Search Results (24)

Polybutadiene (PB) and polyisoprene (PI) rubbers are indispensable synthetic elastomeric materials widely used in tires, footwear, hose, belts, sealants, electricity, construction, and other applications. Nowadays, PB and PI elastomers are produced from butadiene (BD) and isoprene (IP) monomers via transition-metal-mediated coordination polymerization. Transition metal catalytic systems consist of a precise characteristic structural unit at the molecular level: well known as “single-site catalysts” (SSCs). These have experienced a revolutionary advance in the recently developed conjugated dienes synthetic rubber method. Among the SSCs, a class of rare-earth, metal-centered half-sandwich molecule has been identified as a high-performance catalytic system for conjugated dienes polymerization. These novel half-sandwich rare-earth (HSRE) catalytic systems exhibit several irreplaceable advantages compared with the conventional Ziegler–Natta-type catalytic systems. These HSRE catalytic systems can create novel conjugated diene rubbers (CDRs) with high catalytic reactivity, high stereoselectivity, an adjustable polymer chain microstructure, and high molecular weights and are considered to be the next generation of ecofriendly and economic catalytic systems for industrial applications. This paper delivers a concise review of some important synthetic methods for representative HSRE complexes with characteristic structures and of the utilization of some HSRE catalytic systems for the preparation of high-performance CDRs, especially highly stereoregular PI and PB materials. Full article

Towards the efforts to expand the bioactivity and to reduce toxic and adverse properties of known metal-based drugs, various multinuclear complexes have recently been studied. They have shown enhancement of target specificity and selectivity. Different from small organic compounds and traditional metal-based complexes with anticancer activity, iridium(III) multinuclear or heteronuclear metallodrugs have confirmed potential advantages due to their unique biological and chemical diversities, better activity and different anticancer mechanisms. Ir(III) coordination compounds, similar to most Pt group compounds, are of excessive interest because of their potential cytotoxic activity, effective cellular uptake and tolerance by healthy cells. Although mononuclear Ir(III) complex compounds have been extensively studied as promising candidates for antitumor application, the research on the antineoplastic potential of homo- or hetero-multinuclear iridium(III) complexes is not as abundant; nevertheless, intensive investigations have been conducted in the recent years towards developing complexes that are anticipated to have improved therapeutic potential and biotarget selectivity. Multimetallic iridium(III) frameworks have offered interesting possibilities for designing new antitumor agents by exploiting the action of different metal cations at the same time. This method was very successful in the design of homo- and hetero-multinuclear cyclometalated and half-sandwich organometallic Ir(III) compounds. In the described background, many homonuclear and heteronuclear Ir(III) complexes have been estimated and have exposed promising advantages in cancer therapy. This review intends to summarize newly reported innovative and promising multinuclear Ir(III)-based complexes and to afford a wide-ranging overview of current development and perspectives for the practical impact of these complexes in the tumor therapy field. It is anticipated that this analysis will provide significant direction for the further progress of active homonuclear and heteronuclear iridium-based anticancer agents. Full article

The aromatic boron cluster B₈^2– (D_7h) has similar π bonding to C₆H₆, which is named “borozene”. The B₈^2– ligand has been observed to stabilize monovalent Ln(+I) in C_7v-LnB₈⁻ (Ln = La, Pr, Tb, Tm, and Yb) borozene complexes. Low-valency actinide complexes have been reported more rarely, and B₈^2– may be one of the potential ligands. Here, we report a theoretical study on a series of actinide metal-doping octa-boron clusters AnB₈ (An = Pa, U, Np, and Pu). It was found that each species has both half-sandwich and chair-like structures. Except for PaB₈, the half-sandwich structures of UB₈, NpB₈, and PuB₈ are more energetically stable than the chair-like structures, and the half-sandwich clusters of AnB₈ are found to be actinide(II) borozene complexes with the M^II[B₈²⁻] type. For each of the half-sandwich clusters, the B₈²⁻ ligand has σ and π double aromaticity. Various bonding analyses of AnB₈ confirm the covalent interactions between the doped actinide metals and the octa-boron clusters, which further stabilize the complexes and determine the relative stability of AnB₈. As expected, these complexes show high bond dissociation energies, especially PaB₈ with stronger Pa-B covalent bonds. These results demonstrate that the B₈²⁻ doubly aromatic ligand is able to stabilize divalent actinides. Full article

