Rhodium complexes containing chiral P-donor ligands as catalysts for asymmetric hydrogenation in non conventional media

Abstract

Rhodium-catalysed asymmetric hydrogenation using P-donor ligands, such as new fluorinated (R)-BINOL and azadioxaphosphabicyclo[3.3.0]octane derivatives was carried out in different reaction media such as organic solvent (CH2Cl2), ionic liquid ([BMI][PF6]), supercritical carbon dioxide (scCO2) and [BMI][PF6]/scCO2 mixture. The best enantioselectivities were obtained in neat [BMI][PF6], allowing a recycling up to ten times without activity loss. However, the enantioselectivity was lost due to ligand leaching. The ionic liquid phase containing rhodium molecular species was supported on functionalized multi-walled carbon nanotubes in order to improve the recycling, but unfortunately the asymmetric induction was lost upon catalyst immobilization. Rh-catalysed asymmetric hydrogenation was carried out in different reaction media (dichloromethane, scCO2, [BMI][PF6] and the mixture of scCO2/[BMI][PF6]) using chiral P-donor ligands under soft conditions. The best catalytic system was obtained in ionic liquid medium and could be recycled up to ten times without activity loss. The ionic liquid catalytic phase supported on functionalized multi-walled carbon nanotubes did not improve its catalytic behaviour.