Heterobimetallic PtII‐AuI Complexes Comprising Unsymmetrical 1,1‐Bis(diphenylphosphanyl)methane Bridges: Synthesis, Photophysical, and Cytotoxic Studies

Abstract

In the present work, a series of aryl‐cycloplatinated(II) complexes with general formula [Pt(C^N)(Ar)(κ1‐dppm)], 1, [C^N = 7,8‐benzoquinolinyl (bzq) or 2‐phenylpyridinyl (ppy); Ar = C6F5 or p‐MeC6H4, dppm = 1,1‐bis(diphenylphosphanyl)methane] was employed in the reaction with AuCl(SMe2) in order to generate heterobimetallic PtII‐AuI complexes, [Pt(C^N)(Ar)(µ‐dppm)Au(Cl)], 2, featuring a dppm bridge between the metal centers. The expectation was to induce metallophilic character into the excited state and to reduce non‐radiative deactivation pathways of the dangling auxiliary κ1‐dppm ligand through molecular motions, to improve the photophysical properties. After characterization of the new complexes by means of NMR spectroscopy and X‐ray crystallography technique, the photophysical properties of all the complexes were investigated by UV/Vis and photoluminescence spectroscopy. Both of the monometallic complexes and heterobimetallic products have shown to be luminescent in different states and temperature conditions. However, by addition of AuI, the impact on the photophysics of the heterobimetallic products in relation to the precursors with dangling dppm is minimal, a finding which can be attributed to the absence of a PtII‐AuI bond in these compounds. Indeed, the character of the excited states of the monomer PtII complexes and their corresponding bimetallic PtII‐AuI ones are similar, as confirmed by density functional theory (DFT) and time resolved DFT (TD‐DFT) calculations. The cytotoxic activities of the compounds along with that of [ClAu(µ‐dppm)AuCl] were evaluated against human breast cancer (MCF‐7), human lung cancer (A549), human ovarian cancer (SKOV3) and non‐tumorigenic epithelial breast (MCF‐10A) cell lines. The highest activity was found for the heterometallic Pt‐Au species, suggesting a cooperative effect of both metallic fragments. The most cytotoxic compound, i.e. [Pt(bzq)(p‐MeC6H4)(µ‐dppm)Au(Cl)], 2b, effectively causes cell death in MCF‐7 cancer cell line by inducing apoptosis. Fluorescence microscopy experiments for 2a were performed.