Initial steps for the thermal decomposition of alkaline-earth metal amidoboranes: a cluster approximationElectronic supplementary information (ESI) available: Fig. S1-S6, Table S1, and optimized structures of all clusters. See DOI: 10.1039/c6cp05835c

A DFT study of thermal decomposition mechanisms of [M(NH 2 BH 3 ) 2 ] 4 clusters with M = Mg, Ca, and Sr is presented. Multi-step reaction pathways leading to elimination of the first H 2 molecule are explored at the M06/TZVP level of theory. For all studied M, the clusters adopt similar structures and exhibit similar transformations along the reaction pathways. Their activation energies decrease in the order Mg < Ca ≤ Sr. Four metal atoms in the cluster form a rigid planar construction that is found to be nearly unchanged during all transformations. Cleavage of the B-H bond in the environment of alkaline-earth metal atoms leads to the "capture" of the released H atom by neighboring metal atoms with the formation of a M 3 H moiety. While the activation energies for the cleavage of H δ − can be as low as 14.3, 22.6 and 23.3 kcal mol −1 for M = Mg, Ca and Sr, respectively, barriers for the subsequent cleavage of H δ + via destruction of the M 3 H moiety are about twice larger. Formation of a M 3 H moiety during the initial steps is a key feature of thermal decomposition of alkaline-earth metal amidoboranes.