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.