Bis(2-(6-methylpyridin-2-yl)-benzimidazolyl)titanium dichloride and titanium bis(6-benzimidazolylpyridine-2-carboxylimidate): Synthesis, characterization, and their catalytic behaviors for ethylene polymerization

A series of 6-(benzimidazol-2-yl)-N-organylpyridine-2-carboxamide were synthesized and transformed into 6-benzimidazolylpyridine-2-carboxylimidate as dianionic tridentate ligands. Bis(2-(6-methylpyridin-2-yl)-benzimidazolyl)titanium dichloride (C1) and titanium bis(6-benzimidazolylpyridine-2-carboxylimidate) (C2-C8) were synthesized in acceptable yields. These complexes were systematically characterized by elemental and NMR analyses. Crystallographic analysis revealed the distorted octahedral geometry around titanium in both complexes C1 and C4. Using MAO as cocatalyst, all complexes exhibited from good to high catalytic activities for ethylene polymerization. The neutral bis(6-benzimidazolylpyridine-2-carboxylimidate)titanium (C2-C8) showed high catalytic activities and good stability for prolonged reaction time and elevated reaction temperature; however, C1 showed a short lifetime in catalysis as being observed at very low activity after 5 min. The elevated reaction temperature enhanced the productivity of polyethylenes with low molecular weights, whereas the reaction with higher ethylene pressure resulted in better catalytic activity and resultant polyethylenes with higher molecular weights. At higher ratio of MAO to titanium precursor, the catalytic system generated better activity with producing polyethylenes with lower molecular weights.