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) (
- NSF-PAR ID:
- 10230785
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 12
- Issue:
- 19
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 6569 to 6579
- 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 Given the importance of Fe–NO complexes in both human biology and the global nitrogen cycle, there has been interest in understanding their diverse electronic structures. Herein a redox series of isolable iron nitrosyl complexes stabilized by a tris(phosphine)borane (TPB) ligand is described. These structurally characterized iron nitrosyl complexes reside in the following highly reduced Enemark–Feltham numbers: {FeNO}8, {FeNO}9, and {FeNO}10. These {FeNO}8–10compounds are each low‐spin, and feature linear yet strongly activated nitric oxide ligands. Use of Mössbauer, EPR, NMR, UV/Vis, and IR spectroscopy, in conjunction with DFT calculations, provides insight into the electronic structures of this uncommon redox series of iron nitrosyl complexes. In particular, the data collectively suggest that {TPBFeNO}8–10are all remarkably covalent. This covalency is likely responsible for the stability of this system across three highly reduced redox states that correlate with unusually high Enemark–Feltham numbers.
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Abstract A nonheme {FeNO}6complex, [Fe(NO)(N3PyS)]2+, was synthesized by reversible, one‐electron oxidation of an {FeNO}7analogue. This complex completes the first known series of sulfur‐ligated {FeNO}6–8complexes. All three {FeNO}6–8complexes are readily interconverted by one‐electron oxidation/reduction. A comparison of spectroscopic data (UV/Vis, NMR, IR, Mössbauer, X‐ray absorption) provides a complete picture of the electronic and structural changes that occur upon {FeNO}6–{FeNO}8interconversion. Dissociation of NO from the new {FeNO}6complex is shown to be controlled by solvent, temperature, and photolysis, which is rare for a sulfur‐ligated {FeNO}6species.
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Abstract A nonheme {FeNO}6complex, [Fe(NO)(N3PyS)]2+, was synthesized by reversible, one‐electron oxidation of an {FeNO}7analogue. This complex completes the first known series of sulfur‐ligated {FeNO}6–8complexes. All three {FeNO}6–8complexes are readily interconverted by one‐electron oxidation/reduction. A comparison of spectroscopic data (UV/Vis, NMR, IR, Mössbauer, X‐ray absorption) provides a complete picture of the electronic and structural changes that occur upon {FeNO}6–{FeNO}8interconversion. Dissociation of NO from the new {FeNO}6complex is shown to be controlled by solvent, temperature, and photolysis, which is rare for a sulfur‐ligated {FeNO}6species.