Abstract
Palladium’s role as a catalyst in organic synthesis is undeniably crucial in modern society, leading to many of the life-saving medicines as well as the agrochemicals that enable food production for the planet, among other essential products. But most of the advances still underway based on this pgm at typical loadings in the 1-5 mol % range assume its availability well into the future. Is this appropriate? Are “earth-abundant” metals in this picture? And what about the use of Pd catalysis in modern organic synthesis that has only existed these past 200 years or so, having been developed mainly in, and dependent upon, waste-generating organic solvents as the reaction medium which are in large measure derived from petroleum. While recycling of precious metals are the norm, significant quantities of organic solvents are burned, leading to CO2 that adds to climate change. Thus, do any of these current practices contribute to sustainability? Hardly.
The reality is that, today, we do have choices as to how to use our tools in the synthetic chemistry toolbox in environmentally respectful ways. Technologies that look towards Nature, with billions of years of “experience” to its credit, perhaps not surprisingly provides the answer: chemistry in water. Mankind itself is living proof that water-insoluble reaction partners can all be accommodated in an aqueous environment. The same can be said for ligated catalysts, whether containing pgms or otherwise. If used for synthetic purposes at the ppm level following Nature’s lead, access to pgms and most notably, palladium, by future generations would be extended… indefinitely.
Among Nature’s not-so-secret solutions for synthetic chemistry, and Pd-catalyzed couplings, in particular, is water-based micellar catalysis. This appraoch is characterized by very little, if any, use of organic solvents, ppm loadings of Pd, recycling of the aqueous reaction medium, and almost no waste. Chemistry in water: it’s our future.
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Biography
Bruce H. Lipshutz is a distinguished professor at University of California holding multiple honors and awards. The Lipshutz research group continues to develop new technologies in green chemistry, with the specific goal being to get organic solvents out of organic reactions, as organic solvents are, by far, responsible for most of the organic waste created by the chemical enterprise, and derive mainly from finite petroleum reserves. To accomplish this goal, the concept of “designer” surfactants has been introduced within the area of aqueous micellar catalysis. The nanoparticles that form in water from these amphiphiles act as nanoreactors, enabling key transition metal-catalyzed cross-couplings, and many other reactions, to be carried out in water under mild conditions. The group has also focused its attention on developing new catalysts for key Pd- and several other transition metal-catalyzed reactions that enable C-C, C-N, and C-H bond formation typically at the parts per million level of the metal. Most recently, these newly developed technologies in chemo-catalysis are being merged with enzymatic processes, done in tandem in 1-pot, and all in water.