Synthesis, structural and toxicological investigations of quarternary phosphonium salts containing the P-bonded bioisosteric CH2F moiety

Abstract

Tertiary alkyl, aryl or amino phosphines PR₃ (R = Me, nBu, C₂H₄CN, NEt₂) and the bis[(2-diphenylphosphino)phenyl]ether (POP) were allowed to react with fluoroiodomethane to produce fluoromethyl phosphonium salts in yields between 60–99%. The compounds were characterized by vibrational and NMR spectroscopy and in most cases also by single crystal X-ray diffraction. Diphenyl(fluoromethyl) phosphine was synthesized as a mixed aryl–alkyl-phosphine and the TEP value (Tolman electronic parameter) was determined in order to explain its low reactivity. The molecular and crystal structures of the new fluoromethyl phosphonium salts [R₃PCH₂F]I with R = Me, C₂H₂CN and NEt₂ as well as of the salt resulting from the fluoromethylation of POP provided additional information on the structural behavior of the bioisoster CH₂F group bonded to phosphorus. Hydrogen bonding in the crystal is compared with that observed in the crystal structure of PPh₃CH₂FI. The toxicity of the sufficiently water soluble salt [Me₃PCH₂F]I was investigated and the toxicological effect of the CH₂F group was compared to that of the bioisoster CH₂OH group in THPS.