The sodium borohydride - nitroform adduct

14 October 2013 - Chemical Zoo

The combined US navy, US Air Force and the US Defense Threat Reduction Agency were more than happy to fund research into the adduct of sodium borohydride and nitroform as a new high-energy density material aka explosive. The report is titled "BH3C(NO2)3: The First Room-Temperature Stable
(Trinitromethyl)borate" and principal author Bélanger-Chabot points out that the compound is not only explosive but also green because the boron employed is non-toxic (DOI). As if greenness is relevant in warfare. Additional and more sensible rationale, a stable B-C bond in this compound is certain to stabilise an otherwise unstable nitroformate anion. In the meanwhile the initial recipe is dead-simple , mix nitroform and sodium borohydride in glyme and after effervescence the yellow solution contains a quantitative amount of BH3C(NO2)3. The work-up is tricky : The solvent was removed under vacuum between -40 and -8°C over the course of several days. The compound exists thanks to the glyme, remove it by a vacuum and you end up with sodium nitroformate. Even with glyme decomposition takes place within a week at RT.

So the compound is less stable than expected, and the authors suggest that the strong B-C bond is partially offset by reorganisations from planar to tetrahedral on dissociation of the two ionic fragments.

Questions: why is the adduct called a borate when no oxygen is in sight? With respect to the opening line : "Ever since the first report on the nitroformate anion (...) trinitromethyl derivatives have been a subject of significant interest" what is the meaning of "signification interest" given that this first report dates back to 1899, more than a century ago. I guess interest in the electron or radioactivity can be considered "significant" in this timespan but the nitroformate anion?