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  • 1
    Electronic Resource
    Electronic Resource
    Attempts to prepare W2(β-diketonate)4(M4-M) complexes by reductiye elimination fromd 3 -d 3 ditungsten complexes. Preparation and structures of W2 R 2(NMe2)2 (Bu t -acac)2 and W2 R 2(OPr i )2 (Bu t -acac)2 compounds, whereR = Et, Ph, CH2Ph, and BC i (1994)
    Springer
    Journal of cluster science 5 (1994), S. 67-82 
    Details
    ISSN: 1572-8862
    Keywords: Tungsten ; triple bond ; alkoxide ; amide ; β-diketonate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The reactions between 1,2-W2 R 2(NMe2)4 (R=Et and Ph) and 1,2-W2 R 2(OPr i )4 (R=CH2Ph and Bu t ) and Bu t -CHCOCH2COBu t (Bu t -acacH) (4 equiv)in pentane or hexane give, respectively, W2 R 2NMe2)2 (Bu t -acac)2 and W2 R 2(OPr i )2 (Bu t -acac)2 that are remarkably thermally and photochemically robust with respect to further reaction and reductive elimination to give the targeted compounds W2(Bu t -acac)4. The new compounds have been characterized by elemental analysis, infrared, and1H NMR spectroscopy and forR = Et and CH2Ph by single crystal X-ray studies. In each compound there are four coordinate W atoms united by unbridged W-W triple bonds. Crystal data for W2Et2(NMe2)2 (Bu t -acac)2 at −165°C:a=17.115(2) Å,b=10.542(1) Å,c = 19.786(3) Å.β = 98.55(1)°,Z = 4, and space group C2/c; for W2(CH2Ph)2 (OPr i )2 (Bu t -acac)2 at −157°C:a=23.547(5) Å,b = 10.784(2)Å,c = 21.105(5) Å,β = 127.20(1)°,Z = 4, and space group C2/c.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165492
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  • 2
    Electronic Resource
    Electronic Resource
    [Et3PH][W4O3Cl7(PEt3)3]. A 12-electron tetrahedral tungsten cluster with an interesting arrangement of ligands (1993)
    Springer
    Journal of cluster science 4 (1993), S. 259-269 
    Details
    ISSN: 1572-8862
    Keywords: Tungsten ; chloro ; phosphine ; tetranuclear cluster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract From the reaction between W2Cl6(PEt3)2 and H2O in tetrahydrofuran the dark green crystalline compound [Et3PH][W4O3Cl7(PEt3)3] was obtained and characterized by X-ray crystallography. At −155° the cell dimensions werea=b=c=20.392(3) Å,Z=8,d calcd=2.36 g cm−3 in the space group I23. The compound is a triethylphosphonium salt of the [W4O3Cl7(PEt3)3]− anion. The latter contains a tetrahedron of tungsten atoms with W−W=2.61 Å (ave) and may be viewed as a W3(μ-Cl)3Cl3(PEt3)3 cluster capped by ad 0-[WO3Cl]− unit and this has proved useful in examining the bonding within the cluster by use of the M.O. calculational method of Fenske and Hall. The cluster anion has crystallographically imposed C3v symmetry. Theoxo-groups bridge the tungsten atoms in a notably asymmetric manner W−O=1.87(2) Å and 2.04(2) Å with the shorter distances being involved with the capping [WO3Cl]− unit. The W−P bonds lie in the W3(μ3-Cl)3 plane and the three terminal W−Cl bonds are trans to theoxo-bridges.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00703742
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  • 3
    Electronic Resource
    Electronic Resource
    [W4(O)2)(O-i-Pr)8]2 an unusual octanuclear oxo-alkoxide cluster of tungsten (1995)
    Springer
    Journal of cluster science 6 (1995), S. 135-145 
    Details
    ISSN: 1572-8862
    Keywords: Tungsten ; octanuclear cluster ; oxo ; alkoxide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract From the reaction between W4(p-tolyl)2(O-i-Pr)10 and H2, in hydrocarbon solvents, the compound [W4(O)2(O-i-Pr)8]2, 1, has been isolated in ca. 25% yield. Formation of 1 is traced to the decomposition of a compound of formula [W4O-i-Pr)10] n , which has been characterized only by1H NMR spectroscopy. The latter is formed by the stepwise hydrogenolysis of W4(p-tolyl)2(O-i-Pr)10 + H2 → W4(H)(p-tolyl)(O-i-Pr)10 + toluene; W4(H)(p-tolyl)(O-i-Pr)10 → [W4(O-i-Pr)10] n + toluene. In the presence of a small amount of H2O2 the previously characterized compound W4(O)(O-i-Pr)10, 2, is formed. The structure of 1 consists of two pseudo W4 tetrahedra linked through the agency of a pair of alkoxide bridges that bind two tungsten atoms that in turn cap triangles, W3(O)2(O-i-Pr)7, of tungsten atoms. At −176°C the cell dimensions werea=12.600(3),b=14.722(3),c=12.585(2),β=119.77(1),Z=1, andd calcd = 2.240 g cm−3 in the space group P1¯. The W-W distances within these triangles are ca. 2.9 Å whereas the capping W-W atom distances are ca. 2.5 Å. The1H NMR spectrum of 1 in benzene-d6 is consistent with the maintenance of the solid-state structure in solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01175841
