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 viaβ-hydrogen elimination of the polymer after insertion of ethylene.