POLYMERIC ORGANOSILICON SYSTEMS .12. SYNTHESIS AND ANIONIC RING-OPENING POLYMERIZATION OF 1,2,5,6-TETRASILACYCLOOCTA-3,7-DIYNES

Six 1,2,5,6-tetrasilacycloocta-3,7-diynes were synthesized by the reaction of the di-Grignard reagents of 1,2-diethynyldisilanes with 1,2-dichlorodisilanes. The reaction of the di-Grignard reagent of 1,2-diethynyl-1,2-dimethyldiphenyldisilane with 1,2-dichloro-1,2-dimethyldiphenyldisilane gave two isomers, r-1,t-2,t-5,c-6-tetramethyl-1,2,5,6-tetraphenyl-1,2,5,6-tetrasilacycloocta-3,7-diyne (cis-trans-1b) and r-1,t-2,c-5,t-6-tetramethyl-1,2,5,6-tetraphenyl-1,2,5,6-tetrasilacycloocta-3,7-diyne (all-trans-1b) whose configurations were determined by an X-ray diffraction study. cis-trans-1b crystallizes in the trigonal space group R3BAR with cell dimensions a = b = 21.671 (6) angstrom, c = 16.639 (2) angstrom, alpha = beta = 90-degrees, gamma = 120-degrees, V = 6557 (3) angstrom 3, and D(calcd) = 1.167 Mg/m3 (Z = 9), while all-trans-1b crystallizes in the monoclinic space group P2(1)/a with cell dimensions a = 18.308 (6) angstrom, b = 11.339 (3) angstrom, c = 15.352 (4) angstrom, alpha = gamma = 90-degrees, beta = 94.50 (2)-degrees, V = 3186 (2) angstrom 3, and D(calcd) = 1.106 Mg/m3 (Z = 4). Treatment of 1,2,5,6-tetrasilacycloocta-3,7-diynes with a catalytic amount of n-butyllithium in THF at room temperature afforded poly[(disilanylene)ethynylenes] with high molecular weights. The reaction of poly[(1,2-dimethyldiphenyldisilanylene)ethynylene] (1c), whose molecular weight was determined to be 77 900, with a catalytic amount of n-butyllithium in THF at room temperature resulted in depolymerization of the starting polymer to give oligomers with M(w) = 1500. Treatment of poly[(tetraethyldisilanylene)ethynylene] (5c) with a catalytic amount of n-butyllithium under the same conditions led to redistribution to give the polymer which showed a very broad molecular weight distribution. Similarly, poly[(1,2-di-n-hexyldimethyldisilanylene)ethynylene] underwent redistribution in the presence of a trace of n-butyllithium, but the rate of the reaction was determined to be slow. Irradiation of a benzene solution of the poly[(disilanylene)ethynylenes] with a low-pressure mercury lamp resulted in homolytic scission of silicon-silicon bonds to give photodegradation products with low molecular weights. Irradiation of the films prepared from the polymers in air also led to the scission of the silicon-silicon bonds in the polymer backbone to give the products which have silanol and siloxy groups. Treatment of the films prepared from 1c, 5c, and poly[(1,2-diethyldimethyldisilanylene)ethynylene] with antimony pentafluoride vapor afforded conducting films.