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

We have designed and realized an efficient and operationally simple single-flask synthesis of imidodiphosphate-based Bronsted acids. The methodology proceeds via consecutive chloride substitutions of hexachlorobisphosphazonium salts, providing rapid access to imidodiphosphates (IDP), iminoimidodiphosphates (iIDP), and imidodiphosphorimidates (IDPi). These privileged acid catalysts feature a broad acidity range (pKa from similar to 11 to <2 in MeCN) and a readily tunable confined active site. Our approach enables access to previously elusive catalyst scaffolds with particularly high structural confinement, one of which catalyzes the first highly enantioselective (>95:5 er) sulfoxidation of methyl n-propyl sulfide. Furthermore, the methodology delivers a novel, rationally designed super acidic catalyst motif, imidodiphosphorbis(iminosulfonylimino)imidate (IDPii), the extreme reactivity of which exceeds commonly employed super-Bronsted acids, such as trifluoromethanesulfonic acid. The unique reactivity of one such IDPii catalyst has been demonstrated in the first alpha-methylation of a silyl ketene acetal with methanol as the electrophilic alkylating reagent.

Automated summary

A single-flask synthesis method for efficient Bronsted acids was developed, allowing for the rapid production of imidodiphosphate-based compounds. The catalysts exhibit high structural confinement and a wide acidity range, with one catalyst showing highly enantioselective sulfoxidation activity. Additionally, a novel super acidic catalyst motif, IDPii, was discovered, demonstrating extreme reactivity in the alpha-methylation reaction of a silyl ketene acetal with methanol.