Photocatalytic ensemble HP-T@ Au-Fe3O4: Synergistic and balanced operation in Kumada and Heck coupling reactions
Supramolecular catalytic ensemble HP-T@Au-Fe3O4 supported by highly branched assemblies of hexaphenylbenzene (HPB) derivative has been developed. The as prepared HP-T@Au-Fe3O4 nanohybrid materials serve as efficient catalytic system to construct biaryl derivatives through Kumada cross coupling reaction using aryl chloride as one of the coupling partners under mild reaction conditions (visible light irradiation, aqueous media, aerial conditions, short reaction time). Through the cooperative effect of Au NPs and Fe3O4 NPs dual activation of aryl chlorides for the generation of aryl radical intermediates is achieved. On the other hand, oligomeric assemblies contributed significantly toward the enhancement of reaction rate and yield of the product by facilitating the reductive elimination step. Different mechanistic studies confirm the involvement of Au NPs, Fe3O4 NPs and oligomeric assemblies in the synergistic and balanced operation of HP-T@Au-Fe3O4 nanohybrid materials in the efficient completion of catalytic cycle of Kumada coupling reaction. Being magnetic, catalytic ensemble could be recycled upto five catalytic cycles. The as prepared supramolecular photocatalytic ensemble also work efficiently in Heck coupling reactions involving aryl chlorides as well as for aryl iodides as the coupling partner.