A series of pyrazine-based calixarene extractants was prepared by a stepwise functionalization, comprising palladium-catalyzed exhaustive cross-coupling of di- and tetrasubstituted calixarenes bearing chloropyrazine moieties. The extraction behavior of the synthesized ligands was studied on Am–Eu mixtures under acidic feed conditions similar to those prevailing in nuclear wastes. Phosphorylpyrazine-bearing extractants exhibited a very high acid resistivity and a high affinity for americium giving D values as high as 794 at pH 1. The synergistic effect of the chlorinated cobalt bis(dicarbollide) anion [(B9C2H8Cl3)2Co]− (CCD-anion), as well as the effect of the calixarene platform compared to monovalent ligands, was investigated. The presence of 1 mM CCD resulted in a 105 times increase in the D value.
Nikishkin, N., Huskens, J., Ansari, S. A., Mohapatra, P. K., & Verboom, W. (2013). Pyrazine-functionalized calixarenes: synthesis by palladium-catalyzed cross-coupling with phosphorus pronucleophiles and metal ion extraction properties. New journal of chemistry, 37(2), 391-402. https://doi.org/10.1039/C2NJ40791D