Novel hyperbranched ferrocene-containing poly(boro)carbosilanes synthesized via a convenient "a₂ + B₃" approach

We report the synthesis of versatile hyperbranched ferrocene-containing poly(boro)carbosilanes (hb-PBCS) via a convenient "A₂ + B ₃" approach. Two types of hb-PBCS are obtained by the hydrosilylation of 1,1′-bis(dimethylsilyl)ferrocene (A₂) with trivinylmethylsilane (B₃) followed by modification with 9-borabicyclo[3.3.1]nonane (9-BBN) and by the hydroboration of 1,1′-bis(dimethylvinylsilyl)ferrocene (A₂) with the borane-dimethyl sulfide complex (B₃), respectively. Size exclusion chromatography (SEC) results demonstrate that the well-soluble hb-PBCS possess appreciable weight-average molecular weight (M_w,SEC) up to 62-300 g/mol with the polydispersity index (PDI) of 1.95-4.51. The combined characterization by ¹H-²⁹Si heteronuclear multiple-bond correlation (HMBC), ¹¹B nuclear magnetic resonance (NMR), and triple-detection SEC (triple-SEC) confirms the remarkable hyperbranched architecture of hb-PBCS with degrees of branching (DB) between 0.47 and 0.79. The Mark-Houwink-Sakurada exponents of hb-PBCS obtained from triple-SEC are significantly lower (α = 0.36-0.47) than that of their linear analogue (α = 0.69).