阿部 正明

New oxo-centred acetate-bridged triruthenium(III) complexes with a long alkyl-chain disulfide ligand, (NC5H4)CH2NHC(O)(CH2)(n)SS(CH2)(n)C(O)NHCH2(C5H4N) (C5H4N represents a 4-pyridyl residue, n=10; abbreviated as C10PY), have been prepared as a redox-active metal cluster adsorbate on gold electrodes: [Ru-3(O)(CH3CO2)(6)(mpy)(2)(C10PY)]ClO4 5a (mpy=4-methylpyridine), [Ru-3(O)(CH3CO2)(6)(mpy)(2)(C10PY)]CF3SO3 5b. The preparation, spectroscopic and electrochemical properties of 5a,5b are presented and are compared with those of triruthenium(III) analogues of a shorter alkyl-chain disulfide ligand (n=2; abbreviated as C2PY), e.g. [Ru-3(O)(CH3CO2)(6)(mpy)(2)(C2PY)]ClO4 3a and [Ru-3(O)(CH3CO2)(6)(MeIm)(2)(C2PY)]ClO4 4a (MeIm=1-methylimidazole). Characterization of all the compounds was accomplished using H-1 and H-1-H-1 COSY NMR, UV-vis and infrared spectroscopy, elemental analysis, fast-atom bombardment (FAB) mass spectrometry and cyclic voltammetry. Compounds 3a, 4a and 5a,5b in 0.1 M [n-Bu4N]PF6-CH3CN exhibit three {Ru-3(O)} cluster core-based one-electron redox waves which are all reversible in the applied potential range between +1.2 and -2.0 V vs. Ag-AgCl. The redox potentials are dependent on the basicity of the terminal ligands (mpy and MeIm), but are insensitive to the length of the methylene chains of the disulfide ligand (C10PY and C2PY). Self-assembly of 5b on a gold electrode results in the formation of electrochemically stable monolayers which exhibit one-electron redox wave corresponding to the Ru-3 redox process III,III,III-II,III,III in aqueous media containing 0.1 M supporting electrolytes. The redox potentials and the shape of the voltammetric waves of the surface-attached triruthenium complexes are found to be largely dependent upon the nature of anions used (ClO4-, CF3SO3-, NO3-, PF6- and SO42-) and also upon the basicity of terminal ligands on the {Ru-3(O)} cluster moiety.

A dinuclear ruthenium complex [Ru2(dhpta)(μ-O2CCH3)2] - (H5dhpta = 1,3-diamino-2-hydroxypropane-N, N, N', N'-tetraacetic acid) is accumulated on a gold surface by using the ligand substitution reaction of bridging acetate in the complex by terminal benzoate in a self-assembled monolayer with 4-(6-mercaptohexoxy)benzoic acid. The accumulated complex, which shows a surface redox couple corresponding to Ru111Ru111/Ru111Ru11, covers the gold surface completely. The ligand substitution reaction is applicable for the accumulation of other complexes and useful for the designing of functional electrodes.

Novel self-assembled monolayers of a mixed-valent (μ3-oxo)triruthenium(II,III,III) complex containing a terminal CO ligand were constructed on Au(111) electrode surface and were characterized by cyclic voltammetry and in situ Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). A distinctive infrared v(CO) absorption band was observed at 1950 cm-1 for the original {Ru11-CO}Ru111Ru111 complex in an aqueous 0.1 M NaClO4 solution and it shifted to 2060 cm-1 upon one-electron oxidation of the Ru11 center.

Novel self-assembled monolayers of oxide and acetate-bridged triruthenium(III) complexes have been prepared on Au(111) electrode surface. Parent discrete triruthenium(III) complexes with a terminal disulfide ligand, [Ru3(μ3-O)(μ-CH3CO2)6(L)2 (C2PY)]ClO4, where C2PY = {NC5H4CH2NHC(O)(CH2)2S-}2, L = 4-methylpyridine (mpy, 4a) and 1-methylimidazole (MeIm, 4b), were isolated through multistep synthesis. Complex 4a exhibits three reversible redox waves, while complex 4b exhibits two reversible and one irreversible redox waves in (n-C4H9)4NPF6/CH3CN, all ascribed to one-electron redox of the triruthenium cluster core. In aqueous solution containing a 0.1 M supporting electrolyte (NaClO4 or Na2SO4), self-assembled monolayers of 4a and 4b on Au(111) electrodes (4a/Au and 4b/Au) exhibit a single reversible redox wave, ascribed to the Ru3(III,III,III/II,III,III) redox process for the surface-attached clusters. The redox potential and the shape of the cyclic voltammograms of Ru3 cluster modified SAMs were affected by the kind of terminal ligands and supporting electrolytes.

