Synthesis, structure and ethylene polymerisation activity of {η5:η1(N)-1-[(tert-butylamido)diphenylsilyl)]-2,3,4,5-tetramethylcyclopentadienyl}dichlorotitanium(IV)

Abstract

The permethylcyclopentadienyl diphenylsilylene-bridged titanium constrained geometry complex [TiCl2{η5-C5Me4(SiPh2NCMe3-κN)}] (2) was synthesised following the common synthetic route and subsequently characterised by spectral analyses and by single-crystal X-ray diffraction. The comparison of its solid-state structure with that of the parent dimethylsilylene CGC complex [TiCl2{η5-C5Me4(SiMe2NCMe3-κN)}] (1) revealed only negligible geometry differences between their cyclopentadienyl centroid-Ti-N-Si skeletons. A significantly different positioning was however observed for the amine tBu substituent of the DFT-optimised methyl-substituted cationic catalytical species (1a, 2a), which are supposed to be generated from 1 and 2 in the presence of methylaluminoxane (MMAO). A lower ethylene polymerisation activity of 2-MMAO system compared to that of 1-MMAO is compatible with the higher steric congestion at the metallic centre due to the tBu ligand becoming rotated more into the open space in 2b. This arrangement aggravates monomer access throughout the catalytical process and decreases the coordination unsaturation of the central atom through the formation of auxiliary agostic interaction.