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    Bildung Stabiler All-Silicium Varianten von 1,3-Cyclobutandiyl im Gleichgewicht
    (Wiley-Blackwell, 2020) Yıldız, Cem Burak; Leszczyñska, Kinga I.; González-Gallardo, Sandra; Zimmer, Michael; Azizoğlu, Akın; Biskup, Till; Kay, Christopher W.M.; Hüch, Volker; Rzepa, Henry S.; Scheschkewitz, David
    Hauptgruppenanaloga von 1,3-Cyclobutandiylen faszinieren mit ihrer einzigartigen Reaktivitt und ihren elektronischen Eigenschaften. Bisher sind allerdings nur heteronukleare Vertreter isoliert worden. Wir berichten hier ber die Isolierung und Charakterisierung von All-Silicium-1,3-Cyclobutandiylen als stabile Singulettspezies mit geschlossenschaliger Konfiguration aus den reversiblen Reaktionen von Cyclotrisilen c-Si3Tip4 (Tip = 2,4,6-Triisopropylphenyl) mit den N-heterocyclischen Silylenen c-[(CR2CH2)(NtBu)2]Si: (R = H oder Methyl) mit gesttigten Grundger sten. Bei erhçhten Temperaturen werden aus diesen Gleichgewichtsmischungen Tetrasilacyclobutene erhalten. Die analoge Reaktion mit dem ungesttigten N-heterocyclischen Silylen c-(CH)2- (NtBu)2Si: verluft direkt zum entsprechenden Tetrasilacyclobuten ohne Nachweis des angenommenen 1,3-Cyclobutandiyl-Zwischenprodukts
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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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    Diverse reactivity of an electrophilic phosphasilene towards anionic nucleophiles: Substitution or metal-amino exchange
    (WILEY-V C H Verlag Gmbh, 2016) Willmes, Philipp; Junk, Lukas; Huch, Volker; Yıldız, Cem Burak; Scheschkewitz, David
    The reaction of MesLi (Mes=2,4,6-trimethylphenyl) with the electrophilic phosphasilene R-2(NMe2)Si-RSi=PNMe2 (2, R=Tip=2,4,6-triisopropylphenyl) cleanly affords R-2(NMe2)Si-RSi=PMes and thus provides the first example of a substitution reaction at an unperturbed Si=P bond. In toluene, the reaction of 2 with lithium disilenide, R2Si=Si(R)Li (1), apparently proceeds via an initial nucleophilic substitution step as well (as suggested by DFT calculations), but affords a saturated bicyclo[1.1.0]butane analogue as the final product, which was further characterized as its Fe(CO)(4) complex. In contrast, in 1,2-dimethoxyethane the reaction of 1 with 2 results in an unprecedented metal-amino exchange reaction.
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    Equilibrium Formation of Stable All-Silicon Versions of 1,3-Cyclobutanediyl
    (Wiley-VCH Verlag, 2020) Yıldız, Cem Burak; Leszczyñska, Kinga I.; González-Gallardo, Sandra; Zimmer, Michael; Azizoğlu, Akın; Biskup, Till; Kay, Christopher; Hüch, Volker; Rzepa, Henry S.; Scheschkewitz, David
    Main group analogues of cyclobutane-1,3-diyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of all-silicon 1,3-cyclobutanediyls as stable closed-shell singlet species from the reversible reactions of cyclotrisilene c-Si3Tip4 (Tip=2,4,6-triisopropylphenyl) with the N-heterocyclic silylenes c-[(CR2CH2)(NtBu)2]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated N-heterocyclic silylene c-(CH)2(NtBu)2Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3-cyclobutanediyl intermediate.
