Milling Medium‐Free Suzuki Coupling by Direct Mechanocatalysis: From Mixer Mills to Resonant Acoustic Mixers**

Abstract

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, thus indicating that milling balls function primarily as a mixing agent for direct mechanocatalytic Suzuki coupling. The absence of milling balls can be offset by adjusting the rheology using liquid‐assisted grinding (LAG). The LAG sweet spot of 0.25 μL mg ⁻¹ is confirmed for both resonance acoustic mixers (RAMs) and ball‐free mixer mills, and is higher than in the presence of milling balls. RAMs exhibit excellent performance in the Suzuki reaction, achieving yields of 90 % after 60 min and complete conversion after 90 min. The longevity of the milling vessel is significantly improved in a RAM, allowing for at least 20 reactions without deterioration.