Novel ruthenium based electrocatalyst for the convenient reduction of nitrogen-nitrogen bonds in azide to ammonia in aqueous solution

The interaction of azide (N ₃ ⁻ ) ion, at pH 5.3 with [Ru^III(EDTA) (H₂O)]⁻ (EDTA = ethylenediaminetetraacetate) was studied in aqueous solution by polarography and cyclic voltammetry. The product, [Ru^III(EDTA)(N₃)]²⁻ showed a multi-electron reduction step, which is polarographically reversible but, cyclic voltammetrically irreversible, in the potential range − 0.1 to − 0.2 V vs SCE. This reduction step, which was different from the one-electron reduction step of [Ru^III(EDTA)(H₂O)]; (E^1/2 = −0.113V vs SCE) was assigned to the reduction of the coordinated azide ion to ammonia by the irreversible transfer of electrons from Hg-electrode via ruthenium metal. Azide, at pH 5.3, was reduced, electrolytically, for the first time, to ammonia at Hg-pool cathode mediated by [Ru^III(EDTA) (N₃)]²⁻. The turnover number with respect to the formation of ammonia (moles of ammonia per mole of ruthenium per hour) was obtained from the constant potential electrolysis data. On the basis of experimental observations, a probable mechanism has been proposed for the electrocatalytic reduction of azide to ammonia in aqueous solution.     

Recent Chemistry Based on the [RuCp(CH3CN)3]+ Cation: Reappraisalof an Old Precursor

 This article gives an overview of recent chemistry based on the tris-acetonitrile complex [RuCp(CH₃CN)₃]⁺. Due to the labile nature of the CH₃CN ligands, substitution reactions are a dominant feature of this complex. Important derivatives are the highly reactive complexes [RuCp(PR ₃)(CH₃CN)₂]⁺ which are a source of the 14e⁻ fragment [RuCp(PR ₃)]⁺. These species are catalytically active in the redox isomerization of allyl alcohols to give aldehydes and ketones. Furthermore, the cationic complex [RuCp(κ¹(P),η²-PPh₂CH₂CH₂CH*CH₂)(CH₃CN)]PF₆ derived from the reaction of [RuCp(CH₃CN)₃]⁺ with PPh₂CH₂CH₂CH*CH₂ is a model compound for studying coupling reactions of olefins and acetylenes. In addition, [RuCp(CH₃CN)₃]⁺ is a valuable precursor for the synthesis of configurationally stable chiral three-legged piano-stool ruthenium complexes. These are currently being intensively investigated as Lewis acid catalysts in asymmetric synthesis.     

The formation of formic acid upon low-temperature condensation of CO2−H2 and CO−H2O gas mixtures dissociated in electric discharge

The formation of formic acid in the low-temperature condensation of CO₂−H₂ and CO−H₂O gas mixtures dissociated in electric discharge was investigated. The gas-phase concentrations of H^., O^., OH^., and O₂ were measured downstream a microwave discharge in a CO₂−H₂ mixture. Low-temperature (77 K) condensates formed from CO₂−H₂ and CO−H₂O mixtures were studied by ESR. The formation of formic acid in the CO₂−H₂ and CO−H₂O systems was found to be due to the reactions of H^., CO, O^., and O₂ on the condensate surface. A single mechanism of the formation of formic acid in the CO₂−H₂ and CO−H₂O systems was proposed.     

Recent Chemistry Based on the [RuCp(CH3CN)3]+ Cation: Reappraisalof an Old Precursor

