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

Seven asymmetric zinc benzamidinate complexes featuring or lacking side-arm functionalities were synthesized. Using equimolar zinc reagent produced distinct dinuclear motifs [(CH-C = NCH)ZnEt] (R = Bu, 1; (CH)OMe, 2; (CH)NMe, 3). Half the zinc reagent yielded dinuclear [(CH-C = NCH)Zn] (R = Bu, 4) or mononuclear zinc bis(chelate) complexes (R = (CH)OMe, 5; (CH)NMe, 6; CHPy, 7). Molecular structures of 1-4 and 7 were determined 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.