Stereoselective hydrogenation of 1-phenyl-1-pentyne over low-loaded Pd-montmorillonite catalysts Original Research Article

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.