Stability and bonding of carbon(0)-iron-N₂ complexes relevant to nitrogenase co-factor: EDA-NOCV analyses

The factors/structural features which are responsible for the binding, activation and reduction of N₂ to NH₃ by FeMoco of nitrogenase have not been completely understood well. Several relevant model complexes by Holland et al. and Peters et al. have been synthesized, characterized and studied by theoretical calculations. For a matter of fact, those complexes are much different than real active N₂ -binding Fe-sites of FeMoco, which possesses a central C(4-) ion having an eight valence electrons as an μ₆ -bridge. Here, a series of [(S₃ C(0))Fe(II/I/0)-N₂ ]^n- complexes in different charged/spin states containing a coordinated σ- and π-donor C(0)-atom which possesses eight outer shell electrons [carbone, (Ph₃ P)₂ C(0); Ph₃ P→C(0)←PPh₃ ] and three S-donor sites (i.e. ^- S-Ar), have been studied by DFT, QTAIM, and EDA-NOCV calculations. The effect of the weak field ligand on Fe-centres and the subsequent N₂ -binding has been studied by EDA-NOCV analysis. The role of the oxidation state of Fe and N₂ -binding in different charged and spin states of the complex have been investigated by EDA-NOCV analyses. The intrinsic interaction energies of the Fe-N₂ bond are in the range from -42/-35 to -67 kcal/mol in their corresponding ground states. The S₃ C(0) donor set is argued here to be closer to the actual coordination environment of one of the six Fe-centres of nitrogenase. In comparison, the captivating model complexes reported by Holland et al. and Peter et al. possess a stronger π-acceptor C-ring (S₂ C_ring donor, π-C donor) and stronger donor set like CP₃ (σ-C donor) ligands, respectively.