Dinitrogen Binding and Activation: Bonding Analyses of Stable V(III/I)–N(2)–V(III/I) Complexes by the EDA–NOCV Method from the Perspective of Vanadium Nitrogenase

[Image: see text] The FeVco cofactor of nitrogenase (VFe(7)S(8)(CO(3))C) is an alternative in the molybdenum (Mo)-deficient free soil living azotobacter vinelandii. The rate of N(2) reduction to NH(3) by FeVco is a few times higher than that by FeMoco (MoFe(7)S(9)C) at low temperature. It provides a N source in the form of ammonium ions to the soil. This biochemical NH(3) synthesis is an alternative to the industrial energy-demanding production of NH(3) 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–N(2) 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)–N(2) (1–4) to provide deeper insights into the fundamental bonding aspects of V–N(2) bond, showing the interacting orbitals and corresponding pairwise orbital interaction energies (ΔE(orb(n))). The computed intrinsic interaction energy (ΔE(int)) of V–N(2)–V bonds is significantly higher than those of the previously reported Fe–N(2)–Fe bonds. Covalent interaction energy (ΔE(orb)) is more than double the electrostatic interaction energy (ΔE(elstat)) of V–N(2)–V bonds. ΔE(int) values of V–N(2)–V bonds are in the range of −172 to −204 kcal/mol. The V → N(2) ← V π-backdonation is four times stronger than V ← N(2) → V σ-donation. V–N(2) bonds are much more covalent in nature than Fe–N(2) bonds.