Insight into trifluoromethylation - experimental electron density for Togni reagent I

3,3-Dimethyl-1-(trifluoromethyl)-1,3-dihydro-1-lambda 3,2-benziodoxole represents a popular reagent for trifluoromethylation. The sigma hole on the hypervalent iodine atom in this Togni reagent is crucial for adduct formation between the reagent and a nucleophilic substrate. The electronic situation may be probed by high resolution X-ray diffraction: the experimental charge density thus derived shows that the short intermolecular contact of 3.0 angstrom between the iodine and a neighbouring oxygen atom is associated with a local charge depletion on the heavy halogen in the direction of the nucleophile and visible polarization of the O valence shell towards the iodine atom. In agreement with the expectation for lambda 3-iodanes, the intermolecular O center dot center dot center dot I-C-aryl halogen bond deviates significantly from linearity.