Synergistic Steric and Electronic Ligand Engineering Unlocks High‐Performance Schiff Base for Lactide Ring‐Opening Polymerization

ABSTRACT Advancing the catalytic precision for the ring‐opening polymerization (ROP) of lactide is essential for the scalable and sustainable production of polylactic acid (PLA). Here, we report a ligand engineering strategy for Schiff base salen catalysts, where the synergistic combination of a π‐extended naphthalene spacer and an electron‐deficient benzoic acid moiety is harnessed to tailor the metal center's activity and selectivity. A library of ligands and their Cu (II), Mn (II), and Ni (II) complexes was synthesized and structurally authenticated. Screening identified the Cu (II) complex bearing the naphthalene‐benzoic acid hybrid ligand (HNA‐DABA@Cu) as a standout performer, delivering PLA in 49.4% isolated yield with > 94% monomer conversion under optimized conditions (150°C, 12 h, catalyst/monomer = 1:2000) and affording polymer with molecular weight (Mw) of ~180 kDa. Comprehensive characterization (XRD, FT‐IR, SEM, EA and HR‐ESI‐MS) reveals that the synergistic ligand framework promotes the formation of a well‐defined Cu (II) active site embedded in a highly crystalline molecular assembly, as evidenced by the sharp XRD reflections and the needle‐like single‐domain morphology. This work establishes that the concerted steric and electronic modulation offered by judiciously paired functional groups is a potent design principle for developing high‐performance catalysts in controlled polymerization.