Oxidation of molybdenum and tungsten metals by molybdenum and tungsten hexafluorides in acetonitrile. Preparation of the 1:1 pentafluoride acetonitrile complexes

Molybdenum and tungsten metal powders are oxidized by their respective hexafluorides in the presence of acetonitrile at room temperature to give the 1:1 pentafluoride, acetonitrile complexes, MF₅.NCMe, M = Mo or W. Their i.r. spectra are consistent with C_4v symmetry for the MF₅N moiety. The tungsten pentafluoride complex appears to be stable with respect to disproportionation at room temperature.     

Arene derivatives of molybdenum and tungsten Communication 1. Anisole tricarbonyl complexes of molybdenum and tungsten

Conclusions The reaction of anisole with the molybdenum and tungsten hexacarbonyls gave the previously unknown antsole complexes (C₆H₅OCH₃)M(CO)₃.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2090–2091, September, 1973.The authors express their gratitude to P. V. Petrovskii for assistance in taking and discussing the NMR spectra.     

Synthesis and reactivity of molybdenum and tungsten bis(dinitrogen) complexes supported by diphosphine chelates containing pendant amines

Molybdenum and tungsten bis(dinitrogen) complexes of the formula M(N(2))(2)(PNP)(2) (M = Mo and W) and W(N(2))(2)(dppe)(PNP), supported by diphosphine ligands containing a pendant amine of the formula (CH(2)PR(2))(2)NR' = P(R)N(R')P(R) (R = Et, Ph; R' = Me, Bn), have been prepared by Mg reduction of metal halides under an N(2) atmosphere. The complexes have been characterized by NMR and IR spectroscopy, X-ray crystallography, and cyclic voltammetry. Reactivity of the target Mo and W bis(dinitrogen) compounds with CO results in the formation of dicarbonyl complexes.     

Preparation and properties of molybdenum and tungsten dinitrogen complexes: XX. Reactions of a tungsten-dinitrogen complex with water or alcohols in the presence of ketones. Conversion of ligating dinitrogen into ketazines and isolation of a novel chelate diazo complex as an intermediate

Ammonia is formed by treatment of cis-[W(N₂)₂ (PMe₂ Ph)₄] with water (in THF) or alcohols at 50°C. Addition of KOH to the systems, especially those containing n-alcohols such as 1-butanol and 1-pentanol, remarkably increases the yields of ammonia. On the other hand, ketazines are produced in high yields when ketones such as acetone and butanone are added to the systems. The reaction of the dinitrogen complex with 2,4-pentanedione in methanol or ethanol gives a novel chelate diazo complex [$\text{W(NNC(Me)CHCO}$Me)(acac)(PMe₂Ph)₃]. Mechanisms of these reactions are discussed.     

Some organoperoxo complexes of molybdenum and tungsten

Several new peroxo complexes of molybdenum and tungsten containing different organic ligands have been prepared. The complexes have the compositions [Mo(O)(O₂)L₂], [Mo(O)₂(O₂)L(H₃O)]⁺, [Mo(O)(O₂)L′] and [W(O)(O₂)L₂] [L = oxoquinolino, aniline-2- carboxylate, 2-aminophenoxide, picolinato or 2-carboxylatoquinolino ligand; L′ = N-(2- oxophenyl)salicylidenimino ligand], respectively. The complexes were found to oxidize allyl alcohol, and also PPh₃ and AsPh₃, to their oxides. The IR spectra of the complexes indicate that the frequency of the v₁-mode of the M(O₂) grouping, which is essentially an OO stretch, decreases with the increase in atomic number of metals in a particular group.     

