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Abstract Some bacterial heme proteins catalyze the coupling of two NO molecules to generate N2O. We previously reported that a heme Fe–NO model engages in this N−N bond‐forming reaction with NO. We now demonstrate that (OEP)CoII(NO) similarly reacts with 1 equiv of NO in the presence of the Lewis acids BX3(X=F, C6F5) to generate N2O. DFT calculations support retention of the CoIIoxidation state for the experimentally observed adduct (OEP)CoII(NO⋅BF3), the presumed hyponitrite intermediate (P.+)CoII(ONNO⋅BF3), and the porphyrin π‐radical cation by‐product of this reaction, and that the π‐radical cation formation likely occurs at the hyponitrite stage. In contrast, the Fe analogue undergoes a ferrous‐to‐ferric oxidation state conversion during this reaction. Our work shows that cobalt hemes are chemically competent to engage in the NO‐to‐N2O conversion reaction.
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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 N2O could not be identified. Computations predict that iron‐hyponitrite complexes are the key species, leading from NO to N2O. 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)(CH3CN)2](OTf)2, cleavage of hyponitrite and formation of an Fe2(NO)2diamond core is observed. With less Lewis‐acidic [Fe2(BMPA‐PhO)2(OTf)2] (2), reaction with Na2N2O2in polar aprotic solvent leads to the formation of a red complex,3. X‐ray crystallography shows that3is a tetranuclear iron‐hyponitrite complex, [{Fe2(BMPA‐PhO)2}2(μ‐N2O2)](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 of3is found to induce N2O formation, supporting the hypothesis that hyponitrite is a viable intermediate in NO reduction.
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- Award ID(s):
- 2002885
- PAR ID:
- 10558557
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 63
- Issue:
- 49
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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