Mechanochemical Tuning of Pd(BIAN–NHC) Allyl/Cinnamyl Complexes for Enhanced Cross-Coupling

Abstract

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. Employing a weak base (K₂CO₃) at room temperature, these optimized catalysts promote the coupling of diverse aryl halides,including challenging aryl chlorides with arylboronic acids or amines. Excellent yields (up to 99%) are achieved with remarkably low catalyst loadings (as low as 0.062-0.125 mmol%). 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.