Ring-Opening Polymerization of ε-Caprolactone and Styrene Oxide-CO Coupling Reactions Catalyzed by Chelated Dehydroacetic Acid-Imine Aluminum Complexes.

A series of chelated dehydroacetic acid-imine-based ligands ~ was synthesized by reacting dehydroacetic acid with 2-t-butylaniline, ()-1-phenyl-ethylamine, 4-methoxylbenzylamine, and 2-(aminoethyl)pyridine, respectively, in moderate yields. Ligands ~ reacted with AlMe in toluene to afford corresponding compounds (), (), (), and (). All the ligands and aluminum compounds were characterized by IR spectra, H and C NMR spectroscopy. Additionally, the ligands ~ and corresponding aluminum derivatives , , and were characterized by single-crystal X-ray diffractometry. The catalytic activities using these aluminum compounds as catalysts for the ε-caprolactone ring-opening polymerization (ROP) and styrene oxide-CO coupling reactions were studied. The results show that increases in the reaction temperature and selective solvent intensify the conversions of ε-caprolactone to polycaprolactone. Regarding the coupling reactions of styrene oxide and CO, the conversion rate is over 90% for a period of 12 h at 90 °C. This strategy dispenses the origination of cyclic styrene carbonates, which is an appealing concern because of the transformation of CO into an inexpensive, renewable and easy excess carbon feedstock.