Disilylfluoronium ions - Synthesis, structure, and bonding

The synthesis of disilylfluoronium ions 4 with a naphthalene-1,8-diyl backbone via the corresponding arenium ions 3 is reported. The cations were isolated in the form of their [B(C₆F₅)₄] ^- salts. The borates 3[B(C₆F₅)₄] and 4[B(C₆F₅)₄] are active in catalytic hydrodefluorination reactions using fluorodecane as substrate. Methylphenyl-substituted arenium ions 3c,d undergo an interconversion reaction via a formal 1,3-methyl group migration at room temperature. This rearrangement was shown by DFT methods to proceed by a multiple-step sequence involving a methonium-like transition state. The NMR parameters for disilylfluoronium ions 4 indicate, in agreement with DFT calculations, the presence of a symmetric Si-F-Si linkage in these cations. QTAIM, NBO, and VB analyses reveal that the high ionic contributions to the bonding in the SiFSi moiety are responsible for the symmetric structures of these cations.