[Re(bpy-tBu)(CO)4](OTf) (bpy-tBu = 4,4′-di-tert-butyl-2,2′-bipyridine, OTf = trifluoromethanesulfonate) (1) and [Re(bpy)(CO)4](OTf) (bpy = 2,2′-bipyridine) (2) were synthesized and studied as proposed intermediates in the electrocatalytic reduction of carbon dioxide (CO2) by Re(bpy-R)(CO)3X. Both compounds demonstrated increased current responses in cyclic voltammograms under CO2. Complex 1 was also characterized by X-ray crystallography. Infrared-spectroelectrochemistry (IR-SEC) of 1 and 2 indicated that upon exposure of the cationic tetracarbonyl compounds to a reducing potential, a CO ligand is labilised and [Re(bpy-R)(CO)3(CH3CN)]+ species are formed. This is proposed to occur via an electron-transfer-catalysed process wherein a catalytic amount of reduced species propagates a ligand exchange reaction. Addition of a catalytic amount of potassium intercalated graphite (KC8), a chemical reductant, to a solution of 1 or 2 also yielded quantitative formation of [Re(bpy-R)(CO)3(CH3CN)]+, which indicates that the CO loss is catalysed by electron transfer, and not the electrode itself.
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