Catalysis Today 235 (2014) 226–236 Contents lists available at ScienceDirect Catalysis Today j o ur na l ho me page: www.elsevier.com/locate/cattod Enantioselective hydrogenation of 1-phenyl-1,2-propanedione on immobilised cinchonidine-TiO 2 catalysts Cristian H. Campos a , Cecilia C. Torres a , Ana B. Dongil a , Doris Ruiz a , José L.G. Fierro b , Patricio Reyes a,∗ a Edmundo Larenas 129/Departamento de Fisicoquímica, Facultad de Ciencias Químicas, Universidad de Concepción, Concepción, Chile b Instituto de Catálisis y Petroleoquímica, CSIC, Marie Curie 2, Cantoblanco 28049, Madrid, Spain a r t i c l e i n f o Article history: Received 14 November 2013 Received in revised form 19 April 2014 Accepted 29 April 2014 Available online 12 June 2014 Keywords: TiO2 catalysts Immobilised cinchonidine 1-Phenyl-propane-1,2-dione Enantioselective hydrogenation a b s t r a c t The enantioselective hydrogenation of 1-phenyl-1,2-propanodione (PPD) was investigated using cinchonidine-immobilised Pt/TiO 2 catalysts. Prior to metal deposition, TiO 2 was chirally modified by the direct anchoring of cinchonidine (CD) using trimethoxysilane as coupling agent (TMS-CD). The cat- alysts were prepared using a high H 2 pressure reduction-deposition method and were characterised by elemental analysis (C, H and N), TG, DRIFT, 13 C and 29 Si solid-state NMR, N 2 adsorption–desorption isotherms, XRD, XPS and HR-TEM. The catalytic activity was evaluated in a batch reactor at 298 K and 40 bar using cyclohexane as solvent with various cinchonidine concentrations. The results indicate that the enantioselectivity was sensitive to the CD surface concentration and the enantiomeric excess of the target product, 1-R-phenyl-1-hydroxy-2-propanone, was in the range of 25–51%. The best catalyst was the one supported on TiO 2 with a nominal content of 10 wt% TMS-CD. The effect of the H 2 pressure, the concentration of substrate, solvent and recyclability of the catalyst were studied. The results obtained confirmed that the variation of reaction conditions affects both the activity and enantioselectivity due to the substrate adsorption on the metal active sites. Concerning the solvent effect, the enantiomeric excess decreased non-linearly upon increasing the solvent dielectric constant; this was attributed to the interactions between solvents and TMS-CD on the surface. In the catalyst recycling studies, the enan- tiomeric excess decreased up to 40% after the 3rd reuse. The drop of activity and enantiomeric excess was attributed to the hydrogenation of the immobilised CD. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Asymmetric catalysis has become a challenging subject in the field of organic synthesis and catalysis over the past three decades, both from the theoretical and practical points of view [1–3]. Among the numerous enantioselective heterogeneous reactions, the Pt/cinchona-catalysed hydrogenation of -ketoesters is one of the few successful examples with more than 95% enantiomeric excess (e.e.) under favourable reaction conditions [4]. Another typ- ical reaction is the hydrogenation of -diketones, which was first reported by Vermeer et al. in 1993 [5]. Due to the conjugated keto groups of the reactant, the hydrogenation consists of two consecu- tive steps. 1-Phenyl-1,2-propanedione (PPD) is a suitable molecule to investigate the enantioselective hydrogenation of conjugated carbonyl bonds [6–12]. It contains a phenyl ring and two carbonyl groups. Under the reaction conditions, in the presence of CD, the ∗ Corresponding author. E-mail addresses: ccampos@udec.cl (C.H. Campos), preyes@udec.cl (P. Reyes). main product is (R)-1-hydroxy-1-phenylpropanone, an important intermediate in the synthesis of drugs [13]. The commercial application of these systems requires an effec- tive method of catalyst recovery and re-use because of economic and environmental concerns. Several methods for the recycling of chiral catalysts have been described [14–18] and a number of reactions have been conducted with this new type of catalysts, especially since the successful immobilisation of CD [19–21]. In previous papers, we investigated the enantioselective hydrogena- tion of PPD over two types of CD immobilisation: (1) using it as a stabiliser on Pt nanoclusters supported on SiO 2 [22,23], and (2) anchoring it on SiO 2 and -Al 2 O 3 oxides surfaces [20,21]. The catalysts not only exhibited similar enantioselectivity (i.e., 50% enantiomeric excess for the hydrogenation of PPD) but also exhib- ited novel catalytic properties, i.e., high regioselectivity to C O adjacent to phenyl groups, which differs from their conventional heterogeneous counterparts. As an extension of these previous studies, we describe in this paper the catalytic performance of Pt supported on CD modified TiO 2 -anatase in the enantioselective hydrogenation of PPD. We http://dx.doi.org/10.1016/j.cattod.2014.04.030 0920-5861/© 2014 Elsevier B.V. All rights reserved.