Synthesis, Characterization, and Catalytic Behaviors in Isoprene Polymerization of Pyridine-Oxazoline-Ligated Cobalt Complexes.

A family of pyridine-oxazoline-ligated cobalt complexes LCoCl- were synthesized and characterized. Determined via single-crystal X-ray diffraction, complexes and ligated by two ligands, displayed a distorted tetrahedral coordination of a cobalt center. The X-ray structure indicated the pyridine-oxazoline ligands acted as unusual mono-dentate ligands by coordinating only to N. Upon activation with AlEtCl (diethylaluminum chloride), these cobalt complexes all exhibited high catalytic activity (up to 2.5 × 10 g·mol·h), affording -1,4--3,4-polyisoprene with molecular weights of 4.4-176 kg mol and a narrow Ð of 1.79-3.42, suggesting a single-site nature of the active sites. The structure of cobalt catalysts and reaction parameters, especially co-catalysts and the reaction temperature, all have significant influence on the polymerization activity but not on the microstructure of polyisoprene.