Synthesis of Anthracene-Bridged Dinuclear Phenoxyiminato Organotitanium Catalysts with Enhanced Activity, Thermal Stability, and Comonomer Incorporation Ability toward Ethylene (Co)polymerization
Shaofeng Liu, Yanhong Xing, Quande Zheng, Yutong Jia, Zhibo Li
Abstract
Dinuclear titanium complexes syn-Ti2 and anti-Ti2 bearing anthracene-bridged bisphenoxyimine ligands (syn-L and anti-L) have been prepared and characterized by NMR and elemental analyses. The molecular structure of syn-Ti2 was defined by X-ray diffraction, revealing a separation of 7.183 Å between the two Ti centers. The mononuclear complex [(2,6-iPr2-C6H3N═CH-C6H2-3,5-tBu-2-O)TiCl3(THF)] (Ti1) was also prepared for control experiments. In the presence of MAO as a cocatalyst, syn-Ti2 and anti-Ti2 were active toward ethylene homopolymerization but had distinct catalytic properties. The complex syn-Ti2 with a shorter metal–metal separation exhibited higher activity and produced polymers with higher molecular weights, in comparison to anti-Ti2, having a longer metal–metal separation, and the mononuclear catalyst control Ti1 under identical conditions. More importantly, the complex syn-Ti2 exhibited excellent thermal stability and thus the a greater activity can be obtained at 100 °C, which is a preferred temperature for industrial operations. For ethylene/1-hexene copolymerization, the activity, Mw, and incorporation of 1-hexene by syn-Ti2 were 2.3×, 3.2×, and 6.0× those of anti-Ti2 under identical conditions.