Homogenous palladium(II) pyrazolyl complexes and corresponding Pd-SILP material as catalysts for the selective hydrogenation of furfural

The search for renewable sources of energy has resulted in the focus of the use of biomass and biomass-derived platform chemicals for the generation of energy. One such chemical—furfuryl alcohol—which has several industrial applications can be obtained from furfural via hydrogenation using catalysts. Novel N^S (pzyraolyl-thio) and N^Se (pyrazolyl-selenium) bidentate ligands and their corresponding palladium(II) complexes were synthesized and evaluated as catalysts for the hydrogenation of furfural. The catalysts are active for the solventless chemoselective hydrogenation of furfural with TON around 1600 obtained. The role of the sulfur or selenium donor atoms as well as the presence of bulky groups on the catalysts influencing catalytic activity was investigated. Bulky groups present were found to slightly increase catalytic activity while the large size of selenium as compared to sulfur was not found to significantly impact catalytic activity. The complexes were found to hydrogenate furfural by homogenous means with likely palladium-bicarbonate intermediate species being observed. The recyclability of the homogenous catalysts by heterogenization using a supported ionic liquid phase (SILP) approach was investigated. Graphical abstract: [Figure not available: see fulltext.].