Bis-N-heterocyclic carbene silver(I) and palladium(II) complexes: Efficient antiproliferative agents against breast cancer cells

AnewPd(II)-N-heterocyclic carbene (NHC) complex 2 was derived from a binuclear Ag(I)-NHC complex 1. H-1 NMR spectra of complexes showed uniquely different characteristic behavior of bridging methylene protons than compared with the ligand. X-ray crystallography showed that palladium at the center of bis-NHC units in 2 was found in square-planar geometry. Ligand and complexes were tested against breast cancer cells (MCF-7). The ligand did not show considerable antiproliferative activity (IC50 181.0 +/- 3.0 mu M) whereas complexes showed significant activity (1: 0.5 +/- 0.1 mu M; 2: 2.5 +/- 0.2 mu M) compared with the standard drug, tamoxifen (2.4 +/- 0.2 mu M).