The Ion-Like Supersilylium Compound tBu3Si-F-Al[OC(CF3)3]3

The ion-like silylium compounds tBu(3)Si-F-Al[OC(CF3)(3)](3) and Me3Si-F-Al[OC(CF3)(3)](3) were prepared by degradation of the halonium salts [R3Si-X-SiR3][Al{OC(CF3)(3)}(4)] {1a(X): R = tBu, X = Br, I; 1b(X): R = Me, X = Br, I}. The bromonium and iodonium salts 1a(Br), 1a(I), 1b(Br), and 1b(I) were quantitatively obtained from R3SiX (R = Me, tBu) and [Ag][Al{OC(CF3)(3)}(4)] in dichloromethane at -50 degrees C. However, the related fluoronium and chloronium salts, [R3Si-X-SiR3][Al{OC(CF3)(3)}(4)] {1a(X): R = tBu, X = F, Cl; 1b(X): R = Me, X = F, Cl}, could not be generated under these conditions. Generally, at low temperatures (< -50 degrees C) the halonium salts 1a(Br), 1a(I), 1b(Br), and 1b(I) are stable compounds. However, at higher temperatures 1a(Br), 1a(I), 1b(Br), and 1b(I) undergo R3SiX (R = Me, tBu; X = Br, I) elimination to form the highly reactive silyl cations [R3Si](+) (R = Me, tBu). Two different decomposition pathways were observed in the thermolysis of halonium compounds 1a(Br), 1a(I), 1b(Br), and 1b(I): (1) the silylium cations [R3Si](+) reacted with dichloromethane, forming 1a(Cl) as well as 1b(Cl); (2) the silylium cations [R3Si](+) degraded the counteranion to give tBu(3)Si-F-Al[OC(CF3)(3)](3) and Me3Si-F-Al[OC(CF3)(3)](3) along with epoxide C4F8O. Both ion-like silylium compounds could be isolated, and single crystals of tBu(3)Si-F-Al[OC(CF3)(3)](3) (orthorhombic, Pnma) as well as Me3Si-F-Al[OC(CF3)(3)](3) (orthorhombic, P2(1)2(1)2(1)) were grown from dichloromethane at room temp. Supersilylium [tBu(3)Si](+) has higher Lewis acidity than [Me3Si](+), as demonstrated by the reaction of 1a(I) with Me3SiF. Thereby the fluoronium ion 1b(F), along with tBu(3)SiF and tBu(3)SiI, was formed.