Periodic Reporting for period 2 - Mechanocat (Using milling balls as catalysts – Understanding the novel concept of direct mechanocatalysis)
Berichtszeitraum: 2022-05-01 bis 2023-10-31
The project Mechanocat develops a novel concept of catalysis neither utilizing light, thermal heating nor an electric potential as in conventional catalysis, but simply mechanical energy. In this mechanochemical approach denoted as “direct mechanocatalysis”, mechanical energy is provided by the collision of milling balls inside a ball mill. The catalyst is neither dissolved (as in homogenous catalysis), nor a powder or bed of shaped bodies (as in heterogeneous catalysis), but the milling ball itself. In this project we study how even in the absence of any solvent, solid reactants can be brought into reactions mechanocatalytically - only using milling balls that refresh their catalytically active surface constantly during their continuous collisions. We showcase this concept for a type of reactions that is commonly in the hand of homogeneous catalysis – C-C-cross coupling reactions catalysed by Pd, Cu or Ni. Understanding this novel concept involves 1) identifying reactions and reactants that can be applied to direct mechanocatalysis, 2) elaborating how mechanochemical reaction parameters such as milling speed, ball size and ball roughness replace common reaction parameters such as concentration or type of solvent and 3) elucidating the underlying mechanisms by employing in situ characterization techniques that allow for the monitoring of the reaction directly inside the moving milling vessels.
We believe direct mechanocatalysis to be ground-breaking as it involves reactants that can hardly be brought into reaction via conventional approaches because of low solubility or limited stability in solution. Our solid-state approach will be fundamentally different from the conventional solution-based procedures, and we foresee new reactions to be possible. This approach is highly sustainable as it makes the use of any solvent obsolete and may develop to a new type of catalysis due to the exceptionally facile catalyst separation after synthesis; simply taking the milling ball out of the vessel.
We believe direct mechanocatalysis to be ground-breaking as it involves reactants that can hardly be brought into reaction via conventional approaches because of low solubility or limited stability in solution. Our solid-state approach will be fundamentally different from the conventional solution-based procedures, and we foresee new reactions to be possible. This approach is highly sustainable as it makes the use of any solvent obsolete and may develop to a new type of catalysis due to the exceptionally facile catalyst separation after synthesis; simply taking the milling ball out of the vessel.
Until now we were successful to conduct four important cross-coupling reactions under direct mechanocatalytic conditions – Suzuki-, Sonogashira-, Heck-, and Glaser-coupling. Moreover, we developed a coating concept which allowed us to coat thin catalyst layers onto the surfaces of cheap steel milling balls and vessels, thus even lowering the amount of necessary catalyst greatly. We developed strong in situ characterization techniques, which not only proved our major hypothesis that the catalysis is indeed proceeding on the surface of the milling ball, but also have revealed the underlying reaction mechanism, which appeared to be different to conventional solvent-based reaction mechanisms.
We developed two new methodologies that go beyond the state of the art: Firstly, we established the concept of "Direct Mechanocatalysis" where catalytic reactions are carried out in ball mills utilizing the milling ball itself as the catalyst. This innovative approach offers several advantages, including the potential for near-infinite catalyst reuse and the elimination of ligands and solvents from the reaction system. By harnessing the catalytic properties of the milling ball, direct mechanocatalysis represents a significant advancement in catalytic methodologies.
Secondly, we developed a methodology for Coating of Milling Equipment. - The introduction of this technique proved to be a gamechanger in the field. By applying a thin layer of a catalytically active material onto cheap steel milling balls, the catalytic activity remains unchanged while significantly reducing costs. This breakthrough not only enables more cost-effective catalytic processes but also extends the applicability of the method. Complex structures, such as milling vessels, can now be made catalytically active through the coating process, further expanding the range of potential applications and catalytic transformations.
Secondly, we developed a methodology for Coating of Milling Equipment. - The introduction of this technique proved to be a gamechanger in the field. By applying a thin layer of a catalytically active material onto cheap steel milling balls, the catalytic activity remains unchanged while significantly reducing costs. This breakthrough not only enables more cost-effective catalytic processes but also extends the applicability of the method. Complex structures, such as milling vessels, can now be made catalytically active through the coating process, further expanding the range of potential applications and catalytic transformations.