The synthesis of four new silver complexes of bidentate N-heterocyclic carbenes, derived from imidazolium-linked cyclophanes, has been achieved via a simple complexation reaction of the imidazolium-linked cyclophanes with the basic metal source Ag(2)O. The cyclophane structures contain two imidazolyl links between ortho-, meta- and mixed ortho/meta-substituted aromatic rings. The new silver carbene systems are thermally stable and have been characterised by NMR spectroscopy and X-ray crystallography. Three of the complexes have a dimeric structure of the form [L(2)Ag(2)](2+) in the solid state that is rigid on the NMR timescale in solution. The fourth complex has a neutral structure of the form [L(AgBr)(2)], the NMR studies suggesting some lability of the L-Ag bonding in solution.

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A range of mercury-imidazolylidene complexes have been prepared by reaction of imidazoliumlinked cyclophanes with mercury(II) acetate. For cyclophanes based on meta-xylyl groups the mercury complexes are mononuclear and exhibit unprecedented structures in which the mercury atom is bound within the cyclophane ring, the two NHC donors being mutually trans. For cyclophanes based on ortho-xylyl or 2,6-lutidinediyl groups the mercury complexes are dinuclear with a [Hg(μ-L) 2 Hg] core, in which each mercury atom is coordinated by one NHC from each cyclophane unit. The mononuclear and dinuclear complexes have been structurally characterized. Studies of the NHC-pyridinophane mercury complex indicated that the NHC-Hg bonding is labile, suggesting that the dinuclear complex based on the [Hg(μ-L) 2 Hg] core existed in equilibrium with a mononuclear complex [HgL]. The labile nature of the NHC-Hg bonding was further established by a redox transmetalation reaction of a dinuclear NHC-Hg(II) complex with a Pd(0) source, which afforded an NHC-Pd(II) complex.

N-Heterocyclic carbenes (NHCs) complexed with silver represent new, broad-spectrum antimicrobial and anticancer agents, normally with low toxicity profiles, and they provide a range of versatile structures for targeted biological applications. Most of these complexes have shown higher cytotoxicity than cisplatin, a potent anticancer drug. This study reviews the design, synthesis, structural characterization, and biological applications of silver complexes derived from both functionalized and nonfunctionalized NHC ligands. Specifically, silver complexes of functionalized and nonfunctionalized imidazole-and benzimidazole-based NHC systems employed in antimicrobial and anticancer applications are [a] www.eurjic.org MICROREVIEW with azolium salts at ambient/high temperature. Finally, the third method involves treatment of silver salts with azolium salts under basic phase-transfer conditions. [11][12][13] The use of Ag 2 O has made the synthesis of silver(I)-NHC complexes much easier and more convenient. In recent years, numerous silver-NHC complexes have been designed and synthesized according to the second method, mainly for antibacterial and anticancer activities. In 2007, Youngs et al. [14] reviewed the synthesis, characterization, and applications of silver(I)-NHC complexes for antibiotic applications. The present review on a similar topic provides a timely and critical overview of the field from the point of view of synthetic and biomedical applications, through comprehensive accounts of different methods for the synthesis of silver(I)-NHC complexes that have appeared in the literature, together with their reactivities and stabilities, since the aforementioned review. The reviews by Youngs et al. [15] and Morel and Gautier et al. [16] in 2009 focused on the applications only of imidazole-based complexes, particularly as anticancer agents.Silver-NHCs are also potent antibacterial agents and efficient candidates in the preparation of other transition metal-NHC complexes by transmetallation. Here we report recent developments in the synthesis, structures, and biological applications of silver(I) complexes of functionalized, nonfunctionalized, and nanoparticle-supported NHCs derived from both imidazole and non-imidazole cores. Several crystallographic and spectroscopic data for complexes re-Srinivasa Budagumpi was born in Karnataka, India in 1983. He received his M.Sc. in inorganic chemistry from Gulbarga University, Gulbarga, India, in 2005. Later he obtained his Ph.D. from Karnatak University, Dharwad, India, under the guidance of Prof. Vidyanand K. Revankar in 2010. During his doctoral studies he worked on the bimetallic transitionmetal chemistry of ligands having heterocyclic diazine bridging modules. Subsequently, from 2010-2012, he completed postdoctoral assignments with Prof. Il Kim and Dr. Rosenani A. Haque at Pusan National University, Busan, Republic of Korea, and Universiti Sains Malaysia, Penang, Malaysia, respectively. During his tenure in the Haque laboratory he worked on the synthesis of group XII ...

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