Tungsten Complexes Research Articles

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.

Complexes of WOCl4 and WSCl4 with neutral N- and O-donor ligands: Synthesis, spectroscopy and structures

The complexes [WOCl4(L)] and [WSCl4(L)] (L = OPPh3, OPMe3, pyridine, 2,2′-bipyridyl), [{WOCl4}2(µ-L-L)] and [{WSCl4}2(µ-L-L)] (L-L = Ph2P(O)(CH2)nP(O)Ph2 (n = 1, 2)) have been prepared from WOCl4 or WSCl4 and the ligands in anhydrous CH2Cl2 solution, and characterised by microanalysis, IR and NMR (1H, 31P{1H}) spectroscopy. X-Ray crystal structures are reported for [WOCl4(OPPh3)], [{WOCl4}2(µ-Ph2P(O)(CH2)P(O)Ph2)] and [{WSCl4}2(µ-Ph2P(O)(CH2)2P(O)Ph2)]. All, except those of 2,2′-bipyridyl, are six-coordinate with the neutral donor trans to WO or WS. Spectroscopic data suggest that the [WOCl4(2,2′-bipy)] and [WSCl4(2,2′-bipy)] are seven-coordinate. Comparison of the structural and spectroscopic data for the two series of complexes indicate little difference in Lewis acidity between the two tungsten(VI) moieties. Decomposition of [WOCl4(OPMe3)] in solution gave the cyclic trimer [W3O3(µ-O)3Cl6(OPMe3)3], the structure of which revealed a six-membered W3O3 ring core with very asymmetric oxido-bridges. The structure of the tungsten(V) complex [WOCl3(2,2′-bipy)] is also reported.

Propene complexes of molybdenum and tungsten stabilized by intramolecular coordination of the 1-(quinol-8-yl)indenyl ligand.

We report herein a new class of mixed propene-indenyl complexes of molybdenum and tungsten stabilized by a strong N→M intramolecular coordination. The complexes [{η5:κN-1-(C9H6N)C9H6}(η2-C3H6)M(CO)2][BF4] (M = Mo, W) were obtained in nearly quantitative yields by the protonation of the η3-allyl ligand in compounds [(η3-C3H5){η5-1-(C9H6N)C9H6}M(CO)2] (M = Mo, W). In contrast to known η2-alkene molybdenum and tungsten compounds, the species presented here are easily isolated in the solid state. The tungsten compound [{η5:κN-1-(C9H6N)C9H6}(η2-C3H6)W(CO)2][BF4] is stable at room temperature, and its structure was unambiguously confirmed by X-ray diffraction. The reactivity of both propene complexes toward several monodentate donors was examined. In the case of dimethyl sulfide, ligand exchange takes place to afford [{η5:κN-1-(C9H6N)C9H6}M(CO)2(SMe2)][BF4] (M = Mo, W) while acetonitrile induces η5→η3 haptotropic rearrangement to give [{η3:κN-1-(C9H6N)C9H6}M(CO)2(NCMe)2][BF4] (M = Mo, W).

Molybdenum and tungsten complexes with carbon dioxide and ethylene ligands.

The first examples of stable metal complexes with coordinated ethylene and carbon dioxide ligands are reported. Reaction of tris(ethylene) complexes mer-M(C2H4)3(PNP) (M = Mo and W; PNP = 2,6-bis(diphenylphosphinomethyl)pyridine) with CO2 yields the corresponding, mixed cis-M(C2H4)2(CO2)(PNP) derivatives. X-ray studies reveal six-coordinate structures exhibiting η2-ethylene and κ2-C,O carbon dioxide coordination. Remarkably, the formation of the molybdenum CO2 adduct occurs also in the solid state at room temperature, under 4 bar of CO2, in a nearly quantitative manner.

Mono-oxo molybdenum(vi) and tungsten(vi) complexes bearing chelating aryloxides: synthesis, structure and ring opening polymerization of cyclic esters.

