Highly efficient metal() porphyrin and salen complexes for the polymerization of -lactide under ambient conditions

Ligated metal( iii ) complexes, Al( iii ), In( iii ), Cr( iii ), and Co( iii ), containing tetraphenylporphyrin (TPP) and cyclohexylsalen (Cy-salen) ligands were investigated for the polymerization of rac -lactide ( rac -LA). A combination of metal complexes, co-catalyst, and co-initiator was shown to be highly efficient for the ring-opening polymerization of rac -LA at room temperature. Influences of metal centers, ligands, and co-catalysts were investigated. Higher Lewis acidity of metal centers and ligands enhanced catalytic activity. Ionic co-catalysts showed increased polymerization rates. Polymerization of rac -LA catalyzed by tetraphenylporphyrin aluminum chloride ((TPP)AlCl) and bis(triphenylphosphine)iminium chloride (PPN + Cl − ) in cyclohexene oxide (CHO) as a solvent produced isotactic-enriched polylactide. The order of reactivities based on the metals supported by the TPP ligand is Cr( iii ) > Al( iii ) > In( iii ) > Co( iii ) while the reactivities of the catalysts supported by Cy-salen ligands are in the order In( iii ) > Cr( iii ) > Al( iii ) > Co( iii ). Metal( iii ) complexes supported by porphyrin and salen ligands were highly efficient for rac -lactide polymerization at room temperature giving isotactic-enriched PLA.