Electron-transfer Reactions of Multidentate Ligand Cobalt(III) Complexes. IV. The Reductions of Cobalt(III) Complexes of Amino Acids by Iron(II) in Aqueous and Water-methanol Solutions

Abstract
The kinetics of the Fe(II) reductions of trans(O,Cl)-Co(dien)(am)Cl+ (am=glycine, α-alanine, β-alanine, leucine, and proline) and trans(N)-Co(am)2(ox) (am=glycine, α-alanine, β-alanine, ox=oxalate, and dien= diethylenetriamine) have been made spectrophotometrically in an aqueous solution. Except for the β-alanine complex, the reactivities of the Co(III) complexes are not very different when the amino acid is replaced by the other one. The greater reactivities of the β-alanine complexes may be due to the steric strain on the six-membered β-alanine chelate ring. The rates of the reductions of cis(N)-Co(α-ala)2(ox) and cis(N)-Co(β-ala)2(ox) by Fe(II) are greatly affected by the addition of methanol to the aqueous solutions; the rate increases with an increase in the mol fraction of methanol. The replacement of water molecules in the solvation sphere of the reductant by the methanol molecules is considered to be one of the reasons for the greater rate in water-methanol solutions.

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