Dinitrogen Binding Relevant to FeMoco of Nitrogenase: Clear Visualization of σ‐Donation and π‐Backdonation from Deformation Electron Densities around Carbon/Silicon‐Iron Site

Abstract

Dinitrogen (N2) binding and electron transfer reduction of N2 to ammonia (NH3) by the FeMoco cofactor of the nitrogenase enzyme are captivating. They are a part of the textbook for general chemistry. The nature of N2 bonding by reduced FeMoco is speculated based on the experimental evidence. The inorganic core MoFe7S9C1− possesses a Fe6(μ6‐C4−) unit. The mode of N2‐binding at one of the Fe‐centers of the elusive Fe6(μ6‐C4−) unit and the role of light element C4− is intriguing. In the past, the mode of N2‐binding and the kinetics of N2 reduction have been studied by spectroscopic and other tools. Herein, we report on the energy decomposition analysis coupled with natural orbital for chemical valence (EDA‐NOCV) calculations/analyses to shed light on the deeper insight of the N2 binding and especially on the influence of the C‐atom of previously reported Fe‐complexes with an EP3 donor set (E=C, Si). The role of the C‐atom in the iron‐carbon site has been studied by elaboration with deformation electron densities. The intrinsic interaction energy of the bond between Fe and N2 and pairwise orbital interactions between them have been quantitatively estimated. The influence of σ‐donation of three phosphine ligands and their effects on the Fe−N2 bond have been thoroughly studied.