Metal Arene Research Articles

Low-pressure dendrite-free sulfide solid-state battery with 3D LiSi@Li-Phen-Ether anode

Low-pressure dendrite-free sulfide solid-state battery with 3D LiSi@Li-Phen-Ether anode

Neutral inverse-sandwich rare-earth metal complexes of the benzene tetraanion.

Rare-earth metal complexes of the parent benzene tetraanion and neutral inverse-sandwich rare-earth metal arene complexes have remained elusive. Here, we report the first neutral inverse-sandwich rare-earth metal complexes of the parent benzene tetraanion supported by a monoanionic β-diketiminate (BDI) ligand. Reduction of the trivalent rare-earth metal diiodide precursors (BDI)MI2(THF) (BDI = HC(C(Me)N[C6H3-(3-pentyl)2-2,6])2; M = Y, 1-Y; M = Sm, 1-Sm) in benzene or para-xylene by potassium graphite yielded the neutral inverse-sandwich rare-earth metal arene complexes [(BDI)M(THF) n ]2(μ-η6,η6-arene) (M = Y, Sm; arene = benzene, 2-M; arene = para-xylene, 3-M). Single crystal X-ray diffraction, spectroscopic and magnetic characterization studies, together with density functional theory (DFT) calculations confirm that these neutral rare-earth metal arene complexes possess an [M3+-(arene)4--M3+] electronic structure with strong metal-arene δ interactions. The arene exchange reactivity shows that 2-Sm has higher stability than 3-Sm. Furthermore, 2-Sm can behave as a four-electron reductant to reduce unsaturated organic substrates. Particularly, while the reaction of 2-Sm with 1,3,5,7-cyclooctatetraene (COT) yielded (BDI)Sm(η8-COT) (4-Sm), 2-Sm reacted with 1,4-diphenylbutadiyne to afford (BDI)Sm(η4-C4Ph2) (5-Sm), the first rare-earth metallacyclopentatriene complex.

Accessing five oxidation states of uranium in a retained ligand framework

Understanding and exploiting the redox properties of uranium is of great importance because uranium has a wide range of possible oxidation states and holds great potential for small molecule activation and catalysis. However, it remains challenging to stabilise both low and high-valent uranium ions in a preserved ligand environment. Herein we report the synthesis and characterisation of a series of uranium(II–VI) complexes supported by a tripodal tris(amido)arene ligand. In addition, one- or two-electron redox transformations could be achieved with these compounds. Moreover, combined experimental and theoretical studies unveiled that the ambiphilic uranium–arene interactions are the key to balance the stabilisation of low and high-valent uranium, with the anchoring arene acting as a δ acceptor or a π donor. Our results reinforce the design strategy to incorporate metal–arene interactions in stabilising multiple oxidation states, and open up new avenues to explore the redox chemistry of uranium.

Liquid metal arene complex for next-generation batteries

Lithium metal batteries have received attention as next-generation systems owing to their high energy density compared to that of commercial lithium-ion batteries. However, low stability and cycle life with dendrite growth hinder the practical application of metal anodes. To conquer these limitations, studies utilizing dendrite-free liquid-phase anodes, such as liquid metal and liquid metal arene complexes (LMACs), have been conducted. LMAC is more controllable and stable than liquid metal; therefore, the use of LMAC has been recently investigated in various systems. Herein, a detailed overview of LMAC, including the principle, and characteristics has been provided. Additionally, based on recent research utilizing LMAC as an anode or a lithiation source, obstacles limiting the practical application of LMAC along with future research directions are discussed. • Liquid metal arene complex is a dendrite free electrode and lithiation agent. • Redox potential of liquid metal arene complex is easily adjustable. • Formation and redox mechanism, characteristics, and applications are discussed. • Challenges which have not been mentioned in previous research are summarized.

