The Power of the Proton: From Superacidic Media to Superelectrophile Catalysis

摘要

Superacidic media became famous in connection with carbocations. Yet not all reactive intermediates can be generated, characterized, and eventually isolated from these Bronsted acid/Lewis acid cocktails. The counteranion, that is the conjugate base, in these systems is often too nucleophilic and/or engages in redox chemistry with the newly formed cation. The Bronsted acidity, especially superacidity, is in fact often not even crucial unless protonation of extremely weak bases needs to be achieved. Instead, it is the chemical robustness of the aforementioned counteranion that determines the success of the protolysis. The advent of molecular Bronsted superacids derived from weakly coordinating, redox-inactive counteranions that do withstand the enormous reactivity of superelectrophiles such as silicon cations completely changed the whole field. This Perspective summarizes general aspects of medium and molecular Bronsted acidity and shows how applications of molecular Bronsted superacids have advanced from stoichiometric reactions to catalytic processes involving protons and in situ generated superelectrophiles.