Suzuki-Miyaura coupling reactions using novel metal oxide supported ionic palladium catalysts

Palladium substituted CeO₂, SnO₂ and their mixed oxides have been synthesized in quantitative yields out of non-toxic and inexpensive precursors using a simple and rapid single step solution combustion method. The resulting oxides, especially the mixed oxides Ce_0.79Sn_0.20Pd_0.01O_2-δ, Sn_0.79Ce_0.20Pd_0.01O_2-δ and Sn_0.99Pd_0.01O_2-δ proved to be highly active (TOF > 12,000 h⁻¹) for Suzuki-Miyaura cross-couplings of phenylboronic acid with various bromoarenes. The reactions were carried out in ambient air at moderate temperatures using environmentally friendly aqueous ethanol solutions as reaction solvents. Minimal amounts of palladium in the product solution ( < 0.14 mg/L), the reaction kinetics as well as catalyst poisoning tests support the thesis that the reaction proceeds via dissolved palladium species in a homogeneous reaction mechanism. Nevertheless, the synthesized catalysts could be reused for at least five times with only minor changes in activity and no changes in the crystal structure, indicating the high potential of the investigated catalysts as quasi-heterogeneous CC coupling catalysts.