Dinitrogen Binding and Activation: Bonding Analyses of Stable V(III/I)-N2-V(III/I) Complexes by the EDA-NOCV Method from the Perspective of Vanadium Nitrogenase.

Abstract

The FeVco cofactor of nitrogenase (VFe7S8(CO3)C) is an alternative in the molybdenum (Mo)-deficient free soil living azotobacter vinelandii. The rate of N2 reduction to NH3 by FeVco is a few times higher than that by FeMoco (MoFe7S9C) at low temperature. It provides a N source in the form of ammonium ions to the soil. This biochemical NH3 synthesis is an alternative to the industrial energy-demanding production of NH3 by the Haber–Bosch process. The role of vanadium has not been clearly understood yet, which has led chemists to come up with several stable V–N2 complexes which have been isolated and characterized in the laboratory over the past three decades. Herein, we report the EDA–NOCV analyses of dinitrogen-bonded stable complexes V(III/I)–N2 (1–4) to provide deeper insights into the fundamental bonding aspects of V–N2 bond, showing the interacting orbitals and corresponding pairwise orbital interaction energies (ΔEorb(n)). The computed intrinsic interaction energy (ΔEint) of V–N2–V bonds is significantly higher than those of the previously reported Fe–N2–Fe bonds. Covalent interaction energy (ΔEorb) is more than double the electrostatic interaction energy (ΔEelstat) of V–N2–V bonds. ΔEint values of V–N2–V bonds are in the range of −172 to −204 kcal/mol. The V → N2 ← V π-backdonation is four times stronger than V ← N2 → V σ-donation. V–N2 bonds are much more covalent in nature than Fe–N2 bonds.