Diiron Complexes of 1,8-Naphthyridine-Based Dinucleating Ligands as Models for Hemerythrin
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- 作者：Chuan He ; Amy M. Barrios ; Dongwhan Lee ; Jane Kuzelka ; Roman M. Davydov ; and Stephen J. Lippard
- 刊名：Journal of the American Chemical Society
- 出版年：2000
- 出版时间：December 27, 2000
- 年：2000
- 卷：122
- 期：51
- 页码：12683 - 12690
- 全文大小：112K
- 年卷期：v.122,no.51(December 27, 2000)
- ISSN：1520-5126
文摘
The hydroxo-bridged diiron(II) compounds [Fe2(BPEAN)(
-OH)(OTf)](OTf)2 (1) and [Fe2(BEPEAN)(-OH)](OTf)3 (2) were prepared by using 1,8-naphthyridine-based dinucleating ligands BPEANand BEPEAN, where BPEAN = 2,7-bis{bis[2-(2-pyridyl)ethyl]aminomethyl}-1,8-naphthyridine and BEPEAN= 2,7-bis{bis[2-(2-(5-ethyl)pyridyl)ethyl]aminomethyl}-1,8-naphthyridine. When compound 2 was treated withexcess 30% aqueous H2O2 in acetonitrile at -40 
C, a red-brown species (3) was produced. The UV-visspectrum of 3 exhibited an absorption maximum at 505 nm (
= 1500 M-1 cm-1), close to that observed foroxyHr. Resonance Raman experiments revealed an isotope-sensitive O-O stretching band at 868 cm-1. Whena mixture of 1:1 H2O2/D2O2 (25% in 1:1 H2O/D2O) was used to generate 3, a broader Raman band centeredat 870 cm-1 appeared, indicating the peroxide group to be protonated. The 1H ENDOR spectrum of 3,cryoreduced to the diiron(II,III) state, showed a signal with A 
12 MHz that disappeared when D2O2 in D2Owas used to generate 3, providing further evidence for the presence of a hydroperoxide ligand bound to iron.The EPR spectrum of the cryoreduced sample revealed that 3 has a (-oxo)diiron(III) core, a conclusionsupported by Mössbauer spectroscopy. The Mössbauer spectrum exhibited the unusual quadrupole splittingvalues that are characteristic of the diiron(III) center of oxyHr. Thus, all spectroscopic properties of 3 areconsistent with it being a hydroperoxo-bound (-oxo)diiron(III) complex. The hydroperoxide ligand is moreresistant to deprotonation than in mononuclear iron(III) analogues, which may reflect the presence of a hydrogenbond between the hydroperoxide and bridging oxide groups. At room temperature, acetonitrile/water solutionsof 3 decayed to iron(II) species, releasing the iron-bound hydroperoxide group to form O2.
-OH)(OTf)](OTf)2 (1) and [Fe2(BEPEAN)(-OH)](OTf)3 (2) were prepared by using 1,8-naphthyridine-based dinucleating ligands BPEANand BEPEAN, where BPEAN = 2,7-bis{bis[2-(2-pyridyl)ethyl]aminomethyl}-1,8-naphthyridine and BEPEAN= 2,7-bis{bis[2-(2-(5-ethyl)pyridyl)ethyl]aminomethyl}-1,8-naphthyridine. When compound 2 was treated withexcess 30% aqueous H2O2 in acetonitrile at -40 C, a red-brown species (3) was produced. The UV-visspectrum of 3 exhibited an absorption maximum at 505 nm ( = 1500 M-1 cm-1), close to that observed foroxyHr. Resonance Raman experiments revealed an isotope-sensitive O-O stretching band at 868 cm-1. Whena mixture of 1:1 H2O2/D2O2 (25% in 1:1 H2O/D2O) was used to generate 3, a broader Raman band centeredat 870 cm-1 appeared, indicating the peroxide group to be protonated. The 1H ENDOR spectrum of 3,cryoreduced to the diiron(II,III) state, showed a signal with A 12 MHz that disappeared when D2O2 in D2Owas used to generate 3, providing further evidence for the presence of a hydroperoxide ligand bound to iron.The EPR spectrum of the cryoreduced sample revealed that 3 has a (-oxo)diiron(III) core, a conclusionsupported by Mössbauer spectroscopy. The Mössbauer spectrum exhibited the unusual quadrupole splittingvalues that are characteristic of the diiron(III) center of oxyHr. Thus, all spectroscopic properties of 3 areconsistent with it being a hydroperoxo-bound (-oxo)diiron(III) complex. The hydroperoxide ligand is moreresistant to deprotonation than in mononuclear iron(III) analogues, which may reflect the presence of a hydrogenbond between the hydroperoxide and bridging oxide groups. At room temperature, acetonitrile/water solutionsof 3 decayed to iron(II) species, releasing the iron-bound hydroperoxide group to form O2.