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

Abstract

A series of cobalt complexes bearing imine‐pyridine‐oxazoline ligands were successfully synthesized and characterized. Upon activation with diethylaluminum chloride (AlEt2Cl), these cobalt complexes exhibited high catalytic activity in isoprene polymerization and provided cis‐1,4‐co‐3,4 polyisoprene (cis‐1,4/3,4 ≈ 2:1). Among them, a complex featuring a diphenylmethyl substituent, demonstrated the highest thermal stability, maintaining a catalytic activity of up to 1.06×105 g·mol‐1·h‐1 at 70 °C. Single‐crystal X‐ray diffraction analysis showed that this complex adopted a trigonal bipyramidal configuration via N,N,N‐tridentate coordination to cobalt center. Both the ligand architecture and the polymerization temperature were 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 was systematically investigated.