Eco-Friendly Catalyst Development: Bidentate Nitrogen Ligands in the Suzuki-Miyaura Reaction of Aryl Iodides and Bromides in Green Solvents.

Palladium (0) catalysts generated in situ from inexpensive and environmentally benign nitrogen-based bidentate pyridinium amidate ligands and simple Pd(II) salts enable highly efficient Suzuki–Miyaura cross-coupling reactions of aryl iodides and bromides. These catalysts operate at remarkably low palladium loadings (0.1–0.005 mol %) with a TON up to 17800 and afford high product yields across a broad substrate scope (51–96%) using potassium carbonate (K2CO3) as base in a hydroxyethyl pyrrolidone/water (6/4) green solvent system. This protocol minimizes metal contamination in the final products and facilitates efficient palladium recovery, bringing down palladium consumption. The process mass intensity (PMI) was initially close to 30 and decreased to 8 with the recovery of solvents and palladium as Pd/C (over 90%). Density functional theory (DFT) calculations suggest that the rate-determining step of the Suzuki–Miyaura reaction with these ligands is the transmetalation process.