Synthesis and X-ray crystal structure of [Me₂Si(C ₅Me₂H₂)(^tBuN)]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

Dimethylsilylene bridged 3,4-dimethylcyclopentadienyl/amido titanium and zirconium complexes, namely [Me₂Si(C₅Me₂H ₂)(^tBuN)]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 ZrCl ₄, 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), [Me ₂Si(C₅Me₂H₂)(^tBuN)] TiCl₂ exhibited a higher incorporation ratio of 1-octene at 80 C compared to the tetramethyl-Cp substituted CGC, [Me₂Si(C ₅Me₄)(^tBuN)]TiCl₂, which was judged by the density and ¹³C 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)( ^tBuN)]MCl₂ during the (co)polymerization and specifically, no agostic interactions available in the propagation and termination steps of the (co)polymerization.