[RuIII(EDTA)(H2O)]− catalyzed oxidation of biologically important thiols by H2O2

[Ru^III(EDTA)(H₂O)]^? (EDTA^4? = ethylenediaminetetraacetate) catalyzes the oxidation of biological thiols, RSH (RSH = cysteine, glutathione, N-acetylcysteine, penicillamine) using H₂O₂ as precursor oxidant. The kinetics of the oxidation process were studied spectrophotometrically as a function of [Ru^III(EDTA)(H₂O)]^?, [H₂O₂], [RSH], and pH (4–8). Spectral analyses and kinetic data are suggestive of a catalytic pathway in which the RSH reacts with [Ru^III(EDTA)] catalyst complex to form [Ru^III((EDTA)(SR)]^2? intermediate species. In the subsequent reaction step the oxidant, H₂O₂, reacts directly with the coordinated S of the [Ru^III((EDTA)(SR)]^2? intermediate leading to formation of the disulfido (RSSR) oxidation product (identified by HPLC and ESI-MS studies) of thiols (RSH). Based on the experimental results, a working mechanism involving oxo-transfer from H₂O₂ to the coordinated thiols is proposed for the catalytic oxidation.     

RuIII(edta) catalyzed hydrogenation of bicarbonate to formate

Selective hydrogenation of bicarbonate to formate catalyzed by a ruthenium(III) complex, [Ru^III(edta)] (edta^4? = ethylenediaminetetraacetate), at moderate H₂ pressure (2–8 atm) and temperature (30–40 °C) is reported. Formation of formate, the only reduction product, was identified by ¹³C NMR analysis of the resultant reaction mixture. Based on the spectral data, a working mechanism (admittedly speculative) involving the formation of ruthenium(III)-bicarbonate complex, [Ru^III(edta)(HCO₃)]^2?, is proposed for the catalytic reaction.     

Kinetics and mechanism of substitution of [RuIII(Hedtra)(H2O)] (Hedtra = N-hydroxyethylethylenediaminetriacetate) with iodide ion in aqueous solution

Summary The interaction of iodide ion with [Ru^III(Hedtra)(H₂O)] (Hedtra = N-hydroxyethylethylenediaminetriacetate) was investigated by spectrophotometry, electrochemical and stopped-flow techniques. The rate of formation of a red [Ru^III(Hedtra)I]^– complex was found to be first order both with respect to [Ru^III(Hedtra)(H₂O)] and [I^–]. Rate and activation parameters are consistent with the proposed associative interchange mechanism. Experimental results are discussed with reference to the data available for other ligand substitutions of the [Ru^III(Hedtra)(H₂O)] complex.     

Redox properties of ruthenium(III/II)–edta complexes with o-phenylenediamine and o-benzoquinone diimine ligands

The reaction of [Ru^III(edta)(H₂O)]⁻ with o-phenylenediamine (opda) in water, under aerobic conditions, affords the diamagnetic [Ru^II(edta)(bqdi)]²⁻ product (where edta stands for the ethylenediaminetetraacetate co-ligand, and bqdi represents the non-innocent o-benzoquinone α,α^′-diimine ligand). In the current communication, the redox chemistry of this system in aqueous solution is described in details on the basis of electrochemical and spectroelectrochemical studies. The electrochemical behavior of “free” opda is rather complicated with further chemical reactions following the irreversible two-proton/two-electron oxidation (opda→bqdi+2e⁻+2H⁺), whereas its complex is electrochemically well-behaved with two chemically reversible redox processes: the monoelectronic couple associated with the metal ion (Ru^III/Ru^II) and another bielectronic step centered on the coordinated ligand (bqdi/opda). The set of UV–Vis electronic spectra were obtained by electrolytical generation, in situ, of all the redox species accessible in the CV working conditions (i.e., the starting [Ru^II(edta)(bqdi)]²⁻, the fully oxidized [Ru^III(edta)(bqdi)]⁻, and the fully reduced [Ru^II(edta)(opda)]²⁻ species), which are stable and totally interconvertible. The electrochemistry and absorption spectroscopy of these complexes in water were found to be comparable with the tetraammine counterparts. A remarkable difference in redox behavior between the diimine- and the analogous dioxolene-complexes was also revealed by comparison of the system reported herein with the one derived from catechol, and rationalized in terms of the quite efficient π-accepting electronic nature of the bqdi ligand.     

