Selective Hydrogenation of Furfural to Furfuryl Alcohol Catalysed by Ruthenium Complexes Containing Phosphorus-Nitrogen Ligands

Two ruthenium (II) complexes containing heterobidentated phosphorous–nitrogen ligands were studied as homogeneous catalysts in the hydrogenation of furfural, a key step in the transformation of biomass to biofuels or renewable chemicals. The catalysts exhibited high percentages of conversion towards the formation of furfuryl alcohol. The studied ruthenium (II) complexes are able to maintain their catalytic activities in substrate/catalyst ratios ranging from 1000/1 to 6000/1. The reaction is sensitive to hydrogen pressure and the substrate concentration. The maximum conversion is achieved at a pressure of 40 bar and a substrate/catalyst ratio of 3000/1 (TOF 3000 h−1). In situ 1H-NMR (proton nuclear magnetic resonance) analysis suggests that the presence of a phosphorous–nitrogen ligand improves the catalytic activity of the complex by stabilizing the intermediate ruthenium-dihydride, which is considered the active species in the hydrogenation reactions. © 2021 John Wiley & Sons, Ltd.