Stereoselectivity in electron-transfer reactions in chiral media

The oxidation of [Co(edta)](2-) by [IrCl6](2-) proceeds by both inner-sphere and outer-sphere electron-transfer pathways. In the presence of added [Co(en)(3)](3+), the outer-sphere pathway is enhanced. When optically active [Co(en)(3)](3+) is used, the [Co(edta)](-) formed is optically active, reflecting a 1.5% DK selectivity. It is proposed that the selectivity arises from preferential formation and reactivity of the DK ion pair, {[Co(edta)](2-), [Co(en)(3)](3+)}. Direct reaction of [Co(edta)](-) with [Co(en)(3)](2+) has also been investigated in the optically active solvent, (S)-(-)- 1,2- propylene carbonate. The induction is small, forming 0.75% Delta-[Co(en)(3)](3+), consistent with the important role for hydrogen bonding in determining the precursor stereoselectivity to the exclusion of solvent.