Chemistry of organosilicon compounds. 292. An NMR study of the formation of silyloxonium ions by using tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as counteranion

The capability of tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) as a counteranion for organosilicenium ions was investigated by NMR spectroscopy. Although reactions of hydrosilanes with trityl-TFPB did not give the corresponding silicenium ions as long-lived species in dichloromethane-d2, the reactions produced rather stable silyloxonium ions in the presence of ethers at low temperatures. The evidence for the formation of cyclic silyloxonium ions was obtained by monitoring thc reaction of 3-ethoxypropylsilanes with trityl-TFPB by NMR spectroscopy. The use of TFPB as a non-nucleophilic counteranion was crucial for the formation of the silyloxonium ions; silyl perchlorates did not show significant interaction with ethers.