A series of new chelating bidentate (SS) alkylimidazole-2-thione-Ru(II)/Os(II) complexes (3a_i, 3a_ii, 3a_iii, 3b_ii/4a_iii, 4b_i, 4b_ii), and the tridentate (SNS) pyridine-2,6-diylimidazole-2-thione-Ru(II)/Os(II) complexes (5b_i, 5c_iv/6bi, 6c_i, 6c_iv) in the forms [M^II(cym)(L)Cl]PF₆ and [M^II(cym)(L)]PF₆ (M = Ru or Os, cym = η⁶-p-cymene, and L = heterocyclic derivatives of thiourea) respectively, were successfully synthesized. Spectroscopic and analytical methods were used to characterize the complexes and their ligands. Solid-state single-crystal X-ray diffraction analyses revealed a “piano-stool” geometry around the Ru(II) or Os(II) centers in the respective complexes. The complexes were investigated for in vitro chemotherapeutic activities against human cervical carcinoma (HeLa) and the non-cancerous cell line (Hek293) using the MTT assay. The compounds 3a_ii, 5c_iv, 5b_i, 4a_iii, 6c_i, 6c_iv, and the reference drug, 5-fluorouracil were found to be selective toward the tumor cells; the compounds 3a_i, 3a_iii, 3b_ii, 4b_i, 4b_ii, and 6b_i, which were found not to be selective between normal and tumor cell lines. The IC₅₀ value of the tridentate half-sandwich complex 5b_i (86 ± 9 μM) showed comparable anti-proliferative activity with the referenced commercial anti-cancer drug, 5-fluorouracil (87 ± 15 μM). The pincer (SNS) osmium complexes 6c_i (36 ± 10 μM) and 6c_iv (40 ± 4 μM) were twice as effective as the reference drug 5-fluorouracil at the respective dose concentrations. However, the analogous pincer (SNS) ruthenium complex 5c_iv was ineffective and did not show anti-proliferative activity, even at a higher concentration of 147 ± 1 μM. These findings imply that the higher stability of the chelating (SS) and the pincer (SNS) ligand architectures in the complexes improves the biological (anti-proliferative) activity of the complexes by reducing the chance of ligand dissociation under physiological conditions. In general, the pincer (SNS) osmium complexes were found to be more cytotoxic than their ruthenium analogues, suggesting that the anti-proliferative activity of the imidazole-2-thione-Ru/Os complexes depends on the ligand’s spatial coordination, the nature of the metal center, and the charge of the metal complex ions. Full article

A series of C- and B-substituted nido-carborane derivatives with a pendant pyridyl group was prepared. The synthesized compounds were used as ligands in the complexation reactions with bis(triphenylphosphine)nickel(II) and palladium(II) chlorides to give six new metallacomplexes with unusual η⁵:κ¹(N)-coordination of the metal center. The single crystal structures of 1-(NC₅H₄-2′-S)-1,2-C₂B₁₀H₁₁, 1-(NC₅H₄-2′-CH₂S)-1,2-C₂B₁₀H₁₁, Cs [7-(NC₅H₄-2′-CH₂S)-7,8-C₂B₉H₁₁] closo- and nido-carboranes and 3-Ph₃P-3-(4(7)-NC₅H₄-2′-S)-closo-3,1,2-NiC₂B₉H₁₀ and 3-Ph₃P-3-(4(7)-NC₅H₄-2′-CH₂S)-closo-3,1,2-NiC₂B₉H₁₀ metallacarboranes were determined using single crystal X-ray diffraction. Full article

Due to their fascinating topological structures and application prospects, coordination supramolecular complexes have continuously been studied by scientists. However, the controlled construction and property study of organometallic handcuffs remains a significant and challenging research subject in the area of supramolecular chemistry. Hence, a series of tetranuclear organometallic and heterometallic handcuffs bearing different size and metal types were rationally designed and successfully synthesized by utilizing a quadridentate pyridyl ligand (tetra-(3-pyridylphenyl)ethylene) based on three Cp*Rh (Cp* = η⁵-C₅Me₅) fragments bearing specific longitudinal dimensions and conjugated planes. These results were determined with single-crystal X-ray diffraction analysis technology, ESI-MS NMR spectroscopy, etc. Importantly, the photoquenching effect of Cp* groups and the discrepancy of intermolecular π–π stacking interactions between building block and half-sandwich fragments promote markedly different photothermal conversion results. These results will further push the synthesis of topological structures and the development of photothermal conversion materials. Full article

