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.

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 (Δ E orb( n ) ). The computed intrinsic interaction energy (Δ E int ) of V-N 2 -V bonds is significantly higher than those of the previously reported Fe-N 2 -Fe bonds. Covalent interaction energy (Δ E orb ) is more than double the electrostatic interaction energy (Δ E elstat ) of V-N 2 -V bonds. Δ E 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.