Ring-Opening Polymerization of ε-Caprolactone and Styrene Oxide-CO2 Coupling Reactions Catalyzed by Chelated Dehydroacetic Acid-Imine Aluminum Complexes

A series of chelated dehydroacetic acid-imine-based ligands (LH)-H-1~(LH)-H-4 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 (LH)-H-1~(LH)-H-4 reacted with AlMe3 in toluene to afford corresponding compounds AlMe2L1 (1), AlMe2L2 (2), AlMe2L3 (3), and AlMe2L4 (4). All the ligands and aluminum compounds were characterized by IR spectra, H-1 and C-13 NMR spectroscopy. Additionally, the ligands (LH)-H-1~(LH)-H-4 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 epsilon-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 epsilon-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 & DEG;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.

Automated summary

A series of chelated dehydroacetic acid-imine-based ligands were synthesized and reacted with AlMe3 to obtain corresponding compounds. The ligands and compounds were characterized by various spectroscopic techniques. The catalytic activities of these compounds in ε-caprolactone ring-opening polymerization and styrene oxide-CO2 coupling reactions were investigated.