Isoelectronic Pt(II)- and Au(III)-N-heterocyclic carbene complexes: a structural and biological comparison

To elucidate the intrinsic biological activities displayed by platinum versus gold-based organometallic reagents, the isoelectronic and isostructural square planar complexes [Pt(C boolean AND N)(C)Cl][PF6] (2) and [Au(C boolean AND N)(C)Cl][PF6](2) (3), which are supported by a common N-heterocyclic carbene, 1-methyl-2-pyridin-2-yl-2H-imidazo[1,5-a]pyridin-4-ylidene (1), were synthesized. The complexes were characterized using a range of spectroscopic techniques as well as single crystal X-ray diffraction and a series of computational studies were also performed to gain additional insight into their fundamental electronic bonding structures. The cytotoxicities of the complexes were tested in vitro against non-small lung carcinoma (A549), colorectal carcinoma (HCT-116) and human hepatocellular carcinoma (HepG2) cell lines. The measured IC50 values showed that the Au(III)-NHC complex is more potent than its Pt analogue.