The Flexibility of Tetra(N‐Heterocyclic Carbene) Ligands Controls the Nuclearity and Geometry of Polynuclear MI‒NHC Assemblies

A series of tetrakisimidazolium salts bearing two di(phenylimidazolium)amine groups linked by differently substituted anthracenes has been prepared. These are H4‐1a(PF6)4 (anthracene bridge), H4‐1b(PF6)4 (phenyl‐anthracene‐phenyl bridge), H4‐1c(PF6)4 (anthracene‐phenyl bridge) and H4‐1d(PF6)4 (anthracene‐phenyl‐anthracene bridge). X‐ray crystallography showed that those ligand precursors having the di(phenylimidazolium)amine connected directly to the anthracene experience restricted rotation about the N−Canthracene bond. Depending on their flexibility, the reaction of the tetrakisimidazolium salts with Ag2O followed by transmetalation with [AuCl(THT)] yielded octanuclear ([Au8(1a)4](PF6)8), tetranuclear ([Au4(1b)2](PF6)4), hexanuclear ([Au6(1c)3](PF6)6) or octanuclear ([Au8(1d)4](PF6)8) assemblies, demonstrating the direct bonding strategy can be employed for the selective synthesis of polynuclear poly‐NHC (NHC = N‐heterocyclic carbene) metallosupramolecular assemblies.