Titanium, zirconium and vanadium complexes of 2-(benzimidazolyl, benzothiazolyl, and benzoxazolyl) pyridine as catalyst precursors for ethylene polymerization

• Ti, Zr and V complexes with heterocyclic ligands.
• Activation with MAO gives ethylene polymerization catalysts.
• Structure–property-relationship studies.
• A 1,2-bis(benzothiazole) vanadium complex showed the highest activity.
• Broad molecular weight distributions indicate more than one active site in the catalyst.

Dissymmetric chelating complexes of Ti, Zr and V with 2-(benzimidazolyl, benzothiazolyl, and benzoxazolyl) pyridine ligands were synthesized and characterized. After activation with methylalumoxane (MAO) in solution, these complexes could be applied as ethylene polymerization catalysts. Their activities depend on the metal and the substituents at the pyridine ring and the heterocycle. Structure–property-relationship studies revealed that the titanium and vanadium catalyst systems showed higher polymerization activities than the zirconium analogues. The benzoxazolyl moiety containing vanadium complex 29, with a methyl substituent in the 6-membered ring in meta position to the nitrogen atom in the 5-membered ring, and an unsubstituted pyridine ring showed the highest activity (1154.8 kg PE/mol cat h). The produced polyethylenes exhibited high molecular weights and broad molecular weight distributions. Obviously different active sites are generated in the course of these polymerization reactions.

The complexes with the heterocyclic ligands can be activated with methylalumoxane (MAO) and then be applied for catalytic ethylene polymerization. Structure–property-relationship studies showed that the vanadium benzoxazolyl pyridine complex 29/MAO had the best performance.Figure optionsDownload as PowerPoint slide