Phosphonium borate acids [HPPh2(C6F5)][B(C6F5)4] (2), [HPMes2(C6F5)][B(C6F5)4] (3) and [HPMes(C6F5)2][B(C6F5)4] (4) were synthesized via heterolytic dihydrogen cleavage in the presence of triisopropylsilylium and characterized by spectroscopic and crystallographic methods. Brønsted acid catalysis using compounds 2–4 proved to be efficient for a number of challenging reactions (namely ionic hydrogenation, hydroamination and hydroarylation), owing to the restrained nucleophilicity of the sterically hindered conjugate bases. Reactivity of compounds 2–4 suggests that their pKavalues are similar to that of diethyl oxonium acid. © 2016 Elsevier Ltd