The Chemistry of Polynuclear Silver N-Heterocyclic Carbene Complexes

Polynuclear (tri-, tetra-, penta-, hexa-, polymeric-) silver N-heterocyclic carbene (Ag-NHC) complexes can be synthesized by reacting imidazolium salts (e.g., Cl, Br, PF₆) with Ag₂O, followed by anionic exchanges in some cases. The first polynuclear (tetra-) Ag-NHC complex was reported in 2002. Since then, these complexes have been explored in the literature for a variety of applications, including transmetallation, sensing, antimicrobial agents, and anticancer treatments, owing to their versatile properties. The labile silver-carbene bonds facilitate efficient ligand exchange with other transition metals such as Au, Cu, and Pd providing an efficient route to a variety of transition metal-NHC complexes with diverse applications. Tetranuclear Ag-NHC complexes that exhibit substantial fluorescence intensity have been used as sensors to detect persistent pollutants like 2,6-dichloronitroaniline with high sensitivity. Additionally, some trinuclear Ag-NHC complexes have demonstrated better antiproliferative activity than known chemotherapeutic drugs like 5-fluorouracil and cisplatin, highlighting the potential of these complexes as more stable and selective therapeutic agents. Overall, this review underscores the versatility of polynuclear Ag-NHC complexes across diverse fields, while emphasizing the importance of structural modifications to optimize their efficacy and minimize toxicity.