Syntheses, structures and catalysis of tetranuclear zinc N-alkoxide ketoiminate complexes for ring-opening polymerization of rac-lactide

Abstract Two tetranuclear zinc complexes 2a and 2b bearing tridentate N-alkoxide ketoiminate ligands have been synthesized and fully characterized by single-crystal X-ray structure analysis, NMR spectroscopy together with elemental analyses. Both of 2a and 2b can act as active catalysts in the ring-opening polymerization (ROP) of racemic-lactide (rac-LA) without additional co-initiators, either in solution or under industrially preferred melt conditions (130 °C no solvent). To be noted, 2a and 2b show remarkable activities for bulk rac-LA polymerization even with low catalyst loading of 0.1 mol%, yielding polymers with high molecular weights (Mn) of up to 91200 g/mol (2b), and very high turnover frequencies (TOF) of 19000 h−1 (2b) and 19800 h−1 (2a).