Electron-deficient cyclopropenium cations as Lewis acids in FLP chemistry

Abstract

Cyclopropenium cations incorporating electron deficient substituents are Lewis acidic despite the presence of π-electrons. The chloride and electron affinities are examined computationally and experimentally, respectively. These cations form classic Lewis acid-base adducts with PPh₃, while sterically demanding phosphines yield frustrated Lewis pairs (FLPs) which participate in FLP additions. Depending on the basicity of the phosphine used, addition to alkynes or alkyne deprotonation is observed. In either case, new C–C bonds are formed, thus extending the utility of the concept of FLP chemistry to these delocalized π-cations.