scCO₂-Flow Asymmetric Hydrogenation

Significance

Development of a continuous-flow reaction system for the asymmetric hydrogenation using supercritical carbon dioxide (scCO₂) as a reaction medium was described. A flow reactor (pressure bottle) was charged with the almina-supported chiral Rh-phosphine complex 2 which was prepared by mixing commercially available Almina-PTA-[Rh(cod)₂]BF₄ and chiral phosphines. Supercritical carbon dioxide (scCO₂), hydrogen gas, and dimethyl itaconate as a test substrate were continuously charged through a mixing device. Various temperature and pressure conditions were examined and representative results were shown above. Eleven chiral phosphine ligands were tested and a ferrocenyl-type phosphine, JosiPhos 001, was found to catalyze the asymmetric hydrogenation of dimethyl itaconate with up to 83% ee.