The coordination of rare-earth metal ions (Ln³⁺) to polyoxometalates (POM) is regarded as a way of modifying and controlling their properties, such as single-molecular magnetism or luminescent behavior. The half-sandwich complexes of Ln³⁺ with monolacunary Keggin POMs (Ln³⁺/POM = 1:1) are of particular interest, since the Ln³⁺ retains its ability to coordinate extra ligands. Thus, the knowledge of the exact structures of 1:1 Ln/POM complexes is important for the development of reliable synthetic protocols for hybrid complexes. In this work, we isolated three 1:1 Gd³⁺/POM complexes of the general formula Cat₄Gd(PW₁₁O₃₉)·xH₂O (Cat = K⁺ or Me₄N⁺). Complex (Me₄N)₂K₂[Gd(H₂O)₂PW₁₁O₃₉]·5H₂O (1) is polymeric, revealing a layered structural motif via bridging Gd³⁺ and K⁺ ions. Complexes (Me₄N)₆K₂[Gd(H₂O)₃PW₁₁O₃₉]₂·20H₂O (2) and (Me₄N)₇K[Gd(H₂O)₃PW₁₁O₃₉]₂·12H₂O (3) are classified as dimeric; the difference between them consists of the different crystal packing of the polyoxometalates, which is induced by a variation in the cationic composition. Isostructural complexes have also been characterized for praseodymium, europium, terbium and dysprosium. The coordination number of Ln³⁺ (8) persists in all the compounds, while the binding mode of the POM varies, giving rise to different architectures with two or three H₂O co-ligands per Ln³⁺. However, whatever the particular structure and exact composition, the {Ln(PW₁₁O₃₉)} moieties are always involved in bonding with each other with the formation either of polymeric chains or dimeric units. In water, these aggregates can dissociate with the formation of [Ln(H₂O)₄PW₁₁O₃₉]^4-. This behavior must be taken into account when choosing L for the design of hybrid {Ln(L)POM} complexes. Full article

While platinum-based compounds such as cisplatin form the backbone of chemotherapy, the use of these compounds is limited by resistance and toxicity, driving the development of novel complexes with cytostatic properties. In this study, we synthesized a set of half-sandwich complexes of platinum-group metal ions (Ru(II), Os(II), Ir(III) and Rh(III)) with an N,N-bidentate ligand comprising a C-glucosaminyl group and a heterocycle, such as pyridine, pyridazine, pyrimidine, pyrazine or quinoline. The sugar-containing ligands themselves are unknown compounds and were obtained by nucleophilic additions of lithiated heterocycles to O-perbenzylated 2-nitro-glucal. Reduction of the adducts and, where necessary, subsequent protecting group manipulations furnished the above C-glucosaminyl heterocycles in their O-perbenzylated, O-perbenzoylated and O-unprotected forms. The derived complexes were tested on A2780 ovarian cancer cells. Pyridine, pyrazine and pyridazine-containing complexes proved to be cytostatic and cytotoxic on A2780 cells, while pyrimidine and quinoline derivatives were inactive. The best complexes contained pyridine as the heterocycle. The metal ion with polyhapto arene/arenyl moiety also impacted on the biological activity of the complexes. Ruthenium complexes with p-cymene and iridium complexes with Cp* had the best performance in ovarian cancer cells, followed by osmium complexes with p-cymene and rhodium complexes with Cp*. Finally, the chemical nature of the protective groups on the hydroxyl groups of the carbohydrate moiety were also key determinants of bioactivity; in particular, O-benzyl groups were superior to O-benzoyl groups. The IC₅₀ values of the complexes were in the low micromolar range, and, importantly, the complexes were less active against primary, untransformed human dermal fibroblasts; however, the anticipated therapeutic window is narrow. The bioactive complexes exerted cytostasis on a set of carcinomas such as cell models of glioblastoma, as well as breast and pancreatic cancers. Furthermore, the same complexes exhibited bacteriostatic properties against multiresistant Gram-positive Staphylococcus aureus and Enterococcus clinical isolates in the low micromolar range. Full article

