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

Electron-transfer reactions between the µ-peroxo-cobalt(III) complexes [(H<SUB>3</SUB>N)<SUB>5</SUB>Co(μ-O<SUB>2</SUB>)Co(NH<SUB>3</SUB>)<SUB>5</SUB>]<SUP>4+</SUP>(1), [(H<SUB>3</SUB>N)<SUB>4</SUB>Co(μ-O<SUB>2</SUB>)(μ-NH<SUB>2</SUB>)Co(NH<SUB>3</SUB>)<SUB>4</SUB>]<SUP>3+</SUP>(2), and [(L-L)<SUB>2</SUB>Co(μ-O<SUB>2</SUB>)(μ-NH<SUB>2</SUB>)Co(L-L)<SUB>2</SUB>]<SUP>3+</SUP>[L-L = ethylenediamine (3), 2,2'-bipyridyl (4), or 1,10-phenanthroline (5)] and [Ru(bipy)<SUB>3</SUB>]<SUP>3+</SUP>(bipy = 2,2'-bipyridyl) have been investigated. The reactants have been generated by the electron-transfer quenching of the excited state of [Ru(bipy)<SUB>3</SUB>]<SUP>2+</SUP> 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)