Polymerization of butadiene, isoprene and 1-substituted dienes using cobalt catalysts

Cobalt complexes carrying 6-(N-di-tert-butylphosphinoxide)-2-(2′-R-2H’-benzoimidazole)- aminepyridine (R = H, Co1; ethyl, Co2 and benzyl, Co3) ligand were prepared and characterized by FT-IR, UV–vis and elemental analysis. Single crystal X-ray diffraction analysis revealed that Co2 displayed a distorted trigonal bipyramid configuration via N, N, O-tridentate coordination to cobalt center. Activated with AlEt2Cl or MAO, all cobalt complexes are notably active in butadiene and isoprene polymerization, affording cis-1,4 polybutadiene and cis-1,4/3,4 polyisoprene, respectively. The formed catalysts are also efficient for 1-phenyl-1,3-butadiene and 1-(4′-methoxylphenyl)-1,3-butadiene polymerizations, but surprisingly result in partially cyclic product probably arising from Friedel-Craft reaction of formed internal olefin with pending aryl group. Copolymerization of isoprene with 1-substituted-1,3-butadiene is able to afford a series of high molecular weight copolymers with 1.4–8.7 mol-% incorporation rate that free of cyclization. The effects of the substitution pattern of monomer on the polymerization reactivity are also evaluated.