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Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.inorgchem.1c00475

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.inorgchem.0c03469

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Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

DOI： 10.1246/BCSJ.20190291

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>A mononuclear copper complex bearing a ‘histidine brace’ is synthesised and characterised as an active-site model of mononuclear copper monooxygenases such as lytic polysaccharide monooxygenases (LPMOs) and particulate methane monooxygenase (pMMO).</p>

DOI： 10.1039/d0cc01392g

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/chem.201902669

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Much recent attention has been focused on the structure and reactivity of transition-metal superoxide complexes, among which mononuclear copper(II)-superoxide complexes are recognized as key reactive intermediates in many biological and abiological dioxygen-activation processes. So far, several types of copper(II)-superoxide complexes have been developed and their electrophilic reactivity has been explored in C–H and O–H bond activation reactions. Here we demonstrate that a mononuclear copper(II)-(end-on)superoxide complex supported by a N-[(2-pyridyl)methyl]-1,5-diazacyclooctane tridentate ligand can induce catalytic C–C bond formation reaction between carbonyl compounds (substrate) and the solvent molecule (acetone), giving β-hydroxy-ketones (aldol). Kinetic and spectroscopic studies at low temperature as well as DFT calculation studies support a nucleophilic reactivity of the superoxide species toward the carbonyl compounds, providing new insights into the reactivity of transition-metal superoxide species not only in biological oxidation reactions but also in synthetic organic chemistry.

DOI： 10.1038/s42004-019-0115-6

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/anie.201901608

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/ange.201802779

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/ejic.201800436

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley-VCH Verlag  

A tyrosinase-mediated arylation towards a variety of different building blocks is presented. Utilizing phenol or simple substituted phenols, the corresponding quinones are synthesized in a two-step procedure by an enzyme-catalyzed oxidation (tyrosinase from Aspergillus oryzae). The activated intermediates undergo a 1,4-addition with selected β-dicarbonyl compounds. Starting from phenol, yields of isolated product for the hydroxylation-oxidation-arylation sequence range from 43–77 %, whereas substituted acceptors provided 9–55 %, only. Different substitution patterns on phenol revealed that electron donating functionalities are preferentially accepted to electron withdrawing ones, whereas ortho-substituted phenols are not accepted at all.

DOI： 10.1002/ejoc.201800188

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DOI： 10.1002/zaac.201800083

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Copper(I) and copper(II) complexes supported by a bulky tetradentate N4 ligand, [CuI(TIPT3tren)(CH3CN)]ClO4 (1) and [CuII(TIPT3tren)Cl]BF4 (2), were synthesized and characterized, where TIPT is 2,2′′,6,6′′-tetraisopropyl-1,3′:5′,1′′-terphenyl and tren is tris(2-aminoethyl)amine. The copper(II) chloride complex 2 exhibits a trigonal-bipyramidal structure, as usually observed for the tren ligand system, in which the chloride ligand occupies an axial position and is encapsulated in an isolated cavity consisting of three TIPT substituents. Such a trigonal-bipyramidal structure is stabilized in acetone, in which hydrogen-bonding interactions between the anilino N–H groups and the oxygen atom of the acetone molecules, entrapped in the hydrophobic clefts between the TIPT substituents, play an important role. The reaction of copper(I) complex 1 and O2 in an acetone-containing solvent at –110 °C gave end-on copper(II) superoxide complex 3 together with putative side-on copper(III) peroxide complex 4, as was evident from detailed studies by variable-temperature UV/Vis, resonance Raman, and 1H and 2H NMR spectroscopy. The formation of 3 and 4 was also validated by DFT calculations.

DOI： 10.1002/ejic.201800029

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

A bis(μ-oxido)dinickel(III) complex was synthesized and characterized by single crystal X-ray diffraction, resonance Raman, and ESI-mass measurements. Magnetic susceptibility measurements by SQUID and EPR spectroscopy reveal that the complex has a triplet ground state, which is unprecedented for high-valent metal (M) complexes with [M2(μ-O)2] diamond core. DFT studies indicate ferromagnetic coupling of the nickel(III) centers. The complex exhibits hydrogen abstraction reactivity and oxygenation reactivity toward external substrates.

DOI： 10.1002/anie.201802779

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DOI： 10.1016/j.ica.2017.09.017

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

This paper presents catalytic amination reaction of alkyl group with tosyl azide in the presence of Rh(III) catalyst supported by a ligand with redox ability (Redox-noninosent ligand). In the former report of rhodium complex with aniline ligands on the both axial positions, the very slow ligand exchange shackles the catalytic reaction. The presented rhodium complex becomes mono anion with chloride ligand on the axial position, and ligand exchange on the axial position was largely accelerated. From the reaction system, My fujita isolated another complex with a partially decomposed ligand with radical character.

DOI： 10.1021/acs.inorgchem.8b00289

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier S.A.  

