Polymerization of butadiene and isoprene using α-diimine cobalt catalysts bearing electron donor at the N-aryl of imine

Abstract

Cobalt dibromide supported by α-diimine ligand ortho-positioned with sulfur and oxygen donor are synthesized and characterized. Single X-ray diffraction result shown the oxygen donor is connected with the metal center in complex Co4, resulting in a triangle bipyramidal configuration. With AlEt2Cl as an activator, the formed catalysts are able to efficiently catalyze butadiene polymerization following in an essential cis-1,4 chemoselectivity at 1/2000–1/6000 catalyst feeding. These catalysts are more active and robust for isoprene polymerization under identical conditions, affording polyisoprene rich in cis-1,4 fraction randomly incorporated with 3,4 units. The number average molecular weights (Mns) of the formed polymers are determined to be 1.1–7.8 × 105, higher than those found for polybutadiene (0.4–9.3 × 104). The O-Me donor in the N-Aryl impacts positively on the activity and the molecular weight of the resultant polymer. The catalysts show a stable chemoselectivity despite the activator and catalyst feeding, applied temperature, even the catalyst structure are varied.