Summary.  This article gives an overview of recent chemistry based on the tris-acetonitrile complex [RuCp(CH₃CN)₃]⁺. Due to the labile nature of the CH₃CN ligands, substitution reactions are a dominant feature of this complex. Important derivatives are the highly reactive complexes [RuCp(PR ₃)(CH₃CN)₂]⁺ which are a source of the 14e⁻ fragment [RuCp(PR ₃)]⁺. These species are catalytically active in the redox isomerization of allyl alcohols to give aldehydes and ketones. Furthermore, the cationic complex [RuCp(κ¹(P),η²-PPh₂CH₂CH₂CH*CH₂)(CH₃CN)]PF₆ derived from the reaction of [RuCp(CH₃CN)₃]⁺ with PPh₂CH₂CH₂CH*CH₂ is a model compound for studying coupling reactions of olefins and acetylenes. In addition, [RuCp(CH₃CN)₃]⁺ is a valuable precursor for the synthesis of configurationally stable chiral three-legged piano-stool ruthenium complexes. These are currently being intensively investigated as Lewis acid catalysts in asymmetric synthesis. Received May 31, 2000. Accepted June 13, 2000     

Electrochemical behaviour of [Ru(L)(CO)2Cl2] [Ru(L)(CO)Cl3][Me4N] and [Ru(L)(CO)2(CH3CN)2][CF3SO3]2 complexes (L = 2,2′- bipyridine or 4,4′-isopropoxycarbonyl-2,2′-bipyridine)

The clectrochemical behaviour of the complexes [Ru^II(L)(CO)₂Cl₂], [Ru^II(L)(CO)Cl₃][Me₄N] and [Ru^II(L)(CO)₂(CH₃CN)₂][CF₃SO₃]₂ (L = 2,2′-bipyridine or 4,4′-isopropoxycarbonyl-2,2′-bipyridine) has been investigated in CH₃CN. The oxidation of [Ru(L)(CO)₂Cl₂] produces new complexes [Ru^III(L)(CO)(CH₃CN)₂Cl]²⁺ as a consequence of the instability of the electrogenerated transient Ru^III species [Ru^III(L)(CO)₂Cl₂]⁺. In contrast, the oxidation of [Ru^II(L)(CO)Cl₃][Me₄N] produces the stable [Ru^III(L)(CO)Cl₃] complex. In contrast [Ru^II(L)(CO)₂(CH₃CN)₂][CF₃SO₃]₂ is not oxidized in the range up to the most positive potentials achievable. The reduction of [Ru^II(L)(CO)₂Cl₂] and [Ru^II(L)(CO)₂(CH₃CN)₂][CF₃SO₃]₂ results in the formation of identical dark blue strongly adherent electroactive films. These films exhibit the characteristics of a metal-metal bond dimer structure. No films are obtained on reduction of [Ru^II(L)(CO)Cl₃][Me₄N]. The effect of the substitution of the bipyridine ligand by electron-withdrawing carboxy ester groups on the electrochemical behaviour of all these complexes has also been investigated.     

Effect of sodium cation on the electrochemical reduction of CO<Subscript>2</Subscript> at a copper electrode in methanol

The electrochemical reduction of CO₂ with a Cu electrode in methanol was investigated with sodium hydroxide supporting salt. A divided H-type cell was employed; the supporting electrolytes were 80 mmol dm⁻³ sodium hydroxide in methanol (catholyte) and 300 mmol dm⁻³ potassium hydroxide in methanol (anolyte). The main products from CO₂ were methane, ethylene, carbon monoxide, and formic acid. The maximum current efficiency for hydrocarbons (methane and ethylene) was 80.6%, at −4.0 V vs Ag/AgCl, saturated KCl. The ratio of current efficiency for methane/ethylene, r _f(CH₄)/r _f(C₂H₄), was similar to those obtained in LiOH/methanol-based electrolyte and larger relative to those in methanol using KOH, RbOH, and CsOH supporting salts. In NaOH/methanol-based electrolyte, the efficiency of hydrogen formation, a competing reaction of CO₂ reduction, was suppressed to below 4%. The electrochemical CO₂ reduction to methane may be able to proceed efficiently in a hydrophilic environment near the electrode surface provided by sodium cation.     

