synthesis and characterization of new dicationic ruthenium and iridium complexes bearing a dipyridylamine ligand (dpa) are reported. These complexes display an unusual zwitterionic molecular structure in the solid state. The iridium complex [Cp*Ir(dpa)(OSO3)] (Ir1) was found to be very efficient in base-free hydrogenation of levulinic acid into γ-valerolactone (GVL). TONs as high as 174000 in hydrogenation
The selective and efficient transfer hydrogenation of levulinic acid into gamma-valerolactone was performed with new ruthenium and iridium catalysts bearing dipyridylamine (dpa) ligands. Reactions were performed in the presence of formic acid and triethylamine using catalyst loading as low as 0.05 mol % with a ruthenium complex (turnover number = 1980). Recyclability of a ruthenium catalyst was demonstrated by running 6 consecutive reactions in almost quantitative yields.