Ethylene and propylene polymerization by the new substituted bridged (cyclopentadienyl)(fluorenyl) zirconocenes

Eight Cs ‐symmetric complexes, R 1 R 2 C(Cp)(Flu)MCl 2 [R 1 = R 2 = CH 3 CH 2 CH 2 , M = Zr (1), Hf (2); R 1 = R 2 = p CH 3 OC 6 H 4 , M = Zr (3), Hf (4); R 1 = p t BuC 6 H 4 , R 2 = Ph, M = Zr (5), Hf (6); R 1 = R 2 = p t BuC 6 H 4 , M = Zr (7); R 1 = R 2 = PhCH 2 , M = Zr (8)] have been synthesized and characterized. Zirconocenes all showed the same high catalytic activities in ethylene polymerization as complex Ph 2 C(Cp)(Flu)ZrCl 2 (9). However, in the propylene polymerization, the catalytic activities decreased in the order 5 ≈ 9 > 7 > 8. Introduction of t Bu decreased the activities, probably due to the bulk steric hindrance. The polypropylene produced by 5 and 7 with t Bu substituent showed a higher molecular weight ( M η) than that produced by 9. The 13 C NMR spectrum revealed the polymers from 7 and 8 to have shorter average syndiotactic block length than polymer produced by 9. It was noted that [ mm ] stereodefect of polypropylene by 8 could not be observed from 13 C NMR, which showed that the benzyl on bridge carbon 8 prevented chain epimerization and enatiofacial misinsertion in polymerization. Copyright © 2005 John Wiley & Sons, Ltd.