Dehydrocoupling polymerization of arylsilanes with chloro(aryloxy)bis(cyclopentadienyl)zirconium complex catalysts

Complexes generated by treating chloro(aryloxy)bis(cyclopentadienyl)zirconium [3; aryloxy=2,6-di-tert-butyl-4-methylphenoxy (3a), 2,6-diisopropylphenoxy (3b), phenoxy (3c), 2,3,4,5,6-pentafluorophenoxy (3d), and 2,6-dimethoxyphenoxy (3e)] with one equivalent of n-BuLi catalyze dehydrocoupling polymerization of arylsilanes 1 [aryl=phenyl (1a), p-methoxyphenyl (1b), p-dimethylaminophenyl (1c), p-methylthiophenyl (1d)] at room temperature to afford corresponding polysilanes. Their catalytic performance was compared with the conventional system generated from dichlorobis(cyclopentadienyl)zirconium (4) and two equivalents of n-BuLi. The reaction of 1a using 3a/n-BuLi, 3b/n-BuLi or 3c/n-BuLi gave high-molecular-weight polysilanes (Mw=13.3×103 and Mn=5.8×103 with 3a; Mw=10.4×103 and Mn=4.2×103 with 3b; Mw=8.8×103 and Mn=5.3×103 with 3c). Formation of the polysilane was fast in comparison with 4, in particular when the catalyst was ligated by a sterically demanding (3a) or electron-withdrawing (3d) aryloxy group. The time course of the gel permeation chromatography profiles suggested that complex 3a showed faster chain growth than 3d, 3e and 4. The extent of the formation of undesired cyclics was relatively small (<10%) in the sterically demanding 3a/n-BuLi- or 3b/n-BuLi-catalyzed reaction.