Iron(<scp>III</scp>) Complexes with the Ligand N′,N′‐Bis[(2‐pyridyl)methyl]ethylenediamine (uns‐penp) and Its Amide Derivative N‐Acetyl‐N′,N′‐bis[(2‐pyridyl)methyl]ethylenediamine (acetyl‐uns‐penp)

Xu, Jing‐Yuan; Astner, Jorg; Walter, Olaf; Heinemann, Frank W.; Schindler, Siegfried; Merkel, M.; Krebs, Bernt

doi:10.1002/ejic.200500902

Cited by 18 publications

(16 citation statements)

References 79 publications

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“…1a) shows that L acts as a pentadentate ligand with an N 4 O donor set where the N 4 subset binds to one iron center while the oxygen atom coordinates to the other iron site. This structure resembles that of a recently described complex of a closely related ligand11, both of which have a (μ-oxo)diiron(III) unit that is supported by two carboxamido bridges. The fact that the bridging moieties are connected to the terminal ligands results in smaller Fe-(μ-O)-Fe angles than found typically for closely related (μ-oxo)bis(μ-carboxylato)diiron(III) complexes12, and these (μ-oxo)bis(μ-carboxamido)diiron(III) complexes have the shortest Fe-Fe distances (~3 Å) in this class of complexes.…”

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confidence: 73%

A diiron(iv) complex that cleaves strong C–H and O–H bonds

et al. 2009

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The controlled cleavage of strong C-H bonds like those of methane poses a significant challenge for chemists. In nature methane is oxidized to methanol by soluble methane monooxygenase via a diiron (IV) intermediate called Q. To model the chemistry of MMO-Q, an oxo-bridged diiron(IV) complex has been generated by electrochemical oxidation and characterized by several spectroscopic methods. This novel species has an Fe IV/III redox potential of +1.50 V vs. ferrocene (>2 V vs. NHE), the highest value thus far determined electrochemically for an iron complex. This species is quite an effective oxidant. It can attack C-H bonds as strong as 100 kcal mol −1 and reacts with cyclohexane a hundredto a thousand-fold faster than mononuclear Fe IV =O complexes of closely related ligands. Strikingly, this species can also cleave the strong O-H bonds of methanol and tert-butanol instead of their weaker C-H bonds, representing the first example of O-H bond activation for iron complexes.The controlled cleavage of strong C-H bonds like those of methane remains an elusive goal and one of great industrial and practical importance. In nature, methane hydroxylation occurs by oxygen activation through the action of soluble and particulate methane monooxygenases (MMOs) found in methane-metabolizing bacteria [1][2][3][4] . The much better characterized soluble MMOs have a nonheme diiron active site that reacts with O 2 to produce an oxo-bridged diiron (IV) oxidant called Q that effects the transformation [5][6][7][8] . The generation of a diiron(IV) complex that can oxidize strong C-H bonds thus represents an appealing challenge for synthetic chemists.To date, only two types of (μ-oxo)diiron(IV) complexes have been characterized. The first example, represented by two complexes of tetraamido macrocyclic ligands (TAML) characterized by Ghosh et al., is stable at room temperature, but no oxidation chemistry involving C-H bond cleavage has been reported 9 . The second example, recently reported by Xue et al., utilizes the neutral tetradentate N4 ligand tris(3,5-dimethyl-4-methoxypyridylmethyl)amine to form [Fe IV 2 (μ-O) 2 (N4) 2 ] 4+ and serves as a synthetic precedent for the Fe IV 2 (μ-O) 2 core proposed for MMO-Q 10 . This complex is stable for only 1 hour at −40 °C and can attack the weak C-H bonds of dihydroanthracene. These (μ-oxo)diiron(IV) complexes thus exhibit reactivities that fall far short of that associated with the diiron active site of soluble MMO. In this study, we report a much more strongly oxidizing (μ-oxo)diiron(IV) complex, obtained by electrochemical oxidation of its (μ-oxo)diiron(III) precursor, that is capable of cleaving not only the strong C-H bonds of cyclohexane but also the even stronger O-H bonds of aliphatic alcohols. The starting point for this study isIts structure (Fig. 1a) shows that L acts as a pentadentate ligand with an N 4 O donor set where the N 4 subset binds to one iron center while the oxygen atom coordinates to the other iron site. This structure resembles that of a recently described c...

