A team led by the UniSysCat researchers Martin Oestreich and Martin Kaupp has succeeded in producing very special catalysts, so-called Lewis superacids, which are capable of breaking strong chemical bonds and significantly accelerating chemical reactions. For the first time, they synthesized halogen-substituted silicon cations – compounds, which are among the strongest Lewis acids ever isolated. These new powerful catalysts are of great interest in green chemistry and recycling, for example for the decomposition of per- and polyfluoroalkyl substances (PFAS), also known as „forever chemicals“.
Lewis acids are chemical compounds that bind electron pairs. Because of this property, they are often used to accelerate chemical reactions. Lewis superacids can even break the strongest chemical bonds. However, they are so incredibly reactive that they are extremely difficult to produce and handle.
Silicon-containing cations are known for their strong Lewis acidity and their ability to promote reactions that are not easily accessible with traditional catalysts, making them promising tools for advancing synthetic chemistry. Until now, the newly developed halogen-substituted silicon cations have so far only been the subject of theoretical and gas-phase studies. The group of Martin Oestreich at TU Berlin, which specializes on the synthesis of silicon-based catalysts, has now succeeded for the first time in producing these new compounds in the condensed phase - using protolysis instead of hydride transfer, which is the conventional and in this case unsuitable synthesis route.
The researchers characterized the new catalysts using NMR spectroscopy and X-ray crystallography. DFT calculations by the group of Martin Kaupp support the understanding of the stabilization of the new superacids. An evaluation of the Lewis acidity based on experimental and calculated fluoride-ion affinities confirms that the halogen-substituted silicon cations are among the strongest Lewis acids ever synthesized.
The introduction of the new route for synthesizing exceptionally reactive silicon-based Lewis acids opens the door to a new promising and unexplored reactivity in catalysis. We are looking forward to the application of the new super reactive catalysts in green chemistry.
This study has been published in Nature Chemistry: Tobias Randt, Morten Lehmann, Elisabeth Irran, Martin Kaupp, Hendrik F. T. Klare, and Martin Oestreich, Isolation of halogen-substituted silylium ions, Nature Chemistry https://doi.org/10.1038/s41557-025-01880-2