Exploring Meerwein-Ponndorf-Verley Reduction Chemistry for Biomass Catalysis Using a First-Principles Approach

Liquid phase catalytic hydrogenation of decomposition products of sugar molecules is challenging, but essential to produce platform chemicals and green chemicals from biomass. The Meerwein-Ponndorf-Verley (MPV) reduction chemistry is an excellent choice for the hydrogenation of keto compounds. The energy landscapes for the liquid phase catalytic hydrogenation of ethyl levulinate (EL) and furfural (FF) by Sn(IV) and Zr(IV) zeolite-like catalytic sites utilizing the hydrogen atoms from an isopropanol (IPA) solvent are explored using quantum chemical methods. The computed apparent activation free energy for the catalytic hydrogenation of EL by a Sn(IV) zeolite-like catalyst model site is (21.9 kcal/mol), which is close to the Al(III)-isopropoxide catalyzed (20.7 kcal/mol) EL hydrogenation indicating the similar efficiency of the Sn(IV) zeolite-like catalyst compared with the Al(III) catalyst used in the traditional MPV reactions. The catalytic efficiency of metal isopropoxides for the catalytic hydrogenation of EL is computed to be Al(III) > Sn(IV) > Zr(IV) in IPA solution, in agreement with experiment. Calculations were also performed with furfuryl alcohol as the source for hydrogen for the conversion of EL to gamma-valerolactone using the Sn(IV) catalytic site. The barrier (22.7 kcal/mol) suggests a hydrogenation using aromatic primary alcohol as a hydrogen donor and using a Sn(IV) catalyst is feasible. In terms of reaction mechanisms, an intramolecular hydride transfer through a six membered transition state was found to be the turnover controlling transition state of liquid phase catalytic hydrogenation of carbonyl compounds considered in this study.