Au-NHC complexes with thiocarboxylate ligands: Synthesis, structure, stability, thiol exchange and in vitro anticancer activity

Abstract

Novel complexes of form (NHC)Au(SCOR) (NHC = N-heterocyclic carbene, SCOR− = thiocarboxylate ligand) were synthesised and characterised by spectroscopic techniques and X-ray diffraction studies. The results of NMR and X-ray studies indicated that thiocarboxylate ligands are comparable with NHCs in their electron donor ability. The complexes were stable at room temperature in the solid state but in solution underwent disproportionation reactions to form equilibria with [Au(NHC)2]+ and [Au(SCOR)2]−. In solution, the thiocarboxylate ligand in (NHC)Au(SCOR) underwent rapid exchange with other thiocarboxylate or thiolate ligands. The (NHC)Au(SCOR) complexes showed toxicity against cisplatin-resistant ovarian cancer cells (OVCAR-8), with IC50 < 10 μM, in the range exhibited by cationic [Au(NHC)2]+ complexes well-known for their promising anticancer activity.