Two series of aluminum complexes containing salicylbenzoxazole ligands were successfully synthesized and characterized by 1H and 13C NMR spectroscopy and elemental analysis. Alkane elimination reactions of salicylbenzoxazole ligands (HLn) with trimethylaluminum (AlMe3) in the molar ratio of 1:1 and 2:1 afforded four-coordinate aluminum complexes (LAlMe2) and five-coordinate aluminum complexes (L2AlMe), respectively. All complexes were obtained in moderate to high yields. In the presence of 1 equivalent of benzyl alcohol, all aluminum complexes were effective initiators for rac-lactide polymerization. All polymerizations showed living characteristic as evidenced by a linear relationship between the percentage conversion and the number average molecular weight and the narrow molecular weight distributions that remain relatively constant during the course of polymerizations. The kinetic studies revealed that the polymerization was a first-order dependence on the concentration of monomer. The electronic and steric effects of the ligand substituents and the number of chelating ligands around metal center were found to have a significant impact on the stereoselectivity and catalytic activities of rac-lactide polymerization.

Synthesis of aluminum complexes containing salicylbenzoxazole ligands and their application in the ring-opening polymerization of <i>rac</i>-lactide

248th National Meeting (2014)

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Synthesis of aluminum complexes containing salicylbenzoxazole ligands and their application in the ring-opening polymerization of rac-lactide