Use Of Transition Metal Complexes Research Articles

Alternative of cisplatin - Introduction of rhodium analogues

The use of transition metal complexes as anti-cancer agents became most practiced since the discovery and approval of cis-platin in 1978. Different analogues of platinum complexes were discovered and further investigated to find maximum efficiency on the target. But it was soon realized, the Pt-complexes had numerous side effects like resistance, neurotoxicity, etc. by which they couldn't reach to their final expectation. Hence, scientists researched other efficient alternatives, which can defeat the limitations of platinum analogues and shows capability in induced tumour cell death. In this review, we attempted to discuss how rhodium analogues can be a better alternative than cis-platin as an anti-cancer agent.

Ru-terpyridine complexes containing clotrimazole as potent photoactivatable selective antifungal agents

The overuse of antimicrobial agents in medical and veterinary applications has led to the development of antimicrobial resistance in some microorganisms and this is now one of the major concerns in modern society. In this context, the use of transition metal complexes with photoactivatable properties, which can act as drug delivery systems triggered by light, could become a potent strategy to overcome the problem of resistance. In this work several Ru complexes with terpyridine ligands and the clotrimazole fragment, which is a potent antimycotic drug, were synthesized. The main goal was to explore the potential photoactivated activity of the complexes as antifungal agents and evaluate the effect of introducing different substituents on the terpyridine ligand. The complexes were capable of delivering the clotrimazole unit upon irradiation with visible light in a short period of time. The influence of the substituents on the photodissociation rate was explained by means of TD-DFT calculations. The complexes were tested against three different yeasts, which were selected based on their prevalence in fungal infections. The complex in which a carboxybenzene unit was attached to the terpyridine ligand showed the best activity against the three species under light, with minimal inhibitory concentration values of 0.88 μM and a phototoxicity index of 50 achieved. The activity of this complex was markedly higher than that of free clotrimazole, especially upon irradiation with visible light (141 times higher). The complexes were more active on yeast species than on cancer cell lines.

An Overview of Palladium-Catalyzed Fabrication of Some Heterocyclic Frameworks

Abstract: Heterocycles are the largest family of organic compounds due to their wide applications as therapeutic agents, synthetic intermediates, scaffolds, building blocks or fine chemicals. Heterocyclic compounds are continuously used in material science, biotechnology, pharmaceutical and agrochemical industries. In the past few years, the use of transition metal complexes especially palladium as a heterogeneous catalyst has become a trend for the synthesis of various organic compounds. Pd-catalyzed reactions have proven to be effective ways for synthesising a variety of heterocyclic compounds, which are a popular class of molecules in chemical study. Hence, in this review we have discussed the palladium catalyzed synthesis of various heterocyclic compounds i,e. furan, indole, quinoline, coumarin and some other heterocycle derivatives.

Synthesis of α‐Aryl Carbonyls via Photoinduced Formation of C−C Bonds

AbstractThe present review aims to provide an overview of recent developments in photochemical and photocatalyzed synthesis of α‐aryl carbonyls via formation of C(sp)2−C(sp)3bonds. The approaches described are based on the use of light as the exclusive energy source for the generation of highly reactive carbon radicals, cations or radical ions as the key intermediates of the process. Such strategies efficiently compete with traditional routes, that require the combined use of transition metal complexes, ligands, additives and often harsh reaction conditions.

Small molecule activation by well-defined compounds of heavy p-block elements.

The creative design and exploration of new bonding motifs and molecular architectures in main group chemistry have pushed the boundaries of reactivity in this field of research. In this context, the activation of small molecules represents a set of benchmark reactions and offers valuable opportunities for the development of innovative synthetic methods. In addition to significant progress by use of transition metal complexes and compounds of lighter p-block elements, compounds based on heavy p-block elements (with the principle quantum number n > 4) have seen major advances in recent years. Fundamental properties originating from their high atomic number (such as the size, energy, and polarizability of atomic orbitals) set them apart from more established species in small molecule activation. Challenges and opportunities arising from this scenario are analyzed and highlighted.

