Through-Space Electronic Conjugation Enhances Co-Electrocatalytic Reduction of CO2 to CO by a Molecular Cr Complex

The electrocatalytic reduction of CO2 represents an appealing method for converting renewable energy sources into value-added chemical feedstocks. Here, we report a co-electrocatalytic system for the reduction of CO2 to CO comprised of a molecular Cr complex, Cr(tbudhbpy)Cl(H2O) 1, where 6,6′-di(3,5-di-tert-butyl- 2-phenolate)-2,2′-bipyridine = [tbudhbpy]2- and dibenzothiophene-5,5-dioxide (DBTD) as a redox mediator which achieves high activity (1.51-2.84 x 105 s–1) and quantitative selectivity. Under aprotic or protic conditions, DBTD produces a co-electrocatalytic response with 1 by coordinating trans to the site of CO2 binding and mediating electron transfer from the electrode with quantitative efficiency for CO. This assembly is in part reliant on through-space electronic conjugation between the π frameworks of DBTD and the bpy fragment of the catalyst ligand, with important contributions from dispersion interactions and weak sulfone coordination to Cr. Experimental and computational results suggest that this interaction stabilizes a key intermediate in a new aprotic catalytic pathway and lowers the rate-determining transition state under protic conditions. To the best of our knowledge through-space electronic conjugation has not been explored in molecular electrocatalytic systems.