Ammonia + diborane + sodium?

03 June 2010 - Random chemistry

What do you get when you add together ammonia , diborane and sodium?. No university chemistry laboratory is complete without these chemicals and it may come as a surprise that it took until 2010 before this question was answered. Limiting the mix to just two components gives ammonia borane (add diborane as the monomeric THF adduct and ammonia), the ammonia/sodium electride solution or sodium triborohydride (NaB3H8, related to sodium borohydride) by reaction of diborane with sodium metal. The order in which to add the chemicals is therefore important.

Daly et al (DOI) of the University of Illinois at Urbana-Champaign decided to add sodium metal to a solution of ammonia borane in THF. At room temperature the first stop is the salt Na(NH2-BH3), then at reflux the formation of the aminodiboranate Na(BH3-NH2-BH3) with evolution of hydrogen is reported. This compound refuses to form crystals but by adding erbium chloride the aminodiboranate (isoelectronic to propane) could be studied as a ligand to erbium. According to the X-ray analysis 4 of the 6 boron hydrogen atoms chelate to the erbium center. Next question: what do you get when you add ammonia, diborane and sodium together all at once?