Kinetics of Reduction of Some Surfactant-Cobalt(III) Complexes by Iron(II)

The electron transfer kinetics of the reaction between the surfactant-cobalt(III) complex ions, cis-[Co(en)₂(C₁₂H₂₅NH₂)₂]³⁺, cis-α-[Co(trien)(C₁₂H₂₅NH₂)₂]³⁺(en:ethylenediamine, trien:triethylenetetramine, C₁₂H₂₅NH₂ : dodecylamine) by iron(II) in aqueous solution was studied at 298, 303, 308 K by spectrophotometry method under pseudo-first-order conditions using an excess of the reductant in self-micelles formed by the oxidant, cobalt(III) complex molecules, themselves. The rate constant of the electron transfer reaction depends on the initial concentration of the surfactant cobalt(III) complexes. ΔS^# also varies with initial concentration of the surfactant cobalt(III) complexes. By assuming outer-sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of the self-micelles formed by the surfactant cobalt(III) complexes in the reaction medium. The rate constant of each complex increases with initial concentration of one of the reactants surfactant-cobalt(III) complex, which shows that self micelles formed by surfactant-cobalt(III) complex itself has much influence on these reactions. The electron transfer reaction of the surfactant-cobalt(III) complexes was also carried out in a medium of various concentrations of β-cyclodextrin. β-cyclodextrin retarded the rate of the reaction.     

Microheterogeneous mediated electron transfer reaction (ETR) of surfactant cobalt(III) complexes by Fe2+: Effect of pyridine substituent as co ligand

The outer sphere electron transfer reaction of surfactant cobalt(III) complexes, Cis-[Co(en)₂(4CNP)(C₁₂H₂₅NH₂)](ClO₄)₃ 1, Cis-[Co(trien)(4CNP)(C₁₂H₂₅NH₂)](ClO₄)₃ 2 and Cis-[Co(trien)(4AMP)(C₁₂H₂₅NH₂)](ClO₄)₃ 3 (en: ethylenediamine, trien: triethylenetetramine, 4CNP: 4-cyanopyridine, 4AMP: 4-aminopyridine, C₁₂H₂₅NH₂: dodecylamine) have been investigated by Fe²⁺ ion in liposome vesicles (DPPC) and ionic liquids medium at different temperatures under pseudo first order conditions using an excess of the reductant. In the presence of ionic liquid medium the second order rate constant for this electron transfer reaction was found to increase with increasing concentration of ionic liquids. Below the phase transition temperature of DPPC, the rate decreased with increasing concentration of DPPC, while above the phase transition temperature the rate increased with increasing concentration of DPPC for the same complexes has also been studied. Experimentally the reactions were found to be second order and the electron transfer postulated as outer sphere. The results have been discussed in terms of increased hydrophobic effect, self aggregation and the presence of pyridine ligand containing 4-amino and 4-cyano substituent.     

Synthesis of allyl-transition metal complexes by phase transfer catalyzed reactions of metal carbonyl halides: III. Considerations of the mechanisms

Mechanisms are proposed for the hydroxide ion-initiated reactions of metal carbonyl halides which lead to allyl-transition metal complexes under phase transfer conditions. Evidence is presented for intermediate anionic metallocarboxylic acids in reactions leading to η³-allyl products of molybdenum, iron, ruthenium and manganese, whereas η¹ complexes are shown to result from halide displacement reactions in which simple metal carbonyl anions are generated. In some cases phosphorus-containing ligands inhibit the hydroxide-promoted reactions of metal carbonyl halides with allyl bromide; a rationale involving decreased acidity of the carbonyl ligands is presented. Syntheses of η³-C₃H₅Mn(CO)₃P(OCH₃)₃ and η³-C₃H₅Mn(CO)₂[P(OCH₃)₃]₂ by phase transfer catalysis are also described.     

Efficient transfer hydrogenation of ketones in the presence of ruthenium N-heterocyclic carbene catalysts

Novel ruthenium carbene complexes have been in situ generated and tested for the transfer hydrogenation of ketones. Applying Ru(cod)(methylallyl)₂ in the presence of imidazolium salts in 2-propanol and sodium-2-propanolate as base, turnover frequencies up to 346 h⁻¹ have been obtained for reduction of acetophenone. A comparative study involving ruthenium carbene and ruthenium phosphine complexes demonstrated the higher activity of ruthenium carbene complexes.     

