Methanol Production from Aqueous Formaldehyde Using Ruthenium Imidazolylamine Complexes: Ligand-Tuned Selectivity

The transformation of aqueous formaldehyde to H₂ and methanol is respectively governed by competing dehydrogenation and hydrogenation pathways in water. Herein, we demonstrated the tuning of product selectively, H₂ vs methanol from aqueous formaldehyde over molecular arene Ru complexes bearing furan, thiophene, imidazole-based methanol and methylamine ligands under moderate condition. A distinct ligand effect was observed, where furan- and thiophene-based ligands favored formaldehyde dehydrogenation, while imidazolyl methylamine-based ligands favored formaldehyde hydrogenation to methanol under analogous conditions. Among the standard catalysts, arene Ru imidazolylamine catalyst outperformed others with 86% methanol yield at 90 °C. Extensive control experiments, kinetic isotope experiments along with density functional theory (DFT) studies showed hydrido species of arene Ru imidazolylamine catalyst prefers hydrogenation of formaldehyde to methanol over the dehydrogenation pathway.