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 degrees C). The polymers have been characterized by a combination of H-1{H-1} NMR, C-13{H-1} 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 (D = 1.04-1.12) and moderate isotactic preference (P-m = 0.56-0.72), with polymerization outcome correlating with ligand substituents.