Polymeric Organosilicon Systems. 22. Synthesis and Photochemical Properties of Poly[(disilanylene)oligophenylylenes] and Poly[(silylene)biphenylylenes]

Poly[4,4′-(tetramethyldisilanylene)biphenylylene] (1a), poly[4,4′-(tetraethyldisilanylene)-biphenylylene] (1b), and poly[4,4′-(1,2-dimethyl-1,2-diphenyldisilanylene)biphenylylene] (1c) were prepared by the condensation reaction of the respective 4,4′-bis(chlorosilyl)biphenyls with sodium. Poly[4,4′-(dimethylsilylene)biphenylylene] (1d), poly[4,4′-(methylphenylsilylene)biphenylylene] (1e), and poly[3,3′-(dimethylsilylene)biphenylylene] (1f) were obtained from the nickel-catalyzed dehalogenative coupling of the products formed from the reaction of the respective bis(bromophenyl)-substituted silanes with magnesium. Poly[(disilanylene)-terphenylylenes] 2a-c and poly[(disilanylene)quaterphenylylenes] 3a-c were also synthesized by the similar nickel-catalyzed dehalogenative coupling reactions of di-Grignard reagents prepared from the respective bis(4-bromophenyl)-substituted disilanes, with p-dibromobenzene and 4,4′-dibromobiphenyl, respectively. The disilanylene-substituted polymers 1a‒c, 2a‒c, and 3a‒c were found to be photoactive. Irradiation of the thin solid films prepared from these polymers in air resulted in scission of the Si‒Si bonds, leading to the formation of degradation products including silanol and siloxy units. Poly[(silylene)biphenylylenes] 1d‒f were found to be inert toward UV irradiation. Photochemical behavior of the disilanylene-substituted polymers was also investigated in solution, and photoactivities of these polymers were found to decrease with increasing the degree of an extension of the π-electron system. The results of crystal orbital calculations for poly[(disilanylene)oligophenylylenes] have also been reported.