Resumen de Silica supported rhodium metal nanoparticles stabilized with (-)-diop. Effect of ligand concentration and metal loading on the enantioselective hydrogenation of ketones
Doris Ruiz, Claudio Mella Schmidt, José Luis García Fierro, Patricio Reyes
Supported nanoparticles (NPs) in presence of chiral ligand (L) were synthesized for their use in enantioselective hydrogenation reactions. Catalysts were obtained by chemical reduction from rhodium chloride hydrate, RhCl3x3H2O, in presence of (-)-DIOP ligand ((4R,5R)-4,5-Bis(diphenylphosphino-methyl)-2,2-dimethyl-1,3-dioxolane) that allows to control NPs growing and to obtain solids having chiral surfaces. Chirally stabilized rhodium NPs on SiO2 were characterized using techniques such as: TEM, electron diffraction, EDS, nitrogen adsorption-desorption isotherms and XPS. This work includes the study of some variables such as metal loading and ligand concentration and their effect in metal core sizes, catalytic activity and enantioselectivity. Catalysts properties have also been evaluated in the hydrogenation of substrates: acetophenone (AP), 1-phenyl-1,2-propanedione (PPD), 3,4-hexanedione (HD), 2,3-butanedione (BD) and ethyl pyruvate (EP) as reaction test. Ligand plays a fundamental role in the synthesis of NPs and enantioselectivity in hydrogenations reactions. That is, due to it generates metal particle size < 5.8 nm compared with unstabilized systems that generate average diameter around 14 nm. Results indicate increased activity in catalytic systems obtained from the stabilization of NPs. Enantioselectivity levels reach values up to 53% due to the chiral ligand is on the catalysts surface.
