Zwitterionic Complexes of Group 4 Metal Chlorides Containing a Bis(imino)phenoxide Scaffold: Synthesis, Characterization and Polymerization Studies

Chlorides of group 4 metals containing the bis(imino)phenoxide ligand scaffold were synthesized from a direct reaction between the respective ligand and metal chlorides MCl4 (M=Ti, Zr and Hf). These complexes were thoroughly characterized using various spectroscopic methods and single crystal X-ray diffraction studies. They are potent catalysts for the polymerization of rac-lactide (rac-LA), L-lactide (L–LA), ϵ-caprolactone (ϵ-CL), epoxides such as, rac-cyclohexene oxide (rac-CHO), rac-propylene oxide (rac-PO), rac-styrene oxide (rac-SO) and ethylene, resulting in polymers with high number average molecular weights (Mn) and narrow molecular weight distributions (MWDs). The kinetic and mechanistic studies associated with the polymerization of lactide, ϵ-CL and CHO has been investigated in details.