Synthesis and X-ray crystal structure of [Me2Si(C5Me2H2)((BuN)-Bu-t)]MCl2 (M = Ti, Zr) bearing a 3,4-dimethylcyclopentadienyl ring: Investigation of the substitution effect on the cyclopentadienyl (Cp) ring for catalytic performance in ethylene/1-octene (co)polymerization

Abstract

Dimethylsilylene bridged 3,4-dimethylcyclopentadienyl/amido titanium and zirconium complexes, namely [Me2Si(C5Me2H2)((BuN)-Bu-t)]MCl2 (M = Ti, Zr), were synthesized by the reactions of the dilithium salt of the ligand with the corresponding inexpensive metal precursors TiCl4(THF)(2) and ZrCl4, respectively. These complexes were characterized by spectroscopic techniques and single crystal X-ray diffraction analysis. In addition, the obtained complexes exhibited high catalytic activities in the polymerization of ethylene and copolymerization of ethylene/1-octene, and afforded PE and poly(ethylene-co-1-octene)s with high molecular weights. Especially, the dimethyl-Cp substituted constrained geometry complex (CGC), [Me2Si(C5Me2H2)((BuN)-Bu-t)]TiCl2 exhibited a higher incorporation ratio of 1-octene at 80 degrees C compared to the tetramethyl-Cp substituted CGC, [Me2Si(C5Me4)((BuN)-Bu-t)]TiCl2 , which was judged by the density and C-13 NMR analysis of the obtained copolymer. This is presumably due to the steric and electronic effects of the two vicinal methyl groups in [Me2Si(C5Me2H2)((BuN)-Bu-t)]MCl2 during the (co)polymerization and specifically, no agostic interactions available in the propagation and termination steps of the (co)polymerization. (C) 2013 Elsevier Ltd. All rights reserved.