Estimations of Fe 0/-1 -N 2 interaction energies of iron(0)-dicarbene and its reduced analogue by EDA-NOCV analyses: crucial steps in dinitrogen activation under mild conditions.

Metal complexes containing low valence iron atoms are often experimentally observed to bind with the dinitrogen (N 2 ) molecule. This phenomenon has attracted the attention of industrialists, chemists and bio-chemists since these N 2 -bonded iron complexes can produce ammonia under suitable chemical or electrochemical conditions. The higher binding affinity of the Fe-atom towards N 2 is a bit 'mysterious' compared to that of the other first row transition metal atoms. Fine powders of α-Fe 0 are even part of industrial ammonia production (Haber-Bosch process) which operates at high temperature and high pressure. Herein, we report the EDA-NOCV analyses of the previously reported dinitrogen-bonded neutral molecular complex (cAAC R ) 2 Fe 0 -N 2 (1) and mono-anionic complex (cAAC R ) 2 Fe -1 -N 2 (2) to give deeper insight of the Fe-N 2 interacting orbitals and corresponding pairwise intrinsic interaction energies (cAAC R = cyclic alkyl(amino) carbene; R = Dipp or Me). The Fe 0 atom of 1 prefers to accept electron densities from N 2 via σ-donation while the comparatively electron rich Fe -1 centre of 2 donates electron densities to N 2 via π-backdonation. However, major stability due to the formation of an Fe-N 2 bond arises due to Fe → N 2 π-backdonation in both 1 and 2. The cAAC R ligands act as a charge reservoir around the Fe centre. The electron densities drift away from cAAC ligands during the binding of N 2 molecules mostly via π-backdonation. EDA-NOCV analysis suggests that N 2 is a stronger π-acceptor rather than a σ-donor.