Photochemical Reduction of Carbon Dioxide Catalyzed by a Ruthenium‐Substituted Polyoxometalate

A polyoxometalate of the Keggin structure substituted with Ru^III, ⁶Q₅[Ru^III(H₂O)SiW₁₁O₃₉] in which ⁶Q=(C₆H₁₃)₄N⁺, catalyzed the photoreduction of CO₂ to CO with tertiary amines, preferentially Et₃N, as reducing agents. A study of the coordination of CO₂ to ⁶Q₅[Ru^III(H₂O)SiW₁₁O₃₉] showed that 1) upon addition of CO₂ the UV/Vis spectrum changed, 2) a rhombic signal was obtained in the EPR spectrum (g_x=2.146, g_y=2.100, and g_z=1.935), and 3) the ¹³C NMR spectrum had a broadened peak of bound CO₂ at 105.78 ppm (Δ_1/2=122 Hz). It was concluded that CO₂ coordinates to the Ru^III active site in both the presence and absence of Et₃N to yield ⁶Q₅[Ru^III(CO₂)SiW₁₁O₃₉]. Electrochemical measurements showed the reduction of Ru^III to Ru^II in ⁶Q₅[Ru^III(CO₂)SiW₁₁O₃₉] at ?0.31 V versus SCE, but no such reduction was observed for ⁶Q₅[Ru^III(H₂O)SiW₁₁O₃₉]. DFT‐calculated geometries optimized at the M06/PC1//PBE/AUG‐PC1//PBE/PC1‐DF level of theory showed that CO₂ is preferably coordinated in a side‐on manner to Ru^III in the polyoxometalate through formation of a Ru? O bond, further stabilized by the interaction of the electrophilic carbon atom of CO₂ to an oxygen atom of the polyoxometalate. The end‐on CO₂ bonding to Ru^III is energetically less favorable but CO₂ is considerably bent, thus favoring nucleophilic attack at the carbon atom and thereby stabilizing the carbon sp² hybridization state. Formation of a O₂C–NMe₃ zwitterion, in turn, causes bending of CO₂ and enhances the carbon sp² hybridization. The synergetic effect of these two interactions stabilizes both Ru–O and C–N interactions and probably determines the promotional effect of an amine on the activation of CO₂ by [Ru^III(H₂O)SiW₁₁O₃₉]^5?. Electronic structure analysis showed that the polyoxometalate takes part in the activation of both CO₂ and Et₃N. A mechanistic pathway for photoreduction of CO₂ is suggested based on the experimental and computed results.     

Kinetics of the ?OH-radical initiated reactions of acetic acid and its deuterated isomers

Kinetics of the ^•OH-initiated reactions of acetic acid and its deuterated isomers have been investigated performing simulation chamber experiments at T = 300 ± 2 K. The following rate constant values have been obtained (± 1σ, in cm³ molecule⁻¹ s⁻¹): k ₁(CH₃C(O)OH + ^•OH) = (6.3 ± 0.9) × 10⁻¹³, k ₂(CH₃C(O)OD + ^•OH) = (1.5 ± 0.3) × 10⁻¹³, k ₃(CD₃C(O)OH + ^•OH) = (6.3 ± 0.9) × 10⁻¹³, and k ₄(CD₃C(O)OD + ^•OH) = (0.90 ± 0.1) × 10⁻¹³. This study presents the first data on k ₂(CH₃C(O)OD + ^•OH). Glyoxylic acid has been detected among the products confirming the fate of the ^•CH₂C(O)OH radical as suggested by recent theoretical studies.     

A Ruthenium‐Based Biomimetic Hydrogen Cluster for Efficient Photocatalytic Hydrogen Generation from Formic Acid

A ruthenium‐based biomimetic hydrogen cluster, [Ru₂(CO)₆(μ‐SCH₂CH₂CH₂S)] ( 1 ), has been synthesized and, in the presence of the P ligand tri(o‐tolyl)phosphine, demonstrated efficient photocatalytic hydrogen generation from formic acid decomposition. Turnover frequencies (TOFs) of 5500 h^?1 and turnover numbers (TONs) over 24 700 were obtained with less than 50 ppm of the catalyst, thus representing the highest TOFs for ruthenium complexes as well as the best efficiency for photocatalytic hydrogen production from formic acid. Moreover, 1 showed high stability with no significant degradation of the photocatalyst observed after prolonged photoirradiation at 90 °C.     