Oxidation of captopril by hydrogen peroxide and peroxomonosulfate ion catalyzed by a ruthenium(III) complex: kinetic and mechanistic studies

The complex [Ru^III(edta)(H₂O)]^? (edta^4? = ethylenediaminetetraacetate) catalyzes the oxidation of captopril (CapSH) using primary oxidants, hydrogen peroxide (H₂O₂) and peroxomonosulfate (\( {\text{HSO}}_{5}^{ - } \)). The kinetics of the oxidation reaction were studied as a function of both oxidant (H₂O₂, \( {\text{HSO}}_{5}^{ - } \)) and substrate (CapSH) concentrations using stopped-flow and rapid scan stopped-flow techniques. Spectral and kinetic data are suggestive of a pathway involving rapid formation of the intermediate complex [Ru^III(edta)(CapS)]^2? followed by direct attack of the oxidant (H₂O₂ or \( {\text{HSO}}_{5}^{ - } \)) at the S atom of the coordinated CapS^?. ESI–MS and HPLC analysis of the reaction products showed that captopril disulfide (CapSSCap) is the major oxidation product. A probable mechanism in agreement with the spectral and kinetic data is presented.     

Alcohol oxidation reactions catalyzed by ruthenium–carbonyl complexes of thioarylazoimidazoles

Alcohols are oxidized by N‐methylmorpholine‐N‐oxide (NMO), Bu^tOOH and H₂O₂ to the corresponding aldehydes or ketones in the presence of catalyst, [RuH(CO)(PPh₃)₂(SRaaiNR′)]PF₆ ( 2 ) and [RuCl(CO)(PPh₃)(S_κRaaiNR′)]PF₆ ( 3 ) (SRaaiNR′ ( 1 ) = 1‐alkyl‐2‐{(o‐thioalkyl)phenylazo}imidazole, a bidentate N(imidazolyl) (N), N(azo) (N′) chelator and S_κRaaiNR′ is a tridentate N(imidazolyl) (N), N(azo) (N′), S_κ‐R is tridentate chelator; R and R′ are Me and Et). The single‐crystal X‐ray structures of [RuH(CO)(PPh₃)₂(SMeaaiNMe)]PF₆ ( 2a ) (SMeaaiNMe = 1‐methyl‐2‐{(o‐thioethyl)phenylazo}imidazole) and [RuH(CO)(PPh₃)₂(SEtaaiNEt)]PF₆ ( 2b ) (SEtaaiNEt = 1‐ethyl‐2‐{(o‐thioethyl)phenylazo}imidazole) show bidentate N,N′ chelation, while in [RuCl(CO)(PPh₃)(S_κEtaaiNEt)]PF₆ ( 3b ) the ligand S_κEtaaiNEt serves as tridentate N,N′,S chelator. The cyclic voltammogram shows Ru^III/Ru^II (~1.1 V) and Ru^IV/Ru^III (~1.7 V) couples of the complexes 2 while Ru^III/Ru^II (1.26 V) couple is observed only in 3 along with azo reductions in the potential window +2.0 to ?2.0 V. DFT computation has been used to explain the spectra and redox properties of the complexes. In the oxidation reaction NMO acts as best oxidant and [RuCl(CO)(PPh₃)(S_κRaaiNR′)](PF₆) ( 3 ) is the best catalyst. The formation of high‐valent Ru^IV=O species as a catalytic intermediate is proposed for the oxidation process. Copyright © 2014 John Wiley & Sons, Ltd.     

Oxidation of Ru(III)‐Bound Thiocyanate with Peroxomonosulfate: Kinetic and Mechanistic Studies

The reaction of [Ru^III(edta)(SCN)]^2? (edta^4? = ethylenediaminetetraacetate; SCN^? = thiocyanate ion) with the peroxomonosulfate ion (HSO₅^?) has been studied by using stopped‐flow and rapid scan spectrophotometry as a function of [Ru^III(edta)], [HSO₅^?], and temperature (15–30ºC) at constant pH 6.2 (phosphate buffer). Spectral analyses and kinetic data are suggestive of a pathway in which HSO₅^? effects the oxidation of the coordinated SCN^? by its direct attack at the S‐atom (of SCN^?) coordinated to the Ru^III(edta). The high negative value of entropy of activation (ΔS^≠ = ?90 ± 6 J mol^?1 deg^?1) is consistent with the values reported for the oxygen atom transfer process involving heterolytic cleavage of the O‐O bond in HSO₅^?. Formation of SO₄^2?, SO₃^2?, and OCN^? was identified as oxidation products in ESI‐MS experiments. A detailed mechanism in agreement with the spectral and kinetic data is presented.     

