Arylation of indole at C2 catalyzed by palygorskite grafted covalent organic frameworks supported palladium catalyst

A heterogeneous palladium catalyst, palygorskite grafted covalent organic frameworks supported palladium (Pd-Pal/COF), was successfully prepared by a simple method. A series of C2 aromatic indole derivatives were synthesized under mild reaction conditions. Pd-Pal/COF catalyst can be reused at least 5 times with inappreciable metal leaching. Undoubtedly, facile synthesis, mild reaction conditions, a wide scope of reactants, and recyclability make the catalyst systems potentially useful in organic synthesis. For the synthesized heterogeneous catalysts, palygorskite as a matrix, the unique structure and good dispersion of palygorskite result in the excellent catalytic activity and good cycle stability of the Pd-Pal/COF catalyst, comparing with the traditional clay catalyst. The result further expands the application scope of clay in the catalytic field.