Catalytic Asymmetric Sulfoxidation by Chiral Manganese Complexes:  Acetylacetonate Anions as Chirality Switches

Three manganese(II) complexes, namely [Mn(1)(ClO4)2] (3), [Mn(1)(acac)2] (4), and [Mn2(1)(acac)4] (5), were isolated from solutions of Mn(ClO4)2 or Mn(acac)2, and an easily accessible diimine ligand (1S,2S)-N,N‘-bis-pyridin-2-ylmethylene-cyclohexane-1,2-diamine (1). Their structure was determined by X-ray crystallography, and these complexes proved to be catalysts for asymmetric sulfide oxidation by H2O2. Enantiomeric excesses ranging from 5% to 62% were obtained with a variety of aryl alkyl sulfides. We also observed an interesting “chirality switch” effect by the achiral acac anion reversing the enantioselectivity of the complex [Mn(1)(ClO4)2] from the S to the R sulfoxide enantiomer.