Synthesis of poly(hydrosilane)s, image and their reactivity studies towards allyl/vinylsilanes

New poly(hydrosilane)s, View the MathML source–[RR2′Si(CH2)3SiH]n–(R=R′=Et(1a);R=Ph,R′=Me(2a);R=Me,R′=Ph(3a)) have been synthesized by catalytic dehydrocoupling of the corresponding carbosilane monomers 1–3 using Cp2TiCl2/2.2BuLi as the catalyst. Hydrosilylation reaction of 1a or 2a with allyltrimethyl/triethoxyvinyl/trichlorovinylsilane in the presence of AIBN as free radical catalyst affords the polysilanes 1b–d and 2b–d, respectively, bearing Si–Me/Si–OEt/Si–H functional groups appended on the carbosilyl side chain. UV absorption spectra of 1a–3a reveal a shoulder like absorption without any peak at 250–260 nm while the polysilanes 1b–d and 2b–d exhibit a distinct absorption with λmax 274–299 nm and ε: 671–887 (Si repeat unit)−1 dm3 cm−1. A discernable bathochromic shift in the λmax value is invariably observed in the polysilanes bearing appended SiMe3 or Si(OEt)3 group in comparison to that observed for the polysilanes bearing sterically less bulky SiH3 group incorporated on carbosilyl side chain. The polysilanes, 4b–d derived from chemical modification of poly(phenylsilane) also exhibit similar spectral behavior (λmax 314–328 nm; ε = 1500–2700 (Si repeat unit)−1 dm3 cm−1). These changes indicate that electronic properties of these polysilanes are sensitive to nature of pendant substituents on silicon backbone.