Single-site achiral and chiral C3-symmetric complexes LMOR, where M = Mg and Zn, L = an η3-trispyrazolyl- or η3-trisindazolyl-borate ligand and R = Et, tBu, Ph, or SiMe3, have been synthesized and employed in the ring-opening polymerization of l-, rac-, and meso-lactide in CH2Cl2 at 25 °C and below. The polymerization occurs by acyl cleavage and gives rise to polylactide, PLA, with PDI of 1.1−1.25 up to 90% conversion. Studies of the kinetics of polymerization reveal first order behavior in both lactide and metal catalyst. For L = tris(3-tert-butylpyrazolyl)borate, (tBupz)3BH, polymerization of ∼500 equiv of l-lactide proceeds to 90% conversion within 1 h and 6 d for the magnesium and zinc catalysts, respectively. The zinc complexes are, however, more tolerant to air and moisture and solid samples where R = SiMe3 are persistent in air for several days. The rate of polymerization is also significantly influenced by the nature of the η3-L spectator ligand. Chiral C3-symmetric catalysts, where L = tris(indaz...