Non‐heme high‐spin (hs) {FeNO}8complexes have been proposed as important intermediates towards N2O formation in flavodiiron NO reductases (FNORs). Many hs‐{FeNO}8complexes disproportionate by forming dinitrosyl iron complexes (DNICs), but the mechanism of this reaction is not understood. While investigating this process, we isolated a new type of non‐heme iron nitrosyl complex that is stabilized by an unexpected spin‐state change. Upon reduction of the hs‐{FeNO}7complex, [Fe(TPA)(NO)(OTf)](OTf) (
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] (
- PAR ID:
- 10553670
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie
- Volume:
- 136
- Issue:
- 49
- ISSN:
- 0044-8249
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 1 ), the N‐O stretching band vanishes, but no sign of DNIC or N2O formation is observed. Instead, the dimer, [Fe2(TPA)2(NO)2](OTf)2(2 ) could be isolated and structurally characterized. We propose that2 is formed from dimerization of the hs‐{FeNO}8intermediate, followed by a spin state change of the iron centers to low‐spin (ls), and speculate that2 models intermediates in hs‐{FeNO}8complexes that precede the disproportionation reaction. -
Abstract Non‐heme high‐spin (hs) {FeNO}8complexes have been proposed as important intermediates towards N2O formation in flavodiiron NO reductases (FNORs). Many hs‐{FeNO}8complexes disproportionate by forming dinitrosyl iron complexes (DNICs), but the mechanism of this reaction is not understood. While investigating this process, we isolated a new type of non‐heme iron nitrosyl complex that is stabilized by an unexpected spin‐state change. Upon reduction of the hs‐{FeNO}7complex, [Fe(TPA)(NO)(OTf)](OTf) (
1 ), the N‐O stretching band vanishes, but no sign of DNIC or N2O formation is observed. Instead, the dimer, [Fe2(TPA)2(NO)2](OTf)2(2 ) could be isolated and structurally characterized. We propose that2 is formed from dimerization of the hs‐{FeNO}8intermediate, followed by a spin state change of the iron centers to low‐spin (ls), and speculate that2 models intermediates in hs‐{FeNO}8complexes that precede the disproportionation reaction. -
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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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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Abstract A novel metal‐organic framework (MOF) containing one‐dimensional, Fe2+chains bridged by dipyrazolate linkers and
N ,N ‐dimethylformamide (DMF) ligands has been synthesized. The unusual chain‐type metal nodes feature accessible coordination sites on adjacent metal centers, resulting in motifs that are reminiscent of the active sites in non‐heme diiron enzymes. The MOF facilitates direct reduction of nitric oxide (NO), producing nearly quantitative yields of nitrous oxide (N2O) and emulating the reactivity of flavodiiron nitric oxide reductases (FNORs). The ferrous form of the MOF can be regenerated via a synthetic cycle involving reduction with cobaltocene (CoCp2) followed by reaction with trimethylsilyl triflate (TMSOTf).