Intermetallic Palladium-Zinc Nanoparticles for the Ultraselective Hydrogenative Rearrangement of Furan Compounds

The tandem hydrogenative rearrangement of furan aldehydes/ketones into cyclopentanones is crucial for synthesizing biobased fine chemicals but remains challenging because of the complexity of the tandem reaction network. Herein, intermetallic PdZn nanoparticle-supported catalysts were prepared, which showed a high catalytic efficiency for synthesizing 3-methyl cyclopentanone with a 96.3% yield from 5-methyl furfural at the hitherto lowest temperature of 120 °C. Furthermore, they exhibited catalytic generality for the synthesis of cyclopentanones with yields above 90% from other furan aldehydes (i.e., furfural, 5-hydroxymethyl furfural, and 5-ethyl furfural) and furan ketones (i.e., 2-furan methyl ketone and 2-furan ethyl ketone). Investigations into the catalytic mechanism showed that H₂ was heterolytically activated on the Pd-Zn pair to form H^--Pd-Zn-H₃O⁺ via an ionic water-mediated pathway, which not only functioned as unconventional active sites for the carbonyl group hydrogenation step but also provided Brønsted acid sites for ring opening and intramolecular aldol condensation steps. This study presents an exciting strategy for the bifunctional catalysis of challenging substrates by generating transient H⁺-H^- pairs using advanced intermetallic alloy catalysts.