The 48-electron cluster Cp*IrCp(2)Co(2)(CO)(3) has two known isomers, one with a terminal carbonyl ligand and two edge-bridging carbonyls (1) and the other with three edge-bridging carbonyls (2). The rate of their interconversion is dramatically dependent on the number of electrons in the cluster. NMR studies establish that 2 is the thermodynamically favored isomer and that the isomerization is slow at ambient temperatures in the 48 e(-) complex (k(isom) approximate to 10(-6) s(-1) at 298 K). In contrast, isomerization proceeds very rapidly (k(isom)=400 s(-1)) through the 47-electron monocation as part of an efficient electron-transfer-catalyzed process. Cyclic voltammetry and square-wave voltammetry were used to measure the isomerization rate of the monocation. The catalytic nature of the anodically-induced isomerization was diagnosed by theoretical modeling of the electrode responses and by infrared spectroelectrochemistry using a fiber-optic probe of an electrolysis solution. Reductions of the cluster isomers give 49-electron monoanions. The anion 1(-) isomerizes over the period of a bulk electrolysis to 2(-), setting the limits of k(isom) between 10(-1) and 10(-3) s(-1) for 1(-). The relative rate of the cluster isomerization increases, therefore, in the order 48 e(-) much less than 49 e(-) much less than 47 e(-), with relative rates of 1:approximate to 10(4):10(8). Rate enhancements are rationalized in terms of changes in occupancies involving redox orbitals either bonding or antibonding with respect to the trimetallic framework. The results constitute a rare example of the determination of a reaction rate through three oxidation states of a complex.