Mononuclear nine-coordinate Na[SmIII(edta)(H2O)3] · 5H2O and one dimensional unlimited ladderlike eight-coordinate {[SmIII(Hpdta)(H2O)] · 2H2}On Complexes: Synthesis and Structural Determination

The Na[Sm^III(edta)(H₂O)₃] · 5H₂O (H₄edta = ethylenediamine-N,N,N′,N′-tetraacetic acid) and {[Sm^III(Hpdta)(H₂O)] · 2H₂O} _n (H₄pdta = propylenediamine-N,N,N′,N′-tetraacetic acid) complexes were prepared with heat-refluxing and acidity-adjusting methods, respectively. And their composition and structures were determined by elemental analyses and single-crystal X-ray diffraction techniques. The Na[Sm^III(edta)(H₂O)₃] · 5H₂O complex shapes a mononuclear structure, and crystallizes in the orthorhombic crystal system with space group Fdd2. The central Sm^III ion is nine-coordinated by one hexadentate edta ligand and three water molecules. The crystal data are as follows: a = 19.139(10) ?, b = 35.00(2) ?, c = 11.928(10) ?, V = 7989(9) ?³, Z = 16, D _c = 2.014 g/cm³, μ = 3.046 mm⁻¹, F(000) = 4848, R = 0.0439, and wR = 0.0941 for 3434 observed reflections with I ≥ 2σ(I). The SmN₂O₇ part in [Sm^III(edta)(H₂O)₃]⁻ complex anion forms a pseudo-monocapped square antiprismatic polyhedron. The {[Sm_III(Hpdta)(H₂O)] · 2H₂O} _n complex is prepared with protonated pdta ligand firstly, which forms one dimensional unlimited ladderlike eight-coordinated structure, and crystallizes in the monoclinic crystal system with space group P2₁/n. The central Sm^III ion, in one construction unit, is coordinated by two nitrogen atoms from one hexadentate pdta ligand and six oxygens from the same pdta ligand, one water molecule and one carboxylic group of neighbour pdta ligand, respectively. The crystal data are as follows: a = 12.720(3) ?, b = 9.3800(19) ?, c = 14.420(3) ?, β = 96.11(3)°, V = 1710.7(6) ?³, Z = 2, D _c = 1.971 g/cm³, μ = 3.492 mm⁻¹, F(000) = 1004, R = 0.0225 and wR = 0.0607 for 3182 observed reflections with I ≥ 2σ(I). Otherwise, each part of SmN₂O₆ in {[Sm^III(Hpdta)(H₂O)] · 2H₂O} complex segment adopts a pseudo-square antiprismatic polyhedron.     

Syntheses and structural determinations of the nine-coordinate rare earth metal: Na4[DyIII(dtpa)(H2O)]2·16H2O,Na[DyIII(edta)(H2O)3]·3.25H2O and Na3[DyIII(nta)2(H2O)]·5.5H2O

Three complexes, Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O, Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O and Na₃[Dy^III (nta)₂(H₂O)]?·?5.5H₂O, have been synthesized in aqueous solution and characterized by FT–IR, elemental analyses, TG–DTA and single-crystal X-ray diffraction. Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O crystallizes in the monoclinic system with P2₁/n space group, a?=?18.158(10)?Å, b?=?14.968(9)?Å, c?=?20.769(12)?Å, β?=?108.552(9)°, V?=?5351(5)?ų, Z?=?4, M?=?1517.87?g?mol^?1, D _c?=?1.879?g?cm^?3, μ?=?2.914?mm^?1, F(000)?=?3032, and its structure is refined to R ₁(F)?=?0.0500 for 9384 observed reflections [I?>?2σ(I)]. Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O crystallizes in the orthorhombic system with Fdd2 space group, a?=?19.338(7)?Å, b?=?35.378(13)?Å, c?=?12.137(5)?Å, β?=?90°, V?=?8303(5)?ų, Z?=?16, M?=?586.31?g?mol^?1, D _c?=?1.876?g?cm^?3, μ?=?3.690?mm^?1, F(000)?=?4632, and its structure is refined to R ₁(F)?=?0.0307 for 4027 observed reflections [I?>?2σ(I)]. Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O crystallizes in the orthorhombic system with Pccn space group, a?=?15.964(12)?Å, b?=?19.665(15)?Å, c?=?14.552(11)?Å, β?=?90°, V?=?4568(6)?ų, Z?=?8, M?=?724.81?g?mol^?1, D _c?=?2.102?g?cm^?3, μ?=?3.422?mm^?1, F(000)?=?2848, and its structure is refined to R ₁(F)?=?0.0449 for 4033 observed reflections [I?>?2?σ(I)]. The coordination polyhedra are tricapped trigonal prism for Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O and Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O, but monocapped square antiprism for Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O. The crystal structures of these three complexes are completely different from one another. The three-dimensional geometries of three polymers are 3-D layer-shaped structure for Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O, 1-D zigzag type structure for Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O and a 2-D parallelogram for Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O. According to thermal analyses, the collapsing temperatures are 356°C for Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O, 371°C for Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O and 387°C for Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O, which indicates that their crystal structures are very stable.     