To discuss the relationship between the structure and the oxygen reduction reaction (ORR) activity of pyridylmethylamine copper complexes containing carboxy groups, CuII complexes of a N,N-bis(2-pyridylmethyl)phenylmethylamine tridentate ligand (L1) or its carboxy derivatives (2-{[bis(2-pyridylmethyl)amino]methyl}benzoic acid: L2, 3-{[bis(2-pyridylmethyl)amino]methyl}benzoic acid: L3, or 4-{[bis(2-pyridylmethyl)amino]methyl}benzoic acid: L4) were synthesized and characterized. The X-ray crystal structures of mononuclear CuII complexes ligated by L2–L4 were obtained as dichloride complexes, and a crystallographic analysis revealed that all of them have a square pyramidal geometry. The ESR spectroscopy showed that these complexes also had a square pyramidal geometry in a neutral aqueous solution. Cyclic voltammetry analysis in a neutral aqueous solution suggested that only the CuII complex of L2 shows intramolecular interaction between the carboxy group and copper ion in the aqueous solution. The introduction of a carboxy group dramatically increased the amount of the CuII complexes adsorbed on carbon black, which can slightly increase the ORR activity.

DOI： 10.1016/j.ica.2017.10.031

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Inc.  

Copper(II) complexes supported by N3-tridentate ligands, consisting of a rigid cyclic diamine (8-membered cyclic-diamine
L8 or 7-membered cyclic-diamine
L7) and a 2-(2-pyridyl)ethyl (-CH2CH2Py) group, were synthesized and structurally characterized. Reaction of the copper(II) complexes and cumene hydroperoxide (CmOOH) in the presence of triethylamine in CH3CN gave the corresponding cumylperoxide complexes L8CuIIOOCm and L7CuIIOOCm. The UV–vis and EPR spectra suggested that L8CuIIOOCm takes a tetrahedrally distorted structure, whereas L7CuIIOOCm has a planar geometry in solution. Resonance Raman spectra of these alkylperoxide complexes indicated that the O-O stretching vibration energy of L8CuIIOOCm (νO–O = 878 cm− 1) is somewhat lower than that of L7CuIIOOCm (νO–O = 881 cm− 1). Such a difference in O-O bond strength is reflected to the reactivity difference of these two alkylperoxide complexes. Namely, the reactivity L8CuIIOOCm toward CHD (1,4-cyclohexadiene) as well as solvent molecule (CH3CN) is higher than that of L7CuIIOOCm due to the weaker O-O bond of the former complex as compared to that of the latter complex. Geometric effects on the reactivity induced by the supporting ligands are discussed.

DOI： 10.1016/j.jinorgbio.2017.08.016

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A new tridentate N-3 ligand (TMG(3)tach) consisting of cis,cis-1,3,5-triaminocydohexane (tach) and three N,N,N',N'-tetramethylguanidino (TMG) groups has been developed to prepare copper complexes with a tetrahedral geometry and a labile coordination site. Treatment of the ligand with (CuX2)-X-II (X = Cl and Br) gave copper(II)-halide complexes, [Cu-II(TMG(3)tach)Cl](+) (2(Cl)) and [Cu-II(TMG(3)tach)Br](+) (2(Br)), the structures of which have been determined by X-ray crystallographic analysis. The complexes exhibit a four-coordinate structure with C-3 symmetry, where the labile halide ligand (X) occupies a position on the trigonal axis. 2(Br) was converted to a methoxido-copper(II) complex [Cu-II(TMG(3)tach)(OMe)]-(OTO (2(OMe)), also having a similar four-coordinate geometry, by treating it with an equimolar amount of tetrabutylammonium hydroxide in methanol. The methoxido-complex 2(OMe) was further converted to the corresponding phenolato-copper(II) (2(Ar)) and thiophenolato-copper(II) (2(SAr)) complexes by ligand exchange reactions with the neutral phenol and thiophenol derivatives, respectively. The electronic structures of the copper(II) complexes with different axial ligands are discussed on the basis of EPR spectroscopy and DFT calculations.

DOI： 10.1021/acs.inorgchem.7b01154

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

A stable nickel(II)-aminoxyl radical complex was generated by the reaction of a nickel(II) complex supported by a tren ligand (tris (2-aminoethyl)amine) having bulky m-terphenyl substituents (TIPT: 3,5-bis(2,6-diisopropylphenyl)phenyl) and m-CPBA (m-chloroper-oxybenzoic acid). The formation mechanism of the nickel(II)-aminoxyl radical complex was examined.