Two half-sandwich iridium(III) and rhodium(III) complexes with 11H-indeno[1,2-b]quinoxalin-11-one oxime (IQ-1) ligand were prepared by the reaction of the proligand with [M(Cp*)Cl₂]₂ (M = Ir, Rh) dimers. The reaction between IQ-1 and [Ir(Cp*)Cl₂]₂ in methanol gave the complex [Ir(Cp*)(IQ-1)Cl] (1), which crystallized in a centrosymmetric space group as a true racemate. Whereas complex [Rh(Cp*)(IQ-1)Cl] (2) in the form of a racemic conglomerate was obtained by the reaction of [Rh(Cp*)Cl₂]₂ and IQ-1 in methanol. The crystal structures of complexes 1 and 2 (R and S enantiomers) were determined by X-ray diffraction analysis, and the structural features were compared in order to understand the structural factors leading to the spontaneous enantiomer resolution of the rhodium(III) complex. In the crystal packing of 1, intermolecular C–H···C contacts between a pair of enantiomers link the molecules into centrosymmetric dimers and lead to the formation of heterochiral crystals of 1. In contrast, the intramolecular contacts CH···Cl and CH···C in complex 2 bind all three ligands around the chiral Rh(III) metal center. In addition, a combination of intermolecular CH···O and CH···C contacts leads to the formation of a homochiral supramolecular structure. These interactions altogether reinforce the spontaneous resolution in complex 2. Full article

The geometrical structure, electronic and magnetic properties of B-endoped C₆₀ (B@C₆₀) ligand sandwich clusters, TM&(B@C₆₀)₂ (TM = V, Cr), and their one-dimensional (1D) infinite molecular wires, [TM&(B@C₆₀)]_∞, have been systematically studied using first-principles calculations. The calculations showed that the TM atoms can bond strongly to the pentagonal (η⁵-coordinated) or hexagonal rings (η⁶-coordinated) of the endoped C₆₀ ligands, with binding energies ranging from 1.90 to 3.81 eV. Compared to the configurations with contrast-bonding characters, the η⁶- and η⁵-coordinated bonding is energetically more favorable for V-(B@C₆₀) and Cr-(B@C₆₀) complexes, respectively. Interestingly, 1D infinite molecular wire [V&(B@C₆₀)-η⁶]_∞ is an antiferromagnetic half-metal, and 1D [Cr&(B@C₆₀)-η⁵]_∞ molecular wire is a ferromagnetic metal. The tunable electronic and magnetic properties of 1D [TM&(B@C₆₀)]_∞ SMWs are found under compressive and tensile stains. These findings provide additional possibilities for the application of C₆₀-based sandwich compounds in electronic and spintronic devices. Full article

The controlled synthesis of organometallic supramolecular macrocycles cages remains interesting and challenging work in the field of supramolecular chemistry. Here, two tetranuclear rectangular macrocycles and an octuclear cage were designed and synthesized utilizing a rigid and functionalized pillar linker, 2,6-bis(pyridin-4-yl)-1,7-dihydrobenzo [1,2-d:4,5-d′]diimidazole (BBI4PY) based on three half-sandwich rhodium building blocks bearing different sizes. X-ray crystallography in combination with ¹H NMR spectroscopy elucidated that the two building blocks with shorter spacers only result in rectangular macrocycles. However, the building block of bulkier size to avoid the π-π stacking interactions between two ligands BBI4PY led to the formation of an octuclear cage complex. The latter cage contains two types of metal ions, namely Rh³⁺ and Cu²⁺, showing significant characteristics of heterogeneous metal-assembling compounds. In addition, the cage accommodates two free isopropyl ether solvent molecules, thus displaying host–guest behavior. Full article

Enantiopure N-heterocyclic carbene half-sandwich metal complexes of the general formula [Cp*M(C^C:)I] (M = Rh, Ir; C^C: = NI-NHC; NI-H = Naphthalimide; NHC = N-heterocyclic carbene) are reported. The rhodium compound was obtained as a single isomer displaying six membered metallacycle and was resolved on chiral column chromatography to the corresponding enantiomers (S)-[Cp*Rh(C^C:)I] (S)-2 and (R)-[Cp*Rh(C^C:)I] (R)-2. The iridium congener, however, furnishes a pair of regioisomers, which were resolved into (S)-[Cp*Ir(C^C:)I] (S)-3 and (R)-[Cp*Ir(C^C:)I] (R)-3 and (S)-[Cp*Ir(C^C:)I] (S)-4 and (R)-[Cp*Ir(C^C:)I] (R)-4. These regioisomers differ from each other, only by the size of the metallacycle; five-membered for 3 and six-membered for 4. The molecular structures of (S)-2 and (S)-4 are reported. Moreover, the chiroptical properties of these compounds are presented and discussed. These compounds display exceptional stable configurations at the metal center in solution with enantiomerization barrier ΔG^≠ up to 124 kJ/mol. This is because the nature of the naphthalimide-NHC clamp ligand and the iodide ligand contribute to their configuration’s robustness. In contrast to related complexes reported in the literature, which are often labile in solution. Full article

