Dehydrogenation of LiAlH4 in HMPA

In this study, hydrogen desorption from LiAlH4 in HMPA solution was investigated. One equiv. H atom per LiAlH4 was evolved from the solution at ambient temperature. Heating the solution to ∼90 °C led to the evolution of three more H atoms. Unlike the solid-state thermal decomposition, LiAlH4 in solution does not decompose to the Li3AlH6 intermediate. In fact, Li3AlH6 was found to be unstable in HMPA. Two equiv. H atoms were found to detach from Li3AlH6 upon mixing it with HMPA at ambient temperature. Subsequent heating of the resulting solution to 90 °C resulted in the dehydrogenation of ca. 4 equiv. H atoms.