PdCuCeO–TPAB: a new catalytic system for quasi-heterogeneous Suzuki–Miyaura cross-coupling reactions under ligand-free conditions in water

Abstract

In this contribution, we report a simple and clean method for preparation of a single-phase Pd_0.04Cu_0.04Ce_0.92O_2−δ (PdCuCeO) solid-solution oxide and its application in quasi-heterogeneous Suzuki–Miyaura cross-coupling reactions. The catalyst was characterised fully and all the characterisation techniques strongly suggest that the Pd²⁺ and Cu²⁺ ions were successfully incorporated into the lattice of ceria. The as-prepared PdCuCeO solid-solution oxide was tested on Suzuki–Miyaura cross-coupling reactions under ligand free conditions using water as a sole solvent and tetrapropylammonium bromide (TPAB) as a phase transfer catalyst. It was discovered that TPAB acts as scavenger of Pd and the resulting material (Pd/TPAB) is able to catalyse the Suzuki–Miyaura coupling reaction. The Suzuki–Miyaura coupling of aryl iodides, bromides as well as activated aryl chlorides was efficiently performed by this PdCuCeO–TPAB catalytic system. The PdCuCeO–TPAB catalytic system also displayed good functional group tolerance and good to excellent isolated yields were obtained. Catalyst leaching and recyclability studies revealed that PdCuCeO acts as a Pd reservoir and that the reactions are essentially quasi-heterogeneous occurring over the recoverable Pd/TPAB aggregates. Only a negligible amount of palladium (<0.1 ppm) was detected by ICP-OES in the product solution.