Encapsulation of inorganic and organic guest molecules into an organometallic hexacationic arene osmium metalla-prism: Synthesis, characterisation and anticancer activity

The arene osmium metalla-prism [(p-cymene)6Os6(donq)3(tpt)2]6+ ([2]6+) (donq = 5,8-dioxydo-1,4-naphthoquinonato, tpt = 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine) has been prepared from the dinuclear arene osmium precursor [(p-cymene)2Os2(donq)Cl2] (1) in the presence of the tridentate panel tpt and silver triflate. The assembly of the arene osmium metalla-prism has also been achieved in the presence of one equivalent of planar guest molecules, Pt(acac)2 (acac = acetylacetonato) and 1-(4,6-dichloro-1,3,5-triazin-2-yl)pyrene (pyrene-R), to give the corresponding guest-encapsulated systems, [Pt(acac)2⊂2]6+ and [pyrene-R⊂2]6+. All complexes were isolated as triflate salts and characterised by infrared, UV–visible, NMR and by elemental analysis. The empty metalla-prism has also been characterised by mass spectrometry. The cytotoxicities of the dinuclear and hexanuclear osmium complexes have been established using ovarian A2780 and A2780cisR cancer cell lines and compared with the cytotoxicities of their ruthenium analogues.

Graphical abstractThe arene osmium metalla-cage [(p-cymene)6Os6(donq)3(tpt)2]6+ (donq = 5,8-dioxydo-1,4-naphthoquinonato, tpt = 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine) has been prepared together with the host-guest systems, [Pt(acac)2⊂cage]6+ and [pyrene-R⊂cage]6+ (pyrene-R = 1-(4,6-dichloro-1,3,5-triazin-2-yl)pyrene). The cytotoxicities of the host-guest systems and the empty metalla-cage have been established using ovarian A2780 and A2780cisR cancer cell lines. Comparison with their ruthenium analogues suggests a different mode of activity for these osmium derivatives.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Preparation of hexacationic water-soluble osmium metalla-cage. ► Encapsulation of organic and inorganic molecules in the cavity of the metalla-cage. ► Enhancement of cytotoxicity due to encapsulation. ► Different activity than the ruthenium analogues.