TREN and TMPA capped calix[6]arene metal complexes as ds-DNA/RNA binders

TREN and TMPA capped calix[6]arene metal complexes as ds-DNA/RNA binders

Binding and stabilization effect of arene ruthenium(Ⅱ) polypyridyl complexes toward the triple-helical RNA poly(U)•poly(A)⁎poly(U)

To determine the binding properties of η 6 ‑arene Ru(Ⅱ) complexes with RNA triplexes, two arene Ru(Ⅱ) complexes [( ŋ 6 -C 6 H 6 )Ru( m -npip)Cl] + (Ru 1 ) and [( ŋ 6 -C 6 H 6 )Ru( m -fpip)Cl] + (Ru 2 ) have been synthesized and characterized in this study. The obtained results will contribute to our understanding of the binding of arene Ru(Ⅱ) complexes with RNA triplexes. • ←6 -C 6 H 6 = benzene ring, m -npip = 2-(3′‑nitro)imidazo[4,5- f ][1,10]phenanthroline. • m -fpip = 2-(3′‑fluorine)imidazo[4,5- f ][1,10]phenanthroline. • Complexes [(← 6 -C 6 H 6 )RuLCl]PF 6 (Ru 1 , L = m -npip; Ru 2 , L = m -fpip) were synthesized. • Binding properties of Ru 1 and Ru 2 with poly(U)*poly(A)•poly(U) were investigated. • This work is the first example of arene metal complexes with triple-helical nucleic acids . To determine the binding properties of η 6 ‑arene Ru(Ⅱ) complexes with the RNA triplex poly(U)•poly(A)⁎poly(U), two arene Ru(Ⅱ) complexes, [( ŋ 6 -C 6 H 6 )Ru( m -npip)Cl] + (Ru 1 ) and [( ŋ 6 -C 6 H 6 )Ru( m -fpip)Cl] + (Ru 2 ), have been synthesized and characterized in this study. The binding of Ru 1 and Ru 2 with the triplex RNA poly(U)•poly(A)⁎poly(U) have been investigated by viscosity measurement and various spectroscopic methods. Results demonstrate that the RNA-binding behaviors of Ru 1 and Ru 2 are intercalation mode. From the analyses of electronic absorption spectra and fluorescence spectra, we observed that the binding affinity for Ru 2 is remarkably stronger than that for Ru 1 . Furthermore, thermal denaturation studies reflect that Ru 1 and Ru 2 selectively stabilize the RNA triplex, among them, Ru 1 can stabilize the Hoogsteen base-paired strand poly(U) (the third strand), while it is little effect on the Watson-Crick base-paired duplex poly(U)•poly(A) (the template duplex). Contrary to Ru 1 , Ru 2 can stabilize both the template duplex and the third-strand, and Ru 2 is more effective for stabilization of the third-strand. To our knowledge, this work is the first example of arene metal complexes interacting with triple-helical nucleic acids. The obtained results suggest that subtle differences of substituent on the intercalation ligand may be the important factor affecting on the binding properties of the both arene Ru(Ⅱ) complexes with the RNA triplex, when Ru 1 and Ru 2 contain the same ancillary ligands.

Theoretical Investigation of Catalytic Water Splitting by the Arene-Anchored Actinide Complexes.

Actinide complexes, which could enable the electrocatalytic H2O reduction, are not well documented because of the fact that actinide-containing catalysts are precluded by extremely stable actinyl species. Herein, by using relativistic density functional theory calculations, the arene-anchored trivalent actinide complexes (Me,MeArO)3ArAn (marked as [AnL]) with desirable electron transport between metal and ligand arene are investigated for H2 production. The metal center is changed from Ac to Pu. Electron-spin density calculations reveal a two-electron oxidative process (involving high-valent intermediates) for complexes [AnL] (An = P-Pu) along the catalytic pathway. The electrons are provided by both the actinide metal and the arene ring of ligand. This is comparable to the previously reported uranium catalyst (Ad,MeArO)3mesU (Ad = adamantine and mes = mesitylene). From the thermodynamic and kinetic perspectives, [PaL] offers appreciably lower reaction energies for the overall catalytic cycle than other actinide complexes. Thus, the protactinium complex tends to be the most reactive for H2O reduction to produce H2 and has the advantage of its experimental accessibility.

