Controlled Reactivity of Viologens in Alkaline Solutions Via Cucurbit[7]uril Complexation

Abstract

A series of N‐alkyl‐ and N‐aryl‐viologens has been studied in alkaline solutions. In this work, we evaluated the deuteration rate of the viologens in D2O solutions of pH values ranging from 7.3 to 12.7. Kinetic experiments and computational calculations showed the high reactivity of H‐C(2) bonds toward deprotonation of N‐aryl‐pyridinium moieties compared to N‐alkyl‐pyridinium moieties, even in hybrid N‐aryl/N‐alkyl dissymmetric viologens. However this high H‐C(2) reactivity in liquid phase contrasted with the proton fragmentation mechanism observed in the gas phase by mass spectrometry. The H/D exchange rate of viologens in very strong alkaline conditions could be significantly reduced using cucurbit[7]uril (CB[7]) as supramolecular protecting group. Ultimately, CB[7] inclusion led to a selective protection of H‐C(2) group of N‐aryl‐pyridinium of dissymmetric viologens, and induced a supramolecular regioselective deuteration.