Synthesis and structural characterization of monomeric aluminum keto‐imine complexes: Catalytic activity toward CO2/styrene oxide coupling and ε‐caprolactone ring opening polymerization

Abstract

AbstractA series of benzoylacetone‐imine ligands, PhCOCHCMeNHR (L1H, R = CH2Ph; L2H, R = CH2Ph‐4‐Me; and L3H, R = CH2Ph‐4‐OMe), are first synthesized following the condensation of benzoylacetone and 4‐substituted benzylamine. Later, reacting L1H–L3H with one equivalent of AlMe3 in toluene, the monomeric Al derivatives are generated, (PhCOCHCMeNR)AlMe2 (1, R = CH2Ph; 2, R = CH2Ph‐4‐Me; 3, R = CH2Ph‐4‐OMe). All the ligands and metal derivatives are characterized by 1H and 13C NMR spectroscopy. Single crystal X‐ray diffraction analysis reveals the geometry of all ligands and complex 2. As supporting catalysts, the Al derivatives, 1–3, are effective to initiate the coupling of CO2 and styrene oxide to form cyclic carbonates. Although employing TBAI (tetra‐n‐butylammonium iodide), TBAC, tetrabutylammonium chloride, and TBAB (tetra butyl ammonium bromide) as cocatalyst, the optimized catalytic system exhibits the best conversion of epoxide in presence of TBAI under the reaction temperature and time, respectively, 90°C and 6 hr, respectively. The ring opening polymerization of ε‐caprolactone is also appraised subjecting the Al derivatives, 1–3, as catalysts in presence of benzyl alcohol and all the conversions of ε‐caprolactone reach over 95% at the reaction condition of 100°C and 1 hr.