August 12, 2016
Chemical synthesis can transform commodity chemicals into complex life-saving drugs, household products, or advanced materials. But this “alchemy” can also produce huge amounts of toxic waste or require harsh and dangerous conditions—and often relies on expensive and rare metals to spark reactions.
In recent reports in the journals Dalton Transactions and the Journal of the American Chemical Society, the research team of Liviu Mirica, Associate Professor of chemistry in Arts & Sciences at Washington University in St. Louis, has developed novel methods for generating the building blocks of important compounds with nickel.
The work expands scientists’ toolbox for nickel-based chemistry. It contributes to the movement of “green chemistry” toward a 21st century of sustainable synthesis, with chemical transformations that are more efficient, produce fewer by-products and, most importantly, create less waste.
Mirica’s lab researches how to create these new compounds in as few steps as possible and with more sustainable catalysts, like nickel.
Carbon-hydrogen (C-H) bonds are considered unreactive and can be difficult to coax into creating a new carbon-carbon (C-C) bond. So chemists like Wen Zhou, the postdoctoral scholar, who is the first author of the two recent reports, rely on metals to “activate the bond,” and make it more reactive.
The rare metals palladium and platinum have been used for decades, but are expensive. Nickel, in the same chemical group, could be used for similar reactions if its properties were understood better.
New four-pronged molecule
The scientists’ key development was the creation of a new four-pronged molecule, known as a tetradentate ligand, which acts like the pocket of a baseball glove to grasp the nickel atom. When carbon-containing compounds also bind to the nickel centre, the electrons can reposition to form a new C-C bond.
The right balance of stability and reactivity allowed the scientists to create new bonds with inexpensive, safe and abundant nitriles, a class of carbon-containing compounds that can be turned into a whole range of useful chemical groups in simple synthetic steps.
The hope is nickel could replace the more costly rare metals that have been used for years in the chemical industry.