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 cyclohexane gave two isomeric dimers, 7,7,8,8-tetramethyl-3,12-bis(pentamethyldisilanyl)-13,14-bis(trimethylsilyl)-7,8-disilatricyclo[7.3.1.1(2,6)]tetradeca-3,5,9,11-tetraene (4) and 7,7,8,8-tetramethyl-3,12-bis(pen-tamethyldisilanyl)-10,14-bis(trimethylsilyl)-7,8-disilatricyclo[7.3.1.1(2,6)]tetradeca-3,5,9(13),11-tetraene (5), in a ratio of 1:1. Similar photolysis of 1-(pentamethyldisilanyl)-4-(trimethylsilyl)benzene afforded the two isomeric dimers 7 and 8, analogous to 4 and 5, in a ratio of 3:2. Heating 4 at 200-degrees-C for 2 h produced 2-[4-(pentamethyldisilanyl)-6-(trimethylsilyl)cyclohexa-1,3-dienyl]-1-[4-(pentamethyldisilanyl)-2-(trimethylsilyl)phenyl]tetramethyldisilane (3) in 85% yield. Treatment of 7 at 200-degrees-C for 2 h afforded 1-[2,4-bis(trimethylsilyl)phenyl]-2-[4,6-bis-(trimethylsilyl)cyclohexa-1,3-dienyl]tetramethyldisilane (6) in 95% yield. Compound 8 also afforded 6 under the same conditions in 90% yield. The structure of 8 was verified by an X-ray crystallographic study. Compound 8 crystallizes in the space group Cc with cell dimensions of a = 13.158(6) angstrom, b = 18.04(1) angstrom, c = 15.88(1) angstrom, beta = 104.77(4)-degrees, and V = 3645(4) angstrom3 (Z = 4).