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.