Lewis Base-Induced Valence Tautomerism in a Phosphorus Cation Enables the Activation of Strong Element-Fluorine Bonds

Main-group compounds show drastic differences in properties and reactivity between their n and n+2 oxidation states. While this often precludes transition-metal mimetic redox catalysis, precise control over prevalent oxidation states in a switchable compound could offer promising avenues for main-group-mediated processes. We demonstrate that hypercoordination-induced valence tautomerism unlocks high effective Lewis acidity in a phosphorus cation. By employing a redox-non-innocent, pincer-coordinated phosphenium(+III) cation, we enable low-barrier inversion at phosphorus coupled with valence tautomerism. Counterintuitively, adding a neutral Lewis base does not quench the cation's electrophilicity; instead, it triggers valence tautomerism, generating a formal phosphorus(+V) cation. This hypercoordinated species exhibits enhanced reactivity and is capable of abstracting fluoride from stable inorganic anions like [SbF 6 ] -. Furthermore, in the presence of hydrosilanes, metal-free catalytic hydrodefluorination of fluoroalkanes is achieved.