Synthesis and Characterization of Poly-NHC-Derived Silver(I) Assemblies and Their Transformation into Poly-Imidazolium Macrocycles

Abstract

Three metallosupramolecular assemblies composed of two bis-NHCs and two silver atoms, [4](PF6)2, two tetra-NHCs and foursilver atoms, [7](PF6)4, and two tri-NHCs and three silver atoms[8](BF4)3, have been prepared. Assemblies [4](PF6)2and [7](PF6)4feature NHC ligands decorated with terminal olefin groups.Irradiation of [4](PF6)2yielded complex [5](PF6)2with twoterminal cyclobutane rings linking the two bis-NHC ligands.Liberation of the macrocyclic tetrakisimidazolium salt H4-6(PF6)4was achieved by reaction of [5](PF6)2with NH4Cl/NH4PF6. No [2+2] cycloaddition was observed upon irradiation of [7](PF6)4,apparently due to an unfavorable orientation of the olefingroups. Irradiation of complex [8](BF4)3with three internal pairsof olefin groups leads to [9](BF4)3as a mixture of two isomersthat differ on the relative orientation of the internal cyclobutanerings. Reaction of [9](BF4)3with NH4Cl/NH4BF4yields an isomermixture of the novel cage-line hexakisimidazolium salt H6-10(BF4)6

Three poly-imidazolium salts with appended olefins were obtained. Subsequent reaction with Ag2O enabled the preparation of the related poly-NHC-derived silver assemblies, which, depending on the relative orientation of the pendant olefins, underwent [2+2] cyclization of the olefins upon irradiation. The macrocyclic poly-imidazolium salts can be achieved by de-metallation using NH4Cl.