Stable [M2F11]– (M = Nb, Ta) Salts of Protonated 1,3-Dimethoxybenzene

The 3:1 molar reactions of MF5 (M = Nb, 1a; M = Ta, 1b) with 1,3-dimethoxybenzene in CHCl3 led to the formation of the arenium salts [2,4-(OMe)(2)C6H5][M2F11] (M = Nb, 3a; M = Ta, 3b) in good yields. The reactions took place with the intermediate formation of (MF5)(2)[(2)-1,3-(OMe)(2)C6H4] (M = Nb, 2a; M = Ta, 2b), followed by single-electron oxidation of the arene and production of MF4 (identified by means of EPR spectroscopy as the acetonitrile adduct). Compounds 3a and b were fully characterised both in solution (NMR) and in the solid-state (X-ray, IR and elemental analysis), while 2a and b were identified by NMR spectroscopy in CD2Cl2 solution. The reactions of 1,3-dimethoxybenzene with Ag[NbF6] or Ag[Sb2F11] in CD2Cl2/CHCl3 afforded [2,4-(OMe)(2)C6H5](+). It was found that 1,3-dimethoxybenzene was inert towards the addition of aqueous H[SbF6] under comparable experimental conditions.