Room Temperature Electro-carboxylation of Styrene and Stilbene Derivatives: A Comparative Study

The use of carbon dioxide as a comparatively cheap, abundant and non-toxic C-1 synthon is a topic of considerable interest and importance. The electrochemical addition of carbon dioxide across carbon-carbon double bonds is one of the more promising of such procedures, offering the possibility to convert a range of alkene substrates to valuable carboxylated products. However, much remains unknown about both the mechanism of reaction and how to influence product specificity during electro-carboxylation of alkenes. Herein, we explore the electrochemical addition of carbon dioxide (1 atm) to a range of olefinic substrates using nickel working electrodes and magnesium anodes at room temperature, producing the mono-substituted carboxylate derivatives preferentially (with no formation of the Markovnikov isomers of these mono-substituted carboxylate derivatives when the starting materials are non-symmetrical). These findings are rationalized using both experimental and computational methods, suggesting that the choice of Ni as a working electrode is critical in determining the reaction outcomes that are observed. Moreover, we also present direct evidence that a pathway whereby the alkene substrates are first reduced at the electrode surface and then react with dissolved CO2 is operating. Together, these results offer the potential for selective access to a range of valuable mono-carboxylic acids via the reduction of the corresponding alkene precursors in the presence of carbon dioxide.