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.