DOI： 10.1039/c7dt01789h

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Werner type six-coordinate rhodium((III)) complexes coordinated by a planar trianionic ligand and two axial aniline ligands are synthesised. The trianionic ligand behaves as a redox-active ligand to form a ligand radical species upon one-electron oxidation of the complex. The rhodium((III)) complexes catalyse C-H amination of external substrates such as xanthene with tosylazide as the nitrene source. DFT-calculation and kinetic deuterium isotope effects indicate that a di-radical rhodium((III)) complex formed by one-electron transfer from the redox-active ligand to the nitrene group works as a reactive intermediate to induce aliphatic C-H activation.

DOI： 10.1039/c7cc01840a

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Language：English   Publisher：ROYAL SOC CHEMISTRY  

DOI： 10.1039/c7cc90176c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Thermally stable TM1459 cupin superfamily protein from Thermotoga maritima was repurposed as an osmium (Os) peroxygenase by metal-substitution strategy employing the metal-binding promiscuity. This novel artificial metalloenzyme bears a datively bound Os ion supported by the 4-histidine motif. The well-defined Os center is responsible for not only the catalytic activity but also the thermodynamic stability of the protein folding, leading to the robust biocatalyst (T-m approximate to 120 degrees C). The spectroscopic analysis and atomic resolution X-ray crystal structures of Os-bound TM1459 revealed two types of donor sets to Os center with octahedral coordination geometry. One includes trans-dioxide, OH, and mer-three histidine imidazoles (O3N3 donor set), whereas another one has four histidine imidazoles plus OH and water molecule in a cis position (O2N4 donor set). The Os-bound TM1459 having the latter donor set (O2N4 donor set) was evaluated as a peroxygenase, which was able to catalyze cis-dihydroxylation of several alkenes efficiently. With the low catalyst loading (0.01% mol), up to 9100 turnover number was achieved for the dihydroxylation of 2-methoxy-6-vinyl-naphthalene (50 mM) using an equivalent of H2O2 as oxidant at 70 degrees C for 12 h. When octene isomers were dihydroxylated in a preparative scale for 5 h (2% mol cat.), the terminal alkene octene isomers was converted to the corresponding diols in a higher yield as compared with the internal alkenes. The result indicates that the protein scaffold can control the regioselectivity by the steric hindrance. This protein scaffold enhances the efficiency of the reaction by suppressing disproportionation of H2O2 on Os reaction center. Moreover, upon a simple site-directed mutagenesis, the catalytic activity was enhanced by about 3-fold, indicating that Os-TM1459 is evolvable nascent osmium peroxygenase.

DOI： 10.1021/jacs.7b00675

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A new Ce-IV complex [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)(2)-2-O)(2)}(NO3)(2)] (1), bearing a dianionic pentadentate ligand with an N3O2 donor set, has been prepared by treating (NH4)(2)Ce(NO3)(6) with the sodium salt of ligand L1. Complex 1 in the presence of TEMPO and 4 angstrom molecular sieves (MS4A) has been found to serve as a catalyst for the oxidation of arylmethanols using dioxygen as an oxidant. We propose an oxidation mechanism based on the isolation and reactivity study of a trivalent cerium complex [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)(2)-2-O)(2)}(NO3)(THF)] (2), its side-on -O-2 adduct [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)(2)-2-O)(2)}(NO3)](2)(-(2):(2)-O-2) (3), and the hydroxo-bridged Ce-IV complex [Ce{NH(CH2CH2N=CHC6H2-3,5-(tBu)(2)-2-O)(2)}(NO3)](2)(-OH)(2) (4) as key intermediates during the catalytic cycle. Complex 2 was synthesized by reduction of 1 with 2,5-dimethyl-1,4-bis(trimethylsilyl)-1,4-diazacyclohexadiene. Bubbling O-2 into a solution of 2 resulted in formation of the peroxo complex 3. This provides the first direct evidence for cerium-catalyzed oxidation of alcohols under an O-2 atmosphere.

DOI： 10.1002/chem.201503846

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Language：Japanese  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The reaction of [Cu-I(TIPT(3)tren) (CH3CN)]ClO4 (1) and cumene hydroperoxide (C6H5C-(CH3)(2)OOH, ROOH) at-60 degrees C in CH2Cl2 gave a Cu-II- alkylperoxide/anilino radical complex 2, the formation of which was confirmed by UV vis, resonance Raman, EPR, and CSI-mass spectroscopy. The mechanism of formation of 2, as well as its reactivity, has been explored.

DOI： 10.1021/jacs.5b04104

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Selective hydroxylation of benzene to phenol has been achieved using H2O2 in the presence Of a catalytic amount of the nickel complex [Ni-II(tepa)](2+) (2) (tepa = tris[2-(pyridin-2-yl)ethyl]amine) at 60 degrees C. The maximum yield of phenol was 21% based on benzene without the formation of quinone or diphenol. In an endurance test of the catalyst, complex 2 showed a turnover number (TON) of 749, which is the highest value reported to date for molecular catalysts in benzene hydroxylation with H2O2. When toluene was employed as a substrate instead of benzene, cresol was obtained as the major product with 90% selectivity. When (H2O2)-O-18 was utilized as the oxidant, O-18-labeled phenol was predominantly obtained. The reaction rate for fully deuterated benzene was nearly identical to that of benzene (kinetic isotope effect = 1.0). On the basis of these results, the reaction mechanism is discussed.

