Syntheses and Properties of Fluorous Quaternary Phosphonium Salts that Bear Four Ponytails; New Candidates for Phase Transfer Catalysts and Ionic Liquids

Abstract

AbstractThe fluorous tertiary phosphine [Rf6(CH2)2]3P [Rfn=CF3(CF2)n−1] and excess PhCH2Br, CH3(CH2)3OSO2CF3, or Rf6(CH2)2OSO2CF3 react (CF3C6H5, 45–110 °C) to give the phosphonium salts (PhCH2)[Rf6(CH2)2]3P+ Br− (2, 71 %), [CH3(CH2)3][Rf6(CH2)2]3P+ CF3SO3− (3, 65 %), or [Rf6(CH2)2]4P+ CF3SO3− (4, 83 %). The phosphines [Rf6(CH2)2]2[Rf8(CH2)2]P and [Rf8(CH2)2]3P are similarly elaborated with Rf6(CH2)2I, Rf8(CH2)2I, or Rf8(CH2)2Br (DMF, 115 °C) to [Rf8(CH2)2]4‐x[Rf6(CH2)2]xP+ I− (x=3, 7; 2, 8; 1, 9; 0, 10) or [Rf8(CH2)2]4P+ Br− (80–60 %). The salts exhibit melting points between 110 °C and 43 °C, with lower values favored by less symmetrical cations, Rf6 segments, and triflate and bromide anions. Solubilities decrease in the solvent sequence CF3C6F5 (all salts at least moderately soluble, room temperature)>acetone>THF>CF3C6H5>CF3C6F11>CH3C6H5, Et2O, CH2Cl2, hexane (all salts insoluble at elevated temperatures); some appreciably increase upon heating. Partition coefficients are very biased towards fluorous phases (>93:<7). The salts can be quite efficient at extracting picrate from water into CF3C6F5 (97–86 % for 2, 4, 9, 10) or CF3C6H5 (85–66 % for 2‐4), demonstrating their potential for phase transfer catalysis. A CF3C6F5 solution of Rf8(CH2)3I and aqueous NaCl react at 100 °C in the presence (but not the absence) of 9 to give Rf8(CH2)3Cl.