Lewis Superacidic Tellurenyl Cation-Induced Electrophilic Activation of an Inert Carborane.

The aryltellurenyl cation [2-(tBuNCH)C H Te] , a Lewis super acid, and the weakly coordinating carborane anion [CB H ] , an extremely weak Brønsted acid (pK =131.0 in MeCN), form an isolable ion pair complex [2-(tBuNCH)C H Te][CB H ], in which the Brønsted acidity (pK 7.4 in MeCN) of the formally hydridic B-H bonds is dramatically increased by more than 120 orders of magnitude. The electrophilic activation of B-H bonds in the carborane moiety gives rise to a proton transfer from boron to nitrogen at slightly elevated temperatures, as rationalized by the isolation of a mixture of the zwitterionic isomers 12- and 7-[2-(tBuN{H}CH)C H Te(CB H )] in ratios ranging from 62 : 38 to 80 : 20.