Luminescent Heterobimetallic PtII-AuI Complexes Bearing N-Heterocyclic Carbenes (NHCs) as Potent Anticancer Agents.

This study aims to probe into new series of heterobimetallic PtII-AuI complexes with a general formula of [Pt(p-MeC6H4)(dfppy)(µ-dppm)Au(NHC)]OTf, NHC = IPr, 2; IMes, 3; dfppy = 2-(2,4-difluorophenyl)pyridinate; dppm = 1,1-bis(diphenylphosphino)methane, which are the resultant of the reaction between [Pt(p-MeC6H4)(dfppy)(κ1-dppm)], 1, with [AuCl(NHC)], NHC = IPr, B; IMes, C, in the presence of [Ag(OTf)]. In the heterobimetallic complexes, the dppm ligand is settled between both metals as an unsymmetrical bridging ligand. Several techniques are employed to characterize the resulting compounds. Moreover, the photophysical properties of the complexes are investigated by means of UV-vis and photoluminescence spectroscopy. Furthermore, the experimental study is enriched by ab initio calculations (density functional theory (DFT) and time-dependent DFT (TD-DFT)) to assess the role of Pt and Au moieties in the observed optical properties. It is revealed that 1-3 is luminescent in the solid state and solution at different temperatures. In addition, the achieved results indicate the emissive properties of 1-3 are originated from a mixed 3IL/3MLCT excited state with major contribution of intraligand charge transfer (dfppy). A comparative study is conducted into the cytotoxic activities of starting materials and 1-3 against different human cancer cell lines such as the pancreas (MIA-PaCa2), breast (MDA-MB-231), cervix (HeLa), and noncancerous breast epithelial cell line (MCF-10A). The achieved results suggest the heterobimetallic PtII-AuI species as optimal compounds that signify the existence of cooperative and synergistic effects in their structures. The complex 3 is considered as the most cytotoxic compound with the maximum selectivity index in our screened complex series. Moreover, it is disclosed that 3 effectively causes cell death by inducing apoptosis in MIA-PaCa2 cells. Furthermore, the finding results by fluorescent cell microscopy manifest cytoplasmic staining of 3 rather than nucleus.

Photophysical Properties and Kinetic Studies of 2-Vinylpyridine-Based Cycloplatinated(II) Complexes Containing Various Phosphine Ligands.

A series of cycloplatinated(II) complexes with general formula of [PtMe(Vpy)(PR3)], Vpy = 2-vinylpyridine and PR3 = PPh3 (1a); PPh2Me (1b); PPhMe2 (1c), were synthesized and characterized by means of spectroscopic methods. These cycloplatinated(II) complexes were luminescent at room temperature in the yellow-orange region's structured bands. The PPhMe2 derivative was the strongest emissive among the complexes, and the complex with PPh3 was the weakest one. Similar to many luminescent cycloplatinated(II) complexes, the emission was mainly localized on the Vpy cyclometalated ligand as the main chromophoric moiety. The present cycloplatinated(II) complexes were oxidatively reacted with MeI to yield the corresponding cycloplatinated(IV) complexes. The kinetic studies of the reaction point out to an SN2 mechanism. The complex with PPhMe2 ligand exhibited the fastest oxidative addition reaction due to the most electron-rich Pt(II) center in its structure, whereas the PPh3 derivative showed the slowest one. Interestingly, for the PPhMe2 analog, the trans isomer was stable and could be isolated as both kinetic and thermodynamic product, while the other two underwent trans to cis isomerization.