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Yoshimitsu Tachi

Publications and source records attributed to Yoshimitsu Tachi.

At least 19 recordsLinked to original sources
PubMed2006

Modeling the mononuclear, dinuclear, and trinuclear copper(I) reaction centers of copper proteins using pyridylalkylamine ligands connected to 1,3,5-triethylbenzene spacer.

The structure and O2-reactivity of copper(I) complexes supported by novel ligands, Pye2 (1,3,5-triethyl-2,4-bis((N-benzyl-N-(2-(pyridin-2-yl)ethyl)-)aminomethyl)benzene), Pye3 (1,3,5-triethyl-2,4,6-tris((N-benzyl-N-(2-(pyridin-2-yl)ethyl))aminomethyl)benzene), MePym2 (1,3,5-triethyl-2,4-bis((N-benzyl-N-(6-methylpyridin-2-ylmethyl))aminomethyl)benzene), and MePym3 (1,3,5-triethyl-2,4,6-tris((N-benzyl-N-(6-methylpyridin-2-ylmethyl))aminomethyl)benzene) have been examined. The ligands are designed to construct mono-, di-, and trinuclear copper(I) complexes by connecting two or three pyridylalkylamine metal-binding sites to a 1,3,5-triethylbenzene spacer. Thus, the reaction of the ligands with [CuI(CH3CN)4]X (X = PF6, CF3SO3) or CuICl gave the expected mononuclear copper(I) complexes [CuI(Pye2)(CF3SO3)] (1) and [CuI(Pye3)](CF3SO3) (2), dinuclear copper(I) complex [CuI2(MePym2)(Cl)]CuICl2 (3), and trinuclear copper(I) complex [CuI3(MePym3)(CH3CN)3](CF3SO3)3 (4), the structures of which were determined by X-ray crystallographic analysis. The mononuclear copper(I) complexes, 1 and 2, exhibit a distorted three-coordinate T-shape structure and a trigonal planar structure, respectively, which are very close to the coordination geometry of the CuA site of PHM (peptidylglycine alpha-hydroxylating monooxygenase) and the CuB site of CcO (cytochrome c oxidase). Notably, 1 and 2 showed a significantly high oxidation potential (990 mV vs SCE), thus showing virtually no reactivity toward O2. On the other hand, the metal centers of the dinuclear and trinuclear copper(I) complexes, 3 and 4, exhibit a distorted trigonal planar geometry and a trigonal pyramidal geometry, respectively. In contrast to the mononuclear copper(I) complexes, these dinuclear and trinuclear copper(I) complexes reacted with O2 to induce an aromatic ligand hydroxylation reaction involving an NIH-shift of one of the ethyl substituents on the benzene spacer. The NIH-shift of the alkyl substituent on the aromatic ring is strong evidence of the electrophilic aromatic substitution mechanism, although the active oxygen intermediate could not be directly detected during the course of the reaction. The biological relevance of the copper(I) complexes is also discussed on the basis of structure and O2-reactivity.

Benzene Derivatives↗
PubMed2006

NiII(TPA) as an efficient catalyst for alkane hydroxylation with m-CPBA.

A simple Ni(II)(TPA) complex [TPA = tris(2-pyridylmethyl)amine] has been demonstrated to act as an efficient turnover catalyst for alkane hydroxylation with m-CPBA (m-chloroperbenzoic acid), in which contribution of a NiO(+) (nickel-oxo) type active oxygen species is suggested.

Journal Article↗
PubMed2006

Structure and O2-reactivity of copper(I) complexes supported by pyridylalkylamine ligands.

The structure and O2-reactivity of a series of copper(I) complexes supported by the pyridylalkylamine ligands are summarized, and the ligand effects such as the chelate ring size effect (five- vs. six-membered ring), the denticity effect (tetradentate vs. tridentate vs. didentate), the steric effect of 6-methylpyridine and the steric and/or electronic effects of N-alkyl substituents are discussed in detail.

Journal Article↗
PubMed2006

Significant enhancement of monooxygenase activity of oxygen carrier protein hemocyanin by urea.

Oxygenation of a series of p-substituted phenols to the corresponding catechols (phenolase activity) by the (mu-eta2:eta2-peroxo)dicopper(II) species of Octopus hemocyanin has been directly examined for the first time by using a UV-vis spectroscopic method in a 0.5 M borate buffer solution containing 8 M urea under anaerobic conditions. Preliminary kinetic studies have indicated that the reaction involves an electrophilic aromatic substitution mechanism as in the case of phenolase reaction of tyrosinase. The oxygenation of phenols by hemocyanin also proceeded catalytically when the reaction was carried out under aerobic conditions.

