Lithium Half‐Salen Complexes: Synthesis, Structural Characterization and Studies as Catalysts for <i>rac</i> ‐Lactide Ring‐Opening Polymerization

Seven lithium complexes supported by sterically and electronically diverse phenoxyimine ligands were synthesized characterized X-ray diffraction, NMR spectroscopy elemental microanalysis. These show high activity (kobs ≤7.43×10−2 s−1) for rac-lactide ring-opening polymerization (ROP) in the presence of co-initiator benzyl alcohol (BnOH), with exception Li4 which features an unusual polymeric ladder structure. Overall, catalyst correlates to aggregation state; catalysts low states display increased propagation rates attributed improved metal accessibility kinetic mobility. The nature ligand substituents solvent influence both solid- solution-state. While can initiate ROP without BnOH, addition this significantly increases rate switching mechanism from a coordination-insertion activated monomer pathway, changing resultant poly(lactic acid) architecture cyclic linear.