Role of electronic structure of ruthenium polypyridyl dyes in the photoconversion efficiency of dye‐sensitized solar cells: Semiempirical investigation

ZINDO/S calculations on cis‐Ru(4,4′‐dicarboxy‐2,2′‐bipyridine)₂(X)₂ and cis‐Ru(5,5′‐dicarboxy‐2,2′‐bipyridine)₂(X)₂ complexes where X = Cl^?, CN^?, and NCS^? reveal that the highest occupied molecular orbital (HOMO) of these complexes has a large amplitude on both the nonchromophoric ligand X and the central ruthenium atom. The lowest‐energy metal to ligand charge transfer (MLCT) transition in these complexes involves electron transfer from ruthenium as well as the halide/pseudohalide ligand to the polypyridyl ligand. The contribution of the halide/pseudohalide ligand(X) to the HOMO affects the total amount of charge transferred to the polypyridyl ligand and hence the photoconversion efficiency. The virtual orbitals involved in the second MLCT transition in 4,4′‐dicarboxy‐2,2′‐bipyridine complexes have higher electron density on the ? COOH group compared to the lowest unoccupied molecular orbital and hence a stronger electronic coupling with the TiO₂ surface and higher injection efficiency at shorter wavelengths. In comparison, the virtual orbitals involved in the second MLCT transition in 5,5′‐dicarboxy‐2,2′‐bipyridine complexes have lesser electron density on the ? COOH group, leading to a weaker electronic coupling with the TiO₂ surface and therefore lower efficiency for electron injection at shorter wavelengths for these complexes. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Synthesis,characterization and catalytic studies of iron(III), cobalt(II), nickel(II) and copper(II) complexes containing triphenylphosphine and β-diketones

A series of new β-diketonato complexes have been synthesized from the reactions of iron(III), cobalt(II), nickel(II) and copper(II) Ph₃P complexes with β-diketones (acetylacetone, benzoylacetone and dibenzoylmethane). All the complexes have been characterized by elemental analyses, spectral studies (i.r., electronic., magnetic., e.p.r., ¹H-n.m.r.) and cyclic voltammetry. The new complexes have been used as catalysts for aromatic coupling and oxidation reactions. Higher catalytic activity has been observed for the nickel(II) complexes compared to the other complexes.     

Theoretical study on photooxidation mechanism of ruthenium complex [Ru(II)‐(bpy)2(TMBiimH2)]2+ with molecular oxygen

Photoinduced reactions of ruthenium complexes with molecular oxygen have attracted a lot of experimental attention; however, the reaction mechanism remains elusive. In this work, we have used the density functional theory method to scrutinize the visible‐light induced photooxidation mechanism of the ruthenium complex [Ru(II)‐(bpy)₂(TMBiimH₂)]²⁺ (bpy: 2, 2‐bipyridine and TMBiimH₂: 4, 5, 4, 5‐tetramethyl‐2, 2‐biimidazole) initiated by the attack of molecular oxygen. The present computational results not only explain very well recent experiments, also provide new mechanistic insights. We found that: (1) the triplet energy transfer process between the triplet molecular oxygen and the metal‐ligand charge transfer triplet state of the ruthenium complex, which leads to singlet molecular oxygen, is thermodynamically favorable; (2) the singlet oxygen addition process to the S₀ ruthenium complex is facile in energy; (3) the chemical transformation from endoperoxide to epidioxetane intermediates can be either two‐ or one‐step reaction (the latter is energetically favored). These findings contribute important mechanistic information to photooxidation reactions of ruthenium complexes with molecular oxygen. © 2016 Wiley Periodicals, Inc.     

Quantum-chemical simulation of the active center of vitamin B12

The electronic structure of porphin and corrin complexes of cobalt differing with respect to the oxidation state of the central ion has been investigated by the MO-LCAO-SCF-CNDO method with the Kai-Nishimoto parameters for transition metals. On the basis of an analysis of the distribution of the electron density and the structure of the energy spectrum, it has been shown that the oxidation-reduction processes of the complexes are accompanied by restructuring of the energy spectrum, and the differences between the electronic structures of porphin and corrin complexes have been discussed. It has been established that cobalt(I) porphin has stronger nucleophilic properties than does cobalt(I) corrin. The electronic structure of hexacoordinate complexes in which an imidazole molecule and a molecule of L (L = H₂O, CH₃ ⁺, CN^–) are axially coordinated has been calculated. The mechanisms of the dissociation of cobalt alkyl complexes and the differences between the processes of the heterolytic dissociation of porphin and corrin complexes have been discussed. It has been shown that the elimination of a CH₃ ⁺ cation, which plays an important role in biomethylation reactions, is more favorable in corrin complexes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 4, pp. 400–409. July–August, 1986.     

