New frustrated Lewis pair catalyzed addition reactions

• Applicant: Professor Dr. Jan Paradies
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 258396946

The coexistence of a Lewis-acidic and a Lewis-basic site in solution, which leaves the individual reactivity unquenched, was introduced as the phenomenon of a frustrated Lewis pair (FLP). This feature led to the metal-free hydrogen cleavage and later to the activation of other small molecules, e. g. carbon dioxide, carbon monoxide or nitro oxides. The hydrogenation is the most appealing reaction in FLP-chemistry to date due to the high significance in chemistry. On the one hand, the biggest gain of FLP-chemistry is its complementarity to transition metal-based hydrogenations. A number of substrates e. g. halide- or diazonium-containing molecules are incompatible with transition metal-catalyzed hydrogenations. For those, FLP-chemistry can advance to a powerful and complementary method in process and research chemistry. On the other hand, novel FLP-mediated bond-activations (C-H or C-Si) must be found to advance this concept to a more general level. The presented research program targets both central issues of FLP-chemistry: (1) The FLP-catalyzed hydrogenation will be advanced to a powerful tool for the hydrogenation of transition-metal incompatible substrates, e. g. halide-bearing compounds, azo-derivatives or diazonium salts. These compound classes are currently reduced by stoichiometric reaction with borohydrides, hydrazine or sodium sulfite, giving rise to large amounts of waste material and safety hazards. Here, the FLP-catalyzed hydrogenation is the key technology to circumvent these issues. (2) The FLP-chemistry will be extended to transfer reactions of X-Y fragments, e. g. C-H, N-H and C-Si bonds, across multiple bonds. In analogy to the H-H transfer to olefins metal-free hydroaminations, hydrotrifluoromethylations and silylcyanations of unsaturated compounds will open new aspects of FLP-catalyzed reactions. The common overlap of both approaches is the simultaneous modulation of electronic and steric properties of the borane-derived Lewis-acids. Thereby the Lewis-acid's reactivity can be tuned to the application. These developments will not only broaden the FLP's reactivity but will also permit higher functional group tolerance. This will also lead to significant stability improvements of the borane towards air and moisture affording powerful methods for organic synthesis.

• DFG Programme: Research Grants