The electrochemical reduction of [Ni( sacsac )2] ( sacsac = C5H7S2- = pentane-2,4-dithionate) has been investigated by cyclic voltammetry and controlled-potential electrolysis in acetone/tetra- butylammonium tetrafluoroborate (0.1 M). The reactions of the reduction product(s) with CO, CO2, CH3I, C12H25SH, light and water have been surveyed. At a scan rate of 100 mV s-1, [Ni( sacsac )2] (0.5 mM ) undergoes a quasi-reversible one-electron reduction (∆ Ep = 88 mV) at -1.543 V (v. Fc+/0) and an irreversible four-electron oxidation at +0.635 V. The oxidation generates the 3,5-dimethyl-1,2-dithiolium cation, as evidenced by the observation of the (known) reduction of this cation at -0.840 V. The initial product of the reduction of [Ni( sacsac )2] is a Lewis base, and reacts with light, water, CO, CO2, CH3I and C12H25SH. These reactions have been followed by electrochemical and spectroscopic methods. They appear to be biomimetic for a number of reactions observed for nickel enzymes.