Covalently immobilization of palladium(II) tetrasulfophthalocyanine on keratin protein grafted graphene oxide nanosheets: a new high‒performance catalyst for C‒C coupling reactions

Palladium‒catalyzed cross‒coupling reactions as extraordinary powerful and widespread methods are found in all areas of chemistry which used to construct carbon–carbon and carbon–heteroatom bonds.1-3Since irreversible precipitation of palladium in the reaction media affected its catalytic activities, to settle the matter, a controlled and reversible release of palladium from macrocyclic complexes as a novel method was proposed.In this study, wool keratin protein as amphiphilic biomaterial was extracted from natural wool and used to modify the surface of graphene oxide nanosheets. An aqua soluble palladium(II) complex with a phthalocyanine ligand possessing covalently binding ability was immobilized on keratin protein grafted graphene oxide nanosheets. The covalently supported palladium(II) tetrasulfophthalocyanine complex revealed efficient catalytic reactivity by controlled temporary release of active species for Heck and Sonogashira coupling reactions in aqueous solution. Heck coupling of styrene and Sonogashira coupling of phenylacetylene with different aryl halides wassuccessfully catalyzed by the synthesized palladium(II) tetrasulfophthalocyanine covalently supported on keratin protein grafted graphene oxide nanosheets as a novel catalyst precursor. The controlled release of palladium active species prevents the formation of inactive palladium agglomerates under harsh conditions and consequently this controlled release leads to high catalytic performances.