Hydrogen-Release Mechanisms in Lithium Amidoboranes

Abstract

Alkali-metal amidoboranes have been recently highlighted as materials that satisfy many of the criteria required to make hydro en-storage media. It is, therefore, crucial for us to understand the dehydrogenation mechanism of these materials for further development towards making successful hydrogen-storage media. In the present study, we attempt to shed light on the mechanisms involved in the loss of one molar equivalent of H-2 from solid lithium amidoboranes by using high-level ab initio calculations of monomeric and dimeric compounds in the gas phase. In the lithium amidoborane dimer, H-2 is released by the formation of LiH, which is followed by a redox reaction of the dihydrogen bond formed between the strongly basic H- in LiH and H delta+ bonded to N. In the dehydrogenation process, the Li cation catalyzes the intermolecular N-B bond formation, this could lead to new pathways for N-B polymerization. After the release of the first molecule of H-2, a Li cation binds to a nitrogen atom, resulting in a lowering of the energy barrier for the second dehydrogenation process per dimer, These results will be useful for the design of future hydrogen-storage media.