Study on the separation of rac and meso isomers and the reactivity of group 4 bridged metallocene complexes

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A C_2-symmetric group 4 bridged metallocene is known to be the excellent catalyst for isospeciic polymerization of propylene. However, the synthesis of the metallocene usually accompanies the formation of an achiral meso isomer which must be excluded before use because it catalyzes atactic polymerization. We found the convenient method to separate the meso isomer of silylenebis (trimethylcyclopentadienyl) zirconium dichloride (1) by selectively deriving it to the readily crystallizable μ-oxo complex. The method was also found to be applicable to the isomer separation of the related metallocenes. The μ-oxo complexes were readily converted to the original meso isomers and to an η^2-acetate complex by treating with hydrogen chloride and acetic acid, respectively. The reactions of meso isomer of 1 with methyllithium and phenylethynyllithium gave methyl and phenylethynyl derivatives and the corresponding μ-oxo complexes. The structures of μ-oxo complexes and η^2-acetate complexes were determined by X-ray crystallographic analysis. Attempts to convert meso isomer of 1 to the rac isomer were not successful.