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Recently, the research activity in the field of the stereospecific polymerization of conjugated dienes has focused on the use of catalysts based on organometallic complexes having a well-defined structure and containing ligands of various types (e.g., phosphines, bis-imines, and pyridylimines), since it has been observed that the nature of the ligand, as expected on the basis of the diene polymerization mechanism proposed several years ago by Porri, is able to exert a strong influence on the polymerization regioand stereoselectivity, on the polymer molecular weights and their distribution, and in some cases to impart a living feature to the catalysts themselves. In this Perspective we highlight the most recent results obtained in this field and discuss possible future developments in this area.

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The thermodynamics of the reaction of an ethylene molecule with the Cp2TiCH3Cl/Al(CH3)2Cl system (Cp = η5‐C5H5), as a model for olefin polymerization with homogeneous Ziegler‐Natta catalysts, was investigated via quantum mechanical DFT calculations. The comparison of the calculated energies for three possible titanium‐olefin coordinated intermediates, the ionic complex Cp2TiCH3(C2H4)+/Al(CH3)2Cl 2−, the bimetallic complex Cp2TiCH3(C2H4)δ+ · Al(CH3)2Cl 2δ− and the olefin‐separated ion pair Cp2TiCH 3+/C2H4/Al(CH3)2Cl 2−, shows that the most feasible polymerization mechanism occurs via olefin‐separated ion pair.