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

To elucidate the mechanisms of iron-mediated nitrite reduction, we synthesized and fully characterized Fe(III)-NO₂ ^- complexes featuring distinct κ¹-O (nitrito) and κ¹-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 κ¹-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 κ¹-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.