Chiral induction in anion–anion electron transfer in aqueous solution catalyzed by a chiral cation

The oxidation of cobalt(II) chelate complexes [CoY]2−, where Y=edta (ethylenediaminetetraacetate), pdta (1,2-propanediaminetetraacetate) and cydta (trans-1,2-cyclohexanediaminetetraacetate), by [Co(mal)3]3− (mal=malonate) was catalyzed by chiral [Co(en)3]3+ to yield optically active products with the enantiomeric excesses which increase with increasing concentration of chiral [Co(en)3]3+. Substituents on the ethylenediamine backbone of [CoY]2− had significant effects on the sign and the magnitude in the stereoselectivity. The results are interpreted in terms of a chiral induction mechanism in which the ion pair between [CoY]2− and chiral [Co(en)3]3+ is stereoselectively oxidized by [Co(mal)3]3−. A model is proposed for the relative orientation of oxidant, reductant, and catalysis complexes.