Synthesis of a heterodinuclear ruthenium(II)–platinum(II) complex linked by l-cysteine methyl ester

A potential anticancer heterodinuclear ruthenium(II)–platinum(II) complex, [ruthenium(II)(4,4′-dimethyl-2,2′-bipyridine)₂(5-(l-cysteine-methyl ester)-1,10-phenanthroline)-trans-chlorodiammineplatinum(II)] chloride, [Ru(Me₂bipy)₂(5-(l-cysteine-Me)-phen)-trans-Pt(NH₃)₂Cl]Cl₃, was synthesised. l-Cysteine methyl ester was used to link the two metal centres, as more conventional straight chain diaminoalkanes and 2-mercaptoethylamine failed to couple to the phenanthroline ligand. From the precursor mononuclear ruthenium(II) complexes, which were separated into their Δ- and Λ-isomers by column chromatography, the dinuclear complex was synthesised and characterised by ¹H and ¹³C NMR, UV–Vis, circular dichroism, fluorescence and electrospray ionisation mass spectrometry.     

Ruthenium(II) 2-hydroxybenzophenone N(4)-substituted thiosemicarbazone complexes

New ruthenium(II) complexes with 2-hydroxybenzophenone N(4)-substituted (Me, Ph and/or piperidyl) thiosemicarbazones have been prepared and characterised by elemental analysis, molar conductivity, thermal analysis, spectroscopy (i.r., ¹H-n.m.r. and u.v.–vis.) and by cyclic voltammetry. The thiosemicarbazones coordinate to ruthenium(II) as mononegative tridentate ligands via the deprotonated hydroxyl group, N¹ nitrogen and thione sulphur centres. The redox properties, nature of the electrode processes and the stability of the complexes towards oxidation in CH₂Cl₂ are discussed. The change in the E _1/2 values of the complexes can be related to the basicity of the N(4)-substituents. All the complexes display an irreversible one-electron charge-transfer couple in the potential range studied. This revised version was published online in June 2006 with corrections to the Cover Date.     

Some benzimidazole amide complexes of ruthenium(II)

The synthesis and characterisation of ruthenium(II) complexes with 2-amidobenzimidazoles are reported. The complexes RuCl₂(DMSO)₄ and RuCl₂(PPh₃) react with 2-(acetamido)benzimidazole (AB) and 2-(benzamido)benzimidazole (BB) it acetone to give products of the type [Ru(L)₂(N−O)₂]Cl₂ [L=DMSO, PPh₃, N−O=AB, BB). The displacement reactions are faster in the case of methyl (AB) than phenyl (BB) substituted ligands. The ligands are bifunctional chelating agents coordinating through the tertiary nitrogen of benzimidazole ring and amide oxygen. The complexes are characterised based on their elemental analysis, conductivity data, infrared,¹H and³¹P nmr spectra. Acis-geometry is proposed for all the complexes reported.     

Complex Formation of Acetic Acid with Ca(II) and Mg(II) Under Physiological Conditions

Potentiometric titrations of aqueous acetic acid alone and in the presence of Ca(II) or Mg(II) ions have been carried out under physiological conditions at the temperature 37 °C and ionic strength 0.15 mol⋅dm⁻³ (NaCl) at different ligand-to-metal ratios. Changes in pH were monitored with a glass electrode calibrated daily in terms of the hydrogen ion concentrations. Titration data within the pH range 2.5 to 6.6 were analyzed to determine stability constants using the SUPERQUAD program. Different combinations of complexes were considered during the calculation procedure for both systems, but evidence was found only for mononuclear ML and ML₂ species. Speciation calculations based on the corresponding constants were then used to simulate the species’ distributions.     

