Structural features of the reduced form of the nickel superoxide dismutase (Ni-SOD) active site have been modeled with asymmetric NiN2S2 complexes (Et4N)[Ni(nmp)(SR)] (R = C6H4-p-Cl (2) and ((SBu)-Bu-t) (3)) obtained via S,S-bridge splitting of the dimeric metallosynthon, [Ni-2(nmp)(2)] (1). Complexes 2 and 3 are irreversibly oxidized at potentials within the window needed for SOD activity, 236 and 75 mV versus Ag/AgCl, respectively. The exogenous thiolato-S in 2 and 3 serves as a proton acceptor, suggesting potential involvement of Cys6 in Ni-SOD for H+ storage between SOD half reactions.