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(iPr2-bimy)2]­PF6 (3), [Au­(FPyr)2]­PF6 (4), [Au­(FPyr)­(iPr2-bimy)]­PF6 (5), [AuCl3(iPr2-bimy)] (6), [AuCl3(FPyr)] (7), [AuCl2(iPr2-bimy)2]­PF6 (8), [AuCl2(FPyr)2]­PF6 (9), and [AuCl2(FPyr)­(iPr2-bimy)]­PF6 (10), bearing the benzimidazole-derived iPr2-bimy (1,3-diisopropylbenzimidazolin-2-ylidene) and/or the pyrazole-derived FPyr (1,2,3,4,6,7,8,9-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 μM.