Tungsten Complexes Research Articles

Chemocatalytic Conversion of Dinitrogen to Ammonia Mediated by a Tungsten Complex

Whereas molybdenum dinitrogen complexes have played a major role as catalytic model systems of nitrogenase, corresponding tungsten complexes were in most cases found to be catalytically inactive. Herein, we present a modified pentadentate tetrapodal (pentaPod) phosphine ligand in which two dimethylphosphine groups of the pentaPodMe (P5Me) ligand have been replaced with phospholanes (Pln). The derived molybdenum complex [Mo(N2)P5Pln] generates 22 and the analogous tungsten complex [W(N2)P5Pln] 7 equivalents of NH3 from N2 in the presence of 180 equiv.s of SmI2(thf)2/H2O, rendering the latter the first tungsten complex chemocatalytically converting N2 to NH3. In contrast, the tungsten complex [W(N2)P5Me] generates ammonia from N2 only in a slightly overstoichiometric fashion. The reasons for these reactivity differences are investigated with the help of spectroscopic and electrochemical methods.

Comparison of protonation and anion binding preference of Chatt-type tungsten dinitrogen complex: DFT studies

In this paper, preference of protonation and anion binding to Chatt-type tungsten complex [W(Ph2(Ch2)2Ph2)2(N2)2] was investigated. Optimization of metal complexes [W(PH2(CH2)2PH2)2(N2)2], [W(PH2(CH2)2PH2)2N2FH], [W(PH2(CH2)2PH2)2(N2)2H] and [W(PH2(CH2)2PH2)2N2F] was carried out using density functional theory (DFT). Diethyl ether solution of HBF4 was used as a proton source. DFT calculations were carried out to understand the reactivity pattern shown by Chatt-type dinitrogen (N2) complex. Thermodynamic energy values for the protonation of coordinated dinitrogen followed by anion binding; anion binding followed by protonation; and simultaneous reaction of protonation of dinitrogen and anion binding have been calculated. The energy values revealed that the protonation of dinitrogen followed by anion binding is preferable over anion binding followed by protonation.

Understanding the Carbyne Formation from C2H2 Complexes.

Nature chooses a high-valent tungsten center at the active site of the enzyme acetylene hydratase to facilitate acetylene hydration to acetaldehyde. However, the reactions of tungsten-coordinated acetylene are still not well understood, which prevents the development of sustainable bioinspired alkyne hydration catalysts. Here we report the reactivity of two bioinspired tungsten complexes with the acetylene ligand acting as a four-: [W(CO)(C2H2)(PymS)2] (1) and a two-electron donor: [WO(C2H2)(PymS)2] (3), with PMe3 as a nucleophile to simulate the enzyme's reactivity (PymS = 4-(trifluoromethyl)-6-methylpyrimidine-2-thiolate). In dichloromethane, compound 1 was found to react to the cationic carbyne [W≡CCH2PMe3(CO)(PMe3)2(PymS)]Cl (2-Cl) while 3 reacts to the vinyl compound [WO(CH═CHPMe3)(PMe3)3(PymS)]Cl (4-Cl). The formation of the latter follows the common rules applied to η2-alkyne complexes, whereas the carbyne formation was not expected due to the challenging 1,2-H shift. To understand these differences in behavior between seemingly similar acetylene complexes, stepwise addition of the nucleophile in various solvents was investigated by synthetic, spectroscopic, and computational approaches. In this manuscript, we describe that only a four-electron donor acetylene complex can react to the carbyne over the η1-vinyl intermediate and that 1,2-H shift can be assisted by an H-transfer reagent (in this case, the decoordinated PymS ligand). Furthermore, to favor the attack of PMe3 at W coordinated acetylene, the metal center needs to be electron-poor and crowded enough to prevent nucleophile coordination. Finally, the intricate role of the anionic PymS ligand in the vicinity of the first coordination sphere models the potential involvement of amino acid residues during acetylene transformations in AH.