DOI： 10.1021/jacs.5b01814

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Language：English   Publishing type：Part of collection (book)   Publisher：Springer Japan  

Recent studies of redox non-innocence of β-diketiminate ligands are introduced. Reduction of Yb3+ and Al3+ as well as Li+ and Be2+ complexes using strong electron-transfer reductants induces the ligand-based one- and/or two-electron reduction, whereas electron-transfer oxidation of bis(β-diketiminato)-Ni2+ complexes gives Robin and Day class III mixed-valence complexes, having an unpaired electron completely delocalized between the two ligands. Furthermore, a new trianionic tetradentate ligand is developed by introducing two phenolate moieties on the nitrogen atoms of a β-diketiminate ligand to mimic the active site of galactose oxidase. In the copper(II) complex of this ligand, oxidation reaction also takes place at the ligand moiety to provide phenoxyl–copper(II) complexes.

DOI： 10.1007/978-4-431-55357-1_42

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCI PUBL CO INC  

A new type of nickel and palladium complexes with non-innocent beta-diketiminate ligand having redox active phenol groups, 2,4-di-tert-butyl-6-(((1E, 2E)-3-((3,5-di-tert-butyl-2-hydroxyphenyl) amino)-2-nitroallylidene) amino) phenol (LH3, fully protonated form) have been developed, and the structure, physical properties, and reactivity of their one-electron and two-electron oxidized complexes, [M-II(L center dot 2-)] and [M-II(L-)](+) (M = Ni-II or Pd-II) have been examined in detail. The two-electron oxidized forms of both complexes, [M-II(L-)](+), exhibited hydrogen atom abstraction ability from 1,4-cyclohexadiene (CHD) comparable to its copper analog [Cu-II(L-)](+) (Dalton Trans. 2013; 42: 2438-2444). The one-electron oxidized form of palladium complex, [Pd-II(L center dot 2-)], was also found to oxidize CHD, whereas the nickel analog, [Ni-II(L center dot 2-)], exhibited photo-induced oxidation ability of CHD.

DOI： 10.1142/S1088424615500248

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A functionalized beta-dialdimine was prepared, bearing a 3,3-dimethylindoleninyl group at the meso-position and two N-phenolic groups. The structure contains three labile protons, which can be lost or migrate through tautomerism to provide an N2O2 coordination core. A number of divalent and trivalent metal ions (Cu-II, Ni-II, Co-II/III, and Mn-III) were accommodated inside the core, forming a series of intensely colored products consisting of a tricyclic MN2O2 chelate. In the resulting divalent metal complexes, the dialdimine ligand is deprotonated only at the two phenolic oxygen atoms and is thus dianionic, whereas in the trivalent metal complexes, the dialdiminato ligand is triply deprotonated. The copper and nickel complexes adopt square-planar geometries, whereas in the trivalent cobalt and manganese complexes, two neutral ancillary ligands complete an octahedral geometry around the metal center. In each case, the denticity of the diimino-diiminato ligand is four. The electrochemical oxidation of the copper and nickel complexes was studied by cyclic voltammetry.

DOI： 10.1002/ejic.201402745

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Copper(I) complexes supported by a series of N-3-tridentate ligands bearing a rigid cyclic diamine framework such as 1,5-diazacyclooctane (L8, eight-membered ring), 1,4-diazacyclohexane (L7, seven-membered ring), or 1,4-diazacyclohexane (L6, six-membered ring) with a common 2-(2-pyridyl)ethyl side arm were synthesized and their reactivity toward O-2 were compared. The copper(I) complex of L8 preferentially provided a mononuclear copper(II) end-on superoxide complex S as reported previously [Itoh, S., et al. J. Am. Chem. Soc. 2009, 131, 2788-2789], whereas a copper(I) complex of L7 gave a bis(mu-oxido)dicopper(111) complex O at a low temperature (-85 degrees C) in acetone. On the other hand, no such active-oxygen complex was detected in the oxygenation reaction of the copper(I) complex of L6 under the same conditions. In addition, O-2-reactivity of the copper(I) complex supported by an acyclic version of the tridentate ligand (LA, PyCH2CH2N(CH3)CH2CH2CH2N(CH3)(2); Py = 2-pyridyl) was examined to obtain a mixture of a (mu-eta(2):eta(2)-peroxido)dicopper(II) complex P-s and a bis(mu-oxido)dicopper(III) complex O. Careful inspection of the crystal structures of copper(I) and copper(II) complexes and the redox potentials of copper(I) complexes has revealed important geometric effects of the supporting ligands on controlling nudearity of the generated copper active-oxygen complexes.

