Nickel-Catalyzed Cyclopolymerization of Hexyl- and Phenylsilanes

[Ni­(dmpe)₂] (dmpe = 1,2-bis­(dimethylphosphino)­ethane) catalyzed the dehydrogenative polymerization of hexylsilane in toluene at room temperature to produce a mixture of acyclic and cyclic poly­(hexylsilanes). A simlar reaction at 70 °C resulted in selective cyclopolymerization of hexylsilane to yield a cyclic polymer with an average molecular weight of M_n = 1450 (M_w/M_n = 1.01, GPC polystyrene standard). The ¹H NMR, ²⁹Si­{¹H} DEPT NMR, and IR spectroscopic data indicated the presence or absence of the −SiH₂R end groups of the polymer and its acyclic or cyclic structure. Addition of hexylsilane to the solution of the poly­(hexylsilanes) containing the acyclic polymer (M_n = 1330) and heating the mixture in the presence of 5 mol % of [Ni­(dmpe)₂] catalyst formed a polymer composed of the cyclic molecules without a change in the average molecular weight. The polymerization of phenylsilane catalyzed by [Ni­(dmpe)₂] also yielded the cyclic poly­(phenylsilane). The reaction using a mixture of [Ni­(cod)₂] (cod = 1,5-cyclooctadiene) and PMe₃ as the catalyst produced acyclic and/or cyclic poly­(phenylsilanes) depending on the conditions. 9,9-Dihydrosilafluorene reacted with [PdMe₂(dmpe)] to afford a persilylated palladacyclopentane, [Pd­(SiC₁₂H₈)₄(dmpe)], with four 1,1-silafluorene units.