Synthesis and studies of spectroscopic and electrochemical properties of dinuclear ruthenium(<Emphasis Type="SmallCaps">II</Emphasis>) and manganese(<Emphasis Type="SmallCaps">II</Emphasis>) complexes

New dinuclear ruthenium manganese complexes of general composition (bpy)₂Ru(L)MnCl_x(H₂O)₂ (L is 1,10-phenanthroline-5,6-dione, 3,3′-dicarboxy-2,2′-bipyridyl, or bis(pyrazolyl); x = 2 or 4) were synthesized by the reaction of (bpy)₂Ru(L) with MnCl₂ · 4H₂O. These compounds and the starting mononuclear ruthenium complexes were studied by spectrophotometric and electrochemical methods in MeCN. The position of the charge-transfer band Ru^II → L in the spectra depends on the donor-acceptor characteristics of the ligand L. For the dinuclear complex under study, the formal potentials of reversible one-electron oxidation of Ru^II are in the range of 0.9–1.2 V (vs. the standard hydrogen electrode), whereas oxidation of Mn^II occurs at more positive (by 0.1–0.2 V) potentials. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2281–2285, October, 2005.     

Thiocyanate-selective electrode based on N-salicylidene-benzylamineato copper(II) complex

Highly selective poly(vinyl chloride) (PVC) membrane electrode based on N-salicylidene-benzylamineato copper(II) complexes [Cu(SBA)₂] as new carriers towards thiocyanate-selective electrode was reported. The influence of membrane composition, pH and possible interfering anions were investigated on the response properties of the electrode. The resulting electrode exhibits anti-Hofmeister selectivity sequence: SCN⁻ > ClO₄⁻ > Sal⁻ > I⁻ > Br⁻ > NO₃⁻ > NO₂⁻ > SO₃²⁻ > H₂PO₄⁻ > Cl⁻ > SO₄²⁻, and a near-Nernstian potential linear range for thiocyanate from 1.0 × 10⁻¹ to 9.0 × 10⁻⁷ M with a detection limit of 7.0 10⁻⁷ M and a slope of , over a wide pH range of 3.0–9.0 in phosphate buffer solution at 20°C. The proposed electrode has a fast response time of about 5–10 s and can be used for at least 3 months without any considerable divergence in potential. The electrode was successfully applied to the determination of thiocyanate in waste water and human urine and saliva samples. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 3, pp. 293–299. The text was submitted by the authors in English.     

Synthesis and characterization of ruthenium(ii) complexes of 5-hydroxyflavones

Bis(dimethyl sulfoxide)bis(flavonato)ruthenium(II) complexes, RuL₂(DMSO)₂, were synthesized by the reaction of dichlorotetrakis(dimethyl sulfoxide)ruthenium(II) with the sodium salts of 5-hydroxyflavone, 5-hydroxy-4′-methoxyflavone and 5-hydroxy-3′,4′,5′,7-tetramethoxyflavone, ( L ). The complexation was followed by ¹H nmr spectroscopy. The 1:1 kinetically favoured tris(dimethyl sulfoxide)chloroflavonatoruthenium(II) complexes, RuLCl(DMSO)₃, were initially formed and then transformed into the thermodynamically more stable ones. Each one of these complexes, by reacting with another equivalent of lig-and L, also gave rise to a mixture of 1:2 kinetic species, from which the 1:2 thermodynamically more stable bis(dimethyl sulfoxide)bis(flavonato)ruthenium(II) complexes, RuL₂(DMSO)₂, were formed. The complexes were characterized by extensive studies involving ¹H, ¹³C nuclear magnetic resonance, infrared and ultraviolet-visible spectroscopy, mass spectrometry, cyclic voltammetry and elemental analysis. Such 1:2 complexes exhibited properties of two nonequivalent flavonate ligands and also of two non-equivalent dimethyl sulfoxide ligands; one of these dimethyl sulfoxide ligands is considered to be S-bonded and the other O-bonded. Also two quasireversible one-electron redox steps were observed at 0.53 to 0.57 and 0.44 to 0.41 V (vs Saturated Calomel Electrode). The spectroscopic results obtained allow for the discussion of stereochemistry of each bis(dimethyl sulfoxide)bis(flavonato)ruthenium(II) complex and to postulate its possible structure as one corresponding to the more anisochronous species.     

