Tetragonal phosphorus(v) cations as tunable and robust catalytic Lewis acids

Abstract

The synthesis and catalytic reactivity of a class of water-tolerant cationic phosphorus-based Lewis acids is reported. Corrole-based phosphorus(v) cations of the type [ArP(cor)][B(C[subscript 6]F[subscript 5])[subscript 4]] (Ar = C[subscript 6]H[subscript 5], 3,5-(CF[subscript 3])[subscript 2]C[subscript 6]H[subscript 3]; cor = 5,10,15-(C[subscript 6]H[subscript 5])[subscript 3]corrolato[superscript 3-], 5,10,15-(C[subscript 6]F[subscript 5])[subscript 3]corrolato[superscript 3-]) were synthesized and characterized by NMR and X-ray diffraction. The visible electronic absorption spectra of these cationic phosphacorroles depend strongly on the coordination environment at phosphorus, and their Lewis acidities are quantified by spectrophotometric titrations. DFT analyses establish that the character of the P-acceptor orbital comprises P-N antibonding interactions in the basal plane of the phosphacorrole. Consequently, the cationic phosphacorroles display unprecedented stability to water and alcohols while remaining highly active and robust Lewis acid catalysts for carbonyl hydrosilylation, C[subscript sp3]-H bond functionalization, and carbohydrate deoxygenation reactions.