The use of silylethers and silylthioethers in syntheses of oxohalide and thiohalide compounds of molybdenum and tungsten

Tungsten(VI) selenide tetrachloride, WSeCl4 - synthesis, properties, coordination complexes and application of [WSeCl4(SenBu2)] for CVD growth of WSe2 thin films

WSeCl₄ was obtained in good yield by heating WCl₆ and Sb₂Se₃in vacuo. Green crystals grown by sublimation were shown by single crystal X-ray structure analysis to contain square pyramidal monomers with apical WSe, and powder X-ray diffraction (PXRD) analysis confirmed this to be the only form present in the bulk sample. Density functional theory (DFT) calculations using the B3LYP-D3 functional replicated the structure, identified the key bonding orbitals, and were used to aid assignment of the IR spectrum of WSeCl₄. Reaction of WSeCl₄ with ligands L gave [WSeCl₄(L)] (L = MeCN, DMF, thf, py, OPPh₃, 2,2'-bipy, SeMe₂, SeⁿBu₂), whilst the dimers [(WSeCl₄)₂(μ-L-L)] were formed with L-L = Ph₂P(O)CH₂P(O)Ph₂, 1,4-dioxane and 4,4'-bipyridyl. The complexes were characterised by microanalysis, IR and ¹H NMR spectroscopy, and single crystal X-ray structures determined for [WSeCl₄(L)] (L = OPPh₃, MeCN, DMF) and [(WSeCl₄)₂(μ-L-L)] (L-L = 1,4-dioxane, 4,4'-bipyridyl). All except the 2,2'-bipy complex, which is probably seven-coordinate, contain six-coordinate tungsten with the neutral donor trans to WSe. Alkylphosphines, including PMe₃ and PEt₃, decompose WSeCl₄ upon contact, forming phosphine selenides (SePR₃). In contrast, the selenoether complexes [WSeCl₄(SeMe₂)] and [WSeCl₄(SeⁿBu₂)] were isolated and characterised. The crystal structure of the minor W(VI) by-product, [(WSeCl₄)₂(μ-SeMe₂)], was determined and using SMe₂, a few crystals of the W(V) species, [{WCl₃(SMe₂)}₂(μ-Se)(μ-Se₂)], were obtained and structurally characterised. The isolated W(VI) complexes are compared with those of WOCl₄ and WSCl₄ and the combination of experimental and computational data are consistent with WSeCl₄ being a weaker Lewis acid and its complexes significantly less stable than those of the lighter analogues, especially in solution. Low pressure chemical vapour deposition (LPCVD) using [WSeCl₄(SeⁿBu₂)] in the range 660-700 °C (0.1 mmHg) produced highly reflective thin films, which were identified to be WSe₂ by grazing incidence X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XRD analysis of the thinner films revealed them to be highly oriented in the <00l> direction.

Synthesis, properties and structural features of molybdenum(v) oxide trichloride complexes with neutral chalcogenoether ligands