Ring-opening metathesis polymerization of Norbornene-derived cyclic olefins using Iminomethyl-hydroxyl-ligated tungsten Complexes: Fast reaction and tunable cis/trans selectivity

Highly active tungsten complexes supported by (Z)-1-(((2-hydroxyphenyl)imino)methyl)naphthalen-2-ol (LA) and (Z)-4-chloro-2-(((2-hydroxyphenyl)imino)methyl)phenol (LB) were synthesized and characterized. The ring-opening metathesis polymerization activities were assessed using iBu3Al as the co-initiator at room temperature. A 100% conversion of norbornene to high-molecular-weight polynorbornene (PNB) was obtained within 10 min with tunable cis/trans selectivity of resultant polymer depending on the ligand architecture.

Single Site W(0) versus Re(I)‐Dipyridophenazine‐ Based Conjugated Porous Polymer for CO2 Photoreduction

Herein, the synthesis and characterization of two robust tungsten and rhenium carbonyl complexes integrated into an organic polymer (CPP‐Re, CPP‐W) are reported. These polymers are obtained by a Suzuki coupling reaction between the corresponding dibromo metal‐carbonyl substituted dipyrido[3,2‐a:2′,3′‐c]phenazine complex and 1,3,5‐triphenylbenzene‐4′,4″,4″,4‴‐triboronic acid and integrated catalytic active sites and photosensitizer since they have not only nitrogen sites to coordinate metal active centers as rhenium or tungsten but photoactive units with good charge‐separating ability which can significantly improve the CO2 photoreduction reaction (CO2PRR). These polymers show similar activity in solid–gas CO2PRR in absence of sacrificial agents to produce syn gas (CO + H2) but CPP‐W selectivity to products change regarding CPP‐Re being able to produce also large amount of more demanding electron products such as methane and ethane. Moreover, the single‐site Re‐ or W‐CPP catalysts could prevent the dimerization of complexes that produces its deactivation. This work shows the potential of CPPs as matrices to support single active centers for heterogeneous catalysis.

Tungsten speciation in hydrothermal fluids

Understanding the speciation and thermodynamic properties of aqueous tungsten (W) complexes under various conditions is essential for predicting W transport in hydrothermal fluids relevant to ore formation and geothermal systems. Although previous experimental and geochemical modelling studies have provided insights into W solubility in hydrothermal systems, a comprehensive molecular-level understanding of W in hydrothermal fluids remains elusive.In this study, we employed ab initio molecular dynamics (MD) simulations to determine the speciation and coordination geometries of W(VI) complexes in NaCl, NaHS, and NaF-bearing brines at temperatures up to 600 °C and pressures up to 2 kbar. These theoretical calculations were complemented by synchrotron in-situ X-ray Absorption Spectroscopy measurements of W(VI) in chloride-, sulfide-, and fluoride-rich solutions under pressures of 600 bar and temperatures ranging from 25 to 429 °C. The speciation and geometrical properties obtained from ab initio MD simulations are in reasonably good agreement with the in-situ X-ray Absorption Spectroscopy data. Our study reveals that W-Cl complexes are not stable, and W is transported as tungstates (H2WO4(aq), HWO4− and WO42−)in NaCl-rich fluids. In sulfur-rich fluids under near-neutral pH and reduced conditions (sulfide predominant), S2− ions gradually replace O2− in tungstates to form thiotungstate complexes (WO4-xSx2−, where x = 1, 2, 3, 4). The MD results suggest that fluoride (F−) plays a significant role in W transport by forming WO3F− and WO3F22− complexes, or their hydrated ions. We employed thermodynamic integration to determine the formation constants of the WO3F− and WO3F22− complexes at temperatures up to 600 °C and 2 kbar, and extrapolated these properties across a broader range of temperatures and pressures. This study underscores the significance of W-F complexes in W transportation in fluoride-bearing, acidic to neutral (pH < 8) hydrothermal fluids. In contrast, W is most likely transported as thiotungstate complexes in sulfur-bearing hydrothermal fluids within a neutral to alkaline pH range (e.g., pH 5–8.5 at 300 °C) under reduced (sulfide-stable) conditions in the Earth’s crust. Existing models for W transport in hydrothermal ore fluids need to consider the influence of W-F and thiotungstate species.

