A polyphenylene support for Pd catalysts with exceptional catalytic activity

We describe a solid polyphenylene support that serves as an excellent platform for metal-catalyzed reactions that are normally carried out under homogeneous conditions. The catalyst is synthesized by palladium-catalyzed Suzuki coupling which directly results in formation of palladium nanoparticles confined to a porous polyphenylene network. The composite solid is in turn highly active for further Suzuki coupling reactions, including non-activated substrates that are challenging even for molecular catalysts. A major goal in catalysis is to combine the advantages of molecular catalysts and heterogeneous processes, ideally maintaining—or even improving—the reactivity and selectiv- ity of the molecular catalysts, while facilitating product recovery and catalyst recycling. (1-3) However, in fine-chem- icals synthesis molecular catalysts are predominantly used, partly because typical solids do not provide the nonpolar environments often required for organic reactions. This is often easier realized with metal complexes and suitable ligands and solvents, which provide the required geometry and stabilize the transition state of the reaction. (4-6) Polymers as less conventional supports could provide a "solvent"-like reaction environment, onto which ligands and metal com- plexes can be grafted to provide the catalytic functionality. (7, 8) Polymeric solids based on polystyrene, (9, 10) polydivinylben- zene (PDVB), (11) polyacrylate derivatives, (12) covalent organic frameworks (COF), (13) and hybrid metal-organic frame- works (14-16) have recently been explored as carriers for catalytic metal nanoparticles. Commercially, polymeric catalyst supports are limited to ion-exchange resins, for example, the Amberlyst series based on polystyrene-co-divinylbenzene. Also carbon materials are widely applied when an apolar carrier material is required to host metal catalytic species. (17) In our search for intermediate materials between carbons and the polymers listed above, we decided to study the performance of polyphenylene (PPhen) in catalysis. In this polymer, all the carbon atoms are sp 2 hybridized. The thermal and chemical stability of PPhen is higher than those of most other polymers, while it still provides a "solvent-like" reaction environment, suggesting its