Complexes of oxotrichloromolybdenum(v) with neutral group 16 donor ligands, [MoOCl₃(L-L)] (L-L = RS(CH₂)₂SR, R = ⁱPr, Ph; MeS(CH₂)₃SMe; MeSe(CH₂)₂SeMe; MeSe(CH₂)₃SeMe), [{MoOCl₂(EMe₂)}₂(μ-Cl)₂] (E = S, Se, Te), [(MoOCl₃)₂{o-C₆H₄(EMe)₂}]_n (E = Se or Te) and [(MoOCl₃)₂{MeTe(CH₂)₃TeMe}]_n, have been obtained by reaction of the ligands with [MoOCl₃(thf)₂] or MoOCl₃ in either CH₂Cl₂ or toluene, and characterised by microanalysis, IR and UV-visible spectroscopy and magnetic measurements. The telluroethers are the first examples containing Mo in a positive oxidation state. X-ray crystal structures are reported for the six-coordinate fac-[MoOCl₃{MeS(CH₂)₃SMe}], mer-[MoOCl₃{ⁱPrS(CH₂)₂SⁱPr}] and mer-[MoOCl₃{MeSe(CH₂)₂SeMe}], as well as the six-coordinate chloride-bridged dimers, [{MoOCl₂(SMe₂)}₂(μ-Cl)₂] and [{MoOCl₂(SeMe₂)}₂(μ-Cl)₂]. The structure of the mixed-valence decomposition product, [Mo^IVCl{o-C₆H₄(TeMe)₂}₂(μ-O)Mo^VOCl₄], was also determined. In toluene solution MoOCl₄ is reduced by MeS(CH₂)₃SMe to produce the Mo(v) complex, [MoOCl₃{ MeS(CH₂)₃SMe}]. Crystal structures of the previously unknown diphosphine analogue, [MoOCl₃{Me₂P(CH₂)₂PMe₂}], and the mixed-valence derivative [Mo^IVCl{Me₂P(CH₂)₂PMe₂}₂(μ-O)Mo^VOCl₄] are also reported for comparison and help to clarify earlier contradictory literature reports. In contrast to the dimeric EMe₂ complexes, [{MoOCl₂(EMe₂)}₂(μ-Cl)₂], PMe₃ forms the monomeric complex, fac-[MoOCl₃(PMe₃)₂].

Isolation of a Homoleptic Non-oxo Mo(V) Alkoxide Complex: Synthesis, Structure, and Electronic Properties of Penta-tert-Butoxymolybdenum

Treatment of [MoCl₄(THF)₂] with MOtBu (M = Na, Li) does not result in simple metathetic ligand exchange but entails disproportionation with formation of the well-known dinuclear complex [(tBuO)₃Mo≡Mo(OtBu)₃] and a new paramagnetic compound, [Mo(OtBu)₅]. This particular five-coordinate species is the first monomeric, homoleptic, all-oxygen-ligated but non-oxo 4d¹ Mo(V) complex known to date; as such, it proves that the dominance of the Mo═O group over (high-valent) molybdenum chemistry can be challenged. [Mo(OtBu)₅] was characterized in detail by a combined experimental/computational approach using X-ray diffraction; UV/vis, MCD, IR, EPR, and NMR spectroscopy; and quantum chemistry. The recorded data confirm a Jahn-Teller distortion of the structure, as befitting a d¹ species, and show that the complex undergoes Berry pseudorotation. The alkoxide ligands render the disproportionation reaction, leading the formation of [Mo(OtBu)₅] to be particularly facile, even though the parent complex [MoCl₄(THF)₂] itself was also found to be intrinsically unstable; remarkably, this substrate converts into a crystalline material, in which the newly formed Mo(III) and Mo(V) products cohabitate the same unit cell.

Thioether complexes of WSCl4, WOCl4 and WSCl3 and evaluation of thiochloride complexes as CVD precursors for WS2 thin films

Thioether complexes of WECl₄ and WECl₃ (E = S, O) are prepared and characterised; the dinuclear [(WSCl₄)₂{ⁱPrS(CH₂)₂SⁱPr}] is shown to be an effective single source precursor for low pressure CVD of WS₂ thin films.

Straightforward formation of carbocations from tertiary carboxylic acids via CO release at room temperature

We report an unprecedented mode of reactivity of carboxylic acids. A series of tertiary carboxylic acids, containing at least one phenyl α-substituent, undergo loss of carbon monoxide at room temperature (295 K), by a one pot reaction with 0.5-1 molar equivalents of WCl₆ in dichloromethane. A plausible mechanism for the Ph₃CCO₂H/WCl₆ reaction, leading to [CPh₃][WOCl₅] and Ph₃CCl, is proposed on the basis of DFT calculations. The analogous reactions involving CEt(Ph)₂CO₂H, CMe(Ph)₂CO₂H and CMe₂(Ph)CO₂H selectively afforded stable hydrocarbons (alkene or indene, depending on the case), apparently resulting from the rearrangement of elusive tertiary carbocations.

