Silicon-carbon unsaturated compounds. 71. Thermolysis of 1,2-bis(acyl)tetrakis(trimethylsilyl)disilane with disubstituted acetylenes

The thermolysis of 1,2-di(adamantoyl)tetrakis(trimethylsilyl)disilane (1a) with diphenylacetylene at 140 degrees C for 24 h afforded 1-[(E)-1,2-diadamantyl-2-(trimethylsiloxy)ethenyloxy]-2,3-diphenyl-1-[tris(trimethylsilyl)silyl]-1- silacycloprop-2-ene (2a) and 3,4-diadamantyl-2,2-bis(trimethylsiloxy)-1,1-bis(trimethylsilyl)1,2-disilacyclobut-3-ene (3a) in 43% and 41% yields, respectively. Similarly, the cothermolysis of 1,2-di(pivaloyl)tetrakis(trimethylsilyl)disilane (1b) with diphenylacetylene gave 1-[(E)-1,2-di(tert-butyl)2-(trimethylsiloxy)ethenyloxy]-2,3-diphenyl-1-[tris(trimethylsilyl)silyl]-1-silacycloprop-2-ene (2b) in 52% yield, along with a mixture of unidentified products. The reaction of 1a with bis(trimethylsilyl) acetylene under the same conditions produced 1-[(E)-1,2-diadamantyl-2-(trimethylsiloxy)ethenyloxy]-2,3-bis(trimethylsilyl)-1-[tris(trimethylsilyl)silyl]-1-silacycloprop-2-ene and 3a in 54% and 23% yield, while 1b with bis(trimethylsilyl) acetylene gave 1-[(E)-1,2-di(tert-butyl)-2-(trimethylsiloxy)ethenyloxy]-2,3-bis(trimethylsilyl)-1-[tris(trimethylsilyl)silyl]-1-silacycloprop-2-ene in 62% yield. The results of X-ray crystallographic analysis for the 1-silacycloprop-2-ene 2a are described. Computational analyses for successive isomerization of a simplified model, 1,2-di(acetyl) tetra(silyl) disilane to a silylene intermediate, [(E)-1,2-dimethyl-2-siloxyethenyloxy]tri(silyl)silylsilylene via trans-3,4-dimethyl-3,4-di(siloxy)-1,2-di(silyl)-1,2-disilacyclobut-1-ene, are described. The results of the calculations for the real models having the same substituents as 1b are also reported.