DOI： 10.1021/ic501461n

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Nickel complexes of a series of beta-diketiminate ligands (L-R(-), deprotonated form of 2-substituted N-[3-(phenylamino)allylidene]aniline derivatives (LH)-L-R, R = Me, H, Br, CN, and NO2) have been synthesized and structurally characterized. One-electron oxidation of the neutral complexes [Ni-II(L-R(-))(2)] by AgSbF6 or [Ru-III(bpy)(3)](PF6)(3) (bpy = 2,2'-bipyridine) gave the corresponding metastable cationic complexes, which exhibit an EPR spectrum due to a doublet species (S = 1/2) and a characteristic absorption band in near IR region ascribable to a ligand-to-ligand intervalence charge-transfer (LLIVCT) transition. DFT calculations have indicated that the divalent oxidation state of nickel ion (Ni-II) is retained, whereas one of the beta-diketiminate ligands is oxidized to give formally a mixed-valence complex, [Ni-II(L-R(-))(L-R(center dot))](+). Thus, the doublet spin state of the oxidized cationic complex can be explained by taking account of the antiferromagnetic interaction between the high-spin nickel(11) ion (S = I) and the organic radical (S = 1/2) of supporting ligand. A single-crystal structure of one of the cationic complexes (R = H) has been successfully determined to show that both ligands in the cationic complex are structurally equivalent. On the basis of theoretical analysis of the LLIVCT band and DFT calculations as well as the crystal structure, the mixed-valence complexes have been assigned to Robin Day class III species, where the radical spin is equally delocalized between the two ligands to give the cationic complex, which is best described as [Ni-II(L-R(0.5 center dot-))(2)](+). One-electron reduction of the neutral complexes with decamethylcobaltocene gave the anionic complexes when the ligand has the electron-withdrawing substituent (R = CN, NO2, Br). The generated anionic complexes exhibited EPR spectra due to a doublet species (S = 1/2) but showed no LLIVCT band in the near-IR region. Thus, the reduced complexes are best described as the d(9) nickel(I) complexes supported by two anionic beta-diketiminate ligands, [Ni-1(L-R(-))(2)](-). This conclusion was also supported by DFT calculations. Substituent effects on the electronic structures of the three oxidation states (neutral, cationic, and anionic) of the complexes are systematically evaluated on the basis of DFT calculations.

DOI： 10.1021/ic5006693

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Oxidative C-H bond cleavage of toluene derivatives and sulfoxidation of thioanisole derivatives by a nonheme iron(IV)-oxo complex, [(N4Py)Fe-IV(O)](2+) (N4Py = N,N-bis (2-pyridylmethyl)-N-bis (2-pyridyl)methylamine), were remarkably enhanced by the presence of triflic acid (HOTf) and Sc(OTf)(3) in acetonitrile at 298 K. All the logarithms of the observed second-order rate constants of both the oxidative C-H bond cleavage and sulfoxidation reactions exhibit remarkably unified correlations with the driving forces of proton-coupled electron transfer (PCET) and metal ion-coupled electron transfer (MCET) in light of the Marcus theory of electron transfer when the differences in the formation constants of precursor complexes between PCET and MCET were taken into account, respectively. Thus, the mechanisms of both the oxidative C-H bond cleavage of toluene derivatives and sulfoxidation of thioanisole derivatives by [(N4Py)Fe-IV(O)](2+) in the presence of HOTf and Sc(OTf)(3) have been unified as the rate-determining electron transfer, which is coupled with binding of [(N4Py)FeIV(O)](2+) by proton (PCET) and Sc(OTf)(3) (MCET). There was no deuterium kinetic isotope effect (KIE) on the oxidative C-H bond cleavage of toluene via the PCET pathway, whereas a large KIE value was observed with Sc(OTf)(3), which exhibited no acceleration of the oxidative C-H bond cleavage of toluene. When HOTf was replaced by DOTf, an inverse KIE (0.4) was observed for PCET from both toluene and [Ru-II(bpy)(3)](2+) (bpy =2,2'-bipyridine) to [(N4Py)Fe-IV(O)](2+). The PCET and MCET reactivities of [(N4Py)FeIV(O)](2+) with Bronsted acids and various metal triflates have also been unified as a single correlation with a quantitative measure of the Lewis acidity.

DOI： 10.1021/ic403124u

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Rates of formation of a non-heme iron(IV)-oxo complex, [Fe-IV(O)(N4Py)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), via electron-transfer oxidation of [Fe-III(OH)(N4Py)](2+) in acetonitrile (MeCN) containing H2O (0.56 M) were accelerated as much as 390-fold by addition of proton acceptors such as CF3COO-, TsO- (p-MeC6H4SO3-), NsO(-) (o-NO2C6H4SO3-), DNsO(-) (2,4-(NO2)(2)C6H3SO3-), and TfO- (CF3SO3-). The acceleration effect of proton acceptors increases with increasing basicity of the proton acceptors. The one-electron oxidation potential of [Fe-III(OH)(N4Py)](2+) was shifted from 1.24 to 0.96 V vs SCE in the presence of TsO- (10 mM). The electron-transfer oxidation of Fe-III-OH complex was coupled with the deprotonation process by proton acceptors in which deuterium kinetic isotope effects were observed when H2O was replaced by D2O.