Animals↗
PubMed2006

A functional model for pMMO (particulate methane monooxygenase): Hydroxylation of alkanes with H2O2 catalyzed by beta-diketiminatocopper(II) complexes.

The reaction of copper(II) complexes supported by a series of beta-diketiminate ligands ((R1,R2)L, [(Dipp)N-C(R(2))-C(R(1))-C(R(2))-N(Dipp)](-), Dipp=2,6-diisopropylphenyl; see ) and H(2)O(2) has been examined spectroscopically at a low temperature. The beta-diketiminatocopper(II) complexes with R(2)=H (no substituent on the beta-carbon) provided a copper-oxygen intermediate that exhibited the same spectroscopic features as those of the bis(mu-oxo)dicopper(III) complex generated by the reaction of corresponding beta-diketiminatocopper(I) complex and O(2). On the other hand, the beta-diketiminatocopper(II) complexes with methyl substituent on the beta-carbon (R(2)=Me) did not produce such an intermediate in the same reaction. The beta-diketiminatocopper(II) complexes carrying an electron-withdrawing substituent on the alpha-carbon (R(1)=NO(2) or CN) but no beta-substituent (R(2)=H) exhibited a high catalytic activity in the oxygenation reaction of alkanes with H(2)O(2). Mechanism of the catalytic oxygenation reaction as well as the substituent effects of the ligands on the copper(II)-H(2)O(2) reactivity is discussed.

Alkanes↗
PubMed2005

Structure and photoluminescence property of two-dimensional coordination polymer complexes involving Cu(I)(6)X(6)(X = Cl, Br, I) hexagon prism cluster supported by a tripodal tripyridine ligand with 1,3,5-triethylbenzene spacer.

Treatment of cuprous halide (Cu(I)X, X = Cl, Br, and I) and a tripodal tripyridine ligand (L) consisting of a 1,3,5-triethylbenzene spacer gave a unique two-dimensional (2D) polymer sheet structure involving a rare Cu(I)(6)X(6) hexagon prism cluster unit, which exhibits intense fluorescence around 448-476 nm.

Journal Article↗
PubMed2004

C-S bond formation reaction between a phenolate and disulfide-bridged dicopper(I) complexes.

A novel C-S bond formation reaction took place, when a lithium phenolate derivative was treated with a disulfide-bridged dicopper(I) complex or a bis(micro-thiolato)dicopper(II) complex under very mild conditions. The reaction has been suggested to proceed via a disulfide-bridged (micro-phenoxo)dicopper(I) complex as the common reaction intermediate. Copper(II) complexes of the modified ligands containing a thioether group (products of the C-S bond formation reaction) have been isolated and structurally characterized by X-ray analysis as model compounds of the active site of galactose oxidase. Mechanism of the C-S bond formation reaction is also discussed in relation to the biosynthetic mechanism of the organic cofactor Tyr-Cys of galactose oxidase.

Binding Sites↗
PubMed2004

Supramolecular and coordination polymer complexes supported by a tripodal tripyridine ligand containing a 1,3,5-triethylbenzene spacer.

By By combining a tripodal tripyridine ligand containing a 1,3,5-triethylbenzene spacer (L) with several divalent transition-metal chlorides, we have selectively prepared a capsule-type supramolecular complex, [PdII3(L)2Cl6] x 2H2O, and one-dimensional (1D) coordination polymer complexes, ([CuII(L)Cl2] x C2H5OH)n, ([CoII3(L)2Cl6] x 2CH2Cl2)n, and ([ZnII3(L)2Cl6] x 2H2O)n, with a zigzag polymer chain, a linear polymer chain, and a ladder polymer chain structure, respectively. All the structures were established in detail by single-crystal X-ray diffraction analysis, and the factors inducing the structural differences among the complexes are discussed by taking account of the differences in coordination geometry (square planar vs tetrahedral) as well as metal-ligand binding strength in the complexes.

Journal Article↗
PubMed2004

Dicopper-dioxygen complex supported by asymmetric pentapyridine dinucleating ligand.

