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  • 1
    Electronic Resource
    Electronic Resource
    Metal π-complexes of benzene derivatives. Part. 38Part 37: [1].. Pentaphenyltriphosphane(5) as a chelating η12-ligand. Unusual formation of an interannular -(PPh)3-bridge at bis(benzene)chromium (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1718-1724 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [(l-6):(1′-6′)-η-Pentaphenyltriphosphane(5)]chromium (8), which is formed from bis(lithio-η6-benzene)-chromium and dichlorophenylphosphane, and which is prepared more rationally from bis(chloro-η6-benzene)-chromium and K2P3Ph3, is the first sandwich complex featuring an interannular oligophosphane bridge -(PPh)n-, n ≥ 2; 31P{1H}- and 1H-NMR spectra suggest that the stereoisomer 8-meso1 is formed exclusively and that the -(PPh)3- link in this triphospha[3]chromocyclophane is non-fluxional in the range 193 〈 T 〈 348 K.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740813
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  • 2
    Electronic Resource
    Electronic Resource
    Chromium Sandwich Complexes of Polycyclic Aromatic Hydrocarbons: Triphenylene and Fluoranthene as η6 Ligands (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1391-1401 
    Details
    ISSN: 1434-1948
    Keywords: Polycycles ; Sandwich complexes ; Site preference ; Cyclic voltammetry ; NMR and EPR spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sandwich complexes bis(η6-triphenylene)chromium (12) and bis(η6-fluoranthene)chromium (13) have been prepared by means of metal atom/ligand vapor cocondensation. Whereas for triphenylene exclusive coordination to the peripheral rings is observed, the situation is more complicated for fluoranthene. According to NMR evidence initial metal coordination to the benzene (B) as well as to the naphthalene (N) section of the fluoranthene ligand occurs, leading to the isomers 13(I) (η6-B, η6-B), 13(II) (η6-B, η6-N) and 13(III) (η6-N, η6-N). Since the substitutional lability of the chromium-naphthalene bond largely exceeds that of the chromium-benzene bond, the isomer distribution depends on the workup conditions; 13(I) is clearly the most stable isomer. Crystal structure determinations performed for the salts [12][BPh4] and [13][I] point to the preference for syn orientation of the polycyclic aromatic hydrocarbons and to a minute metal slippage in the peripheral direction. The triphenylene complex 12 features the electrochemically reversible redox couples 12 (+/0, metal-centered), 12 (0/-, ligand-centered) and 12 (-/2-, ligand-centered), the latter displaying a redox splitting of 300 mV. Conversely, for the fluoranthene complex 13, secondary reduction 13 (-/2-) is irreversible. This finding is consistent with the larger redox splitting of ca. 480 mV which indicates more extensive interligand interaction in the dianion 132-, thereby favoring metal-ligand cleavage. While the radical cations 12+· and 13+· are amenable to EPR study, the radical anions 12-· and 13-· are too unstable. Instead, the radical anions of the free ligands are observed by EPR upon electrochemical reduction. In the case of 12, the temporary existence of the radical anion 12-· is indicated, however.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    The Radical Anion of trans-10b, 10c-Dihydropyrene (1975)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 58 (1975), S. 1245-1253 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The radical anion of trans-10b, 10c-dihydropyrene (V), which is formed upon reduction of the isomeric [2.2]metacyclophane-1,9-diene (III) with solvated electrons, has been identified by its ESR.-spectrum. The large coupling constant (19.1 Gauss), due to the two equivalent β-protons in the alkyl bridge, gives evidence of an important hyperfine interaction between the σ-MO's of the C(sp3)-H bonds and the singly occupied π-MO of the fourteen-membered perimeter. This finding supports the assumption that the unexpected energy sequence of the lowest antibonding perimeter MO's in the dihydropyrene V and its 10b, 10c-dimethyl derivative (VI) is determined by hyperconjugation rather than by the inductive effect of the alkyl bridge.When the solution of V○ in 1,2-dimethyoxyethane (DME) is brought in contact with an alkali metal mirror, an immediate conversion of VΦ into the radical anion of pyrene (IV) occurs. The anion IVΦ also results from reduction of [2.2.2](1,3,5)cyclophane-1,9,17-triene (VIII) with potassium in DME, whereas the radical anions of 4,5,9,10-tetrahydropyrene (II) and its 2,7-dimethyl-derivative (IX) are obtained by corresponding reactions of [2.2]metacyclophane (I) and [2.2.2](1,3,5)cyclophane (VII), respectively.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19750580502
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  • 4
    Electronic Resource
    Electronic Resource
    Aromatic Radical Anions with Parallel or Crossed Triple Bonds (1977)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 60 (1977), S. 2530-2538 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proton hyperfine data are reported for the radical anions of 1,8-di (propyn-1-yl)-naphthalene (I), 7,8,12,13-tetradehydro-10,11-dihydro-9H-cyclodeca[d,e]naphthalene (II) and 2,2′-di(propyn-1-yl)-biphenyl (III), as well as of 5,6,11,12-tetradehydro-7,8,9,10-tetrahydro-dibenzo[a,c]cyclodecene (IV) and its 8,8,9,9-tetradeuterio-derivative (IV-d4). The triple bonds in I and II can be regarded as roughly parallel, while those in IV (and IV-d4) may be considered as crossed. The π-spin distributions in I⊖ to IV⊖ are discussed in terms of simple MO models which suggest a weekly bonding interaction between the acetylenic fragments in IV⊖, in contrast to III⊖ where such an effect appears to be negligible. The importance of an analogous interaction in I⊖ and II⊖ is difficult to deduce, since its inclusion into a MO model does not substantially affect the π-spin distribution in these radical anions.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19770600806
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