Electronically-coupled MM quadruply-bonded complexes of molybdenum and tungsten

The reaction of M2(O2CBu(t))4 (M = Mo, W) with a dicarboxylic acid in toluene yields compounds of general formula [M2]-O2C-X-CO2-[M2] ([M2] = M2(O2CBu(t))3; X = conjugated spacer). The M2 units are electronically coupled via interactions between the M2 delta and dicarboxylate pi* orbitals, and the magnitude of this coupling is revealed by electronic structure calculations and spectroscopic data. These compounds show intense metal to ligand charge transfer (MLCT) absorptions in the visible region of the electronic spectrum that are temperature and solvent dependent. Evidence of electronic coupling is seen in their cyclic voltammograms, which show two successive one-electron oxidations. The extent of electronic coupling in the mixed valence radical cations [M2]-O2C-X-CO2-[M2]+, generated by oxidation with one equivalent of AgPF6 or FeCp2PF6, is evaluated by EPR and UV-vis-NIR spectroscopic data, and delocalized behavior is observed in compounds with W2 units separated by up to 13.6 angstroms. The simplicity of the frontier M2 orbital interactions with the bridge pi orbitals provides a convenient system with which to study electron transfer in mixed valence systems, as compared to the extensively studied, but more complicated, dinuclear t(2g)6/t(2g)5 mixed valence compounds. Oligomeric and polymeric compounds incorporating M2 units have also been synthesized, having general formula [M2(O2CR)2(O2C-Thio-CO2)]n (Thio = n-hexyl substituted ter- and quinque-thiophenes). They can be deposited as thin films by spin coating, and show photoluminescence and electroluminescence. These metallo-polythiophenes show potential for application in electronic materials. (     

Nucleophilic attack on bent molybdenum and tungsten metallocene complexes

Reactions of some [M(η⁵-C₅H₅)₂L₂]ⁿ⁺ complexes (M  Mo, W; L = ligand; n = 0, 1, 2) with NaBH₄ and LiAlH₄ are reported. New neutral and cationic hydride derivatives of the type [M(η⁵-C₅H₅)₂HL]^m+ (m = 0, 1) are described, in particular the six halohydride complexes [M(η⁵-C₅H₅)₂HX]. The deuteration studies were carried out, but the results do not lead to definite conclusions about the mechanism.     

Reactivity of carbyne and carbene complexes of molybdenum and tungsten

Summary The interconversion of carbyne, carbyne and hydride complexes derived from protonations oftrans-[M(CNMe)₂(dppe)₂](M = Mo or W) has been studied. The initial site of protonation is shown to be the isonitrile nitrogen and all protonations proceed through the common carbyne intermediatetrans-[M(CNHMe)(CNMe)(dppe)2]⁺. The CNHMe group in traps-[M(CNHMe)₂(dppe)₂]²⁺ is shown to be susceptible to electrophilic attack at N and nucleophilic attack at ligating C, the new complexestrans-[W(CNH2Me)(CNHMe)(dppe)₂](BF₄)₃ andtrans-[Mo(CHNHMe)(CNHMe)(dppe)2]BF4 being formed, respectively.     

Synthesis, structure, and electrochemical studies of molybdenum and tungsten dinitrogen, diazenido, and hydrazido complexes that contain aryl-substituted triamidoamine ligands

One-electron reduction of [ArN(3)N]MoCl complexes (Ar = C(6)H(5), 4-FC(6)H(4), 4-t-BuC(6)H(4), 3,5-Me(2)C(6)H(3)) yields complexes of the type [ArN(3)N]Mo-N=N-Mo[ArN(3)N], while two-electron reduction yields ([ArN(3)N]Mo-N=N)(-) derivatives (Ar = C(6)H(5), 4-FC(6)H(4), 4-t-BuC(6)H(4), 3,5-Me(2)C(6)H(3), 3,5-Ph(2)C(6)H(3), and 3,5-(4-t-BuC(6)H(4))(2)C(6)H(3)). Compounds that were crystallographically characterized include ([t-BuC(6)H(4)N(3)N]Mo)(2)(N(2)), Na(THF)(6)([PhN(3)N]Mo-N=N)(2)Na(THF)(3), [t-BuC(6)H(4)N(3)N]Mo-N=N-Na(15-crown-5), and ([Ph(2)C(6)H(3)N(3)N]MoNN)(2)Mg(DME)(2). Compounds of the type [ArN(3)N]Mo-N=N-Mo[ArN(3)N] do not appear to form when Ar = 3,5-Ph(2)C(6)H(3) or 3,5-(4-t-BuC(6)H(4))(2)C(6)H(3), presumably for steric reasons. Treatment of diazenido complexes (e.g., [ArN(3)N]Mo-N=N-Na(THF)(x)) with electrophiles such as Me(3)SiCl or MeOTf yielded [ArN(3)N]Mo-N=NR complexes (R = SiMe(3) or Me). These species react further to yield ([ArN(3)N]Mo-N=NMe(2))(+) species in the presence of methylating agents. Addition of anionic methyl reagents to ([ArN(3)N]Mo-N=NMe(2))(+) species yielded [ArN(3)N]Mo(N=NMe(2))(Me) complexes. Reduction of [4-t-BuC(6)H(4)N(3)N]WCl under dinitrogen leads to a rare ([t-BuC(6)H(4)N(3)N]W)(2)(N(2)) species that can be oxidized by two electrons to give a stable dication (as its BPh(4)(-) salt). Reduction of hydrazido species leads to formation of Mo=N in low yields, and only dimethylamine could be identified among the many products. Electrochemical studies revealed expected trends in oxidation and reduction potentials, but also provided evidence for stable neutral dinitrogen complexes of the type [ArN(3)N]Mo(N(2)) when Ar is a relatively bulky terphenyl substituent.     

