Fluorination
mediated by the cyclic hypervalent fluoroiodane reagent
(1) often requires an exogenous Lewis acid. The widely
accepted Lewis-acid-activation model is that a given Lewis acid binds
to the oxygen atom of 1 (O-coordination) to polarize
the I–O bond. Computational studies of silver-mediated geminal
difluorination of styrenes with 1 reveal a new “F-coordination”
model that is energetically much preferred over the commonly accepted
“O-coordination” model. The calculations rationalize
the regioselective formation of the geminal difluorination product.