Chiral Organic Salt Supported Pd Nanoparticles as Selective Heterogeneous Catalysts of Hydrogenation Reactions

In this study, we report the synthesis of a new type of chiral crystalline organic porous salt CF2 derived from the ionic reaction between tetrakis(4-sulfophenyl)methane (TSPM) and the tetra-(S)-prolylamide of tetrakis(4-aminophenyl)methane, (S)-TPPM, and its ability to stabilize 2 nm palladium nanoparticles to give a novel, nonpyrophoric, chiral, catalytic material Pd@CF2. The preparation of the catalyst was very simple and conducted in water. The heterogeneous catalytic performance of Pd@CF2 was tested in hydrogen reductions of olefins and substituted nitroaromatic compounds using Pd/C as a comparison to determine the specific features of the novel catalyst. Although both types of catalysts exhibited similar catalytic activity in case of reductions of diphenylacetylene and nitrobenzene, Pd@CF2 predominantly promoted the reduction of p-nitrobenzaldehyde to p-aminobenzyl alcohol whereas Pd/C gave p-toluidine. The reduction of p-dinitrobenzene led to predominant formation of p-nitrophenylhydroxylamine if promoted by the novel catalyst and to a mixture of products if promoted by Pd/C. In addition, the introduction of p-alkoxy groups onto nitrobenzenes slowed down the reduction with Pd@CF2 but had no influence on Pd/C activity. A hypothesis ascribing these observations to dissimilar equilibrium distributions of nitro and polar groups within the organic framework and the palladium metal surface is proposed to rationalize the selectivity of the novel catalytic material. © 2024 Wiley-VCH GmbH.