ansa-metallocene derivatives .32. Zirconocene complexes with a spirosilane bridge: Syntheses, crystal structures and properties as olefin polymerization catalysts

Chiral ansa-zirconocene complexes with a trimethylene link between the Si bridge atom and an alpha-position of each C-5 ring ligand were prepared; two representatives, with i-propyl and t-butyl groups as beta-substituents, were structurally characterized, The properties of these complexes with respect to MAO-activated propene polymerization were studied in comparison with those of their Me(2)Si-bridged analogs. The t-butyl-substituted spirosilane complex gives a polymer with relatively high content of 3,1-insertions. These increased regioirregularities appear to be associated with decreased coordination gap aperture and increased lateral extension angles of the spirosilane-bridged zirconocene complexes; this notion is supported by a molecular-mechanics analysis of alternative olefin-insertion transition states.