A Little Palladium Does A Lot Of Cross-Coupling

As part of their efforts in developing greener chemistry, Bruce H. Lipshutz and his group at the University of California, Santa Barbara, have already pared Suzuki-Miyaura cross-coupling reactions down to no organic solvent, little if any heating, and a minimum of palladium catalyst. But the fact that their recyclable aqueous reaction system still requires a relatively expensive amount of scarce palladium has bothered Lipshutz. His group has now found a way to reduce the amount of palladium further. Working in collaboration with Novartis, the researchers discovered that some types of inexpensive, commercially available FeCl₃ naturally contain parts-per-million amounts of the precious metal. When the team processes the iron salt into nanoparticles, there’s just enough palladium on board to catalyze cross-couplings (Science 2015, DOI: 10.1126/science.aac6936). The chemistry is made possible by a designer surfactant Lipshutz invented, called TPGS-750-M, that when added to water forms lipophilic nanomicelles. The size and structure of these tiny reaction vessels control the flux of reactants, catalyst, and product into and out of the nanomicelles to optimize reaction rates. The researchers show that the new iron nanoparticles contain about one-hundredth the amount of palladium typically used in cross-coupling reactions and that it’s free with the purchase of FeCl₃.