Aluminum derivatives incorporating 4,4′-methylenebis(cyclohexyl) linked dehydroacetic acid-imine ligands: structural aspects, CO2/styrene oxide coupling reaction

Abstract

A series of methylene-bis-cyclohexyl amine ligands, LMeH2, LPhH2 and LDAH2 are generated from the reaction of 4,4′-methylenebis(cyclohexylamine) with 2,4-pentanedione, benzoylacetone, and dehydroacetic acid, respectively in methanol. Later, the combination of LMeH2, LPhH2, and LDAH2 with two equivalents of AlMe3 in methylene chloride initiate the di-aluminum compounds, LMe[AlMe2]2, LPh[AlMe2]2 and LDA[AlMe2]2. As supporting catalysts, the Al-derivatives are effective in the coupling of CO2 with epoxide to form cyclic carbonates. Interestingly, the optimized catalyst system displays > 90% conversion of the epoxides in solvent free condition while employing TBAI (tetra-n-butylammonium iodide) and TBAB (tetra butyl ammonium bromide) as co-catalyst.