Pyridinamide Ion Pairs: Design Principles for Super-Nucleophiles in Apolar Organic Solvents.

A comprehensive analytical protocol combining conductivity, diffusion-ordered NMR (DOSY), and photometric kinetic measurements is employed to analyze the nucleophilic reactivity of pyridinamide ion pairs in low-polarity organic solvents. The association patterns of these systems are found to strongly depend on cation size, with larger cations favoring the formation of cationic triple ion sandwich complexes together with free and highly nucleophilic anions. Kinetic studies using the ionic strength-controlled benzhydrylium method demonstrate that pyridinamide ions exhibit significantly higher nucleophilicities as compared to established organocatalysts, particularly in low-polarity solvents. Nucleophilicities are furthermore found to correlate well with Brønsted basicities measured in water and with Lewis basicities calculated in dichloromethane. Taken together, these findings provide quantitative guidelines for the future design of highly active Lewis base catalysts.