Coordination Compounds of Niobium(IV) Oxide Dihalides Including the Synthesis and the Crystallographic Characterization of NHC Complexes

The 1:1 molar reactions of NbOX3 with SnBu3H, in toluene at 0 °C in the presence of oxygen/nitrogen donors, resulted in the formation of NbOX2L2 (X = Cl, L2 = dme, 2a; X = Br, L2 = dme, 2b; X = Cl, L = thf, 2c; X = Cl, L = NCMe, 2d; dme = 1,2-dimethoxyethane, thf = tetrahydrofuran), in good yields. The 1:2 reactions of freshly prepared 2d and 2b with the bulky NHC ligands 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, Imes, and 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene, Ixyl, respectively, afforded the complexes NbOCl2(Imes)2, 3, and NbOBr2(Ixyl)2, 4, in 50-60% yields. The reactions of 2b with NaOR, in tetrahydrofuran, gave NbOCl(OR) (R = Ph, 5; R = Me, 6) in about 60% yields. All the products were characterized by analytical and spectroscopic techniques; moreover DFT calculations were carried out in order to shed light on synthetic and structural features. Compounds 3 and 4, whose molecular structures have been ascertained by X-ray diffraction, represent very rare examples of crystallographically characterized niobium-NHC systems.

Synthesis of a highly reactive form of WO2Cl2, its conversion into nanocrystalline mono-hydrated WO3 and coordination compounds with tetramethylurea

A new form of WO₂Cl₂ was prepared from WCl₆. Conversion of WO₂Cl₂ into nanocrystalline WO₃·H₂O occurred upon air exposure at room temperature. The first coordination complexes of WO₂Cl₂ with an alkylurea are reported.

The chemistry of high valent tungsten chlorides with N-substituted ureas, including urea self-protonation reactions triggered by WCl6

N-Substituted ureas are oxidized by WCl₆in dichloromethane, resulting in protonated urea saltsviaactivation of C–H and/or N–H bonds.

The chlorinating behaviour of WCl6 towards α-aminoacids

WCl₆ behaves as a selective chlorinating agent towards the carboxylic function of primary and secondary α-aminoacids. The initial formation of α-ammonium acylchloride salts may be followed by HCl elimination and, in the case of l-proline derived species, a clean cyclization reaction.

Tungsten(VI) N-Heterocyclic Carbene Complexes: Synthetic, Structural, and Computational Study

The reaction of WOCl₄ with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (Idipp) leads to an orange solid whose spectroscopic data are consistent with the 1:1 adduct [WOCl₄(Idipp)]. Computational studies at the DFT level further support this formulation. Exposure of this compound to the atmosphere results in rapid hydrolysis to various imidazolium salts. If air diffuses very slowly into solutions of [WOCl₄(Idipp)], it also undergoes slow hydrolysis to form [WO₂Cl₂(Idipp)]. This has been crystallographically characterized and is the first five-coordinate, 1:1 adduct of WO₂Cl₂. This complex has also been subject to DFT calculations, and its metal-ligand bonding has been explored. The carbene-metal interaction is primarily σ-donor in nature. The mechanism of the hydrolysis has also been probed by computational methods, revealing a plausible, low-energy reaction pathway.

Sulfinylamine metathesis at oxo metal species--convenient entry into imido metal chemistry

The exchange of terminal metal oxo functionalities by N-organo and N-sulfonylimido functionalities via metathesis with bent, thus very reactive sulfinyl amines R-NSO and sulfinyl sulfonylamides R-SO(2)-NSO is described. It is demonstrated that in many cases sulfinyl amine metathesis offers a more convenient entry into imido complex synthesis than the much better investigated isocyanate metathesis at oxo complexes or condensation reactions with amines and silylated amines. Improved syntheses for some known key compounds and several new complexes of the type [V(NR)Cl(3)] and [M(NR)(2)Cl(2)] (M = Cr, Mo, W) are described. Emphasis is put on the synthesis of formerly unknown base free Lewis acids with electron-withdrawing N-substituents such as haloaryl and sulfonylaryl. Surprisingly, even [CrO(2)Cl(2)] is selectively transformed by sulfinylamines into aryl imido derivatives without any reduction by sulfur dioxide. The molecular structures of novel haloaryl imido complexes [Cr(NAr)(2)Cl(2)] Ar = C(6)F(5) and 2,4,6-Cl(3)C(6)H(2) as determined by X-ray crystallography are reported.

