Tungsten(VI) and mixed tungsten,molybdenum(VI) complexes of tartaric acid

A number of studies of species formed in the tungsten(VI) oxide-R,R-(+)-tartaric acid-water system have been carried out(^1–3). While various species have been proposed, it is generally accepted that three main ones predominate. Two have tungsten: (+)-tartaric acid [(+)-tartH₄] ratios of 11 and the third has the same ratio of 12. This latter species cannot be that proposed by Avaloset al. ⁽³⁾ since both ligands in their structure would have to be present as unidentates.Recently we have shown⁽⁴⁾ that high resolution¹H and¹³C n.m.r. studies were particularly useful in delineating the complexes formed in aqueous solution in the analogous molybdenum(VI) system. Thus, we turned our attention to the corresponding tungsten(VI) complexes, especially in view of the controversy surrounding the nature of the species formed in aqueous solution with (+)-tartH₄. The results of our studies, presented below, indicate that only a few species are formed, and that these are quite analogous, as might be expected, to the previously described molybdenum(VI) species⁽⁴⁾. In addition we have observed the formation of a mixed dimeric species [MoWO⁴{(+)-tart}₂]^4–, whose structure is akin to the mono-metallic complexes, as well as the well-characterized antimony(III) and arsenic(III) dimers of (+)-tartH₄ ⁽⁵⁾.     

Synthesis,characterization, X-ray structural analysis and study of oxidative properties of tetraethylammonium chlorochromate

Tetraethylammonium chlorochromate(VI), Et₄N[CrO₃Cl] is easily synthesized in nearly quantitative yield using a direct reaction of chromium(VI) oxide and tetraethylammonium chloride and characterized by elemental analysis, IR, UV/Visible, ¹H-NMR and ¹³C-NMR techniques and single-crystal X-ray diffraction analysis (monoclinic system, space group C2(#5), with a = 12.023(3), b = 7.998(2), c = 14.527(4) Å, β = 114.187(4)°, V = 1274.4(6) ų and Z = 4). X-ray data determined the CH ··· O hydrogen bond that forms between the ethyl hydrogen of the cation and oxygen of the anion. This compound is a versatile reagent for efficient and selective oxidation of organic substrates, in particular for alcohols to their corresponding aldehydes or ketones, under mild conditions.     

Molybdenum(VI) complexation by amino-acids. Part 1 Species in aqueous solution of sodium molybdate and L-aspartate

Summary The complexation of molybdenum(VI) by L-aspartate in dilute aqueous solutions, at pH 6, was studied using u.v. spectrophotometry,¹H and¹³C n.m.r. spectroscopy. A single complex anion, [MoO₃(C₄H₅NO₄)]^2–, is observed in solution. The conformation of the aspartate ion in the complex was determined and shown to be consistent with it acting as a terdentate ligand. The formation constant of the complex was determined at different ionic strengths. Job's method has been employed, here and elsewhere, to study the stoichiometry of the complex. However, the result is strongly affected by polymerization of molybdenum(VI): this effect is discussed.     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. 58. Zur Kenntnis von 2-(Dimethylaminomethyl)ferrocenyl-Verbindungen des Vanadiums,Molybdäns,Wolframs, Thoriums und Urans

Contributions to the Chemistry of Transition Metal Alkyl Compounds. 58 On 2-(Dimethylaminomethyl)ferrocenyl Compounds of Vanadium, Molybdenum, Tungsten, Thorium, and Uranium Earlier results according to which dimethylaminomethylferrocenyl groups (FcN) are able to form stable organometallic chelate compounds were confirmed by synthesis of the heterobimetallic chelate compounds (FcN)₂VO · Li(acac) II , (FcN)MoO₂(acac) III , (FcN)WOCl₃ IV , (FcN)Th(acac)₃ V , and (FcN)UO₂(acac) VI from the corresponding metal acetylacetonates or oxidchlorides and (FcN)Li I . The new compounds were characterized by elemental analysis, the i.r., ¹H-n.m.r., and electron spectra and by their effective magnetic moments.     

