The hydrogen-bridged disilyl cation 6 with an 1,8-naphthalenediyl backbone was synthesized and was characterized by NMR spectroscopy and X-ray crystallography, supported by quantum mechanical computations. The SiHSi linkage is symmetrical, corresponding to a single minimum potential, and the structural parameters are in agreement with the presence of a two electron-three center bond in 6. Treatment of disilyl cation 6 with alkyl fluorides yields the disilylfluoronium ion 10. The SiFSi group in the disilyl fluoronium ion 10 is symmetrical with an average SiF bond length of 175.9(8) and a bent angle beta = 130 degrees. Both cations catalyze the hydrodefluorination reaction of alkyl and benzyl fluorides to give alkanes.