The Effect of Selenium-Based Ligands on Tungsten Acetylene Complexes.

Bioinspired tungsten acetylene complexes containing pyridine-2-selenolato (PySe) or 6-methyl-pyridine-2-selenolato (6-MePySe) ligands were synthesized. 77Se NMR spectroscopy allowed for an assessment of the resonance structures in the pyridine-2-selenolato ligands and the rationalization of chemoselectivity observed in regard to 1,2 migratory insertion of HC≡CH. [W(CO)(C2H2)(CHCH-PySe)(PySe)] is formed exclusively via insertion of HC≡CH into the W-N bond, while the use of bulkier 6-MePySe allows for the isolation of [W(CO)(C2H2)(6-MePySe)2], which only partially reacts with excess HC≡CH to give [W(CO)(C2H2)(CHCH-6-MePySe)(6-MePySe)]. Oxidation of [W(CO)(C2H2)(6-MePySe)2] with pyridine-N-oxide gave the tungsten(IV) complex [WO(C2H2)(6-MePySe)2]. Complexes [W(CO)(C2H2)(6-MePySe)2] and [WO(C2H2)(6-MePySe)2] react with trimethyl phosphine to carbyne complex [W(CO)(CCH2PMe3)(PMe3)2(6-MePySe)]Cl and alkylidene complex [WO(CHCHPMe3)(PMe3)2(6-MePySe)]Cl, respectively. The addition of substituted alkynes to [W(CO)3(PySe)2] via thermal decarbonylation gave complexes [W(CO)(MeC≡CMe)(PySe)2] and [W(CO)(HC≡Ct-Bu)(PySe)2], respectively. The here presented complexes are relevant for the modeling of the active site of acetylene hydratase from Pelobacter acetylenicus, in which a tungsten atom is enclosed in a sulfur-rich coordination sphere. A recently published theoretical study concluded that the exchange of sulfur for selenium would increase the activity of the enzyme. Our findings contrast this claim as comparative analysis concludes negligible structural and electronic differences between the selenium-based and previously published sulfur-based complexes.

Iodine-mediated substitution of terminal ligands in [{M6I8}I6]2– (M = Mo, W) by DMSO

The family of octahedral iodide cluster complexes of molybdenum and tungsten – [{M6I8}L6]n – exhibit a unique set of properties with significant practical potential. Due to the strong influence of terminal ligands L on these properties, the search for new simpler, more convenient and cheaper approaches for their substitution is an urgent task. This work demonstrates a new one-step method for terminal ligand substitution using well-known and readily available complexes [{M6I8}I6]2–. The synthetic technique involves the addition of molecular iodine to the reaction mixture in order to bind the released I– ions, thereby facilitating the reaction process. As a result, two new cluster complexes with dimethyl sulfoxide ligands [{M6I8}(DMSO)6](I3)4 (M = Mo (1), W (2)) have been obtained and structurally characterized. The optical properties of the obtained compounds have been studied both in solid state and in solution, and Eg values have been calculated from the solid-state absorption spectra. The presence of I3– anions has been shown to quench the emission of the cluster complexes, explaining the absence of luminescence in the obtained compounds.

Synthesis of 1-Azatriene Complexes of Tungsten: Metal-Promoted Ring-Opening of Dihydropyridine.

For nearly a century, chemists have explored how transition-metal complexes can affect the physical and chemical properties of linear conjugated polyenes and heteropolyenes. While much has been written about higher hapticity complexes (η4-η6), less is known about the chemistry of their η2 analogues. Herein, we describe a general method for synthesizing 5,6-η2-(1-azatriene) tungsten complexes via a 6π-azaelectrocyclic dihydropyridine ring-opening that is promoted by the π-basic nature of {WTp(NO)(PMe3)}. This study includes detailed spectroscopic and crystallographic data for the η2-dihydropyridine and η2-1-azatriene complexes, both of which were prepared as single regio- and stereoisomers.

