Influence of the acidity of oxidized Pd/silica–alumina catalysts on their performances in the Suzuki coupling

• Oxidized Pd on silica–alumina catalysts are active and selective for the Suzuki coupling.
• No leaching is observed and the catalysts are still efficient after 3 runs.
• TOF and productivity are optimized for a support containing 10% of silica.
• Optimum of performances is obtained with the most acidic catalyst.
• The importance of the support acidity in the Suzuki coupling is demonstrated.

Suzuki coupling is a crucial reaction for the preparation of many high value compounds, especially for the synthesis of pharmaceuticals. Pd-based heterogeneous catalysts are highly regarded for achieving this reaction. However, the knowledge of the Suzuki mechanism with this type of catalysts is relatively limited. In the present paper, the influence of the acidity of heterogeneous catalysts on the Suzuki coupling has been methodically investigated on palladium supported on silica–alumina. A Suzuki coupling model reaction was used to assess if any correlation exists between the performances of the prepared catalysts and their acidity. The results have demonstrated that, the Pd being in an oxidized state, the acid sites at the heterogeneous catalyst surface participate actively to the mechanism of the Suzuki coupling. An optimum of total acidity of the catalysts leading to a peak of performances (conversion and selectivity) was identified. Several assumptions concerning the implication of the catalytic support in the different steps of the Suzuki coupling mechanism are proposed and discussed. Furthermore, the recyclability of the catalyst has been demonstrated, revealing that our catalysts really behave heterogeneously.

Oxidized Pd supported on silica–alumina solid catalysts show optimum performances (TOF and productivity) in the Suzuki coupling when their content in silica (x) is 10%, which corresponds to the formulation with the highest acidity.Figure optionsDownload high-quality image (110 K)Download as PowerPoint slide