Synthesis, spectral and electrochemical behaviour of cytosinato bridged complexes of ruthenium(II) and platinum(II) with 1-alkyl-2-(arylazo)imidazoles

Dechlorination of M(RaaiR′) _n Cl₂ by AgNO₃ produced [M(RaaiR′) _n (MeCN)₂]⁺² [M = Ru(II), n = 2; Pt(II), n = 1; RaaiR′ = 1-alkyl-2-(arylazo)imidazole)] which upon reaction with the nucleobase cytosine (C) in MeCN solution gave cytosinato bridged dimeric compounds which were isolated as perchlorate salts [M₂(RaaiR′) _n (C)₂](ClO₄)₂ · H₂O. The products were characterized by IR, u.v.–vis., ¹H-n.m.r. spectroscopy and cyclic voltammetry. In MeCN solution the ruthenium complexes exhibit a strong MLCT band at 550–555 nm and two redox couples positive to SCE due to two metal-center oxidation along with ligand reduction, negative to SCE. The platinum complexes show a weak transition at 500–520 nm in MeCN and exhibit only ligand reduction in cyclic voltammetry. The coordination of the ligand was supported by ¹H-n.m.r. spectral data.     

Chemiluminescence method for the determination of mitoxantrone by the enhancement of the tris-(4,7-diphenyl-1,10-phenanthrolinedisulfonic acid)ruthenium(II)–cerium(IV) system

2,5-Dimercapto-1,3,4-thiadiazole (DMTD) self-assembled monolayer on gold electrode was prepared and investigated by electrochemical measurement. The DMTD/Au electrode exhibited a significantly increased sensitivity and selectivity for Pb(II) in acetate buffer (pH 5.5) at a potential of −1.0 V (vs Ag/AgCl) for 4 min by anodic stripping voltammetry. The influence of various experimental parameters on the voltammetric response was studied. Under the optimized working conditions, the dependence of the stripping peak current response on concentration of Pb(II) was linear in the range of 1–45 μmol L⁻¹ with a correlation coefficient of 0.9988, and the detection limit was 0.10 μmol L⁻¹. The relative standard deviation of the results was 3.4% for six successive determinations of a 20 μmol L⁻¹ Pb(II) solution. A study of interfering substances was also performed. The method was applied to the determination of Pb(II) in water samples with satisfactory results. Correspondence: Hong Qun Luo, School of Chemistry and Chemical Engineering, Southwest University, 400715 Chongqing, China     

Ruthenium(II) mediated C-H activation of substituted acetophenone thiosemicarbazones: Synthesis, structural characterization, luminescence and electrochemical properties

Treatment of [RuHCl(CO)(AsPh₃)₃] with 4′-substituted acetophenone thiosemicarbazone derivatives in methanol under reflux afford a series of air stable new ruthenium(II) cyclometalated complexes containing thiosemicarbazone of general formula [Ru(L)(CO)(AsPh₃)₂]. The 4′-substituted acetophenone thiosemicarbazone ligands behave as a dianionic terdentate C, N and S donors (L) and coordinates to ruthenium via aromatic carbon, the imine nitrogen and thiol sulfur. The compositions of the complexes have been established by elemental analysis, and spectral methods (FT-IR, UV-Vis, ¹H NMR, ESI-MS) and X-ray crystallography. In chloroform solution all the complexes exhibit metal-to-ligand charge transfer transitions (MLCT) in the visible region and are emissive at room temperature with quantum yield of 0.001-0.005. The crystal structure of one of the complexes [Ru(4CAP-PTSC)(CO)(AsPh₃)₂] (4) has been solved by single crystal X-ray crystallography and it indicates the presence of a distorted octahedral geometry in these complexes. All the complexes exhibit a quasi reversible one electron reduction (Ru^II/Ru^I) in the range −0.83 to −0.86 V. The formal potential of all the couples correlate linearly with the Hammett constant of the para substituent in phenyl fragment of the acetophenone thiosemicarbazone ligands.     