X-ray photoelectron spectra of polyhydrido complexes of tungsten and molybdenum

X-Ray photoelectron spectroscopy has been applied to study MH₄L₄(M = or Mo, L = PHPh₂, PMePh₂, PEtPh₂, PBuPh₂, PEt₂Ph, P(OPr-i)₃ or $\text{1}\text{2}$ dppe). It has been shown that tungsten in these compounds has a negative charge whereas the charge of molybdenum is almost zero.     

有机钼,钨化合物研究I.FISCHER型卡宾络合物的合成和性质

我们合成了六个新的钼、钨季铵盐[(CO)5MC(O)R]N(CH3)4和钨的卡宾络合物,并研究了它们的某些性质。经元素分析、IR和1H NMR的鉴定,确证了它们的结构。由这些络合物组成的催化体系,其中某些能使单取代乙炔聚合,有的还能使双取代己炔聚合。     

Temperature dependent electrochemical investigations of molybdenum and tungsten oxobisdithiolene complexes

To achieve a better understanding why thermophilic and hyperthermophilic organisms use tungsten instead of molybdenum within the active sites of their molybdopterin dependent oxidases, electrochemical investigations of model complexes for the active sites of enzymes belonging to the DMSO reductase (molybdenum) and the aldehyde oxidoreductase (tungsten) family have been undertaken. Cyclic voltammetry and differential pulse voltammetry of four pairs of molybdenum and tungsten oxobisdithiolene compounds show huge differences in the response of their redox potentials to rising or decreasing temperatures, depending on the substituents at the dithiolene group. The mnt2- compounds (1a, 1b) respond with decreasing redox potentials E(1/2) to rising temperatures whereas all other compounds show positive gradients deltaE/deltaT. In every case the values for the gradients for the tungsten compounds are greater than those for the molybdenum compounds. Six of the investigated compounds are known in the literature and two compounds were newly synthesized. These two new compounds include the pyrane subunit of the native molybdopterin ligand and should therefore be even better models for the active site of the molybdopterin containing enzymes. The molybdenum/tungsten pair with these new ligands shows a remarkably small difference for the redox potentials of the transition M(IV) <--> M(V) of only 30 mV at 25 degrees C and the reversion of the usual order with higher potentials for the molybdenum than the tungsten compound at a temperature of 70 degrees C; a temperature that is in the range where usually tungsten containing enzymes instead of molybdenum containing ones are found.     

Phosphaalkenyl germylenes and their gold, tungsten and molybdenum complexes

The new bis(phosphaalkenyl) germanium(II) compound (NHC)Ge(CCl=PMes*)(2) reacts with L(2)M(CO)(4) (M = Mo, W) to give bidentate complexes with an unexpected coordinating behaviour involving the Ge(II) centre and one phosphorus atom, and with AuI or Me(2)SAuCl to afford the monodentate complexes coordinated at the germanium(II) atom.     

Syntheses and structures of molybdenum and tungsten pentabenzylcyclopentadienyl complexes: new chlorination reactions

[M(CpBz)(CO)₃CH₃] (M=Mo, 2a, W, 2b; CpBz=C₅(CH₂Ph)₅) have been prepared and reacted with PCl₅ and PhI · Cl₂. Depending on the metal and on the chlorinating reagent used [Mo(CpBz)(η²-COCH₃)Cl₃], 3, [W(CpBz)Cl₄], 4, [Mo(CpBz)(CO)₃Cl], 5 and [Mo(CpBz)Cl₄], 6 have been obtained. The molecular structures of all compounds are reported and two conformations have been characterised for the benzyl substituents. In complexes 2a, 2b and 5 one phenyl ring bends towards the metals while in 3 and 4 the five phenyls point opposite to the metals.     

