Facile entry to germanate and stannate complexes [(η6-arene)RuCl(η2-dppm)]+[ECl3]- (E = Ge, Sn) as potent anti-cancer agents

Homo and heteromultimetallic complexes containing a group 8 transition metal and μ-diphosphine bridging ligands involved in anticancer research: A review

Herein, we present a comprehensive review focusing on synthetic strategies, detailed structural analysis, and anticancer activity investigations of complexes following the general formula [LnM(μ-diphosphine)M'Lm] where M = group 8 metal; M' = any transition metal; μ-diphosphine = bridging ligand; Ln and Lm = ligand spheres). Both homo- and heteromultimetallic complexes will be discussed in detail. We review in vitro, in vivo and in silico anticancer activity investigations, in an attempt to draw comparisons between the various complexes and derive structure-activity relationships (SAR). This review solely focuses on complexes falling under the general formula stated above that have been studied for their anticancer activities, other complexes falling into that scheme but which have not undergone anticancer testing are not included in this review. We compare the anticancer activities of these complexes to their mononuclear counterparts, and a positive control (cisplatin) when possible and present a summary of all existing data to date and attempt to draw some conclusions on the future development of these complexes.

Ionic mononuclear [Fe] and heterodinuclear [Fe,Ru] bis(diphenylphosphino)alkane complexes: Synthesis, spectroscopy, DFT structures, cytotoxicity, and biomolecular interactions

Iron(II) and Ru(II) half-sandwich compounds encompass some promising pre-clinical anticancer agents whose efficacy may be tuned by structural modification of the coordinated ligands. Here, we combine two such bioactive metal centres in cationic bis(diphenylphosphino)alkane-bridged heterodinuclear [Fe²⁺, Ru²⁺] complexes to delineate how ligand structural variations modulate compound cytotoxicity. Specifically, Fe(II) complexes of the type [(η⁵-C₅H₅)Fe(CO)₂(κ¹-PPh₂(CH₂)_nPPh₂)]{PF₆} (n = 1-5), compounds 1-5, and heterodinuclear [Fe²⁺, Ru²⁺] complexes, [(η⁵-C₅H₅)Fe(CO)₂(μ-PPh₂(CH₂)_nPPh₂))(η⁶-p-cymene)RuCl₂]{PF₆} (n = 2-5) (compounds 7-10), were synthesized and characterised. The mononuclear complexes were moderately cytotoxic against two ovarian cancer cell lines (A2780 and cisplatin resistant A2780cis) with IC₅₀ values ranging from 2.3 ± 0.5 μM to 9.0 ± 1.4 μM. For 7-10, the cytotoxicity increased with increasing Fe⋅⋅⋅Ru distance, consistent with their DNA affinity. UV-visible spectroscopy suggested the chloride ligands in heterodinuclear 8-10 undergo stepwise substitution by water on the timescale of the DNA interaction experiments, probably affording the species [RuCl(OH₂)(η⁶-p-cymene)(PRPh₂)]²⁺ and [Ru(OH)(OH₂)(η⁶-p-cymene)(PRPh₂)]²⁺ (where PRPh₂ has R = [-(CH₂)₅PPh₂-Fe(C₅H₅)(CO)₂]⁺). One interpretation of the combined DNA-interaction and kinetic data is that the mono(aqua) complex may interact with dsDNA through nucleobase coordination. Heterodinuclear 10 reacts with glutathione (GSH) to form stable mono- and bis(thiolate) adducts, 10-SG and 10-SG₂, with no evidence of metal ion reduction (k₁ = 1.07 ± 0.17 × 10^-1 min^-1 and k₂ = 6.04 ± 0.59 × 10^-3 min^-1 at 37 °C). This work highlights the synergistic effect of the Fe²⁺/Ru²⁺ centres on both the cytotoxicity and biomolecular interactions of the present heterodinuclear complexes.

Rhodium and ruthenium complexes of methylene-bridged, P-stereogenic, unsymmetrical diphosphanes

Enantiopure P-stereogenic methylphosphane-boranes (S_P)-P(BH₃)PhArMe (ArMe; Ar = 1-naphthyl (NpMe), and 2-biphenylyl (BiphMe)) have been used to prepare diphosphanes of the type ArPhPCH₂PR₂ (R = Ph, iPr or tBu; ArR). The ligands have been reacted with [Rh(COD)₂]BF₄ to furnish the corresponding six monochelated [Rh(COD)(ArR)]BF₄ organometallic compounds (RhArR) or, depending on the reaction conditions, the bis(chelated) coordination compound [Rh(BiphiPr)₂]BF₄ as a mixture of cis and trans isomers. The crystal structure of cis-[Rh(BiphiPr)₂]BF₄ was obtained. The coordination of the BiphR with [RuCl(μ-Cl)(η⁶-p-cymene)₂]₂ under different conditions produced cationic chelated complexes of the type [RuCl(η⁶-p-cymene)(κ²-BiphR)]PF₆ (RuBiphR) and the neutral monocoordinated complex [RuCl₂(η⁶-p-cymene)(κ¹-BiphPh)] (RuBiphPh') with the uncoordinated P-stereogenic moiety. The Rh(I) complexes were used in the catalytic hydrogenation of functionalized olefins and the Ru(II) complexes were tested in the transfer hydrogenation of acetophenone. Both precursors displayed good activities with moderate enantioselectivities.

