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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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Unsymmetrically substituted sterically tuned Pd(II)–NHC complexes of the general formula [PdCl2(NHC)2] (NHC = 1-allyl-3-methylimidazolin-2-ylidene, 7; 1-allyl-3-butylimidazol-2-ylidene, 8; 1-benzyl-3-butyl imidazolin-2-ylidene, 9) were prepared through transmetallation from their corresponding Ag(I)–NHC complexes. The Pd complexes were structurally characterized by different spectroscopic and X-ray diffraction methods. Complexes 7 and 9 adopted a trans–anti arrangement of the NHC ligands, whereas complex 8 adopted a cis–syn arrangement. Preliminary antibiogram studies using Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria showed that Ag(I)–NHC complexes demonstrate higher activity compared with Pd(I)–NHC complexes. Furthermore, Pd(II)–NHC complexes were evaluated for their anticancer potential using the human colorectal cancer cell line. A higher anticancer activity was observed for complexes 8 and 9, with 26.5 and 6.6 mM IC50 values, respectively.

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A series of Ag(I) complexes (6-9) derived from imidazol-2-ylidenes was synthesized by reacting Ag 2 O with an o-, m-, p-xylyl or 1,3,5-triazine-linked imidazolium salts (1-4) and then characterizing these using various spectro-analytical techniques. Additionally, triazine-linked bis-imidazolium salt 5 was characterized using the single-crystal X-ray diffraction method. Complexes 6-9 were formed from the N-heterocyclic carbene ligand precursors 1-3 as PF 6 salts in good yields. Conversely, salt 5 does not form Ag(I) complex even under various reaction conditions. Using ampicillin as a standard, complexes 6-9 were tested against bacteria strains Escherichia coli and Staphylococcus aureus as Gram-negative and Gram-positive bacteria, respectively, showing potent antimicrobial activities against the tested bacteria even at minimum inhibition concentration and bacterial concentration levels. Furthermore, the potential anticancer activities of the reported complexes were evaluated against the human colorectal cancer (HCT 116) cell lines, using 5-fluorouracil as a standard drug. The highest anticancer activities were observed for complex 8 with an IC 50 value of 3.4 mM, whereas the lowest was observed for complex 9 with an IC 50 value of 18.1 mM. Copyright