Voltammetric Studies with Adhered Microparticles and the Detection of a Dependence of Organometallic Cis+→ Trans+First-Order Isomerization Rate Constants on the Identity of the Ionic Liquid

Abstract

Voltammetric studies employing electrode surfaces modified with microparticles of redox active solid can be used conveniently to obtain thermodynamic and kinetic information in ionic liquids in cases where a first-order chemical reaction of rapidly dissolved electrolyzed product is coupled to the electron-transfer process. Experimental and theoretical verification of this concept is provided. A study based on the voltammetric oxidation of durene (J. Phys. Chem. A 2003, 107, 745) to its cation radical contains a first-order followup chemical reaction that is almost independent of whether organic solvent (electrolyte) or ionic liquid media are used. In contrast, it has now been found that the rate constants (kf) for the first-order cis+ → trans+ isomerization reactions that accompany the one-electron oxidation of microparticles of the organometallic compounds cis-[Mn(CN)(CO)2{P(OPh)3}(DPM)] (DPM = Ph2PCH2PPh2) or cis-[W(CO)2(DPE)2] (DPE = Ph2PCH2CH2PPh2) depend significantly on the identity of the ionic liquid. In the case of trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate ionic liquid, kf is similar to the value found in conventional organic solvent (electrolyte) media, but significantly faster than that in the ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate, (1-ethyl-3-methylimidazolium)bis[(trifluoromethyl)sulfonyl]amide, and (N-butyl-N-methylpyrrolidinium)bis[(trifluoromethyl)sulfonyl]amide. No simple correlation of kf values with the physical or chemical properties of these ionic liquids has been elucidated.