Transformation of Tetrafluoroethylene Using Transition-Metal Complexes

AbstractTetrafluoroethylene (TFE) is an industrial organofluorine feedstock that is used predominantly to fabricate fluorinated polymers. TFE exhibits excellent potential as a building block for synthesizing organofluorine compounds, which are increasingly gaining attention as functional materials, pharmaceuticals, and agrochemicals. In particular, the use of transition-metal complexes in the transformation of TFE is of great interest, considering their widespread use in syntheses of organofluorine compounds over the last few decades. This review highlights studies on the transformation of TFE into organofluorine compounds using transition-metal complexes, except for polymerizations. Our review covers cross-coupling reactions via C–F bond cleavage, fluoroalkylation reactions, multicomponent couplings, and olefin metathesis.1 Introduction2 Palladium Complexes3 Copper Complexes4 Nickel Complexes5 Ruthenium Complexes6 Rhodium Complexes7 Summary and Perspective

Predicting Small Molecule Activation including Catalytic Hydrogenation of Dinitrogen Promoted by a Dual Lewis Acid.

For decades, N2 activation and functionalization have required the use of transition metal complexes. Thus, it is one of the most challenging projects to activate the abundant dinitrogen through metal-free systems under mild conditions. Here, we demonstrate a proof-of-concept study on the catalytic hydrogenation of dinitrogen (with activation energy as low as 15.3 kcal mol-1 ) initiated by a dual Lewis acid (DLA) via density functional theory (DFT) calculations. In addition, such a DLA could be also used to activate a series of small molecules including carbon dioxide, formaldehyde, N-ethylenemethylamine, and acetonitrile. It is found that aromaticity plays an important role in stabilizing intermediates and products. Our findings provide an alternative approach to N2 activation and functionalization, highlighting a great potential of DLA for small molecule activation.

Synthesis, characterization, and biological activities of zinc(II), copper(II) and nickel(II) complexes of an aminoquinoline derivative.

Interest is increasingly focused on the use of transition metal complexes as biochemical, medical, analytical, pharmaceutical, agronomic, anticancer, and antibacterial agents. In this study, three complexes of [Zn(H2L)Cl] (1), [Cu(H2L)(H2O)(NO3)] (2) and [Ni(H2L)(NO3)].2H2O (3) were synthesized from a 2-chloroquinoline-3-carbaldehyde derived ligand [H3L = ((E)-2-(((2-((2-hydroxyethyl)amino)quinolin-3-yl)methylene)amino)ethanol. The compounds were characterized using physicochemical and spectroscopic methods. The results demonstrate that the free ligand behaves as a tridentate ligand with one oxygen and two nitrogen (ONN) donor atoms in 1:1 metal:ligand ratio. The formation constants of the complexes were found to be (K Zn(II) = 2.3 × 106, K Cu(II) = 2.9 × 106, and K Ni(II) = 3.8 × 105). The thermodynamic parameters indicated that the reactions were spontaneous with exothermic nature of metal-ligand interaction energies. Based on the analyses of the experimental (EDX, FTIR, PXRD, MS and TGA) and DFT results, a distorted tetrahedral, a distorted square pyramidal and square planar geometry for Zn(II), Cu(II) and Ni(II) complexes, respectively, were proposed. The B3LYP calculated IR frequencies and TD-B3LYP calculated absorption spectra were found to be in good agreement with the corresponding experimental results. The powder XRD data confirmed that the Zn(II), Cu(II) and Ni(II) complexes have polycrystalline nature with average crystallite sizes of 27.86, 33.54, 37.40Å, respectively. In vitro antibacterial activity analyses of the complexes were studied with disk diffusion method, in which the complexes showed better activity than the precursor ligand. Particularly the Cu(II) complex showed higher percent activity index (62, 90%), than both Zn(II) (54, 82%) and Ni(II) (41, 68%) complexes against both E. coli and P. aeruginosa, respectively. Using the DPPH assay, the complexes were further assessed for their antioxidant capacities. All metal complexes showed improved antioxidant activity than the free ligand. Zn(II) and Cu(II) complexes, which had IC50 values of 10.46 and 8.62μg/ml, respectively, showed the best antioxidant activity. The calculated results of Lipinski's rule of five also showed that the target complexes have drug-like molecular nature and similarly, the results of binding mode of action of these compounds against E. coli DNA gyrase B and P. aeruginosa LasR.DNA were found to be in good agreement with the in vitro biological activities.

