Chemie mit Methan: Studieren geht über Probieren!

Abstract

Konzeptionelle Überlegungen zu und mechanistische Aspekte von vier scheinbar einfachen chemischen Umsetzungen, die in der Chemie von Methan von Bedeutung sind, werden in diesem Aufsatz behandelt: 1) die metallvermittelte Dehydrierung unter Bildung von Metallcarbenkomplexen, 2) die Wasserstoffabstraktion als Schlüsselschritt der oxidativen Dimerisierung von Methan, 3) der Mechanismus der CH4→CH3OH‐Umwandlung, und 4) die Reihenfolge der C‐H‐ und O‐H‐Bindungsaktivierung und die Frage nach dem geschwindigkeitsbestimmenden Schritt in der selektiven Oxidation von Methanol zu Formaldehyd. Moderne Gasphasenexperimente, in Verbindung mit Elektronenstrukturrechnungen, liefern Einblicke in elementare Reaktionsschritte auf molekularer Ebene und enthüllen reaktionsmechanistische Details. Die Ergebnisse dieser Untersuchungen werden, wo dies angebracht erscheint, mit Beobachtungen aus entsprechenden Studien in Lösung oder auf Oberflächen verglichen.

Doping Effects in Cluster‐Mediated Bond Activation

“…(2)]. [11] While platinum is crucial to activate methane and to initially form ap latinum-carbene complex, [9,25,26] the presence of ac oinage metal M( M= Cu, Ag, Au)i se ssential for the actual coupling of the carbene fragment with ammonia, as shown by experimental and relativistic DFT studies. [12,[27][28][29][30][31] As depicted in Figure 1, none of the homonuclear cluster ions [MM] + (M = Cu, Ag, Au,Pt) mediates the C À Nc oupling.…”

Gold‐Mediated CI Bond Activation of Iodobenzene

“…[2c] Instead, catalytic activity was attributed to the in situ formation of gold clusters by degradation of the Au I complex. [8] The stoichiometry of the metallic reactant ion can be confidently assigned by the unique mass and often-distinctive isotopic signature of the metal. [2c] Gas-phase studies represent a powerful way of uncovering the intrinsic reactivity of metallic ions [6,7] and the mechanisms of their CÀX bond activation reactions.…”

“…[2c] Gas-phase studies represent a powerful way of uncovering the intrinsic reactivity of metallic ions [6,7] and the mechanisms of their CÀX bond activation reactions. [8] The stoichiometry of the metallic reactant ion can be confidently assigned by the unique mass and often-distinctive isotopic signature of the metal. It can then be mass-selected using well-established tandem mass-spectrometry-based approaches and its reactivity directly probed by monitoring the changes in its abundance as well as the formation of ionic products.…”

Vacuum Ultraviolet Photoionization Studies of PtCH2 and H‐Pt‐CH3: A Potential Energy Surface for the Pt+CH4 Reaction

“…has led to extensive gas-phase studies of reactions of metal atoms, ions, and clusters with methane (see references [1][2][3] and references therein). These studies provide valuable information regarding reaction mechanisms, the energetics and structures of intermediates and of critical barriers.…”