The Ion‐Like Supersilylium Compound t Bu 3 Si–F–Al[OC(CF 3 ) 3 ] 3

The ion‐like silylium compounds t Bu 3 Si–F–Al[OC(CF 3 ) 3 ] 3 and Me 3 Si–F–Al[OC(CF 3 ) 3 ] 3 were prepared by degradation of the halonium salts [R 3 Si–X–SiR 3 ][Al{OC(CF 3 ) 3 } 4 ] { 1a (X): R = t Bu, 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 R 3 SiX (R = Me, t Bu) and [Ag][Al{OC(CF 3 ) 3 } 4 ] in dichloromethane at –50 °C. However, the related fluoronium and chloronium salts, [R 3 Si–X–SiR 3 ][Al{OC(CF 3 ) 3 } 4 ] { 1a (X): R = t Bu, X = F, Cl; 1b (X): R = Me, X = F, Cl}, could not be generated under these conditions. Generally, at low temperatures (< –50 °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 R 3 SiX (R = Me, t Bu; X = Br, I) elimination to form the highly reactive silyl cations [R 3 Si] + (R = Me, t Bu). 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 [R 3 Si] + reacted with dichloromethane, forming 1a (Cl) as well as 1b (Cl); (2) the silylium cations [R 3 Si] + degraded the counteranion to give t Bu 3 Si–F–Al[OC(CF 3 ) 3 ] 3 and Me 3 Si–F–Al[OC(CF 3 ) 3 ] 3 along with epoxide C 4 F 8 O. Both ion‐like silylium compounds could be isolated, and single crystals of t Bu 3 Si–F–Al[OC(CF 3 ) 3 ] 3 (orthorhombic, Pnma ) as well as Me 3 Si–F–Al[OC(CF 3 ) 3 ] 3 (orthorhombic, P 2 1 2 1 2 1 ) were grown from dichloromethane at room temp. Supersilylium [ t Bu 3 Si] + has higher Lewis acidity than [Me 3 Si] + , as demonstrated by the reaction of 1a (I) with Me 3 SiF. Thereby the fluoronium ion 1b (F), along with t Bu 3 SiF and t Bu 3 SiI, was formed.