Synthesis, characterization, X-ray structural analysis and study of oxidative properties of a chlorochromate(VI) complex with benzyltriphenylphosphonium cation

Benzyltriphenylphosphonium chlorochromate(VI), [(PhCH₂)Ph₃P][CrO₃Cl], BTriPPCC, is easily synthesized in a nearly quantitative yield by direct reaction of Cr(VI) oxide and benzyltriphenylphosphonium chloride. The complex was characterized by physico-chemical and spectroscopic methods. The use of phosphonium counter ion, improves the quality of the BTriPPCC crystals. The compound was indeed crystallized and structurally characterized by X-ray diffraction at 170(2) K. This compound is a versatile reagent for the efficient and selective oxidation of organic substrates, in particular of alcohols to the corresponding aldehydes or ketones, in mild conditions. Due to the stability and solubility of BTriPPCC, the reactions can be performed at room temperature and the separation of the products is easy.     

Reactions in [2H]3-acetonitrile between trimethyl phosphite copper(I) or iron(II) cations and phosphorus pentafluoride or tungsten hexafluoride [1]

Fluorination of trimethyl phosphite in reactions between phosphorus pentafluoride or tungsten hexafluoride and the cations Cu[P(OMe)₃]₄⁺ or [FeP(OMe)_3n(NCMe)_6?n]²⁺, n=5 or 4, in [²H]₃-acetonitrile is influenced both by the metal and by the solvent. Mixtures of phosphorus(III and V) and tungsten(VI) fluorides are obtained whose origin can be understood in terms of kinetic control by Cu^I or Fe^II, labile and inert towards substitution respectively, and the Lewis base properties of CD₃CN. ¹⁹F and ³¹P n.m.r. spectroscopy was used to study the reactions and the n.m.r. parameters of PF₅·P(OMe)₃ are reported.     

Tetramethylammonium fluorochromate(VI): a new and efficient oxidant for organic substrates

Tetramethylammonium fluorochromate(VI), (CH₃)₄N⁺CrO₃F⁻ (TMAFC), was prepared and used for quantitative oxidation of several organic substrates. This new compound is more efficient and has certain advantages over similar oxidizing agents in terms of the amount of oxidant and solvent required, short reaction times and high yields.     

Addition de l'Hexafluoroacétone sur les Acides Carboxyliques—Mise en Évidence par RMN 1H et 19F. Application à l'Analyse d'un Mélange d'Acides

The compound HO? C(CF₃)₂? O₂CR results from nucleophilic addition of a carboxylic acid to the carbonyl group of hexafluoroacetone. I.r. and n.m.r. (¹H, ¹⁹F) spectroscopy have been used to show that the addition is reversible. The addition is favoured by a lowering of the temperature and by the use of acids in which the group R is electron donating. Moreover, the chemical shift of the CF₃ groups (or of the OH group) in the addition product is dependent on the nature of R. Thus, this reversible addition can be used as a method for the analysis of a mixture of carboxylic acids by n.m.r. spectroscopy.     

Synthesis,structure and electrochemical properties of a dioxomolybdenum(VI) complex with a ferrocene-containing ligand

Summary Bis[ferrocene aldehyde benzoylhydrazonato(1-)-N ¹,O]- dioxomolybdenum(VI) has been synthesized and characterized by x-ray diffraction and i.r.,¹H n.m.r. and electronic spectroscopies. The CH₂Cl₂/hexane solvate crystallizes in space group P2₁/n witha=11.149(6),b=20.463(8),c= 15.541(5) Å, =90.40(3)° andZ=4. The structure has been refined to R_w=0.049 based on 2886 independent reflections. The complex has distorted octahedral geometry with the two bidentate ligands coordinated through the oxygen and the azomethine nitrogen atoms. The MoO ₂ ²⁺ unit has the expectedcis geometry and the Mo-N bonds aretrans to the oxo-groups. The chelate rings are nearly planar but the cyclopentadienyl and phenyl rings are twisted out of the chelate rings. The electrochemical behaviour of the compound is also discussed: the two ferrocenyl groups appear to be independent with respect to oxidation and the molybdenum centre displays a nearly reversible one-electron reduction.     

