Ring-Opening Polymerization of ε-Caprolactone and Styrene Oxide-CO₂ Coupling Reactions Catalyzed by Chelated...

A series of chelated dehydroacetic acid-imine-based ligands L~L 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~L reacted with AlMe₃ in toluene to afford corresponding compounds AlMe (1), AlMe (2), AlMe (3), and AlMe (4). All the ligands and aluminum compounds were characterized by IR spectra, ¹H and ¹³C NMR spectroscopy. Additionally, the ligands L~L 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-CO₂ 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 CO₂, 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 CO₂ into an inexpensive, renewable and easy excess carbon feedstock.