Immobilization of a homogeneous macromolecular copper catalyst for the oxidative coupling of phenols

Abstract

In order to combine the advantages of both homogeneous and heterogeneous catalysis, an immobilized macromolecular copper catalyst was prepared by radical graft copolymerization of styrene and 4-vinylpyridine on nonporous silica spheres and by subsequent complex formation of copper(II) chloride with these grafted macromolecular pyridine ligands. The oxidative coupling of 2,6-disubstituted phenols was chosen to test the catalytically active species, i.e. dihydroxo-bridged copper dimers. The immobilized polymeric catalysts show a remarkable activity: reaction rates up to 70% compared to nonbound macromolecular analogues can be achieved. Moreover, they can easily be re-used several times without loss of activity, while the mechanism of the coupling reaction is not influenced.