Synthesis, Characterization, and Nitrogenase-Relevant Reactions of an Iron Sulfide Complex with a Bridging Hydride

The
FeMoco of nitrogenase is an iron–sulfur cluster with
exceptional bond-reducing abilities. ENDOR studies have suggested
that E4, the state that binds and reduces N2, 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 N2. These results add experimental
support to hydride-based pathways for nitrogenase.