COMPARISON OF THE CATALYTIC REDUCTION OF DIOXYGEN BY NERUTHENINO(II))-4-PYRIDYL)PORPHYRINATO]COBALT(II) IN SOLUTION AND ON GRAPHITE ELECTRODE SURFACES

The ammineruthenio(II))-4-pyridylporphinato]cobalt(II) complex that ca talyzes the four-electron reduction of O-2 at graphite electrode surfa ces on which it has been assembled has now been prepared in homogeneou s solution. The preparative procedure for the catalyst is described, a nd the kinetics of its catalysis of the reduction of O-2 by chemical r eductants in homogeneous solution are reported. In solution, only two- electron reductions of O-2 are obtained and the rate of intramolecular electron-transfer from the four Ru(NH3)(5)-py(2+) centers on the peri phery of the catalyst molecule to an O-2 molecule coordinated to the C o(II) center in the porphyrin ring is shown to be quite slow. Possible reasons for the contrasting mechanistic behavior of the catalyst in s olution and on graphite electrodes are suggested.