Novel self-assembled monolayers of oxide and acetate-bridged triruthenium(III) complexes have been prepared on Au(111) electrode surface. Parent discrete triruthenium(III) complexes with a terminal disulfide ligand, [Ru-3(mu(3)-O)(mu- CH3CO2)(6)(L)(2)(C2PY)]ClO4, where C2PY = {NC5H4CH2NHC(O)(CH2)(2)S-}(2), L = 4-methylpyridine (mpy, 4a) and 1-methylimidazole (MeIm, 4b), were isolated through multistep synthesis. Complex 4a exhibits three reversible redox waves, while complex 4b exhibits two reversible and one irreversible redox waves in (n-C4H9)(4)NPF6/CH3CN, all ascribed to one-electron redox of the triruthenium cluster core. In aqueous solution containing a 0.1 M supporting electrolyte (NaClO4 or Na2SO4), self-assembled monolayers of 3a and 4b on Au(111) electrodes (4a/Au and 4b/Au) exhibit a single reversible redox wave, ascribed to the Ru,(III,III,III/II,III,III) redox process for the surface-attached clusters. The redox potential and the shape of the cyclic voltammograms of Ru, cluster modified SAMs were affected by the kind of terminal ligands and supporting electrolytes. (C) 1999 Elsevier Science S.A. All rights reserved.

Tetranuclear Mo2Rh2 Complexes Obtained from Reactions between Triple Cubane-Type Oxide Cluster [(Cp*Rh)4Mo4O16] (Cp* = h5-C5(CH3)5) and Methanethiol: [{Cp*Rh(m-SCH3)3MoO2}2(m-O)] and [{Cp*Rh(m-SCH3)3MoO}2(m-X)(m-Y)] (X, Y = O and X = O, Y = S). Synthesis, X-ray Structures, and Dynamic Behavior in Nonaqueous Media

A series of side-on peroxide-bridged binuclear copper complexes [Cu2(NnPY2)(O2)]2+ (where n = 3-5), which have been proposed to adopt a butterfly Cu2O2 geometry due to the constraints placed on the Cu-Cu distance by the alkyl chain linker of length -(CH2)(n)- have been studied using absorption and resonance Raman spectroscopy and theoretical techniques. The four components of the peroxide to copper(II) charge-transfer transitions have been identified for the first time in the [Cu2(NnPY2)(O2)]2+ (where n = 3-5) complexes. The observed shift of the peroxide O-O stretch by 25 cm-1 to higher energy and the changes observed in the energy and intensity of absorption bands including the presence of an additional band at 23 800-20 400 cm-1 (420-490 nm) (not seen in planar side-on peroxide-bridged dicopper cores) are correlated to the butterfly structure using transition dipole vector coupling and valence bond configuration interaction models. The identification of an absorption band at 23 800-20 400 cm-1 (420-490 nm) associated with the butterfly side-on peroxide-bridged dicopper core is important since the isomeric, bis(μ-oxo) core is also characterized by an absorption band in this region. The changes in bonding associated with a butterfly distortion of the Cu2O2 core are defined, and the reactivity of the butterfly core with respect to electrophilic aromatic substitution and H atom abstraction reactions is compared with that of the planar side-on peroxide-bridged dicopper core using the frontier molecular orbital description.

The Mo(0) and Mo(VI) complexes of tris(2-pyridylmethyl)amine (tpa), Mo(CO)3(tpa) and Mo(O)3(tpa)·H2O, were synthesized. Structural analyses revealed tridentate coordination of tpa in both compounds. The fluxional behavior of both species was investigated by variable-temperature 'HNMR spectroscopy.

