ELECTROCATALYSIS OF THE REDUCTION OF DIOXYGEN BY ADSORBED COBALT 5,10,15,20-TETRAARYLPORPHYRINS TO WHICH ONE-RU, 2-RU, OR 3-RU(NH3)52+ CENTERS ARE COORDINATED

The reactions of Ru(NH3)5OH22+ with the pyridine sites in (5-(4-pyridy l)-10, 15,20-triphenylporphyrinato)cobalt-(II), (4-pyridyl)-15,20-diph enylporphyrinato)cobalt(II), -(trifluoromethyl)-phenyl)porphyrinato(co balt(II), (4-pyridyl)-10,20-diphenylporphyrinato)cobalt(II), and 5-tri s(4-pyridyl)-20-phenylporphyrinato)cobalt(II) adsorbed on pyrolytic gr aphite electrodes produce the mono-, di-, and triruthenated complexes. The adsorbed complexes act as catalysts for the reduction of dioxygen . The mono- and diruthenated complexes catalyze the two-electron reduc tion of dioxygen to hydrogen peroxide, whereas the triruthenated compl ex catalyzes the four-electron reduction to water. The preparation and electrocatalytic behavior of the catalysts are described. A compariso n of the catalysts has provided additional insight into the mechanisms by which they operate in catalyzing the electroreduction of dioxygen.