A Terminal N2 Complex of High-Spin Iron(I) in a Weak, Trigonal Ligand Field.

The role of Fe in biological and industrial N2 fixation has inspired the intense study of small molecule analogues of Fe-(NxHy) intermediates of potential relevance to these processes. Although a number of low-coordinate Fe-(N2) featuring varying degrees of fidelity to the nitrogenase active site are now known, these complexes frequently feature strongly donating ligands that either enforce low- or intermediate-spin states or result in linear Fe-(N2)-Fe bridging motifs. Given that the nitrogenase active site uses weak-field sulfide ligands to stabilize its reactive Fe center(s), N2 binding to high-spin Fe is of great interest. Herein, we report the synthesis and characterization of the first terminal N2 complex of high-spin (S = 3/2) Fe(I) as well as a bridging Fe-(N2)-Fe analogue. Electron paramagnetic resonance and solution magnetic moment determination confirm the high-spin state, and vibrational experiments indicate a substantial degree of activation of the N≡N bond in these complexes. Density functional theory calculations reveal an electronic structure for the terminal adduct featuring substantial delocalization of unpaired spin onto the N2 ligand.