The electrochemical reduction of 1/1 complexes resulting from coordination of M(II) (M = Fe, Co, Ni) cations with new tetraaza tetradentate ligands involving bipyridyl and pyridyl-1,2,4-triazine units has been analyzed in DMF as solvent. These complexes undergo stepwise reductions associated with chemical steps. Addition of strong protic acid (HClO4) changed dramatically the redox pattern without alteration of the M(II)-ligand coordination. The one-electron reduced complexes of Fe(II) and Co(II) allowed the catalytic reduction of molecular oxygen in protic solutions.