The FeMoco of nitrogenase is an iron-sulfur cluster with exceptional bond-reducing abilities. END OR studies have suggested that E-4, the state that binds and reduces N-2, contains bridging hydrides as part of the active-site iron-sulfide cluster. However, there are no examples of any isolable iron-sulfide cluster with a hydride, which would test the feasibility of such a species. Here, we describe a diiron sulfide hydride complex that is prepared using a mild method involving C-S cleavage of added thiolate. Its reactions with nitrogenase substrates show that the hydride can act as a base or nucleophile and that reduction can cause the iron atoms to bind N-2. These results add experimental support to hydride-based pathways for nitrogenase.