Synthesis, structure, and redox behaviour of a novel cis-dioxomolybdenum(VI) dinuclear complex with a quadradentate dithiocarbamate

A novel dinuclear cis-dioxomolybdenum(VI) complex [{MoO₂(Bz₂endtc)}₂] coordinated with a quadradentate dithiocarbamate (Bz₂endtc²⁻: ((2-(dithiocarboxybenzylamino)ethyl)benzylamino)-methanedithioate(2−)) has been synthesised. The structural features of [{MoO₂(Bz₂endtc)}₂] have been elucidated by X-ray crystal analysis, elemental analysis and ¹³C NMR, IR and FAB⁺ mass spectroscopy: two almost identical cis-dioxomolybdenum(VI) centres are bridged by the two Bz₂endtc²⁻ ligands and each molybdenum(VI) centre has a distorted octahedral geometry with four sulphur atoms and two terminal oxo ligands lying in a cis position to each other. There is unlikely to be electronic interaction between the two cis-dioxomolybdenum(VI) centres in [{MoO₂(Bz₂endtc)}₂] because the MoMo distance is long (=7.337 Å). In the [{MoO₂(Bz₂endtc)}₂]/PPh₃ system, the oxygen atom transfer reaction (Eq. (A)) occurs to give a tetranuclear oxomolybdenum(VI,V) complex formulated as [MoO₂(Bz₂endtc)₂Mo₂O₃(Bz₂endtc)₂MoO₂] which has one μ-oxomolybdenum(V) moiety.

(A)     

Synthesis, crystal and molecular structure, spectroscopic and electrochemical studies of trichloro-oxo(4,6-dimethylpyrimidine-2(1H)-thione)(triphenylphosphine oxide)rhenium(V) complex

Reaction of 4,6-dimethylpyrimidine-2(1H)-thione (Me₂pymSH) with mer-[ReOCl₃(Me₂S)(OPPh₃)] synthon in 1:1 molar ratio in refluxing acetone, results in the replacement of the Me₂S ligand to form the mer-[ReOCl₃(Me₂pymSH)(OPPh₃)] species. X-ray diffraction shows that the structure of the title compound consists of monomeric units with a distorted octahedral coordination around the rhenium(V) centre which includes the axial ReO and Re---OPPh₃ bonds, and in which three Cl⁻ ions and a S-monodentate neutral Me₂pymSH ligand act as equatorial ligands. The compound was also characterised using electrochemical measurements and UV–Vis–NIR and IR spectroscopy.     

Dinuclear Ni(II) and Cu(II) complexes with indolecarboxamide ligand: Synthesis, structure and properties

A potential tetradentate indolecarboxamide ligand, H₄L³ is synthesized and investigated for its coordination abilities towards Ni(II) and Cu(II) ions. Two H₄L³ ligands in their tetra-deprotonated form [L³]⁴⁻, were found to coordinate two metal centers resulting in the formation of [Ni₂(L³)₂]⁴⁻ (5) and [Cu₂(L³)₂]⁴⁻ (6) complexes. The crystal structure of 6 displays the formation of a dinuclear structure where two fully deprotonated ligands, [L³]⁴⁻ hold two copper(II) ions together. Even more interesting is the fact that both deprotonated ligands, [L³]⁴⁻ coordinate the copper ions in an identical and symmetrical fashion. The Na⁺ cations present in the complex 6 stitch together the dinuclear units resulting in the formation of a coordination chain polymer. Four sodium ions connect two dinuclear units via interacting with the O_amide groups. Further, Na⁺ cations were found to coordinate several DMF molecules; some of them are terminal and a few are bridging in nature. The solution state structure (determined by the NMR spectral analysis) of the diamagnetic complex 5 also supported the fact that two deprotonated ligands, coordinate two nickel ions in an identical and symmetrical fashion. Absorption spectral studies reveal that the solid-state square-planar geometry is retained in solution and both complexes do not show any tendency to coordinate potential axial ligands. The variable-temperature magnetic measurements and EPR spectra indicate spin-spin exchange between two copper centers in complex 6. The electrochemical results for both complexes show three irreversible oxidative responses that correspond to the oxidation of first and second metal ion followed by the ligand oxidation, respectively.     

