Homoleptic phenyl isocyanide complexes of molybdenum and tungsten: zerovalent six-coordinate versus divalent seven-coordinate

Electrochemical and chemical oxidations of Mo(CNPh)₆ and W(CNPh)₆ have been shown to yield seven-coordinate [M(CNPh)₇]²⁺. These catons, stabilized as their PF₆^? salts, can be obtained in yields of 80%. The redox and substitution chemistry of these new complexes have been explored. A convenient synthesis of W(CNPh)₆ has been devised starting from W₂(dmhp)₄ (dmhp is the anion of 2,4-dimethyl-6-hydroxypyrimidine).     

Preparation and properties of molybdenum and tungsten dinitrogen complexes : `XVI. Electrochemical properties of tungsten and molybdenum diazoalkane complexes

Diazoalkane complexes of type [MF(NNCRR′)(dpe)₂][BF₄] (M = Mo or W; dpe = Ph₂PCH₂CH₂PPh₂), which are easily derived from bis(dinitrogen) complexes [M(N₂)₂(dpe)₂], undergo consecutive one- and two-electron oxidations and reductions under voltammetric conditions at a platinum electrode. The ESR spectra of the species generated by the controlled potential electrolysis show that primary oxidation occurred on the metal atom (M = Mo) and reduction on the two nitrogen atoms in the diazoalkane ligands (M = Mo or W).     

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.     

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.     

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. (     

Tungsten imido complexes as precursors to tungsten carbonitride thin films

Thin films of tungsten carbonitride have been formed on glass by low-pressure chemical vapour deposition (LP)CVD at 550 degrees C from four closely related precursors: [W(mu-N(t)Bu)(N(t)Bu)Cl(2)(H(2)N(t)Bu)](2), [W(N(t)Bu)(2)Cl(2)(TMEDA)] (TMEDA = N,N,N',N'-tetramethylethylenediamine), [W(N(t)Bu)(2)Cl(2)(py)(2)] (py = pyridine) and [W(N(t)Bu)(2)Cl(N{SiMe(3)}(2))]. The grey mirror-like films were grown with a nitrogen or ammonia bleed gas. In all cases the chlorine content of the deposited films was less than 1 at% and the oxygen content of the films was lower for those grown using ammonia. Surprisingly, the use of ammonia did not significantly change the carbon content of the resulting films. Despite the coordination environment around the metal being essentially the same and the materials having a comparable volatility, some differences in film quality were observed. The films were uniform, adhesive, abrasion resistant, conformal and hard, being resistant to scratching with a steel scalpel. X-Ray powder diffraction patterns of all the films showed the formation of beta-WN(x)C(y). As a comparison the aerosol-assisted chemical vapour deposition (AA)CVD of [W(mu-N(t)Bu)(N(t)Bu)Cl(2)(H(2)N(t)Bu)](2) was investigated and amorphous tungsten carbonitride films were deposited.     

Synthesis and characterization of low-coordinate divalent aryl transition-metal halide analogues of grignard reagents: precursors for reduction to metal-metal-bonded complexes

The synthesis and characterization of the series of divalent first-row aryl transition-metal(II) halide compounds [Cr(mu-Cl)Ar']2 (1) and (Li(OEt2)Ar'MI2]2 (M=Mn (2), Fe (3), and Co (4); Ar'=C6H3-2,6-(C6H3-2,6-iPr2)2) are described. 1-4 were prepared by the addition of one equiv of Ar'Li to the respective transition-metal dihalides. They were characterized by UV-vis spectroscopy, magnetic measurements, and by X-ray crystallography. In dimeric 1, each chromium center has quasi-four-coordinate, square-planar geometry, in which the metal is terminally bound to a terphenyl ligand through the ipso carbon of the central ring and to two bridging chloride ligands. There is a further interaction between chromium and an ipso carbon from one of the flanking -C6H3-2,6iPr2 rings. In contrast, for the iodo derivatives 2-4, LiI is not eliminated upon addition of LiAr' to MI2. Instead, the diethyl ether solvated adducts, [Li(OEt2)Ar'MI2]2 (M=Mn (2), Fe (3), or Co (4)) were isolated. These possess a distorted cubane Li2M2I4 core, in which the lithiums are bound to an ether and the transition metals are bound to a terphenyl group. Magnetic measurements between 2 and 300 K reveal the expected weak antiferromagnetic exchange coupling in each of the complexes.     

