Protonation of the polyhedral anion [closo-B10H10](2-) under superacidic conditions apparently generates an electrophilic intermediate, [B10H13](+), that forms 6-R-nido-B10H13 (R = aryl, alkyl, triflate) derivatives by electrophilic aromatic substitution, C-H bond activation, or ion-pair collapse, respectively. The proposed mechanism of formation of the 6-R-nido-B10H13 derivatives via the boranocation [B10H13](+) is discussed. The synthesis of carboranes, starting from 6-R-nido-B10H13 decaboranes, and single-crystal X-ray diffraction analyses of several 6-R-nido-B10H13 decaboranes and carboranes are described.