The mechanism of hydrogen abstraction by high valence transition metal oxo compounds

• Published in: Journal of energy chemistry 2016-11, Vol.25 (6), p.1045-1050
• Main Authors: Fu, Gang, Yuan, Ruming, Wan, Huilin, Xu, Xin
• Format: Article
• Language: English
• Subjects: C[sbnd]H bond activation; DFT calculation; Oxygen radical; Polanyi relationship; Valence bond state correlation diagram
• ISSN: 2095-4956
• DOI: 10.1016/j.jechem.2016.10.006

We present here a systematic theoretical study to explore the underlying mechanisms of the H abstraction reaction from methane. Various abstracting agents have been modeled, using oxygen radicals and a set of high valence metal oxo compounds. Our calculations demonstrate that although H abstraction from CH3–H by metal oxoes can be satisfactorily fitted into the Polanyi correlation on the basis of oxygen radicals, the mechanisms behind are significantly different. The frontier orbital analyses show that there are three electrons and three active orbitals(3e,3o) involved in H abstraction by oxygen radicals; whereas an additional orbital of π*M – Ois involved in H abstraction by M=O, resulting in a(4e,4o) interaction. In terms of valence bond state correlation diagram, we find that H abstraction by a metal oxo may benefit from the contribution of ionic resonance structures, which could compensate the penalty of opening the M–O π bond. We believe that these findings can help to design more effective catalysts for the activation of light alkanes.