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⁺ .