One-Electron Oxidized Nickel(II)−(Disalicylidene)diamine Complex:  Temperature-Dependent Tautomerism between Ni(III)−Phenolate and Ni(II)−Phenoxyl Radical States

Shimazaki, Yasuhisa; Tani, Fumito; Fukui, Kôichi; Naruta, Yoshinori; Yamauchi, Osamu

doi:10.1021/ja035806o

Cited by 192 publications

(230 citation statements)

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“…2.15 [54]. The spectrum of the one-electron oxidized Ni(Salcn) complex shows the signals at gav = 2.05, which is different from the spectrum of the characteristic Ni(III) signals [39][40][41]. The g values of these oxidized Ni complexes supported formation of the Ni(II)-phenoxyl radical complex as the main species with some contribution from Ni(II) ion, which is in good agreement with the results of the solid state characterizations in [39,40].…”

Section: Magnetic Properties Of One-electron Oxidized Metal Salen-typmentioning

confidence: 83%

“…Such a trend is also applied to the salen-type complexes, and most of the Cu(II) and group 10 metal(II) salen-type complexes exhibited two reversible redox waves in the range of 0 to 1.5 V vs NHE, due to having two phenolate moieties [29][30][31][39][40][41][42][43][44][45][46][47]. On the other hand, the metal centered one-and two-electron oxidized complexes may possibly be generated in the similar potential range.…”

Section: Scheme 1 Proposed Mechanism Of Galactose Oxidase (Go)mentioning

confidence: 92%

“…The oneelectron oxidation of Ni(Salcn) in DMF caused a color change to purple, exhibiting a new absorption band at 476 nm. In CH2Cl2, however, a different UV-vis absorption spectrum was detected with the bands at 1100, 900 and 415(shoulder) nm (Figure 12) [39]. The CH2Cl2 solution showed an EPR signal similar to that of the solid sample, indicating the Ni(II)-phenoxyl radical species, while the DMF solution of the oxidized species showed the characteristic Ni(III) signals.…”

Section: Characterization Of One-electron Oxidized M(ii) Salen-type Cmentioning

confidence: 98%

“…The present argument is focused on recent advances in the chemistry related with the synthesis, characterization, and reactivity of some of the one-electron oxidized metal(II)-salen type complexes, especially the complexes of group 10 metal(II) ions, Ni(II), Pd(II), and Pt(II) [39][40][41][42][43], and Cu(II) complexes [44][45][46][47] (Figure 3). Various useful and interesting salen-type complexes have been synthesized and characterized until now [48], and detailed electronic structural studies have recently been reported for a dinuclear chelating salen-type ligand having a catechol and a tetra(amino)tri(hydroxy)phenyl moiety [49,50].…”

Section: Scheme 1 Proposed Mechanism Of Galactose Oxidase (Go)mentioning

confidence: 99%

“…The small potential differences are due to the substitution of the phenolate moiety and the ligand structure. However, there are some different electronic structures among the one-electron oxidized forms of the complexes in Table 1, i.e., a M III -phenolate ground state complex, a M II -phenoxyl radical where the radical electron is fully delocalized on two phenolate moieties, a relatively localized M II (phenolate)(phenoxyl) complex, and a M II (dinitrogen ligand radical)(phenolate)2 species [39][40][41][42][43][44][45][46][47]. The similarity of the potentials indicates that formation of all of the oxidized species is due to a simple electron transfer without significant structural changes.…”

Section: Scheme 1 Proposed Mechanism Of Galactose Oxidase (Go)mentioning

confidence: 99%

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Oxidation Chemistry of Metal(II) Salen-Type Complexes

Shimazaki¹

2013

Electrochemistry

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Section: Magnetic Properties Of One-electron Oxidized Metal Salen-typmentioning

confidence: 83%

Section: Scheme 1 Proposed Mechanism Of Galactose Oxidase (Go)mentioning

confidence: 92%

Section: Characterization Of One-electron Oxidized M(ii) Salen-type Cmentioning

confidence: 98%

Section: Scheme 1 Proposed Mechanism Of Galactose Oxidase (Go)mentioning

confidence: 99%

Section: Scheme 1 Proposed Mechanism Of Galactose Oxidase (Go)mentioning

confidence: 99%

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Oxidation Chemistry of Metal(II) Salen-Type Complexes

Shimazaki¹

2013

Electrochemistry

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Metal Coordinated Phenoxyl Radicals

