The reaction shows negligible background reactivity in DCM even after prolonged reaction times, and the presence of 20 mol-% of bidentate m/p-1, as well as of non-iodinated 3-H also did not induce any additional product formation. The iodinated analog 3, however, showed catalytic activity. As we envision a two-point binding motif between the two oxygen atoms of the nitro group and two iodine substituents, it is conceivable that the increase in activity between m/p-1 and 3 is due to a further halogen bonding interaction with the third iodine center of 3 and the  system of the substrate. This hypothesis was corroborated when the transition state of the initial addition step, catalyzed by carborane-derived catalyst 3, was modeled via DFT calculations (M06-2X-D3/def3-TZVP(D)): two iodine substituents form halogen bonds to an oxygen atom of the nitro group each, while the third one indeed binds to the -carbon. All of these interactions are close to linearity, and the two halogen bonds to oxygen are somewhat stronger than the one to carbon (RXB = 0.80 and 0.81 versus 0.85). The reaction barrier was calculated to be about 26 kcal/mol. More detailed investigations of the whole reaction mechanism, including a potential involvement of water, will be necessary to confirm the rate-determining step. These calculations though are outside the scope of this study. A short solvent screening revealed best catalysis results in toluene (see SI). This is interesting insofar as hydrogen bond donors often show low solubility in toluene. Thus, this strong performance in such an apolar environment demonstrates the particular characteristics of neutral halogen bond donors as "hydrophobic counterparts" to the naturally more polar hydrogen bond donors. Whilst no catalyst decomposition of 3 could be detected by NMR, the reaction was performed in the presence of sodium thiosulfate to quench any traces of iodine present (as a possible decomposition product). When the reaction temperature was increased from room temperature to 45°C, satisfying yields above 80% could be obtained after 48h. The kinetic profile of the reaction under these conditions is shown below (Figure ), which also illustrates that no rate acceleration was observed with the analogous fluorinated XB donor 4. Under these same conditions, CBr4 also remained inert. Overall, even though the carborane-based neutral catalyst does not reach the performance of a dicationic chalcogen bond donor, its activity in a challenging reaction like the present one nevertheless clearly highlights the superiority of the new catalysts over classical fluorinated variants.