Synthesis, structure and cytotoxicity studies of four-coordinate bis (cis-bis(diphenylphosphino)ethene) gold(I) complexes, [Au(dppey)2]X

Abstract

Four-coordinate 1:2 gold(I) complex salts with cis–bis(diphenylphosphino)ethene, [Au(dppey)2]X have been synthesized for X = PF6−, CF3SO3−, BF4−, Cl−, Br− and BPh4− and characterized by NMR spectroscopy and electrospray mass spectrometry. Single crystal X-ray structure determinations show the BF4−, Cl− and Br− complexes to be isostructural, although with different degrees of hydration, while the BPh4− complex crystallizes as an acetone solvate with two molecules in the asymmetric unit. The Au(P–P)2 core for the BF4−, Cl− and Br− complexes adopts D2 symmetry with Au–P bond lengths 2.3980(7)–2.4009(7) Å and inter-ligand P–Au–P angles 114.78(2)–127.82(2))°. The Au(P–P)2 core in the BPh4− complex is unsymmetrical with Au–P bond lengths 2.364(1)–2.420(1) Å and inter-ligand P–Au–P angles 104.76(5)–137.50(4)°. In vitro cytotoxicity studies show the PF6−, CF3SO3−, BF4−, Cl−, Br− and I− complexes to be potent and selective growth inhibitors of the human cell lines MCF7 (hormone-dependent breast cancer), MDA-MB-231 (hormone-independent breast cancer), MM96L (melanoma), CI80-13S (cisplatin resistant ovarian cancer) and a normal cell line NFF (neonatal foreskin fibroblasts), achieving IC50 values between 13 and 196 nM. The halogen and triflate salts were approximately twice as potent towards the MCF7 and MDA-MB-231 cell lines compared to the PF6− and BF4− derivatives; while the cytotoxicity of all complexes towards the sensitive CI80-13S and MM96L cancer cell lines was approximately 10-fold greater than that displayed towards the normal human cell line (NFF).