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2,5-Hexanedione was converted into the bisfulvene 2, then treated with two molar equivalents of methyllithium to yield the [4-cyclopentadienylidene-4,7,7-trimethyl-4,5,6,7-tetrahydroindenyl] dilithio compound 4. Hydrolysis, followed by treatment with acetone/pyrrolidine, gave the corresponding fulvene system 5. Reaction of 5 with methyllithium followed by treatment with ZrCl 4  furnished the ring-annulated C 1- bridged ansa-metallocene 8, bearing a tert-butyl substituent at the Cp ring, as a 1:1 mixture of two diastereoisomers. Treatment of the fulvene 5 with LiAlH 4  followed by ZrCl 4  yielded the respective isopropyl-substituted ansa-metallocene diastereomers 9a and 9b. Complex 9b was separated by fractional crystallization and characterized by X-ray diffraction. Complexes 8 and 9 provide active homogeneous Ziegler-type catalyst systems upon activation with excess methylalumoxane producing low molecular weight isotactic polypropylene with high catalyst activities.

A Rigid C 1 -Bridged Ansa-Zirconocene-Derived Catalyst System Suited for Stereoselective Low Molecular Weight Polypropylene Formation