ELECTRON-TRANSFER REACTIONS OF COPPER(III)-PEPTIDE COMPLEXES WITH HEXACHLOROIRIDATE(III)

Oxidation-reduction reactions involving the peptide complexes of copper(III) and copper(II) provide the first opportunity to determine the speed of electron-transfer reactions between these oxidation states as well as providing an example of electron transfer between two predominantly square-planar complexes. Although the reactions between IrCl63- and copper(III)-peptides are uphill electron transfers, the reactions can be forced in this direction by taking advantage of the relatively rapid reaction of acids with the copper(II)-peptides compared to the analogous reactions of the copper(III)-peptides. Application of Marcus' theory for outer-sphere electron transfer to the neutral copper(III)-peptides permits calculation of an apparent self-exchange rate constant for the copper(III)-copper(II) species as 7X107 M-1 s-1 (25.0°C, 0.1 M ionic strength). An alternative mechanism with electron transfer via a chloride bridge between iridium and copper also is possible. © 1979, American Chemical Society. All rights reserved.