Palladium-Catalyzed Insertion of 1,2- and 1,4-Quinones into Si−Si Bonds and Its Application to the Modification of Si−Si-Bond-Containing Polymers

Abstract

Me3SiSiMe3 reacted with 1,2- and 1,4-quinones (p-benzoquinone (2a), its derivatives, 1,2- and 1,4-naphthoquinone, 9,10-phenanthraquinone (2f), 9,10-anthraquinone) in the presence of palladium catalysts to give the corresponding bis(trimethylsiloxy) aromatics in excellent to moderate yields. Active palladium catalysts were PdCl2L2 (L = tertiary phosphine) and Pd(dibenzylideneacetone)2−2P(OCH2)3CEt, among which PdCl2(PEt3)2 was in general the most efficient. A 1,2-disilacyclohexane cleanly underwent the reaction with 2f to form a 10-membered cyclic adduct. The reaction of Me3SiSiMe2SiMe3 with 2a also afforded p-(Me3SiO)2C6H4, via formal extrusion of a silylene unit. Treatment of cis-(PhMe2Si)2Pt(PMe2Ph)2 with 2a gave p-(PhMe2SiO)2C6H4, indicative of the involvement of bis(silyl)palladium species in the catalysis. Quinones 2a,f smoothly underwent the palladium-catalyzed insertion into the Si−Si bonds of (SiMePhSiMePh-p-C6H4)n (9a), (SiMe2SiMe2CH2CH2)n, and (SiMe2SiMe2O)n to give partially or exhaustively modified polymers with arylenedioxy units incorporated in the backbones. A polysilane, (SiMe2)n, also reacted with 2a to provide a polymer with −SiMe2−O−p-C6H4−O− linkages. Upon UV irradiation, a partially modified polymer obtained from 9a and 2f showed a smaller extent of decrease in molecular weight than did the original polymer. Modification with 2f improved the thermal stability of 9a in thermogravimetric analysis.