A Monomeric Side-On Peroxo Manganese(III) Complex: Mn(O2)(3,5-iPr2pzH)(HB(3,5-iPr2pz)3)

Kitajima, Nobumasa; Komatsuzaki, Hidehito; Hikichi, Shiro; Osawa, Masahisa; Moro‐oka, Yoshihiko

doi:10.1021/ja00104a061

Cited by 151 publications

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“…61,62,66,67 The Fe-O bond length of 1b also compares well with the 1.89 and 1.90 Å distances observed for the Mn-O bonds in [Mn(TPP)(η 2 -O 2 )] -68 but is longer than the average 1.86 Å Mn-O distance associated with [Mn III -(Tp 3,5-iPr2 )(3,5-iPr 2 pzH)(η 2 -O 2 )]. 69 Features in the outer sphere can be fit with carbon scatterers at 3, 4.1, and 4.6 Å. These results represent the first structural insights for a synthetic non-heme Fe-η 2 -O 2 complex.…”

Section: Peroxo Deriwatiwes Of Non-heme Iron Complexesmentioning

confidence: 63%

End-On and Side-On Peroxo Derivatives of Non-Heme Iron Complexes with Pentadentate Ligands: Models for Putative Intermediates in Biological Iron/Dioxygen Chemistry

et al. 2003

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Mononuclear iron(III) species with end-on and side-on peroxide have been proposed or identified in the catalytic cycles of the antitumor drug bleomycin and a variety of enzymes, such as cytochrome P450 and Rieske dioxygenases. Only recently have biomimetic analogues of such reactive species been generated and characterized at low temperatures. We report the synthesis and characterization of a series of iron(II) complexes with pentadentate N5 ligands that react with H 2 O 2 to generate transient low-spin Fe III −OOH intermediates. These intermediates have low-spin iron(III) centers exhibiting hydroperoxo-to-iron(III) charge-transfer bands in the 500−600-nm region. Their resonance Raman frequencies, ν O-O , near 800 cm -1 are significantly lower than those observed for high-spin counterparts. The hydroperoxo-to-iron(III) charge-transfer transition blue-shifts and the ν O-O of the Fe−OOH unit decreases as the N5 ligand becomes more electron donating. Thus, increasing electron density at the low-spin Mononuclear iron(III) peroxide species are implicated as intermediates in the mechanisms of oxygen activating biomolecules such as cytochrome P450, 1 heme oxygenase, 2 the antitumor drug bleomycin, 3 and Rieske dioxygenases, 4,5 as well as superoxide reductases from anaerobic bacteria. [6][7][8][9] Experimental evidence for some of these intermediates has

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Section: Peroxo Deriwatiwes Of Non-heme Iron Complexesmentioning

confidence: 63%

End-On and Side-On Peroxo Derivatives of Non-Heme Iron Complexes with Pentadentate Ligands: Models for Putative Intermediates in Biological Iron/Dioxygen Chemistry

et al. 2003

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“…In the case of 4, we wish to avoid possible difficulties associated with the counterion of this cationic metal-dioxygen complex. With respect to 9, Kitajima et al (34) reported two isomeric forms (''blue'' and ''brown'') having identical OO values and OOO bond lengths but varying in whether a hydrogen bond was observed between the pyrazole and oxygen fragments in the crystal structures. We elect not to address this complication here.…”

Section: Methodsmentioning

confidence: 99%

Variable character of O—O and M—O bonding in side-on (η ² ) 1:1 metal complexes of O ₂

Cramer

Tolman

Theopold

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

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The structures and the OOO and MOO bonding characters of a series of reported side-on ( 2 ) 1:1 metal complexes of O2 are analyzed by using density functional theory calculations. Comparison of the calculated and experimental systems with respect to OOO bond distance, OOO stretching frequency, and OOO and MOO bond orders provides new insights into subtle influences relevant to O2 activation processes in biology and catalysis. The degree of charge transfer from the generally electronrich metals to the dioxygen fragment is found to be variable, such that there are species well described as superoxides, others well described as peroxides, and several cases having intermediate character. Increased charge transfer to dioxygen takes place via overlap of the metal dxy orbital with the in-plane * orbital of O2 and results in increased MOO bond orders and decreased OOO bond orders. Comparison of theory and experiment over the full range of compounds studied suggests that reevaluation of the OOO bond lengths determined from certain x-ray crystal structures is warranted; in one instance, an x-ray crystal structure redetermination was performed at low temperature, confirming the theoretical prediction. Librational motion of the coordinated O2 is identified as a basis for significant underestimation of the OOO distance at high temperature. With the longstanding goal of understanding in detail how dioxygen binds and is activated at metal centers in biological and catalytic systems, great effort has been expended to characterize the structures, physicochemical properties, and reactivity of metal-dioxygen complexes (1-8). As the initially formed species in most oxidation processes, 1:1 metal-O 2 adducts are of special interest, particularly in view of their postulated involvement in enzymes that react with dioxygen at an isolated monometallic active site, such as Cu in dopamine ␤-monooxygenase or galactose oxidase (9). Two binding modes have been identified in 1:1 metal-O 2 complexes, end-on ( 1 ) and side-on ( 2 ). These adducts have been further defined as superoxo or peroxo complexes, primarily on the basis of x-ray structural data (OOO bond distance) and vibrational spectroscopy (OOO stretching frequency, OO ) (1-4). Thus, compounds with an OOO bond length of Ϸ1.4-1.5 Å and OO between Ϸ800 and 930 cm Ϫ1 are designated as peroxides, whereas those with OOO Ϸ1.2-1.3 Å and OO Ϸ1,050-1,200 cm Ϫ1 fall into the superoxide category. On this basis, and keeping in mind the caveat that it is often difficult to assess experimentally the actual amount of charge transferred to dioxygen on complexation, the majority of the known 2 1:1 compounds are generally agreed to be best described as peroxo complexes (1,5,8).Reports of , Tris(3,5-dimethylpyrazol-1-yl)hydroborate) (13) (Scheme 1). In the course of the investigation of 6, for which intermediate character of the dioxygen unit was found (14, 15), we noted puzzling incongruities among the data reported for these complexes (Table 1). For example, whereas 1 and 2 (as reported in ref. 11, d...

