Stable carbocations have been prepared at room temperature with benzene as solvent and tetrakis(pentafluorophenyl)borate (TPFPB) as anion by the addition of solvated triethylsilylium TPFPB or of tributylgermylium TPFPB to 1,1-diphenylethene. These carbocations are stabilized by σ conjugation with nonadjacent group 14 atoms and respectively constitute stable saturated β-silyl and β-germyl carbocations. NMR parameters, including the 29Si chemical shift, the 13C chemical shifts of the cationic, aryl, and methylene carbons, and the one-bond 13C−1H coupling constant of the methylene group adjacent to the group 14 element, define the distribution of positive charge between carbon and (through σ conjugation) silicon or germanium. The extent of hyperconjugation is estimated quantitatively by comparison with models. The NMR parameters indicate that the cations are open rather than bridged.
Available at: http://works.bepress.com/yan_zhao/43/