Anodic oxidation of the important half-sandwich compound CoCp(CO)(2), 1, has been studied under gentle electrolyte conditions, e.g., chlorinated hydrocarbons with weakly coordinating anion (WCA) supporting electrolyte anions. The 17-electron cation 1(+) produced at E-1/2(1) = 0.37 V vs FeCp20/+ undergoes a surprising reaction with neutral 1 to form the dimer radical cation [Co2Cp2(CO)(4)](+), 2(+), which has a metal-metal bond unsupported by bridging ligands. The dimer radical is oxidized at a slightly more positive potential (E-1/2 = 0.47 V) to the corresponding dication 2(2+). Observation of the oxidation of 2(+) is without precedent in confirming a radical-substrate (R-S) dimerization process by direct voltammetric detection of the R-S intermediate, K-eq = 3 x 10(4) M-1 for [2(+)]/[1][1(+)]. The R-S mechanism and the reaction products have been characterized by voltammetry, electrolysis, fiber-optic IR spectroscopy, and ESR measurements. DFT calculations indicate that removal of an electron from 1 results in rehybridization in 1(+), thereby opening the metal center for interaction with the neutral compound 1, which has a relatively basic metal center. The LUMO of the dimer dication 2(2+) is metal-metal antibonding, and its half-occupancy in 2(+) results in lengthening of the Co-Co bond from 2.64 angstrom to 3.14 angstrom. Inclusion of solvent in the (COSMO) calculations shows that solvation effects are necessary to account for the fact that E-1/2(2) > E-1/2(1). These results show the importance of medium effects in probing the fundamental redox chemistry of half-sandwich metal complexes.