Cyclic (Amino)(Aryl)Nitrenium Cations with Lewis Acidity Controlled by Remote Substituents

Abstract

Comprehensive SummaryN‐Heterocyclic nitrogen Lewis acids are important in synthetic chemistry. Stable cyclic (amino)(aryl)nitrenium cations, cyc‐1+—cyc‐3+, were synthesized by chemical oxidation of aryl azo compounds with different substituents, iPr, H and I, at the para positions of the phenyl group. The excited triplet states of cyc‐1+—cyc‐3+ abstract H‐atoms step by step to generate radical intermediates cyc‐1H•+—cyc‐3H•+ traced by EPR spectroscopy and products cyc‐1H2+—cyc‐3H2+ characterized by single crystal X‐ray diffraction. The Lewis acidity of species cyc‐1+—cyc‐3+ are remote substituent‐dependent. Cyc‐2+—cyc‐3+ have much higher acidity than those previously reported congeners based on energies of LUMOs. The electrophilicity enables them to form Lewis adducts with neutral Lewis base Me3P, and to gain one‐electron to produce neutral radicals cyc‐1•—cyc‐3•.