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  • 4
    Electronic Resource
    Electronic Resource
    Alkoxide Clusters of Molybdenum and Tungsten as Templates for Organometallic Chemistry: Comparison with Carbonyl Clusters of the Later Transition ElementsDedicated to Professor Donald C. Bradley (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 432-444 
    Details
    ISSN: 0570-0833
    Keywords: Cluster compounds ; Transition metals ; Metal-metal interactions ; Molybdenum ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Alkoxide and carbonyl ligands complement each other because they both behave as “π buffers” to transition metals. Alkoxides, which are π donors, stabilize early transition metals in high oxidation states by donating electrons into vacant dπ orbitals, whereas carbonyls, which are π acceptors, stabilize later transition elements in their lower oxidation states by accepting electrons from filled dπ orbitals. Both ligands readily form bridges that span M—M bonds. In solution fluxional processes that involve bridge-terminal ligand exchange are common to both alkoxide and carbonyl ligands. The fragments [W(OR)3], [CpW(CO)2], [Co(CO)3], and CH are related by the isolobal analogy. Thus the compounds [(RO)3W ≡ W(OR)3], [Cp(CO)2W≡W(CO)2Cp], hypothetical [(CO)3Co≡Co(CO)3], and HC≡CH are isolobal. Alkoxide and carbonyl cluster compounds often exhibit striking similarities with respect to substrate binding - e.g., [W3(μ3-CR)(OR′)9] versus [Co3(μ3-CR)(CO)9] and [W4(C)(NMe)(OiPr)12] versus [Fe4(C)(CO)13] - but differ with respect to M—M bonding. The carbonyl clusters use eg-type orbitals for M—M bonding whereas the alkoxide clusters employ t2g-type orbitals. Another point of difference involves electronic saturation. In general, each metal atom in a metal carbonyl cluster has an 18-electron count; thus, activation of the cluster often requires thermal or photochemical CO expulsion or M—M bond homolysis. Alkoxide clusters, on the other hand, behave as electronically unsaturated species because the π electrons are ligand-centered and the LUMO metal-centered. Also, access to the metal centers may be sterically controlled in metal alkoxide clusters by choice of alkoxide groups whereas ancillary ligands such as tertiary phosphanes or cyclopentadienes must be introduced if steric factors are to be modified in carbonyl clusters. A comparison of the reactivity of alkynes and ethylene with dinuclear alkoxide and carbonyl compounds is presented. For the carbonyl compounds CO ligand loss is a prerequisite for substrate uptake and subsequent activation. For [M2(OR)6] compounds (M = Mo and W) the nature of substrate uptake and activation is dependent upon the choice of M and R, leading to a more diverse chemistry.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198904321
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  • 5
    Electronic Resource
    Electronic Resource
    The σ2π4 Triple Bond between Molybdenum and Tungsten Atoms: Developing the Chemistry of an Inorganic Functional Group (1986)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 21-30 
    Details
    ISSN: 0570-0833
    Keywords: Metal-metal interactions ; Molybdenum ; Multiple bonds ; Cluster compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Numerous analogies between organic and inorganic chemistry have emerged in recent years. The most prominent example is the isolobal relationship. Many reactions have shown that metal-metal double and triple bonds exhibit a pattern of reactivity similar to that of alkenes and alkynes. In compounds containing a σ2π4 triple bond between molybdenum and tungsten atoms, the M—M bond order can be increased from three to four by reductive elimination or decreased from three to two or one by oxidative addition. Complexes with M≡M bonds can be used to prepare clusters or can serve as catalysts. In this review relationships between structure (electronic and stereochemical) and reactivity that are characteristic for modern inorganic chemistry are discussed.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198600211
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