Chiral manganese and iron complexes of binaphthyl Schiff bases: syntheses, crystal structures and asymmetric epoxidation of alkenes

The chiral binaphthyl Schiff-base manganese complexes [MnL(X)] [H2L = 2,2'-bis(3-R-1-5-R-2-2-hydroxybenzylideneimino)-1,1'-binaphthyl; R-1 = R-2 = Cl, X = O2CMe 1; R-1 =-Et, R-2 = NO2, X = O2CMe 2; R-1 = R-2 = Cl, X = acac (acetylacetonate) 3] and an iron analogue [FeL(acac)] 4 (R-1 = R-2 = Cl) have been prepared. The crystal structures of the racemic forms of 3 . CH2Cl2 and 4 . 2H(2)O exhibit non-planar cis-beta configurations with dihedral angles of 85.5 and 72.1 degrees respectively between the two naphthalene rings. Complexes (R)-1 to 3 are active catalysts for the asymmetric epoxidation of alkenes by PhIO. The oxidation of cis-beta-methylstyrene by (R)-2 in toluene at -20 degrees C gave an enantiomeric excess of 76%.