Catalytic Behavior of Cobalt Complexes Bearing Imine-Pyridine-Oxazoline Ligands in Isoprene Polymerization

A series of cobalt complexes bearing imine-pyridine-oxazoline ligands are successfully synthesized and characterized. Upon activation with diethylaluminum chloride (AlEt2Cl), these cobalt complexes exhibit high catalytic activity in isoprene polymerization and provide cis-1,4-co-3,4 polyisoprene (cis-1,4/3,4 approximate to 2:1). Among them, a complex featuring a diphenylmethyl substituent demonstrates the highest thermal stability, maintaining a catalytic activity of up to 1.06 x 105 g mol-1 h-1 at 70 degrees C. Single-crystal X-ray diffraction analysis shows that this complex adopts a trigonal bipyramidal configuration via N,N,N-tridentate coordination to the cobalt center. Both the ligand architecture and the polymerization temperature are found to play critical roles in determining the catalytic performance and the structural properties of the resulting polymers. Furthermore, the influence of various polymerization parameters on catalytic activity and selectivity are systematically investigated.