Electrochemical Reductive Deprotonation of an Imidazole Ligand in a Bipyridine Tricarbonyl Rhenium(I) Complex



The reduction pathway of fac-[ReI(imH)(CO)3(bpy)]+ was studied in situ by UV/Vis/NIR–IR spectroelectrochemistry with an OTTLE cell. The complex underwent 1e reduction of the 2,2′-bipyridine (bpy) ligand and intramolecular electron transfer, which resulted in the conversion of the axial imidazole (imH) ligand to 3-imidazolate (3-im). This step was followed by two bpy-based 1e reductions to ultimately produce five-coordinate [Re(CO)3(bpy)] and free 3-im. The identity of the reduction product fac-[Re(3-im)(CO)3(bpy)] has been proven by partial chemical deprotonation of the parent complex followed by IR spectroelectrochemistry. This is the first time that the reductive electrochemical conversion of metal-coordinated imidazole to terminal 3-imidazolate has been observed.