Detailed Electrochemical Analysis of the Redox Chemistry of Tetrafluorotetracyanoquinodimethane TCNQF4, the Radical Anion [TCNQF4]•-, and the Dianion [TCNQF4]2- in the Presence of Trifluoroacetic Acid

The electrochemistry of 2,3,5,6-tetrafluoro-7,7, 8,8-tetracyanoquinodimethane (TCNQF(4)), [TCNQF(4)](center dot-), and [TCNQF(4)](2-) have been studied in acetonitrile (0.1 M [Bu4N]-[ClO4]). Transient and steady-state voltammetric techniques have been utilized to monitor the generation of [TCNQF(4)](center dot-) and [TCNQF(4)](2-) anions as well as their reactions with trifluoroacetic acid (TFA). In the absence of TFA, the reduction of TCNQF(4) occurs via two, diffusion controlled, chemically and electrochemically reversible, one-electron processes where the reversible formal potentials are 0.31 and -0.22 V vs Ag/Ag+. Unlike the TCNQ analogues, both [TCNQF(4)](center dot-) and [TCNQF(4)](2-) are persistent when generated via bulk electrolysis even under aerobic conditions. Voltammetric and UV-vis data revealed that although the parent TCNQF(4), does not react with TFA, the electrochemically generated radical anion and dianion undergo facile protonation to yield [HTCNQF(4)](center dot), [HTCNQF(4)](-) and H(2)TCNQF(4) respectively. The voltammetry can be simulated to give a complete thermodynamic and kinetic description of the complex, coupled redox and acid-base chemistry. The data indicate dramatically different equilibrium and rate constants for the protonation of [TCNQF(4)](center dot-). (K-eq = 3.9 x 10(-6), k(f) = 1.0 x 10(-3) M-1 s(-1)) and [TCNQF(4)](2-) (K-eq = 3.0 x 10(3), k(f) = 1.0 x 10(10) M-1 s(-1)) in the presence of TFA.