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.