New polymerization of dienes and related monomers catalyzed by late transition metal complexes

This article reviews recent studies on the polymerization of 1,6-heptadienes and 2-aryl- and 2-alkoxy-1-methylenecyclopropanes catalyzed by Co, Fe, and Pd complexes. Co and Fe complexes with bis(imino)pyridine ligands catalyze the cyclopolymerization of 1,6-heptadiene in the presence of MMAO to produce the polymer, which contains five-membered rings in the monomer units. The polymers with cis- or trans-five-membered rings are obtained selectively, depending on the complex used in the polymerization. The catalyst, prepared from the Co complex having a bis(imino)pyridine ligand and MMAO, promotes the polymerization of 2-aryl-1-methylenecyclopropanes without ring-opening. The reaction under ethylene atmosphere produces alternating copolymer of the two monomers to yield the polymers composed of the C4 repeating unit with a 1,1-cyclopropanediyl group. The alternating copolymer of ethylene and 7-methylenebicyclo[4.1.0]heptane undergoes thermal rearrangement to afford the polymer with CC double bond in main chain. A radical pathway is proposed. Dinuclear π-allylpalladium complexes with bridging Cl ligands initiate living polymerization of 2-alkoxy-1-methylenecyclopropanes, which accompanies ring-opening of the monomer, to afford the polymers composed of the C₃ repeating units having alkoxy and vinylidene groups. A cyclic dinuclear π-allylpalladium complex reacts with 2-alkoxy-1-methylenecyclopropane in the presence of pyridine to produce the living polymer with macrocyclic structures. Block copolymerization of the two monomers that contain OR or O(CH₂CH₂O)R as the substituents on the three-membered ring, results in the polymers with hydrophobic and hydrophilic segments.