There are several reported methods for Cu-catalyzed iododeboronation, each with subtle variations in copper source, ligand, and associated reaction conditions. Related copper-catalyzed or -mediated halodeboronation reactions, such as the equivalent fluorination reaction, also operate with similar reaction conditions. This general reaction class therefore has broad applications across synthetic chemistry and specific applications in bio-facing fields. Very limited mechanistic information is available on the halodeboronation reaction in general, with a tentative mechanistic description of the iododeboronation largely based on the framework of the Chan-Lam reaction (Scheme 1b). This proposed mechanism involves transmetalation of the arylorganoboron compound to Cu(II), giving a Cu(II)(aryl) species, followed by disproportionation to Cu(III), and anion exchange/reductive elimination to give the aryl iodide product and Cu(I). Aerobic reoxidation of Cu(I) to Cu(II) closes the cycle. Despite the importance and influence that ligand stereoelectronics exert on redox processes at metal centers, robust identification of intermediate ligand structure and speciation states remains a general problem in Cu-mediated oxidative catalysis. This renders the study of key mechanistic events, such as transmetalation, disproportionation, and oxidative turnover, difficult to understand and, therefore, control through rational catalyst design. The main knowledge in this area arises from several key studies of catalytic reactions. Hartwig identified a Cu(III) intermediate in solution and proposed a mechanism for transmetalation of arylboronic acid pinacol (ArBpin) esters in a fluorodeboronation reaction using an F + reagent, with ligands proposed for this key intermediate and event. Stahl, Watson, and Schaper proposed ligand sets for related Chan-Lam etherification and amination reactions, with broadly similar descriptions of rate-limiting transmetalation. Computational analysis of Chan-Lam amination reactions have aligned closely, although with some differences in the interpretation of the ratelimiting event. While integral to many Cu-based oxidative coupling reactions, there is limited information on the disproportionation event or oxidative turnover. Here we report a detailed mechanistic description of the Cucatalyzed iododeboronation reaction using a combination of structural, spectroscopic, and computational analyses. For the first time, this includes an assessment of ligand structure at all stages of the proposed catalytic cycle. More broadly, this analysis has provided insight into the transmetalation, disproportionation, and oxidative turnover events that underpin many Cumediated oxidative coupling reactions.