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

Abstract

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. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim