A series of Mo(CO)₃(a-diimine)(CH₃CN) compounds (a-diimine ligands used include 2,2'-bipyridine, 2,2'-biquinoline, 1,10-phenanthroline and substituted derivatives) was prepared from the corresponding Mo(CO)₄(a-diimine) complexes via reflux in acetonitrile. These compounds all exhibit quasi-reversible one-electron oxidations in acetonitrile yielding the corresponding [Mo(CO)₃(a-diimine)(CH₃CN)]⁺ radicals. The electrogenerated seventeen-electron complexes can be oxidized in a second, irreversible, one-electron process which is coupled to coordination by solvent, yielding the seven-coordinate Mo²⁺ complex, [Mo(CO)₃(bpy)(CH₃CN)₂]²⁺. In addition, the [Mo(CO)₃(a-diimine)(CH₃CN)]⁺ species are susceptible to nucleophilic attack by the solvent, resulting in net disproportionation reactions. These ligand-induced disproportionations follow first order kinetics, the rate constants of which were found to be influenced by steric and electronic factors. In addition to the Mo⁰ starting compound, disproportionation yields the same seven-coordinate Mo²⁺ species that is formed by direct oxidation of [Mo(CO)₃(a-diimine)(CH₃CN)]⁺. This compound is unstable toward additional acetonitrile substitution and decomposes to [Mo(CO)₂(a-diimine)(CH₃CN)₃²⁺]. The infrared spectra of the Mo²⁺ oxidation products, as well those of the electrogenerated Mo⁺ complexes, were obtained via infrared spectroelectrochemistry and will be discussed.