Tuning the thiolen: Al(III) and Fe(III) thiolen complexes for the isoselective ROP of rac-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 (P _m = 0.79-0.89) and well-defined melting temperatures (T _m = 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 CO ₂, 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 (A = 1.04-1.12) and moderate isotactic preference (P _m = 0.56-0.72), with polymerization outcome correlating with ligand substituents.