The Sonogashira Reaction Catalyzed by Palladium Leached from Ordered Mesoporous Carbon

The Sonogashira carbon–carbon coupling reaction between iodobenzene and phenylacetylene was performed using palladium nanoparticles formed directly inside the pores of ordered mesoporous carbon as catalyst. The nanoparticles were generated by two methods, a phase-transfer method and a microemulsion procedure. The coupling reaction was performed using different bases and varying amounts of palladium and the yields and reaction profiles were determined by 1H NMR. Recycling experiments were also performed and the recyclability was found to be very dependent on the choice of base. From the so-called Maitlis’ filtration test it was shown that soluble palladium species were present in solution and these were found to be active in catalyzing the coupling reaction. The degree of leaching depended on the type of base used. The results hint at the Sonogashira reaction being an example of homogeneous rather than heterogeneous catalysis, as has recently been suggested by other authors as well.