Tunable zinc benzamidinate complexes: coordination modes and catalytic activity in the ring-opening polymerization of l-lactide

Abstract

Seven asymmetric zinc benzamidinate complexes featuring or lacking side-arm functionalities were synthesized. Using equimolar zinc reagent produced distinct dinuclear motifs [(C₆H₅-C = NC₆H₅)ZnEt]₂ (R = tBu, 1; (CH₂)₂OMe, 2; (CH₂)₂NMe₂, 3). Half the zinc reagent yielded dinuclear [(C₆H₅-C = NC₆H₅)₂Zn]₂ (R = tBu, 4) or mononuclear zinc bis(chelate) complexes (R = (CH₂)₂OMe, 5; (CH₂)₂NMe₂, 6; CH₂Py, 7). Molecular structures of 1–4 and 7 were determined via single-crystal X-ray diffraction. Altering benzamidinate substituents modifies both coordination modes and catalytic activities in ring-opening polymerization of L-lactide. Specifically, complex 7 exhibits enhanced catalytic activity at 25 °C using 100 equivalents of L-lactide with a turnover frequency of 1820 h⁻¹.