Hydrogenation of Biomass-Derived Levulinic Acid into γ-Valerolactone Catalyzed by Palladium Complexes

The selective catalytic hydrogenation and cyclization of levulinic acid (LA) into valuable ?-valerolactone (GVL) catalyzed by different palladium compounds was achieved in water under mild conditions with high yields. Either formic acid (FA) or molecular hydrogen (H-2) was used as a hydrogen source. The precatalyst [(dtbpe)PdCl2] (dtbpe = 1,2-(bis-di-tert-butylphosphino)ethane) (1) was highly active in the processes of LA hydrogenation (TON of 2100 and TOF of 2100 h(-1)) and in the dehydrogenation of formic acid to produce H-2 and carbon dioxide. The catalytically active complexes [(dtbpe)Pd(H)Cl)] (2) and [(dtbpe)(2)Pd-2(mu-H)(3)](+) (3) and the catalytically inactive complex [(dtbpe)(2)Pd-2(mu-H) (mu-CO)](+) (4) all formed in situ and were identified as species resulting from FA decomposition.