The mono-oxo aryloxide complexes [M(O)(L1)2] (M = Mo (1·hexane), W(2·2MeCN)) have been prepared from [Mo(O)(Cl)4] or [W(O)(Ot-Bu)4] and two equivalents of the di-phenol 2,2'-ethylidenebis(4,6-di-tert-butylphenol) L1H2, respectively. Use of in situ generated [Mo(O)(Ot-Bu)4] with two equivalents of L1H2 also led to the isolation of 1·2MeCN. In the presence of adventitious oxygen, attempts to generate in situ [Mo(O)(Ot-Bu)4] and reaction with one equivalent of L1H2 afforded the bi-metallic complex [Mo(O)(L1)(μ-O)Li(THF)(MeCN)]2·2MeCN (3·2MeCN). Use of the tetra-phenol α,α,α',α'-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-p-xyleneH4 (L2H4) with [Mo(O)(Oi-Pr)4] led to the isolation of {[Mo(O)]L2}2 (4), whilst the analogous tungsten complex {[W(O)]L2}2 (5) was isolated from the reaction of L2H4 with [W(O)(Ot-Bu)4]. Similar reaction of p-tert-butylcalix[4]areneH4 (L3H4) with [Mo(O)(Oi-Pr)4] afforded ([Mo(O)L3(NCMe)]·3MeCN (6). Modifications of known routes were employed to access complexes [W(Cl)2L3]·3.5MeCN (7·3.5MeCN) and [W(O)L3(NCMe)] (8), whilst use of [WO(Ot-Bu)4] with L3H4 unexpectedly afforded [W(Ot-Bu)2L3]·MeCN (9·MeCN). The molecular crystal structures for 1-9 are reported, and the ability of these complexes to act as catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL) and ω-pentadecalactone (ω-PDL) has been investigated. The molybdenum complexes 1 and 4 were the best performers for ε-Cl and δ-VL, but all complexes exhibited poor control and were also inactive toward the ROP of PDL.

Highly regioselective complexation of tungsten with Eu@C82/Eu@C84: interplay between endohedral and exohedral metallic units induced by electron transfer.

Interactions between the inner and outer units through a fullerene cage are of fundamental importance for the creation of molecular spintronics and machines, but the mechanism of such through-cage interplay is still unclear. In this work, we have designed and synthesized two prototypical compounds which contain only a single europium atom inside the cage and merely a tungsten atom coordinating outside to clarify the interactions between the endohedral and exohedral metallic units. They are obtained by reacting a tungsten complex W(CO)4(Ph2PC2H4PPh2) (1) with the corresponding metallofullerenes in a highly regioselective manner (2a for Eu@C 2(5)-C82 and 2b for Eu@C 2(13)-C84). On the one hand, the endohedral Eu-doping has changed the LUMO distribution on C 2(5)-C82/C 2(13)-C84 dramatically, via electron transfer, which governs the addition pattern of the exohedral tungsten resulting in surprisingly high regioselectivity. On the other hand, the exohedral tungsten coordination with Eu@C 2(5)-C82/Eu@C 2(13)-C84 has restricted the motion of the internal europium ion to some extent by changing the electrostatic potentials, as confirmed by the X-ray results of 2a, 2b and the corresponding pristine metallofullerenes cocrystallized with Ni(OEP) (OEP is the dianion of octaethylporphyrin). We now make it clear that the interplay between the endohedral and exohedral metallic units can be realized in a single system by means of intramolecular charge transfer, which may arouse interest in the design and utilization of novel metallofullerene-based molecular devices.

Synthesis of noble molybdenum and tungsten complexes for hydrocracking catalyst of heavy oil

This paper reports the synthesis of six potential catalyst precursors for hydrocracking reactions for vacuum residue refinement. New group 6 transition metal complexes, (LM(CO)3) (M=Mo or W, L1=3-phenyl-1-propyne,L2=4-phenyl-1-butyne, and L3=5-phenyl-1-pentyne) were prepared by simply stirring M(CO)3(RCN)3 in THF solution. New compounds were applied as a catalyst precursor for hydrocracking of vacuum residue and the catalytic activity was compared to the commercially available material, Mo-octoate. LMo(CO)3 showed similar activities to Mo-octoate. Among all, L3Mo(CO)3 which had the longest alkyl chain showed a comparable result of low yield for coke and gas products.

Thiophene site activation: Synthesis and structures of Fischer carbene complexes with 3,3′- and 2,3′-bithienyl substituents