DOI： 10.1021/ic302573x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Evidence of an autocatalytic radical chain pathway has been reported in formation of a non-heme iron(IV)-oxo complex by oxidation of an iron(II) complex with dioxygen and isopropanol in acetonitrile at 298 K. The radical chain reaction is initiated by hydrogen abstraction from isopropanol by the iron(IV)-oxo complex.

DOI： 10.1039/c3cc38727e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The rate of oxidation of 2,5-dimethoxybenzyl alcohol (2,5-(MeO)(2)C6H3CH2OH) by [Fe-IV(O)(N4Py)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)-methylamine) was enhanced significantly in the presence of Sc(OTf)(3) (OTf- = trifluoromethanesulfonate) in acetonitrile (e.g., 120-fold acceleration in the presence of Sc3+). Such a remarkable enhancement of the reactivity of [Fe-IV(O)(N4Py)](2+) in the presence of Sc3+ was accompanied by the disappearance of a kinetic deuterium isotope effect. The radical cation of 2,5-(MeO)(2)C6H3CH2OH was detected in the course of the reaction in the presence of Sc3+. The dimerized alcohol and aldehyde were also produced in addition to the monomer aldehyde in the presence of Sc3+. These results indicate that the reaction mechanism is changed from one-step hydrogen atom transfer (HAT) from 2,5-(MeO)(2)C6H3CH2OH to [Fe-IV(O)(N4Py)](2+) in the absence of Sc3+ to stepwise Sc3+-coupled electron transfer, followed by proton transfer in the presence of Sc3+. In contrast, neither acceleration of the rate nor the disappearance of the kinetic deuterium isotope effect was observed in the oxidation of benzyl alcohol (C6H5CH2OH) by [Fe-IV(O)(N4Py)(2+) in the presence of Sc(OTf)(3). Moreover, the rate constants determined in the oxidation of various benzyl alcohol derivatives by [Fe-IV(O)(N4Py)](2+) in the presence of Sc(OTf)(3) (10 mM) were compared with those of Sc3+-coupled electron transfer from one-electron reductants to [Fe-IV(O)(N4Py)](2+) at the same driving force of electron transfer. This comparison revealed that the borderline of the change in the mechanism from HAT to stepwise Sc3+-coupled electron transfer and proton transfer is dependent on the one-electron oxidation potential of benzyl alcohol derivatives (ca. 1.7 V vs SCE).

DOI： 10.1021/ic3016723

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Publisher：Journal of the American Chemical Society  

Sulfoxidation of thioanisoles by a non-heme iron(IV)-oxo complex, [(N4Py)Fe IV(O)] 2+ (N4Py = N,N-bis(2-pyridylmethyl)-N- bis(2-pyridyl)methylamine), was remarkably enhanced by perchloric acid (70% HClO 4). The observed second-order rate constant (k obs) of sulfoxidation of thioaniosoles by [(N4Py)Fe IV(O)] 2+ increases linearly with increasing concentration of HClO 4 (70%) in acetonitrile (MeCN)at 298 K. In contrast to sulfoxidation of thioanisoles by [(N4Py)Fe IV(O)] 2+, the observed second-order rate constant (k et) of electron transfer from one-electron reductants such as [Fe II(Me 2bpy) 3] 2+ (Me 2bpy = 4,4-dimehtyl-2,2′-bipyridine) to [(N4Py)Fe IV(O)] 2+ increases with increasing concentration of HClO 4, exhibiting second-order dependence on HClO 4 concentration. This indicates that the proton-coupled electron transfer (PCET) involves two protons associated with electron transfer from [Fe II(Me 2bpy) 3] 2+ to [(N4Py)Fe IV(O)] 2+ to yield [Fe III(Me 2bpy) 3] 3+ and [(N4Py)Fe III(OH 2)] 3+. The one-electron reduction potential (E red) of [(N4Py)Fe IV(O)] 2+ in the presence of 10 mM HClO 4 (70%) in MeCN is determined to be 1.43 V vs SCE. A plot of E red vs log[HClO 4] also indicates involvement of two protons in the PCET reduction of [(N4Py)Fe IV(O)] 2+. The PCET driving force dependence of log k et is fitted in light of the Marcus theory of outer-sphere electron transfer to afford the reorganization of PCET (λ = 2.74 eV). The comparison of the k obs values of acid-promoted sulfoxidation of thioanisoles by [(N4Py)Fe IV(O)] 2+ with the k et values of PCET from one-electron reductants to [(N4Py)Fe IV(O)] 2+ at the same PCET driving force reveals that the acid-promoted sulfoxidation proceeds by one-step oxygen atom transfer from [(N4Py)Fe IV(O)] 2+ to thioanisoles rather than outer-sphere PCET. © 2012 American Chemical Society.

