds through the intermediates formyl tris(trimethylsilyl)silane (4) and Lithium bis[tris(trimethylsilyl)silyl]methoxide (5). In diethyl ether, the alkoxide 5 spontaneously eliminates lithium trimethylsilanolate thereby generating 1,1-bis(trimethylsilyl)-2-[tris(trimethylsilyl)silyl]silene (9), which undergoes a formal [2+2] cycle addition with the carbonyl compound 4 to afford 13. This was verified by crossover experiments. In pentane, the alkoxide 5 is moderately stable. Thus, the intermediate 5, prepared by reaction of 1 with tert-butyl formate in pentane, was protonated with water to give the di(hypersilyl)methanol 6 in good yield. The structure of 6 was elucidated by an X-ray crystal structure analysis, which expectedly revealed tremendous distortions of the molecular skeleton. Thus, the spatial demand of the two extended hemispherical (Me3Si)(3)Si groups forces a widening of the Si-C-Si angle at the central sp(3) carbon atom to a value of 135.5 degrees.