Mechanochemical tuning of Pd(BIAN-NHC) allyl/cinnamyl complexes for enhanced cross-coupling

The development of efficient and sustainable catalytic systems for cross-coupling reactions remains a central goal in synthetic chemistry. Building upon established palladium-NHC catalyst platforms, we report a novel class of air-stable palladium complexes, Pd(BIAN-NHC)Cl(η³-allyl/cinnamyl), which serve as highly effective precatalysts for both Buchwald-Hartwig amination and Suzuki-Miyaura cross-coupling under exceptionally mild, solvent-free ball milling conditions. On employing a weak base (K₂CO₃) at room temperature, these optimized catalysts promote the coupling of diverse aryl halides, including challenging aryl chlorides with aryl boronic acids or amines. Excellent yields (up to 99%) are achieved with remarkably low catalyst loadings (as low as 0.062-0.125 mol%). The catalysts exhibit high robustness, operational simplicity, and alignment with green chemistry principles, making them practical and sustainable alternatives. Mechanistic insights suggest that the BIAN-NHC ligand framework enhances the stability and reactivity of the palladium center, facilitating efficient catalytic turnover. This work establishes Pd(BIAN-NHC)Cl(η³-allyl/cinnamyl) complexes, particularly the BIAN-IPr^#-cinnamyl variant, as versatile and eco-friendly catalysts for advanced cross-coupling applications.