Synthesis and characterization of fluorinated phosphonium ionic liquids

Abstract

A wide variety of phosphonium ionic liquids containing fluorous ponytails R_fn (R_fn = –(CF₂)_n–1CF₃; n = 4, 6, 10) are synthesized by the reaction of R_fn-(CH₂)₂-I with trialkylphosphines (R₃P; R = Me, ⁿBu, ⁿOct). The efficacy of multiple metathetical routes to anion exchange have been investigated, thus the corresponding BF₄^–, PF₆^–, tosylate (OTs^–) and triflate (OTf^–) derivatives have also been prepared. All compounds have been comprehensively characterized by multinuclear NMR spectroscopy, ESI-MS, DSC, and TGA/SDTA, and in the case of [Me₃PCH₂CH₂R_f4][I] by single crystal X-ray diffraction. These materials range from high melting solids (e.g., [Me₃P(CH₂)₂R_f4][I] T_m = 195 °C) to very low melting liquids (e.g., [ⁿOct₃P(CH₂)₂R_f4][OTf] T_g = –64 °C), and they all have high thermal decomposition points (295 to 394 °C). Incorporation of the more weakly coordinating BF₄^– and PF₆^– yielded a significant increase in the melting point of the materials, in contrast to OTf^– and OTs^– derivatives, which all exhibited significantly depressed melting points.Key words: phosphonium ionic liquids, alternative solvents, fluorine, phosphorus, fluorous ponytails.