Synthesis, characterization and photophysics of bimetallic manganese(I) and ruthenium(II) complexes

A series of new manganese(I) and ruthenium(II) monometallic and bimetallic complexes made of 2,2′-bipyridine and 1,10-phenanthroline ligands, [Mn(CO)₃(NN)(4,4′-bpy)]⁺, [{(CO)₃(NN)Mn}₂(4,4′-bpy)]²⁺ and [(CO)₃(NN)Mn(4,4′-bpy)Ru(NN)₂Cl]²⁺ (NN = 2,2′-bipyridine, 1,10-phenanthroline; 4,4′-bpy = 4,4′-bipyridine) are synthesized and characterized, in addition to already known ruthenium(II) complexes [Ru(NN)₂Cl(4,4′-bpy)]⁺ and [Cl(NN)₂Ru(4,4′-bpy)Ru(NN)₂Cl]²⁺. The electrochemical properties show that there is a weak interaction between two metal centers in Mn–Ru heterobimetallic complexes. The photophysical behavior of all the complexes is studied. The Mn(I) monometallic and homobimetallic complexes have no detectable emission. In Mn–Ru heterobimetallic complexes, the attachment of Mn(I) with Ru(II) provides interesting photophysical properties.     

Formation and structure of diruthenium complexes Ru2(CO)6−n (PPh3) n {μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} (n=1, 2)

Ruthenium carbonyl triphenylphosphine complexes Ru₂(CO)_6−n (PPh₃) _n {μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} (n=1, 2) were obtained by the reaction of complex Ru₂(CO)₆{μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} containing the ruthenacyclopentadiene moiety with PPh₃ in refluxing toluene. The complexes were characterized by IR and by¹H,¹³C, and³¹P NMR spectroscopy, and by X-ray analysis. The monophosphine derivative is identical to the complex formed by fragmentation of the Ru₃(CO)₈(PPh₃){μ-C(CH=CHPh)C(Ph)C(CH=CHPh)C(Ph)} cluster and contains the PPh₃ ligand at the ruthenium atom of the ruthenacyclopentadiene moiety. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1836–1843, September, 1998     

Arene Ruthenium(II) Complexes Bearing the κ-P or κ-P,κ-S Ph2P(CH2)3SPh Ligand

Neutral [Ru(η⁶-arene)Cl₂{Ph₂P(CH₂)₃SPh-κP}] (arene = benzene, indane, 1,2,3,4-tetrahydronaphthalene: 2a, 2c and 2d) and cationic [Ru(η⁶-arene)Cl(Ph₂P(CH₂)₃SPh-κP,κS)]X complexes (arene = mesitylene, 1,4-dihydronaphthalene; X = Cl: 3b, 3e; arene = benzene, mesitylene, indane, 1,2,3,4-tetrahydronaphthalene, and 1,4-dihydronaphthalene; X = PF₆: 4a–4e) complexes were prepared and characterized by elemental analysis, IR, ¹H, ¹³C and ³¹P NMR spectroscopy and also by single-crystal X-ray diffraction analyses. The stability of the complexes has been investigated in DMSO. Complexes have been assessed for their cytotoxic activity against 518A2, 8505C, A253, MCF-7 and SW480 cell lines. Generally, complexes exhibited activity in the lower micromolar range; moreover, they are found to be more active than cisplatin. For the most active ruthenium(II) complex, 4b, bearing mesitylene as ligand, the mechanism of action against 8505C cisplatin resistant cell line was determined. Complex 4b induced apoptosis accompanied by caspase activation.     

Ortho-metallated ruthenium(III) complexes with some acid hydrazide based Schiff bases

Ortho-metallated ruthenium(III) complexes with Schiff bases (H₂L) derived from one mole equivalent each of benzaldehyde and acid hydrazides are described. Reactions of H₂L with [Ru(PPh₃)₃Cl₂] in presence of NEt₃ (1:1:2 mole ratio) under aerobic conditions in methanol provide the complexes having the general formula trans-[Ru(L)(PPh₃)₂Cl] in 55-60% yields. The complexes have been characterized with the help of elemental analysis, magnetic susceptibility, electrochemical and various spectroscopic (infrared, electronic and EPR) measurements. The +3 oxidation state of the metal centre in these complexes is confirmed by their one-electron paramagnetic nature. Molecular structures of two representative complexes have been determined by X-ray crystallography. In each complex, the metal ion is in a distorted octahedral CNOClP₂ coordination sphere. The dianionic C,N,O-donor ligand (L²⁻) together with the chloride form a CNOCl square-plane and the P-atoms of the two PPh₃ molecules occupy the two axial sites. The electronic spectra of the complexes in dichloromethane solutions display several absorptions due to ligand-to-metal charge transfer and ligand centred transitions. In dichloromethane solutions, the complexes display a ruthenium(III) → ruthenium(IV) oxidation in the potential range 0.35-0.98 V (vs. Ag/AgCl). All the complexes in frozen (110 K) dichloromethane-toluene (1:1) solutions display rhombic EPR spectra.     

