C–F bond activation of trifluoroethanol and trifluoroacetic acid catalysed by the dimolybdate anion,[Mo 2 O 6 (F)] − †

Abstract

Two gas-phase catalytic cycles involving C–F bond activation of trifluoroethanol and trifluoroacetic acid were detected by multistage mass spectrometry experiments. A binuclear dimolybdate centre [Mo₂O₆(F)]⁻ acts as the catalyst in each cycle. The first cycle, entered via the reaction of [Mo₂O₆(OH)]⁻ with trifluoroethanol and elimination of water to form [Mo₂O₆(OCH₂CF₃)]⁻, proceeds via four steps: (1) oxidation of the alkoxo ligand and its elimination as aldehyde; (2) reaction of [Mo₂O₅(OH)]⁻ with trifluoroethanol and elimination of water to form [Mo₂O₅(OCH₂CF₃)]; (3) decomposition of the alkoxo ligand via loss of 1,1 difluoroethene; and (4) reaction of [Mo₂O₆(F)]⁻ with a second equivalent of trifluoroethanol to regenerate Mo₂O₆(OCH₂CF₃)]⁻. Steps (2) and (3) do not occur at room temperature and require collisional activation to proceed. The second cycle is entered via the reaction of [Mo₂O₆(OH)]⁻ with trifluoroacetic acid and elimination of water to form [Mo₂O₆(O₂CCF₃)]⁻ and involves two steps only: (1) fluoride transfer to a molybdenum centre to form [Mo₂O₆(F)]⁻; (2) reaction of [Mo₂O₆(F)]⁻ with trifluoroacetic acid and loss of water to regenerate [Mo₂O₆(O₂CCF₃)]⁻. Comparisons are made with the chemistry of [Mo₂O₆(OH)]⁻ reacting with acetic acid.

Keywords

Dimolybdate trifluoroethanol trifluoroacetic acid C–F bond activation gas-phase mass spectrometry

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