A half-metallocene of hetero fused cyclopentadienyl lanthanide complexes under the activation of organoborate and aluminum alkyls generate the corresponding cationic active species, which can catalyze copolymerizations of ethylene and α-olefins such as norbornene (NB), dicyclopentadiene (DCPD), and conjugated dienes, with high activities to give a series of ethylene-based copolymers ranging from crystalline high strength plastics to elastomers with widely variable glass transition temperatures and melting temperatures, some of which cannot be achieved by the present catalysts.