Catalytic Reduction of N2 to NH3 by an Fe–N2 Complex Featuring a C‑Atom Anchor

While recent spectroscopic studies have established the presence of an interstitial carbon atom at the center of the iron–molybdenum cofactor (FeMoco) of MoFe-nitrogenase, its role is unknown. We have pursued Fe–N2 model chemistry to explore a hypothesis whereby this C-atom (previously denoted as a light X-atom) may provide a flexible trans interaction with an Fe center to expose an Fe–N2 binding site. In this context, we now report on Fe complexes of a new tris­(phosphino)­alkyl (CPiPr3) ligand featuring an axial carbon donor. It is established that the iron center in this scaffold binds dinitrogen trans to the Calkyl-atom anchor in three distinct and structurally characterized oxidation states. Fe–Calkyl lengthening is observed upon reduction, reflective of significant ionic character in the Fe–Calkyl interaction. The anionic (CPiPr3)­FeN2– species can be functionalized by a silyl electrophile to generate (CPiPr3)­Fe–N2SiR3. (CPiPr3)­FeN2– also functions as a modest catalyst for the reduction of N2 to NH3 when supplied with electrons and protons at −78 °C under 1 atm N2 (4.6 equiv NH3/Fe).