Ruthenium‐Catalyzed C‐H Bond Activation/Arylation Accelerated by Biomass‐Derived Ligands

A variety of ligands are being explored extensively to achieve enhanced performance for ligand assisted C‐H bond activation/functionalization reactions. We explored here several readily available biomass‐derived ligands as effective additives to significantly enhance the catalytic activity of arene‐Ru(II) dimer for ortho C‐H bond arylation in a water‐based catalytic reaction. We achieved almost 7‐fold enhancement in the catalytic activity with [(η6‐p‐cymene)RuCl2]2 catalyst in the presence of levulinic acid ligand at 80 °C. Mass investigations revealed the in‐situ formation of a ruthenium‐levulinate complex, which presumably plays a crucial role in the formation of the important cycloruthenated intermediate by facilitating the initial activation of ortho C‐H bond of 2‐phenylpyridine. Density functional theoretical studies also inferred that the ligand assisted route is energetically more favorable, where the acetyl group is found to be involved in the deprotonation step. Readily available biomass‐derived ligands significantly improved the catalytic activity of [(η6‐p‐cymene)RuCl2]2 for ortho C‐H bond activation/arylation of 2‐phenylpyridine with a variety of (hetero)aryl chlorides under water‐based reaction conditions. The ligand levulinic acid achieved 7‐fold enhancement, as the ligand‐assisted route is energetically more favorable.