Tuning the Thiolen: Al(III) and Fe(III) Thiolen Complexes for the Isoselective ROP of <i>rac</i>-Lactide

A series of five iron and aluminum complexes bearing {ONSO} imine thiobis­(phenolate) ligands have been prepared and applied to the ring-opening polymerization (ROP) of rac-lactide. Fe­(1)Cl produced polylactide with a very strong isotactic bias (Pm = 0.79–0.89) and well-defined melting temperatures (Tm = 154–181 °C). The polymers have been characterized by a combination of 1H­{1H} NMR, 13C­{1H} NMR, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, and powder X-ray diffraction. Fe­(1)Cl has also been shown to activate CO2, at atmospheric pressure and concentrations, to form a carbonato-bridged dimer. Fe­(2–5)Cl and Al­(1–5)­Me were also active for lactide ROP demonstrating good-molecular-weight control (Đ = 1.04–1.12) and moderate isotactic preference (Pm = 0.56–0.72), with polymerization outcome correlating with ligand substituents.