Ring-Opening Polymerization of ε-Caprolactone and Styrene Oxide-CO 2 Coupling Reactions Catalyzed by Chelated Dehydroacetic Acid-Imine Aluminum Complexes.

A series of chelated dehydroacetic acid-imine-based ligands L 1 H ~ L 4 H was synthesized by reacting dehydroacetic acid with 2-t-butylaniline, ( S )-1-phenyl-ethylamine, 4-methoxylbenzylamine, and 2-(aminoethyl)pyridine, respectively, in moderate yields. Ligands L 1 H ~ L 4 H reacted with AlMe 3 in toluene to afford corresponding compounds AlMe 2 L 1 ( 1 ), AlMe 2 L 2 ( 2 ), AlMe 2 L 3 ( 3 ), and AlMe 2 L 4 ( 4 ). All the ligands and aluminum compounds were characterized by IR spectra, 1 H and 13 C NMR spectroscopy. Additionally, the ligands L 1 H ~ L 4 H and corresponding aluminum derivatives 1 , 3 , and 4 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 2 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 2 , 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 2 into an inexpensive, renewable and easy excess carbon feedstock.