Chiral catalysts for the asymmetric cycloaddition of carbon dioxide with epoxides

Several chiral BINADCo(III)X (BINAD = Bis(1,1 '-2-hydroxy-2 '-alkoxy-3-naphthylidene)-1,2-cyclohexanediamine, X = OAC, CF(3)CO(2), CCl(3)CO(2), OTs, p-NO(2)PKO(2)) complexes were synthesized and used to catalyze the asymmetric cycloaddition of carbon dioxide with epoxideS under mild condition to afford chiral cyclic carbonates. The best catalyst of (S,S,S,S)-BINADCo(III)(OAc) 9b and phenyltrimethylammonium tribromide (PTAT) can provide propylene carbonate with the highest ee being 95% at -20 degrees C. (C) 2008 Elsevier Ltd. All rights reserved.