Tungsten Complexes Research Articles

Syntheses, characterizations, and reactivities of new 1,4,7-trimethyl-l,4,7-triazacyclononane (Me3tacn) molybdenum and tungsten complexes

The reported complexes of [(Me3tacn)M0(CO)3] (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane; M = W, 1a; Mo, 1b), [(Me3tacn)MII(CO)3I](PF6) (M = W, 2a; Mo, 2b), [(Me3tacn)MVOCl2](PF6) (M = W, 3a; Mo, 3b), and [(Me3tacn)MVIO3]·4H2O (M = W, 4a; Mo, 4b) were synthesized as tungsten and molybdenum precursors according to the works by Wieghardt [20,21,24]. Reaction of 2a with sodium dialkyl dithiocarbamate afforded complexes [(Me3tacn)WII(CO)2(S2CNR2)]I (R = Me, 5a; iPr, 6a). Similar reaction using 2b gave rise to the isolations of complexes [(Me3tacn)MoII(CO)2(S2CNR2)](PF6) (R = Me, 5b; iPr, 6b; nPr, 7). Hydrolysis of 3b in acetonitrile gave a dimeric molybdenum complex [{(Me3tacn)MoVO(OH)}2(μ-O)](PF6)2·2MeCN (8). Treatment of 4b with sodium diisopropyl dithiocarbamate in the presence of HPF6 yielded [(Me3tacn)MoVIO2S] (9), while the similar reaction with S8 powder yielded the oxotetrasulfido complex [(Me3tacn)MoIVO(S4)] (10). All complexes are well characterized by electronic, infrared, and NMR spectroscopies, and the solid-state structures of 1a/b, 2a, 3b, 4a/b, 5a/b, 6a/b, and 7–10 have been also established by single-crystal X-ray diffraction. The electrochemical properties of these molybdenum and tungsten complexes were also investigated in the paper.

Pentagonal bipyramidal complexes of WOCl4 and WSCl4 with diphosphine and diarsine ligands

The seven-coordinate tungsten(VI) complexes, [WOCl4{o-C6H4(EMe2)2}] and [WSCl4{o-C6H4(EMe2)2}] (E = P, As), have been prepared by reaction of WOCl4 or WSCl4 with the ligands in anhydrous CH2Cl2 or toluene, and fully characterised by microanalysis, IR, 1H and 31P{1H} NMR spectroscopy. The X-ray crystal structures of [WOCl4{o-C6H4(AsMe2)2}] and [WSCl4{o-C6H4(PMe2)2}] have been determined and revealed pentagonal bipyramidal geometries with axial O/Cl or S/Cl. Attempts to isolate similar complexes with o-C6H4(PPh2)2, PMe3 or AsEt3 were unsuccessful, due to facile reduction of the tungsten centre. Several reduction products have also been identified crystallographically, including the tungsten (V) species, [WOCl3{o-C6H4(PMe2)2}], [WOCl3{o-C6H4(PMe2)(P(O)Me2)}] and [WCl4{o-C6H4(PPh2)2}2][WCl6].

Bioinspired Mo, W and V complexes bearing a highly hydroxyl-functionalized Schiff base ligand

A series of bioinspired dioxidomolybdenum(vi), dioxidotungsten(vi) and oxidovanadium(v) complexes [MoO2(H2LSaltris)], [WO2(H2LSaltris)] and [VO(HLSaltris)]2 were prepared by the reaction of a hydroxyl-rich Schiff base proligand N-(1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl)-3,5-di-tert-butylsalicylaldimine (H4LSaltris) with metal precursors in methanol solutions. Molybdenum and tungsten complexes crystallize as mononuclear molecules, whereas the vanadium complex forms dinuclear units. From the complexes, [VO(HLSaltris)]2 shows activity in the oxidation of 4-tert-butylcatechol and 3,5-di-tert-butylcatechol, mimicking the action of the dicopper enzyme catechol oxidase.

Formation and properties of phosphaquinomethane tungsten(0) complexes - isolation and conversion of primary radical coupling products.

A rational approach to phosphaquinomethane metal(0) complexes, based on dearomatization of the phenylene unit in [W(CO)5](R)P(Cl)-C6H5-CPh2, is described, including theoretical studies on mechanisms and structures. Furthermore, the first phosphaquinone tungsten complex with reversible redox properties is reported thus illustrating the beneficial stabilization of ligation.

Luminescent tungsten(vi) complexes as photocatalysts for light-driven C-C and C-B bond formation reactions.

