Diborane(4) Azides: Surprisingly Stable Sources of Transient Iminoboranes

Herein we describe the first examples of isolable electron-precise diboranes(4) that bear azide moieties: the acyclic 1,2-diazido-1,2-bis(dimethylamino)diborane(4) and the cyclic 1,4-diaryl-2,3-diazido-1,4-diaza-2,3-diborinines (aryl=mesityl, 2,6-xylyl, 4-tolyl). The reported examples are not only stable enough to be observed and isolated (putative transient diborane(4) azides previously reported by our group spontaneously decompose even below room temperature), but some of them are even robust enough to undergo controlled pyrolysis without explosive decomposition at temperatures well above 100 °C. In two cases, the controlled pyrolysis allows the isolation of complex diazaboretidines, which are the apparent dimerization products of endocyclic boryl-iminoboranes.