Sterically tuned Ag(i)- and Pd(ii)-N-heterocyclic carbene complexes of imidazol-2-ylidenes: Synthesis, crystal structures, and in vitro antibacterial and anticancer studies

Abstract

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 μM IC50 values, respectively. © The Royal Society of Chemistry 2013.