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Thermal activation of Cp*W(NO)(η2-CPhCH2)(CH2SiMe3) (1) in neat hydrocarbon solutions transiently generates Cp*W(NO)(η2-PhC⋮CH) (A), which subsequently activates solvent C−H bonds. For example, the thermolysis of 1 in benzene solution generates quantitatively Cp*W(NO)(η2-CPhCH2)(Ph) (2). The thermolysis of 1 in solutions of methyl-substituted arenes such as toluene or p-, m-, or o-xylene provides mixtures of aryl and benzyl vinyl complexes of the general formulas Cp*W(NO)(η2-CPhCH2)(aryl), Cp*W(NO)(η2-CPhCH2)(η1-benzyl), or Cp*W(NO)(η2-benzyl)(η1-CPhCH2). Similarly, the thermolysis of 1 in (Me3Si)2O affords Cp*W(NO)(η2-CPhCH2)(CH2SiMe2OSiMe3) (10). Mechanistic and kinetic studies support the proposal that the formation of A from 1 by elimination of silane is the rate-controlling process in these reactions. Intra- and intermolecular selectivity studies reveal that the strongest C−H bond (yielding the stronger M−C bond) is the preferred site of reactivity, as expected. Dual C−H bond activation of aliphatic hydrocarbons occurs during the thermal activation of 1 in solutions of these substrates. Consequently, metallacycles of the form Cp*W(NO)(η2-CH(η2-Ph)CH2CH(R)CH2) [(11) R = nPr; (12) R = nBu; (13) R = tBu; and (14) R = OEt] result from the dehydrogenation of n-pentane, n-hexane, 2,2-dimethylbutane, and diethyl ether, respectively. This dual C−H activation process displays a selectivity for substrates that contain an ethyl substituent. Dual C−H bond activation of 2,3-dimethyl-2-butene in the presence of 1 under thermolysis conditions regioselectively affords Cp*W(NO)(η3-endo-CH2C(Me)C(Me)CH2(η1-CPhMe)) (15). Attempts to trap acetylene complex A with PMe3 result in the formation of the metallacyclopropane complex Cp*W(NO)(CH2SiMe3)(η2-CH2CPh(PMe3)) (16). All new complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of compounds 11, 15, and 16 have been established by X-ray diffraction methods.
Sprache
Englisch
Identifikatoren
ISSN: 0276-7333
eISSN: 1520-6041
DOI: 10.1021/om9904450
Titel-ID: cdi_crossref_primary_10_1021_om9904450
Format
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