Novel Metal Nanoparticles Stabilized with (2R,4R)-2,4-bis(diphenylphosphino) Pentane on SiO2. Their Use as Catalysts in Enantioselective Hydrogenation Reactions

Metal nanoparticles (NPs) have been reduced with NaBH4 from Pt, Rh and Ir precursors salts in presence of (2R,4R)-2,4- bis(diphenylphosphino pentane), ((R,R)-BDPP), and SiO2. This synthesis procedure with a chiral ligand generates chiral stabilized NPs of small and narrowly distributed core sizes depending of metal precursor, metallic loading and ligand stabilizer concentration. These novel catalysts with chiral surface have been used in enantioselective hydrogenation of ethyl pyruvate as a reference substrate and 1-phenylpropane- 1,2-dione, acetophenone, 2,3-butanedione and 3,4-hexanedione, all scarcely studied ketones. Catalysts were characterized by TEM, EDS, electron diffraction, N2 adsorption-desorption isotherms and XPS. Catalytic results indicate high conversion levels and enantioselectivities up to 78% in the hydrogenation of some substrates, due to the presence of chiral ligand on metal surface. All results are promising because is the first report of high enantiomeric excess (ee) in hydrogenations using these kind of heterogeneous catalytic systems.