Ethene Polymerization Behavior of MAO-Activated Dichloridotitanium Complexes Bearing Bi- and Tetradentate Salicylaldimine Derivatives

摘要

New chiral bridged tetradentate (N2O2)TiIVCl2-type complexes bearing dimethylbiphenyl (1-Ti–3-Ti) and previously published binaphthyl-bridged (4-Ti) complex were synthesized with high yields. This was achieved by treating the corresponding Schiff-base ligand (H2L) precursors with Ti(NMe2)4, followed by conversion of these diamido complexes to LTiCl2 derivatives by the addition of excess of Me3- SiCl. A series of unbridged titanium complexes 5-Ti–8-Ti with similar substituents at the phenoxy group were studied and their polymerization properties, after methylalumin- oxane (MAO) activation, compared with the above bridged complexes. It was found that the catalysts bearing chiral tetradentate biaryl-bridged salicylaldimine ligands produce multimodal polyethylene (PE) with low activity [below 10 kgPE/(molTihbar)] while their unbridged analogues provide activities that are 10–1000 times greater under similar reaction conditions. The reasons for this dramatic difference in polymerization activities are discussed based on the stabilities of the different cationic species configurations. Scheme