Synthesis and Metallation of Unsymmetric Tetrakisimidazolium Macrocycles

The synthesis of the unsymmetric macrocyclic tetrakismidazolium salts H4‐4(PF6)4 and H4‐5(PF6)4 featuring a 2,6‐pyridinylene‐ and a 2‐bromo‐1,3‐xylylene‐bridged bisimidazolium unit is described. Reaction of macrocycle H4‐4(PF6)4 with Ag2O yields the tetranuclear complex [6](PF6)4 composed of four AgI ions sandwiched in between two tetra‐NHC ligands. The 2,6‐pyridinylene‐bridged bisimidazolium moiety of the macrocycles can be site‐selectively deprotonated and metallated with RuII or RhI to give the pincer complexes [8](PF6)3‐[11](PF6)3. Introduction of a second metal in these complexes by deprotonation/metallation and oxidative addition to the 2‐bromo‐1,3‐xylylene‐bridged bisimidazolium moiety of the macrocycles proved not possible. Two unsymmetric macrocyclic tetrakisimidazulim salts have been site‐selectively metallated at the pyridine‐bridged bisimidazolium site to give complexes [8](PF6)3‐[11](PF6)3 while the subsequent metallation of the bromoxylene‐bridged bisimidazoliums site to give heterobimetallic complexes by a deprotonation/oxidative addition reaction sequence failed due to the steric constraints of the macrocycle.