Kinetic-potentiometric assay of formaldehyde in pharmaceutical and industrial samples, monitored by copper solid ion selective electrode, after its reaction with the copper(II)-bis-(ethylenediamine) complex

A kinetic-potentiometric method is described for the quantitative assay of formaldehyde (HCHO) in pharmaceutical and industrial preparations. It is based on the reaction of HCHO with (ethylenediamine)-Cu(II)-sulfate [Cu(CH₂NH₂)₂(H₂O)₂] · SO₄. The changes in potential, resulting from the release of the Cu(II) cations, are monitored with a Cu(II)-ion selective electrode. The calibration curve for the HCHO is linear in the concentration range 50–250 mg L⁻¹, with a limit of detection of 8.5 mg L⁻¹. The method shows very good reproducibility with an RSD of 2.6% for successive injections (n = 5) of 150 mg L⁻¹ HCHO primary solution, while it is interference free. The method was successfully tested in various industrial and pharmaceutical preparations.     

A new octahedral cobalt(III) complex of (1,8)- bis (2-hydroxybenzamido)-3,6-diazaoctane incorporating phenolate-amide-amine coordination: synthesis, X-ray crystal structure, ligand substitution and redox activity with sulfur(IV) and l -ascorbic acid

The octahedral complex, [Co^III(HL)]·9H₂O (H₄L = (1,8)-bis(2-hydroxybenzamido)-3,6-diazaoctane) incorporating bis carboxamido-N-, bis sec-NH, phenolate, and phenol coordination has been synthesized and characterized by analytical, NMR (¹H, ¹³C), e.s.i.-Mass, UV–vis, i.r., and Raman spectroscopy. The formation of the complex has also been confirmed by its single crystal X-ray structure. The cyclic voltammetry of the sample in DMF ([TEAP] = 0.1 mol dm⁻³, TEAP = tetraethylammonium perchlorate) displayed irreversible redox processes, [Co^III(HL)] → [Co^IV(HL)]⁺ and [Co^III(HL)] → [Co^II(HL)]⁻ at 0.41 and −1.09 V (versus SCE), respectively. A slow and H⁺ mediated isomerisation was observed for the protonated complex, [Co^III(H₂L)]⁺ (pK = 3.5, 25 °C, I = 0.5 mol dm⁻³). H₂Asc was an efficient reductant for the complex and the reaction involved outer sphere mechanism; the propensity of different species for intra molecular reduction followed the sequence: [{[Co^III(HL)],(H₂Asc)}–H]⁻ <<< {[Co^III(H₂L)],(H₂Asc)}⁺ < {[Co^III(HL)],(H₂Asc)}. A low value (ca. 3.7 × 10⁻¹⁰ dm³ mol⁻¹ s⁻¹, 25 °C, I = 0.5 mol dm⁻³) for the self exchange rate constant of the couple [Co^III(HL)]/[Co^II(HL)]⁻ indicated that the ligand HL³⁻ with amido (N-) donor offers substantial stability to the Co^III state. HSO₃⁻ and [Co^III(HL)] formed an outer sphere complex {[Co^III(HL)],(HSO₃⁻)}, which was slowly transformed to an inner sphere S-bonded sulfito complex, [Co^III(H₂L)(HSO₃)] and the latter was inert to reduction by external sulfite but underwent intramolecular S^IV → Co^III electron transfer very slowly. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and characterization of the [Ru<Subscript>3</Subscript>O(CH<Subscript>3</Subscript>COO)<Subscript>6</Subscript>(py)<Subscript>2</Subscript>(BPE)Ru(bpy)<Subscript>2</Subscript>Cl](PF<Subscript>6</Subscript>)<Subscript>2</Subscript> dimer

