Solvent-Free Suzuki-Miyaura Coupling Unleashed by Mechanochemical Pd(II)-NHC Catalysis

The Suzuki-Miyaura cross-coupling is a pivotal method for constructing C–C bonds in biaryl synthesis. Conventional palladium-catalyzed solution-phase reactions are hampered by high catalyst loadings, complex catalyst compositions, toxic solvents, and requirements for inert atmospheres and elevated temperatures. Here, we report the first mechanochemical Suzuki-Miyaura coupling employing well-defined, air-stable dimeric Pd(II)-NHC precatalysts. This solvent-free strategy efficiently couples aryl bromides with boronic acids at low Pd loadings (0.1–0.5 mol %) within 60 min, surpassing both Pd(OAc)2 and phosphine-based mechanochemical systems. The system demonstrates broad chemoselectivity across 102 substrates, stemming from the superior σ-donation and steric tunability of the NHC ligands. DFT calculations reveal a reduced energy barrier for Pd-SIMes in the rate-determining step and a narrower HOMO–LUMO gap relative to phosphine-based analogues, consistent with their enhanced catalytic efficiency and selectivity.