SILICON-CARBON UNSATURATED-COMPOUNDS .47. DIMERIZATION OF SILENES GENERATED FROM 1,4-BIS(PENTAMETHYLDISILANYL)BENZENE AND 1-(PENTAMETHYLDISILANYL)-4-(TRIMETHYLSILYL)BENZENE AND MOLECULAR-STRUCTURE OF A DIMER

The photolysis of 1,4-bis(pentamethyldisilanyl)benzene in hexane or cy clohexane gave two isomeric dimers, atricyclo[7.3.1.1(2,6)]tetradeca-3 ,5,9,11-tetraene (4) and cyclo[7.3.1.1(2,6)]tetradeca-3,5,9(13),11-tet raene (5), in a ratio of 1:1. Similar photolysis of 1-(pentamethyldisi lanyl)-4-(trimethylsilyl)benzene afforded the two isomeric dimers 7 an d 8, analogous to 4 and 5, in a ratio of 3:2. Heating 4 at 200-degrees -C for 2 h produced anyl)-2-(trimethylsilyl)phenyl]tetramethyldisilane (3) in 85% yield. Treatment of 7 at 200-degrees-C for 2 h afforded th ylsilyl)cyclohexa-1,3-dienyl]tetramethyldisilane (6) in 95% yield. Com pound 8 also afforded 6 under the same conditions in 90% yield. The st ructure of 8 was verified by an X-ray crystallographic study. Compound 8 crystallizes in the space group Cc with cell dimensions of a = 13.1 58(6) angstrom, b = 18.04(1) angstrom, c = 15.88(1) angstrom, beta = 1 04.77(4)-degrees, and V = 3645(4) angstrom3 (Z = 4).