Synthesis, characterization, X-ray molecular structure and catalase-like activity of a non-heme iron complex: Dichloro[N-propanoate-N,N-bis-(2-pyridylmethyl)amine]iron(III)

In this work we present the synthesis and characterization of the complex dichloro[N-propanoate-N,N-bis-(2-pyridylmethyl)amine]iron(III) [Fe^III(PBMPA)Cl₂]. The ligand LiPBMPA was synthesized through the Michael reaction of BMPA with methylacrylate, followed by alkaline hydrolysis. The complex [Fe^III(PBMPA)Cl₂] has been synthesized by the reaction of the ligand with FeCl₃ · H₂O and was mainly characterized by cyclic voltammetry, conductivimetry, and electronic, infrared and Mössbauer spectroscopies, and by X-ray structural analysis, which showed an iron center coordinated by one carboxylate oxygen in a monodentate way, one tertiary amine, two pyridine groups and two chloride ions. It has been proposed that in water the chloride ligands are shifted by the solvent molecules and the species [Fe^III(PBMPA)(H₂O)₂]Cl₂ is predominant. The catalase-like activity of the complex was tested in water, and it proved to be active in the hydrogen peroxide dismutation. Kinetics studies were conducted following the initial rates method. The reaction is first order in relation to both the complex and the hydrogen peroxide. Based on the presence of a lag phase that depends on the initial complex concentration, we propose that the active species that shows in situ catalase-like activity, is a binuclear complex.     

Synthesis, characterization and thermal decomposition of dioxouranium(VI) complexes with N,N-diarylidene-S-propyl-thiosemicarbazone: Crystal structure of [UO2(L)(C4H9OH)]

Reactions of salicyl- and 3,5-dichlorosalicylaldehyde-S-propyl-thiosemicarbazones with salicyl- and 3,5-dichlorosalicylaldehyde in the presence of UO₂(CH₃COO)₂ in different alcohols yielded stable solid complexes corresponding to the general formula [UO₂(L)ROH] (R: propyl-, butyl-, pentyl-, and octyl-). The complexes were characterized by means of elemental analysis, IR and ¹H NMR spectroscopies. The thermal stabilities of the alcohol solvated complexes were investigated in air and nitrogen atm., and determined their decomposition phases. In the crystal structure of the [UO₂(L)(C₄H₉OH)], the U(VI) centre is seven-coordinated in a distorted pentagonal bipyramidal geometry involving O,O,N,N atoms of two phenolic and two imine groups and one oxygen atom of alcohol molecule in basal plane and two O atoms of dioxo group in apical positions. The title structure is stabilized by one intramolecular interaction of types C-H?Cl and by two intermolecular interactions of types O-H?O and C-H?π (benzene) leading to the molecular chain along the [0 1 0] direction.     

Synthesis, crystal structure and photoelectric property of Mn(II/IV) coordination complexes

Three novel coordination complexes [Mn(tpha)(phen)]_n (1); [Mn(na)₂(H₂O)₂]_n (2); {[Mn(phen)₂(OH)Cl] · Cl · (OH) · (C₉H₁₁NO₂) · 2H₂O} (3) have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction (H₂tpha = terephthalic acid, Hna = nicotinic acid, phen = 1,10-phenanthroline). The tpha groups in complex 1 bridge the Mn(II) ions to an infinite 3D framework. Complex 2 exhibits a 2D network structure in which the Mn(II) ions are linked by nicotinic groups. Complex 3 is connected to a 2D coordination supramolecule by hydrogen bonds. The results of surface photovoltage spectra (SPS) of complexes 1-3 indicate that they all exhibit positive surface photovoltage (SPV) responses in the range of 300-800 nm. However, the intensity, position and numbers of SPV responses are obviously different. The distinctions can be mainly attributed to their structures, valences and coordination environments of the manganese ions in the three complexes. Moreover the external field induced surface photovoltage spectra (FISPS) of the three complexes have been measured.     

