Mechanistic Variants in Gas-Phase Metal-Oxide Mediated Activation of Methane at Ambient Conditions

Jilai, Li and Shaodong, Zhou and Jun, Zhang and Maria, Schlangen and Dandamudi, Usharani (2016) Mechanistic Variants in Gas-Phase Metal-Oxide Mediated Activation of Methane at Ambient Conditions. Journal of the American Chemical Society, 138. pp. 11368-11377.

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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 aciditybasicity 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.

Item Type:	Article
Uncontrolled Keywords:	activation of methane Metal oxides
Subjects:	500 Natural Sciences and Mathematics > 04 Chemistry and Allied Sciences > 24 Organic Chemistry
Divisions:	Lipid Science and Traditional Foods
Depositing User:	Food Sci. & Technol. Information Services
Date Deposited:	07 Nov 2016 11:12
Last Modified:	07 Nov 2016 11:12
URI:	http://ir.cftri.res.in/id/eprint/12411

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