Facile Synthesis and Versatile Reactivity of an Unusual Cyclometalated Rhodium(I) Pincer Complex

The synthesis of the reactive PN(C^H) ligand 2‐di(tert‐butylphosphanomethyl)‐6‐phenylpyridine ( 1^H ) and its versatile coordination to a Rh^I center is described. Facile C?H activation occurs in the presence of a (internal) base, thus resulting in the new cyclometalated complex [Rh^I(CO)(κ³‐P,N,C‐ 1 )] ( 3 ), which has been structurally characterized. The resulting tridentate ligand framework was experimentally and computationally shown to display dual‐site proton‐responsive reactivity, including reversible cyclometalation. This feature was probed by selective H/D exchange with [D₁]formic acid. The addition of HBF₄ to 3 leads to rapid net protonolysis of the Rh?C bond to produce [Rh^I(CO)(κ³‐P,N,(C?H)‐ 1 )] ( 4 ). This species features a rare aryl C?H agostic interaction in the solid state, as shown by X‐ray diffraction studies. The nature of this interaction was also studied computationally. Reaction of 3 with methyl iodide results in rapid and selective ortho‐methylation of the phenyl ring, thus generating [Rh^I(CO)(κ²‐P,N‐ 1^Me )] ( 5 ). Variable‐temperature NMR spectroscopy indicates the involvement of a Rh^III intermediate through formal oxidative addition to give trans‐[Rh^III(CH₃)(CO)(I)(κ³‐P,N,C‐ 1 )] prior to C?C reductive elimination. The Rh^III–trans‐diiodide complex [Rh^I(CO)(I)₂(κ³‐P,N,C‐ 1 )] ( 6 ) has been structurally characterized as a model compound for this elusive intermediate.     

Thermodynamics of Formation of Ru(III) and Ru(IV)-μ-Peroxo Complexes

Abstract

Reaction of one half and one equivalents of H₂O₂ with K[Ru^III(pdta-H)Cl].2H₂O gives rise to the μ-peroxo complexes [Ru^III (pdta-H)]₂H₂O₂ and [Ru^IV(pdta-H)]₂O₂, respectively. Equilibrium constants for the formation of the various peroxo species were determined between pH 3-11, in the temperature range 283-313 K and with μ = 0.10 M in KC1. The existence of the various peroxo species was substantiated by potentiometry, spectrophotometry and electrochemical studies. Thermodynamic quantities associated with the formation of the (pdta)Ru^III and (pdta)Ru^IV-μ-peroxo species and their hydrolysis products are reported.     

A Highly Oxidizing and Isolable Oxoruthenium(V) Complex [RuV(N4O)(O)]2+: Electronic Structure,Redox Properties,and Oxidation Reactions Investigated by DFT Calculations

The electronic structure and redox properties of the highly oxidizing, isolable Ru^V?O complex [Ru^V(N₄O)(O)]²⁺, its oxidation reactions with saturated alkanes (cyclohexane and methane) and inorganic substrates (hydrochloric acid and water), and its intermolecular coupling reaction have been examined by DFT calculations. The oxidation reactions with cyclohexane and methane proceed through hydrogen atom transfer in a transition state with a calculated free energy barrier of 10.8 and 23.8 kcal mol^?1, respectively. The overall free energy activation barrier (ΔG^≠=25.5 kcal mol^?1) of oxidation of hydrochloric acid can be decomposed into two parts: the formation of [Ru^III(N₄O)(HOCl)]²⁺ (ΔG=15.0 kcal mol^?1) and the substitution of HOCl by a water molecule (ΔG^≠=10.5 kcal mol^?1). For water oxidation, nucleophilic attack on Ru^V?O by water, leading to O? O bond formation, has a free energy barrier of 24.0 kcal mol^?1, the major component of which comes from the cleavage of the H? OH bond of water. Intermolecular self‐coupling of two molecules of [Ru^V(N₄O)(O)]²⁺ leads to the [(N₄O)Ru^IV? O₂? Ru^III(N₄O)]⁴⁺ complex with a calculated free energy barrier of 12.0 kcal mol^?1.     

