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

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 Moller-Plesset (MP2) optimised geometries. H-2 elimination is impossible from the unimolecular CH3NH2 because of a high energy barrier. The results show that all catalysts can facilitate H-2 loss from CH3NH2. However, borane or alane has no real catalytic effect because the H-2 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.