Oxyanion Reduction with Iron Catalysts

The development of synthetic models that mimic the highly specialized coordination spheres of metalloenzymes remains a primary goal in inorganic synthesis, particularly for the reduction of kinetically inert oxyanions. This work describes the design and reactivity of a bio-inspired nonheme iron framework, [N(afaCy)3Fe]OTf2, emphasizing the role of secondary coordination sphere interactions in facilitating challenging multi-electron/multi-proton transfer processes. By tailoring the ligand architecture to stabilize reactive intermediates, we demonstrate the selective catalytic reduction of nitrogen oxyanions (NO3– and NO2–) to N2 or NH3. Mechanistic insights obtained through isotopic labeling, spectroscopic characterization, and computational analysis identify a key hydroxylamine intermediate, illustrating how structural modifications to the iron center dictate divergent reaction pathways. Furthermore, the complex demonstrates a distinct selectivity profile in the oxygen reduction reaction (ORR), favoring a two-electron/two-proton pathway to produce hydrogen peroxide, an uncommon result for nonheme iron catalysts that underscores the influence of the local chemical environment on redox transformations. These results highlight the importance of precise structural control in the synthesis of iron-based complexes for the transformation of diverse chemical feedstocks and the advancement of sustainable catalysis.