Synthesis, crystal structure and esterification of a novel iron(III) 18-metallacrown-6 complex

The trianionic heptadentate ligand, (Z)-3-(5′-chlorosalicylhydrazinocarbonyl) propenoic acid, has been synthesized and reacted with FeCl₃·6H₂O, to produce the complex [Fe^III₆(C₁₂H₈N₂O₅Cl)₆(H₂O)₄(CH₃OH)₂]·8H₂O·4CH₃OH. In the self-assembly process the ligand was esterified and transferred into (Z)-methyl 3-(5′-chlorosalicylhydrazinocarbonyl) propenoate. In the crystal structure, the neutral Fe(III) complex contain a 18-membered metallacrown ring consisting of six Fe(III) and six trianionic ligands. The 18-membered metallacrown ring is formed by the succession of six structural moieties of the type [Fe(III)-N-N]. Due to the meridional coordination of the ligands to the Fe³⁺ ions, the ligands enforce the stereochemistry of the Fe³⁺ ions as a propeller configuration with alternating Λ/Δ forms. The metallacrown can be treated with SnCl₂ or Zn powder to obtain purified ester.     

Synthesis, characterization and crystal structure of novel mononuclear peroxotungsten(VI) complexes. Insulinomimetic activity of W(VI) and Nb(V) peroxo complexes

Two new mononuclear peroxo complexes of tungsten of the formula (gu)₂[WO₂(O₂)₂] (1) and (gu)[WO(O₂)₂(quin-2-c)] (2a) (where gu⁺ = guanidinium ion, and quin-2-c = quinoline-2-carboxylate ion) have been synthesized and characterized by elemental analysis, infrared, Raman, UV-visible and ¹H NMR spectroscopies. The crystal structure of (gu)[WO(O₂)₂(quin-2-c)] · H₂O (2b) determined by X-ray diffraction indicates that the side-on peroxo groups and the bidentate quinaldate ligand bind the W(VI) centre leading to an hepta coordination mode. The guanidinium ion occurring as a counterion and the hydrogen-bound interactions stabilize the complexes. The in vitro insulin-mimetic effect of the complexes has been evaluated by the inhibitory effect on free fatty acid release in isolated fat adipocytes treated with epinephrine. Moreover the niobate analogues, synthesized and characterized previously, (gu)₃[Nb(O₂)₄] and (gu)₂[Nb(O₂)₃(quin-2-c)] · H₂O have been tested for the insulin-like activity.     

Synthesis and reactivity of cationic bipyridine tungsten(0) and molybdenum(0) nitrosyl complexes

A variety of Group 6 mono bipyridine (bpy) complexes were prepared, and substitution reactions of [(bpy)(MeIm)M(CO)₂(NO)]PF₆ complexes (MeIm = 1-methylimidazole, M = W or Mo) were investigated. Nitrosylation of complexes having the general formula (bpy)(L)M(CO)₃ (L = a variable ligand) gave cationic complexes of the form [(bpy)(L)M(CO)₂(NO)]PF₆. The structure of [(bpy)(MeIm)W(CO)₂(NO)]PF₆ was confirmed by single-crystal X-ray diffractometry. [(bpy)(MeIm)M(CO)₂(NO)]PF₆ complexes undergo facile substitutions with mono-, tri- and tetra-dentate ligands, yielding di- or mono-carbonyl mononitrosyl complexes. The structures of [(bpy)(PMe₃)₂W(CO)(NO)]PF₆ and [(dien)(PMe₃)W(CO)(NO)]PF₆ (dien = diethylenetriamine) were determined by X-ray diffraction.     

