Diamidopyrazoles: A new class of anion receptors

The synthesis of a series of 3,5-diamidopyrazoles is reported. The anion binding properties of these systems were examined via (1)H NMR, UV/Vis and ITC titration techniques. Target compound 2a acts as a selective receptor for phosphate and sulfate anions in DMSO, whereas N-methylated 2b and the unmethylated species 4d show no appreciable binding affinity. Insights into the binding events occurring in solution came from the solid state structures of compounds 2a and 4a, 4b, and 4d, which were deduced from single crystal X-ray diffraction analyses.