Unusual products arising from the tandem dehydrogenation of Mg(BH4)2 and pyrrolidine

Abstract

The dehydrogenation of Mg(BH₄)₂ in the presence of O-Lewis base donors has been widely explored but there have been very few studies of dehydrogenation of the borohydride in the presence of N-Lewis bases. Mg(BH₄)₂ has been found to react with pyrrolidine at room temperature to form BH₃-pyrrolidine adduct. Upon heating, further dehydrogenation reactions occur to form bis(pyrrolidino)borane, tris(pyrrolidino)borane and other B–N intermediates. Reacting Mg(BH₄)₂ and pyrrolidine in a 1 : 6 molar ratio exclusively yields tris(pyrrolidino)borane which is in accordance with predicted stoichiometric factors. The formation of these products contrasts with the routine production of higher boranes and/or intractable polymers from the dehydrogenation of Mg(BH₄)₂ in the presence O-Lewis bases. The amount of H₂ released in these reactions was determined both by the Parr autoclave pressure readings and the eudiometer measurements. Both measurements align with the values predicted by the stoichiometric factors associated by the proposed pathway.