Electrocatalysis in Ionic Liquids

Ionic liquids were originally developed for applications as low-temperature electrolytes because of their excellent electrical conductivity. Although they are likely to be suitable media for electrocatalysis of organic reactions, so far only few electrochemical reactions have been carried out in ionic liquids. 

The complexes Ni(BF4)2(bipy)3 and NiCl2(bipy), the reduction of which occurs at potentials in the range of —1.1 to —1.8 V, were used as catalysts in the ionic liquid medium. 

In the presence of PhBr and PhCH2Br, both Ni(BF4)2(bipy)3 and NiCl2(bipy) showed classical catalytic behavior. A peak for the product of the first oxidative addition of the reduced nickel complex appeared at p = —1.4 to —1.5V when the reactant was Ar(Ni)Br. In this case, the electrochemical catalysis was carried out by maintaining the potential of the working electrode at E = —1.4 V vs. silver. 

The product of the electrochemical reaction was extracted with cyclohexane. The yields observed in the reactions of PhBr and PhCH2Br were 35 and 75%, respectively. In the reaction of PhCH2Br, no toluene was formed, indicating that the process was highly selective and that the reduction of the halogenated substrate was avoided. It was further verified that, at the end of the electrolysis, the catalytic system completely regained its reversibility. The nickel(II) catalyst remained totally in the ionic liquid after the extraction of products, and the catalyst system was reusable. 

The formation of conducting polymers upon the oxidation of benzene and pyrrole in ionic liquids has also been reported.(2d ). 

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Ejigu A, Walsh DA (2014) The role of adsorbed ions during electrocatalysis in ionic liquids. 

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