Tungsten Centers Research Articles

Oxidative addition of cyclopropenyl cations to zerovalent molybdenum and tungsten centers. Synthesis of .eta.3-cyclopropenyl and .eta.3-oxocyclobutenyl complexes of molybdenum(II) and tungsten(II). Crystal and molecular structures of [Mo(.eta.5-C5H5)(.eta.3-C3Ph2R)(CO)2] (R = Ph, tert-Bu)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOxidative addition of cyclopropenyl cations to zerovalent molybdenum and tungsten centers. Synthesis of .eta.3-cyclopropenyl and .eta.3-oxocyclobutenyl complexes of molybdenum(II) and tungsten(II). Crystal and molecular structures of [Mo(.eta.5-C5H5)(.eta.3-C3Ph2R)(CO)2] (R = Ph, tert-Bu)Russell P. Hughes, John W. Reisch, and Arnold L. RheingoldCite this: Organometallics 1985, 4, 10, 1754–1761Publication Date (Print):October 1, 1985Publication History Published online1 May 2002Published inissue 1 October 1985https://doi.org/10.1021/om00129a012RIGHTS & PERMISSIONSArticle Views180Altmetric-Citations23LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Syntheses of Monomeric, Dimeric, and Trimeric Complexes of Tungsten(VI), (V), (IV), and (III) with the 1,4,7‐Triazacyclononane (L) Ligand. Crystal Structures of Dimeric [W2L2(μ2OH)2Br2]Br2 · 2H2O and of Trimeric [W3L3(μ30)(μ2‐0)3][ZnBr4]2

AbstractReactions of WL(CO)3 (L = 1, 4, 7‐triazacyclononane; C6H15N3) with bromine under different conditions afford the monomeric WVI compound, WO2LBr2, or the monomeric WV complex, WOLBr3. The former dimerizes in aqueous solution, yielding the [W2O5L2]2+ cation. Two diamagnetic isomers of the WV ‐dimer, [W2O4L2]2+, have been prepared : a yellow form with terminal oxo groups in cis‐positions with respect to each other and a red species containing two terminal oxo‐groups in trans‐positions. The cationic WIV ‐trinuclear cluster, [W3O4L3]4+, has been isolated as the tetrabromozincate(2‐) salt and its structure has been determined by single crystal X‐ray diffraction. [W3O4L3][ZnBr4]2 crystallizes in the monoclinic space group P21/c with a = 12.698(2) Å, b = 21.267(6) Å, c = 15.687(7) Å, β = 92.94(3)0, and V = 4222 Å3, dealed. = 2.79 g cm−3 for Z = 4, and mol wt 1773.2. The structure was solved by direct methods using 7399 unique reflections with I≥ 2.5 σ (I). Final residuals were R1 = 0.089 and R2 = 0.096. The structure consists of [W3L3O4]4+ cations of the M3X13 cluster type and isolated ZnBr42− anions. Three tungsten atoms occupy the corners of an equilateral triangle bridged by three μ2‐oxo‐ and one μ3‐oxo‐ligands; each tungsten atom has a distorted octahedral environment of three oxygen and three nitrogen atoms. The short W ‐ W distances of 2,52 Å and the diamagnetism indicate metal‐metal bonding.The green, diamagnetic binuclear WIII complex, [W2L2(μOH)2Br2]Br2 · 2 H2O, has been prepared by reduction of monomeric WLOBr3 in strongly acidic solution with zinc powder. The complex has been characterized by a single‐crystal X‐ray diffraction study; it crystallized in the orthorhombic space group Pnnm with a = 13.837(5) Å, b = 11.657(6) Å, c = 7.832 Å, and V = 1263 Å3, dcalcd. = 2.67 g cm−3 for Z = 2, and mol wt 1015.8. The structure was solved by direct methods using 783 unique reflections with I ⩾ 2.5 σ(1). Final residuals were R1 = 0.062 and R2 = 0.084. The structure consists of dimeric cations [W2L2(μOH)2Br2]2+, bromide anions and molecules of water of crystallization. The tungsten centers are in a distorted octahedral environment of the tridentate N‐donor igand, one coordinated bromide and two μ2‐hydroxo bridges (edge sharing), respectively. The bromide ligands are in trans‐positions with respect to each other. The four‐membered W2(μOH)2 ring is planar. The WW distance of 2.477(3) Å together with its diamagnetism imply the presence of a strong metal‐metal bond between the tungsten(II1) centers (σ2π2δ2).

Dialkylallenylidenekomplexe mit Pentacarbonylfragmenten der VIb Metalle/Dialkylallenylidene Complexes with Pentacarbonyl Fragments of VI b Metals

Abstract In the context of the synthesis of allenylidene compounds, the reaction of methylpropiolate with a (OC)5CrO(C2H5)2 complex was investigated. The species pentacarbonyl- (methylpropiolate)chromium(0) (1), 2,4-bis(methoxycarbonyl)-cyclobut-2-en-1-yliden-1- pentacarbonylchromium(0) (2) and cis-2,4-dimethoxycarbonyl-1,3-butadien-1 -yliden-1 - pentacarbonylchromium (3) were isolated. Attempts to synthesize allenylidene complexes from 1 were unsuccessful. Di-iso-propyl or di-tert-butylallenylidene complexes with chromium or tungsten centers (4a, 4b, 5a, 5b) were finally obtained by the photochemical reaction of pentacarbonylpropargylates, (OC)5MC(O)C ≡ CCR2O2-, M = Cr, W, and subsequent desoxygenation. The complexes 4 a, b were characterized as triphenylphosphane adducts, di-iso-propylallenylidenetriphenylphosphorane complexes (6a und 6b). The structure of 6 a was determined by X-ray methods.

Electron paramagnetic resonance of the tungsten derivative of rat liver sulfite oxidase.

Sulfite oxidase purified from livers of tungsten-treated rats has been used for EPR studies of tungsten substituted at the molybdenum site of the enzyme in a fraction of the molecules. The EPR signal of W(V) in sulfite oxidase is quite similar to that of Mo(V) in its line shape and in its sensitivity to the presence of anions such as phosphate and fluoride. Hyperfine interaction with a dissociable proton is also observed in both signals. The pH-dependent alteration in line shape exhibited by the Mo(V) EPR signal of the rat liver enzyme. Incomplete reduction of the tungsten center at pH 9 is indicated by attenuated signal intensity at this pH. The W(V) signal has g values lower than those of the Mo(V) signal, has a much broader resonance envelope, and is much less readily saturated by increasing microwave power. Kinetic studies on the reduction of the heme and tungsten centers of sulfite oxidase have shown that reduction of de-molybdo forms of sulfite oxidase by sulfite is catalyzed by the residual traces of native molybdenum-containing molecules. Reduction is accomplished by electron transfer involving intermolecular heme-heme interaction. The W(V) signal is generated only after all the heme centers are reduced. The rate and extent of heme reduction at pH 9 are the same as at pH 7. Studies on the reoxidation of W(V) and reduced heme by O2 and by cytochrome c suggest that the cytochrome b5 of sulfite oxidase is the site of electron transfer to cytochrome c, whereas oxidase activity is the property of the molybdenum center. It appears that the tungsten center in sulfite oxidase is incapable of oxidizing sulfite.