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.     

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.     

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.     

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.     

Studies of low-coordinate iron dinitrogen complexes

Understanding the interaction of N2 with iron is relevant to the iron catalyst used in the Haber process and to possible roles of the FeMoco active site of nitrogenase. The work reported here uses synthetic compounds to evaluate the extent of NN weakening in low-coordinate iron complexes with an FeNNFe core. The steric effects, oxidation level, presence of alkali metals, and coordination number of the iron atoms are varied, to gain insight into the factors that weaken the NN bond. Diiron complexes with a bridging N2 ligand, L(R)FeNNFeL(R) (L(R) = beta-diketiminate; R = Me, tBu), result from reduction of [L(R)FeCl]n under a dinitrogen atmosphere, and an iron(I) precursor of an N2 complex can be observed. X-ray crystallographic and resonance Raman data for L(R)FeNNFeL(R) show a reduction in the N-N bond order, and calculations (density functional and multireference) indicate that the bond weakening arises from cooperative back-bonding into the N2 pi orbitals. Increasing the coordination number of iron from three to four through binding of pyridines gives compounds with comparable N-N weakening, and both are substantially weakened relative to five-coordinate iron-N2 complexes, even those with a lower oxidation state. Treatment of L(R)FeNNFeL(R) with KC8 gives K2L(R)FeNNFeL(R), and calculations indicate that reduction of the iron and alkali metal coordination cooperatively weaken the N-N bond. The complexes L(R)FeNNFeL(R) react as iron(I) fragments, losing N2 to yield iron(I) phosphine, CO, and benzene complexes. They also reduce ketones and aldehydes to give the products of pinacol coupling. The K2L(R)FeNNFeL(R) compounds can be alkylated at iron, with loss of N2.     

2,5-Dianilinoterephthalate bridged MM quadruply bonded complexes of molybdenum and tungsten

From the reactions between 2,5-dianilinoterephthalic acid and M2(O2CBut)4 in toluene the dicarboxylate bridged complexes [(ButCO2)3M2]2{micro-1,4-(CO2)(2)-2,5-(NHPh)2C6H2}, (M=Mo) and (M=W) have been isolated. The compounds are air sensitive, sparingly soluble in aromatic hydrocarbons but appreciably soluble in tetrahydrofuran. Electronic structure calculations employing density functional theory on the model compounds [(HCO2)3M2]2{micro-1,4-(CO2)(2)-2,5-(NHPh)2C6H2}, indicate that the ground state structure contains a planar bridge and that for molybdenum the HOMO is a bridge based molecular orbital. However, the compounds show reversible oxidation waves (CV and DPV) that for both M=Mo and W are metal based oxidations. Furthermore, the cations + and + are shown to be valence trapped and fully delocalized respectively. The magnitude of the electronic coupling of the two M2 centers, Hab, can be estimated as 383 cm-1 for + and 1500 cm-1 for + based on the corresponding low energy IVCT or charge resonance bands.     

过氧钨、钼酸化合物催化氧化苯甲醇合成苯甲醛的研究

合成了六种过氧钨酸、钼酸盐,考察了它们在无溶剂、无卤素条件下用30%H2O2氧化苯甲醇合成苯甲醛反应中的催化活性。结果表明,该体系是一种高效的环境友好催化体系。三种过氧钨酸盐在反应过程中显示了较高的活性,在70℃下,反应2h,苯甲醛的收率和选择性都分别达到95.1%和96.2%。相比较而言,三种过氧钼酸盐的催化活性要低的多。实验考察了催化剂加入量、H2O2加入量、温度、时间等条件对催化剂活性的影响,确立了最佳反应条件为:0.08mmol催化剂,苯甲醇与H2O2的最佳摩尔比为1∶1.1,反应温度为70℃,反应时间为2h。