Direct Mechanocatalysis without Milling Media – From Mixer Mills to Resonant Accoustic Mixers

Here we describe the development of a sustainable and cost-effective approach for catalytic cross-coupling reactions in mechanochemistry. It is found that the substrate's impact with the vessel wall alone is sufficient to initiate the reaction, indicating that milling balls primarily serve as mixing agents rather than energy carriers. The absence of milling balls can be offset by adjusting the rheology using liquid-assisted grinding (LAG). The η-sweet spot of 0.25 μl/mg is confirmed for both resonance acoustic mixer (RAM) and ball-free mixer mills and is higher than in the presence of milling balls. The RAM exhibits excellent performance in the Suzuki reaction, achieving yields of 90% after 60 minutes and complete conversion after 90 minutes. The longevity of the milling vessel is significantly improved in the RAM, allowing for at least 20 reactions without deterioration.