The polymetallic [Ru₃O(CH₃COO)₆(py)₂(BPE)Ru(bpy)₂Cl](PF₆)₂ complex (bpy = 2,2′-bipyridine, BPE = trans-1,2-bis(4-pyridil)ethylene and py = pyridine) was assembled by the combination of an electroactive [Ru₃O] moiety with a [Ru(bpy)₂(BPE)Cl] photoactive centre, and its structure was determined using positive ion electrospray (ESI-MS) and tandem mass (ESI-MS/MS) spectrometry. The [Ru₃O(CH₃COO)₆(py)₂(BPE)Ru(bpy)₂Cl]²⁺ doubly charged ion of m/z 732 was mass-selected and subject to 15 eV collision-induced dissociation, leading to a specific dissociation pattern, diagnostic of the complex structure. The electronic spectra display broad bands at 409, 491 and 692 nm ascribed to the [Ru(bpy)₂(BPE)] charge-transfer bands and to the [Ru₃O] internal cluster transitions. The cyclic voltammetry shows five reversible waves at −1.07 V, 0.13 V, 1.17 V, 2.91 V and −1.29 V (vs SHE) assigned to the [Ru₃O]^{−1/0/+1/+2/+3} and to the bpy^0/−1 redox processes; also a wave is observed at 0.96 V, assigned to the Ru^+2/+3 pair. Despite the conjugated BPE bridge, the electrochemical and spectroelectrochemical results indicate only a weak coupling through the π-system, and preliminary photophysical essays showed the compound decomposes under visible light irradiation.     

Mechanism of formic acid decomposition on P?Mo heteropolyacid

Hydrated (undecomposed) form of heteropolyacid H₃PMo₁₂O₄₀/SiO₂ exhibits a higher activity in the formic acid decomposition than the corresponding dehydrated sample. The formic acid decomposition takes place on strong Br?nsted acid sites of the heteropolyacid.Ab initio SCF MO LCAO method was used for the calculation of the electronic state of two surface complexes of HCOOH molecule (S1 and S2) coordinated to a proton H⁺. The S1 complex is formed by proton addition to the carbonyl oxygen, whereas the S2 complex is formed proton addition to the oxygen atom of the C−O−H fragment of HCOOH. The selective weakening of the C−O bond and localization of the positive charge on the (O=C−H) fragment in the protonated complex S2 are favorable for the decomposition of formic acid to CO and H₂O.     

Synthesis and magnetic properties of polymeric complexes containing ruthenium(II)-ruthenium(III) tetracarboxylato units linked by cyanato,thiocyanato, and selenocyanato ligands

Polymeric complexes of ruthenium(II)-ruthenium(III) tetracarboxylato units linked by cyanato, thiocyanato, and selenocyanato ligands [Ru₂{O₂C(CH₂)_mCH₃}₄(L)] _n (m = 0, 4–7; L = OCN⁻, SCN⁻, and SeCN⁻) were prepared and characterized based on the elemental analyses, IR, and diffuse reflectance spectra. Magnetic susceptibilities were measured at the temperature range of 4.5 K to 300 K, where the interdimer antiferromagnetic interactions were revealed. The strongest interaction was exhibited in case of m = 7 and L = OCN⁻. ¹H-NMR spectra of [Ru{O₂C(CH₂)₇CH₃}₄(SCN)] _n in CD₂Cl₂ showed broad signals which can be ascribed to polymeric species, as the addition of tetrabutylammonium thiocyanate caused sharper signals due to the formation of [Ru₂{O₂C(CH₂)₇CH₃}₄(SCN)₂]⁻ adduct as the main species in the solution. Dedicated to Professor Milan Melník on the occasion of his 70th birthday     

Chemistry of ruthenium in N2P2X2 (X = Cl, Br) coordination sphere: Synthesis, characterization and reactivities

