Coordination diversity of Ag(I) and Hg(II) towards symmetrically and non-symmetrically substituted imidazol-2-ylidenes: Synthesis, crystal structures, nitrile reactivity, and Hofmann-type elimination studies

Two mesityl bridged bis-1H-imidazolium salts having bromide/hexafluorophosphate counter ions have been prepared, compared with similar ortho-xylyl bridged salts and characterized by various spectral and X-ray diffraction techniques. The salt having 2-cyanoethyl substituents undergoes hydrolysis to produce compartmental 1H-imidazolium salts. Further, these salts are involved in the Hofmann-type elimination to produce bis-imidazole and Ag(I)- and Hg(II)-coordination compounds when treated with Ag2O and Hg(OAc)2 in different ratios. Furthermore, a 3-nitrile-substituted imidazolium salt was prepared and treated with the aforementioned metal sources to evaluate the elimination reaction. However, it forms stable N-heterocyclic carbene (NHC) complex without eliminating any of the cyano-substitutions. Both, imidazolium salts and Ag(I)- and Hg(II)-coordination/NHC complexes have been characterized by 1H and, 13C NMR, FTIR spectral, and elemental and single crystal X-ray diffraction analyses.

Imidazolium salt with 2-cyanoethyl substituents undergoes hydrolysis to produce 1H-imidazolium salt. Further, this salt is involved in the Hofmann-type elimination when treated with Ag2O/Hg(OAc)2. However, analogues imidazolium salt with bis-benzonitrile substitution forms stable NHC complexes.Figure optionsDownload as PowerPoint slideHighlights
► Two bis-1H-imidazolium salts (3a/b) were synthesized and characterized.
► Both 3a/b undergo Hofmann-type elimination when treated with Ag2O/Hg(OAc)2.
► To compare the reactivity, bis-benzonitrile imidazolium salt (7) was prepared.
► Salt 7 did not undergo elimination upon treatment with the mentioned metal sources.