Observation of Room Temperature B–Cl Activation of the HCB₁₁Cl₁₁^– Anion and Isolation of a Stable Anionic Carboranyl Phosphazide

The perchlorinated carba-closo-dodecaborate anion is typically inert toward B–Cl functionalization. We present here the observation of two competing reactions that occur with this anion at ambient temperature. When this molecule is treated with n-BuLi and subsequently reacted with tosyl azide, a cycloaddition occurs and results in chloride substitution at a B–Cl vertex. The competing and dominant pathway is a substitution reaction to form the azide N3CB11Cl11–. This rare anionic carboranyl azide reacts with PPh3 in FC6H5 to afford a stable anionic phosphazide. When dissolved in tetrahydrofuran, the phosphazide is in equilibrium with free PPh3 and N3CB11Cl11–. Both the triazole and phosphazide are characterized by single-crystal X-ray diffraction, NMR and IR spectroscopy, and high-resolution mass spectrometry.