Syntheses, Characterizations, and a Preliminary Comparative Cytotoxicity Study of Gold(I) and Gold(III) Complexes Bearing Benzimidazole- and Pyrazole-Derived N-Heterocyclic Carbenes

A series of Au(I) and Au(III) mono-, homobis-, and heterobis(carbene) complexes, [AuCl(FPyr)] (2), [Au-(Pr-l(2)-bimy)(2)]PF6 (3), [Au(FPyr)(2)]PF6 (4), [Au(FPyr)(Pr-i(2)-bimy)}PF6 (5), [AuCl3(Pr-i(2)-bimy)] (6), [AuCl3(FPyr)] (7), [AuCl2(Pr-i(2)-bimy)(2)]PF6 (8), [AuCl2(FPyr)(2)]PF6 (9), and [AuCl2(FPyr)(iPr2-bimy)]PF6 (10), bearing the benzimidazole-derived Pr-i(2)-bimy (1,3-diisopropylbenzimidazolin-2-ylidene) and/or the pyrazole-derived FPyr octahydropyridazino[1,2-a]indazolin-11-ylidene) N-heterocyclic carbene (NHC) ligands have been synthesized. Complexes 2-10 have been fully characterized using multinuclei NMR spectroscopy, ESI mass spectrometry, and elemental analysis. X-ray diffraction analyses have been performed on 2, 3, 5, 6, and 8. Together with the previously reported [AuCl(iPr2-bimy)] (1), the cytotoxic activities of all 10 complexes have been studied in vitro with the NCI-H1666 non-small cell lung cancer cell line. The cationic bis(carbene) complexes 3-5 and 8-10. show better cytotoxicity in comparison to cisplatin. In particular, the heterobis(carbene) complexes 5 and 10 have superior activity, with IC50 values of around 0.2 mu M.