Hydrogen-release mechanisms in lithium amidoboranes

Chemistry. 2009;15(22):5598-604. doi: 10.1002/chem.200900092.


Alkali-metal amidoboranes have been recently highlighted as materials that satisfy many of the criteria required to make hydrogen-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.