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 synthesis of the arenium salts [2,4-(OMe)2C6H5][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)2C6H4] (M = Nb, 2a; M = Ta, 2b), followed by monoelectron oxidation of the arene and production of MF4 (identified via EPR as the acetonitrile adduct). Compounds 3a,b were fully characterized both in solution (NMR) and in the solid state (X-ray and elemental analysis), while 2a,b were recognized by NMR in CD2Cl2 solution. The reactions of 1,3-dimethoxybenzene with Ag[NbF6] or Ag[Sb2F11] in CD2Cl2/CHCl3 afforded [2,4-(OMe)2C6H5]+. 1,3-dimethoxybenzene was inert toward the addition of H[SbF6](aq) under comparable experimental conditions.