Based on the totality of the dataset, an illustrative description of the proposed key events of the catalytic cycle is provided in Scheme 5. In summary, a combination of experimental and computational investigations has provided the first complete description of the Cu-catalyzed iododeboronation reaction. This analysis has revealed the key role of the ligand in three critical steps -facilitating transmetalation via H-bonding to the boronate and promoting the key oxidative events (disproportionation and turnover). More specifically, ligand speciation is a key operationligand loss is required at disproportionation, but gain is required at oxidative turnover, which provides a basis for understanding of ligand stoichiometry. These data therefore add to the wider knowledge base of Cu-mediated oxidative coupling reactions and may support understanding and development of related processes, including the related fluorodeboronation reaction.