Homoleptic Zr and Hf Complexes of Imino/Bis(imino)phenoxide Scaffolds: Synthesis, Structural Characterization and Their Catalytic Activity in the ROP of Cyclic Esters

A series of homoleptic iminophenoxide and bis(imino)phenoxide supported Zr and Hf complexes 1–10 has been synthesized and characterized by NMR, mass spectrometry and elemental analysis. Structural analysis of the selected complexes by single crystal X-ray diffraction method revealed that the complexes are monomeric in their solid state with distorted dodecahedral geometries. These complexes are found to be potential single-site catalysts for ring-opening polymerization (ROP) of lactide (LA) and ϵ-caprolactone (ϵ-CL) and afforded controlled molecular weight (Mn) polyesters with narrow molecular weight distributions (MWDs) of 1.12-1.28. Kinetic studies revealed that the polymerization rate have shown to be first order dependency on lactide. The low molecular weight oligomer analysis imparted that the polymerization proceeds through the coordination-insertion mechanism.