title: Mechanistic Variants in Gas-Phase Metal-Oxide Mediated Activation of Methane at Ambient Conditions.
abstract: The C-H bond activation of methane mediated by a prototypical heteronuclear metal-oxide cluster, [Al2Mg2O5](•+), was investigated by using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) in conjunction with high-level quantum mechanical calculations. Experimentally, hydrogen-atom abstraction from methane by the cluster ion [Al2Mg2O5](•+) takes place at ambient conditions. As to the mechanism, according to our computational findings, both the proton-coupled electron transfer (PCET) and the conventional hydrogen-atom transfer (HAT) are feasible and compete with each other. This is in distinct contrast to the [XYO2](+) (X, Y = Mg, Al, Si) cluster oxide ions which activate methane exclusively via the PCET route (Li, J.; Zhou, S.; Zhang, J.; Schlangen, M.; Weiske, T.; Usharani, D.; Shaik, S.; Schwarz, H. J. Am. Chem. Soc. 2016, 138, 7973-7981). The electronic origins of the mechanistically rather complex reactivity scenarios of the [Al2Mg2O5](•+)/CH4 couple were elucidated. For the PCET mechanism, in which the Lewis acid-base pair [Al(+)-O(-)] of the cluster acts as the active site, a clear correlation has been established between the nature of the transition state, the corresponding barrier height, the Lewis acidity-basicity of the [M(+)-O(-)] unit, as well as the bond order of the M(+)-O(-) bond. Also addressed is the role of the spin and charge distributions of a terminal oxygen radical site in the direct HAT route. The knowledge of the factors that control the reactivity of PCET and HAT pathways not only deepens our mechanistic understanding of metal-oxide mediated C-H bond activation but may also provide guidance for the rational design of catalysts.
authors: Institut für Chemie, Technische Universität Berlin , Straße des 17. Juni 135, 10623 Berlin, Germany.|Institute of Theoretical Chemistry, Jilin University , Changchun 130023, People's Republic of China.
authors: Jilai
authors: J
authors: Li
authors: Institut für Chemie, Technische Universität Berlin , Straße des 17. Juni 135, 10623 Berlin, Germany.
authors: Shaodong
authors: S
authors: Zhou
authors: Institute of Theoretical Chemistry, University of Cologne , Greinstraße 4, 50939 Cologne, Germany.
authors: Jun
authors: J
authors: Zhang
authors: Institut für Chemie, Technische Universität Berlin , Straße des 17. Juni 135, 10623 Berlin, Germany.
authors: Maria
authors: M
authors: Schlangen
authors: Department of Lipid Science, CSIR-Central Food Technological Research Institute , Mysore, 570 020, India.
authors: Dandamudi
authors: D
authors: Usharani
authors: Institute of Chemistry and the Lise-Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University of Jerusalem , 91904 Jerusalem, Israel.
authors: Sason
authors: S
authors: Shaik
authors: Institut für Chemie, Technische Universität Berlin , Straße des 17. Juni 135, 10623 Berlin, Germany.
authors: Helmut
authors: H
authors: Schwarz