Deprotonation of the reactive α-thiophene ring positions of 3,3′-bithiophene and 2,3′-bithiophene afforded, after metalation with group 6 transition metal carbonyls and alkylation, a diverse range of mono- and biscarbene complexes. The bithienyl isomers differ in the number of active α-positions but representative examples of Fischer monocarbene complexes of all possible isomers were obtained. For 3,3′-bithienyl, the carbene fragment is in the electronically favoured C2-positions on the “inside” of the bithienyl and is structurally and electronically significantly different from the carbene substituent in the “outside” C5-positions. In the unsymmetrically substituted 2,3′-bithienyl scaffold, in addition to [M(CO)5{C(OEt)-2′-(2,3′-BT)}] and [M(CO)5{C(OEt)-5′-(2,3′-BT)}], a carbene moiety in the C5-position of the T2-thienyl ring, [M(CO)5{C(OEt)-5-(2,3′-BT)}], was also formed. In the same reaction mixture of the mono(ethoxycarbene) complexes, biscarbene complexes were obtained. In contrast, the major biscarbene complexes display the carbene fragments in the sterically favoured outside C5,C5′-positions. The unexpected formation of the 2,2′-bithienyl biscarbene complex, [{M(CO)5C(OEt)}2-5,5′-(2,2′-BT)] as well as the formation of the biscarbene complexes [{M(CO)5C(OEt)}2-2,5-(3,3′-BT)] and [{M(CO)5C(OEt)}2-2′,5′-(2,3′-BT)] with both carbene moieties on the same thiophene ring, were observed. By a modified method of synthesis, a mixed metal biscarbene complex of chromium and tungsten in the C2,C5-positions on the same thiophene ring could be isolated for both 3,3′-bithienyl and thiophene [{Ma/b(CO)5C(OEt)}2-2,5-(T/3,3′-BT)]. The formation of a monocarbene complex of 2,3′-bithienyl, [W(CO)5C(OEt)-5-(2,3′-BT){C(O)(OEt)}2-2′,5′] betrays the presence of an unstable triscarbene intermediate [{W(CO)5C(OEt)}3-5,2′,5′-(2,3′-BT)]. The molecular structures of most of the major isomers were confirmed by single crystal X-ray studies.

Highly effective green oxidation of aldehydes catalysed by recyclable tungsten complex immobilized in organosilanes-modified SBA-15

Abstract A simple and eco-friendly approach for green oxidation of aldehydes has been proposed, which employed highly efficient heterogeneous catalysts tungsten-doped modified silica SBA-15 (W-SBA-15) as catalysts and H2O2 as a green oxidant. W-SBA-15 were synthesized by immobilizing tungsten species on modified SBA-15 and first used in the aldehydes oxidation reaction. W-SBA-15-APTS (0.002 g, APTS, a kind of modifier) displayed an equivalent catalytic activity comparable to that of homogenous catalyst (H2WO4, 0.5 g) and maintained excellent catalytic activity over 20 cycles. The pore diameter, ca. 7.94–9.14 nm, of W-SBA-15 provides a suitable mesoscopic environment for the substrate, and the product can diffuse freely during the oxidation of glutaraldehyde (GA). Effective but different catalytic performance of W-SBA-15 for the oxidation of other aldehydes suggests the universal applicability of W-SBA-15. The possible mechanism of the oxidation state of tungsten species in W-SBA-15-APTS was proposed; tungsten species are not only attached to APTS but also incorporated into the framework of SBA-15.

Synthesis, crystal structure and catalytic activity of an oxo-diperoxo tungsten(VI) complex containing an oxazine ligand for selective oxidation of sulfides

A novel oxo-diperoxo tungsten(VI) complex, [WO(O2)2(Hphox)], was prepared by reaction of WO3 in H2O2 with an oxazine-type ligand, 2-(2′-hydroxylphenyl)oxazine (Hphox). The complex was characterized by FTIR, 1H NMR and elemental analysis. The single-crystal X-ray diffraction studies revealed a seven-coordinate tungsten center with a distorted octahedral geometry. The [WO(O2)2(Hphox)] complex was applied as a catalyst in efficient and selective oxidation of sulfide to sulfoxide using 30% H2O2 or UHP (urea hydrogen peroxide) as oxidants. This catalyst showed excellent catalytic activities and high selectivities in producing a variety of aryl and alkyl sulfoxides under mild conditions. To get an insight into the mechanisms of oxidation of sulfides, the mechanistic studies were monitored by UV–Vis spectroscopy.

Bis(Imido) Tungsten Complexes: Efficient Precatalysts for the Homogeneous Dimerization of Ethylene

The ethylene dimerization performance of a range of bis(imido)tungsten precatalysts, after activation with aluminum cocatalysts, has been assessed. The best-performing system achieved an activity of 409 410 (mol C2H4)(mol W)−1h–1 [79.6 wt % 1-butene] with a 1-butene selectivity of 82.4 wt % [290 770 (mol C2H4)(mol W)−1h–1 activity]. In addition to selected previously reported variants, the symmetrical bis(imido)tungsten(VI) complexes [WCl2(NPh)2(tmeda)] (3) and [WCl2(NR)2(dme)] [R = 2,4,6-trifluorophenyl, 7; 2,4,6-triphenylphenyl, 8; 2,4,6-tris(trifluoromethyl)phenyl, 9], were prepared. A series of unsymmetrical bis(imido)tungsten(VI) complexes [WCl2(NDipp)(NR)(dme)] (R = iPr, 11; tBu, 12; 2,4,6-trimethylphenyl, 13; 2,4,6-trichlorophenyl, 14; 2,4,6-trifluorophenyl, 15; 2,6-dinitrophenyl, 16; 2,4,6-triphenylphenyl, 17) were also synthesized using an improved version of a previous preparative route that eases purification. The molecular structures of complexes 5–13 and 15–17 were determined by X-ray crystal...

