Catalytic Reduction of N_2 to NH_3 by an Fe-N_2 Complex Featuring a C-Atom Anchor

摘要

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-N_2 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-N_2 binding site. In this context, we now report on Fe complexes of a new tris(phosphino)alkyl (CP~(iPr)_3) ligand featuring an axial carbon donor. It is established that the iron center in this scaffold binds dinitrogen trans to the C_(alkyl)-atom anchor in three distinct and structurally characterized oxidation states. Fe-C_(alkyl) lengthening is observed upon reduction, reflective of significant ionic character in the Fe-C_(alkyl) interaction. The anionic (CP~(iPr)_3)FeN_2~- species can be functionalized by a silyl electrophile to generate (CP~(iPr)_3)Fe-N_2SiR_3· (CP~(iPr)_3)FeN_2~- also functions as a modest catalyst for the reduction of N_2 to NH_3 when supplied with electrons and protons at -78 ℃ under 1 atm N_2 (4.6 equiv NH_3/Fe).