Axial Ligand and Spin‐State Influence on the Formation and Reactivity of Hydroperoxo–Iron(III) Porphyrin Complexes

The present study focuses on the formation and reactivity of hydroperoxo–iron(III) porphyrin complexes formed in the [Fe^III(tpfpp)X]/H₂O₂/HOO^? system (TPFPP=5,10,15,20‐tetrakis(pentafluorophenyl)‐21H,23H‐porphyrin; X=Cl^? or CF₃SO₃^?) in acetonitrile under basic conditions at ?15 °C. Depending on the selected reaction conditions and the active form of the catalyst, the formation of high‐spin [Fe^III(tpfpp)(OOH)] and low‐spin [Fe^III(tpfpp)(OH)(OOH)] could be observed with the application of a low‐temperature rapid‐scan UV/Vis spectroscopic technique. Axial ligation and the spin state of the iron(III) center control the mode of O? O bond cleavage in the corresponding hydroperoxo porphyrin species. A mechanistic changeover from homo‐ to heterolytic O? O bond cleavage is observed for high‐ [Fe^III(tpfpp)(OOH)] and low‐spin [Fe^III(tpfpp)(OH)(OOH)] complexes, respectively. In contrast to other iron(III) hydroperoxo complexes with electron‐rich porphyrin ligands, electron‐deficient [Fe^III(tpfpp)(OH)(OOH)] was stable under relatively mild conditions and could therefore be investigated directly in the oxygenation reactions of selected organic substrates. The very low reactivity of [Fe^III(tpfpp)(OH)(OOH)] towards organic substrates implied that the ferric hydroperoxo intermediate must be a very sluggish oxidant compared with the iron(IV)–oxo porphyrin π‐cation radical intermediate in the catalytic oxygenation reactions of cytochrome P450.     

Olefin epoxidation catalyzed by [Ru(TDL)(tmeda)H2O] complexes (TDL = tridentate Schiff-base ligand; tmeda = tetramethylethylenediamine)

Mixed-chelate complexes of ruthenium have been synthesized using tridentate Schiff-base ligands (TDLs) derived from condensation of 2-aminophenol or 2-aminobenzoic acid with aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde), and tmeda (tetramethylethylenediamine). [Ru^III(hpsd)(tmeda)(H₂O)]⁺ (1), [Ru^III(hppc)(tmeda)(H₂O)]²⁺ (2), [Ru^III(cpsd)(tmeda)(H₂O)]⁺ (3) and [Ru^III(cppc)(tmeda)(H₂O)]²⁺ (4) complexes (where hpsd²⁻ = N-(hydroxyphenyl)salicylaldiminato); hppc⁻ = N-(2-hydroxyphenylpyridine-2-carboxaldiminato); cpsd²⁻ = (N-(2-carboxyphenyl)salicylaldiminato); cppc⁻ = N-2-carboxyphenylpyridine-2-carboxaldiminato) were characterized by microanalysis, spectral (IR and UV–vis), conductance, magnetic moment and electrochemical studies. Complexes 1–4 catalyzed the epoxidation of cyclohexene, styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 4-nitrostyrene, cis- and trans-stilbenes effectively at ambient temperature using tert-butylhydroperoxide (t-BuOOH) as terminal oxidant. On the basis of Hammett correlation (log k_rel vs. σ⁺) and product analysis, a mechanism involving intermediacy of a [Ru–O–OBu^t] radicaloid species is proposed for the catalytic epoxidation process.     