Efficient catalytic alkyne metathesis with a fluoroalkoxy-supported ditungsten(III) complex.

The molybdenum and tungsten complexes M2(OR)6 (Mo2F6, M = Mo, R = C(CF3)2Me; W2F3, M = W, R = OC(CF3)Me2) were synthesized as bimetallic congeners of the highly active alkyne metathesis catalysts [MesC≡M{OC(CF3)nMe3−n}] (MoF6, M = Mo, n = 2; WF3, M = W, n = 1; Mes = 2,4,6-trimethylphenyl). The corresponding benzylidyne complex [PhC≡W{OC(CF3)Me2}] (WPhF3) was prepared by cleaving the W≡W bond in W2F3 with 1-phenyl-1-propyne. The catalytic alkyne metathesis activity of these metal complexes was determined in the self-metathesis, ring-closing alkyne metathesis and cross-metathesis of internal and terminal alkynes, revealing an almost equally high metathesis activity for the bimetallic tungsten complex W2F3 and the alkylidyne complex WPhF3. In contrast, Mo2F6 displayed no significant activity in alkyne metathesis.

Time-resolved analysis of dissolution phenomena in photoelectrochemistry – A case study of WO3 photocorrosion

Photocorrosion is one of the main challenges in photoelectrochemical water splitting. Traditional methods for degradation assessment, such as chronoamperometry or electrolyte/electrode post-analysis, provide limited information on the degradation mechanisms and kinetics. To address this issue, a new setup, which is based on a light source, an electrochemical cell, and an on-line inductively coupled plasma mass spectrometer (ICP-MS), has been developed. The first results on the photocorrosion of a commercial WO3 powder on Au are demonstrated in this work. It is shown that, in the absence of light, WO3 is stable in a wide potential range. On the other hand, in the presence of light, it dissolves proportionally to the anodic photocurrent. The latter is explained by the formation of aqueous tungsten complexes with the electrolyte that are thermodynamically more stable than WO3. As can be anticipated from these initial results, the novel method will enable the characterization of a wide range of photoelectrochemical materials, and thus eventually lead to the development of long-term stable devices.

Computational study of acetylene hydration by bio-inspired group six catalyst models

A combination of density functional theory and natural bond orbital analysis was employed to study two bio-inspired catalyst models that mimic the acetylene hydratase active site. The Group 6 metals (Cr, Mo, W) and substituents (CN, H, CH3) on the dithiolate supporting ligands were used to evaluate the effect of metal identity and supporting ligand on free energy barriers and the thermodynamics of the reaction. In catalyst model 1, a metal-bound hydroxo ligand (MIV-OH) acts as a general base, while in catalyst model 2, a propionate plays the role of general base. The calculations showed that in both chromium complexes 1 and 2, acetylene does not bind to the metal in the reactant catalysts, suggesting that Cr is not a soft enough acid in the 4+ formal oxidation state to bind acetylene. The comparison of calculated free energies for molybdenum and tungsten complexes reveals that for models 1 and 2, Mo complexes have lower free energy barriers and are more exergonic as compared to the W variant. Comparing the energy profiles of complexes 1 and 2 indicates that on average, complex 2 has lower barrier energies in comparison to 1, while model 1 has a more exergonic ΔGrxn for acetylene hydration. NBO analysis suggests a metallocyclopropene constitutes the more faithful representation of the Mo and W reactants rather than a π-acetylene. Furthermore, calculations indicate that for both complexes 1 and 2, using electron withdrawing substituents such as CN on dithiolate supporting ligands lowers the activation free energies compared to CH3 and H substituents. Analysis of the impact of polarity through use of different continuum solvents on the reaction coordinate suggest that a less polar active site is more favorable for acetylene hydration.

