Halogen bonded associates of iodonium salts with 18-crown-6: does structural flexibility or structural rigidity of the σ-hole donor provide efficient substrate ligation?

Abstract

¹H NMR titration of 18-crown-6 with diphenyliodonium triflate and dibenziodolium triflate indicated that the acyclic iodine(III)-containing species has a higher binding constant value compared with the cyclic analogue. Formation of triple associates diphenyliodonium⋯18-crown-6⋯diphenyliodonium was observed in CD₃CN. DFT calculations and QTAIM analysis indicated that the acyclic iodonium salt forms a higher number of interactions with the crown ether compared with the cyclic cation, which results in the formation of triple associates. The formation of dibenziodolium⋯18-crown-6⋯dibenziodolium triple associates turned out to be energetically unfavorable, which agrees with the experimentally obtained data.