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    Reactivity enhancement of a diphosphene by reversible N-heterocyclic carbene coordination
    (Royal Society of Chemistry, 2018) Dhara, Debabrata; Kalita, Pankaj; Mondal, Subhadip; Narayanan, Ramakirushnan Suriya; Mote, Kaustubh R.; Huch, Volker; Zimmer, Michael; Yıldız, Cem Burak; Scheschkewitz, David; Chandrasekhar, Vadapalli; Jana, Ankul
    Diphosphene TerMesP = PTerMes (1; TerMes = 2,6-Mes2C6H3; Mes = 2,4,6-Me3C6H2) and NHCMe42 (NHCMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene) exist in an equilibrium mixture with the NHCMe4-coordinated diphosphene 3. While uncoordinated 1 is inert to hydrolysis, the NHC adduct 3 readily undergoes hydrolysis to afford a phosphino-substituted phosphine oxide with the liberation of NHCMe4. On this basis, conditions suitable for the catalytic use of NHCMe4 were identified. Similarly, while the hydrogenation of free diphosphene 1 with H3N·BH3 is very slow, 3 reacts instantaneously with H3N·BH3 at room temperature to afford a dihydrodiphosphane. © 2018 The Royal Society of Chemistry.
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    Reactivity of heavier vinyl anions [(CH3)2-rfeti=E'(CH3)]- (E, E' = C, Si, Ge) toward carbon monoxide: A computational study
    (American Chemical Society, 2017) Yıldız, Cem Burak; Scheschkewitz, David
    The structures of heavier vinyl anions [(CH3)2E=E'(CH3)]- (E, E' = C, Si, Ge) and their abilities to activate carbon monoxide were investigated by DFT. Particularly, heteronuclear species exhibit a strong influence of the position of the heavier of the two group 14 elements (E or E') with strongly differing singlet-triplet gaps as a measure of tetrylene character. The reactions of CSi and CGe (E' = Si, Ge) with CO proceed in a concerted manner via [1 + 2] or [2 + 2] cycloadditions to a variety of potential products, whereas those of positional isomers as well as digerma and sila-germa analogues occur in a stepwise fashion. The three-membered rings derived from tetrylene-like vinyl anions (E' = Si, Ge and E = C) are dominated by keto resonance structures, while an enol structure is observed for the product obtained from SiC. Allene-like isomers could only be optimized in case of E = Si, Ge. © 2017 American Chemical Society.
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    Reactivity of NHC/diphosphene-coordinated Au(i)-hydride
    (Royal Society of Chemistry, 2021) Dhara, Debabrata; Scheschkewitz, David; Chandrasekhar, Vadapalli; Yıldız, Cem B.; Jana, Anukul
    We report the reactivity of isolable Au(i)-hydride stabilized by an NHC-coordinated diphosphene towards substrates containing C-C and N-N multiple bonds (NHC = N-heterocyclcic carbene). Reactions with dimethyl acetylenedicarboxylate and azobenzene lead to a trans-addition of the Au(i)-H across the C-C triple bond and the N-N double bond, respectively. In contrast, the reaction with ethyl diazoacetate affords a gold(i)-hydrazonide as the 1,1-addition product to the terminal nitrogen atom. With phenyl acetylene, the corresponding Au(i)-alkynyl complex is obtained under the elimination of dihydrogen. Strikingly, diphosphene-containing Au(i)-hydride is more reactive-affording different products in some cases-than a related NHC-stabilized Au(i)-hydride without the mediating diphosphene moiety.
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    Reactivity of NHC/diphosphene-coordinated Au(i)-hydride
    (Royal Society of Chemistry, 2021) Dhara, Debabrata; Scheschkewitz, David; Chandrasekhar, Vadapalli; Jana, Anuku; Yıldız, Cem B.
    We report the reactivity of isolable Au(i)-hydride stabilized by an NHC-coordinated diphosphene towards substrates containing C-C and N-N multiple bonds (NHC = N-heterocyclcic carbene). Reactions with dimethyl acetylenedicarboxylate and azobenzene lead to a trans-addition of the Au(i)-H across the C-C triple bond and the N-N double bond, respectively. In contrast, the reaction with ethyl diazoacetate affords a gold(i)-hydrazonide as the 1,1-addition product to the terminal nitrogen atom. With phenyl acetylene, the corresponding Au(i)-alkynyl complex is obtained under the elimination of dihydrogen. Strikingly, diphosphene-containing Au(i)-hydride is more reactive - affording different products in some cases - than a related NHC-stabilized Au(i)-hydride without the mediating diphosphene moiety.
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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