Self-assembled monolayers (SAMs) of non-heme diiron(III) biomimetic complexes have been prepared on Au(111) electrode surfaces to explore redox properties of diiron centers in aqueous solution in a wide pH range. The diiron(III) SAMs exhibited the proton-coupled electron-transfer reaction (1H+/le) in water.

A reaction of the triple cubane-type organometallic polyoxomolybdate cluster, [(Cp * Rh)4Mo4O16] · 2H2O (1 · 2H2O), with 1,2-benzenedithiol gives a 1,2-benzenedithiolate-bridged dinuclear complex, [(Cp * Rh)2(μ(S)-1,2-C6H4S2-S,S′)2] (2), and another dinuclear complex, [(Cp * Rh)2(μ(S)-1,2-C6H4S2-S,S′)(μ(S)-1,2-C6H4S(SO2)-S,S′)] (3), both of which are characterized by the single-crystal X-ray diffraction method. The former complex, 2, is also obtained from a reaction of [(Cp * RhCl)2(μ-Cl)2] with 1,2-benzenedithiol in the presence of NaOCH3, and the latter, 3, from oxygenation of 2 with t-BuOOH. The 1H NMR study in CD2Cl2 indicates that complex 2 changes gradually to a coordinatively unsaturated mononuclear complex, [Cp * Rh(1,2-C6H4S2-S,S′)] (4). An analogous mononuclear iridium(III) complex, [Cp * Ir(1,2-C6H4S2-S,S′)] (5), is also prepared and characterized by X-ray structural analysis. © 1997 Elsevier Science S.A.

A mononuclear rhenium(V) complex having a BF3 moiety on one of the two oxo ligands, trans-[ReV(O)(OBF3)(1-MeIm)4](BF4) (1-MeIm = 1-methylimidazole), was isolated and characterized. Two one-electron redox waves were observed in 0.1 M (n-C4H9)4NPF6/CH3CN (M = mol dm-3).

A new series of oxo-centered acetate-bridged triruthenium comlexes having two redox-active N-methyl-4,4'-bipyridinium ions (mbpy(+)) have been prepared, and their reversible multistep and multielectron electrochemical properties are reported: [Ru(III)(2)Ru(II)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(CO)](2+) and [Ru(III)(3)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(L)](3+) (L = H(2)O, pyrazine (pz), pyridine (py), imidazole (Him), and 4-(dimethylamino)pyridine (dmap)). Among these series, the CO complex, [Ru(III)(2)Ru(II)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(CO)](ClO(4))(2).2DMF (1b.2DMF) was structurally characterized by X-ray crystallography. 1b.2DMF crystallizes in the monoclinic space group P2(1)/m (No. 11) with a = 8.740(6) Å, b = 32.269(6) Å, c = 10.276(4) Å, beta = 103.37(5) degrees, V = 2820(2) Å(3), Z = 2, d(calcd) = 1.636 g cm(-)(3), and R = 0.071 (R(w) = 0.074) for 5277 independent reflections (|F(o)| > 3sigma(|F(o)|). The (CO)Ru.Ru distance (3.410(2) Å) is appreciably longer than the other Ru.Ru distance (3.276(2) Å), indicating that the trinuclear core is in the valence-trapped Ru(III)(2)Ru(II)(CO) oxidation state. The cyclic voltammogram of [Ru(III)(2)Ru(II)(&mgr;(3)-O)(&mgr;-CH(3)CO(2))(6)(mbpy(+))(2)(CO)](PF(6))(2) (1a) shows a total of seven reversible one-electron redox steps at E(1/2) = +0.90, +0.26, -1.07, -1.17, -1.56, -1.97, and -2.32 V and one irreversible step at E(pc) = -2.99 V vs Fc/Fc(+) in a 0.1 M [(n-C(4)H(9))(4)N]PF(6)-CH(3)CN solution (M = mol dm(-)(3)). All of the waves are clearly assignable to the triruthenium "Ru(3)(&mgr;(3)-O)" core-based or mbpy(+) ligand-based processes. The splitting of each ligand-based redox processes (mbpy(+)/mbpy(*) and mbpy(*)/mbpy(-)) into two one-electron steps indicates that electronic interactions between two terminal ligands occur through the triruthenium cluster core. Other mixed-ligand Ru(III)(3) analogs also show multistep redox behavior involving a total of eight or nine electrons. While the extent of interactions between ligands is much smaller than that found in the CO complex, it is systematically changed by the nature of L; with more basic L, interactions between two mbpy(+) ligands become larger.