Volatile and thermally stable tungsten organometallic complexes (RCp)W(CO)2(η3-2-tert-butylallyl) as potential thin film deposition precursor

Two organometallic tungsten complexes (RCp)W(CO)2(η3-2-tert-butylallyl) (R = methyl or ethyl, Cp = cyclopentadienyl) as precursors capable of growing tungsten-containing thin films, are constructed bearing heteroleptic ligand system. The syntheses adopt a rationally designed approach excluding the use of extreme conditions and involving facile purification procedures. The two complexes are authenticated by nuclear magnetic resonance (NMR) and elemental analysis, as well as Fourier transform-infrared (FT-IR) spectroscopy. Thermal property evaluations, including thermogravimetric and vapor pressure tests, reveal favorable thermal stability and volatility which are essential for a typical ALD process. It is noteworthy that both precursors possess relatively low-melting point and specifically, the one bearing ethyl-Cp group is in liquid phase at room temperature. Such design concept of heteroleptic ligand system and substructure tuning pave the way to develop liquid precursors which are imperative demand in microelectronic industry.

Oxidation of PPh3 by oxygen catalyzed by biomimetic tungsten complex: oxo-transfer process thermodynamics

Oxidation of PPh3 by oxygen catalyzed by biomimetic tungsten complex: oxo-transfer process thermodynamics

Exploration of the Tungsten(VI) complex of hydroxamic acid's RNA binding affinity, histone deacetylase inhibitory activity, and antioxidant activity

Ribonucleic acid (RNA) is a versatile molecule, thus the opportunity to target RNA is abundant. Hence, the current exploration deals with the interaction of a metal complex of hydroxamic acid with t-RNA, along with HDAC8 inhibition activity and antioxidant activity. Binding characteristics of complex 1, Bis(N-phenylbenzohydroxamato)Tungsten(VI), which is represented as [N-PBHA-W(VI)] with Torula yeast RNA (t-RNA) were investigated by using several types of spectroscopic techniques, measurements of viscosity, and computational study through molecular docking. The intrinsic binding constant, Kb was evaluated for complex 1 which shows changes in the shift of absorption spectra, and the intensity of spectra also varies. From fluorescence measurement, the binding constant of complex 1 towards t-RNA is 6.64 ± 0.05 × 105 M−1. Stern-Volmer quenching constant was calculated. Two displacement method sare performed by using the fluorescence spectroscopic technique which discloses a groove mode of binding. The groove mode of binding is also uncovered by viscosity measurement, which was observed by increasing the complex 1 concentration. An electrochemical investigation was carried out by using cyclic voltammetry. A circular dichroism study was also employed, which further suggests a strong binding occurred between the metal complex used and t-RNA. The docked postures of t-RNA with complex 1 expose the strong interactions which suggest a minor groove mode of binding. All the experimental evidence indicates that the interaction of complex 1 with t-RNA is a minor groove mode of binding which complements the molecular docking results. In-silico studies of HDAC8 inhibition activity of complex 1 reveal that the inhibition takes place mainly by hydrophobic interaction. DPPH–radical scavenging method employed for the antioxidant activity.

Isolation and characterization of a bis(dithiolene)-supported tungsten-acetylenic complex as a model for acetylene hydratase

