Homo- and Heteroligated Salicylaldiminato Titanium Complexes with Different Substituents Ortho to the Phenoxy Oxygens for Ethylene and Ethylene/1-Hexene (Co)polymerization

A series of homoligated (1c–1e) and heteroligated (2a–2e) salicylaldiminato titanium dichloride complexes with different substituents ortho to the phenoxy oxygens were efficiently prepared. X-ray diffraction studies on these new dichloride complexes 2b, 2d, and 2e reveal a distorted octahedral coordination of the central metal. In the presence of dried methylaluminoxane, all the complexes exhibit high ethylene polymerization productivities. Surprisingly, complex 1d incorporating an o-(trimethylsilyl)ethynyl group displays the highest activity [5.26 × 103 kg of polyethylenes (mol Ti)−1 h–1]. In ethylene/1-hexene copolymerization, the heteroligated complexes 2a–2e display improved activities and intermediate incorporation ability compared with their homoligated counterparts 1a–1f. The activity and incorporation ability for 1-hexene are highly dependent on the nature of the ortho-substituents. Among them, (trimethylsilyl)ethynyl-substituted precatalyst (1d) achieves the highest incorporation ratio (27.3 mol %), while ethynyl-substituted precatalyst (2c) achieves the highest copolymerization activity [2.89 × 103 kg of copolymers (mol Ti)−1 h–1].