A meso-tetra(4-pyridyl)cobaltporphyrin modified with four [mu (3)-O-Ru-3(Ac)(6)(py)(2)](+) clusters (CoTCP = cobalt tetraclusterporphyrin) has been synthesized and characterized by H-1-NMR and UV-Vis spectroscopy, electrochemistry and spectroelectrochemistry. The facility of CoTCP to form adherent and durable films on a glassy carbon surface has been exploited in the preparation of modified electrodes exhibiting outstanding catalytic activity in the tetraelectronic reduction of dioxygen to water. This finding has been confirmed from the linear behavior and the slope of the Levich plots up to 4000 rpm, as well as from the high current densities, e.g. up to 2.8 mA cm(-2) obtained for the modified electrodes. The enhanced activity has been interpreted in terms of the electronic activation of the cobalt porphyrin by the peripheral triangular ruthenium cluster complexes, as supported by detailed spectroelectrochemical data confirming a significant electronic coupling between the cobalt porphyrin and [mu (3)-O-Ru-3(Ac)(6)](+) groups.