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, [(Me3 Si)3 E]+ (E=O, S), by reacting [Me3 Si-H-SiMe3 ][B(C6 F5 )4 ] and Me3 Si[CB] (CB- =carborate=[CHB11 H5 Cl6 ]- , [CHB11 Cl11 ]- ) with Me3 Si-E-SiMe3 . In the reaction of Me3 Si-O-SiMe3 with [Me3 Si-H-SiMe3 ][B(C6 F5 )4 ], a ligand exchange was observed in the [Me3 Si-H-SiMe3 ]+ cation leading to the surprising formation of the persilylated [(Me3 Si)2 (Me2 (H)Si)O]+ oxonium ion in a formal [Me2 (H)Si]+ instead of the desired [Me3 Si]+ transfer reaction. In contrast, the expected homoleptic persilylated [(Me3 Si)3 S]+ ion was formed and isolated as [B(C6 F5 )4 ]- and [CB]- salt, when Me3 Si-S-SiMe3 was treated with either [Me3 Si-H-SiMe3 ][B(C6 F5 )4 ] or Me3 Si[CB]. However, the addition of Me3 Si[CB] to Me3 Si-O-SiMe3 unexpectedly led to the release of Me4 Si with simultaneous formation of a cyclic dioxonium dication of the type [Me3 Si-μO-SiMe2 ]2 [CB]2 in an anion-mediated reaction. DFT studies on structure, bonding and thermodynamics of the [(Me3 Si)3 E]+ and [(Me3 Si)2 (Me2 (H)Si)E]+ ion formation are presented as well as mechanistic investigations on the template-driven transformation of the [(Me3 Si)3 E]+ ion into a cyclic dichalconium dication [Me3 Si-μE-SiMe2 ]2 2+ .