Synthesis, characterization and redox behaviour of benzoyldiazenido- and oxorhenium complexes bearing N,N- and S,S-type ligands

The reactions of [ReCl₂{η²-N₂C(O)Ph}(PPh₃)₂] (1) with 2-aminopyrimidine (H₂Npyrm), 2,2′-bipyridine (bpy) and tetraethylthiuram disulfide (tds), in MeOH upon reflux, lead to the new η¹-(benzoyldiazenido)rhenium(III) complexes [ReCl{η¹-N₂C(O)Ph}(HNpyrm)(PPh₃)₂] (2) and [ReCl₂{η¹-N₂C(O)Ph}(bpy)(PPh₃)] (3), and the known oxo(diethyldithiocarbamato)dirhenium(v) complex [Re₂O₂(μ-O){Et₂NC(S)S}₄] (4), respectively. The Et₂NC(S)S ligands in 4 result from S-S bond rupture of tds molecules. The obtained compounds have been characterized by IR, ¹H, ³¹P{¹H} and ¹³C{¹H} NMR spectroscopies, FAB⁺-MS, elemental and single-crystal X-ray diffraction (for 2 and 4) analyses. Complex 2 represents the first structurally characterized Re compound derived from 2-aminopyrimidine. Besides, the redox behaviour of 2-4 in CH₂Cl₂ solution has been studied by cyclic voltammetry, and the Lever electrochemical ligand parameter (E_L) has been estimated, for the first time, for HNpyrm. The electrochemical results are discussed in terms of electronic properties of the Re centres and the ligands.     

Synthesis, structure and characterization of a new tetrameric tungsten-oxo complex [WO2Cl2(THF)]4

WOCl₄ reacts with (Me₃Si)₂O and excess THF to give [WO₂Cl₂(THF)]₄ (1), a new tetrameric tungsten(VI)-oxo complex, which was characterized and crystal structure was determined by X-ray crystallography. Complex 1 has a roughly square planar tetranuclear structure bridged by μ-oxo ligands. Each tungsten atom is coordinated by two bridging oxygens, one terminal oxygen, two “axial” chlorine atoms and one “equatorial” O-bonded THF ligand. One of the two μ-oxo ligands is similar to the terminal oxygen atom and the other one is similar to the coordinated oxygen atom of the THF ligand, respectively, which confirmed a previous proposal. Four WO₃Cl₂(THF) octahedral are associated by sharing corners. Complex 1 is different from three known tetrameric tungsten analogues in its structural arrangement and properties.     

Synthesis, crystal structure, and reactivity of a four-coordinate iron(II) chloride complex bearing the sterically demanding tert-butyl-tris(3-isopropylpyrazolyl)borato ligand

The salt elimination reaction between FeCl₂(THF)_1.5 and the sterically hindered thallium tert-butyl-tris(3-isopropylpyrazolyl)borate, Tl[t-BuTp^i-Pr], affords the new air and moisture-sensitive, high-spin, four-coordinate complex Fe[t-BuTp^i-Pr]Cl (1) in 52% yield. Compound 1 has been characterized by elemental analysis, paramagnetic ¹H NMR, and X-ray crystal structure determination. Fe[t-BuTp^i-Pr]Cl is monomeric, and the homoscorpionate ligand is κ³-coordinated. The Fe(II) ion lies in a trigonally distorted tetrahedral environment with average N-Fe-N and N-Fe-Cl angles of 89.4(2)° and 125.7(2)°, respectively. Upon reactions with methyllithium followed by carbonylation, the six-coordinate acetyl-dicarbonyl derivative Fe[t-BuTp^i-Pr](CO)₂{C(O)Me} was identified by IR spectroscopy. The reaction of 1 with ethylmagnesiumbromide furnished a mixture of mononuclear Grignard complexes Mg[t-BuTp^i-Pr]X (X = Et, Cl, Br), resulting formally from a facile and quantitative replacement of the [Fe-Cl]⁺ fragment by [Mg-X]⁺.     

