Electrochemical synthesis could become an attractive means to exploit the largely available and thus cheap C1 building block, CO2. However, major developments in the identification of (energy) efficient catalysts are still required. The C–C bond formation between an unsaturated hydrocarbon and CO2 is an elegant synthetic process to form dicarboxylic acids.1 Theoretical studies of heterogeneous electrocatalyis under aprotic conditions are still challenging, mostly because the electrochemical potential and the solvent should be accounted for. Focusing on two side-reactions of the carboxylation reaction (intrinsic reactivity of CO22 and reaction with traces of water3), we have established an efficient combination between the explicit treatment of the electrochemical potential and an implicit solvent description. Our experimental results identify the onset potential for the C–C coupling between butadiene and CO2 to be -1.3 V vs. SHE. However, the kinetics are sluggish and -2.5 V are necessary in practice. Our extensive computational investigation identifies the first carboxylation reaction as the rate limiting step. In the vicinity of the onset potential this step is, unfortunately, a chemical step and the overpotential does, therefore, not substantially accelerate the production of the diacid. The generation of almost ”free” CO2- radicals at potentials around -2.5 V opens a more facile reaction path. Our computations have, furthermore, elucidated that the activation energies for the first carboxylation reaction are significantly lower over Ni(111) than over Pt(111), explaining the superior catalytic activity of Ni compared to Pt. For the design of an improved catalyst one would need to lower the activation energy, which might be achieved by modifying the morphology (e.g. steps) of the electrode. 1 CH Li, GQ Yuan, XC Ji, XJ Wang, JS Ye, HF Jiang, Electrochim Acta 2011, 56, 1529. 2 SN Steinmann, C Michel, R. Schwiedernoch, P. Sautet Phys. Chem. Chem. Phys. 2015, 17, 13949. 3 SN Steinmann, C Michel, R. Schwiedernoch, JS Filhol P. Sautet Chem. Phys. Chem. 2015, 16, 2307.

Mechanistic study of the electro-carboxylation of alkenes

251st National Meeting (2016)

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