A dicopper(I) complex supported by a novel asymmetric pentapyridine dinucleating ligand, consisting of tetradentate and tridentate metal-binding sites, has been synthesized and characterized. The dicopper(I) complex reacted with molecular oxygen at a low temperature to give an unprecedented mu-peroxo dicopper(II) complex presumably having a mu-eta1:eta2 binding mode, the spectroscopic features and the reactivity of which have been explored in detail.

Journal Article↗
PubMed2004

Quantitative evaluation of d-pi interaction in copper(I) complexes and control of copper(I)-dioxygen reactivity.

Crystal structures of the copper(I) complexes 1(X), 2, and 3 of a series of tridentate ligands L1(X), L2, and L3, respectively (L1(X): p-substituted derivatives of N,N-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine; X=H, Me, OMe, Cl, NO(2); L2: N,N-bis[2-(2-pyridyl)ethyl]-2-methyl-2-phenylethylamine; L3: N,N-bis[2-(2-pyridyl)ethyl]-2,2-diphenylethylamine) were solved to demonstrate that all the copper(I) complexes involve an eta(2) copper-arene interaction with the phenyl ring of the ligand sidearm. The Cu(I) ion in each complex has a distorted tetrahedral geometry consisting of the three nitrogen atoms (one tertiary amine nitrogen atom and two pyridine nitrogen atoms) and C(1)-C(2) of the phenyl ring of ligand sidearm, whereby the Cu-C distances of the copper-arene interaction significantly depend on the para substituents. The existence of the copper-arene interaction in a nonpolar organic solvent (CH(2)Cl(2)) was demonstrated by the observation of an intense MLCT band around 290 nm, and the magnitude of the interaction was evaluated by detailed analysis of the (1)H and (13)C NMR spectra and the redox potentials E(1/2) of the copper ion, as well as by means of the ligand-exchange reaction between the phenyl ring and CH(3)CN as an external ligand. The thermodynamic parameters DeltaH(o) and DeltaS(o) for the ligand-exchange reaction with CH(3)CN afforded a quantitative measure for the energy difference of the copper-arene interaction in the series of copper(I) complexes. Density functional studies indicated that the copper(I)-arene interaction mainly consists of the interaction between the d(z(2) ) orbital of Cu(I) and a pi orbital of the phenyl ring. The copper(I) complexes 1(X) reacted with O(2) at -80 degrees C in CH(2)Cl(2) to give the corresponding (micro-eta(2):eta(2)-peroxo)dicopper(II) complexes 4, the formation rates k(obs) of which were significantly retarded by stronger d-pi interaction, while complexes 2 and 3, which exhibit the strongest d-pi interaction showed significantly lower reactivity toward O(2) under the same experimental conditions. Thus, the d-pi interaction has been demonstrated for the first time to affect the copper(I)-dioxygen reactivity, and represents a new aspect of ligand effects in copper(I)-dioxygen chemistry.

Journal Article↗
PubMed2003

Substituent effects of beta-diketiminate ligands on the structure and physicochemical properties of copper(II) complexes.

Substituent effects of beta-diketiminate ligands on the structure and physicochemical properties of the copper(II) complexes have been systematically investigated by using 3-iminopropenylamine derivatives R1LR3H, R3-N=CH-C(R1)=CH-NH-R3, where R1 is Me, H, CN, or NO2, and R3 is Ph, Mes (mesityl), Dep (2,6-diethylphenyl), Dipp (2,6-diisopropylphenyl), or Dtbp (3,5-di-tert-butylphenyl). When the ligands with R3=Ph or Dtbp were treated with CuII(OAc)2, bis(beta-diketiminate) copper(II) complexes exhibiting distorted tetrahedral geometries were obtained, the crystal structures of which were nearly the same as each other regardless of the alpha-substituent (R1); dihedral angles between the two beta-diketiminate coordination planes are 62.5 +/- 1.2 degrees, and the Cu-N bond lengths are 1.959 +/- 0.008 A. The distorted tetrahedral structures are maintained in solution, but the spectroscopic features, especially gII values of the ESR spectra and the d-d bands of the absorption spectra, as well as the electrochemical behaviors of the complexes, are significantly affected by the electronic nature of R1. The ligands with R3=Mes and Dep, on the other hand, gave di(mu-hydroxo)dicopper(II) complexes, and their crystal structures as well as spectroscopic and electrochemical features have also been explored. Furthermore, the ligand with the more sterically encumbered aromatic substituent (Dipp) provided a mononuclear four-coordinate square planar copper(II) complex supported by one beta-diketiminate ligand and one didentate acetate ion. Thus, the beta-diketiminate ligands with a variety of substituents (R1 and R3) have been explored to provide coordinatively unsaturated (four-coordinate) mononuclear and dinuclear copper(II) complexes with significantly different coordination geometry and properties.

