The Observation of Dianions Generated by Electrochemical Reduction of trans-Stilbenes in Ionic Liquids at Room Temperature

Abstract

Three highly aprotic bis(trifluoromethylsulfonyl)amide (NTf2(-)) based ionic liquids (ILs) containing the cations trihexyl(tetradecyl)phosphonium (P6,6,6,14(+)), N-butyl-N-methylpyrrolidinium (Pyrr4,1(+)), and (trimethylamine)(dimethylethylammine)dihydroborate ((N111)(N112)BH2(+)) have been examined as media for room temperature voltammetric detection of highly basic stilbene dianions electrochemically generated by the reduction of trans-stilbene (t-Stb) and its derivatives (4-methoxy-, 2-methoxy-, 4,4'-dimethyl-, and 4-chloromethyl-). Transient and steady-state data in the ILs were compared with results obtained in the molecular solvent acetonitrile. In all media examined, the t-Stb(0/•-) process is chemically and electrochemically reversible with a heterogeneous charge transfer rate constant in CH3CN of 1.5 cm s(-1), as determined by Fourier transformed AC voltammetry. However, further reduction to the dianion was always irreversible in this molecular but weakly acidic solvent. On the other hand, a substantial level of chemical reversibility for the reduction of t-Stb(•-) to t-Stb(2-) on the time scale of cyclic voltammetry is achieved when the concentration of trans-stilbene, [t-Stb], appreciably exceeds the concentration of adventitious water or other proton sources. In particular, these conditions are met when [t-Stb] ≥ 0.1 M in thoroughly dehydrated and purified ILs, while in the presence of CH3CN, t-Stb(2-) still suffers fast irreversible protonation under these stilbene concentration conditions. The E0/•-(0) values (vs Fc(0/+)) for substituted trans-stilbenes in acetonitrile and (N111)(N112)BH2-NTf2 do not differ substantially, nor do the E0/•-(0) and E•-/2-(0) differences or other aspects of the voltammetric behavior.

Electrochemistry and Spectroelectrochemistry of 1,4-Dinitrobenzene in Acetonitrile and Room-Temperature Ionic Liquids: Ion-Pairing Effects in Mixed Solvents

“…The large ΔEp could be explained by the uncompensated resistance, assuming reversible electron transfers (keeping the ΔE12° value small). The increase in stability of very basic dianions in RTIL at higher substrate concentrations was also reported by Abdul-Rahim et al, 26 for the voltammetry of trans-stilbene in another NTf2 RTIL. The chemical irreversibility of the wave was attributed to the reaction of the stilbene dianion with trace water.…”

Rare Earth Arene-Bridged Complexes Obtained by Reduction of Organometallic Precursors

“…It was found that Y 2 -naph is the strongest reducing agent while Y 2 -anth is the weakest, with Y 2 -stilbene being in the middle of the series. This series parallels the reduction potential of the bridging arenes in the free form (Abdul-Rahim et al, 2013;Connelly and Geiger, 1996). Consequently, the reaction of Y 2 -stilbene and 2,2′-bipyridine (bipy) or phenylacetylene (PhCCH) resembled the reactivity of As remarked in this section, group 3 metals prefer binding to the central C-C bond rather than an aromatic ring as observed for uranium (Diaconescu and Cummins, 2012).…”

The role of cations in the reduction of 9-fluorenone in bis(trifluoromethylsulfonyl)imide room temperature ionic liquids

“…[5][6][7] Hence, the most active field in electrochemistry, together with RTILs, is currently focused on electrodeposition, [8][9][10] supercapacitors, 11 batteries, [12][13][14] and the study of the heterogeneous electron transfer of electroactive organic compounds in RTILs. [15][16][17][18][19][20][21] It is important to note that the ''stabilization'' of radicals and radical anions has been observed in few cases (such as nitroderivatives, 15,16 halogenated compounds, 22,23 acetophenone, 24 stilbene, 25 and superoxide ions 26 ). Following this approach, it is possible to determine the electrocatalytic properties of some RTILs, understanding as electrocatalytic properties the fact that the same reduction or oxidation process can take place at a lower potential value depending on the composition of the RTILs.…”