Bis(amidophenolato)phosphonium: Si−H Hydride Abstraction and Phosphorus‐Ligand Cooperative Activation of C−C Multiple Bonds

The first bis(amidophenolato)phosphonium salts are prepared and fully characterized. The perfluorinated derivative represents the strongest monocationic phosphorus Lewis acid on the fluoride and hydride ion affinity scale isolable to date. This affinity enables new reactions, such as hydride abstraction from Et(3)SiH, the first phosphaalkoxylation of an alkyne or a phosphorus catalyzed intramolecular hydroarylation. All properties and reactions are scrutinized by theory and experiment. Substantial σ‐ and π‐acidity provides the required affinity for substrate activation, while phosphorus‐ligand cooperativity substantially enriches the reactivity portfolio of phosphonium ions.