Calix[4]pyrrolato Stibenium: Lewis Superacidity by Antimony(III)-Antimony(V) Electromerism.

Lewis superacids enable the activation of highly inert substrates. However, the permanent presence of a Lewis superacidic center comes along with a constantly increased intolerance toward functional groups or ambient conditions. Herein, we describe a strategy to unleash Lewis superacidity by electromerism. Experimental and computational results indicate that coordinating a Lewis base to Δ-calix[4]pyrrolato-antimony(III) triggers a ligand redox-noninnocent coupled transfer into antimony(V)-state that exhibits Lewis superacidic features. Lewis acidity by electromerism establishes a concept of potential generality for powerful yet robust reagents and on-site substrate activation approaches.