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A series of zinc (Zn1−Zn6) and aluminum (Al6) complexes supported by phenoxyimine ligands (L1− L6) bearing nitrogen-containing second coordination spheres were synthesized and investigated for ring-opening polymerization (ROP) of rac-lactide (rac-LA). The ligands L1−L4 and L6 bearing sterically opened nitrogen donors resulted in dynamic NNO-chelates associated with facile nitrogen−metal coordination interactions. The bulky ligand L5 resulted in L 2 Zn-type complex Zn5 by disproportionation. The zinc complexes exhibited catalytic activities in ROP of cyclic monomers, including rac-LA, ε-caprolactone (CL), δ-valerolactone (VL), and trimethylene carbonate (TMC). The zinc complex Zn6 bearing a bulky triphenylsilyl substituent at the 3-position of the phenoxy moiety exhibited good stereochemical control during the ROP of rac-LA to produce highly heterotactic PLAs at ambient temperature (P r = 0.90) as well as low temperature (−30 °C, P r = 0.94) with narrow molecular weight distributions (M w /M n < 1.2). The aluminum complex Al6 catalyzed not only homopolymerization of the above cyclic monomers but also copolymerization of rac-LA with CL/VL at high temperature.

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