Pushing redox potentials to highly positive values using inert fluorobenzenes and weakly coordinating anions

Abstract

While the development of weakly coordinating anions (WCAs) received much attention, the progress on weakly coordinating and inert solvents almost stagnated. Here we study the effect of strategic F-substitution on the solvent properties of fluorobenzenes C6FxH6−x (xFB, x = 1–5). Asymmetric fluorination leads to dielectric constants as high as 22.1 for 3FB that exceeds acetone (20.7). Combined with the WCAs [Al(ORF)4]− or [(FRO)3Al-F-Al(ORF)3]− (RF = C(CF3)3), the xFB solvents push the potentials of Ag+ and NO+ ions to +1.50/+1.52 V vs. Fc+/Fc. The xFB/WCA-system has electrochemical xFB stability windows that exceed 5 V for all xFBs with positive upper limits between +1.82 V (1FB) and +2.67 V (5FB) vs. Fc+/Fc. High-level ab initio calculations with inclusion of solvation energies show that these high potentials result from weak interactions of the ions with solvent and counterion. To access the available positive xFB potential range with stable reagents, the innocent deelectronator salts [anthraceneF]+∙[WCA]− and [phenanthreneF]+∙[WCA]− with potentials of +1.47 and +1.89 V vs. Fc+/Fc are introduced.