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 γ-valerolactone (GVL) catalyzed by different
palladium compounds was achieved in water under mild conditions with
high yields. Either formic acid (FA) or molecular hydrogen (H2) 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 H2 and carbon dioxide. The catalytically
active complexes [(dtbpe)­Pd­(H)­Cl)] (2) and [(dtbpe)2Pd2(μ-H)3]+ (3) and the catalytically inactive complex [(dtbpe)2Pd2(μ-H) (μ-CO)]+ (4) all formed in situ and were identified as species resulting from
FA decomposition.