Luminescent Heterobimetallic Pt^II–Au^I Complexes Bearing N-Heterocyclic Carbenes (NHCs) as Potent Anticancer Agents

Abstract

This study aims to probe into new series of heterobimetallic Pt II −Au I complexes with a general formula of [Pt(p-MeC 6 H 4 )(dfppy)(μ-dppm)Au(NHC)]OTf, NHC = IPr, 2; IMes, 3; dfppy = 2-(2,4-difluorophenyl)pyridinate; dppm = 1,1bis(diphenylphosphino)methane, which are the resultant of the reaction between [Pt(p-MeC 6 H 4 )(dfppy)(κ 1 -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 3 IL/ 3 MLCT 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 Pt II −Au I 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.

Trans-to-cis isomerization of a platinum(II) complex with two triphosphine ligands via coordination with gold(I) ion

“…[Pt(Ar)(phenylpyridinates)(κ 1 -dppm)] [22,23]. To elucidate this ability, we examined the reaction of [1](NO3)2 with two equivalents of [Au(tu)2]Cl, which is one of the well-known Au I sources [34], in methanol.…”

“…In this complex, two uncoordinated P atoms in [1] 2+ are bound by {Au I (tu)} + units through the Au-P bonds (Scheme 1). This means that [1](NO3)2 can function as a ditopic P-donating metalloligand [20][21][22][23]. Notably, while the initial [1](NO3)2 is the trans isomer, the [1] 2+ unit observed in [2] 4+ adopted the cis configuration.…”

Trans-to-cis isomerization of a platinum(II) complex with two triphosphine ligands via coordination with gold(I) ions

“…The [Pt(triphos) 2 ](NO 3 ) 2 complex contained two unbound PPh 2 groups. Consequently, these groups were anticipated to function as coordination sites for other metal ions, similar to the role of P-donating metalloligands with free phosphine groups, e.g., 1,1'-bis(diphenylphosphino)ferrocene (dppf) [33], (-PhPC 5 H 4 FeC 5 H 4 -) 3 [21], and [Pt(Ar) phenylpyridinates (κ 1 -dppm)] [22,23]. To probe this ability, we examined the reaction of [Pt(triphos) 2 ](NO 3 ) 2 with two equivalents of [Au(tu) 2 ]Cl, which is a well-known Au I source [34], in methanol.…”

“…In this complex, the two uncoordinated P atoms in [Pt(triphos) 2 ] 2+ were bound by {Au I (tu)} + units through Au-P bonds (Scheme 1). This meant that [Pt(triphos) 2 ](NO 3 ) 2 functioned as a ditopic P-donating metalloligand [20][21][22][23]. Notably, while the initial [Pt(triphos) 2 ](NO 3 ) 2 adopted the trans isomer, the [Pt(triphos) 2 ] 2+ unit observed in [Pt(triphos) 2 {Au(tu)} 2 ] 4+ adopted the cis configuration.…”