Since the e-sulfinylation is a net reductive process, its mechanism is clearly distinct from the established electrochemical amination 48, 49 and etherification 50 reactions. A cyclic voltammetry study (Figure ) revealed an irreversible reduction of SO2 at -0.78 V against Ag/AgCl standard electrode in CH3CN, and a reversible reduction at similar potential when DIPEA was present, indicating that the amine coordination to SO2 profoundly changes its redox behavior. Since diminished yield of sulfinate 2 was observed without DIPEA, long-lived SO2 •-might be beneficial for an efficient reaction. When the reaction was monitored by HPLC throughout its entire course (Figure ), little conversion of aryl iodide 1 and NMPI was observed during the first 2 F/mol. As 2 equiv of SO2 was employed, this is in agreement with the preferential reduction of SO2 over other constituents in the reaction. Therefore, it is proposed that the plausible mechanism would first involve single-electron reduction of SO2, followed by the reduction of the Ni(II) complex (Figure , step I). The low-valent Ni species would undergo oxidative addition with aryl iodide (step II), and SO2 •-would substitute iodide and reduce the Ni center (step III). The SO2-coordinated aryl Ni complex then undergoes SO2 insertion to give an Ni-sulfinate species (step IV), where substitution by a halide releases aryl sulfinate product from the Ni center (step V). While a workable yield of sulfinate 2 was recorded in the absence of NMPI, it is thought that NMPI acted as a reductive mediator, 75, 76 which also mitigates direct reduction of aryl iodide 1 on the cathode. Although an Ni(I/III/II) system is proposed herein, we cannot exclude the involvement of other possible low-valent Ni-catalytic cycles. In conclusion, the first Ni-catalyzed sulfinylation of aryl halides has been enabled at room temperature using electrochemistry. The employment of an inexpensive catalyst and SO2 stock solution not only provides a mild and economical alternative to canonical Pd catalysis, but also represents a chemoselective method with admirable tolerance to various functional groups that is currently absent in other methods. The scalability and practicality of this reaction were demonstrated in both batch and flow, with convenient access to various S(VI) functional groups, such as sulfonyl fluorides, sulfone and sulfonamide, in a one-pot fashion.