Template Syntheses of Copper(II) Complexes from Arylhydrazones of Malononitrile and their Catalytic Activity towards Alcohol Oxidations and the Nitroaldol Reaction: Hydrogen Bond‐Assisted Ligand Liberation and E/Z Isomerisation

A one‐pot template condensation of 2‐(2‐(dicyanomethylene)hydrazinyl)benzenesulfonic acid (H₂L¹, 1 ) or 2‐(2‐(dicyanomethylene)hydrazinyl)benzoic acid (H₂L², 2 ) with methanol (a), ethylenediamine (b), ethanol (c) or water (d) on copper(II), led to a variety of metal complexes, that is, mononuclear [Cu(H₂O)₂(κO¹,κN² L^1a] ( 3 ) and [Cu(H₂O)(κO¹,κN³ L^1b)] ( 4 ), tetranuclear [Cu₄(1 κO¹,κN²:2 κO¹ L^2a)₃‐(1 κO¹, κN²:2 κO² L^2a)] ( 5 ), [Cu₂(H₂O)(1 κO¹, κN²:2 κO¹ L^2c)‐(1 κO¹,1 κN²:2 κO¹,2 κN¹‐ L^2c)]₂ ( 6 ) and [Cu₂(H₂O)₂(κO¹,κN²‐ L^1dd)‐(1 κO¹,κN²:2 κO¹ L^1dd)(μ‐H₂O)]₂ ? 2 H₂O ( 7? 2 H₂O), as well as polymer‐ ic [Cu(H₂O)(κO¹,1 κN²:2 κN¹ L^1c)]_n ( 8 ) and [Cu(NH₂C₂H₅)(κO¹,1 κN²:2 κN¹L^2a)]_n ( 9 ). The ligands 2‐SO₃H‐C₆H₄‐(NH)N?C{(CN)[C(NH₂)‐(?NCH₂CH₂NH₂)]} (H₂L^1b, 10 ), 2‐CO₂H‐C₆H₄‐(NH)N?{C(CN)[C(OCH₃)‐(?NH)]} (H₂L^2a, 11 ) and 2‐SO₃H‐C₆H₄‐(NH)N?C{C(?O)‐(NH₂)}₂ (H₂L^1dd, 12 ) were easily liberated upon respective treatment of 4 , 5 and 7 with HCl, whereas the formation of cyclic zwitterionic amidine 2‐(SO₃^?)? C₆H₄? N?NC(? C?(NH⁺)CH₂CH₂NH)(?CNHCH₂CH₂NH) ( 13 ) was observed when 1 was treated with ethylenediamine. The hydrogen bond‐induced E/Z isomerization of the (HL^1d)^? ligand occurs upon conversion of [{Na(H₂O)₂(μ‐H₂O)₂}(HL^1d)]_n ( 14 ) to [Cu(H₂O)₆][HL^1d]₂ ? 2 H₂O ( 15 ) and [{CuNa(H₂O)‐(κN¹,1 κO²:2 κO¹ L^1d)₂}K_0.5(μ‐O)₂]n ? H₂O ( 16 ). The synthesized complexes 3 – 9 are catalyst precursors for both the selective oxidation of primary and secondary alcohols (to the corresponding carbonyl compounds) and the following diastereoselective nitroaldol (Henry) reaction, with typical yields of 80–99 %.     

N,N′-Bis(aryl)pyridine-2,6-dicarboxamide complexes of ruthenium: Synthesis,structure and redox properties

Reaction of five N,N′-bis(aryl)pyridine-2,6-dicarboxamides (H₂L-R, where H₂ denotes the two acidic protons and R (R = OCH₃, CH₃, H, Cl and NO₂) the para substituent in the aryl fragment) with [Ru(trpy)Cl₃](trpy = 2,2′,2″-terpyridine) in refluxing ethanol in the presence of a base (NEt₃) affords a group of complexes of the type [Ru^II(trpy)(L-R)], each of which contains an amide ligand coordinated to the metal center as a dianionic tridentate N,N,N-donor along with a terpyridine ligand. Structure of the [Ru^II(trpy)(L-Cl)] complex has been determined by X-ray crystallography. All the Ru(II) complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the [Ru^II(trpy)(L-R)] complexes shows a Ru(II)–Ru(III) oxidation within 0.16–0.33 V versus SCE. An oxidation of the coordinated amide ligand is also observed within 0.94–1.33 V versus SCE and a reduction of coordinated terpyridine ligand within −1.10 to −1.15 V versus SCE. Constant potential coulometric oxidation of the [Ru^II(trpy)(L-R)] complexes produces the corresponding [Ru^III(trpy)(L-R)]⁺ complexes, which have been isolated as the perchlorate salts. Structure of the [Ru^III(trpy)(L-CH₃)]ClO₄ complex has been determined by X-ray crystallography. All the Ru(III) complexes are one-electron paramagnetic, and show anisotropic ESR spectra at 77 K and intense LMCT transitions in the visible region. A weak ligand-field band has also been shown by all the [Ru^III(trpy)(L-R)]ClO₄ complexes near 1600 nm.     

