Preparation and crystal structures of the complexes (eta(5)-C5H3TMS-CMe2-eta(C13H8)-C-5)MCl2 and [3,6-di(t)ButC(13)H(6)-SiMe2-(NBu)-Bu-t]MCl2 (M = Hf, Zr or Ti): mechanistic aspects of the catalytic formation of a isotactic-syndiotactic stereoblock-type polypropylene

The reaction of MCl4, (M = Zr or Hf) with the dilithium salt of 2-(3-trimet hylsilyl-cydopentadienyl)-2-florenylpropane in pentane leads to the formati on of the complexes (eta (5)-C5H3TMS-CMe2-eta (5)-C13H8)MCl2 (M = Zr or Hf; TMS = trimethylsilyl). The X-ray diffraction data show that both the fluor enyl and cyclopentadienyl groups are 175 bonded to the transition metal in these complexes in the solid phase. The polymerization data and the polymer microstructure, however, clearly indicate that at least after the activati on with MAO the active species formed with these molecules show very dynami c bonding behavior and their substituted cyclopentadienyl group changes its hapticity rapidly and frequently during the course of the polymerization. (C) 2001 Published by Elsevier Science B.V. All rights reserved.