Unexpected Mechanistic Variants in the Thermal Gas-Phase Activation of Methane

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• 作者：Helmut Schwarz ; Patricio González-Navarrete ; Jilai Li ; Maria Schlangen ; Xiaoyan Sun ; Thomas Weiske ; Shaodong Zhou
• 刊名：Organometallics
• 出版年：2017
• 出版时间：January 9, 2017
• 年：2017
• 卷：36
• 期：1
• 页码：8-17
• 全文大小：652K
• ISSN：1520-6041

文摘

In this review gas-phase studies conducted (mostly) at the Berlin laboratory of the authors are presented. The focus will be on describing mechanistic variants we (and others) came across recently in investigating the thermal activation of methane in the gas phase under idealized conditions. Typical examples include the discussion of those hydrogen-atom-transfer processes that do not follow the well-established conventional pathways in which oxyl radicals play a decisive role. This is the case when the spin is located at a metal center, as in [Al₂O₂]^•+, and the C–H bond cleavage follows a proton-coupled electron-transfer mechanism. Also, examples will be presented in which a high spin density at a bridging oxygen atom can be generated by judicious “doping” of the cluster oxides. Further, the particular role Lewis-acidic sites play in the methane activation by closed-shell metal-oxide ions will be highlighted. Then, aspects of the dissociative adsorption of CH₄ on rather small cluster ions will be analyzed; here, among other factors, e.g., the role of relativistic bond stabilization, intriguing ligand effects will be reported. Finally, in the context of Fischer–Tropsch-related chemistry, we will describe novel C–C coupling reactions occurring at room temperature with CH₄. Common to most systems studied is the synergy between experiment and computational chemistry, and for a few examples remarkable mechanistic commonalities with reactions at a surface were encountered.