To provide the mechanistic information of nitrogenase at a molecular level, much effort has been made to develop synthetic metal complexes that have enzyme-like reactivity. Herein we obtain an iron(II) complex binding with a tris(thiolato)phosphine ligand, [P(Ph)(4)][Fe(PS3 '')(CH3CN)] [1; PS3 '' = P(C6H3-3-Me3Si-2-S)(3)(3-)] that catalyzes the reduction of hydrazine, an intermediate and a substrate of nitrogenase. The substrate- and product-bound adducts, [N(Bu)(4)] [Fe-(PS3 '')(N2H4)] (2) and [N(Et)(4)][Fe(PS3 '')(NH3)] (3), respectively, are also synthesized. This work provides the feasibility that the late stage of biological nitrogen fixation can be conducted at a single iron site with a sulfur-rich ligation environment.