Synthesis and Structure of the First Bridgehead Silylium Ion

We report the first successful synthesis of the long-sought arene-solvated bridgehead silylium ion [Si4Me3(CH2)6]­[CHB11Cl11] by hydride abstraction from the tetrasilaadamantyl derivative HSi4Me3(CH2)6 with the trityl salt [Ph3C]­[CHB11Cl11] in toluene, benzene, or bromobenzene solution. The silylium···arene complex was characterized by X-ray diffraction analysis and by NMR spectroscopy and was studied computationally. NMR studies show that the silylium species undergoes a dynamic solvate exchange in BrPh/MePh mixed solvent.