Heterogeneous Copper-Free Sonogashira Cross-Coupling Reactions Catalyzed by a Recyclable Orthopalladated Azo-Complex

In this work, the preparation of titania-supported Pd catalyst deriving from pincer-type orthopalladated azo-complex is presented. The new highly dispersed Pd catalyst was prepared through a pH-controlled adsorption method and fully characterized by FT-IR, XRD, TGA, FE-SEM, TEM and N₂ adsorption/desorption techniques. The Pd/TiO₂ nano-catalyst was then applied as an efficient heterogeneous catalyst for copper-free Sonogashira cross-coupling reactions of a representative range of aryl iodides, bromides, and chlorides with phenylacetylene with the very low catalyst Pd-loading. The coupling products were obtained in high yields in environmentally friendly reaction media. The catalyst was successfully recycled over six runs, with no significant loss of catalytic activity.