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

The tetrakisimidazolium salt H-4-2(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 AgBF(4)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 H-8-5(BF4)(8). The tetrakisimidazolium salt H-4-2(BF4)(4)and the oktakisimidazolium salt H-8-5(BF4)(8)have been used as multivalent anion receptors and their anion binding properties towards six different anions have been compared.