Dinuclear macrocyclic quinoline bridged mercury and silver bis(N-heterocyclic carbene) complexes: Synthesis, structure, and spectroscopic studies

Abstract

Quinoline bridged imidazolium precursors 5,8-bis(N-R- imidazolylidenylmethylene)quinoline PF6- salts [H 2L](PF6)2 [R = Me (1a), R = naphthylmethyl (1b)] were prepared by quaternization of N-methylimidazole and N-naphthylmethylimidazole with 5,8-bis(bromomethyl)quinoline, respectively. Reaction of the imidazolium ligands 1a and 1b with Hg(OAc)2 and Ag2O in acetonitrile gave the macrocyclic transition metal carbene complexes [Hg2L2](PF6)4 (2a and 2b) and [Ag2L2](PF6)2 (3a and 3b), respectively. All the N-heterocyclic carbene complexes were characterized in detail by NMR, ESI-MS, and elemental analysis. Structures of complexes 2a and 3a were determined by X-ray diffraction studies. Structural studies revealed that the coordination arrangement of the central mercury atom in complex 2a displays a tricoordinate mode and the molecular conformation results in a"closed" form with the bridging quinoline functionality in the macrocycle, whereas the silver complex 3a does not show an coordiantion between the bridging quinoline and the AgI ion, which results in an "open" conformation of the macrocycle. The HgII and Ag I NHC complexes showed similar UV absorption and luminescence in acetonitrile solutions. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.