Acid Activation in Phenyliodine Dicarboxylates: Direct Observation, Structures, and Implications

The use of the hypervalent iodine reagents in oxidative processes has become a staple in modern organic synthesis. Frequently, the reactivity of λ³ iodanes is further enhanced by acids (Lewis or Brønsted). The origin of such activation, however, has remained elusive. Here, we use the common combination of PhI(OAc)₂ with BF₃·Et₂O as a model to fully explore this activation phenomenon. In addition to the spectroscopic assessment of the dynamic acid–base interaction, for the first time the putative PIDA·BF₃ complex has been isolated and its structure determined by X-ray diffraction. Consequences of such activation are discussed from a structural and electronic (DFT) points of views, including the origins of the enhanced reactivity.