Reactions of silanes with bis(cyclopentadienyl)dialkylzirconium complexes

A systematic comparison between the dimethylzirconocene (DMZ) and dimethyltitanocene (DMT) catalyzed dehydrocoupling of organosilanes is reported. The polymerization rates of primary silanes are about ten times faster for DMZ than for DMT, but the characteristics of the polymers produced are essentially identical. Variations of molecular weight and molecular weight distribution with varying monomer and reaction time, and the relative amounts of linear and cyclic polymer are also essentially the same for the two catalysts.Oligomerizations of phenylmethylsilane, diphenylsilane, and 1,2-diphenyldisilane are described. The compound Cp₂Zr(SiPhMeH)(μ-H)₂(SiPhMe₂)ZrCp₂ (1b) is isolated from the reaction of phenylmethylsilane with DMZ and its structure confirmed by crystallography and ¹H-NMR spectroscopy. The compound Cp₂Zr(Me)(μ-H)₂(SiPh₂H)ZrCp₂ (1d) is isolated from the reaction of diphenylsilane with DMZ and its structure assigned by NMR spectroscopy. A number of other hydride bridged species are observed by ¹H-NMR in the reactions of DMZ with phenylmethyl-, diphenyl-, and n-butylmethylsilanes and their structures are tentatively assigned. The implications of these observations on the mechanism of transformation of DMZ into active catalyst and our current views of the polymerisation mechanism are also discussed. Key words: silanes, dehydrocoupling, titanocene, zirconocene, polysilanes.