Syntheses of 2,5-Dimethylcyclopentadienyl ansa-Zirconocene Complexes and Their Reactivity for Ethylene/Norbornene Copolymerization

C1-bridged and Me₂Si-bridged 2,5-dimethylcylcopentadienyl ansa-zirconocene complexes, [Me(H)C(C₅H₄)(2,5-Me₂C₅H₂)]ZrCl₂ (6), [(CH₃CH₂CH₂)(H)C(C₅H₄)(2,5-Me₂C₅H₂)]ZrCl₂ (9), [(Me)(H)C(2,5-Me₂C₅H₂)₂]ZrCl₂ (13), and [Me₂Si(2,5-Me2C₅H₂)₂]ZrCl₂ (15), are prepared by using 2-bromo-3-methoxy-2,5-dimethylcyclopentene (7) as a starting material. Solid structures of 6 and 13 were determined by X-ray crystallography. The C1-bridged zirconocene complexes 6, 9, and 13 are highly active for ethylene/norbornene copolymerization with high incorporation of norbornene, while the Me₂Si-bridged complex 15 shows relatively low activity. Complex 9 shows the highest activity and the highest incorporation of norbornene among the complexes, but the molecular weight of the obtained polymer is relatively low.