Acetylene hydratase is currently the only known mononuclear tungstoenzyme that does not catalyze a net redox reaction. The conversion of acetylene to acetaldehyde is proposed to occur at a W(IV) active site through first-sphere coordination of the acetylene substrate. To date, a handful of tungsten complexes have been shown to bind acetylene, but many lack the bis(dithiolene) motif of the native enzyme. The model compound, [W(O)(mnt)2]2−, where mnt2− is 1,2-dicyano-1,2-dithiolate, was previously reported to bind an electrophilic acetylene substrate, dimethyl acetylenedicarboxylate, and characterized by FT-IR, UV–vis, potentiometry, and mass spectrometry (Yadav, J; Das, S. K.; Sarkar, S., J. Am. Chem. Soc., 1997, 119, 4316–4317). By slightly changing the electrophilic acetylene substrate, an acetylenic-bis(dithiolene)‑tungsten(IV) complex has been isolated and characterized by FT-IR, UV–vis, NMR, X-ray diffraction, and X-ray absorption spectroscopy. Activation parameters for complex formation were also determined and suggest coordination-sphere reorganization is a limiting factor in the model complex reactivity.

Synthesis of Collidine from Dinitrogen via a Tungsten Nitride.

The synthesis of pyridines from dinitrogen in homogeneous solution is known to be challenging considering that an N2 cleavage step needs to be combined with two N-C coupling steps. Herein, a tungsten complex bearing a tailor-made 2,2'-(tBu2As)2-substituted tolane ligand scaffold was shown to split N2 to afford the corresponding tungsten nitride, which is not the case for the corresponding (iPr2As)2-substituted derivative. The former nitride was then reacted with 2,4,6-trimethylpyrylium triflate, which led to the formation of a tungsten oxo complex, along with collidine. Over the course of this reaction, the O atom of the pyrylium starting material was replaced with an N atom via a hitherto unprecedented skeletal editing process.

A Versatile Comproportionation Route to Construct Mono‐Imido Trichlorido Complexes of Molybdenum(V) and Tungsten(V)

AbstractWe report the facile and high‐yielding multi‐gram synthesis of pentavalent heavy group VI mono‐imido complexes with the general formula M(NR)Cl3Ln (M=Mo, W, R=Aryl or Alkyl, L=DME n=1 or Py n=2) following a comproportionative imido group transfer procedure starting from the corresponding bis‐imido complexes and MCl4. The procedure works well for both aryl and alkyl imido ligands, in the case of molybdenum but only for alkyl imidos in the case of tungsten. Overall, five mono‐imido complexes have been structurally characterized and purity is established by elemental analysis and EPR spectroscopy.

Tungsten-anisole complex provides 3,6-substituted cyclohexenes for highly diversified chemical libraries.

Medicinal chemists use vast combinatorial molecular libraries to develop leads for new pharmaceuticals. The syntheses of these compounds typically rely on coupling molecular fragments through atoms with planar (sp2) geometry. These so-called flat molecules often lack the protein binding site specificity needed to be an effective drug. Here, we demonstrate a coupling strategy in which a cyclohexene is used as a linker to connect two diverse molecular fragments while forming two new tetrahedral (sp3) stereocenters. These connections are made with the aid of a tungsten complex that activates anisole toward an unusual double protonation, followed by sequential nucleophilic additions. As a result, either cis- or trans-disubstituted cyclohexenes can be prepared with a range of chemical diversity unparalleled by other dearomatization methods.

Synthesis, Structure, and Reactivity of Molybdenum- and Tungsten-Indane Complexes with Tris(pyrazolyl)borate Ligand.

The reaction of molybdenum complexes with a tris(pyrazolyl)borate ligand (Et4N[TpMo(CO)3] and Et4N[Tp*Mo(CO)3] (Tp = hydridotris(pyrazolyl)borate, Tp* = hydridotris(3,5-dimethylpyrazolyl)borate)) and InBr3 at a 1:1 molar ratio afforded molybdenum-indane complexes (Et4N[TpMo(CO)3(InBr3)] 1 and Et4N[Tp*Mo(CO)3(InBr3)] 2). In addition, tungsten-indane complexes, Et4N[TpW(CO)3(InBr3)] 3 and Et4N[Tp*W(CO)3(InBr3)] 4, were obtained by the reaction of corresponding tungsten complexes. Complex 4 reacted with H2O to form the hydrido complex Tp*W(CO)3H, in which the W-In bond was cleaved. On the other hand, 4 reacted with three equiv. of AgNO3 to form Et4N[Tp*W(CO)3{In(ONO2)}] 5, in which three substituents on the In were exchanged while retaining the W-In dative bond. Complexes 1-5 were fully characterized using NMR measurements and elemental analyses, and the structures of 1-5 and Et4N[Tp*W(CO)3] were determined via X-ray crystallography. These are the first examples of mononuclear molybdenum- and tungsten-indane complexes with Mo-In and W-In dative bonds.

