Within large-volume polyolefin materials, the value-adding polyolefins have been commonly produced through the copolymerization of ethylene with α-olefin. The Ⅳ B metal complexes have provided various models of precatalysts toward α-olefin polymerization and copolymerization. Meanwhile those metal complexes have also been used as the intermediates or active species in order to understand the mechanism of olefin copolymerization. Targeting a practicing catalytic system for polyolefin industry, the Ⅳ B metal complexes would meet the demands of highly active catalysis, moreover, the catalytic systems should be remained enough stable at the elevated temperature. To have value-adding materials for higher profits, the catalytic system could be adaptable for polyolefins with various properties through being operated under different parameters; such features have been fitted well to Ⅳ B metal precatalysts, which achieve to produce polyolefins with the molecular weights in the useful range from medium to ultrahigh due to different polymerization conditions as well as functionalized polyolefins through the copolymerization of ethylene with α-olefin containing functional groups. Recent progress of Ⅳ B metal complexes for olefin polymerization and copolymerization has been reviewed herein, focusing on different metal complexes being classified due to groups of their ligands used. Moreover, the correlation between structures of metal complexes and their catalytic activity have been considered along with reaction temperatures.

Contents
1 Introduction
2 Constrained geometry catalysts
3 Imino-amido type catalysts
3.1 Pyridyl-amide catalysts
3.2 Imino-amido catalysts
3.3 Imino-enamido catalysts
3.4 Amidoquinoline catalysts
4 Bridging nitrogenous heterocyclic catalysts
5 Conclusion