The methallyl moieties of [{(η3-C4H7)2Rh} 2(V4O12)]2- couple to yield 2,5-dimethyl-1,5-hexadiene in a selective manner by the action of P(OEt)3, while the reaction of [(η3-C4H7)2Rh(acac)] with P(OEt)3 produces a mixture of organic compounds. The result shows that the vanadate support has a significant influence on the reactivity of organometallic complexes. © 1996 Plenum Publishing Corporation.

A series of new oxo-centered triruthenium, trirhodium, and mixed diruthenium-rhodium complexes having three redox-active terminal ligands, N-methyl-4,4′-bipyridinium ion (mbpy+), were prepared: [Ru3(m3-O)(μ-CH3CO2)6−(mbpy+)3](PF6)3 (1), [Ru3(μ3-O)(μ-CH3CO2)6(mbpy+)3](PF6)4 (2), [Ru3(μ3-O)(μ-C6H5CO2)6(mbpy+)3](PF6)(ClO4)3 (3), [Ru2Rh(μ3-O)(μ-CH3CO2)6(mbpy+)3](ClO4)4 (4), and [Rh3(μ3-O)(μ-CH3CO2)6(mbpy+)3](PF6)4 (5). Their versatile electrochemical properties were investigated by means of cyclic voltammetry, differential-pulse voltammetry, and controlled-potential absorption spectroscopy. Ru3 complexes 1 and 2 provide nine-step 11-electron redox waves (involving eight reversible waves) in 0.1 M (n-C4H9)4NPF6-CH3CN solution in the range from +2.0 to −3.0 V vs ferrocene/ferrocenium (Fc/Fc+) couple at 22°C (M = mol dm−3), consisting of five Ru3(μ3-O) core-based one-electron processes at +1.62, +0.64, −0.34, −1.75, and −2.76 V and the terminal ligand-based steps at −1.23, −1.37, −1.99, and −2.09 V. The two couples of terminal ligand-based processes, mbpy+/mbpy+ and mbpy−/mbpy−, split into two steps in 2:1 current intensity ratio. Complex 3 exhibits similar redox behavior. The Ru2Rh complex 4 exhibits eight-step 10-electron redox waves (involving six reversible waves), with the core-based redox processes at +1.65, +0.74, −0.72, and −1.88 V, mbpy+/mbpy+ steps at −1.14, −1.26, and −1.45 V, and mbpy+/mbpy− steps at −2.14 V (3e). The Rh3 complex 5 shows two-step four-electron redox behavior with a core-oxidation at +0.97 V and one-step three mbpy+ reductions at −1.21 V (3e). The splitting of the ligand-based redox waves are caused by the ligand-ligand interactions through an empty dπ-pπ molecular orbital in the trinuclear M3(μ3-O) framework. © 1995, American Chemical Society. All rights reserved.

Symmetry of the oxo-centered tri-ruthenium(III) complexes, [Ru-3(O)(OOCR)(6)(L)(3)](+) (R=CH3, C6H5; L=pyridine, H2O), is discussed on the basis of the shapes of nu(as)(OCO) bands in infra-red spectra, using comparisons between these complexes and related tri-rhodium(III) and mixed-metal Ru(III)(2)M complexes. It is suggested that the tri-ruthenium(III) complexes have non-threefold symmetry.

Variable-temperature17O NMR together with51V and103Rh NMR studies on newly prepared vanadium oxide-supported organorhodium(I) fragment(s), [(RhCOD)n(V4O12)](4-n)- (n = 1, 2; COD =η4-1,5-cyclooctadiene) indicate that intramolecular rearrangements of RhCOD fragment(s) on a vanadium oxide surface occur in solution. © 1994 Plenum Publishing Corporation.