σ-Arsolido complexes

Mononuclear-σ-arsolyl complexes of molybdenum, tungsten and iron have been prepared via facile transmetallation from tin, allowing their structural characterisation for the first time.

Exploring efficient and air-stable d2 Re(v) alkylidyne catalysts: toward room temperature alkyne metathesis.

Transition metal-catalyzed alkyne metathesis has become a useful tool in synthetic chemistry. Well-defined alkyne metathesis catalysts comprise alkylidyne complexes of tungsten, molybdenum and rhenium. Non-d0 Re(v) alkylidyne catalysts exhibit advantages such as remarkable tolerance to air and moisture as well as excellent functional group compatibility. However, the known Re(v) alkylidynes with a pyridine leaving ligand require harsh conditions for activation, resulting in lower catalytic efficiency compared to d0 Mo(vi) and W(vi) alkylidynes. Herein, we report the first non-d0 alkylidyne complex capable of mediating alkyne metathesis at room temperature, namely, the Re(v) aqua alkylidyne complex Re([triple bond, length as m-dash]CCH2Ph)( Ph PO)2(H2O) (14). The aqua complex readily dissociates a water ligand in solution, confirmed by ligand substitution reactions with other σ-donor ligands. The aqua complex can be readily prepared on a large scale, and is stable to air and moisture in the solid state and compatible with a variety of functional groups. The versatile ability of the catalyst has been demonstrated through examples of alkyne cross-metathesis (ACM), ring-closing alkyne metathesis (RCAM), and acyclic diyne metathesis macrocyclization (ADIMAC) reactions. All in all, this work presents a solution for an efficient and air-stable alkyne metathesis catalytic system based on d2 Re(v)-alkylidynes.

Reactions of (mesityl)n(methyl)2-nsilylene complexes with pyridine-N-oxide (n = 1 and 0): formation of silanone complexes and a disiloxanyloxy complex.

Silanones (OSiR2), a heavier congener of ketones (R2CO), are highly reactive species that are readily converted to oligomeric siloxane (O-SiR2)n. Coordination of silanones to the transition-metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Recently, our group reported the synthesis, structures, and reactivity of dimesityl-substituted silanone complexes Cp*(OC)2M{OSiMes2(L)}(SiMe3) (M = W, Mo, L: Lewis base, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2). Herein, to investigate the effect of substituents on the silicon atom during the formation of a silanone complex, we demonstrated the use of Mes and smaller Me groups. As a result, the formation of Mes(Me)-substituted silanone molybdenum complex Cp*(OC)2Mo{OSiMes(Me)(py)}(SiMe3) (5b, py: pyridine) was suggested, the silanone tungsten complex Cp*(OC)2W{OSiMes(Me)(DMAP)}(SiMe3) (4a, DMAP: 4-(dimethylamino)pyridine) was obtained, and a dimethyl-substituted disiloxanyloxy(dioxo) complex Cp*(O)2W(OSiMe2OSiMe3) (9) was formed. The reaction of 4a with PMe3 proceeded via the elimination of DMAP and migration of the SiMe3 group to the oxygen atom of the silanone ligand to afford Cp*(OC)2W(SiMes(Me)OSiMe3)(PMe3) (11a). The Mo complex Cp*(OC)2Mo(SiMes(Me)OSiMe3)(PMe3) (11b) was produced by the reaction of Cp*(OC)2Mo{SiMes(Me)}(SiMe3) (7b) with pyridine-N-oxide in the presence of PMe3.