Synthesis and characterization of fluorinated phosphonium ionic liquids

Abstract

A wide variety of phosphonium ionic liquids containing fluorous ponytails Rfn (Rfn = –(CF2)n–1CF3; n = 4, 6, 10) are synthesized by the reaction of Rfn-(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 [Me3PCH2CH2Rf4][I] by single crystal X-ray diffraction. These materials range from high melting solids (e.g., [Me3P(CH2)2Rf4][I] Tm = 195 °C) to very low melting liquids (e.g., [nOct3P(CH2)2Rf4][OTf] Tg = –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.