The electrochemical oxidation of fac-Mn(CO)(3)(eta(2)-dpm)Cl (dpm = Ph2PCH2PPh2) is extensively photocatalyzed when a microcrystal - electrode - aqueous (electrolyte) interface is irradiated with light having a wavelength corresponding to that of the 385 nm charge-transfer band. Investigations of the voltammetry of the solid in the presence and absence of light and monitoring the course of the reaction by EPR, electron probe, and electrochemical quartz crystal microbalance techniques indicate that the catalysis is associated with enhanced charge transport caused by doping of fac-Mn(CO)(3)(eta(2)-dpm)Cl with photooxidized mer-[Mn(CO)(3)(eta(2)-dpm)Cl]X, where the anion, X-, is incorporated into the solid after mass transport from the aqueous electrolyte. Photocatalysis also is found for the electrochemical oxidation of cis,mer-Mn(CO)(2)(eta(1)-dpm)(eta(2)-dpm)Br.