DOI： 10.1021/ja211641s

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Sulfoxidation of thioanisoles by a non-heme iron(IV)-oxo complex, [(N4Py)Fe-IV(O)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), was remarkably enhanced by perchloric acid (70% HClO4). The observed second-order rate constant (k(obs)) of sulfoxidation of thioaniosoles by [(N4Py)Fe-IV(O)](2+) increases linearly with increasing concentration of HClO4 (70%) in acetonitrile (MeCN) at 298 K In contrast to sulfoxidation of thioanisoles by [(N4Py)-Fe-IV(O)](2+), the observed second-order rate constant (k(et)) of electron transfer from one-electron reductants such as [Fe-II(Me(2)bpy)(3)](2+) (Me(2)bpy = 4,4-dimehty1-2,2'-bipyridine) to [(N4Py)Fe-IV(O)](2+) increases with increasing concentration of HClO4, exhibiting second-order dependence on HClO4 concentration. This indicates that the proton-coupled electron transfer (PCET) involves two protons associated with electron transfer from [Fe-II(Me(2)bpy)(3)](2+) to [(N4Py)Fe-IV(O)](2+) to yield [Fe-III(Me(2)bpy)(3)](3+) and [(N4Py)Fe-III(OH2)](3+). The one-electron reduction potential (E-red) of [(N4Py)Fe-IV(O)](2+) in the presence of 10 mM HClO4 (70%) in MeCN is determined to be 1.43 V vs SCE. A plot of E-red VS log[HClO4] also indicates involvement of two protons in the PCET reduction of [(N4Py)Fe-IV(O)](2+). The PCET driving force dependence of log k(et) is fitted in light of the Marcus theory of outer-sphere electron transfer to afford the reorganization of PCET (lambda = 2.74 eV). The comparison of the kobs values of acid-promoted sulfoxidation of thioanisoles by [(N4Py)Fe-IV(O)](2+) with the k values of PCET from one-electron reductants to [(N4Py)Fe-IV(O)](2+) at the same PCET driving force reveals that the acid-promoted sulfoxidation proceeds by one-step oxygen atom transfer from [(N4Py)Fe-IV(O)](2+) to thioanisoles rather than outer-sphere PCET.

DOI： 10.1021/ja211941s

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Electron-transfer properties of a nonheme Mn(IV)-oxo complex, [(Bn-TPEN)Mn-IV(O)](2+), reveals that Mn(IV)-oxo complex acts as a stronger one-electron oxidant than the Fe(IV)-oxo analogue. As a result, an electron transfer process in N-dealkylation has been detected by a transient radical cation intermediate, para-Me-DMA(.+), in the oxidation of para-Me-DMA by [(Bn-TPEN)Mn-IV(O)](2+).

DOI： 10.1039/c2cc36291k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Redox inactive metal ions acting as Lewis acids can control electron transfer from electron donors (D) to electron acceptors (A) by binding to radical anions of electron acceptors which act as Lewis bases. Such electron transfer is defined as metal ion-coupled electron transfer (MCET). Mechanisms of metal ion-coupled electron transfer are classified mainly into two pathways, i.e., metal ion binding to electron acceptors followed by electron transfer (MB/ET) and electron transfer followed by metal ion binding to the resulting radical anions of electron acceptors (ET/MB). In the former case, electron transfer and the stronger binding of metal ions to the radical anions occur in a concerted manner. Examples are shown in each case to clarify the factors to control MCET reactions in both thermal and photoinduced electron-transfer reactions including back electron-transfer reactions.

