Sterically congested phosphonium borate acids as effective Brønsted acid catalysts

Phosphonium botate acids were synthesized via heterolytic dihydrogen cleavage in the presence of triisopropylsilylium and characterized by spectroscopic and crystallographic methods. Brønsted acid catalysis using these prepared compounds proved to be efficient for a number of challenging reactions owing to the restrained nucleophilicity of the sterically hindered conjugate bases.