of ketene silyl acetal in sharp contrast to the inertness of normal alkyltin halides like Bu2SnCl2. The increased Lewis acidity of the pentafluorophenyltin halides was proved by 119Sn- and 13C-NMR spectra. On the other hand, the pentafluorophenyl group reduced the reactivities of tin towards both nucleophiles and electrophiles. 19F-NMR spectroscopy was invoked to elucidate this anomaly.