Small molecule redox mediators convey interfacial electron transfer events into bulk solution and can enable diverse substrate activation mechanisms in synthetic electrocatalysis. Here we report that 1,2-diiodo-4,5-dimethoxybenzene (1a) is an efficient electrocatalyst for C-H/E-H coupling that operates at as low as 0.5 mol% catalyst loading. Spectroscopic, crystallographic, and computational results indicate a critical role for a three-electron I-I bonding interaction in stabilizing an iodanyl radical intermediate (i.e., formally I(II) species). As a result, 1a operates at more than 100 mV lower potential than related monoiodide catalysts, which results in improved product yield, higher Faradaic efficiency, and expanded substrate scope. The isolated iodanyl radical is chemically competent in C-N bond formation. These results represent the first examples of substrate functionalization at a well-defined I(II) derivative and bona fide iodanyl radical ca-talysis and demonstrate one-electron pathways as a mechanistic alternative to canonical two-electron hypervalent iodine mechanisms. The observation establishes I-I redox cooperation as a new design concept for the development of metal-free redox mediators.
