On Silylated Oxonium and Sulfonium Ions and Their Interaction with Weakly Coordinating Borate Anions

Attempts have been made to prepare salts with the labile tris(trimethylsilyl)chalconium ions, [(Me 3 Si) 3 E] + (E=O, S), by reacting [Me 3 Si‐H‐SiMe 3 ][B(C 6 F 5 ) 4 ] and Me 3 Si[CB] (CB − =carborate=[CHB 11 H 5 Cl 6 ] − , [CHB 11 Cl 11 ] − ) with Me 3 Si‐E‐SiMe 3 . In the reaction of Me 3 Si‐O‐SiMe 3 with [Me 3 Si‐H‐SiMe 3 ][B(C 6 F 5 ) 4 ], a ligand exchange was observed in the [Me 3 Si‐H‐SiMe 3 ] + cation leading to the surprising formation of the persilylated [(Me 3 Si) 2 (Me 2 (H)Si)O] + oxonium ion in a formal [Me 2 (H)Si] + instead of the desired [Me 3 Si] + transfer reaction. In contrast, the expected homoleptic persilylated [(Me 3 Si) 3 S] + ion was formed and isolated as [B(C 6 F 5 ) 4 ] − and [CB] − salt, when Me 3 Si‐S‐SiMe 3 was treated with either [Me 3 Si‐H‐SiMe 3 ][B(C 6 F 5 ) 4 ] or Me 3 Si[CB]. However, the addition of Me 3 Si[CB] to Me 3 Si‐O‐SiMe 3 unexpectedly led to the release of Me 4 Si with simultaneous formation of a cyclic dioxonium dication of the type [Me 3 Si‐μO‐SiMe 2 ] 2 [CB] 2 in an anion‐mediated reaction. DFT studies on structure, bonding and thermodynamics of the [(Me 3 Si) 3 E] + and [(Me 3 Si) 2 (Me 2 (H)Si)E] + ion formation are presented as well as mechanistic investigations on the template‐driven transformation of the [(Me 3 Si) 3 E] + ion into a cyclic dichalconium dication [Me 3 Si‐μE‐SiMe 2 ] 2 2+ .