Complexes that incorporate both ligand(s) and metal(s) exhibiting cytotoxic activity can especially be interesting to develop multifunctional drug molecules with desired activities. In this review, the limited number of solution results collected in our laboratory on the complexes of Pd(II) and two other platinum group metals—the half-sandwich type, [(η⁶-p-cym)Ru(H₂O)₃]²⁺, and [(η⁵-Cp*)Rh(H₂O)₃]²⁺—with hydroxamic acid derivatives of three amino acids, two imidazole analogues, and four small peptides are summarized and evaluated. Unlike the limited number of coordination sites of these metal ions (four and three for Pd(II) and the organometallic cations, respectively), the ligands discussed here offer a relatively high number of donor atoms as well as variation in their position within the ligands, resulting in a large versatility of the likely coordination modes. The review, besides presenting the solution equilibrium results, also discusses the main factors, such as (N,N) versus (O,O) chelate; size of chelate; amino-N versus imidazole-N; primary versus secondary hydroxamic function; differences between hydrolytic ability of the metal ions studied; and hydrolysis of the coordinated peptide hydroxamic acids in their Pd(II) complexes, which all determine the coordination modes present in the complexes formed in measurable concentrations in these systems. The options for the quantitative evaluation of metal binding effectivity and selectivity of the various ligands and the comparison with each other by using solution equilibrium data are also discussed. Full article

An important challenge in the field of anticancer chemotherapy is the search for new species to overcome the resistance of standard drugs. An interesting approach is to link bioactive ligands to metal fragments. In this work, we have synthesized a set of p-cymene-Ru or cyclopentadienyl-M (M = Rh, Ir) complexes with four chrysin-derived pro-ligands with different -OR substituents at position 7 of ring A. The introduction of a piperidine ring on chrysin led to the highly cytotoxic pro-ligand HL4 and its metal complexes L4-M (SW480 and A549 cell lines, cytotoxic order: L4-Ir > L4-Ru ≈ L4-Rh). HL4 and its complexes induce apoptosis and can overcome cis-platinum resistance. However, HL4 turns out to be more cytotoxic in healthy than in tumor cells in contrast to its metal complexes which displayed higher selectivity than cisplatin towards cancer cells. All L4-M complexes interact with double stranded DNA. Nonetheless, the influence of the metal is clear because only complex L4-Ir causes DNA cleavage, through the generation of highly reactive oxygen species (¹O₂). This result supports the hypothesis of a potential dual mechanism consisting of two different chemical pathways: DNA binding and ROS generation. This behavior provides this complex with a great effectivity in terms of cytotoxicity. Full article

Platinum-based anticancer drugs are most likely the most successful group of bioinorganic compounds. Their apparent disadvantages have led to the development of anticancer compounds of other noble metals, resulting in several ruthenium-based drugs which have entered clinical trials on oncological patients. Besides ruthenium, numerous rhodium complexes have been recently reported as highly potent antiproliferative agents against various human cancer cells, making them potential alternatives to Pt- and Ru-based metallodrugs. In this review, half-sandwich Rh(III) complexes are overviewed. Many representatives show higher in vitro potency than and different mechanisms of action (MoA) from the conventional anticancer metallodrugs (cisplatin in most cases) or clinically studied Ru drug candidates. Furthermore, some of the reviewed Rh(III) arenyl complexes are also anticancer in vivo. Pioneer anticancer organorhodium compounds as well as the recent advances in the field are discussed properly, and adequate attention is paid to their anticancer activity, solution behaviour and various processes connected with their MoA. In summary, this work summarizes the types of compounds and the most important biological results obtained in the field of anticancer half-sandwich Rh complexes. Full article