Reaction of dihydrogen and the borinium cation salt [Mes(2)B][B(C6F5)(4)] gave an arene-stabilized mesityl-borenium cation, which isotopically scrambles HD. Similarly, reaction with triethylsilane gave the diboranium cation [MesB(mu-H)(2)(mu-Mes)BMes](+) featuring three bridge-bonds between two boron centers. Reaction of same (Mes(2)BH)(2) with Bronsted acid also afforded the same diboranium whereas the corresponding reaction with (MesBH(2))(2) yielded the triboron cation [H2B(mu-H)(mu-Mes)B(mu-Mes)(mu-H)BH2](+).