Mild and Robust Redox-Neutral Pd/C-Catalyzed Lignol β-O-4' Bond Cleavage Through a Low-Energy-Barrier Pathway

Abstract

A Pd/C catalyzed redox neutral C¢O bond cleavage of 2-aryloxy-1-arylethanols has been developed. The reactions are carried out at 80 °C, in air, using a green solvent system to yield the aryl ketones in near quantitative yields. Addition of catalytic amounts of a hydrogen source to the reaction mixture activates the catalyst to proceed through a low energy barrier pathway. Initial studies support a transfer hydrogenolysis reaction mechanism that proceeds through an initial dehydrogenation followed by an enol adsorption to Pd/C and a reductive C¢O bond cleavage.

Keywords: heterogeneous catalysis; lignin; palladium; reaction mechanisms; transfer hydrogenolysis.