Dioxomolybdenum(VI) complexes containing 1-alkyl-2-ethyl-3-hydroxy-4-pyridin-4(1H)-ones

Dioxomolybdenum(VI) complexes derived from ethyl maltol (2-ethyl-3-hydroxy-4-pyrone) and 1-alkyl-2-ethyl-3-hydroxy-4-pyridin-4(1H)-ones have been prepared and characterized using physical methods including ¹H- and ¹³C-n.m.r. spectroscopy, i.r., elemental analysis, and X-ray diffraction for the pyrone and 3-methylpyridine pyridinone derivatives. The octahedral complexes have the general formula cis-MoO₂L₂ where L = the deprotonated pyrone or pyridinone ligand.     

IR spectroscopic investigation of the structure of polymeric uranyl di(2-ethylhexyl)phosphate molecules in C6H6 and CCl4 solutions

Using IR spectroscopy, we studied the types of coordination of POO groups in di(2-ethylthexyl)phosphate anionx X⁻ with UO ₂ ²⁺ cations in the C₆H₆ and CCl₄ solutions of the polymer molecules (UO₂X₂)_p. The polymers exhibit tridentate-bridge coordination (I), which is not typical of (MX_n)_p salts where the phosphoryl oxygen atom forms two bonds with U(VI) atoms. When a few U(VI) atoms (≳7%) interact with donar additives, all POO group I change their coordination to the usual bidentate-bridge type, , resulting in a structural transformation of the polymer. The bridging POO group are responsible for the difference in the dimerization and trimerization constants and the constants of the subsequent addition of the monomer molecules UO₂X₂ to the polymer chain (UO₂X₂)_p. It is suggested that type I coordination of X⁻ to U(VI) is due to an extended bond between the 2p²-electrons of the phosphoryl oxygen atom of the X⁻ anion and a vacant f-orbital of the U(VI) atom (p_π−f_π interaction). This unusual type of bond between uranium (VI) and tributyl phosphate (TBP) phosphoryl oxygen was found earlier for the UO₂Cl₂·2TBP complex. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturmoi Khimii, Vol. 35, No. 6, pp. 60–65, November–December, 1994. Translated by K. Shaposhnikova     

Synthesis,molecular and supramolecular structure,spectroscopy and electrochemistry of a dialkoxo-bridged diuranyl(VI) compound

The synthesis, molecular and supramolecular structure, spectroscopy and electrochemistry of a dialkoxo-bridged diuranyl(VI) compound [(UO₂)₂(L)₂(dimethylformamide)₂] (1) derived from the Schiff base ligand H₂L, obtained on condensation of 3-methoxysalicylaldehyde with 2-aminoethanol, have been described. The compound has been characterized by IR, UV–Vis, NMR and mass spectra, as well as by single crystal X-ray structure determination. The title compound crystallizes in the monoclinic P2₁/n space group with the following unit cell parameters a = 10.5713(2) Å, b = 11.9895(2) Å, c = 12.9372(2) Å, β = 102.773(3)° and Z = 2. The structure of 1 reveals that it is a dialkoxo-bridged dinuclear compound of uranium(VI) containing two deprotonated ligands, [L]²⁻, two dimethylformamide (dmf) molecules and two UO₂²⁺ centers. The coordination geometry around the uranium(VI) center is distorted pentagonal bipyramidal; two uranyl oxygens occupy the axial positions, while the basal pentagonal plane is defined by a phenoxo oxygen, two bridging alkoxo oxygens, one imine nitrogen, and one dmf oxygen. Three C–H?O type hydrogen bonds involving one uranyl oxygen, two dmf hydrogens and the imine hydrogen link the dinuclear units into a two-dimensional network. The ESI-MS spectrum of 1 in dimethylsulfoxide exhibits two peaks at m/z = 464.17 and 927.26, which are assignable to [(UO₂)₂L₂H]⁺ (60%) and [(UO₂)₂LH]⁺ (100%) cations, respectively. Cyclic voltammetric measurements of 1 reveal that the uranium(VI) center is reduced quasireversibly at E_1/2 = −1112 mV with ΔE_P = 97 mV.     

