[structure: see text] 4-tert-Butyl-1-cyclohexenyl(phenyl)(tetrafluoroborato)-lambda(3)-iodane forms a discrete supramolecular complex by the reaction with 18-crown-6. Solvolysis of the cyclohexenyl-lambda(3)-iodane in the presence of 18-crown-6 indicates that the complexation with 18-crown-6 tends to decrease the leaving group ability of hypervalent phenyl-lambda(3)-iodanyl groups.