Molybdenum oxo and imido complexes of beta-diketiminate ligands: synthesis and structural aspects

Treatment of [MoO2(eta2-Pz)2] (Pz = 3,5-di-tert-butylpyrazolate) with the diketiminate ligand NacNacH (NacNac = CH[C(Me)NAr]2-, Ar = 2,6-Me2C6H3) at 55 degrees C leads under reduction of the metal to the formation of the dimeric molybdenum(V) compound [{MoO2(NacNac)}2] (1). The compound was characterized by spectroscopic means and by X-ray crystal structure analysis. The dimer consists of a [Mo2O4]2+ core with a short Mo-Mo bond (2.5591(5) A) and one coordinated diketiminate ligand on each metal atom. The reaction of [MoO2(eta2-Pz)2] with NacNacH in benzene at room temperature leads to a mixture of 1 and the monomeric molybdenum(VI) compound [MoO2(NacNac)(eta2-Pz)] (2). From such solutions, yellow crystals of 2 suitable for X-ray structural analysis were obtained revealing the coordination of one bidentate NacNac and one eta2-coordinate Pz ligand. This renders the two oxo groups inequivalent. Further high oxidation state molybdenum compounds containing the NacNac ligand were obtained by the reaction of [Mo(NAr)2Cl2(dme)] (Ar = 2,6-Me2C6H3) and [Mo(N-t-Bu)2Cl2(dme)] (dme = dimethoxyethane) with 1 equiv of the potassium salt NacNacK forming [Mo(NAr)2Cl(NacNac)] (3) and [Mo(N-t-Bu)2Cl(NacNac)] (4), respectively, in good yields. The X-ray structure analysis of 3 revealed a penta-coordinate compound where the geometry is best described as trigonal-bipyramidal.

Molecular oxygen activation by a molybdenum(iv) monooxo bis(β-ketiminato) complex

Molybdenum(IV) monooxo compound that contains bis(beta-ketiminato) ligands activates molecular oxygen forming a molybdenum(VI) monooxo peroxo compound, representing a new entry into molybdenum peroxo derivatives.

Dioxomolybdenum(VI) and dioxotungsten(VI) complexes supported by an amido ligand

Stepwise addition of one equivalent of n-butyllithium and trimethylsilyl chloride to 2-tert-butylmercaptoaniline affords the new ligand 1-(Me3SiNH)-2-(t-BuS)C6H4 (LH), that reacts with one equivalent of butyllithium to its lithium salt LLi. Dioxodichloromolybdenum [MoO2Cl2] and dioxodichlorotungsten dimethoxyethane [WO2Cl2(dme)] react in tetrahydrofuran solution at low temperature with two equivalents LLi to monomeric dioxomolybdenum(VI) [MoO2L2] (1) and dioxotungsten(VI) complex [WO2L2] (2) employing two bidentate amido thioether ligands. The crystallographic determination of the molecular structures of 1 and 2 show evidence for M...S contacts. The reaction of [MoO2Cl2] with LLi in tetrahydrofuran solution at room temperature leads next to 1 to two compounds where silyl group migration from nitrogen to oxygen atoms occurs forming [Mo(=NL')2(OSiMe)2] (3) and [Mo(=NL')2(OSiMe3)L] (4, L' = N-2-t-BuSC6H4) as determined by NMR spectroscopy. Compound 4 was isolated in low yield and its molecular structure determined by X-ray crystallography. Higher yields of a bisimido complex can be obtained by the direct reaction of one equivalent of LLi with [Mo(NAr)2Cl2(dme)] (Ar = 2,6-Me2C6H4) forming [Mo(NAr)2LCl] (5).

