Abstract
A detailed synthetic and mechanistic study for the synthesis of phosphindolium salts from easy accessible (o-alkynylphenyl)phosphanes is reported. Mechanistic investigation indicates a fast protonation at phosphorus as evidenced by the isolation of the phosphonium intermediate, followed by a protophosphonylation reaction across the alkyne moiety. DFT calculations support our mechanistic proposal and indicate a reaction highly exergonic compared to our recently reported phosphinoauration. Photophysical measurements recorded fluorescence quantum yields up to 97% in solution for the phosphindolium core and fluorescence was observed in the solid state.