Immobilised chiral inducer on Pt-based mesoporous titanate nanotubes as heterogeneous catalysts for enantioselective hydrogenation

• Chiral porous titanate nanotubes were synthetized as catalyst supports.
• Pt nanoparticles were deposited and used in asymmetric hydrogenation.
• The catalysts were enantioselective to desired product.
• The best catalyst can be easily recycled and reused.

A new series of chiral porous titanate nanotubes (TNTs) containing (−)-11-trimethoxysilyl-cinchonidine (TMS-CD) moieties were synthesized via direct surface anchorage. These hybrid solids were used as supports for Pt (1 wt%) catalysts and evaluated in heterogeneous enantioselective hydrogenation of 1-phenyl-1,2-propanodione. The supports and catalysts were characterized by a variety of techniques including TGA, N2 adsorption isotherms, solid state NMR (13C and 29Si), XRD, HR-TEM, DRIFTs and XPS. For the best system the hydrogen pressure, solvent effects and recycles were studied. The maximum enantiomeric excess (ee) and the turnover frequency obtained under optimized conditions with 1% Pt/TNT-CD were 37% (at 15 wt% nominal content of TMS-CD) and 165 min−1 (at 10 wt% nominal content of TMS-CD), respectively. The variation of H2 pressure and solvent affects both the activity and enantioselectivity due to the substrate adsorption on the metal active sites. Additionally, these heterogeneous catalysts can also be easily recycled and reused for three times without the loss of activity and enantioselectivity. After the 3rd cycle, catalyst deactivation due to the leaching of Pt nanoparticles and modifier hydrogenation in the feed was detected.

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