Dinitramidoborates: A Fascinating Case of Competing Oxygen and Nitrogen Donors and Tautomerism

Reactions of the BH 4 − anion with equimolar amounts of HN(NO 2 ) 2 or of BH 3 ⋅THF with K[N(NO 2 ) 2 ] − produced a mono‐substituted [BH 3 N(NO 2 ) 2 ] − anion, which contains a B−N connected dinitramido ligand. The reaction of BH 4 − with two equivalents of HN(NO 2 ) 2 afforded the di‐substituted borate anion consisting of two isomers, one with both nitramido ligands attached to B through N and the other one with one ligand attached through N and the other one through O. The disubstituted dinitramidoborates are marginally stable under ambient conditions, and the isomer with two N‐connected ligands was characterized by its crystal structure. A tri‐substituted borate was tentatively identified by NMR in the reaction of BH 4 − with a large excess of HN(NO 2 ) 2 . All of the anions are highly energetic. Theoretical calculations show that the energy differences between the B−N and B−O tautomers are small, explaining the formation of both.