Oxidative decarbonylation of m-terphenyl isocyanide complexes of molybdenum and tungsten: precursors to low-coordinate isocyanide complexes

Synthetic studies are presented addressing the oxidative decarbonylation of molybdenum and tungsten complexes supported by the encumbering m-terphenyl isocyanide ligand CNAr(Dipp2) (Ar(Dipp2) = 2,6-(2,6-(i-Pr)(2)C(6)H(3))(2)C(6)H(3)). These studies represent an effort to access halide or pseudohalide M/CNAr(Dipp2) species (M = Mo, W) for use as precursors to low-coordinate, low-valent group 6 isocyanide complexes. The synthesis and structural chemistry of the tetra- and tricarbonyl tungsten complexes trans-W(CO)(4)(CNAr(Dipp2))(2) and trans-W(NCMe)(CO)(3)(CNAr(Dipp2))(2) are reported. The acetonitrile adducts trans-M(NCMe)(CO)(3)(CNAr(Dipp2))(2) (M = Mo, W) react with I(2) to form divalent, diiodide complexes in which the extent of decarbonylation differs between Mo and W. In the molybdenum example, the diiodide, dicarbonyl complex MoI(2)(CO)(2)(CNAr(Dipp2))(2) is generated, which has an S = 1 ground state in solution. Paramagnetic group 6 MX(2)L(4) complexes are rare, and the structure of MoI(2)(CO)(2)(CNAr(Dipp2))(2) is discussed in relation to other diamagnetic and C(2v)-distorted MX(2)L(4) complexes. Diiodide MoI(2)(CO)(2)(CNAr(Dipp2))(2) reacts further with I(2) to effect complete decarbonylation, producing the paramagnetic tetraiodide complex trans-MoI(4)(CNAr(Dipp2))(2). The reactivity of the trans-M(NCMe)(CO)(3)(CNAr(Dipp2))(2) (M = Mo, W) complexes toward benzoyl peroxide is also surveyed, and it is shown that dicarboxylate complexes can be obtained by oxidative or salt-elimination routes. The reduction behavior of the tetraiodide complex trans-MoI(4)(CNAr(Dipp2))(2) toward Mg metal and sodium amalgam is studied. In benzene solution under N(2), trans-MoI(4)(CNAr(Dipp2))(2) is reduced by Na/Hg to the η(6)-arene-dinitrogen complex, (η(6)-C(6)H(6))Mo(N(2))(CNAr(Dipp2))(2). The diiodide-η(6)-benzene complex (η(6)-C(6)H(6))MoI(2)(CNAr(Dipp2))(2) is an isolable intermediate in this reduction reaction, and its formation and structure are discussed in context of putative low-coordinate, low-valent molybdenum isocyanide complexes.     

Studies relevant to catalytic reduction of dinitrogen to ammonia by molybdenum triamidoamine complexes

In this paper we explore several issues surrounding the catalytic reduction of dinitrogen by molybdenum compounds that contain the [(HIPTNCH2CH2)3N]3- ligand (where HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H3). Four additional plausible intermediates in the catalytic dinitrogen reduction have now been crystallographically characterized; they are MoN= NH (Mo = [(HIPTNCH2CH2)3N]Mo), [Mo=NNH2][BAr'4] (Ar' = 3,5-(CF3)2C6H3), [Mo=NH][BAr'4], and Mo(NH3). We also have crystallographically characterized a 2,6-lutidine complex, Mo(2,6-Lut)+, which is formed upon treatment of MoH with [2,6-LutH][B(C6F5)4]. We focus on the synthesis of compounds that have not yet been isolated, which include Mo=NNH2, Mo=NH, and Mo(NH2). Mo=NNH2, formed by reduction of [Mo=NNH2]+, has not been observed. It decomposes to give mixtures that contain two or more of the following: MoN=NH, Mo triple bond N, Mo(NH3)+, Mo(NH3), and ammonia. Mo=NH, which can be prepared by reduction of [Mo=NH]+, is stable for long periods in the presence of a small amount of CrCp*2, but in the absence of CrCp*2, and in the presence of Mo=NH+ as a catalyst, Mo=NH is slowly converted into a mixture of Mo triple bond N and Mo(NH2). Mo(NH2) can be produced independently by deprotonation of Mo(NH3)+ with LiN(SiMe3)2 in THF, but it decomposes to Mo triple bond N upon attempted isolation. Although catalytic reduction of dinitrogen could involve up to 14 intermediates in a "linear" sequence that involves addition of "external" protons and/or electrons, it seems likely now that several of these intermediates, along with ammonia and/or dihydrogen, can be produced in several reactions between intermediates that themselves behave as proton and/or electron sources.