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“…[6] In biomimetic studies, a number of Mn-peroxido complexes have been synthesized and characterized with a variety of spectroscopic methods including X-ray crystallography. A notable example is the first X-ray crystal structure of a side-on peroxido manganese(III) porphyrin complex ([Mn III -(tpp)(O 2 )] À ; tpp = meso-tetraphenylporphyrin), reported by Valentine and co-workers.[7] The second crystal structure of a monomeric side-on peroxido manganese(III) complex bearing a non-porphyrinic ligand was reported by Kitajima et al [8] However, reactivities of the peroxidomanganese(III) complexes have been rarely investigated in oxidation reactions. In the present work, we synthesized a peroxidomanganese ( …”

mentioning

confidence: 99%

“…Green platelike crystals were obtained upon addition of diethyl ether to a solution of 1 derived from the reaction of [Mn(tmc) length of 1.421 ; Tp Pr = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate; 3,5-Pr 2 pzH = 3,5-diisopropylpyrazolyl). [7,8] The peroxido ligand is symmetrically bound to a manganese ion in a side-on h 2 fashion with an Mn À O bond length of 1.884(2) . The four N atoms of the tmc ligand coordinate to the metal center, and the average MnÀN bond length is 2.265(4) , which is in good agreement with those of other monomeric peroxido Mn III complexes.…”

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confidence: 99%

[Mn(tmc)(O₂)]⁺: A Side‐On Peroxido Manganese(III) Complex Bearing a Non‐Heme Ligand

et al. 2006

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The chemistry of metal-O 2 complexes has attracted much interest in the biological and bioinorganic chemistry communities, as such species are generated as key intermediates in the activation of dioxygen by metalloenzymes and corresponding model compounds. [1] In biomimetic studies, a number of metal-O 2 adducts have been synthesized and characterized with various spectroscopic methods, and their reactivities in the oxidation of organic substrates have been extensively investigated.[2] For example, peroxidoiron(III) complexes with heme and non-heme ligands have been synthesized as chemical models of cytochrome P450 aromatase and Rieske dioxygenases, and their reactivities have been demonstrated in various nucleophilic reactions, such as aldehyde deformylation. [3, 4] Peroxidocopper(III) and -nickel-(III) complexes have been synthesized and characterized recently, but their reactivities have not been well established in oxidative nucleophilic reactions of organic substrates. [2d,e, 5] Peroxidomanganese(III) complexes are also invoked as reactive intermediates in the reactions of Mn-containing enzymes, such as manganese superoxide dismutase, catalase, and the oxygen-evolving complex of photosystem II. [6] In biomimetic studies, a number of Mn-peroxido complexes have been synthesized and characterized with a variety of spectroscopic methods including X-ray crystallography. A notable example is the first X-ray crystal structure of a side-on peroxido manganese(III) porphyrin complex ([Mn III -(tpp)(O 2 )] À ; tpp = meso-tetraphenylporphyrin), reported by Valentine and co-workers.[7] The second crystal structure of a monomeric side-on peroxido manganese(III) complex bearing a non-porphyrinic ligand was reported by Kitajima et al. [8] However, reactivities of the peroxidomanganese(III) complexes have been rarely investigated in oxidation reactions. In the present work, we synthesized a peroxidomanganese (

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A Monomeric Side-On Peroxo Manganese(III) Complex: Mn(O2)(3,5-iPr2pzH)(HB(3,5-iPr2pz)3)

Cited by 151 publications

References 1 publication

End-On and Side-On Peroxo Derivatives of Non-Heme Iron Complexes with Pentadentate Ligands: Models for Putative Intermediates in Biological Iron/Dioxygen Chemistry

End-On and Side-On Peroxo Derivatives of Non-Heme Iron Complexes with Pentadentate Ligands: Models for Putative Intermediates in Biological Iron/Dioxygen Chemistry

Variable character of O—O and M—O bonding in side-on (η ² ) 1:1 metal complexes of O ₂

[Mn(tmc)(O₂)]⁺: A Side‐On Peroxido Manganese(III) Complex Bearing a Non‐Heme Ligand

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A Monomeric Side-On Peroxo Manganese(III) Complex: Mn(O2)(3,5-iPr2pzH)(HB(3,5-iPr2pz)3)

Cited by 151 publications

References 1 publication

End-On and Side-On Peroxo Derivatives of Non-Heme Iron Complexes with Pentadentate Ligands: Models for Putative Intermediates in Biological Iron/Dioxygen Chemistry

End-On and Side-On Peroxo Derivatives of Non-Heme Iron Complexes with Pentadentate Ligands: Models for Putative Intermediates in Biological Iron/Dioxygen Chemistry

Variable character of O—O and M—O bonding in side-on (η 2 ) 1:1 metal complexes of O 2

[Mn(tmc)(O2)]+: A Side‐On Peroxido Manganese(III) Complex Bearing a Non‐Heme Ligand

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Variable character of O—O and M—O bonding in side-on (η ² ) 1:1 metal complexes of O ₂

[Mn(tmc)(O₂)]⁺: A Side‐On Peroxido Manganese(III) Complex Bearing a Non‐Heme Ligand