Ishikawa's Reagent – a Valuable Source for Fluoroorganic Iminium Salts

Abstract

We herein report on iminium salts derived from Ishikawa's reagent Et2N-CF2-CHF-CF3. The reaction with P(C2F5)3F2 afforded [Et2N=CF-CHF-CF3][P(C2F5)3F3] as an ionic liquid. The fluorine atom in the cation in α position to the nitrogen atom is labile towards nucleophilic substitution as demonstrated by the reaction with SnCl2 where an exchange of the fluorine by a chlorine atom took place. Upon contact with water the fluorine atom is substituted by a hydroxyl group. The reaction of Ishikawa's reagent with P(C2F5)2F afforded the zwitterionic [P(C2F5)2F3{C(NEt2)(CHF-CF3)}]. Most likely [Et2N=CF-CHF-CF3][P(C2F5)2F2] was formed transiently. The anion is obviously sufficiently nucleophilic to attack the susceptible α-fluorine atom of the cation. During several months Ishikawa's reagent loses hydrogen fluoride, which reacts with glass producing SiF4 which abstracts a fluoride ion from Ishikawa's reagent affording [Et2N=CF-CHF-CF3][SiF5].