Kinetics and mechanism of electroreduction of ethylenediamine and hydroxyethylenediamine complexes of zinc(II) on a dropping-mercury electrode

The kinetics of electroreduction of ethylenediamine and hydroxyethylenediamine complexes of zinc(II) on a dropping-mercury electrode (DME) in 1 M NaClO₄ solutions of pH 9–11.5 is studied at different ethylenediamine concentrations at 25, 35, and 50°C. One wave with a diffusion limiting current is observed at an overall concentration of zinc(II) complexes of 2 × 10^–5 M and current recording times t ₁ = 0.3–4 s. The polarographic peak that distorts the wave at t ₁ 0.5 s, pH 11.5, and 25°C is due to the accumulation of insoluble reduction products on the electrode surface. The slow electrochemical step on DME involves complexes Znen²⁺, which form in preceding reversible chemical steps from complexes present in solution.__________Translated from Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 397–405.Original Russian Text Copyright © 2005 by Kurtova, Kravtsov, Tsventarnyi.     

Electrochemiluminescence from Ru(bpy)3 immobilized in poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)-poly(vinyl alcohol) composite films

Electrochemical behavior and electrogenerated chemiluminescence (ECL) of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) immobilized in poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)-poly(vinyl alcohol) (PEDOT/PSS-PVA) composite films via ion-exchange have been investigated with tripropylamine (TPA) as the co-reactant at a glassy carbon electrode. The immobilized Ru(bpy)₃²⁺ performed a surface-controlled electrode reaction. The Ru(bpy)₃²⁺ modified electrode showed a fast ECL response to TPA, and was used for the ECL detection of TPA with high sensitivity. The ECL intensity was linearly related to concentrations of TPA over the range from 0.50 μmol L⁻¹ to 0.80 mmol L⁻¹, and the detection limit was 0.10 μmol L⁻¹ (S/N = 3). The as-prepared electrode exhibited good precision and long-term stability for TPA determination.     

Synthesis and characterization of manganese(IV) and ruthenium(III) complexes derived from bis (2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone

Bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone(naohH₄) interacts with manganese(II) acetate in methanol followed by addition of KOH giving [Mn^IV(naoh)(H₂O)₂]. Activated ruthenium(III) chloride reacts with naohH₄ in methanol yielding [Ru^III(naohH₄)Cl(H₂O)Cl₂]. The replacement of aquo by heterocyclic nitrogen donor in these complexes has been observed when the reaction is carried out in presence of heterocyclic nitrogen donors such as pyridine(py), 3-picoline(3-pic) or 4-picoline(4-pic). The molar conductance values in DMF for these complexes suggest non-electrolytic nature. Magnetic moment values suggest +4 oxidation state for manganese in its complexes, however, ruthenium(III) complexes are paramagnetic with one unpaired electron. Electronic spectral studies suggest six coordinate metal ions. IR spectra reveal that naohH₄ coordinates in enol-form and keto-form to manganese and ruthenium, respectively. ESR and cyclic voltammetric studies of the complexes have also been reported.     

Adsorptive stripping voltammetric measurements of trace amounts of platinum(II) and ruthenium(III) in the presence of 1-(2-pyridylazo)-2-naphthol

