Synthesis, structures and anticancer studies of symmetrically and non-symmetrically aliphatic nitrile functionalized silver(I)-N-heterocyclic carbene and palladium(II)-N-heterocyclic carbene complexes

Abstract

The newly designed Ag(I)-NHC and Pd(II)-NHC complexes (where NHC = N-heterocyclic carbene) bearing symmetrically and unsymmetrically nitrile functionalized have been synthesized, starting from the corresponding aliphatic nitrile functionalized benzimidazolium bromide salts. The resulting aliphatic nitrile functionalized benzimidazolium salts (1 and 2) were subsequently deprotonated with the basic metal source Ag2O by in situ deprotonation technique to obtain a mononuclear Ag(I)-NHC complexes (3 and 4). The mononuclear Pd(II)-NHC complexes (5 and 6) were prepared via transmetalation from their respective Ag(I)-NHC complexes, respectively. All compounds were characterized by elemental analyses, FT-IR, 1H- and 13C-NMR. Single crystal structural studies of Ag(I)-NHC complex revealed that the Ag(I) ion exhibits a linear geometry of quasi-parallel pairs of aromatic benzimidazole planes. The synthesized compounds were then screened for potential cytotoxicity on breast cancer cell line (MCF-7), using MTT assay. All the Ag(I)-NHC complexes show better activity with IC50 values ranging from 3.7 – 4.1 µM, while Pd(II)-NHC complexes show the IC50 values ranging from 13.9 – 14.2 µM in comparison with the standard drug, Tamoxifen (IC50 = 11.2 µM). All the respective benzimidazolium salts, however were found to be inactive. The anticancer activity is corresponding to the increasing lipophilicity order of the complexes as 5 < 6 < 3 < 4 (0.49, 0.56, 1.25 and 1.27, respectively).