Unified Approach to Imidodiphosphate-Type Brønsted Acids with Tunable Confinement and Acidity.

We have designed and realized an efficient and operationally simple single-flask synthesis of imidodiphosphate-based Brønsted acids. The methodology proceeds consecutive chloride substitutions of hexachlorobisphosphazonium salts, providing rapid access to imidodiphosphates (IDP), iminoimidodiphosphates (IDP), and imidodiphosphorimidates (IDPi). These privileged acid catalysts feature a broad acidity range (p from ∼11 to <2 in MeCN) and a readily tunable confined active site.