Anions [B12Cl11NH3]– and [B12Cl11OH]2– were prepared in high yields from the known precursors [B12H11NH3]– and [B12H11OH]2– by using SO2Cl2. Reaction monitoring by 11B NMR spectroscopy and ESI‐mass spectrometry indicated that SO2Cl2 serves as a convenient chlorination reagent in both transformations. This chemical is an alternative to SbCl5 or chlorine gas, which have been used in reported procedures. [B12Cl11NMe3]– was prepared in 92 % overall yield from [B12H11NH3]– salts without isolation of the unmethylated intermediate. Starting from [B12Cl11OH]2–, [B12Cl11OS(O)CF3]2– was obtained unexpectedly by using Tf2O in pyridine/CH2Cl2 by a rare reduction process, while [B12Cl11OTs]2– was synthesized by using TsCl in pyridine. All compounds were fully characterized by NMR and IR spectroscopy and ESI‐mass spectrometry. [Ag(MeCN)4][B12Cl11NH3], [Et4N][B12Cl11NH3], [Me4N]2[B12Cl11OH], [Et3NH][Cs][B12Cl11OH], [Ph3PMe]2[B12Cl11OS(O)CF3], and [MePPh3]2[B12Cl11OTs] were studied by X‐ray diffraction.