Ruthenium and Formic Acid Based Tandem Catalytic Transformation of Bioderived Furans to Levulinic Acid and Diketones in Water

Efficient tandem catalytic transformations of bioderived furans, such as furfural, 5-hydroxymethylfurfural (5-HMF), and 5-methylfurfural (5-MF), to levulinic acid (LA) and diketones, 1-hydroxyhexane-2,5-dione (1-HHD), 3-hydroxyhexane-2,5-dione (3-HHD), and hexane-2,5-dione (2,5-HD), was achieved by using water-soluble arene-Ru-II complexes, containing ethylenediamine-based ligands, as catalysts in the presence of formic acid. The catalytic conversion of furans depends on the catalyst, ligand, formic acid concentration, reaction temperature, and time. Experimental evidence, including time-resolved (HNMR)-H-1 spectral studies, indicate that the catalytic reaction proceeds first with formyl hydrogenation followed by hydrolytic ring opening of furans. The ruthenium-formic acid tandem catalytic transformation of fructose to diketones and LA was also achieved. Finally, the molecular structures of the four representative arene-Ru-II catalysts were established by single-crystal X-ray diffraction studies.