An experimental and theoretical study of a heptacoordinated tungsten(VI) complex of a noninnocent phenylenediamine bis(phenolate) ligand

[W(N2O2)(HN2O2)] (H4N2O2 = N,N′-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-1,2-phenylenediamine) with a noninnocent ligand was formed by reaction of the alkoxide precursor [W(eg)3] (eg = the 1,2-ethanediolate dianion) with two equivalents of ligand. The phenol groups on one of the ligands are completely deprotonated and the ligand coordinates in a tetradentate fashion, whereas the other ligand is tridentate with one phenol having an intact OH group. The molecular structure, magnetic measurements, EPR spectroscopy, and density functional theory calculations indicate that the complex is a stable radical with the odd electron situated on the tridentate amidophenoxide ligand. The formal oxidation state of the metal center is W(VI), with the paramagnetic properties being due to the unpaired electron on the ligand.

A Silica-Supported Monoalkylated Tungsten Dioxo Complex Catalyst for Olefin Metathesis

A well-defined silica-supported monoalkylated tungsten dioxo complex [(≡Si–O−)W(═O)2(CH2–tBu)] was prepared by treatment of highly dehydroxylated silica (SiO2-700: silica treated at 700 °C under high vacuum) with an ionic precursor complex [NEt4][W(═O)3(CH2–tBu)]. The identity of the resulting neutral monoalkylated tungsten dioxo surface complex was established by means of elemental microanalysis and spectroscopic studies (IR, solid-state NMR, Raman, and X-ray absorption spectroscopies). The supported tungsten complex was found to act as a precatalyst for the self-metathesis of 1-octene in a batch reactor. The mechanistic implications of this reaction are discussed with the support of DFT calculations highlighting the potential occurrence of thus-far unexplored mechanistic pathways.

Synthesis and Characterization of Tungsten Nitrido Amido Guanidinato Complexes as Precursors for Chemical Vapor Deposition of WNxCy Thin Films.

Tungsten nitrido amido guanidinato complexes of the type WN(NR2)[(NR')2C(NR2)]2 (R = Me, Et; R' = i Pr, Cy) were synthesized as precursors for aerosol-assisted chemical vapor deposition (AACVD) of WNxCy thin films. The reaction of tungsten nitrido amido complexes of the type WN(NR2)3 (R = Me, Et) with two equivalents of a carbodiimide R'N=C=NR' (R' = i Pr, Cy) resulted in two insertions of a carbodiimide into W-N(amido) bonds, affording bis(guanidinato) amido nitrido tungsten complexes. These compounds were characterized by 14N NMR, indicating distinctive chemical shifts for each type of N-bound ligand. Crystallographic structure determination of WN(NMe2)[(N i Pr)2C(NMe2)]2 showed the guanidinato ligands to be non-equivalent. The complex WN(NMe2)[(N i Pr)2C(NMe2)]2 was demonstrated to serve as a precursor for AACVD of WNxCy thin films, resulting in featureless, X-ray amorphous thin films for growth temperatures 200 - 400 °C.

Deprotonation of a formato ligand by a cis-coordinated carbyne ligand within a bis(phenolate) tungsten complex.

Deprotonation of a formato ligand by a cis-coordinated propylidyne ligand in a tungsten(vi) complex [(OSSO)W([triple bond, length as m-dash]CEt)(OCHO)] (3) that contains a tetradentate bis(phenolato) ligand (OSSO = {1,4-dithiabutanediyl-2,2'-bis(4,6-di-tert-butyl-phenolato)}) gave the dioxo complex [(OSSO)WO2] (4) along with CO, ethylene and propylene as major products of decomposition.

Metathesis cleavage of an N[double bond, length as m-dash]N bond in benzo[c]cinnolines and azobenzenes by triply-bonded ditungsten complexes.

A metathesis reaction of a W[triple bond, length as m-dash]W bond and an N[double bond, length as m-dash]N bond was observed by reacting a W-W triply-bonded W(iii)2 complex, (tBuO)3W[triple bond, length as m-dash]W(OtBu)3 (1), with benzo[c]cinnoline derivatives to form biphenyl-linked dinuclear (imido)tungsten complexes 2-4. When azobenzene was used as the substrate, a trans to cis isomerization induced by blue-LED light was essential prior to the metathesis cleavage of the N[double bond, length as m-dash]N bond by the W[triple bond, length as m-dash]W bond of (Me2N)2(TfO)W[triple bond, length as m-dash]W(OTf)(NMe2)2 (6), affording the corresponding imido-bridged dinuclear tungsten complexes 7-9.

Correction: Triphenylstibine-substituted Fischer carbene complexes of tungsten(0): synthesis, structure, DFT and electrochemistry

Correction for ‘Triphenylstibine-substituted Fischer carbene complexes of tungsten(0): synthesis, structure, DFT and electrochemistry’ by Marilé Landman et al., New J. Chem., 2018, 42, 7301–7313.