Exploring the potential of mechanochemistry in solid-state Frustrated Lewis Pair (FLP) chemistry

• Applicants: Professor Dr. Carsten Bolm; Professor Dr. Thomas Wiegand
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 568673451

The chemistry of Frustrated Lewis Pairs (FLPs) has attracted much interest in the past years and is still of high importance. In particular, solid-state FLP reactions have been reported recently with applications in the field of heterogeneous catalysis. Herein, we propose to combine the fields of mechanochemistry with the one of solid-state FLP chemistry. This innovative combination will enable us to prepare highly active phosphane/borane solid-state FLPs, in which mechanochemical grinding of the FLP entities will lead to a maximal interaction interface between such phases. The properties of those activated FLPs will be explored, for instance, in the use of unique ball-milling vessels in which in-situ insertions, trapping, and activation of CO2 will be performed. CO2 capture is currently intensively discussed in the context of climate protection and in using CO2 as a feedstock in chemical synthesis for value added products. The mechanochemical FLP chemistry shall then be extended to (catalytic) hydrogenations and the use of gas mixtures such as CO2 and H2. In the long run, reactions with N2 and N-H-bond activations can be addressed too. The development of novel milling jars shall allow for an efficient in-situ hydrogenation of FLPs under mechanochemical energy input. Furthermore, the concepts will be expanded to solid-state FLP chemistry in resonant-acoustic mixing (RAM) devices. As the central analytic tool solid-state NMR will be used to characterize the reaction products taken from the milling device, without any further post processing of the material. In particular, 11B MAS NMR and the therein manifested quadrupolar-coupling information will serve as a highly sensitive probe to follow the success of FLP reactions such as hydrogenations or CO2 insertion. Proton- and fluorine-detected NMR under fast MAS conditions (MAS frequencies > 100 kHz) will be complementary applied for structural analysis. In addition, internuclear distance measurements (e.g., between the phosphorus Lewis base and the boron Lewis acid or between the phosphorus Lewis bases) will enable further structural insights into the mechanochemically-synthesized FLPs as well as their reaction products as a function of mechanochemical reaction conditions. By using 13C-labelled CO2 as reaction gas, carbon-13 isotope labelling of the CO2-insertion reactions will be achieved enabling further product characterization by heteronuclear distance measurements.

• DFG Programme: Research Grants