Flash-photolysis studies of the electron-transfer reactions of dioxygen complexes of cobalt(III) with tris(2,2′-bipyridyl)ruthenium(III)

Abstract

Electron-transfer reactions between the µ-peroxo-cobalt(III) complexes [(H₃N)₅Co(µ-O₂)Co(NH₃)₅]⁴⁺(1), [(H₃N)₄Co(µ-O₂)(µ-NH₂)Co(NH₃)₄]³⁺(2), and [(L–L)₂Co(µ-O₂)(µ-NH₂)Co(L–L)₂]³⁺[L–L = ethylenediamine (3), 2,2′-bipyridyl (4), or 1,10-phenanthroline (5)] and [Ru(bipy)₃]³⁺(bipy = 2,2′-bipyridyl) have been investigated. The reactants have been generated by the electron-transfer quenching of the excited state of [Ru(bipy)₃]²⁺ by the corresponding µ-superoxo-complexes using flash photolysis. The half-wave potentials measured by polarography for complexes (3), (4), and (5) are 1.00 ± 0.05, 1.04 ± 0.05, and 1.04 ± 0.05 V respectively. The observed rate constants are used to calculate the self-exchange electron-transfer rate constants for the bridged cobalt(III) complexes. The Marcus cross relationship has been used to predict the rate constants determined earlier for the electron-transfer reaction between (3) and the superoxo-forms of complexes (1), (4), and (5).