MULTIPLE INTRAMOLECULAR ELECTRON-TRANSFER IN THE CATALYSIS OF THE REDUCTION OF DIOXYGEN BY COBALT MESO-TETRAKIS(4-PYRIDYL)PORPHYRIN TO WHICH 4 RU(NH3)5 GROUPS ARE COORDINATED

The reaction of Ru(NH3)5OH2(2+) with COP(py)4 (cobalt meso-tetrakis(4-pyridyl)porphyrin) within Nafion coatings on graphite electrodes produces [CoP(pyRu(NH3)5)4]8+. This complex, immobilized within the polyelectrolyte coating, achieves electronic contact with the electrode underlying the coating by means of electron hopping between adjacent pairs of Ru(NH3)5(3+/2+) groups coordinated to the pyridine sites. The four Ru(NH3)5py3+/2+ groups in each molecule do not interact strongly and have essentially the same formal potential. The CoP(pyRu(NH3)5)4(8+) complex acts as a catalyst for the four-electron reduction Of O2 under conditions where mixtures of the same porphyrin with uncoordinated Ru(NH3)6(2+) or Ru(NH3)5py2+ do not. The results provide evidence for the intramolecular delivery of four electrons from the four-coordinated Ru(NH3)5(2+) groups to O2 molecules associated with the Co(II) center of the porphyrin.