Electrocatalytic reduction of bromothiophenes on gold and silver electrodes: An example of synergy in electrocatalysis

•A striking example of adsorption auxiliary enhancing molecular electrocatalysis.•Ag electrocatalysis in aromatic C–Br cleavage is enhanced by an S anchoring atom.•Au electrocatalysis approaching Ag with an S anchoring atom adjacent to Br.•The anchoring atom helps Au to overcome the repulsive surface charge effect.•Au electrocatalysis is modulated by the relative positions of S and Br atoms.

The electroreduction of bromothiophenes on Au and Ag provides a striking model of synergy in electrocatalysis, when a second group specifically interacting with the catalytic surface is present besides the reacting one, providing an auxiliary anchoring effect. The high catalytic activity of Ag for bromobenzene reduction is enhanced in the bromothiophene case. Moreover, Au, having for bromobenzene a much lower and less reproducible catalytic effect than Ag on account of the repulsive effect of its very negative surface charge in the working potential range, approaches Ag activity in the case of 2-bromothiophene, where the anchoring S group is adjacent to the Br group to be cleaved. The beneficial anchoring effect is lower when it has to be shared between two Br leaving groups adjacent to the S group, and becomes negligible in the case of a bromide leaving group in 3-position.

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