DOI： 10.1039/c2cp40459a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Oxidative dimerization of N,N-dimethylaniline (DMA) occurs with a nonheme iron(IV)-oxo complex, [Fe(IV)(O)(N4Py)](2+) (N4Py=N,N-bis(2-pyridylmethyl)-N-bis-(2-pyridyl)methylamine), to yield the corresponding dimer, tetramethylbenzidine (TMB), in acetonitrile. The rate of the oxidative dimerization of DMA by [Fe(IV)(O)(N4Py)](2+) is markedly enhanced by the presence of scandium triflate, Sc(OTf)(3) (OTf = CF(3)SO(3)(-)), when TMB is further oxidized to the radical cation (TMB(center dot+)). In contrast, we have observed the oxidative N-demethylation with para-substituted DMA substrates, since the position of the C-C bond formation to yield the dimer is blocked. The rate of the oxidative N-demethylation of para-substituted DMA by [Fe(IV)(O)(N4Py)](2+) is also markedly enhanced by the presence of Sc(OTf)(3). In the case of para-substituted DMA derivatives with electron-donating substituents, radical cations of DMA derivatives are initially formed by Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), giving demethylated products. Binding of Sc(3+) to [Fe(IV)(O)(N4Py)](2+) enhances the Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), whereas binding of Sc(3+) to DMA derivatives retards the electron-transfer reaction. The complicated kinetics of the Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+) are analyzed by competition between binding of Sc(3+) to DMA derivatives and to [Fe(IV)(O)(N4Py)](2+). The binding constants of Sc(3+) to DMA derivatives increase with the increase of the electron-donating ability of the para-substituent. The rate constants of Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), which are estimated from the binding constants of Sc(3+) to DMA derivatives, agree well with those predicted from the driving force dependence of the rate constants of Sc(3+) ion-coupled electron transfer from one-electron reductants to [Fe(IV)(O)(N4Py)](2+). Thus, oxidative dimerization of DMA and N-demethylation of para-substituted DMA derivatives proceed via Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+).

DOI： 10.1021/ic201545a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The mechanism of sulfoxidation of thioaniosoles by a non-heme iron(IV)-oxo complex is switched from direct oxygen transfer to metal ion-coupled electron transfer by the presence of Sc(3+). The switch in the sulfoxidation mechanism is dependent on the one-electron oxidation potentials of thioanisoles. The rate of sulfoxidation is accelerated as much as 10(2)-fold by the addition of Sc(3+).

DOI： 10.1021/ja200901n

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Rates of electron transfer from a series of one-electron reductants to a nonheme oxoiron(IV) complex, [(N4Py)Fe-IV(O)](2+), are enhanced as much as 10(8)-fold by addition of metal ions such as Sc3+, Zn2+, Mg2+, and Ca2+; the metal ion effect follows the Lewis acidity of metal ions. The one-electron reduction potential of [(N4Py)Fe-IV(O)](2+) is shifted to a positive direction by 0.84 V in the presence of Sc3+ ion (0.20 M).

DOI： 10.1021/ja109056x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Critical biological electron-transfer processes involving high-valent oxometal chemistry occur widely, for example in haem proteins [oxoiron(IV); Fe-IV(O)] and in photosystem II. Photosystem II involves Ca2+ as well as high-valent oxomanganese cluster species. However, there is no example of an interaction between metal ions and oxoiron(IV) complexes. Here, we report new findings concerning the binding of the redox-inactive metal ions Ca2+ and Sc3+ to a non-haem oxoiron(IV) complex, [(TMC)Fe-IV(O)](2+) (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). As determined by X-ray diffraction analysis, an oxo-Sc3+ interaction leads to a structural distortion of the oxoiron(IV) moiety. More importantly, this interaction facilitates a two-electron reduction by ferrocene, whereas only a one-electron reduction process occurs without the metal ions. This control of redox behaviour provides valuable mechanistic insights into oxometal redox chemistry, and suggests a possible key role that an auxiliary Lewis acid metal ion could play in nature, as in photosystem II.

DOI： 10.1038/nchem.731

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Iron(III)-superoxo intermediates are believed to play key roles in oxygenation reactions by non-heme iron enzymes. We now report that a non-heme iron(II) complex activates O(2) and generates its corresponding iron(IV)-oxo complex in the presence of substrates with weak C-H bonds (e.g., olefins and alkylaromatic compounds). We propose that a putative iron(III)-superoxo intermediate initiates the O(2)-activation chemistry by abstracting a H atom from the substrate, with subsequent generation of a high-valent iron(IV)-oxo intermediate from the resulting iron(III)-hydroperoxo species.

DOI： 10.1021/ja103903c

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Event date： 2022.11 - 2022.12

Language：English   Presentation type：Poster presentation  

Country：Japan  

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Event date： 2022.11 - 2022.12

Language：English   Presentation type：Poster presentation  

Country：Japan  

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Event date： 2022.11 - 2022.12

Language：English   Presentation type：Poster presentation  

Country：Japan  

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Event date： 2022.9

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

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Event date： 2022.9

Language：Japanese   Presentation type：Poster presentation  

Venue：名古屋大学東山キャンパス, 愛知県   Country：Japan  

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Event date： 2022.6

Language：Japanese   Presentation type：Poster presentation  

Venue：同志社大学京田辺キャンパス夢告館, 京都府   Country：Japan  

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Event date： 2022.6

Language：English   Presentation type：Symposium, workshop panel (nominated)  

Venue：The Korean Academy of Science and Technology, Seoul   Country：Korea, Republic of  

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Event date： 2022.5

Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

Venue：東京大学農学部弥生講堂一条ホール, 東京都   Country：Japan  

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Event date： 2022.3

Language：English   Presentation type：Oral presentation (general)  

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Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

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Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

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