Efficacy of Prednisolone/Zn Metal Complex and Artemisinin Either Alone or in Combination on Lung Functions after Excessive Exposure to Electronic Cigarettes Aerosol with Assessment of Antibacterial Activity

The use of transition metal complexes as therapeutic compounds has become more and more pronounced. These complexes offer a great diversity of uses in their medicinal applications. Electronic cigarettes (ECs) are an electronic nicotine delivery system that contain aerosol (ECR). The ligation behavior of prednisolone, which is a synthetic steroid that is used to treat allergic diseases and asthma arthritis, and its Zn (II) metal complex were studied and characterized based on elemental analysis, molar conductance, Fourier-transform infrared (FT-IR) spectra, electronic spectra, XRD, scanning electron microscopy (SEM), energy dispersive x-ray (EDX), and transmission electron microscopy (TEM). The FT-IR spectral data revealed that PRD acts as a mono-dentate ligand via oxygen atoms of the carbonyl group. Electronic and FT-IR data revealed that the PRD/Zn (II) metal complexes have square planner geometry. Artemisinin (ART) is the active main constituent of Artemisia annua extract, and it has been demonstrated to exert an excellent antimalarial effect. The experiment was performed on 40 male mice that were divided into the following 7 groups: Control, EC group, PRD/Zn, ART, EC plus PRD/Zn, EC plus ART, and PRD plus combination of PRD/Zn and ART. Serum CRP, IL-6, and antioxidants biomarkers were determined. Pulmonary tissue histology was evaluated. When in combination with Zn administration, PRD showed potent protective effects against pulmonary biochemical alterations induced by ECR and suppressed severe oxidative stress and pulmonary structure alterations. Additionally, PRD/Zn combined with ART prevented any stress on the pulmonary tissues via antioxidant regulation, reducing inflammatory markers CRP and Il-6 and improving antioxidant enzymatic levels more than either PRD or ART alone. Therefore, PRD/Zn combined with ART produced a synergistic effect against any sort of oxidative stress and also improved the histological structure of the lung tissues. These findings are of great importance for saving pulmonary function, especially during pandemic diseases, such as during the COVID-19 pandemic.

Chiral resolution and absolute configuration determination of new metal-based photodynamic therapy antitumor agents

The advent of cisplatin as a cancer drug in the late 1960s generated considerable interest in the use of transition metal complexes as cancer therapy agents. Despite enhanced research in this area, there has yet to be any non-platinum-based transition metal complex cancer drugs approved by the Food and Drug Administration (FDA). Recently a Ru(II) metal-organic dyad (TLD1433) has provided promising results as a photodynamic therapy (PDT) agent for some types of cancer. This particularly effective PDT compound has an oligothiophene chain appended to an imidazophenanthroline ligand which chelates Ru(II). The entire complex is chiral and is synthesized as a racemate. Five such chiral Ru(II) and Os(II) PDT agents were synthesized and their enantiomers separated for the first time. The enantiomers of these compounds are not easily crystalized. However, preparative LC provided sufficient amounts of these novel PDT agents to determine their absolute configurations by vibrational circular dichroism (VCD). The synthesis, separation and absolute configuration determinations are described and discussed in detail.

Transition Metal-Promoted Reactions in Aqueous Media and Biological Settings.

During the last decade, there has been a tremendous interest for developing non-natural biocompatible transformations in biologically relevant media. Among the different encountered strategies, the use of transition metal complexes offers unique possibilities due to their high transformative power. However, translating the potential of metal catalysts to biological settings, including living cells or small-animal models such as mice or zebrafish, poses numerous challenges associated to their biocompatibility, and their stability and reactivity in crowded aqueous environments. Herein, we describe the most relevant advances in this direction, with a particular emphasis on the systems' structure, their mode of action and the mechanistic bases of each transformation. Thus, the key challenges from an organometallic perspective might be more easily identified.