Cover Feature: Rhodium and Iridium Complexes of Anionic Thione and Selone Ligands Derived from Anionic N‐Heterocyclic Carbenes (Chem. Eur. J. 4/2022)

Anionic N-heterocyclic carbenes that bear a weakly coordinating fluoroborate moiety have been used to prepare a new class of anionic imidazolin-2-thione and -selone ligands; their coordination chemistry towards rhodium and iridium was explored to reveal their ability to develop secondary arene–metal interactions with the “wings” of the carbene ligands. More information about these new additions to the family of chalcogenolate ligands and their potential future application in coordination chemistry, bioinorganic chemistry and homogeneous catalysis can be found in the Research Article by M. Tamm et al. (DOI: 10.1002/chem.202104139).

Water-soluble trithiolato-bridged dinuclear ruthenium(II) and osmium(II) arene complexes with bisphosphonate functionalized ligands as anticancer organometallics

Trithiolato-bridged dinuclear ruthenium(II) complexes [Ru2(p-cym)2(SR)3]Cl (p-cym=p-cymene, R=benzyl derivatives) are regarded as the most cytotoxically potent metal(II) arene antineoplastics, but are oftentimes limited by their poor solubility in aqueous media. Thus, we designed bisphosphonate-functionalized ligands for use in a modular two-step complexation process to synthesize six trithiolato-bridged dinuclear ruthenium(II) and osmium(II) arene complexes bearing one to three bisphosphonate-benzylmercaptane derived ligands. In addition to improved aqueous solubility the high affinity of bisphosphonates towards apatite structures found in bone and bone metastases may grant selective targeting properties to functionalized organometallics. The complex stabilities and hydroxyapatite binding behavior were determined by UV/Vis spectroscopy. The bisphosphonate functionalization decreases antiproliferative activity in vitro, which was correlated to lower cellular accumulation, due to the different lipophilic profiles of the drug candidates.

Catalytic SNAr Hydroxylation and Alkoxylation of Aryl Fluorides

AbstractNucleophilic aromatic substitution (SNAr) is a powerful strategy for incorporating a heteroatom into an aromatic ring by displacement of a leaving group with a nucleophile, but this method is limited to electron‐deficient arenes. We have now established a reliable method for accessing phenols and phenyl alkyl ethers via catalytic SNAr reactions. The method is applicable to a broad array of electron‐rich and neutral aryl fluorides, which are inert under classical SNAr conditions. Although the mechanism of SNAr reactions involving metal arene complexes is hypothesized to involve a stepwise pathway (addition followed by elimination), experimental data that support this hypothesis is still under exploration. Mechanistic studies and DFT calculations suggest either a stepwise or stepwise‐like energy profile. Notably, we isolated a rhodium η5‐cyclohexadienyl complex intermediate with an sp3‐hybridized carbon bearing both a nucleophile and a leaving group.

Catalytic SN Ar Hydroxylation and Alkoxylation of Aryl Fluorides.

Nucleophilic aromatic substitution (SN Ar) is a powerful strategy for incorporating a heteroatom into an aromatic ring by displacement of a leaving group with a nucleophile, but this method is limited to electron-deficient arenes. We have now established a reliable method for accessing phenols and phenyl alkyl ethers via catalytic SN Ar reactions. The method is applicable to a broad array of electron-rich and neutral aryl fluorides, which are inert under classical SN Ar conditions. Although the mechanism of SN Ar reactions involving metal arene complexes is hypothesized to involve a stepwise pathway (addition followed by elimination), experimental data that support this hypothesis is still under exploration. Mechanistic studies and DFT calculations suggest either a stepwise or stepwise-like energy profile. Notably, we isolated a rhodium η5 -cyclohexadienyl complex intermediate with an sp3 -hybridized carbon bearing both a nucleophile and a leaving group.

Plecstatin-1 induces an immunogenic cell death signature in colorectal tumour spheroids.

Organometallic metal(arene) anticancer agents were believed to confer low selectivity for potential cellular targets. However, the ruthenium(arene) pyridinecarbothioamide (plecstatin-1) showed target selectivity for plectin, a scaffold protein and cytolinker. We employed a three-dimensional cancer spheroid model and showed that plecstatin-1 limited spheroid growth, induced changes in the morphology and in the architecture of tumour spheroids by disrupting the cytoskeletal organization. Additionally, we demonstrated that plecstatin-1 induced oxidative stress, followed by the induction of an immunogenic cell death signature through phosphorylation of eIF2α, exposure of calreticulin, HSP90 and HSP70 on the cell membrane and secretion of ATP followed by release of high mobility group box-1.

