The electrochemical reduction of the monocation of bis-(cyclo-octadiene)Rh[(COD) 2 Rh + ] has been studied in chlorinated hydrocarbons and d 6 -acetone by cyclic voltammetry, chronoamperometry and exhaustive coulometry. Successive one-electron reductions are observed for the couples (COD) 2 Rh + /(COD) 2 Rh and (COD) 2 Rh/(COD) 2 Rh − at -1.34 V vs. Fc and -1.93 V vs. Fc respectively. The 17-electron Rh(0) radical (COD) 2 Rh abstracts a Cl atom from CH 2 Cl 2 to give the dinuclear complex [(COD)Rh(μ-Cl)] 2 in high yield at 298 K. At subambient temperatures this reaction is suppressed and the dominant decomposition product is apparently (COD)Rh(C 8 H 13 ), formed by H atom abstraction by (COD) 2 Rh from solvent and/or adventitious water. Electrolysis products were characterized by electron spin resonance (ESR), nuclear magnetic resonance (NMR) and mass spectrometry. The reactivity of the radical is rationalized by a bonding model in which the lowest unoccupied molecular orbital (LUMO) is dx 2 −y 2 with some diolefin mixing. ESR measurements are consistent with this model and suggest that the COD ligands form a ligand field around Rh which is closer to square planar than to tetrahedral.