Thomas

2010

Stable Radicals

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The term "phenoxyl" radical was first introduced in 1914 by Pummerer 1 to designate species involved in the oxidation of naphthols and phenanthroles. It was not until the 1960s that the existence of phenoxyls was demonstrated by Electron Paramagnetic Resonance (EPR). The term "stable" is commonly used to designate radicals such as nitroxides, trityls, and so on. Although the term "stable" had been associated with some phenoxyl radicals in 1967, 2 it must be realized that phenoxyl radicals exhibiting stabilities comparable to those of nitroxides were rather rare at this time. During the 1970s, Reichard et al . 3 demonstrated that radicals related to phenoxyls could also arise from mono-electronic oxidation of the phenolic side chain of tyrosines in some proteins, and thus could be involved in biological processes. The new term "tyrosyl" was then introduced to designate these residues, and many other biological systems involving such radicals have been described. 4,5 One of the more important recent advances in tyrosyl radical history was achieved in the 1990s with the characterization of the galactose oxidase (GO) active site. 6 -8 For the first time it was demonstrated that tyrosyls could exist coordinated to a metal ion. To better understand this association, chemists have subsequently developed many complexes involving coordinated phenoxyl radicals. 9 -13 Elucidation of the properties of coordination compounds involving redox active ligands, especially those involving sterically hindered phenolates, is one of the most recent and fascinating topics of interest in bioinorganic chemistry. The challenge in this kind of chemistry is the right description of the electronic structure of the M n+ -OPh entity (where OPh represents a phenolate group) once it has been oxidized by one electron. In principle, either the M (n+1)+ -OPh, that is the oxidation is metal based, or the M n+ -• OPh form, that is the oxidation is ligand based, could be obtained. The right description is thus not obvious and, as will be shown below, it strongly depends on the nature of the metal ion, the denticity of the ligand, the substituents of the phenolate precursor and even the temperature. Coordination is also found to improve the radical stability, and exerts an extraordinary control on their magnetic properties and reactivity (regio-and stereoselective oxidations are promoted by a radical). Stable Radicals: Fundamentals and Applied Aspects of Odd-Electron CompoundsEdited by Robin G. Hicks

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Phenoxyl Radical–Metal Complexes

Shimazaki

2012

Patai's Chemistry of Functional Groups

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The redox chemistry of metal complexes has been widely developed in recent years, affording deep insights into the reaction mechanisms for many useful homogeneous catalytic reactions and enzymatic reactions at the active site of metalloenzymes. During the course of the studies, a large number of novel complexes have been born and well characterized; species formed as a result of redox reactions such as organic and other radicals are especially important not only in inorganic but also in other fields of chemistry. In the early 1990s, it was discovered that the phenoxyl radical can bind with a metal ion as an open‐shell ligand performing a role of an organic radical cofactor in a metalloenzyme, galactose oxidase (GO), which is a single copper oxidase catalyzing two‐electron oxidation of the primary alcohol to the aldehyde. After the discovery of the radical coordination in the active center, many metal?phenoxyl radical complexes have been synthesized and characterized for understanding the detailed mechanism of GO and the properties of the metal complexes with the coordinated phenoxyl radical. This chapter focuses on the synthesis, structures, properties and reactivity of almost all of the metal‐phenoxyl radical complexes. The first few sections describe historical aspects and general properties of the metal‐phenoxyl radical complexes, including a comparison of their properties with those of the high valent metal‐phenolate complexes which are iso‐electronic with the phenoxyl radical complexes. In later sections, the properties of the metal coordinated phenoxyl radical are described in the order of the periodic table.

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One-Electron Oxidized Nickel(II)−(Disalicylidene)diamine Complex: Temperature-Dependent Tautomerism between Ni(III)−Phenolate and Ni(II)−Phenoxyl Radical States

Abstract: The one-electron oxidized species of a Ni(II)-phenolate complex has been shown to be in the Ni(II)-phenoxyl radical state at room temperature and the Ni(III)-phenolate state at < -120 degrees C, indicating that the oxidation state is temperature dependent.

Cited by 192 publications

References 28 publications

Oxidation Chemistry of Metal(II) Salen-Type Complexes

Oxidation Chemistry of Metal(II) Salen-Type Complexes

Metal Coordinated Phenoxyl Radicals

Phenoxyl Radical–Metal Complexes

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