Binding Modes Tuning Nitrite Reduction Reactivity at Iron(III) Centers Triggered by Hydrogen Atom, Hydride, and Proton Transfers

To elucidate the mechanisms of iron‐mediated nitrite reduction, we synthesized and fully characterized Fe(III)‐NO 2 − complexes featuring distinct κ 1 –O (nitrito) and κ 1 –N (nitro) binding modes, supported by a tris (benzenethiolato)phosphine ligand derivative. Interconversion between these two linkage isomers is modulated by a Na + cation in the secondary coordination sphere. These binding motifs direct divergent nitrite reduction pathways. For the κ 1 –O isomer, reduction is initiated by hydrogen atom or hydride transfer to yield an {FeNO} 7 species, whereas protonation results in formation of an {FeNO} 6 complex. Hydrogen atom transfer and protonation are accompanied by hydroxyl radical generation, while hydride transfer produces hydroxide. In contrast, the κ 1 –N isomer undergoes nitrite reduction exclusively via protonation. Detailed computational studies afford a mechanistic rationale for how nitrite binding modes govern distinct nitrite reduction trajectories.