Osmium Arene Germyl, Stannyl, Germanate, and Stannate Complexes as Anticancer Agents

Herein, we describe the synthesis, full spectroscopic characterization, DFT (density functional theory) calculations, and single-crystal X-ray diffraction analyses of a series of osmium arene σ-germyl, germanate, σ-stannyl, and stannate complexes, along with their cytotoxic (anticancer) investigations. The known dimer complexes [OsCl2(η6-C6H6)]2 (1) and [OsCl2(η6-p-cymene)]2 (2) were reacted with PPh3 to form the known mononuclear complex [OsCl2(η6-p-cymene)(PPh3)] (3) and the new complex [OsCl2(η6-C6H6)(PPh3)] (6); complex 3 was reacted with GeCl2·(dioxane) and SnCl2 to afford, by insertion into the Os-Cl bond, the neutral σ-germyl and stannyl complexes [OsCl(η6-p-cymene)(PPh3)(GeCl3)] (7) and [OsCl(η6-p-cymene)(PPh3)(SnCl3)] (11), respectively, as a mixture of enantiomers. Similarly, the reaction of complex 6 with GeCl2·(dioxane) afforded [OsCl(η6-C6H6)(PPh3)(GeCl3)] (9). Complex 2, upon reaction with 1,1-bis(diphenylphosphino)methane (dppm), formed a mixture of [OsCl2(η6-p-cymene)(κ1-dppm)] (4) and [Os(η6-p-cymene)(κ2-dppm)Cl]+Cl- (5) when prepared in acetonitrile and a mixture of 4 and the dinuclear complex [[OsCl2(η6-p-cymene)]2(μ-dppm)] (0) when prepared in dichloromethane. By utilizing either isolated 4 or a mixture of 4 and 5, the synthesis of κ2-dppm germanate and stannate salts, [OsCl(η6-p-cymene)(κ2-dppm)]+GeCl3 - (8) and [OsCl(η6-p-cymene)(κ2-dppm)]+SnCl3 - (10), were accomplished via halide-abstracting reactions with GeCl2·(dioxane) or SnCl2, respectively. All resulting complexes were characterized by means of multinuclear NMR, FT-IR, ESI-MS, and UV/Vis spectroscopy. X-ray diffraction analyses of 4, 8, 9, 10, and 11 were performed and are reported. DFT studies (B3LYP, basis set LANL2DZ for Os, and def2-TZVPP for Sn, Ge, Cl, P, C, and H) were performed on complex 9 and the benzene analogue of complex 11, 11-benzene, to evaluate the structural changes and the effects on the frontier molecular orbitals arising from the substitution of Ge for Sn. Finally, complexes 3 and 7-11 were investigated for potential anticancer activities considering cell cytotoxicity and apoptosis assays against Dalton's lymphoma (DL) and Ehrlich ascites carcinoma (EAC) malignant cancer cell lines. The complexes were also tested against healthy peripheral blood mononuclear cells (PBMCs). All cell lines were also treated with the reference drug cisplatin to draw a comparison with the results obtained from the reported complexes. The study was further corroborated with in silico molecular interaction simulations and a pharmacokinetic study.

A review on 1,1-bis(diphenylphosphino)methane bridged homo- and heterobimetallic complexes for anticancer applications: Synthesis, structure, and cytotoxicity

Herein, we review developments in synthesis, structure, and biological (anti-cancer) activities of 1,1-bis(diphenylphosphino)methane (dppm) bridged homo- and heterobimetallic systems of the type L_mM(μ₂-dppm)M'L_n (M and M' are transition metals which may be different or the same and L_n,m are co-ligands) since the first such reported bimetallic system in 1987 until the present time (2020). As the simplest diphosphine, dppm enables facile formation of bimetallic complexes, where, given the short spacer between the PPh₂ groups, close spatial proximity of the metal centres is ensured. We concentrate on complexes bearing no M-M interaction and contrast biological activities of these complexes with mononuclear counterparts and positive control agents such as cisplatin, in an attempt to elucidate patterns in the biological activities of these complexes.