Catalytic Transfer Hydrogenation of Biomass-Derived Carbonyls over Hafnium-Based Metal-Organic Frameworks.

A series of highly crystalline, porous, hafnium-based metal-organic frameworks (MOFs) have shown to catalyze the transfer hydrogenation reaction of levulinic ester to produce ?-valerolactone using isopropanol as hydrogen donor and the results are compared with the zirconium-based counterparts. The role of the metal center in Hf-MOFs has been identified and reaction parameters optimized. NMR studies with isotopically labeled isopropanol evidences that the transfer hydrogenation occurs via a direct intermolecular hydrogen transfer route. The catalyst, Hf-MOF-808, can be recycled several times with only a minor decrease in catalytic activity. Generality of the procedure was shown by accomplishing the transformation with aldehydes, ketones and ?,?-unsaturated carbonyl compounds. The combination of Hf-MOF-808 with the Brønsted acidic Al-Beta zeolite gives the four-step one-pot transformation of furfural to ?-valerolactone in good yield of 72%.