Syntheses, characterizations and theoretical calculations of rhodium(III) 1,2-naphthoquinone-1-oxime complexes

Rhodium(III) complexes of 1,2-naphthoquinone-1-oxime (1-nqo) [Rh(1-nqo)L₂Cl₂] 1-3 [1, L = 4-methylpyridine (mpy); 2, L = 4-phenylpyridine (ppy); 3, L = 4-acetylpyridine (apy)] were prepared. The structure of complex 1 is analyzed by single crystal X-ray crystallography. All of the complexes were characterized by mass spectrometry, ¹H-¹H COSY NMR and FT-IR. UV-Vis absorption spectroscopy and cyclic voltammetry were employed to investigate the electronic transition behaviors of the complexes. The complexes displayed irreversible metal-localized two-electron reductions from Rh^III to Rh^I on the cyclic voltammogram. While the low-energy absorptions at λ_max of 488-490 nm on the UV-Vis spectra of the complexes were related to metal to 1-nqo ligand charge transfer [MLCT, dπ(Rh) → π∗(1-nqo)] and chloride to 1-nqo ligand charge transfer [LLCT, pπ(Cl) → π∗(1-nqo)] based on the theoretical calculations using time-dependent density functional theory (TD-DFT).     

Functionalised dithiocarbamate complexes: Synthesis and molecular structures of bis(2-methoxyethyl)dithiocarbamate complexes [M{S2CN(CH2CH2OMe)2}2] (M = Ni, Cu, Zn) and [Cu{S2CN(CH2CH2OMe)2}2][ClO4]

The bis(2-methoxyethyl)dithiocarbamate complexes [M{S₂CN(CH₂CH₂OMe)₂}₂] (M = Ni, Cu, Zn, Pd) are readily prepared and the three lighter complexes have been crystallographically characterised. Disproportionation of [Cu{S₂CN(CH₂CH₂OMe)₂}₂] upon addition of Cu(ClO₄)₂ · 6H₂O affords the copper(III) complex [Cu{S₂CN(CH₂CH₂OMe)₂}₂][ClO₄] which has also been crystallographically characterised. Unlike other copper(III) dithiocarbamate salts, there are no intermolecular cation-cation or cation-anion interactions.     

Stabilization of Mn(II) and Mn(III) in mononuclear complexes derived from tridentate ligands with N2O donors: Synthesis, crystal structure, superoxide dismutase activity and DNA interaction studies

A new family of tridentate ligands PhimpH (2-((2-phenyl-2-(pyridin-2-yl)hydazono)methyl)phenol), N-PhimpH (2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)napthalen-1-ol), Me-PhimpH (2-(1-(2-phenyl-2-(pyridine-2-yl)hydrazono)ethyl)phenol) have been synthesized and characterized. The ligands PhimpH and N-PhimpH after deprotonation react with manganese(II) and manganese(III) starting materials affording [Mn(Phimp)₂] (1), [Mn(Phimp)₂](ClO₄) (2), [Mn(N-Phimp)₂] (3), [Mn(N-Phimp)₂](ClO₄) (4). Complexes [Mn(Phimp)₂] (1) and [Mn(N-Phimp)₂] (3) convert to [Mn(Phimp)₂]⁺ (cation of 2) and [Mn(N-Phimp)₂]⁺ (cation of 4) respectively upon oxidation. Ligand Me-PhimpH stabilized only manganese(III) centre resulting [Mn(Me-Phimp)₂](ClO₄) (5). The molecular structures of [Mn(Phimp)₂], 1 and [Mn(Phimp)₂](ClO₄), 2 were determined by single crystal X-ray diffraction. X-ray crystal structures of 1 and 2 have revealed the presence of distorted octahedral MnN₄O₂ coordination sphere having meridionally spanning ligands. Electrochemical studies for the complexes showed Mn(II)/Mn(III), (E_1/2 = 0.14-0.40 V) and Mn(III)/Mn(IV), (E_1/2 = 0.80-1.06 V) couples vs. Ag/AgCl. The redox properties were exploited to examine superoxide dismutase (SOD) activity using Mn(II)/Mn(III) couple. The complexes 1, 2, 4 and 5 have been revealed to catalyze effectively the dismutation of superoxide () in xanthine-xanthine oxidase-nitro blue tetrazolium assay and IC₅₀ values were found to be 0.29, 0.39, 1.12 and 0.76 μM respectively. DNA interaction studies with complex 2 showed binding of DNA in a non-intercalative pathway. Complexes 1, 2 and 4 exhibited nuclease activity in presence of H₂O₂ and inhibition of activity was noted in presence of KI.     

