Efficient Synthesis of Titanium Complexes Bearing Tridentate [N–,N,O–] Anilido-Imine Ligands and Their Catalytic Properties for Ethylene Polymerization

A series of tridentate anilido-imine [N,N,O] ligands 2-(2-(R12-2,6-C6H3NH)­C6H4)­HCN­(4-tBu-6-R2-C6H2OH) [R1 = Me, R2 = tBu (LaH2); R1 = Et, R2 = tBu (LbH2); R1 = iPr, R2 = tBu (LcH2); R1 = Me, R2 = Ad (LdH2); R1 = Et, R2 = Ad (LeH2); R1 = iPr, R2 = Ad (LfH2)] were synthesized and characterized. Reaction of the free ligand LdH2 with TiCl4 in toluene at low temperature affords the zwitterionic complex Ld+H2Ti–Cl4 (1d). The zwitterionic complex can be dissolved in THF to form THF-solvated complex 1d′. Heating 1d in toluene at 40 °C affords the neutral complex LdHTiCl3 (2d) by losing a HCl. Complex 2d can be fully converted to the final complex LdTiCl2 (3d) at 140 °C under vacuum by losing another HCl. Complexes 3a–3c, 3e, and 3f were also synthesized in high yields in the same one-pot procedure. All complexes were characterized by 1H and 13C NMR spectroscopy, and the molecular structures of 1d′, 3b, 3d, and 3e were determined by single-crystal X-ray diffraction analysis. The titanium centers in complexes 3b, 3d, and 3e are five-coordinated with a geometry situated between trigonal bipyramid and square pyramid. Upon activation with alkylaluminum and Ph3C+B­(C6F5)4–, complexes 3a–3f exhibit moderate catalytic activity for ethylene polymerization.