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-Ti-2 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 angstrom between the two Ti centers. The mononuclear complex [(2,6-Pr-i(2)-C6H3N = CH-C6H2-3,5-Bu-i-2-O)TiCl3(THF)] (Ti-1) was also prepared for control experiments. In the presence of MAO as a cocatalyst, syn-Ti-2 and anti-Ti-2 were active toward ethylene homopolymerization but had distinct catalytic properties. The complex syn-Ti-2 with a shorter metalmetal separation exhibited higher activity and produced polymers with higher molecular weights, in comparison to anti-Ti-2, having a longer metalmetal separation, and the mononuclear catalyst control Ti1 under identical conditions. More importantly, the complex syn-Ti-2 exhibited excellent thermal stability and thus the a greater activity can be obtained at 100 degrees C, which is a preferred temperature for industrial operations. For ethylene/1-hexene copolymerization, the activity, Mw, and incorporation of 1-hexene by syn-Ti-2 were 2.3x, 3.2x, and 6.0x those of anti-Ti-2 under identical conditions.