Variable structural bonding modes and antibacterial studies of thiosemicarbazone ligands of ruthenium, rhodium, and iridium metal complexes

Arene metal precursors on treatment with thiosemicarbazone ligands (L1, L2, and L3) yielded a series of cationic mono- and binuclear complexes (1–9) with N∩S bonding mode. In general, the complexes have been formulated as [(p-cymene)Ru(L)Cl]+ and [Cp*2M2(L)2]4+ where L = L1, L2, L3, M = Rh/Ir. Contrary to previous results [1], ruthenium complexes portrayed mononuclear bidentate chelation while rhodium and iridium complexes revealed dinuclear bridging coordination through sulfur and imine nitrogen atoms. All these complexes have been characterized by various spectroscopic techniques and antibacterial studies have been carried out for the complexes as well as the ligands, where 5 and 8 showed good inhibitory antibacterial activity.

Naphthoquinones of natural origin: Aqueous chemistry and coordination to half-sandwich organometallic cations

Abstract Half-sandwich organometallic complexes featuring Ru(II), Os(II) and Rh(III) metal centers and naturally occurring bidentate 2-hydroxy-[1,4]-naphthoquinone ligands (lawsone and phthiocol) have been synthesized and characterized in both solid state and solution phase by analytical, spectroscopic, electrochemical and single crystal X-ray diffraction techniques. Comparative studies revealed the influence of the respective metal center (Ru, Os, Rh), leaving group (Cl, Br, I) and arene (p-cymene, toluene, pentamethylcyclopentadienyl), as well as the naphthoquinone ligand on the structural properties and solution speciation. Additionally, cytotoxicity was tested in SW480, CH1/PA-1 and A549 human cancer cell lines showing a broad range of IC50 values.

The Chatt reaction: conventional routes to homoleptic arenemetalates of d-block elements.

Joseph Chatt was the first to discover in the early 1960s that previously unknown transition metal compounds were accessible and isolable via the reactions of alkali metal arene radical anions with transition metal precursors containing good leaving groups, such as weakly basic neutral or anionic ligands, especially halides. Later Peter Timms confirmed the importance of these early studies with the synthesis of several new bis(arene)metal(0) sandwich compounds by a variant of Chatt's route. Following a brief historical survey of alkali metal arene compounds, first examined in some detail by Wilhelm Schlenk, use of these reagents in the conventional syntheses of anionic homoleptic arene metal complexes of the d-block elements will be described. In several cases these species are quite useful because they function as storable "naked" atomic metal anion reagents, especially in their reactions with carbon monoxide and isocyanides. In view of Chatt's seminal contributions to an often unique route to organometallic and inorganic compounds, it is proposed that this valuable synthetic method be named the "Chatt reaction" in honor of a giant of chemistry.

From Catalysis to Cancer: Toward Structure-Activity Relationships for Benzimidazol-2-ylidene-Derived N-Heterocyclic-Carbene Complexes as Anticancer Agents.

The promise of the metal(arene) structure as an anticancer pharmacophore has prompted intensive exploration of this chemical space. While N-heterocyclic carbene (NHC) ligands are widely used in catalysis, they have only recently been considered in metal complexes for medicinal applications. Surprisingly, a comparatively small number of studies have been reported in which the NHC ligand was coordinated to the RuII(arene) pharmacophore and even less with an OsII(arene) pharmacophore. Here, we present a systematic study in which we compared symmetrically substituted methyl and benzyl derivatives with the nonsymmetric methyl/benzyl analogues. Through variation of the metal center and the halido ligands, an in-depth study was conducted on ligand exchange properties of these complexes and their biomolecule binding, noting in particular the stability of the M-CNHC bond. In addition, we demonstrated the ability of the complexes to inhibit the selenoenzyme thioredoxin reductase (TrxR), suggested as an important target for anticancer metal-NHC complexes, and their cytotoxicity in human tumor cells. It was found that the most potent TrxR inhibitor diiodido(1,3-dibenzylbenzimidazol-2-ylidene)(η6-p-cymene)ruthenium(II) 1bI was also the most cytotoxic compound of the series, with the antiproliferative effects in general in the low to middle micromolar range. However, since there was no clear correlation between TrxR inhibition and antiproliferative potency across the compounds, TrxR inhibition is unlikely to be the main mode of action for the compound type and other target interactions must be considered in future.

