Elucidation of hydrogen-release mechanism from methylamine in the presence of borane, alane, diborane, dialane, and borane–alane

Abstract

The mechanisms of hydrogen release from methylamine with or without borane, alane, diborane, dialane, and borane–alane are theoretically explored. Geometries of stationary points are optimised at the MP2/aug-cc-pVDZ level and energy profiles are refined at the CCSD(T)/aug-cc-pVTZ level based on the second-order Møller–Plesset (MP2) optimised geometries. H₂ elimination is impossible from the unimolecular CH₃NH₂ because of a high energy barrier. The results show that all catalysts can facilitate H₂ loss from CH₃NH₂. However, borane or alane has no real catalytic effect because the H₂ release is not preferred as compared with the B–N or Al–N bond cleavage once a corresponding adduct is formed. The diborane, dialane, and borane–alane will lead to a substantial reduction of energy barrier as a bifunctional catalyst. The similar and distinct points among various catalysts are compared. Hydrogen bond and six-membered ring formation are two crucial factors to decrease the energy barriers.

Keywords:

• hydrogen elimination
• catalysis
• reaction mechanisms

Acknowledgements

We thank the Beijing Key Laboratory of Ionic Liquids Clean Process and State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences for providing computational resources.

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Funding

This work was supported by the Natural Science Foundation of He'nan Province of China [grant number 134300510008], [grant number 144300510032]; Science Foundation of Henan Province [grant number 14A150034]; the Foundation for University Key Teachers from the He'nan Educational Committee.