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 Mn = 1450 (Mw/Mn = 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 (Mn = 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.