LAUSR

Rhodium nanoparticles (Rh NPs) stabilized by natural cinchona alkaloids were synthesized in imidazolium-based ionic liquids using H2 as the reductant. Characterization showed well-dispersed Rh NPs of about 1.96 nm (TEM and HRTEM) and confirmed the ionic liquid and cinchona alkaloid stabilization to the Rh(0) NPs (XPS). When modified by chiral diamine, including (1R,2R)-diphenylethylenediamine ((1R,2R)-DPEN) or cinchona alkaloid derivatives, the Rh NPs catalysts exhibited good activity, chemoselectivity and enantioselectivity in the heterogeneous enantioselective hydrogenation of aromatic ketones. Synergistic effect between (1R,2R)-DPEN and cinchonidine was also observed, which significantly accelerated the reaction rate and enhanced the enantioselectivity. 63.0% enantioselectivity and 98.9% chemoselectivity could be achieved in the acetophenone enantioselective hydrogenation; up to 70.2% enantioselectivity and 100% chemoselectivity was obtained in the isobutyrylbenzene catalytic enantioselective hydrogenation. Catalytic system could be reused several times without significant loss in activity, chemoselectivity as well as enantioselectivity. This catalytic protocol opens the door to heterogeneous enantioselective hydrogenation of aromatic ketones with metal Rh NPs immobilized in ionic liquid.Graphical AbstractCinchona alkaloid and ionic liquid stabilized Rh NPs catalyst, when modified by chiral diamine like (1R,2R)-DPEN, exhibited high activity, high chemoselectivity and good enantioselectivity in the challenging heterogeneous enantioselective hydrogenation of aromatic ketones to corresponding aromatic alcohols under mild conditions. Synergistic effect between (1R,2R)-DPEN and cinchonidine was also observed, which significantly accelerated the reaction rate and enhanced the enantioselectivity. 63.0% enantioselectivity and 98.9% chemoselectivity could be achieved in the acetophenone enantioselective hydrogenation; up to 70.2% enantioselectivity and 100% chemoselectivity was obtained in the isobutyrylbenzene catalytic enantioselective hydrogenation. Catalytic system could be reused several times without significant loss in activity, chemoselectivity as well as enantioselectivity. This catalytic protocol opens the door to heterogeneous enantioselective hydrogenation of aromatic ketones with metal Rh NPs immobilized in ionic liquid.