Harnessing the Lewis Superacidity of Halosilylium Ions: Access to Heteroleptic Silylium Ions without Substituent Redistribution by Halide Abstraction from Halosilanes

• Applicant: Professor Dr. Martin Oestreich
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation ; Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 578037472

The project's ultimate goal is the elaboration of a general method for the synthesis of counteranion-stabilized, heteroleptic silylium ions. Established ways of generating silylium ions typically afford homoleptic silylium ions even when starting from precursors decorated with at least two different aryl/alkyl groups at the silicon atom. The reason behind this phenomenon is substituent scrambling, eventually leading selectively to tertiary silylium ions with three identical aryl and alkyl substituents, respectively. Our laboratory recently discovered that such substituent exchange processes do not occur when previously elusive halogen-substituted silylium ions are involved as reactants. Moreover, these superhalophilic halogen-substituted silylium ions have been found to enable halide abstraction from halosilanes, a deceptively simple but until today unsuccessful route to silylium ions. Based in these findings, the research project aims at (1) the development of a halide-abstraction protocol that (2) proceeds without substituent scrambling, thereby allowing for the first time the preparation of essentially any heteroleptic silylium-ion motif from common halosilanes. Unlike the traditional hydride transfer and protolysis methods, the new technique will open the door to a broad range of counteranion-stabilized, acyclic and cyclic silylium ions with substitution patterns of interest. As part of this study, the synthesis of silylium ions with (per)halogenated aryl substituents will also be targeted, eventually arriving at the unknown tris(pentafluorophenyl)silylium ion as the higher homolog of the corresponding perfluorinated trityl cation and as an isolobal congener of tris(pentafluorophenyl)borane. Application to the synthesis of further “delicate” silylium ions will also be tackled.

• DFG Programme: Research Grants