Reaction of 2-(phenylazo)pyridine (pap) with [Ru(PPh₃)₃X₂] (X = Cl, Br) in dichloromethane solution affords [Ru(PPh₃)₂(pap)X₂]. These diamagnetic complexes exhibit a weakdd transition and two intense MLCT transitions in the visible region. In dichloromethane solution they display a one-electron reduction of pap near − 0.90 V vs SCE and a reversible ruthenium(II)-ruthenium(III) oxidation near 0.70 V vs SCE. The [Ru^III(PPh₃)₂(pap)Cl₂]⁺ complex cation, generated by coulometric oxidation of [Ru(PPh₃)₂(pap)Cl₂], shows two intense LMCT transitions in the visible region. It oxidizes N,N-dimethylaniline and [Ru^II(bpy)₂Cl₂] (bpy = 2,2′-bipyridine) to produce N,N,N′,N′-tetramethylbenzidine and [Ru^III(bpy)₂Cl₂]⁺ respectively. Reaction of [Ru(PPh₃)₂(pap)X₂] with Ag⁺ in ethanol produces [Ru(PPh₃)₂(pap)(EtOH)₂]²⁺ which upon further reaction with L (L = pap, bpy, acetylacetonate ion(acac⁻) and oxalate ion (ox²⁻)) gives complexes of type [Ru(PPh₃)₂(pap)(L)]ⁿ⁺ (n = 0, 1, 2). All these diamagnetic complexes show a weakdd transition and several intense MLCT transitions in the visible region. The ruthenium(II)-ruthenium(III) oxidation potential decreases in the order (of L): pap > bpy > acac⁻ > ox²⁻. Reductions of the coordinated pap and bpy are also observed.     

Novel oxalate-bridged trinuclear FeIII-MII-FeIII (M = Cu and VO) complexes: synthesis and magnetism

Two new heterotrinuclear Fe^III-M^II-Fe^III oxalate-bridged complexes have been prepared, and characterized, namely M^II[(ox)Fe^III(Salen)]₂, [Salen = N,N′-ethylenebis(salicylideneiminate), ox = oxalate, M = Cu (1) and VO (2)]. Based on elemental analysis, conductivity measurements and i.r. spectra, the complexes are proposed to have an oxalate-bridged structure. The magnetic susceptibilities of the complexes were measured over the 4.2–300 K range, giving the exchange integrals J _AB = −4.23 cm⁻¹, J _AA = −2.47 cm⁻¹ for (1) and J _AB = −5.42 cm⁻¹, J _AA = −1.55 cm⁻¹ for (2). These results revealed the operation of an antiferromagnetic spin-exchange interaction between the metal ions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Investigation on sonocatalytic damage of BSA under ultrasonic irradiation by Fe<Superscript>III</Superscript> complexes with some aminocarboxylic acid

The interaction of BSA and Fe^III complexes ([Fe^III(gly)(H₂O)₄]²⁺, [Fe^III(ida)(H₂O)₃]⁺, and [Fe^III(nta)(H₂O)₂], gly—glyane, ida—iminodiacetic acid, nta—triglycolamic acid) as well as the sonocatalytic damage to BSA was studied by UV-vis and fluorescence spectra. In addition, the influences of ultrasonic irradiation time and Fe^III complex concentration were also examined on the sonocatalytic damage to BSA. The results showed that the fluorescence quenching of BSA solution caused by the Fe^III complexes belonged to the static quenching process. The BSA and Fe^III complexes interacted with each other mainly through weak interaction and coordinate actions. The binding association constants (K) and binding site numbers (n) were calculated. The results were as follows: K ₁ = 0.5353 × 10⁴ l mol⁻¹ and n ₁ = 0.9812 for [Fe^III(gly)(H₂O)₄]²⁺, K ₂ = 1.4285 × 10⁴ l mol⁻¹ and n ₂ = 1.0899 for [Fe^III(ida)(H₂O)₃, and K ₃ = 0.4411 × 10⁴ l mol⁻¹ and n ₃ = 0.9471 for [Fe^III(nta)(H₂O)₂]. Otherwise, under ultrasonic irradiation the BSA were obviously damaged by the Fe^III complexes. The damage degree rose up with the increase of ultrasonic irradiation time and Fe^III complex concentration. And that, [Fe^III(nta)(H₂O)₂] exhibited in a way higher sonocatalytic activity than [Fe^III(gly)(H₂O)₄]²⁺ and [Fe^III(ida)(H₂O)₃]⁺.     