Synthesis, characterization, antitumor activity of nickel(Ⅱ) and cobalt (Ⅱ) complexes of 2,2''''-diamino-4,4''''-bithiazole and their interaction with dGMP

New complexes,of bis(2,2'-diamino-4,4'-bithiazole)sulfate nickel(Ⅱ) and bis(2,2'-diami-no-4,4'-bithiazole)sulfate cobalt(Ⅱ),have been prepared.The complexes were characterized by infrared and UV-Vis spectroscopy,1H NMR,elemental analyses and molar conductivity.The effect of these complexes on the DNA synthesis of sarcoma 180 cells has been studied by the technique of isotopic liquid scintillation.The results indicated that complexes show ability to inhibit DNA synthesis of the tumor cells.In order to provide a molecular basis for understanding the biological effects,the probe,[trana-en2Os(η2-H2)](CF3SO3)2 (en,ethylenediamine) as a monitor was first used to explore interaction of the complexes with 2'-deoxyguanosine-5'-monophosphate (dGMP).     

Präparative Darstellung von μ-Disauerstoff-bis-kobalt(II)-Chelaten

Binuclear cobalt chelates with O₂ as bridging ligand have been prepared, using ethylenediamine, triethylenetetramine, tetraethylenepentamine and tris-(2-aminoethyl)-amine as chelating agents and SCN^? and ClO₄^? as anions. They form well characterized crystals which give off molecular oxygen spontaneously in acid solution and, except in the case of the cobalt tetra-ethylenepentamine chelate, reveal the general composition [(Z)Co · μ(O₂, OH) · Co(Z)]X₃, where Z represents the polydentate complexing agents and X the anion. In the presence of ammonia different complexes are produced, in which NH₃ occupies one coordination site of each cobalt, replacing the hydroxo bridge.     

Characterization of the Excited State Properties of Some New Photosensitizers of the Ruthenium (Polypyridine) Family

The photophysical and electron transfer properties of the lowest excited state of nine ruthenium (polypyridine) complexes have been characterized. The complexes studied are Ru (bpy)_3-n (LL)²⁺_n, where n varies from 0 to 3, and LL is 4, 4′-di-t-butyl-2,2′-bipyridine (DTB-bpy), 3, 3′-dimethyl-2, 2′-bipyridine (DM-bpy), or a 2, 2′-diquinolyl derivative (DMCH). The results obtained show that the Ru (bpy)₂(DMCH)²⁺ complex is expected to be a more efficient mediator than Ru (bpy)²⁺₃ in the water-splitting reaction by solar energy.     

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.     

Mechanisms of Cobalt/Phosphine-Catalyzed Cross-Coupling Reactions

>The combination of CoCl₂ with bidentate phosphines is known to catalyze challenging cross-coupling and Heck-type reactions, but the mechanisms of these valuable transformations have not been established. Here, we use electrospray-ionization mass spectrometry to intercept the species formed in these reactions. Our results indicate that a sequence of transmetalation, reductive elimination, and redox disproportionation convert the cobalt(II) precatalyst into low-valent cobalt complexes. These species readily transfer single electrons to alkyl bromides, which thereupon dissociate into alkyl radicals and Br⁻. In cross-coupling reactions, the alkyl radicals add to the cobalt catalyst to form observable heteroleptic complexes, which release the coupling products through reductive eliminations. In the Heck-type reactions, the low abundance of newly formed ionic species renders the analysis more difficult. Nonetheless, our results also point to the occurrence of single-electron transfer processes and the involvement of radicals in these transformations.     

Spectrophotometric Determination of Ruthenium in Solutions of Nitroso and Sulfate Complexes Using Microwave Radiation

It has been shown that ruthenium can be determined in solutions of ammonium nitrosopentachlororuthenate (NH₄)₂[Ru(NO)Cl₅] with nitroso and aquachloro complexes present simultaneously by its reaction with 1,10-phenanthroline and in solutions of sulfate complexes using microwave radiation. It is found by molecular absorption and luminescence studies that the composition of the complex formed corresponds to ruthenium(II) tris-(1,10-phenanthrolinate) {[Ru(Phen)₃]²⁺}. The complexation time is decreased by several tens of times (down to 5 min) compared to conventional heating, and a 100% yield of the complex is achieved. In the presence of HCl, the conversion of nitroso species to aquachloro ruthenium complexes upon microwave irradiation is inefficient. It is found that, compared to [Ru₂OCl₁₀]^4–, [Ru(NO)Cl₅]^2– is more labile in the complexation reactions of ruthenium with 1,10-phenanthroline under microwave irradiation. Regardless of the concentration of H₂SO₄ (1.7–12 M) in the starting solutions, ruthenium sulfate complexes can be converted in a microwave field to more labile chloride complexes.     

