Synthesis of Anthracene-Bridged Dinuclear Phenoxyiminato Organotitanium Catalysts with Enhanced Activity, Thermal Stability, and Comonomer Incorporation Ability toward Ethylene (Co)polymerization
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.
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