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  • 11
    ISSN: 0009-2940
    Keywords: Bis(arene)metal complexes ; Borane, dimesitylphenyl- ; Borane, diisopropylphenyl- ; Cyclic voltammetry ; EPR spectroscopy ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metal π Complexes of Benzene Derivatives, 50. - Arylboranes as Sandwich Ligands: Preparation of [(iPrO)2B(η6-Ph)]2M and [Mes2B(η6-Ph)]2M (M = V, Cr). Redox Properties and EPR Study of M(d5) Neutral Complexes and Boron-Centered Radical AnionsBis(η6-arene)metal complexes bearing peripheral boryl substituents have been prepared by means of metal-atom ligand-vapor cocondensation leading to [(iPrO)2B-η6-C6H5]2Cr (7) and [(iPrO)2B-η6-C6H5]2V (8) as well as by lithiation and subsequent reaction with Mes2BF with formation of [Mes2B-η6-C6H5]2Cr (11) and [Mes2B-η6-C6H5]2V (12). According to the NMR spectra, rotation about the η-C-BR2 bonds in 7 and 11 is free at 25°C, restrictions setting in at -85°C. The neutral radicals 8• and 12• have been studied by EPR spectroscopy: despite of the profound difference in the electron-accepting properties of the groups (iPrO)2B- and Mes2B, the hyperfine coupling constants a(51V) differ by 5% only; the extent of perturbation of the electronic structure manifests itself more clearly in the g tensor, which is tetragonal for 8 but orthorhombic for 12, the degeneracy of the LUMO's e1g being raised in the latter. Cyclovoltammetry on 11 exhibits reversible oxidation as well as reduction processes. Reduction which, according to EPR, is ligand-centered, occurs in two steps which are separated by the redox splitting ΔE1/2 = 570 mV. This value, which is a measure of electronic communication between the two Mes2B groups, lies between those of 1,4-bis(dimesitylboryl)benzene (δE1/2 = 690 mV) and 4,4′-bis(dimesitylboryl)biphenyl (ΔE1/2 = 270 mV). The EPR spectrum of the radical anion 11-• reveals hyperfine coupling to one boron nucleus of a magnitude very similar to that of the free ligand radical anion Mes2BC6H5-•. Therefore, reduction of 11 is ligand-centered, and an intramolecular electron exchange between the boron centers is slow on the EPR time scale. As inferred from the observation of the hyperfine interactions a(53Cr) and a(1H), oxidation of 11 is metal-centered; relative to parent bis(η6-benzene)chromium (9), the two Mes2B groups cause an anodic shift of 290 mV for the couple 11+/0. The radical cations 11+• are prone to protodeborylation, in this aspect resembling the respective silyl derivatives.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 75 (1963), S. 167-167 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 652 (1962), S. 129-139 
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: S-Oxalyl-thiole, die noch nicht untersuchten ersten Glieder der homologen Reihe von Thioestern der Dicarbonsäuren, wurden durch Kondensation von Oxalylchlorid mit Thiolen dargestellt. Die zunächst erhaltenen Oxalyl-dithiole zeichnen sich durch eine außerordentliche Labilität im neutralen Medium aus. Sie hydrolysieren spontan zu den Mono-thioestern, die eine bemerkenswerte Stabilität in saurer Lösung und ein unerwartet langwelliges Absorptionsmaximum besitzen. Die Ursachen dieser Eigenschaften werden in den Polarisationsverhältnissen der Thioester gesehen und diskutiert. Oxalyl-Coenzym A tritt im Stoffwechsel der Oxalsäure bei Mikroorganismen auf. Es wird durch ein Codehydrase II benötigendes spezifisches Enzymsystem glatt zu Glyoxylsäure und Coenzym A reduziert.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 663 (1963), S. 50-58 
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kalium-formylphosphat wurde durch Umsetzen von Formylfluorid mit wäßriger neutraler Kaliumphosphat-Lösung erhalten und daraus das Dilithiumsalz dargestellt. Die Hydrolysegeschwindigkeit der Formylphosphorsäure bei verschiedenen pH-Werten zeigt Minima bei pH 5.5 und 7.2. Dies läßt sich auf den Angriff der Ionen des Wassers auf verschiedene Ionisierungsstufen der Formyl-phosphorsäure zurückführen.  -  Formylfluorid kann auch zur Synthese von Formylthiolen verwendet werden. Man setzt es in Dioxan, das gleichzeitig die entstehende Fluorwasserstoffsäure bindet, mit den Thiolen um. Durch Transthiolierung können weitere, biochemisch wirksame Formylthiole gewonnen werden.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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