Cation-mediated sandwich formation between benzene and pillar[5]arene: a DFT study

ABSTRACTCation–π interactions in alkali metal ion (Li+, Na+ and K+)–pillar[5]arene complexes and sandwiches of pillar[5]arene and benzene formed via alkali metal ions are studied in the light of density functional theory. Several possible modes of interaction between metal ions and pillar[5]arene have been studied. Results suggest that interaction is stronger in the complexes with the metal ion present inside the cavity of the pillar[5]arene as compared to that where the metal ion is outside the cavity. The calculated interaction energy further reveals that though cation–π complexes with larger number of alkali metal ions are unstable, however, corresponding sandwiches are stable, which further support the fact that pillar[5]arene–metal ion complexes can interact with other π–electron-rich species. Absorption spectra of the complexes formed undergo both blue and red shifts as compared to the pillar[5]arene.

Direct Phosphination of Ferrocenium Ion with Tertiary Phosphines by the Mechanism of Oxidative Nucleophilic Substitution

Ferrocenium salts [(C5H5)2Fe]X (X = BF4, PF6) (I+·) react with tertiary phosphines PR3 (PMe3, PEt3, PnBu3, PMe2Ph, and PMePh2) in dichloromethane at room temperature to form a mixture of the corresponding ferrocenylphosphonium salts [(C5H5)FeC5H4PR3]X (III), ferrocene (I), and phosphonium salts [HPR3]X. The same reaction was carried out in an electrochemical cell as the electrolysis of a solution of ferrocene and phosphine in dichloromethane at the oxidation potential of ferrocene. Possible reaction pathways for phosphination of ferrocenium ion were studied by DFT at the M06‐L/6‐311++G(d,p) theory level. The experimental and theoretical studies of this reaction suggest it to proceed according to the Scheme of oxidative nucleophilic substitution of hydrogen in I+· including the following steps: a) nucleophilic exo addition of a phosphine to the cyclopentadienyl ring of I+· to form the radical cation adduct [(η5‐C5H5)Fe·(η4‐C5H5–+PR3)]X (II+·); b) redox reaction of the initial adduct II+· with the starting ferrocenium salt I+· to result in ferrocene (C5H5)2Fe (I) and iron phosphoniocyclopentadiene dication [(η5‐C5H5)Fe+(η4‐C5H5–+PR3)](X)2 (II2+) where the Csp3–H bond is involved in the agostic interaction with the metal atom; and c) deprotonation of the Csp3–H bond in II2+ by the starting phosphine to form III. The relation between the data obtained and current concepts of C–H functionalization in transition metal arene and cyclopentadienyl complexes is discussed.

Reactivity-Enhanced Arene–Metal Complex for the Synthesis of Medium-Sized Rings

Reactivity-Enhanced Arene–Metal Complex for the Synthesis of Medium-Sized Rings

An Organoruthenium Anticancer Agent Shows Unexpected Target Selectivity For Plectin.

Organometallic metal(arene) anticancer agents require ligand exchange for their anticancer activity and this is generally believed to confer low selectivity for potential cellular targets. However, using an integrated proteomics-based target-response profiling approach as a potent hypothesis-generating procedure, we found an unexpected target selectivity of a ruthenium(arene) pyridinecarbothioamide (plecstatin) for plectin, a scaffold protein and cytolinker, which was validated in a plectin knock-out model in vitro. Plectin targeting shows potential as a strategy to inhibit tumor invasiveness as shown in cultured tumor spheroids while oral administration of plecstatin-1 to mice reduces tumor growth more efficiently in the invasive B16 melanoma than in the CT26 colon tumor model.