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confidence: 73%

A diiron(iv) complex that cleaves strong C–H and O–H bonds

et al. 2009

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“…The lower energy visible bands decreasing in absorbance are attributed to 3,5‐DTBC 2− ‐to‐iron(III) LMCT transitions involving two different catecholate ligand orbitals . As reported in many cases, the energy of the LMCT transitions strongly depends on the nature of the ligands, and it reflects the Lewis acidity of the iron centre in the complex . The disappearance of the lower energy catecholate‐to‐iron(III) LMCT band (Fig.…”

Section: Resultsmentioning

confidence: 60%

Catalytic promiscuity of an iron(II)–phenanthroline complex

De¹,

Garai²,

Yadav

et al. 2016

Applied Organom Chemis

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A mononuclear iron(II) complex, [Fe(phen) 3 ]Cl 2 (1) (phen =1,10-phenanthroline), has been synthesized in crystalline phase and characterized using various spectroscopic techniques including single crystal X-ray diffraction. Crystal structure analysis revealed that 1 crystallizes in a monoclinic system with C2/m space group. Complex 1 acts as a functional model for a biomimetic catalyst promoting the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) through radical pathways with a significant turnover number (k cat =3.55 × 10 3 h À1 ) and exhibits catechol dioxygenase activity towards the same 3,5-DTBC substrate at room temperature in oxygen-saturated ethanol medium. The existence of an isobestic point at 610 nm from spectrophotometric data indicates the presence of Fe 3+ À3,5-DTBC adduct favouring an enzyme-substrate binding phenomenon. Upon stoichiometric addition of 3,5-DTBC pretreated with two equivalents of triethylamine to the iron complex, two catecholate-to-iron(III) ligand-to-metal charge transfer bands (575 and 721 nm) are observed and the in situ generated catecholate intermediate reacts with dioxygen (k obs =9.89 × 10 À4 min À1 ) in ethanol medium to afford exclusively intradiol cleavage products along with a small amount of benzoquinone, and a small amount of extradiol cleavage products, which provide substantial evidence for a substrate activation mechanism.

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“…In contrast to the vast number of carboxylate-bridged high oxidation state metal-oxo clusters, amidate-bridged metal-oxo clusters are rare. 75–78 We employed an n -propyl-linked diacetamide proligand (H 2 diam) to replace two acetate moieties. Treatment of 1 with 1 equiv.…”

Section: Resultsmentioning

confidence: 99%

Tetranuclear [Mn^IIIMn₃^IVO₄] Complexes as Spectroscopic Models of the S₂ State of the Oxygen Evolving Complex in Photosystem II

et al. 2018

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Despite extensive biochemical, spectroscopic, and computational studies, the mechanism of biological water oxidation by the Oxygen Evolving Complex (OEC) of Photosystem II remains a subject of significant debate. Mechanistic proposals are guided by the characterization of reaction intermediates such as the S2 state, which features two characteristic EPR signals at g = 2 and g = 4.1. Two nearly isoenergetic structural isomers have been proposed as the source of these distinct signals, but relevant structure−electronic structure studies remain rare. Herein, we report the synthesis, crystal structure, electrochemistry, XAS, magnetic susceptibility, variable temperature CW-EPR, and pulse EPR data for a series of [MnIIIMn3IVO4] cuboidal complexes as spectroscopic models of the S2 state of the OEC. Resembling the oxidation state and EPR spectra of the S2 state of the OEC, these model complexes show two EPR signals, a broad low field signal and a multiline signal, that are remarkably similar to the biological system. The effect of systematic changes in the nature of the bridging ligands on spectroscopy were studied. Results show that the electronic structure of tetranuclear Mn complexes is highly sensitive to even small geometric changes and the nature of the bridging ligands. Our model studies suggest that the spectroscopic properties of the OEC may also react very sensitively to small changes in structure; the effect of protonation state and other reorganization processes need to be carefully assessed.

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Iron(III) Complexes with the Ligand N′,N′‐Bis[(2‐pyridyl)methyl]ethylenediamine (uns‐penp) and Its Amide Derivative N‐Acetyl‐N′,N′‐bis[(2‐pyridyl)methyl]ethylenediamine (acetyl‐uns‐penp)

Abstract: Synthesis and structural characterization of the iron(III) complexes of the tripodal ligands NЈ,NЈ-bis [(2-pyridyl)

Cited by 18 publications

References 79 publications

A diiron(iv) complex that cleaves strong C–H and O–H bonds

A diiron(iv) complex that cleaves strong C–H and O–H bonds

Catalytic promiscuity of an iron(II)–phenanthroline complex

Tetranuclear [Mn^IIIMn₃^IVO₄] Complexes as Spectroscopic Models of the S₂ State of the Oxygen Evolving Complex in Photosystem II

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Iron(III) Complexes with the Ligand N′,N′‐Bis[(2‐pyridyl)methyl]ethylenediamine (uns‐penp) and Its Amide Derivative N‐Acetyl‐N′,N′‐bis[(2‐pyridyl)methyl]ethylenediamine (acetyl‐uns‐penp)

Abstract: Synthesis and structural characterization of the iron(III) complexes of the tripodal ligands NЈ,NЈ-bis [(2-pyridyl)

Cited by 18 publications

References 79 publications

A diiron(iv) complex that cleaves strong C–H and O–H bonds

A diiron(iv) complex that cleaves strong C–H and O–H bonds

Catalytic promiscuity of an iron(II)–phenanthroline complex

Tetranuclear [MnIIIMn3IVO4] Complexes as Spectroscopic Models of the S2 State of the Oxygen Evolving Complex in Photosystem II

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Tetranuclear [Mn^IIIMn₃^IVO₄] Complexes as Spectroscopic Models of the S₂ State of the Oxygen Evolving Complex in Photosystem II