Template‐Controlled Synthesis of Polyimidazolium Salts by Multiple [2+2] Cycloaddition Reactions

Abstract

The tetrakisimidazolium salt H4‐2(Br)4, featuring a central benzene linker and 1,2,4,5‐(nBu‐imidazolium‐Ph‐CH=CH‐) substituents reacts with Ag2O in the presence of AgBF4 to yield the tetranuclear, oktakis‐NHC assembly [3](BF4)4. Cation [3]4+ features four pairs of olefins from the two tetrakis‐NHC ligands perfectly arranged for a subsequent [2+2] cycloaddition. Irradiation of [3](BF4)4 with a high pressure Hg lamp connects the two tetra‐NHC ligands through four cyclobutane linkers to give compound [4](BF4)4. Removal of the template metals yields the novel oktakisimidazolium salt H8‐5(BF4)8. The tetrakisimidazolium salt H4‐2(BF4)4 and the oktakisimidazolium salt H8‐5(BF4)8 have been used as multivalent anion receptors and their anion binding properties towards six different anions have been compared.