Stabilization of sp‐Hybridized Nitrogen Cation by Lewis Acid‐Base Complex Formation with Intramolecular Iodine

Abstract

AbstractHere we show that the sp‐hybridized nitrogen cation is strongly stabilized by a peri‐iodine substituent in the tetralone system. The cation is captured by anionic species such as CF3CO2−, affording hypervalent iodine(III) compounds with a short nitrogen‐iodine (N−I) bond, in which the cation serves as a Lewis acid. Notably, the O−I bond of the O‐trifluoroacetate or O‐acetate is intrinsically weaker than the N−I bond due to its more ionic character and is further weakened by protonation in trifluoroacetic acid. As a result, the oxygen ligand can dissociate in the presence of a Brønsted acid, affording a I+ cation intermediate that retains the N−I bond. We isolated the cation as the tetrafluoroborate, and characterized it experimentally by 1H NMR spectroscopy and X‐ray structure analysis, and theoretically by means of DFT calculation. The results suggest that the N−I bonded cation is intrinsically stable, and is weakly coordinated with water and the BF4 counter anion or trifluoroacetate anion. This cation can be employed as a reagent for α‐oxidation of ketones.