Structural characterization, electrochemistry, and spectroelectrochemistry of trans-dioxorhenium(V) complex with 4-methoxypyridine, [ReO2(4-MeOpy)4]PF6, and characterization of [ReO2(4-MeOpy)4] generated electrochemically

Crystal structure of [ReO₂(4-MeOpy)₄][PF₆] (4-MeOpy = 4-methoxypyridine) complex has been examined by the single crystal X-ray analytical method. This complex shows a trans-dioxo geometry (average Re-O bond length = 1.766(2) Å) and its equatorial plane is occupied by four 4-MeOpy molecules (average Re-N bond length = 2.156(4) Å). Electrochemical reaction of [ReO₂(4-MeOpy)₄]⁺ in CH₃CN solution containing tetra-n-butylammonium perchlorate as a supporting electrolyte has been studied using cyclic voltammetry at 24 °C. Cyclic voltammograms show one redox couple around 0.65 V (E_pa) and 0.58 V (E_pc) [versus ferrocene/ferrocenium ion redox couple, (Fc/Fc⁺)]. Potential differences between two peaks (ΔE_p) at scan rates in the range from 0.01 to 0.10 V s⁻¹ are 65 mV, which is almost consistent with the theoretical ΔE_p value (59 mV) for the reversible one electron transfer reaction at 24 °C. The ratio of anodic peak currents to cathodic ones is 1.04 ± 0.03 and the (E_pa + E_pc)/2 value is constant, 0.613 ± 0.001 V versus Fc/Fc⁺, regardless of the scan rate. Spectroelectrochemical experiments have also been carried out by applying potentials from 0.40 to 0.77 V versus Fc/Fc⁺ with an optically transparent thin layer electrode. It was found that the UV-visible absorption spectra show clear isosbestic points at 228, 276, and 384 nm, and that the electron stoichiometry is evaluated as 1.03 from the Nernstian plot. These results indicate that the [ReO₂(4-MeOpy)₄]⁺ complex is oxidized reversibly to the [ReO₂(4-MeOpy)₄]²⁺ complex. Furthermore, it was clarified that the [ReO₂(4-MeOpy)₄]²⁺ in CH₃CN has the characteristic absorption bands at 236, 278, 330, 478, and 543 nm and their molar absorption coefficients are 4.3 × 10⁴, 4.5 × 10³, 1.0 × 10⁴, and 6.1 × 10³ M⁻¹ cm⁻¹ (M = mol dm⁻³), respectively.     

Synthesis, characterization and crystal structure of manganese (IV) complex derived from salicylic acid

The binuclear manganese (IV) [Mn₂(Hsal)₄(OH)₄] (H₂sal = salicylic acid) complex has been obtained from a complex reaction mixture in methanol consisting of Mn(II)(OAc)₂ · 4H₂O, GS ( a reagent obtained by refluxing glycine and salicylaldehyde in 1:1 molar ratio in methanol), monosodium salicylate and pyridine. The compound contains a distorted octahedral MnO₆ coordination unit of potential importance to high oxidation state manganese bimolecules.     