The realization of photocatalysis for practical synthetic application hinges on the development of inexpensive photocatalysts which can be prepared on a large scale. Herein an air-stable, visible-light-absorbing photoluminescent tungsten(vi) complex which can be conveniently prepared at the gram-scale is described. This complex could catalyse photochemical organic transformation reactions including borylation of aryl halides, such as aryl chloride, reductive coupling of benzyl bromides for C-C bond formation, reductive coupling of phenacyl bromides, and decarboxylative coupling of redox-active esters of alkyl carboxylic acid with high product yields and broad functional group tolerance.

Synthesis and characterization of tungsten Imido/Aminoalkoxide complexes to deposit tungsten oxide thin films

Novel tungsten complexes containing aminoalkoxide ligands were synthesized in solid phase (W(NtBu)2(dmamp)2, 1) and liquid phase (W(NtBu)2(dmamb)2, 2) that were prepared through the metathesis reaction of W(NtBu)2Cl2(py)2 with 2 equiv. of Na(dmamp) and Na(dmamb), respectively. The compounds 1 and 2 were characterized by IR, MS, 1H and 13C NMR spectroscopies, and microanalyses. The molecular structure of 1 shows distorted trigonal bipyramidal geometry by single-crystal X-ray diffraction study. Thermogravimetric analyses of 1 and 2 showed two step weight loss and the residues was expected to be WO2. Thermally decomposed material of 1 under nitrogen atmosphere conforms to WO2 by XRD.

POSSIBILITY OF THE METHOD OF EXPLOSIVE ELECTRON-BEAM EVAPORATION-CONDENSATION IN VACUUM TO OBTAIN THE REFRACTORY AND COMPLEXLY DOPED COMPOUNDS FOR VARIOUS PURPOSES

Background. The method of explosive electron-beam evaporation-condensation of materials in vacuum opens up new possibilities for obtaining materials containing components, with a significant difference in the elasticity of the vapor, as well as complex alloyed compounds. This technology is promising for the production of various types of materials of controlled chemical composition in the form of powder products.Objective. The purpose of the paper is to study the possibilities of the method of electron-beam explosive evaporation-condensation of materials in vacuum to obtain in granular and film form refractory and composite materials based on tungsten and copper, and complex alloyed materials based on titanium.Methods. The method of explosive evaporation-condensation was used to obtain vapor-phase refractory, composite and complex alloyed materials based on the WC–W2C, Cu–W and Ti–Si–Zr–Nb systems. The experiments were carried out on the L-4 electron-beam installation, which was developed by the Scientific and Production Company “ELTEСHMASH” (Vinnytsia, Ukraine) in cooperation with the Frantsevich Institute for Problems of Materials Science, NAS of Ukraine. The changes in the chemical composition and morphology of obtained products depending on the deposition conditions in vacuum were studied.Results. For the first time, refractory alloys and composite materials based on tungsten and copper and complex alloyed compounds based on titanium were obtained in granular form by explosive evaporation-condensation in vacuum. Using this technology makes it possible to control the chemical composition and morphology of the produced powder products, widely used in various fields of science and technology.Conclusions. The technological conditions for the production of materials containing components with a significant difference in vapor pressure by the method of explosive evaporation-condensation in vacuum are determined. The method allows obtaining granular and film deposition products with refining of materials with respect to oxygen and some metal impurities.

Molybdenum and Tungsten Alkylidyne Complexes Containing Mono-, Bi-, and Tridentate N-Heterocyclic Carbenes

New tungsten and molybdenum alkylidyne complexes bearing mono-, bi-, and tridentate N-heterocyclic carbenes (NHCs) have been synthesized. Formation of unprecedented structures in complexes bearing ...

Kinetic advantage of inner sphere electron transfer reactions of copper(III,II) peptide complexes with cyano complexes of iron, molybdenum and tungsten

An inner sphere electron transfer process via a cyanide bridge is proposed for the reactions of Cu(III,II) peptide complexes with Fe(CN)63−,4−, Mo(CN)83−,4− and W(CN)83−,4−. Cu(III) peptide complexes were generated electrolytically from the Cu(II) precursors. The direction of spontaneous reactions is such that Fe(CN)64− and W(CN)84− reduce Cu(III) peptide complexes and Mo(CN)83− oxidizes Cu(II) peptide complexes at pH ca. 10. However, since all reactions are equilibrium processes, by the very fast continuous decomposition of the reduced Cu(II) product in a slightly acidic reaction medium (pH 5), the Mo(CN)84− reduction of Cu(III) peptide complexes could be driven to completion and studied kinetically. Kinetically determined equilibrium constants and electrochemically calculated equilibrium constants are mutually consistent. The experimentally observed inner sphere rate constants, kis, for these reactions are significantly larger than the corresponding outer sphere rate constant, kos, for the outer sphere electron transfer processes calculated with the Marcus theory, with or without work terms. It is concluded that if the kinetic advantage kis/kos is substantially larger than 1, it provides evidence for an inner sphere reaction pathway. The magnitude of the kinetic advantage of the present redox reactions varies from 1 to 63 and is dependent on the metal-to-metal distance in the cyanide-bridged intermediates.

