Synthesis of [2,2′-methylenebis(1,3-dimethylcyclopentadienyl)]zirconium dichloride and its reactivity in ethylene-norbornene copolymerization

An ansa-zirconocene compound, [2,2′-meth-ylenebis(1,3-dimethylcyclopentadienyl)]zirconium dichloride (5), bearing methyl substituents on the carbons adjacent to a bridgehead carbon, was synthesized by key steps of the catalytic Pauson-Khand reaction and the retro-Diels-Aider reaction. The crystal structure of 5 was determined. The small angle (117.15°) between the two centroids of the cyclopentadienyls and a zirconium atom and the absence of any substituents on the positions β with respect to the bridgehead carbon indicate that the coordination site for catalysis is widely opened. Compound 5, when activated with MAO, showed good performance for copolymerization of ethylene with a bulky monomer such as norbornene. The activity and norbornene incorporation ability are much better than those of [Ph₂C(Fluo)(Cp)]ZrCl₂.