Acta Physico-Chimica Sinica ›› 2019, Vol. 35 ›› Issue (9): 1014-1020.doi: 10.3866/PKU.WHXB201811039

Special Issue: 碳氢键活化

• Article • Previous Articles     Next Articles

Thermal Activation of Methane by Diatomic Vanadium Boride Cations

Qiang CHEN1,2,Li-Xue JIANG1,2,3,Hai-Fang LI1,2,3,Jiao-Jiao CHEN1,2,3,Yan-Xia ZHAO1,2,*(),Sheng-Gui HE1,2,3,*()   

  1. 1 State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
    2 Beijing National Laboratory for Molecular Sciences and CAS Research/Education Center of Excellence in Molecular Sciences, Beijing 100190, P. R. China
    3 University of Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2018-11-28 Accepted:2018-12-27 Published:2019-01-03
  • Contact: Yan-Xia ZHAO,Sheng-Gui HE E-mail:chemzyx@iccas.ac.cn;shengguihe@iccas.ac.cn
  • Supported by:
    The project was supported by the National Natural Science Foundation of China(91645203);The project was supported by the National Natural Science Foundation of China(21773253);China Postdoctoral Science Foundation(2017M611002);Beijing Natural Science Foundation, China(2182092);Youth Innovation Promotion Association, Chinese Academy of Sciences(2018041)

Abstract:

Methane activation by transition metal species has been extensively investigated over the past few decades. It is observed that ground-state monocations of bare 3d transition metals are inert toward CH4 at room temperature because of unfavorable thermodynamics. In contrast, many mono-ligated 3d transition metal cations, such as MO+ (M = Mn, Fe, Co, Cu, Zn), MH+ (M = Fe, Co), and NiX+ (X = H, CH3, F), as well as several bis-ligated 3d transition metal cations including OCrO+, Ni(H)(OH)+, and Fe(O)(OH)+ activate the C―H bond of methane under thermal collision conditions because of the pronounced ligand effects. In most of the above-mentioned examples, the 3d metal atoms are observed to cooperate with the attached ligands to activate the C―H bond. Compared to the extensive studies on active species comprising of middle and late 3d transition metals, the knowledge about the reactivity of early 3d transition metal species toward methane and the related C―H activation mechanisms are still very limited. Only two early 3d transition metal species HMO+ (M = Ti and V) are discovered so far to activate the C―H bond of methane via participation of their metal atoms. In this study, by performing mass spectrometric experiments and density functional theory calculations, we have identified that the diatomic vanadium boride cation (VB+) can activate methane to produce a dihydrogen molecule and carbon-boron species under thermal collision conditions. The strong electrostatic interaction makes the reaction preferentially proceed the V side. To generate experimentally observed product ions, a two-state reactivity scenario involving spin conversion from high-spin sextet to low-spin quartet is necessary at the entrance of the reaction. This result is consistent with the reported reactions of 3d transition metal species with CH4, in which the C―H bond cleavage generally occurs in the low-spin states, even if the ground states of the related active species are in the high-spin states. For VB+ + CH4, the insertion of the synergetic V―B unit (rather than a single V or B atom) into the H3C―H bond causes the initial C―H bond activation driven by the strong bond strengths of V―CH3 and B―H. The mechanisms of methane activation by VB+ discussed in this study may provide useful guidance to the future studies on methane activation by early transition metal systems.

Key words: Methane activation, Early transition metal, Boron, Mass spectrometry, Density functional theory

MSC2000: 

  • O643