of the M-NR moiety in intermediate 3 plays a crucial role in the reactivity with C-H bonds, and in particular, imidyl/nitrene character strongly benefits reactivity. Better insight into the electronic configuration was obtained by performing n-electron valence state second-order perturbation theory (NEVPT2) corrected CASSCF calculations on the DFT-optimized M-NR structure. A NEVPT2-CASSCF (10,8) calculation on gauche-i3 including all the metal dorbitals, nitrene orbitals, and p-orbitals of the HMDS-ligands in the active space showed significant multireference character for this intermediate. The lead electronic state, which contributes 55% towards the ground state, features three doubly occupied molecular orbitals (MOs), which represent a bonding combination between the iron and the nitrene nitrogen (Fig. ; see Fig. for all contributions). Two of these MOs represent a π-interaction and one MO a σ-interaction. Furthermore, two singly occupied molecular orbitals (SOMOs) predominantly display the two non-bonding iron dyz and dz 2 orbitals. The other two SOMOs consist of antibonding interactions between the Fe-N bond, one σ*-and one π*-interaction. Finally, the lowest unoccupied molecular orbital (LUMO) represents the second antibonding π*-interaction in the Fe-N bond. This brings the total bond order of the Fe-N bond in the predominant configuration to 2.0. However, due to contributions of higher spin states, significant electron density is transferred from the bonding π-orbitals of the Fe-N bond (occupancy 1.84 and 1.53), to the anti-bonding combination of those orbitals (occupancy 1.16 and 0.47). This shift results in a decreased bond order of 1.32 for the Fe-N interaction, giving rise to Fe-N bond elongation and significant imidyl and nitrene character. Indeed, the DFT computed Fe-N bond length of 1.737 Å exceeds the range of 1.612(2) Å -1.6723 (18) for all known Fe(IV) imido complexes. Notably, two iron imido complexes reported by Deng et al. and Betley et al. show a similar Fe-N bond elongation to 1.708(2) Å and 1.768(4) Å, respectively. However, both these complexes display a significant amount of imidyl radical character. Both the bond length obtained from the DFT optimized structure and the results from the NEVPT2-CASSCF calculations indicate imidyl and nitrene character, thus rationalizing the high reactivity of the complex. 2.7 Substrate scope. Since all mechanistic and kinetic data lend strong support to a molecularly well-defined and homogeneous catalyst, the activity of Fe(HMDS)2 towards various substrates was explored. The functional group tolerance of the reaction was probed by substituting the para-position of the model substrate 1a. Incorporation of a -Me, -OMe, or -Br group (5a-7a) did not give any significant change in yield of aminated product nor any correlation of the reaction rates with Hammett σp parameters (Table , entries 2-4). Substituting the phenyl group with an electron-rich and weakly coordinating thiophene group in 8a was also tolerated (entry 5). Primary benzylic C-H bonds were also activated, but the yield after 3 and