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  • Electrophilic addition  (1)
  • Hydrogen production  (1)
  • 1
    ISSN: 0947-3440
    Schlagwort(e): Carbenes ; Cycloadditions ; Diazo compounds ; Styrene ; Electrophilic addition ; Nitrogen heterocycles ; Photolysis ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The chemistry of 4,5-diazafluorenylidene (3), generated from the diazo compound 3a by photolysis, has been studied with regard to reactivity, multiplicity and selectivity. Reaction of 3 in 2,3-dimethylbutene gave exclusively ketazine 24. The [1 + 2] cycloaddition with styrenes 5-11 afforded cyclopropanes 16-23 in 25-54% yields and 24 as a side product. In these reactions no diazirine intermediate was involved. Irradiation of 3a in methanol afforded the ether 26 (25% yield). The stereoselectivity of 3 was studied by its addition to (E)- and (Z)-β-methylstyrene. A mixture of the (E)- and (Z)-cyclopropanes 22 and 23, respectively, was detected. Thus for 3, triplet multiplicity was concluded. The results of competition experiments with singlet/triplet scavengers (methanol/dimethylbutadiene) demonstrated that an equilibrium between singlet and triplet manifold of 3 exists at room temperature. Selectivity studies with carbene 3 were carried out by evaluating the competition experiments of the cycloaddition of 3 with differently substituted styrenes. A plot of the krel values from the competition studies versus Hammett σ constants gave ρ = -0.65 indicating that carbene 3 reacts as an electrophile.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    ISSN: 0947-3440
    Schlagwort(e): Artificial photosynthesis ; Electron transfer ; Sensitizer-relais assemblies ; Photophysical properties ; Hydrogen production ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Modell Systems for an Artificial Photosynthesis - Synthesis and Electron Transfer Studies of Novel Sensitizer-Relais AssembliesSyntheses and determination of electron transfer rates between sensitizers and electron acceptors for a novel class of bis(4,4′-dimethyl-2,2′-bipyridine)[4,4′-bis(alkoxymethyl)-2,2′-bipyridin]ruthenium(II) complexes 6-8 are described. We report on the formation of supramolecular complexes between the dialkoxybenzene-tethered bisheteroleptic Ru(II)-bipyridine complexes 5, 8 and 1,1′-dimethyl-4,4′-bypiridinium (MV2+) and cyclo-[bis(1,1′-p-xylylene-4,4′-bipyridinium)] (BXV4+), respectively. Evidence for the formation of supramolecular sensitizer-relais assemblies is taken from the viologen radical and hydrogen production rates in sacrificial model systems for artificial photosynthesis.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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