Influence of Alkyl Substituents on the Polymerization Behavior of Asymmetric Ethylene-Bridged Zirconocene Catalysts

A series of substituted indenyl−fluorenyl asymmetric ethylene-bridged ligands have been prepared from the reaction of 1-(9-fluorenyl)-2-bromoethane and the lithium salt of the desired indenyl moiety. The ligands have been converted to the corresponding substituted asymmetric ethylene-bridged metallocenes (M = Zr, Hf). These metallocenes have been evaluated as catalyst precursors for the polymerization of ethylene and propylene. The influence of substitution on the selectivity of the propylene polymerization has been studied. The metallocene [1-(9-fluorenyl)-2-(2,4,7-trimethyl-1-indenyl)ethane]zirconium dichloride was found to produce highly isotactic polypropylene with an [ mmmm ] value of 86%.