Methylmetall-bis(trimethylsilyl)amidoderivate des Aluminiums,Galliums und Arsens

Methyl Metal Bis(trimethylsilyl)amido Derivatives of Aluminium, Gallium, and Arsenic MeAl[N(SiMe₃)₂]₂ (Me ? CH₃) has been prepared by the reaction of AlMe₃ with HN(SiMe₃)₂ in a 1:2 molar ratio. The homologue Gallium compound (as well as the Aluminium derivative) is formed in good yields by the interaction of MeMcl₂ (M = Al, Ga) with Li- and Na[N(SiMe₃)₂], respectively. MeAs[N(SiMe₃)₂]₂ is formed by the reaction of AsCl₃ and Na[N(SiMe₃)₂] in a 1:3 molar ratio. These colourless amido derivatives are monomeric in solution, they have been characterized by analyses, mass, n.m.r. (¹H and ¹³C), and especially by i.r. and Raman spectra.     

Ligand-Supported Facile Conversion of Uranyl(VI) into Uranium(IV) in Organic and Aqueous Media

Reduction of uranyl(VI) to U^V and to U^IV is important in uranium environmental migration and remediation processes. The anaerobic reduction of a uranyl U^VI complex supported by a picolinate ligand in both organic and aqueous media is presented. The [U^VIO₂(dpaea)] complex is readily converted into the cis-boroxide U^IV species via diborane-mediated reductive functionalization in organic media. Remarkably, in aqueous media the uranyl(VI) complex is rapidly converted, by Na₂S₂O₄, a reductant relevant for chemical remediation processes, into the stable uranyl(V) analogue, which is then slowly reduced to yield a water-insoluble trinuclear U^IV oxo-hydroxo cluster. This report provides the first example of direct conversion of a uranyl(VI) compound into a well-defined molecular U^IV species in aqueous conditions.     

Oxocation complexes,Part X. Oxomolybdenum(V) and dioxomolybdenum(VI) complexes with tri- and tetra-dentate Schiff bases

Summary Many new oxomolybdenum(V) and dioxomolybdenum(VI) complexes have been synthesized with tri- and tetradentate Schiff bases derived by the condensation of salicylaldehyde, thiosalicylaldehyde,o-hydroxyacetophenone, 3-carboxysalicyclaldehyde or acetylacetone with aminoalcohols, polymethylenediamines ando-phenylenediamines. Mononuclear oxothiolato Schiff base complexes of molybdenum(V) have been prepared for the first time. Quadridentate Schiff bases derived from salicylaldehyde and substituted salicylaldehydes ando-phenylenediamine have also been successfully employed to isolate dioxomolybdenum(VI) complexes in the solid state, in which two oxygen atoms of the MoO₂ group arecis- to each other, similar to the situation observed for other dioxomolybdenum(VI) complexes of salicylaldehyde-polymethylenediamine Schiff base ligands.Structures have been determined with the help of elemental analyses, magnetic susceptibilities, molar conductances, i.r., electronic and¹H n.m.r. spectral data.For Part IX, K. Dey, R. K. Maiti and J. K. Bhar,Indian J. Chem., in press.     

Synthesis and characterization of mononuclear cadmium(II) and dinuclear uranyl(VI) complexes with <Emphasis Type="Italic">vic</Emphasis>-dioximes

In this study, the mononuclear complexes of cadmium(II) and dinuclear complexes of uranyl(VI) with five vic-dioximes have been obtained. Cadmium(II) forms, with ligands, complexes [(L ^xH)(Cl)(H₂O)(Cd)] with x=1–5. Mononuclear complexes with a metal: ligand ratio of 1:1 were obtained for cadmium(II) with the ligands, and a chloride ion and a water molecule are also coordinated to the cadmium(II) ions. Uranyl(VI) complexes of these ligands are a dinuclear structure with μ-hydroxo-bridges. Uranyl(VI) forms, with ligands, complexes [(L^xH)₂(OH)₂(UO₂)₂] with x=1–5, which have a 2:2 metal:ligand ratio. The structures of the complexes were identified by elemental analysis, i.r., and ¹H-n.m.r. spectra, u.v.–vis. spectroscopy, magnetic susceptibility measurements, conductivity measurements and thermogravimetric analysis (t.g.a.).     

