The 6,13-dihydro-6,13-ethanopentacene-15,16-diimine nickel(II) complex was synthesized and characterized. The nickel complex exhibited high activity toward the homopolymerization of norbornene and copolymerization of norbornene with 5-norbornene-2-carboxylic acid methyl ester in the presence of B(C₆F₅)₃. It was observed that the nickel catalyst with large steric hindrance from polycyclic aromatic systems on the backbone was found to exhibit good thermal stability and afford high incorporation of polar monomers in norbornene copolymerization.