Allyl Complexes of Tungsten from the Rearrangement of Transient Cyclopropyl Precursors

This article explores the contrasting reactivity of cyclopropyl complexes of early transition metals. [Cp*W(NO)(CH2R)(c‐C3H5)] (R = SiMe3, Ph, t‐Bu) generated in THF solution from [Cp*W(NO)(CH2R)Cl] and [Mg(c‐C3H5)2(dioxane)x] readily rearrange to η3‐allyl derivatives [Cp*W(NO)(CH2R)(η3‐C3H5)] by an intramolecular ring opening reaction. Both direct and catalyzed pathways are revealed by kinetic studies. Computational modeling indicates the ring opening reaction is preferred on thermodynamic grounds for tungsten whereas kinetic products arising from β‐H abstraction reactions of cyclopropane are observed for related zirconium and niobium complexes reported previously. The energetic accessibility and the nature of the LUMO in the tungsten complexes promote distal CC bond cleavage in the cyclopropyl ring.

Molecular Routes to Two-Dimensional Metal Dichalcogenides MX2 (M = Mo, W; X = S, Se).

New synthetic access to two-dimensional transition metal dichalcogenides (TMDCs) is highly desired to exploit their extraordinary semiconducting and optoelectronic properties for practical applications. We introduce here an entirely novel class of molecular precursors, [MIV(XEtN(Me)EtX)2] (MIV = MoIV, WIV, X = S, Se), enabling chemical vapor deposition of TMDC thin films. Molybdenum and tungsten complexes of dianionic tridentate pincer-type ligands (HXEt)2NR (R = methyl, tert-butyl, phenyl) produced air-stable monomeric dichalcogenide complexes, [W(SEtN(Me)EtS)2] and [Mo(SEtN(Me)EtS)2], displaying W and Mo centers in an octahedral environment of 4 S and 2 N donor atoms. Owing to their remarkable volatility and clean thermal decomposition, both Mo and W complexes, when used in the chemical vapor deposition (CVD) process, produced crystalline MoS2 and WS2 thin films. X-ray diffraction analysis and atomic-scale imaging confirmed the phase purity and 2D structural characteristics of MoS2 and WS2 films. The new set of ligands presented in this work open ups convenient access to a scalable and precursor-based synthesis of 2D transition metal dichalcogenides.

The heteroscorpionate ligand 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethanol and an easy preparation of its tungsten complex.

The heteroscorpionate ligand 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethanol, C24H26N4O, features in the solid state an intramolecular O-H...N hydrogen bond. A heteroscorpionate tungsten complex, cis-[2,2-bis(3,5-dimethylpyrazolyl)-1,1-diphenylethanolato]chloridodioxidotungsten(VI) tetrahydrofuran monosolvate, [W(C24H25N4O)ClO2]·C4H8O, was prepared by the simple mixing of solutions of the ligand and WOCl4 in tetrahydrofuran. The tungsten complex was isolated after standing for several weeks. The complex exhibits a κ3N,N',O-coordination of the ligand. This simple synthetic procedure allows access to the cis isomer in high yield without additional purification steps. The Hirshfeld surface analysis shows a change of the intermolecular contacts due to the coordination of the WO2Cl unit with the ligand molecule.

Peroxo–tungstate(VI) complexes: syntheses, characterization, reactivity, and DFT studies

Three new oxodiperoxo–tungsten(VI) complexes containing benzene core carboxylic acids, viz., benzoic acid, 2-chlorobenzoic acid, and 3-aminobenzoic acid as co-ligands have been synthesized from reaction of Na2WO6H4, 30% H2O2 and the corresponding co-ligands in aqueous medium. The compounds have been comprehensively characterized by elemental analyses, FT-IR, 1H NMR, UV–Vis spectral studies as well as by mass spectrometric and TGA analyses. The infrared spectra suggest occurrence of terminally bonded W=O as well as triangular bidentate peroxo groups (C2v) and monodentate carboxylate group bound to the WO4+ center. The mass spectra of the compounds are in good agreement with proposed molecular formulations. Thermogravimetric analyses indicate the existence of both lattice and coordinated water molecules in the complexes. Density functional theory (DFT) calculations were used to compute the frequencies of relevant vibrational modes, electronic properties and also to investigate structure of the compounds. Compound potassium(aquo)(2-chlorobenzoato)oxodiperoxo–tungstate(VI)dihydrate acts as an oxidant for bromide ion in aqueous phase bromination of chosen organic substrates to their corresponding bromo-organics.

