Chlorination of 1‑Carba-closo-dodecaborate and 1‑Ammonio-closo-dodecaborate Anions

Fully chlorinated carborate and dodecaborate cages such as [CHB11Cl11]− and [Me3NB12Cl11]− are prominent examples of valuable and chemically rather inert weakly coordinating anions. While both anions can be obtained by chlorination of the precursors [CH12B11]− and [H3NB12H11]− with SO2Cl2 followed by methylation for the synthesis of [Me3NB12Cl11]−, best results were found using photochemical chlorination with SO2Cl2 for [CH12B11]− and thermal chlorination with SO2Cl2 for [H3NB12H11]−. The hexachlorinated anion [n-Pr3NB12H5Cl6]− was formed readily within 30 min by chlorination of [n-Pr3NB12H11]−, but attempts to synthesize isopropyl-substituted ammonio-dodecaborates with a higher chlorination number resulted in the formation of mixtures and partial decomposition. The silver and trityl salts of the anions [CHB11Cl11]−, [Me3NB12Cl11]−, and [n-Pr3NB12H5Cl6]− as well as the contact ion-pair [Et2Al]­[Me3NB12Cl11] were also prepared, and the compounds [Ag­(NCMe)]­[Me3NB12Cl11], [Et2Al]­[Me3NB12Cl11], and [Et4N]­[i-Pr3NB12H5Cl6] were also characterized by X-ray crystallography.