Azolium-based systems: application of an anion exchange resin (A- form) method and 1H NMR analysis of the charged-assisted (C–H)+•anion hydrogen bonds

Abstract

Dedicated to Prof. Rosa M. Claramunt on the occasion of her 65th birthday AbstractThe counteranion exchange of quaternary 1,2,3-triazolium salts was examined using a simple method that permitted halide ions to be swap for a variety of anions using an anion exchange resin (A¯ form). The method was applied to 1,2,3-triazolium-based ionic liquids and the iodideto-anion exchange proceeded in excellent to quantitative yields, concomitantly removing halide impurities. Additionally, an anion exchange resin (N 3¯ form) was used to obtain the benzyl azide from benzyl halide under mild reaction. Likewise, following a similar protocol, bis(azidomethyl)arenes were also synthesized in excellent yields. The results of a proton NMR spectroscopic study of simple azolium-based ion pairs are discussed, with attention focused on the significance of the charged-assisted (C-H) + ···anion hydrogen bonds of simple azolium systems such as 1-butyl-3-methylimidazolium and 1-benzyl-3-methyl-1,2,3-triazolium salts.

Synthesis of 2‐Aryl‐N‐(EWG‐methyl)‐N‐methylpyrrolidinium Salts as Precursors of Ylides Entering the [1,2] Stevens Rearrangement

“…It is well established that the chemical shifts of protons in ammonium salts depend on the counterion electron density. This phenomenon is confirmed by the literature data, [62][63][64][65][66][67][68][69][70][71][72][73] in particular by the examples of imidazole [66][67][68][69][70] and pyrrolidinium salts [70][71][72][73] (ionic liquids).…”

“…The examined anions can be ordered according to decreasing shielding ability: Br À , I À , CH 3 SO 4 À , CF 3 SO 3 À , BF 4 À , which is in accordance with the articles quoted. [62][63][64][65][66][67][68][69][70][71][72][73] In general, the greatest differences occur when changing tetrafluoroborate, methylsulfate or triflate with bromide or iodide and they are more noticeable in case of phenacyl salts [59] Table 5 summarizes differences between values of chemical shifts for protons of the methylene group N + CH 2 EWG for individual cis and trans isomers of salts 3 a and 3 d. The last column shows the respective differences for benzyl protons in individual salts 3 a and 3 d. The impact of the counterion change is stronger for phenacyl salts 3 d and for the methylene groups in trans isomers in both series of the analyzed salts. In case of pyrrolidinium salts, derivatives of (À )-menthol, the distances between two doublets from protons of methylene group connected to the quaternary nitrogen atom were compared.…”