Binuclear Titanium Catalysts Based on Methylene-Bridged Tridentate Salicylaldiminato Ligands for Ethylene Homo- and Copolymerization

Abstract

A series of methylene-bridged salicylaldiminato tridentate [ONS] ligands bearing different alkylthio sidearms and the corresponding binuclear titanium complexes (Ti 2 a , Ti 2 b , Ti 2 c ) were synthesized and characterized by elemental analysis, ESI-MS, FT IR, 1H and 13C NMR. To the best of our knowledge, these were the first non-metallocene tridentate binuclear Ti complexes reported. When activated by modified methylaluminoxane (MMAO), these binuclear Ti complexes displayed extremely high activities in the range of 106 g mol−1 h−1 atm−1 for ethylene polymerization and ethylene/α-olefins copolymerization at atmospheric pressure, producing high molecular weight polymers with narrow polydispersity. Both the catalytic behavior and the spectroscopic characterization indicated that the catalysts assumed symmetric structure and contained single-site active species. Most importantly, the catalytic activities towards ethylene (co)polymerization as well as comonomer incorporation ratios were much higher than that of the corresponding mononuclear complexes. Meanwhile, the properties of polymers and the comonomer incorporation ratios can be effectively tuned by the reaction conditions and the alkylthio side group on ligands. Complex Ti 2 c bearing the long octylthio sidearm showed significantly higher activity for ethylene polymerization than the methylthio functionalized Ti 2 a , presumably due to the increased solubility of the catalyst in the reaction medium. While for copolymerization, complex Ti 2 a demonstrated the highest catalytic activity and comonomer incorporation ratio, due the small steric hindrance of the methylthio side group.