Selective cyclopolymerization of α,ω-dienes and copolymerization with ethylene catalyzed by Fe and Co complexes

Abstract

Fe complexes with bis(imino)pyridine ligands catalyze cyclopolymerization of 1,6-heptadiene in the presence of MMAO (modified methylalumoxiane) co-catalyst to produce the polymer containing five-membered rings in every repeating unit. The complexes with Me, Et, and Cl substituents at the N-aryl groups of the ligand produce the polymer in high yields and in high trans-cis ratio of the five-membered rings. The molecular weights of the polymers, M(n) by GPC, are higher than 6000. The polymerization promoted by the Fe complexes with bulky N-aryl groups of the ligand gives the product in lower yields, and the obtained polymer shows low trans-cis selectivity. Co complex with the ligand having 2,6-diisopropylphenyl groups at the coordinating nitrogen also promotes the cyclopolymerization to afford the polymer with cis-five-membered rings selectively. The polymerization is slower than the Fe-complex-catalyzed reaction, and the rate appears to be independent from the monomer concentration. Cyclopolymerization of the 1,6-heptadienes with phenyl or siloxy substituent at the 4-position is also catalyzed by the Fe and Co complexes in the presence of MMAO. The cyclization during the polymer growth occurs in similar trans-cis selectivity to that of unsubstituted 1,6-heptadiene. The Co complex, with addition of MMAO, catalyzes copolymerization of 1,6-heptadiene and ethylene to yield the copolymer having the trans-five-membered rings in the polyethylene chain, whereas the attempted copolymerization using the Fe catalyst gives a mixture of the homopolymers of the two monomers. The copolymerization by the Co catalyst involves chain transfer via beta-hydrogen elimination of the polymer after insertion of ethylene.