A chiral copper(II) inverse-9-metallacrown-3 complex: Synthesis, crystal structure, ferroelectric and magnetic properties

The reaction of phenyl 2-pyridyl ketoxime (PhPyCNOH) with Cu(NO₃)₂·3H₂O in methanol results in the chiral trinuclear complex [Cu₃(OH)(PhPyCNO)₃(NO₃) (CH₃OH)]·(NO₃) (1), which has been characterized by elemental analysis, IR spectra and single-crystal X-ray diffraction. The structure of 1 exhibits a triangle of Cu(II) ions, centered by a triply bridging hydroxo ligand and with three edge-bridging oximate groups from the three PhPyCNO⁻ ions. Preliminary variable-temperature magnetic susceptibility studies reveal an antiferromagnetically-coupled system showing antisymmetric exchange. Complex 1 crystallizes in an acentric space group (P2₁) that belongs to a polar point group, which displays second harmonic generation response and ferroelectric behavior, and provides a new strategy for designing functional coordination complexes.     

p-Quinquephenyl diamine, C6H5-p-C6H4-p-C6H2(2,3-NH2)-p-C6H4-C6H5, and its corresponding diimine-Ru(II) complex: Crystal structure and electrochemical and optical properties

The molecular structure of an o-phenylenediamine unit-containing oligophenylene (1), Ph-Ph′-Ph′(2,3-NH₂)-Ph′-Ph (Ph = phenyl; Ph′ = p-phenylene; Ph′(2,3-NH₂) = 2,3-diamino-p-phenylene), was determined by X-ray crystallography. 1 has a twisted structure, and forms an intermolecular C-H?π interaction network. The -NH₂ group of 1 was air-oxidized to an imine, NH, group in the presence of [RuCl₂(bpy)₂] (bpy = 2,2′-bipyridyl) and gave a ruthenium(II)-benzoquinone diimine complex [Ru(2)(bpy)₂](PF₆)₂ (2: Ph-Ph′-Ph′(2,3-imine)-Ph′-Ph). The molecular structure of [Ru(2)(bpy)₂](PF₆)₂ was confirmed by X-ray crystallography. [Ru(2)(bpy)₂](PF₆)₂ underwent two-step electrochemical reduction with E^1/2 = −0.889 V and −1.531 V versus Fc⁺/Fc. The E^1/2’s were located at higher potentials by 91 mV and 117 mV, respectively, than those of reported [Ru(bqdi)(bpy)₂](PF₆)₂ (bqdi = benzoquinone diimine). Electrochemical oxidation of [Ru(2)(bpy)₂](PF₆)₂ occurred at a lower potential by 180 mV than that of [Ru(bqdi)(bpy)₂](PF₆)₂. Occurrence of the easier reduction and oxidation of [Ru(2)(bpy)₂](PF₆)₂ than those of [Ru(bqdi)(bpy)₂](PF₆)₂ is ascribed to the presence of a large π-conjugation system in 2.     

Oxoperoxo molybdenum(VI)- and tungsten(VI) complexes with 1-(2′-hydroxyphenyl) ethanone oxime: Synthesis, structure and catalytic uses in the oxidation of olefins, alcohols, sulfides and amines using H2O2 as a terminal oxidant

High yield synthesis of two new oxodiperoxo-molybdate, PPh₄[MoO(O₂)₂(HPEOH)] (1), and -tungstate, PPh₄[WO(O₂)₂(HPEOH)] (2), complexes with 1-(2′-hydroxyphenyl) ethanone oxime (HPEOH₂) as organic ligand has been achieved by adding methanol solution of the ligand to the pale-yellow solution obtained by dissolving molybdic-/tungstic-acid (freshly prepared) in hydrogen peroxide and precipitating the complexes using tetraphenylphosphonium chloride. The orange-yellow complexes have been characterized by elemental analysis, IR, ¹H NMR, UV-Vis spectroscopy and finally by X-ray structure analysis. Both the complexes function as facile olefin epoxidation catalysts with hydrogen peroxide as terminal oxidant and bicarbonate as a co-catalyst at room temperature. Catalytic potentiality of 1 and 2 is also exhibited in the case of oxidation of alcohols, amines and sulfides. The catalysts are very much efficient especially in olefin epoxidation giving high yield, TON (turnover number) and TOF (turnover frequency). The method described is environmentally benign and cost-effective in all the cases.