Synthese,Kristallstruktur und spektroskopische Charakterisierung von Tetraphosphorhexaoxid-monoselenid,P4O6Se

Synthesis, Crystal Structure, and Spectroscopic Characterization of Tetraphosphorus Hexaoxide Monoselenide, P₄O₆Se P₄O₆Se has been synthesized by photochemical reaction between P₄O₆ and elemental selenium in CS₂ in presence of iodine as a catalyst. Single crystals form at purification via sublimation. The compound (m. p. 46°C) crystallizes in the monoclinic space group P2₁/c (no. 14) with a = 1 051.8(2), b = 652.9(1), c = 1 178.6(2) pm, β = 109.29(1)°, Z = 4. Within the limits of experimental error, the molecules exhibit C_3v symmetry. IR, Raman, and ³¹P n.m.r. (solution) spectra of the compound are reported and discussed. The geometry of the Molecule as determined by theoretical methods (SCF level) is in good agreement with the experimental results.     

Ligand‐Supported Facile Conversion of Uranyl(VI) into Uranium(IV) in Organic and Aqueous Media

Reduction of uranyl(VI) to U^V and to U^IV is important in uranium environmental migration and remediation processes. The anaerobic reduction of a uranyl U^VI complex supported by a picolinate ligand in both organic and aqueous media is presented. The [U^VIO₂(dpaea)] complex is readily converted into the cis‐boroxide U^IV species via diborane‐mediated reductive functionalization in organic media. Remarkably, in aqueous media the uranyl(VI) complex is rapidly converted, by Na₂S₂O₄, a reductant relevant for chemical remediation processes, into the stable uranyl(V) analogue, which is then slowly reduced to yield a water‐insoluble trinuclear U^IV oxo‐hydroxo cluster. This report provides the first example of direct conversion of a uranyl(VI) compound into a well‐defined molecular U^IV species in aqueous conditions.     

N(SCl)2 ⊕[MoCl5(NSCl)]⊖, ein Chlorthionitrenokomplex von Molybdän(VI)

N(SCl)₂^⊕ [MoCl₅(NSCl)]^?, a Chlorothionitrene Complex of Molybdenum (VI) . The title compound is formed together with MoCl₃(N₃S₂) by the reaction of MoCl₄ or MoCl₅ with (NSCl)₃ in CH₂Cl₂. The black, crystalline compound was characterized by its i.r. spectrum and an X-ray crystal structure determination. N(SCl)₂^⊕[MoCl₅(NSCl)]^? crystallizes in the monoclinic space group P2₁/n with four formula units per unit cell. The lattice constants are a = 716.3, b = 1627.4, c = 1178.9 pm and β = 100.90°. The [MoCl₅(NSCl)]^? ion posseses an almost linear Mo = N = S grouping with bond lengths that can be interpreted as double bonds. Crystal data for AsPh₄[MoCl₅(NSCl)] are reported.     

Metalla- und Phosphaheterocyclen mit Diamino-Supermesitylboryl-Einheiten

Metalla- and Phosphaheterocycles with Diaminosupermesitylboryl Units RB(NMeLi)₂ is reacted with dimethylmetaldichlorides to give four membered (n = 1) metallacycles of the type (? RB? NMe? MMe₂? NMe? )_n (M = Si, IIa ; M = Ge, IIb ) and the eight membered ring (n = 2) with M = Sn, III . The four membered ring (? RB? NMe? PCMe₃? NMe? ), IV , is formed with Me₃CPCl₂. RBF₂ and lithiated N,N′-dimethylethylenediamine give the five membered ring RB(? NMe? CH₂—)₂, Va . The reaction of RB(NHMe)₂ with trimethylaluminum upon elimination of methane yields the symmetrical eight membered ring system (? RB? NMe? AlMe? NMe? )₂, VI . The compounds are characterized by their m.s. and n.m.r. (¹H, ¹¹B, ¹³C, ²⁹Si, ³¹P, ¹¹⁹Sn and in part ¹⁵N) spectra, and with the exception of III and VI also by elemental analyses. An X-ray structure analysis is provided for III .