The nature of fluoride transfer from complex fluoride anions to carbenium ions

Chemistry of fluoroalkyl cyanides

“…Nitrosonium hexafluorophosphate, NO + PF 6ˉ, was slightly more reactive than NO + BF 4ˉ towards 4-azidobutanenitrile yielding N20 (18%), N25 (72%), 28 (7%), and 29 (3%). 51 It was noted 51 that these results suggest that fluoride transfer from complex fluoride anions occurs through association of the developing Lewis acid with the basic nitrile group, as described in Scheme 21. The reactivities of nitrosonium salts with azidonitriles follow the order of Lewis acidities of the developing Lewis acids (SbF 5 >PF 5 >BF 3 ), and indicate a requirement for association of these developing acids with the nitrile group during nitrosation.…”

“…It was shown that azidonitriles 27 react with NO + BF 4ˉ to produce R F -nitriles N17,N14,N20-29 in nearly quantitative yields. 51 Results from the reactions of a series of azidonitriles 27 with NO + BF 4ˉ in CDCl 3 are given in Table 1. The nature of the reaction and the extent of rearrangement serve to classify this fluoride transfer process as involving carbenium ion intermediates.…”

“…The nature of the reaction and the extent of rearrangement serve to classify this fluoride transfer process as involving carbenium ion intermediates. 51 However, since fluoride substitution does not occur in similar reactions of NO + BF 4ˉ with monofunctional alkyl azides, the authors of the research suggested that fluoride transfer cannot be represented simply as an intermolecular reaction of the tetrafluoroborate anion with a carbenium ion. The nitrile group is involved in the fluoride transfer process in the suggested mechanism.…”

“…51 © AUTHOR Some amounts of H 2 O (1-2 equiv) added to the nitrosonium salt prior to the azidonitrile produced an observable increase in the rate of gas evolution but did not measurably affect the reaction products. 51 Treatment of 4-azidobutanenitrile (27a) with nitrosonium hexafluoroantimonate, NO + SbF 6ˉ, in deuterochloroform containing 1.0 equiv of H 2 O resulted in the product distribution given below (Scheme 20). 51 Scheme 20.…”

“…51 Treatment of 4-azidobutanenitrile (27a) with nitrosonium hexafluoroantimonate, NO + SbF 6ˉ, in deuterochloroform containing 1.0 equiv of H 2 O resulted in the product distribution given below (Scheme 20). 51 Scheme 20. Product distribution after treatment of 4-azidobutanenitrile (27a) with NO + SbF 6ˉ 4-Azidobutanenitrile (27a) reacted three-times slower with NO + BF 4ˉ to give N20 (32%), N23 (61%), 3butenenitrile (28) (6%), and 2-butenenitrile (29) (1%).…”