Ruthenium(II) unsymmetrical N2O2 tetradentate Schiff-base complexes: synthesis,characterization, and catalytic studies

A series of six-coordinate ruthenium(II) complexes [Ru(CO)(L ^x )(B)] (B = PPh₃, AsPh₃ or Py; L ^x = unsymmetrical tetradentate Schiff base, x = 5–8; L⁵= salen-2-hyna, L⁶= Cl-salen-2-hyna, L⁷= valen-2-hyna, L⁸= o-hyac-2-hyna) have been prepared by reacting [RuHCl(CO)(EPh₃)₂(B)] (E = P or As) with unsymmetrical Schiff bases in benzene under reflux. The new complexes have been characterized by analytical and spectroscopic (infrared, electronic, ¹H, ³¹P, and ¹³C NMR) data. An octahedral structure has been assigned for all the complexes. The new complexes are efficient catalysts for the transfer hydrogenation of ketones and also exhibit catalytic activity for the carbon–carbon coupling reactions.     

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.     

G‐quadruplex Nanowires To Direct the Efficiency and Selectivity of Electrocatalytic CO2 Reduction

DNA as a medium for electron transfer has been widely used in photolytic processes but is seldom applied to dark reaction of CO₂ reduction. A G‐quadruplex nanowire (tsGQwire) assembled by guanine tetranucleotides was used to host several metal complexes and further to mediate electron transfer processes in the electrochemical reduction of CO₂ catalyzed by these complexes. The tsGQwire modified electrode increased the Faradaic efficiency of cobalt(II) phthalocyanine (Co^IIPc) 2.5‐folds for CO production than bare Co^IIPc electrode, with a total current density of 11.5 mA cm^?2. Comparable Faradaic efficiency of HCOOH production was achieved on tsGQwire electrode when the catalytic center was switched to a GQ targeting Ru complex. The high efficiency and selectivity of electrocatalytic CO₂ reduction was attributed to the unique binding of metal complexes on G‐quadruplex and electron transfer mediated by GQ nanowire to achieve efficient redox cycling of catalytic centers on the electrode.     

MIXED HALIDE DIALKYL AND ALKYLENEDITHIOPHOSPHATE DERIVATIVES OF RUTHENIUM (III)

Abstract

Mixed chloride dialkyl and alkylenedithiophosphates of ruthenium (III). RuC1_3-n|(S₂P(OR)₂|n (R = Prⁿ, and Ph) and RuCl_3-n,[S₂ POGO]n G =-CMe₂CMe₂,- CH₂CMe₂CH₂-, -CH₂CEt₂CH₂-. and -CMe₂CH₂CHMe-, n = 1,2 have been synthesized for the first time by the reactions of ruthenium trichloride with ammonium dialkyl and alkylenedithiophosphate or alternatively by disproportionation reactions of ruthenium trichloride with ruthenium tris(dialkyl and alkylenedithiophosphates) in different stoichiometric ratios in benzene.

These new complexes have been characterized by elemental analysis, molecular weight determinations, as well as IR and NMR (¹H and ³¹P) data. Chelated structures with bidentate dialkyl and alkylenedithiophosphates groups have been proposed for all these derivatives.     

Five-coordinate low-spin cobalt(II) complexes with benzeneseleninato ions and ethylenediamine as ligands

Summary Five-coordinate bis(benzeneseleninato)tris(ethylenediamine) cobalt (II)complexes are obtained by reaction of Co(H₂O)₂ (XC₆ H4 SeO₂)2 complexes (X = H, p-Cl, m-CI, p-Br, ni-Br, p-Me,p-NO₂) with ethylenediamine. The diaquo complexes (one mole)react with ethylenediamine (three moles)to form O-seleninato derivatives. Spectral and magnetic properties show that the complexes are low-spin (s = 1/2) and,on the basis of the electronic spectra a distorted trigonal geometry,D _3h , is suggested. Assignments for the electronic spectra are proposed. Conductivity data indicate that these derivatives are nonelectrolytes. Both ethylenediamine and [RSeO₂ ]^– behave as monodentate ligands.     

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.