Recent progress in silver(I)-, gold(I)/(III) and palladium(II)-N-heterocyclic carbene complexes: A review towards biological perspectives

N-Heterocyclic carbenes (NHCs) complexes have received a great deal of attention as new broad-spectrum antimicrobial and anticancer agents, which encourage the biological activity against numerous pathogens and human cancer cell lines. The metal-NHC complexes provide a range of versatile structural diversifications for the targeted biological applications with promising acceptable result. Most of the metal-NHC complexes are synthesized through in situ deprotonation or direct metalation techniques using azolium salts, and via transmetalation technique through initially prepared Ag(I)-NHC complexes. This review focuses on the recent reports of synthesis, structural characterization and biological applications of Ag(I)-, Au(I)/(III)-, and Pd(II)-NHC complexes with great efficacy in both in vitro and in vivo studies. Numerous reports have documented that the metal-NHC complexes are great bioactivity potential in comparable or better activity than the standard chemotherapeutic drugs. These complexes can have significant contribution in the field of bioorganometallic chemistry, and thus worthy explored as a medicinal drug in the nearer future.