A polymer‐supported ionic liquid (PSIL) system was reported to be a highly efficient catalyst in nucleophilic fluorination and other nucleophilic substitution reactions using metal salts. In this study we have prepared structurally modified PSIL systems and examined their catalytic activity in nucleophilic fluorination and other substitution reactions in dependence on the length of the alkyl chain linker, counteranion, and the ionic liquid loading in the resin. The PSIL system with a longer alkyl linker had better catalytic activity, and the PSIL system with tetrafluoroborate (BF4‐) as the counteranion showed the best catalytic activity among the other counteranions. The nucleophilic fluorination of 2‐(3‐methanesulfonyloxypropyl)naphthalene (2), as a model compound, with cesium fluoride in the presence of a 0.5 equivs. of an ionic liquid portion of PS[domim][BF4] (polymer‐supported 1‐n‐dodecyl‐3‐methylimidazolium tetrafluoroborate) was completed within 2.5 h, affording the fluoroalkane 3 (96 %). The PSIL system with a higher ionic loading as a catalyst produced a better fluorination, while the PSIL system with a lower loading produced a better bromination. In addition, these PSIL systems had good swelling properties in polar aprotic solvents such as DMF (7.2 mL/g), DMSO (6.5 mL/g) and acetonitrile (5.2 mL/g). Based on the swelling of PSIL, nucleophilic acetoxylation and fluorination reactions were carried out in four different solvents. It was found that the PSIL with a longer alkyl linker had superior catalytic activity due to the longer distance between the polystyrene backbone and ionic liquid portion. The PSIL system with tetrafluoroborate (BF4−) as the counteranion shows the best catalytic activity compared with PSIL systems with other counteranions. These PSIL systems absorb polar aprotic solvents and swell considerably, which is a favorable characteristic in new types of resins for other applications.
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Kim et al. (2006) studied this question.