Stereoselectivity in reactions of metal complexes Part XVIII. Kinetics and stereoselectivity in electron-transfer reactions between [Co(L)H2O]+ (L=N,N′-[(pyridine-2,6-diyl)bis(methylene)]bis[proline] (promp) and N, N′-[(4-methoxypyridine-2,6-diyl)bis(methylene)]bis[proline] (MeO-promp) and optically active iron(II) complexes