Sequential Disproportionation Enables Aggregation of Four Electron-Holes at a Hypervalent Iodine Center

Abstract

The interfacial electron transfer events that underpin electrochemistry effect one-electron oxidation or reduction of substrates. In contrast, selective bond-forming and -breaking in synthetic chemistry requires the choreographed management of two-electron steps. Thus, application of electrochemistry in synthesis requires strategies to aggregate multiple redox equivalents to engender multi-electron reactions. Here we demonstrate that sequential disproportionation reactions can enable selective aggregation of two- or four electron-holes at a hypervalent iodine center. Disproportionation of an anodically generated iodanyl radical (i.e., I(II) species) affords an iodosylbenzene derivative (i.e., I(III) species). Subsequent iodosylbenzene disproportionation can be triggered to provide access to iodoxybenzene (i.e., I(V) species). Both the transient iodanyl radical intermediate that engages in disproportionation to afford I(III) species and the O-bridged bis-I(III) compound that mediates iodosylbenzene disproportionation to afford I(V) species have been directly characterized. These results represent the first example of iodanyl radical disproportionation as a means to access I(III) compounds and demonstrate aggregation of four electron at the one-electron potential by selective and sequential disproportionation chemistry.