The aryltellurenyl cation [2-(tBuNCH)C6 H4 Te]+ , a Lewis super acid, and the weakly coordinating carborane anion [CB11 H12 ]- , an extremely weak Brønsted acid (pKa =131.0 in MeCN), form an isolable ion pair complex [2-(tBuNCH)C6 H4 Te][CB11 H12 ], in which the Brønsted acidity (pKa 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)C6 H4 Te(CB11 H11 )] in ratios ranging from 62 : 38 to 80 : 20.

Department of General and Inorganic Chemistry University of Pardubice Studentská 573 532 10 Pardubice Czech Republic

Faculty of Science University of Hradec Králové Rokitanského 62 500 03 Hradec Králové 3 Czech Republic

G A Razuvaev Institute of Organometallic Chemistry RAS 49 Tropinin St 603950 Nizhny Novgorod Russian Federation

Institut für Anorganische Chemie und Kristallographie Universität Bremen Leobener Straße 7 28359 Bremen Germany

Institut für Experimentalphysik Freie Universität Berlin Arnimallee 14 14195 Berlin Germany

Institute of Inorganic Chemistry Czech Academy of Sciences 250 68 Řež near Prague Czech Republic

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