The behavior of nonaqueous solutions of 1,3,5-tris[12-[[3-(ethylthio)propyl]dimethylsilyl]-1,12-dicarba-closo-dodecaboran-1-yl]benzene (2) and four simpler related compounds on a mercury electrode was studied by cyclic voltammetry and ac impedance measurements. It was established that 2 is attached to mercury in two different ways depending on the applied potential, while the interaction of the other compounds with the electrode is less pronounced. At relatively negative potentials 2 is weakly adsorbed at the electrode. At positive potentials a strongly adsorbing mercury ion complex of 2 is produced and forms a compact surface layer. The influence of the supporting electrolyte and the solvent has been examined.