Applied Catalysis A: General 213 (2001) 133–140 Stereoselective hydrogenation of 1-phenyl-1-pentyne over low-loaded Pd-montmorillonite catalysts Ágnes Mastalir a,∗ , Zoltán Király b , György Szöllösi a , Mihály Bartók a a Department of Organic Chemistry and Organic Catalysis Research Group of the Hungarian Academy of Sciences, University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary b Department of Colloid Chemistry, University of Szeged, Aradi vt. 1, H-6720 Szeged, Hungary Received 20 September 2000; received in revised form 4 December 2000; accepted 5 December 2000 Abstract The catalytic performance of low-loaded, organophilic Pd-montmorillonites (Pd-Ms) prepared in a micellar system was investigated in the liquid-phase hydrogenation of 1-phenyl-1-pentyne. Experiments were undertaken to determine the optimal reaction conditions for the predominant formation of the cis-alkene stereoisomer. The reactant:catalyst (S:C) ratio proved to have a crucial effect on the product distribution and the highest cis-stereoselectivities were obtained by applying S:C ≥ 5000. The organophilic character of the catalysts was utilized to study the solvent effect. The experimental evidence indicated that both THF and toluene may be considered to be appropriate solvents for the above reaction, since they tend to increase the amount of active Pd atoms available for the reactants through swelling and disaggregation of the clay host. When the reaction time did not exceed 90 min, high conversions were obtained and only limited overhydrogenation occurred. Whereas the cis-stereoselectivities observed on Pd-Ms in THF (85–88%) were comparable with that obtained for Lindlar Pd, it emerged that the activities of the Pd-Ms were substantially higher. The amount of a Pd-M required for a similar catalytic performance was therefore considerably lower than that of the Lindlar catalyst. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Palladium; Montmorillonite; 1-Phenyl-1-pentyne; Hydrogenation; Swelling; Stereoselectivity; Lindlar catalyst 1. Introduction Recent advances in the intercalation chemistry of smectite clays initiated growing interest in these minerals as catalysts [1,2] and support materials for transition metals or metal complexes [3–8]. The structure of a smectite clay is lamellar, with parallel layers of tetrahedral silicate and octahedral aluminate sheets, formed by SiO 4 and AlO 6 units, respectively. Montmorillonite clays contain an octahe- dral layer sandwiched between two tetrahedral layers. ∗ Corresponding author. Fax: +36-62-544200. E-mail address: mastalir@chem.u-szeged.hu ( ´ A. Mastalir). Depending on the amount of intercalated water in the interlamellar space, the basal spacing d L determined from XRD measurements may vary between 1 and 5 nm. Isomorphous substitution of Si 4+ by Al 3+ or of Al 3+ by Mg 2+ , Fe 2+ or Ni 2+ produces a net neg- ative charge on the tetrahedral and octahedral sheets, which is balanced by exchangeable hydrated cations such as Na + ,K + , Ca 2+ and Mg 2+ , situated between the clay lamellae. The cation-exchanging property of montmorillonite is based on replacement of the above inorganic cations by others, which may be or- ganic cations of long hydrocarbon chains or cationic surfactants [1,9]. When such species are subjected to cationic exchange, organophilic clays are formed, 0926-860X/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0926-860X(00)00889-9