Cover Feature: Photochemical Unmasking of 1,3‐Dithiol‐2‐ones: An Alternative Route to Heteroleptic Dithiolene Complexes from Low‐Valent Molybdenum and Tungsten Precursors (Eur. J. Inorg. Chem. 23/2019)

The Cover Feature shows the light-induced ring-opening of the 1,3-dithiole-2-one moiety to yield the corresponding highly reactive dithione. The metal precursor with which the in situ prepared dithione reacts needs to be chosen carefully. Particularly suitable reactants are tetracarbonyl-bisphosphane complexes of zero-valent molybdenum and tungsten. The combination generates mono-dithiolene complexes including those with aliphatic backbones, which have not been accessible previously. This photochemical approach constitutes a bridge towards a broad range of such uncommon complexes. More information can be found in the Full Paper by C. Fischer et al.

Bioinspired Tungsten Complexes Employing a Thioether Scorpionate Ligand.

The synthesis and characterization of a series of novel tungsten complexes employing the bioinspired, sulfur-rich scorpionate ligand [PhTt] (phenyltris((methylthio)methyl)borate) are reported. Starting from the previously published tungsten precursor [WBr2(CO)3(NCMe)2], a salt metathesis reaction with 1 equiv of Cs[PhTt] led to the desired complex [WBr(CO)3(PhTt)] (1), making it the first tungsten complex employing a poly(thioether)borate ligand. Surprisingly, the reaction of [WBr2(CO)3(NCMe)2] with an excess of the ligand gave complex [W(CO)2(η2-CH2SMe)(PhTt)] (2) with a bidentate (methylthio)methanide ligand as the major product. Thereby, phenyldi((methylthio)methyl)borane is formed, which was isolated and characterized by NMR spectroscopy. The bromido ligand in [WBr(CO)3(PhTt)] was further substituted by the S,N-bidentate methimazole in order to make the first coordination sphere more sulfur-rich forming [W(CO)2(mt)(PhTt)] (3). Alkyne tungsten complexes employing the sulfur-rich scorpionate ligand were accessible by reaction of [WBr2(CO)(C2R2)2(NCMe)] (R = Me, Ph) with Cs[PhTt] forming [WBr(CO)(C2R2)2(PhTt- S, S')] (R = Me 4, Ph 5), with the potentially tridentate ligand coordinated only via two sulfur atoms. In the case of 4, the higher flexibility of the bidentate coordination leads to the formation of two isomers with respect to the six-membered ring formed by the tungsten center and the two coordinated sulfur atoms of the ligand. All complexes 1-5 were characterized by single-crystal X-ray diffraction analysis.

Syntheses and Structures of Transition Metal Complexes with Phosphanylphosphinidene Chalcogenide Ligands.

The reactivity of the phosphanylphosphinidene complex [(DippN)2W(Cl)(η2-P-P tBu2)]- (1) toward chalcogens (Ch = Se, S) was studied. Reactions of stoichiometric amounts of 1 with chalcogens in DME yielded monomeric tungsten complexes with phosphanylphosphinidene chalcogenide ligands of the formula tBu2P-P-Ch (Ch = Se (in 2) and S (in 5)), which can be regarded as products of the addition of a chalcogen atom to a P═W bond in starting complex 1. The dissolution of selenophosphinidene complex 2 in nondonor solvents led to the formation of a dinuclear complex of tungsten (3) bearing a tBu2P(Se)-P ligand together with [ tBuSe2Li(dme)2]2 and polyphosphorus species. Under the same reaction conditions, thiophosphinidene complex 5 dimerized via the formation of transient complex 7, possessing a thiotetraphosphane-diido moiety tBu2P(S)-P-P-P tBu2. The elimination of the tBu2PS group from 7 yielded stable dinuclear tungsten complex 8 with an unusual phosphinidene tBu2P-P-P ligand. The reaction of 1 with excess chalcogen led to the cleavage of the P-P bond in the tBu2P-P ligand and the formation of [(DippN)2W(PCh4)]22- and [ tBuCh2Li(dme)2]2. The isolated compounds were characterized by NMR spectroscopy and X-ray crystallography. Furthermore, the calculated geometries of the free selenophosphinidenes, tBu2P-P-Se and tBu2P(Se)-P, were compared with their geometries when serving as ligands in complexes 2 and 3.

