Trimeric cluster of lithium amidoborane - The smallest unit for the modeling of hydrogen release mechanism

Abstract

A detailed first-principle DFT M06/6-311++G(d.p) study of dehydrogenation mechanism of trimeric cluster of lithium amidoborane is presented. The first step of the reaction is association of two LiNH2BH3 molecules in the cluster. The dominant feature of the subsequent reaction pathway is activation of H atom of BH3 group by three Li atoms with formation of unique Li3H moiety. This Li3H moiety is destroyed prior to dehydrogenation in favor of formation of a triangular Li2H moiety, which interacts with protic H atom of NH2 group. As a result of this interaction, Li2H2 moiety is produced. It features N--H+-H- group suited near the middle plane between two Li+ in the transition state that leads to H2 release. The transition states of association and hydrogen release steps are similar in energy. It is concluded that the trimer, (LiNH2BH3)3, is the smallest cluster that captures the essence of the hydrogen release reaction.