Reaction of the triple cubane-type cluster [((CPRh)-Rh-*)(4)Mo4O16] with MeSH gave two tetranuclear complexes of [{Cp*Rh(mu-SMe)(3)MoO}2(mu-O)(2)] and [{Cp*Rh-(mu-SMe)(3)MoO}(2)(mu-O)(mu-S)] which were characterized by X-ray structural analysis. The stereodynamics of the two complexes was studied by variable-temperature H-1 and O-17 NMR as well as C-13 NMR spectroscopy.

Crystal structure of an oxo-benzoate-bridged trinuclear ruthenium complex, [Ru3(mu-3-O)(mu-C6H5COO)6(py)3](PF6) (py = pyridine) (1), was determined for the first time for the complexes with a Ru3(III,III,III)(mu-3-O) core. The complex crystallizes in hexagonal space group P6(3) with a=13.619(6), c=19.204(9) angstrom, V=3085(3) angstrom3, and Z=2. The Ru ... Ru distance of 3.350(2) angstrom is similar to those of the trinuclear complexes of other metal ions, [M(III)3(mu-3-O)(mu-RCOO)6(L)3]+(L = neutral unidentate ligand). The complex in 0.1 M (n-C4H9)4NPF6-acetonitrile at 20-degrees-C shows four reversible one-electron processes at E1/2=+ 1.58, +0.71, -0.26, and - 1.54 V vs. Ag/ Ag+ (0.1 M AgClO4). It undergoes pyridine-d5 exchange with the first-order rate constant, 4.9X10(-6) s-1 at 60-degrees-C ([1] = 4.7 mM, [py-d5] = 387 mM). Small modification of the synthetic procedure of the trinuclear complex leads to the precipitation of the crystals of well-known type of dimeric ruthenium (II,III) complex, [Ru2(mu-C6H5COO)4Cl], which crystallizes in monoclinic space group C2/ c with a=21.668(10), b= 10.741(8), c= 12.797(5) angstrom, beta= 110.22(4)-degrees, V=2795(3) angstrom3, and Z=4. The crystal contains infinite zig-zag chain of ... Cl-Ru-Ru-Cl ... along c-axis with Ru-Ru-Cl of 175.5(1)-degrees, Ru-Cl-Ru of 118.1(1)-degrees, and the Ru-Ru distance of 2.290(1) angstrom.

Substitution reactions of py-d5 for the terminal pyridines of the three triruthenium complexes, [Ru3(mu-3-O)(mu-CH3COO)6(py)3]+ (1) (Ru3(III, III, III)), Ru3(mu-3-O)(mu-CH3COO)6(py)3 (2) (Ru3(II, III, III)), and Ru3(mu-3-O)(mu-CH3COO)6(CO)(py)2 (3) (Ru3(II, III, III)), have been studied in CD3CN by following the change in H-1 NMR spectra. The rates are practically independent of [py-d5] (0.05-1.0 mol dm-3). The first-order rate constants are 3 x 10(-5) s-1 at 55-degrees-C (DELTA-H not-equal = 123 +/- 6 kJ mol-1, DELTA-S not-equal = + 41 +/- 19 J K-1 mol-1), 5.9 x 10(-4) s-1 at 50-degrees-C (DELTA-H not-equal = 122 +/- 14 kJ mol-1, DELTA-S not-equal = + 69 +/- 44 J K-1 mol-1), and 3 x 10(-5) s-1 at 55-degrees-C (DELTA-H not-equal = 126 +/- 9 kJ mol-1, DELTA-S not-equal = + 52 +/- 27 J K-1 mol-1) for 1, 2, and 3, respectively. Rate constants appear to depend on the apparent oxidation state of the metal center. While the three Ru ions in 2 are equivalent and each ion has average oxidation number +2(2/3), Ru ions with coordinated py in 3 are in +3 oxidation state as the +2 oxidation state is localized at carbonyl-Ru ion. A dissociative mechanism is proposed for these reactions on the basis of the absence of [py-d5]-dependence, the activation parameters, and the comparison of the rate constants with those of the substitution of methanol-d4 for the terminal water ligands in [Ru3(mu-3-O)(mu-CH3COO)6(H2O)3]+.