Journal Article↗
PubMed2003

Structures and redox reactivities of copper complexes of (2-pyridyl)alkylamine ligands. Effects of the alkyl linker chain length.

Ligand effects on the structures and redox reactivities of copper complexes have been examined using (2-pyridyl)alkylamine derivatives as the supporting ligands, where particular attention has been focused on the effects of the alkyl linker chain length connecting the tertiary amine nitrogen atom and the pyridine nucleus: N[bond]CH(2)[bond]Py (Pym) vs N[bond]CH(2)CH(2)[bond]Py (Pye). X-ray crystallographic analysis of the copper(I) complex of tridentate ligand (Phe)L(Pym2) [N,N-di(2-pyridylmethyl)-2-phenylethylamine] (complex 1) has demonstrated that it possesses a trigonal pyramidal geometry in which a d[bond]pi interaction with an eta(1)-binding mode exists between the metal ion and one of the ortho carbons of the phenyl ring of the ligand side arm (phenethyl). The result shows sharp contrast to the d[bond]pi interaction with an eta(2)-binding mode existing in the copper(I) complex of (Phe)L(Pye2) [N,N-di[2-(2-pyridyl)ethyl]-2-phenethylamine] (complex 2). Such a d-pi interaction has been shown to affect the stability of the copper(I) complex in CH(2)Cl(2). Oxygenation of copper(I) complex 1 supported by (Phe)L(Pym2) produces a bis(mu-oxo)dicopper(III) complex, also being in sharp contrast to the case of the copper(I) complex 2 with ligand (Phe)L(Pye2), which preferentially affords a (micro-eta(2):eta(2)-peroxo)dicopper(II) complex in the reaction with O(2). Such an effect of the alkyl linker chain length of the metal binding site has also been found to operate in the RSSR (disulfide)/2RS(-) (thiolate) redox system. Namely, ligand (S2,R)L(Pym1) (di[2-[(alkyl)(2-pyridinylmethyl)amino]ethyl] disulfide) with the methylene linker group (Pym) induced the reductive disulfide bond cleavage in the reaction with copper(I) ion to give a bis(micro-thiolato)dicopper(II) complex, while the ligand with the ethylene linker group (Pye), (S2,Bn)L(Pye1) (di[2-[(benzyl)(2-(2-pyridinyl)ethyl)amino]ethyl] disulfide), gave a disulfide-dicopper(I) complex. These ligand effects in the Cu(2)[bond]O(2) and Cu(2)[bond]S(2) systems have been discussed by taking into account the difference in electron-donor ability of the pyridine nucleus between the Pym and Pye ligand systems.

Journal Article↗
PubMed2003

Oxidation mechanism of phenols by dicopper-dioxygen (Cu(2)/O(2)) complexes.

The first systematic studies on the oxidation of neutral phenols (ArOH) by the mu-eta(2):eta(2)-peroxo)dicopper(II) complex (A) and the bis(mu-oxo)dicopper(III) complex (B) supported by the 2-(2-pyridyl)ethylamine tridentate and didentate ligands L(Py2) and L(Py1), respectively, have been carried out in order to get insight into the phenolic O-H bond activation mechanism by metal-oxo species. In both cases (A and B), the C-C coupling dimer was obtained as a solely isolable product in approximately 50% yield base on the dicopper-dioxygen (Cu(2)/O(2)) complexes, suggesting that both A and B act as electron-transfer oxidants for the phenol oxidation. The rate-dependence in the oxidation of phenols by the Cu(2)/O(2) complexes on the one-electron oxidation potentials of the phenol substrates as well as the kinetic deuterium isotope effects obtained using ArOD have indicated that the reaction involves a proton-coupled electron transfer (PCET) mechanism. The reactivity of phenols for net hydrogen atom transfer reactions to cumylperoxyl radical (C) has also been investigated to demonstrate that the rate-dependence of the reaction on the one-electron oxidation potentials of the phenols is significantly smaller than that of the reaction with the Cu(2)O(2) complexes, indicative of the direct hydrogen atom transfer mechanism (HAT). Thus, the results unambiguously confirmed that the oxidation of phenols by the Cu(2)O(2) complex proceeds via the PCET mechanism rather than the HAT mechanism involved in the cumylperoxyl radical system. The reactivity difference between A and B has also been discussed by taking account of the existed fast equilibrium between A and B.

