Investigating the prevalence and role of crystalline intermediates in mechanochemical C–H bond activation by in-situ monitoring techniques

• Applicant: Privatdozentin Dr. Franziska Emmerling
• Subject Area: Solid State and Surface Chemistry, Material Synthesis ; Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546802390

Mechanochemical reactions by grinding, milling, twin-screw extrusion, and resonance acoustic mixing etc., offer methodological and environmental advantages for chemical synthesis, constantly attracting increasing attention within the scientific community and industry. In addition to sustainability advantages, the solventless reaction conditions under which mechanochemical transformations occur can facilitate the isolation of otherwise inaccessible products or permit the acceleration of chemical reactions. For example, mechanochemical metal mediated C–H activation and functionalization by ball milling have enabled the synthesis of elusive products and increased reaction yields. As a result, the superiority of mechanochemistry over more traditional approaches (e.g., solution, neat, and microwave) has been alluded to by some authors. However, limited knowledge exists regarding the mechanisms of C–H bond rupture and functionalization by mechanochemistry. This is precisely the goal of this collaborative project: to systematically investigate how mechanochemical C–H activation proceeds, to elucidate the origins of the superiority of ball milling C–H activation approach and translate such understanding into novel opportunities in catalysis and discover new mechanochemical reactions. To achieve this goal, we have decided to join forces and bring together our expertise on mechanochemical organic and organometallic synthesis (Prof. José G. Hernández, UdeA Colombia), and structural characterization and time-resolved in-situ monitoring of mechanochemical reactions (powder X-ray diffraction (PXRD), Raman spectroscopy, thermo-milling, and synchrotron studies, etc.) (Priv.-Doz. Dr. Franziska Emmerling, BAM Germany). If successful, the development of this project will enable in-situ experimental visualization of mechanochemical reactions and potentially the detection of the intermediates involved in the process, which until now have remained a formidable challenge. Preliminary work, by some of us in Colombia, has demonstrated that using [Cp*RhCl2]2 leads to the formation of cocrystals between the reactants prior to the C–H activation step, a sequence that differs from the process in solution. The presence of crystalline intermediates in completely different mechanochemical reactions has also been reported by some of us in Germany, through in-situ monitoring techniques. However, our independent observations correspond to punctual and isolated examples, thus a systematic study is required to determine the prevalence of crystalline intermediates in mechanochemical C–H activation, this is the motivation behind this collaborative research proposal.

• DFG Programme: Research Grants
• International Connection: Colombia
• Partner Organisation: Universidad de Antioquia
• Cooperation Partner: Professor José G. Hernández, Ph.D.