Exploring 5-hydroxymethylfurfural hydrogenation pathways using NHC-stabilized water-soluble nanoparticles of various metals and alloys

Abstract

The catalytic valorization of 5-hydroxymethylfurfural (5-HMF), a key bio-based platform molecule, is central for sustainable chemical production. In this work, we report the aqueous-phase hydrogenation of 5-HMF using a family of water-soluble nanoparticles stabilized by an N-heterocyclic carbene (IMesPrSO₃) ligand. The nanoparticles were comprehensively characterized by BF-TEM, DLS, TGA, ICP-OES, and pair distribution function (PDF) analysis from wide-angle X-ray scattering (WAXS). By only varying the metal core (Ru, Pd, Ir, RuIr₂), and slightly modifying the reaction conditions, we accessed a diverse array of high-value products, including 2,5-bis(hydroxymethyl)furan (2,5-BHMF), 2,5-bis(hydroxymethyl)tetrahydrofuran (2,5-BHMTHF), oxidized cyclopentenones, and 1-hydroxyhexane-2,5-dione (HHD), all under environmentally friendly conditions (30–140 °C, 5 bar H₂, in water). Specifically, the Ru-based nanoparticles showed high selectivity to 2,5-BHMF (90%) at very mild conditions (30 °C), along with a promising recyclability. Reaction products were identified and quantified through extensive NMR spectroscopy, including ¹H, ¹³C, COSY, HSQC, and HMBC experiments. Our findings demonstrate that these truly colloidal catalytic systems can represent a tuneable and robust platform for green and sustainable biomass transformations.