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    Dimerization of a marginally stable disilenyl germylene to tricyclic systems: evidence for reversible NHC-coordination
    (Royal Soc Chemistry, 2016) Nieder, David; Yıldız, Cem Burak; Jana, Anukul; Zimmer, Michael; Huch, Volker; Scheschkewitz, David
    Tetrasiladigermatricyclohexanes in two isomeric forms (chair and doubly-bridged tetrahedron) are obtained by the reaction of MeLi with an alpha-chlorosilyl functionalized NHC-stabilized silagermenylidene. Si-29 NMR at low temperature proves the initial formation of a monomeric NHC-adduct of a disilenyl germylene followed by cyclisation to the isomeric heavy cyclopropene. Addition of an excess of NHC stabilizes the both intermediates and demonstrates the reversibility of rate-determining initial equilibria involving NHC dissociation. Finally, a mixture of two isomeric tricyclic Si4Ge2 species is obtained: at elevated temperature the chair isomer converts to the doubly edge-bridged tetrahedron.
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    Regiodiscriminating reactivity of isolable NHC-coordinated disilenyl germylene and Its cyclic isomer
    (American Chemical Society, 2016) Nieder, David; Huch, Volker; Yıldız, Cem Burak; Scheschkewitz, David
    An isolable NHC-coordinated disilenyl germylene R2Si-SiR-GePh center dot NHCiPr2Me2 (5b: R = 2,4,6-triisopropylphenyl, NHCiPr2Me2 = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) is obtained from the reaction of the a-chloro silyl functionalized heavier vinylidene analogue R2(Cl)Si-RSi-Ge center dot NHCiPr2Me2 with phenyllithium. The disilenyl germylene 5b isomerizes at 40 degrees C to the NHC-adduct of the corresponding heavier cyclopropylidene analogue 6b. Both 5b and 6b display near perfect regiodiscrimination in their reactions with phenylacetylene and xylyl isocyanide, affording in the case of each reagent two different regioisomers of NHC-coordinated cyclic germylenes. DFT calculations reveal that the Si-Si bond accounts for the high reactivity of 5b even at low temperature while in the case of cyclic 6b the low-valent germanium center requires a considerable thermal activation