An extremely sensitive stripping voltammetric procedure for low level measurements of platinum (II, IV) or ruthenium (III, IV) is reported. The method is based on the interfacial accumulation of the platinum (II) or ruthenium (III)-1-(2-pyridylazo)-2-naphthol complex on the surface of a hanging mercury drop electrode, followed by the reduction of the adsorbed complex during the cathodic scan. The peak potential was found to be –0.8 V vs. Ag/AgCl electrode and the reduction current of the adsorbed complex ions of platinum (II) or ruthenium (III) was measured by differential pulse cathodic stripping voltammetry. The optimum experimental conditions were: 1.5×10^–7 mol/l of 1-(2-pyridylazo)-2-naphthol solution of pH 9.3, preconcentration potential of –0.2 V, accumulation time of 3 min and pulse amplitude of 50 mV with 4 mV s^–1 scan rate in the presence of ethanol-water (30% v/v) — sodium sulphate (0.5 mol/l). Linear response up to 6.4 × 10^–8 and 5.1 × 10^–8 mol/l and a relative standard deviation (at 1.2×10^–8 mol/l) of 2.4 and 1.6% (n=5) for platinum (II) and ruthenium (III) respectively were obtained. The detection limits of platinum and ruthenium were 3.2×10^–10 and 4.1×10^–10 mol/l, respectively. The electronic spectra of the Pt(II) — PAN and Ru(III) — PAN complexes were measured at pH 9.3 and the stoichiometric ratios of the complexes formed were obtained by the molar ratio method. The effects of some interfering ions on the proposed procedure were critically investigated. The method was found suitable for the sub-microdetermination of ruthenium (IV) and platinum (IV) after their reduction to ruthenium (III) and platinum (II) with sulphur dioxide in acid media. The applicability of the method for the analysis of binary mixtures of ruthenium (III) and (IV) or platinum (II) and (IV) has also been carried out successfully. The method is simple, rapid, precise, and promising for the determination of the tested metal ions at micro-molar concentration level.     

Reduction of palladium(II) monoglycinate complexes at rotating disc palladium electrode in acid media

Reduction of palladium(II) glycinate complexes in strongly acid 0.5 M NaClO₄ solutions (pH 0.6 and 1.0) with variable palladium(II) complex and free glycine concentration was studied by the taking of cyclic voltammograms at palladium rotating disc electrode. It is shown that it was a chelate monoglycinate palladium(II) complex that was present in all studied solutions and underwent the reduction. The diffusion coefficient of the chelate monoglycinate palladium(II) complex D = (6.5 ± 0.5) × 10⁻⁶ cm²/s was determined from the limiting diffusion current of the complex reduction. The monoglycinate palladium(II) complex reduction occurred in the double-layer segment of the palladium charging curve; it was not complicated by hydrogen adsorption at electrodes. The palladium(II) complex reduction half-wave potential was determined (E _1/2 = ∼0.300 to 0.330 V (SCE)). It is shown that the decreasing of the number of ligands coordinated by palladium via nitrogen atom facilitates the complex reduction process. In particular, the reduction potentials of palladium(II) complexes with different ligand number at palladium electrode shifted markedly toward negative potentials in the series: Pdgly⁺ < Pd(gly)2 < Pd(gly)₄²⁻.     

Ruthenium(III) complexes of amine-bis(phenolate) ligands as catalysts for transfer hydrogenation of ketones

Twelve ruthenium(III) complexes bearing amine-bis(phenolate) tripodal ligands of general formula [Ru(L¹–L³)(X)(EPh₃)₂] (where L¹–L³ are dianionic tridentate chelator) have been synthesized by the reaction of ruthenium(III) precursors [RuX₃(EPh₃)₃] (where E = P, X = Cl; E = As, X = Cl or Br) and [RuBr₃(PPh₃)₂(CH₃OH)] with the tripodal tridentate ligands H₂L¹, H₂L² and H₂L³ in benzene in 1:1 molar ratio. The newly synthesized complexes have been characterized by analytical (elemental and magnetic susceptibility) and spectral methods. The complexes are one electron paramagnetic (low-spin, d⁵) in nature. The EPR spectra of the powdered samples at RT and the liquid samples at LNT shows the presence of three different ‘g’ values (g_x ≠ g_y ≠ g_z) indicate a rhombic distortion around the ruthenium ion. The redox potentials indicate that all the complexes undergo one electron transfer process. The catalytic activity of one of the complexes [Ru(pcr-chx)Br(AsPh₃)₂] was examined in the transfer hydrogenation of ketones and was found to be efficient with conversion up to 99% in the presence of isopropanol/KOH.