Ruthenium Tris-pyrazolylborate Complexes XVII [1]. Structure and Bonding in a Series of Ruthenium Hydrido-tris-(pyrazolyl)-borate Cyclooctadiene Complexes

Summary.  The complexes RuTp(cod)X (X = Br⁻ (2), I⁻ (3), CN⁻ (4)) have been obtained by the reaction of RuTp(cod)Cl (1) with KX in boiling MeOH in high yields. The cationic complexes [RuTp(cod)(py)]⁺ (5), [RuTp(cod)(dmso)]⁺ (6), and [RuTp(cod)(CH₃CN)]⁺ (7) were prepared as the CF₃SO₃ ⁻ salts by reacting 1 with 1 equivalent of AgCF₃SO₃ in the presence of the respective co-ligand in CH₂Cl₂. The crystal structures of 1, 3, 4, 5, 6, and 7 are reported. Structural features are discussed in conjunction with ¹H, ¹³C, and ¹⁵N NMR spectroscopic data revealing a linear correlation of ¹⁵N chemical shifts and Ru-N (trans to X(L)) bond distances. Received August 31, 2000. Accepted (revised) October 23, 2000     

Five coordination modes of 4-aminopyrimidine with N-hydroxy-ethylethylenediaminetriacetatoruthenate(II)

Summary The complex [Ru^II(hedta)(4NH₂pym)]⁻, hedta³⁻ = N-hydroxyethylethylenediaminetriacetate, 4NH₂pym = 4-aminopyrimidine, exists at pH 7 as five different coordination isomers, which are most readily distinguished by their electrochemical waves in comparison with the 2-aminopyridine (2NH₂py) complex. The 2NH₂py complex exhibits N(1) (pyridine bound), exo-NH₂ (amine bound) and N(1), NH₂-chelated species. The 4NH₂pym complex forms N(1), exo-amine and N(3), NH₂-chelated isomers analogues to the 2NH₂py species, but also engages in η² (olefin bound) coordination of the dearomatized 4NH₂pym ring in C(5)–C(6), and another η² type of complex involving electron density between N(1) and N(3) of the ring (η³ form). N(1), η² and η³ isomers have also been detected for unsubstituted pyrimidine (pym), 4-methylprimidine (4CH₃pym) and 2-aminopyrimidine (2NH₂pym). Electrochemical waves (V versus NHE) for the five isomers are assigned as follows: (Ru^II/III) exo-NH₂ (0.06 V), N(1) (0.29 V), η² (0.49 V); (Ru^II/III) η³ (0.76 V); N(3), NH₂-chelated (1.09 V).     

Electrochemical detection of the oxidation of alcohols byN-hydroxyethylethylenediamminetriacetatoruthenate(IV)

The oxidation of [Ru^III(hedta)(H₂O)]=(1) to its Ru^IV monomeric complex at a glassy carbon electrode is abserved to promote oxidation of alcohols bearing an a-hydrogen (i-PrOH benzyl alcohol,sec-phenethyl alcohol). Tertiary substitution blocks the oxidation (t-BuOH). The oxidation of the alcohols is detected by an enhancement in the current of the Ru^IV/III waves at potentials above 0.96V, caused by scavenging (reduction) of Ru^IV by the alcohols. Binuclear complexes which possess Ru^IV bridged by oxo to either a second Ru^IV or to Ru^III in species of composition [LRuORuL]ⁿ⁻, L=hedta³⁻, fail to oxidize the alcohols. The terminal oxo moiety attached to Ru^IV is postulated to facilitate the oxidation of primary and secondary alcohols in a manner analogous to Meyer's [RuO(trpy)(bpy)]²⁺ catalyst. The dissociation of the (III,IV) binuclear complex into its monomers provides a pathway which increases catalytic activity at the expense of the inactive (III, IV) binuclear complex's concentration. TMC 2531