Advancing Zinc Complexes for Ring-Opening Polymerization: Intramolecular Activation of the Chain End via H-Bonding Interaction

The organometallic-catalyzed ring-opening (ROP) of cyclic esters is a powerful approach to synthesizing aliphatic polyesters. However, most organometallic compounds deactivate at high monomer-to-catalyst feed ratios. Thus, development of organometallics with high activity, stability, and controllability remains challenging. Herein, we report the rational design and synthesis of ethyl zinc pre-catalysts supported by (amidoalkyl)pyridine−phenolate ligands. Reaction of the pre-catalyst with an alcohol initiator forms a zinc alkoxide active species, enabling rapid yet controlled ROP via an intramolecular activation mechanism mediated by H-bonding. This strategy ensures high catalytic efficiency at low catalyst concentrations, thereby reducing the catalyst loading. Notably, the optimal zinc catalyst outperforms Sn(Oct)2 in catalytic activity and polymerization control and could efficiently catalyze the ROP of l-lactide (L-LA) under melt conditions, affording PLLA with high molecular weight, isotacticity, and crystallinity. Additionally, the optimal zinc catalyst facilitates the synthesis of random and block copolymers with tailored chain compositions and properties via copolymerization of l-LA with other common cyclic esters. This study provides valuable insights for the design of highly active, stable, and controllable catalysts for polyester synthesis.