DECOMPOSITION OF BIS(SILYLDIAZOMETHYL)POLYSILANES - FORMATION OF POLYSILABICYCLO[L.M.N]ALKANE DERIVATIVES

The photolysis of bis(trimethylsilyldiazomethyl)disilane (4a) in tert-butyl alcohol provided the tert-butyl alcohol adducts 5, 6, 7, 8 and 9. The structures of these products revealed the stepwise formation of asymmetric silenes as intermediates. Gas-phase pyrolysis of 4a and subsequent reaction with methanol and 4-methyl-1,2,4-triazoline-3,5-dione yielded the compounds 13 and 14, which are derived from the 1,4-disilabutadiene intermediate (16) rather than 1,2-disilacyclobutene (15). The photolysis and thermolysis of bis(dimethylphenylsilyl-diazomethyl)trisilane (4b) afforded 21b, 22b, 23b and 24b. Formation of compound 21b is attributed to the head-to-tail [2 + 2]cycloaddition of 1,5-disila-1,4-pentadiene (26b), while that of 23b, 22b and 24b is attributed to head-to-head [2 + 2]cycloaddition of 26b followed by reactions with tert-butyl alcohol and oxygen. Photolysis and pyrolysis of bis(trimethylsilyldiazomethyl)trisilane (4c) and bis(dimethylphenylsilyldiazomethyl)tetrasilane (4d) gave 29, 30 and 21d, which is consistent with an alternative mechanism, i.e. [2 + 3]silene-diazo cycloaddition.