Bis(β-ketoiminate) dioxo tungsten(VI) complexes as precursors for growth of WOx by aerosol-assisted chemical vapor deposition

Bis(β-ketoiminate) dioxo tungsten(VI) complexes WO2L2 (L = acNac, acNacMe, acNacEt) have been synthesized and characterized. The thermal behaviors and possible decomposition mechanisms of these dioxo compounds were studied by TGA, MS and thermolysis. The performance of WO2(acNacMe)2 as an AACVD precursor was evaluated at growth temperatures of 250–550 °C using nitrogen as the carrier gas. The elemental compositions of the as-deposited and sputtered tungsten oxide films were determined by XPS. The morphology and stoichiometry of the as-deposited films were studied by SEM and XRD.

Synthesis of New Mixed-Ligand Complexes of Molybdenum (IV) and Tungsten(IV): Characterization, Structure, Thermal and Anti-microbial Studies

Six new mixed-ligand complexes of Mo(IV) and W(IV) ions have been prepared and characterized. The three new complexes of Mo(IV) ions have the molecular formulae MoC12N2O5H18, MoC15N2O5H22 and MoC14N2O6H19 , while the W(II) ions are WC12N2O5H18, WC15N2O5H22 and WC14N2O6H19. The structures of the complexes were deduced from their ir, 1H nmr, and mass spectral studies. All the complexes were found to exhibit octahedral structures. Their antimicrobial activities against some bacteria and fungi species were found to be moderate.

Studies on Molybdena- and Tungstenacyclobutadiene Complexes Supported by Fluoroalkoxy Ligands as Intermediates of Alkyne Metathesis

The molybdenum and tungsten 2,4,6-trimethylbenzylidynes [MesC≡M{OC(CF3)2Ph}3] (12a, M = Mo; 12b, M = W) were prepared and structurally characterized as related complexes to already known [MesC≡M{OC(CF3)2Me}3] (MoF6, M = Mo; WF6, M = W). While treatment of 12a with 3-hexyne yielded the propylidyne complex [EtC≡Mo{OC(CF3)2Ph}3] (13), the tungsten congener 12b formed isolable metallacyclobutadiene (MCBD) species 14–16 by reaction with 3-hexyne, 1-phenyl-1-propyne, and 2,4-hexadiyne, which can be correlated with the higher electrophilicity of the tungsten complex. Furthermore, the labile MCBD [(C3Et3)Mo{OC(CF3)2Me}3] (17) was isolated at low temperature from the reaction of the highly active MoF6 catalyst with 3-hexyne and could be characterized by X-ray diffraction analysis. At room temperature, the same reaction afforded [EtC≡Mo{OC(CF3)2Me}3] (18), and the equilibrium reaction with 3-hexyne to form 17 was additionally studied by variable temperature NMR spectroscopy, which allowed determining ΔH° and ΔS° fo...

New insight into the DNA binding studies, In-Vitro anti-cancer activity and molecular modelling of dioxo complexes of Molybdenum(VI) and Tungsten(VI) hydroxamic acids

The present study embodies the detail of interaction of Complex 1, Bis(N-phenyl-o-methoxybenzohydroxamato)Molybdenum(VI): [N-PMBHA-Mo(VI)] and Complex 2, Bis(N-phenylbenzohydroxamato)Tungsten(VI): [N-PBHA-W(VI)] with ct-DNA (Calf thymus-DNA) and its consequences by UV–Visible absorption spectroscopy, fluorescence spectroscopy, three-dimensional fluorescence spectroscopy, viscosity measurements and molecular docking. The intrinsic binding constant, Kb of complexes were determined which follows the order as complex 1 > complex 2 along with variation in shift and intensity for the complexes. Fluorescence spectroscopy applied for the determination of Stern–Volmer quenching constant, binding constant and the number of binding sites which reveals groove mode of binding. Non-radiative energy transfer between donor and acceptor molecule exposed by Förster energy transference theory (FRET) studies. The increase in the relative viscosity of ct-DNA with increasing the concentration of the complex 1 and complex 2 is also revealed. FTIR analysis also revealed that both the complexes interacted positively with bases and phosphates of ct-DNA. The docking studies complemented the experimental results revealing minor groove mode of binding for both the complexes. Finally, the in-vitro cytotoxicity studies indicate that the complexes have excellent anticancer activity against the breast cancer cell line, MCF-7, which could be a constructive guideline to produce new generations of anticancer agents.