Shaping the cavity of the macrocyclic ligand in metallocalix[4]arenes: the role of the ligand sphere

The coordination form of calix[4]arene ligands and therefore the cavity of the macrocyclic ligand can be controlled by other ligands in transition metal calix[4]arene complexes, if strong directing coligands such as oxo groups are used. This paper describes the synthesis and characterization of the d(0) transition metal complexes [Cax(OMe)(2)O(2)TiCl(2)] 1 (monoclinic, space group P2(1)/c, lattice constants a = 21.639(4), b = 20.152(3), c = 12.750(3) A, beta = 95.68(3), V = 5532.6(19) A(3)) and [Cax(OMe)(2)O(2)MoO(2)] 2 (monoclinic, space group P2/c, lattice constants a = 12.433(3), b = 16.348(3), c = 24.774(5) A, beta = 99.15(3), V = 4971.6(17) A(3)). Whereas in 1 the calix[4]arene ligand adopts an elliptically distorted cone conformation, the macrocyclic ligand binds in a paco-like conformation to the metal center of 2, in the solid state and in solution. This was predicted by density functional theory calculations on models of different isomers of 1 and 2: cis,cone-1',2', trans,cone-1',2', and cis,paco-1',2'. According to these calculations, the energetic difference of 72.9 kJ/mol between both cis-dioxomolybdenum compounds is quite pronounced in favor of the cis,paco isomer, and 28.0 kJ/mol for the titanium compounds in favor of the cis,cone isomer.

Synthesis, characterization, and electrochemistry of cis-oxothio- and cis-bis(thio)tungsten(VI) complexes of hydrotris(3,5-dimethylpyrazol-1-yl)borate

The complexes TpWO2X react with sulfiding agents such as B2S3 or P4S10 to give the oxothio- and bis(thio)tungsten(VI) complexes TpWOSX (X = Cl(-)) and TpWS2X [X = Cl(-), S2PPh2(-); Tp = hydrotris(3,5-dimethylpyrazol-1-yl)borate]. The reaction of TpWS2Cl with (i) PPh3 in pyridine and (ii) dimethyl sulfoxide affords TpWOSCl in good overall yield. The chloro complexes undergo metathesis with alkali metal salts to yield species of the type TpWOSX and TpWS2X [X = OPh(-), SPh(-), SePh(-), (-)-mentholate]. The diamagnetic complexes exhibit NMR spectra indicative of C(1) (TpWOSX) or C(s) (TpWS2X) symmetry and IR spectra consistent with terminal oxo and thio ligation (nu(W=O), 940-925 cm(-1); nu(W=S) or nu(WS2), 495-475 cm(-1)). Crystals of (R,S)-TpWOS[(-)-mentholate] are monoclinic, space group P2(1), with a = 11.983(2) A, b = 18.100(3) A, c = 13.859(3) A, beta = 91.60(2) degrees, V = 3004.6(8) A(3), and Z = 4. Crystals of TpWS2(OPh)-CH2Cl2 are orthorhombic, space group Pbca, with a = 16.961(4) A, b = 33.098(7) A, c = 9.555(2) A, V = 5364(2) A(3), and Z = 8. The mononuclear, distorted-octahedral tungsten centers are coordinated by a tridentate Tp ligand, an alkoxy or aryloxy ligand, and two terminal chalcogenide ligands. The average W=O and W=S distances are 1.726(7) and 2.125(2) A, respectively, and the O=W=S and S=W=S angles 102.9(3) and 102.9(1) degrees, respectively. The tungsten and sulfur X-ray absorption spectra of TpWOSCl and TpWS2Cl are consistent with the presence of terminal pi-bonded thio ligands in both complexes. The thio complexes generally undergo a reversible one-electron reduction at potentials significantly more positive than their oxo analogues. The chemical, spectroscopic, and electrochemical properties of the complexes are heavily influenced by the presence of W=S pi frontier orbitals.