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) (
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:
- 10121962
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 58
- Issue:
- 49
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 17695-17699
- 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. -
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Abstract A new nonheme iron(II) complex, FeII(Me3TACN)((OSiPh2)2O) (
1 ), is reported. Reaction of1 with NO(g)gives a stable mononitrosyl complex Fe(NO)(Me3TACN)((OSiPh2)2O) (2 ), which was characterized by Mössbauer (δ =0.52 mm s−1, |ΔE Q|=0.80 mm s−1), EPR (S =3/2), resonance Raman (RR) and Fe K‐edge X‐ray absorption spectroscopies. The data show that2 is an {FeNO}7complex with anS =3/2 spin ground state. The RR spectrum (λ exc=458 nm) of2 combined with isotopic labeling (15N,18O) reveals ν(N‐O)=1680 cm−1, which is highly activated, and is a nearly identical match to that seen for the reactive mononitrosyl intermediate in the nonheme iron enzyme FDPnor (ν(NO)=1681 cm−1). Complex2 reacts rapidly with H2O in THF to produce the N‐N coupled product N2O, providing the first example of a mononuclear nonheme iron complex that is capable of converting NO to N2O in the absence of an exogenous reductant. -
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Abstract A new nonheme iron(II) complex, FeII(Me3TACN)((OSiPh2)2O) (
1 ), is reported. Reaction of1 with NO(g)gives a stable mononitrosyl complex Fe(NO)(Me3TACN)((OSiPh2)2O) (2 ), which was characterized by Mössbauer (δ =0.52 mm s−1, |ΔE Q|=0.80 mm s−1), EPR (S =3/2), resonance Raman (RR) and Fe K‐edge X‐ray absorption spectroscopies. The data show that2 is an {FeNO}7complex with anS =3/2 spin ground state. The RR spectrum (λ exc=458 nm) of2 combined with isotopic labeling (15N,18O) reveals ν(N‐O)=1680 cm−1, which is highly activated, and is a nearly identical match to that seen for the reactive mononitrosyl intermediate in the nonheme iron enzyme FDPnor (ν(NO)=1681 cm−1). Complex2 reacts rapidly with H2O in THF to produce the N‐N coupled product N2O, providing the first example of a mononuclear nonheme iron complex that is capable of converting NO to N2O in the absence of an exogenous reductant. -
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Abstract Reactivities of non‐heme iron(IV)‐oxo complexes are mostly controlled by the ligands. Complexes with tetradentate ligands such as [(TPA)FeO]2+(TPA=tris(2‐pyridylmethyl)amine) belong to the most reactive ones. Here, we show a fine‐tuning of the reactivity of [(TPA)FeO]2+by an additional ligand X (X=CH3CN, CF3SO3−, ArI, and ArIO; ArI=2‐(
t BuSO2)C6H4I) attached in solution and reveal a thus far unknown role of the ArIO oxidant. The HAT reactivity of [(TPA)FeO(X)]+/2+decreases in the order of X: ArIO > MeCN > ArI ≈ TfO−. Hence, ArIO is not just a mere oxidant of the iron(II) complex, but it can also increase the reactivity of the iron(IV)‐oxo complex as a labile ligand. The detected HAT reactivities of the [(TPA)FeO(X)]+/2+complexes correlate with the Fe=O and FeO−H stretching vibrations of the reactants and the respective products as determined by infrared photodissociation spectroscopy. Hence, the most reactive [(TPA)FeO(ArIO)]2+adduct in the series has the weakest Fe=O bond and forms the strongest FeO−H bond in the HAT reaction. -
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Abstract Reactivities of non‐heme iron(IV)‐oxo complexes are mostly controlled by the ligands. Complexes with tetradentate ligands such as [(TPA)FeO]2+(TPA=tris(2‐pyridylmethyl)amine) belong to the most reactive ones. Here, we show a fine‐tuning of the reactivity of [(TPA)FeO]2+by an additional ligand X (X=CH3CN, CF3SO3−, ArI, and ArIO; ArI=2‐(
t BuSO2)C6H4I) attached in solution and reveal a thus far unknown role of the ArIO oxidant. The HAT reactivity of [(TPA)FeO(X)]+/2+decreases in the order of X: ArIO > MeCN > ArI ≈ TfO−. Hence, ArIO is not just a mere oxidant of the iron(II) complex, but it can also increase the reactivity of the iron(IV)‐oxo complex as a labile ligand. The detected HAT reactivities of the [(TPA)FeO(X)]+/2+complexes correlate with the Fe=O and FeO−H stretching vibrations of the reactants and the respective products as determined by infrared photodissociation spectroscopy. Hence, the most reactive [(TPA)FeO(ArIO)]2+adduct in the series has the weakest Fe=O bond and forms the strongest FeO−H bond in the HAT reaction.
