The chemistry of rare earth elements (La–Lu, Sc and Y) touches key issues in modern inorganic chemistry including metals criticality, sustainability, and the global carbon cycle. In this talk, I will present on two projects from my research group involving targeted separations chemistry for metals recycling and a new, natural bioinorganic chemistry for the rare earths. Rare earth elements are essential in renewable energies technologies including in permanent magnets for wind turbines, hybrid and electric vehicles, energy efficient lighting phosphors and many others. The rare earths are relatively abundant in the earth’s crust. But the conventional separations chemistry used to purify them proceeds through solvent extraction, a scalable but (stepwise) poorly efficient process that includes an unsustainable environmental burden. We have developed a hydroxylamine ligand, H3TriNOx, and its coordination chemistry. The RE(TriNOx) RE = La–Lu, Y series led to identification of an unusual solubility dependence of the resulting complexes, which afforded a new method for separating rare earth elements, especially for recycling. The TriNOx3– ligand also exhibits redox activity when coordinated to metal cations. We have recently determined that this redox activity can be exploited for metal separations based on variable rates of oxidation. Despite the relatively large abundances of early rare earth elements, it had been widely believed that these elements had no role in biology. Recently, however, a metalloenzyme was discovered that includes cerium, lanthanum and other elements in its active site. This methanol dehydrogenase, Xoxf, catalyzes the conversion of methanol to formaldehyde and, uniquely, to formate. We have developed a tethered quinolone quinone ligand that replicates the structure and function of the active site of the Xoxf metalloenzyme for the first time. We have used this compound to study the reactivity of alcohol dehydrogenation using a benzylic alcohol test substrate. Our results contribute to understanding about why Nature selects for lanthanides in this case and to understanding the reaction mechanism of the Xoxf methanol dehydrogenase.












Eric Schelter (University of Pennsylvania)