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( i Pr 2 -bimy) 2 ]PF 6 ( 3 ), [Au(FPyr) 2 ]PF 6 ( 4 ), [Au(FPyr)( i Pr 2 -bimy)]PF 6 ( 5 ), [AuCl 3 ( i Pr 2 -bimy)] ( 6 ), [AuCl 3 (FPyr)] ( 7 ), [AuCl 2 ( i Pr 2 -bimy) 2 ]PF 6 ( 8 ), [AuCl 2 (FPyr) 2 ]PF 6 ( 9 ), and [AuCl 2 (FPyr)( i Pr 2 -bimy)]PF 6 ( 10 ), bearing the benzimidazole-derived i Pr 2 -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( i Pr 2 -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 IC 50 values of around 0.2 μM.