Biomimetic Materials↗
PubMed2003

Structural modulation of Cu(I) and Cu(II) complexes of sterically hindered tripyridine ligands by the bridgehead alkyl groups.

Structures of Cu(I) and Cu(II) complexes of sterically hindered tripyridine ligands RL = tris(6-methyl-2-pyridyl)methane (HL), 1,1,1-tris(6-methyl-2-pyridyl)ethane (MeL), and 1,1,1-tris(6-methyl-2-pyridyl)propane (EtL), [Cu(RL)(MeCN)]PF(6) (1-3), [Cu(RL)(SO(4))] (4-6), and [Cu(RL)(NO(3))(2)] (7-9), have been explored in the solid state and in solution to gain some insights into modulation of the copper coordination structures by bridgehead alkyl groups (CH, CMe, and CEt). The crystal structures of 1-9 show that RL binds a copper ion in a tridentate facial-capping mode, except for 3, where EtL chelates in a bidentate mode with two pyridyl nitrogen atoms. To avoid the steric repulsion between the bridgehead alkyl group and the 3-H(py) atoms, the pyridine rings in Cu(I) and Cu(II) complexes of MeL and EtL shift toward the Cu side as compared to those in Cu(I) and Cu(II) complexes of HL, leading to the significant differences in the nonbonding interatomic distances, H.H (between the 3-H(py) atoms), N.N (between the N(py) atoms), and C.C (between the 6-Me carbon atoms), the Cu-N(py), Cu-N(MeCN), and Cu-O bond distances, and the tilt of the pyridine rings. The copper coordination geometries in 4-6, where a SO(4) ligand chelates in a bidentate mode, are varied from a square pyramid of 4 to distorted trigonal bipyramids of 5 and 6. Such structural differences are not observed for 7-9, where two NO(3) ligands coordinate in a monodentate mode. The structures of 1-9 in solution are investigated by means of the electronic, (1)H NMR, and ESR spectroscopy. The (1)H NMR spectra show that the structures of 1-3 in the solid state are kept in solution with rapid coordination exchange of the pyridine rings. The electronic and the ESR spectra reveal the structural changes of 5 and 6 in solution. The bridgehead alkyl groups and 6-Me groups in the sterically hindered tripyridine ligand play important roles in modulating the copper coordination structures.

Journal Article↗
PubMed2002

Copper chemistry of beta-diketiminate ligands: monomer/dimer equilibria and a new class of bis(mu-oxo)dicopper compounds.

A series of Cu(I) and Cu(II) complexes of a variety of beta-diketiminate ligands (L(-)) with a range of substitution patterns were prepared and characterized by spectroscopic, electrochemical, and, in several cases, X-ray crystallographic methods. Specifically, complexes of the general formula [LCuCl](2) were structurally characterized and their magnetic properties assessed through EPR spectroscopy of solutions and, in one instance, by variable-temperature SQUID magnetization measurements on a powder sample. UV-vis spectra indicated reversible dissociation to 3-coordinate monomers LCuCl in solution at temperatures above -55 degrees C. The Cu(I) complexes LCu(MeCN) exhibited reversible Cu(I)/Cu(II) redox couples with E(1/2) values between +300 and +520 mV versus NHE (cyclic voltammetry, MeCN solutions). These complexes were highly reactive with O(2), yielding intermediates that were identified as rare examples of neutral bis(mu-oxo)dicopper complexes on the basis of their EPR silence, diagnostic UV-vis absorption data, and O-isotope-sensitive resonance Raman spectroscopic features. The structural features of the compounds [LCuCl](2) and LCu(MeCN) as well as the proclivity to form bis(mu-oxo)dicopper products upon oxygenation of the Cu(I) complexes are compared to data previously reported for complexes of more sterically hindered beta-diketiminate ligands (Aboelella, N. W.; Lewis, E. A.; Reynolds, A. M.; Brennessel, W. W.; Cramer, C. J.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 10600. Spencer, D. J. E.; Aboelella, N. W.; Reynolds, A. M.; Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 2108. Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 1999, 121, 7270). The observed structural and reactivity differences are rationalized by considering the steric influences of both the substituents on the flanking aromatic rings and those present on the beta-diketiminate backbone.

Chemical Phenomena↗