C-F bond activation of trifluoroethanol and trifluoroacetic acid catalysed by the dimolybdate anion, [Mo2O6(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.