Stepwise Synthesis of -imidazolium Macrocycles and Their -Heterocyclic Carbene Metal Complexes.

A modular stepwise synthetic method has been developed for the preperation of -imidazolium macrocycles. Initially a series of three (imidazolylmethyl)benzene precursors were alkylated with 1,2-dibromoethane to produce the corresponding -bromoethylimidazolium bromide salts. In the second step the -bromoethylimidazolium bromide salts were reacted with selected (imidazolylmethyl)benzene molecules to produce a series of two symmetrical and three asymmetrical -imidazolium macrocycles. These -imidazolium salts act receptors for anions and H-NMR titration studies were used to determine the association constants between two of the macrocycles and the halide anions chloride, bromide and iodide. The -imidazolium salts are precursors for -heterocyclic carbene (NHC) ligands and the corresponding silver(I), gold(I), and palladium(II) NHC complexes have been prepared. Varied structures were obtained, which depend on the chosen macrocyclic ligand and metal ion and in the case of the coinage metals Ag(I) and Au(I), mono, di, and hexanuclear complexes were formed.