Synthesis and Structural Characterization of a Non‐Heme Iron Hyponitrite Complex

Abstract Flavodiiron NO reductases (FNORs) are important enzymes in microbial pathogenesis, as they equip microbes with resistance to the human immune defense agent nitric oxide (NO). Despite many efforts, intermediates that would provide insight into how the non‐heme diiron active sites of FNORs reduce NO to N 2 O could not be identified. Computations predict that iron‐hyponitrite complexes are the key species, leading from NO to N 2 O. However, the coordination chemistry of non‐heme iron centers with hyponitrite is largely unknown. In this study, we report the reactivity of two non‐heme iron complexes with preformed hyponitrite. In the case of [Fe(TPA)(CH 3 CN) 2 ](OTf) 2 , cleavage of hyponitrite and formation of an Fe 2 (NO) 2 diamond core is observed. With less Lewis‐acidic [Fe 2 (BMPA‐PhO) 2 (OTf) 2 ] ( 2 ), reaction with Na 2 N 2 O 2 in polar aprotic solvent leads to the formation of a red complex, 3 . X‐ray crystallography shows that 3 is a tetranuclear iron‐hyponitrite complex, [{Fe 2 (BMPA‐PhO) 2 } 2 (μ‐N 2 O 2 )](OTf) 2 , with a unique hyponitrite binding mode. This species provided the unique opportunity to us to study the interaction of hyponitrite with non‐heme iron centers and the reactivity of the bound hyponitrite ligand. Here, either protonation or oxidation of 3 is found to induce N 2 O formation, supporting the hypothesis that hyponitrite is a viable intermediate in NO reduction.