Abstract Two mixed-ligand complexes, [Ru(hfac)2(en)] and [Ru(hfac)(en)2]PF6 (en = ethylenediamine and hfac− = hexafluoroacetylacetonate ion), were synthesized. The oxidative dehydrogenation of their en ligand was studied in acetonitrile solutions. Each complex underwent a Nernstian one-electron oxidation at platinum electrodes. The resultant ruthenium(III) species was converted through a series of slow homogeneous reactions into the corresponding 1,2-diiminoethane ruthenium(II) species. Voltammograms recorded during the course of the reactions suggested the presence of 2-amino-1-iminoethane ruthenium(II) intermediates.