Polymers for Green C-C Couplings

Cleaner and environmentally more friendly cross-coupling reactions can be carried out by the use of polymers as supports. A lot of work has been devoted to attach palladium catalysts on polymers, so they can be easily separated from the reaction mixture and reused. An overview of the methods used for this purpose is given; they include the encapsulation of palladium complexes or palladium nanoparticles by polymers and the synthesis of polymeric ligands that coordinate to palladium. Polymer-supported reagents are also important in making cross-coupling reactions easier to work up and more sustainable. The use of polymer-supported stannanes in the Stille reaction has a special advantage, because organotin derivatives that are used as reagents are toxic. When polymeric tin reagents are used, the separation of the byproducts from the target product is good and the tin-containing byproducts can be recycled, thus tin waste is avoided. Examples of this application will also be discussed.