A new non-cinchona chiral modifier immobilized on Pt/SiO2 catalysts for enantioselective heterogeneous hydrogenation

• An asymmetric chiral non-cinchona type inducer was immobilized on SiO2.
• Pt nanoparticles were deposited on chiral-modified supports.
• A chiral entity not attached directly to the Pt can induce enantio-differentiation.
• Catalytic hydrogenation was 100% regioselective toward the desired product.
• The recycling processes showed high conversion levels and leaching of the inducer.

Pt heterogeneous catalysts were prepared by the covalent immobilization of (4′R,5′S)-4′,5′-dihydro-4′,5′-diphenyl-2-(6-cyanopyridyl)imidazoline (PyIm) as the asymmetric modifier. These novel series of catalysts were studied in the 1-phenyl-1,2-propanodione (PPD) hydrogenation. The effects of the PyIm surface concentration, hydrogen pressure, solvent nature and recycles on the reaction were studied. These modified catalysts represent the first effective immobilized chiral non-Cinchona-type modifier of Pt for the enantioselective hydrogenation. The enantio-differentiation was attributed to the substrate–modifier interactions involving hydrogen bonding between the keto-carbonyl O atom and the NH moiety PyIm. The results confirmed that the variations in the H2 pressure and the solvent affect the activity and the enantioselectivity due to the substrate adsorption on the active sites of the metal. Additionally, this heterogeneous catalyst can be conveniently reused at least five times without loss of its catalytic efficiency, but the enantioselectivity decreased, which may be due to the leaching of the modifier.

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