Spectroscopic,Electrochemical and Computational Characterisation of Ru Species Involved in Catalytic Water Oxidation: Evidence for a [RuV(O)(Py2Metacn)] Intermediate

A new family of ruthenium complexes based on the N‐pentadentate ligand Py₂^Metacn (N‐methyl‐N′,N′′‐bis(2‐picolyl)‐1,4,7‐triazacyclononane) has been synthesised and its catalytic activity has been studied in the water‐oxidation (WO) reaction. We have used chemical oxidants (ceric ammonium nitrate and NaIO₄) to generate the WO intermediates [Ru^II(OH₂)(Py₂^Metacn)]²⁺, [Ru^III(OH₂)(Py₂^Metacn)]³⁺, [Ru^III(OH)(Py₂^Metacn)]²⁺ and [Ru^IV(O)(Py₂^Metacn)]²⁺, which have been characterised spectroscopically. Their relative redox and pH stability in water has been studied by using UV/Vis and NMR spectroscopies, HRMS and spectroelectrochemistry. [Ru^IV(O)(Py₂^Metacn)]²⁺ has a long half‐life (>48 h) in water. The catalytic cycle of WO has been elucidated by using kinetic, spectroscopic, ¹⁸O‐labelling and theoretical studies, and the conclusion is that the rate‐determining step is a single‐site water nucleophilic attack on a metal‐oxo species. Moreover, [Ru^IV(O)(Py₂^Metacn)]²⁺ is proposed to be the resting state under catalytic conditions. By monitoring Ce^IV consumption, we found that the O₂ evolution rate is redox‐controlled and independent of the initial concentration of Ce^IV. Based on these facts, we propose herein that [Ru^IV(O)(Py₂^Metacn)]²⁺ is oxidised to [Ru^V(O)(Py₂^Metacn)]²⁺ prior to attack by a water molecule to give [Ru^III(OOH)(Py₂^Metacn)]²⁺. Finally, it is shown that the difference in WO reactivity between the homologous iron and ruthenium [M(OH₂)(Py₂^Metacn)]²⁺ (M=Ru, Fe) complexes is due to the difference in the redox stability of the key M^V(O) intermediate. These results contribute to a better understanding of the WO mechanism and the differences between iron and ruthenium complexes in WO reactions.     

Heterotrimetallic Coordination Polymers: {CuIILnIIIFeIII} Chains and {NiIILnIIIFeIII} Layers: Synthesis,Crystal Structures,and Magnetic Properties

The use of the [Fe^III(AA)(CN)₄]^? complex anion as metalloligand towards the preformed [Cu^II(valpn)Ln^III]³⁺ or [Ni^II(valpn)Ln^III]³⁺ heterometallic complex cations (AA=2,2′‐bipyridine (bipy) and 1,10‐phenathroline (phen); H₂valpn=1,3‐propanediyl‐bis(2‐iminomethylene‐6‐methoxyphenol)) allowed the preparation of two families of heterotrimetallic complexes: three isostructural 1D coordination polymers of general formula {[Cu^II(valpn)Ln^III(H₂O)₃(μ‐NC)₂Fe^III(phen)(CN)₂ {(μ‐NC)Fe^III(phen)(CN)₃}]NO₃ ? 7 H₂O}_n (Ln=Gd ( 1 ), Tb ( 2 ), and Dy ( 3 )) and the trinuclear complex [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃] ? NO₃ ? H₂O ? CH₃CN ( 4 ) were obtained with the [Cu^II(valpn)Ln^III]³⁺ assembling unit, whereas three isostructural heterotrimetallic 2D networks, {[Ni^II(valpn)Ln^III(ONO₂)₂(H₂O)(μ‐NC)₃Fe^III(bipy)(CN)] ? 2 H₂O ? 2 CH₃CN}_n (Ln=Gd ( 5 ), Tb ( 6 ), and Dy ( 7 )) resulted with the related [Ni^II(valpn)Ln^III]³⁺ precursor. The crystal structure of compound 4 consists of discrete heterotrimetallic complex cations, [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃]⁺, nitrate counterions, and non‐coordinate water and acetonitrile molecules. The heteroleptic {Fe^III(bipy)(CN)₄} moiety in 5 – 7 acts as a tris‐monodentate ligand towards three {Ni^II(valpn)Ln^III} binuclear nodes leading to heterotrimetallic 2D networks. The ferromagnetic interaction through the diphenoxo bridge in the Cu^II?Ln^III ( 1 – 3 ) and Ni^II?Ln^III ( 5 – 7 ) units, as well as through the single cyanide bridge between the Fe^III and either Ni^II ( 5 – 7 ) or Cu^II ( 4 ) account for the overall ferromagnetic behavior observed in 1 – 7 . DFT‐type calculations were performed to substantiate the magnetic interactions in 1 , 4 , and 5 . Interestingly, compound 6 exhibits slow relaxation of the magnetization with maxima of the out‐of‐phase ac signals below 4.0 K in the lack of a dc field, the values of the pre‐exponential factor (τ_o) and energy barrier (E_a) through the Arrhenius equation being 2.0×10^?12 s and 29.1 cm^?1, respectively. In the case of 7 , the ferromagnetic interactions through the double phenoxo (Ni^II–Dy^III) and single cyanide (Fe^III–Ni^II) pathways are masked by the depopulation of the Stark levels of the Dy^III ion, this feature most likely accounting for the continuous decrease of χ_M T upon cooling observed for this last compound.     

