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

Eight Cs‐symmetric complexes, R₁R₂C(Cp)(Flu)MCl₂ [R₁ = R₂ = CH₃CH₂CH₂, M = Zr (1), Hf (2); R₁ = R₂ = p? CH₃OC₆H₄, M = Zr (3), Hf (4); R₁ = p? ^tBuC₆H₄, R₂ = Ph, M = Zr (5), Hf (6); R₁ = R₂ = p? ^tBuC₆H₄, M = Zr (7); R₁ = R₂ = PhCH₂, M = Zr (8)] have been synthesized and characterized. Zirconocenes all showed the same high catalytic activities in ethylene polymerization as complex Ph₂C(Cp)(Flu)ZrCl₂ (9). However, in the propylene polymerization, the catalytic activities decreased in the order 5 ≈ 9 > 7 > 8. Introduction of ^tBu decreased the activities, probably due to the bulk steric hindrance. The polypropylene produced by 5 and 7 with ^tBu substituent showed a higher molecular weight (Mη) than that produced by 9. The ¹³C 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 ¹³C NMR, which showed that the benzyl on bridge carbon 8 prevented chain epimerization and enatiofacial misinsertion in polymerization. Copyright © 2005 John Wiley & Sons, Ltd.