Metal-Free Peralkylation of the <i>closo</i>-Hexaborate Anion

The synthesis of fully alkylated closo-hexaborate dianions is reported. The reaction of [NBu4]­[B6H6Hfac], benzyl bromide, and triethylamine under microwave heating conditions affords persubstituted [NBu4]­[B6(CH2Ar)6Hfac] (Ar = C6H5, 4–Br-C6H4), which have been isolated and characterized by NMR spectroscopy, mass spectrometry, single-crystal X-ray diffraction, and other spectroscopic techniques. Electrochemical studies of these clusters reveal an irreversible one-electron oxidation, likely indicating degradative cage rupture. The observed metal-free alkylation is proposed to proceed as a consequence of the pronounced nucleophilic character of the hexaborate anion. This work represents the first example of a perfunctionalized hexaborate cluster featuring B–C bonds.