First heterobimetallic AgI–CoIII coordination compound with both bridging and terminal –NO2 coordination modes: synthesis,characterization, structural and computational studies of (PPh3)2AgI–(μ‐κ2O,O′:κN‐NO2)–CoIII(DMGH)2(κN‐NO2)

An unusual heterobimetallic bis(triphenylphosphane)(NO₂)Ag^I–Co^III(dimethylglyoximate)(NO₂) coordination compound with both bridging and terminal –NO₂ (nitro) coordination modes has been isolated and characterized from the reaction of [CoCl(DMGH)₂(PPh₃)] (DMGH₂ is dimethylglyoxime or N,N′‐dihydroxybutane‐2,3‐diimine) with excess AgNO₂. In the title compound, namely bis(dimethylglyoximato‐1κ²O,O′)(μ‐nitro‐1κN:2κ²O,O′)(nitro‐1κN)bis(triphenylphosphane‐2κP)cobalt(III)silver(I), [AgCo(C₄H₇N₂O₂)₂(NO₂)₂(C₁₈H₁₅P)₂], one of the ambidentate –NO₂ ligands, in a bridging mode, chelates the Ag^I atom in an isobidentate κ²O,O′‐manner and its N atom is coordinated to the Co^III atom. The other –NO₂ ligand is terminally κN‐coordinated to the Co^III atom. The structure has been fully characterized by X‐ray crystallography and spectroscopic methods. Density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) have been used to study the ground‐state electronic structure and elucidate the origin of the electronic transitions, respectively.     

Pyridine-2-olato chelated ruthenium(II) organometallics incorporating imine-phenol function: spectroscopic,structural, electrochemical,and theoretical studies

The heterogeneous phase reaction of excess sodium salt of 2-hydroxypyridine (OHpy) with [Ru(κ²C,O-RL)(PPh₃)₂(CO)Cl] (1) afforded complexes of the type [Ru(κ¹C-RL)(PPh₃)₂(CO)(Opy)] (2) in excellent yield [κ²C,O-RL is 4-methyl-6-((N-R-arylimino)methyl)phenolato-C²,O), κ¹C-RL is 4-methyl-6-((N-R-arylimino)methyl)phenol-C²) and R is H, Me, OMe, Cl]. The chelation of Opy is attended with the cleavage of Ru-O and Ru-Cl bonds and iminium-phenolato → imine-phenol prototropic shift. The 1→2 conversion is irreversible and the type 2 species are thermodynamically more stable than the acetate, nitrite, and nitrate complexes of 1. The spectral (UV-vis, IR, NMR) and electrochemical data of the complexes are reported. In dichloromethane solution the complexes display one quasi-reversible Ru^III/Ru^II cyclic voltammetric response with E_1/2 in the range 0.65–0.69 V versus Ag/AgCl. The crystal and molecular structures of [Ru(κ¹C-HL)(PPh₃)₂(CO)(Opy)]·2C₆H₆·0.5H₂O, 2(H)·2C₆H₆·0.5H₂O and [Ru(κ¹C-ClL)(PPh₃)₂(CO)(Opy)]·2C₆H₆·0.25H₂O, 2(Cl)·2C₆H₆·0.25H₂O are reported, which revealed a distorted octahedral RuC₂P₂NO coordination sphere. The pairs (P,P), (C,O), and (C,N) define the three trans directions. The electronic structures of the complexes are also scrutinized by density functional theory.