Transition Metal Complexes with HIV/AIDS Inhibitory Properties

The management of HIV in the human body has been a major research area in the quest to either find the cure or the preventative scientific measure. The quest to manage the virus has been successful using some organic molecules which target one or more of the stages of the replication cycle of HIV rendering it inhibited to continue infecting other host cells. However, the approach is now moving to use of transition metal complexes to manage the HIV infection in the host cells and this review highlights the relevant contributions of such as HIV/AIDS inhibitors. There have been increasing number of reports on the trends for transition metal complexes with anticancer and antimicrobial activity hence this probed the need of such a review. Complexes of vanadium, manganese, iron, copper, cobalt, nickel, zinc, ruthenium, platinum and gold have been reported to be active against HIV-1 virus. The complexes discussed in this review showed anti-viral activity compared to the vehicle control.

Charge-transfer processes in metal complexes enable luminescence and memory functions

Molecular transition-metal–ligand complexes are emerging as useful paradigms in materials science. Transition metal complexes have diverse metal d electron configurations, oxidation states, coordination numbers and geometries such that they can undergo a diverse array of electronic transitions. Metal-to-ligand charge-transfer transitions and their associated excited states are especially attractive given their rich redox properties and robustness. This chemistry is accessible by appropriate choice of low-valence metal centres and strong π-acceptor ligands. An in-depth fundamental understanding of their charge-transfer, assembly and structure–property relationships is important to allow us to rationally design complexes and tune their characteristics for an intended application. In addition to their attractive light-harvesting and photocatalytic applications, this Perspective describes recent developments in the use of transition metal complexes as materials in phosphorescent organic light-emitting diodes and resistive memory devices. Metal–ligand complexes undergo diverse charge-transfer processes when stimulated by light or electric fields. This Perspective describes how these processes can be exploited in photosensitizers, luminophores and resistive memory materials.

TiO2 Photocatalysis in the Aromatic “Redox Tag”-Guided Intermolecular Formal [2 + 2] Cycloadditions

Light has the potential to serve as green and sustainable reagent to catalyze chemical reactions. Stemming from the pioneering work of Honda and Fujishima in 1972, titanium dioxide (TiO2) has occupied a central place in the research field of semiconductor photocatalysis. The excited electron/hole pair generated upon irradiation in aqueous aerobic conditions produces reactive oxygen species (ROSs) at the surface, which are account for subsequent redox transformations. They rapidly convert organic compounds into CO2 and H2O via carbon-carbon bond cleavage, therefore, semiconductor photocatalysis has generally been recognized as redox options in inorganic chemistry rather than organic chemistry where carbon-carbon bond formation is a focal point for extensive research efforts. While semiconductor photocatalysis is a heterogeneous process, a homogeneous alternative can be provided by the use of transition metal complexes, which is now well- known as “photoredox catalysis”. The early works by MacMillan, Yoon, and Stephonson have triggered the explosive growth in the general area of new reaction developments in this class. Arguably, heterogeneous semiconductor photocatalysis has taken a backseat to homogeneous photoredox catalysis in the field of organic chemistry. For TiO2 photocatalysis to be effective in carbon-carbon bond formation, the reactions must be carried out in dry anaerobic conditions in order not to produce ROSs that can damage organic compounds. We have been developing carbon-carbon bond formations by electrocatalysis in lithium perchlorate (LiClO4)/nitromethane (CH3NO2) electrolyte solution.1 Our reaction design involves the aromatic “redox tag” concept,2 that is, an aromatic ring that provides both the oxidant and the reductant in the overall net redox neutral carbon-carbon bond formations. In most cases, the use of LiClO4/CH3NO2 electrolyte solution is critical, which exhibits remarkable property as a Lewis acid to facilitate the reactions of carbon-centered radical cations with carbon nucleophiles, even unactivated alkenes. Our reaction development is also characterized by the importance of an intramolecular electron transfer process, which is recently presented by Melchiorre as an elegant “electron relay” mechanism. We anticipated that the use of LiClO4/CH3NO2 electrolyte solution would pave the way for carbon-carbon bond formations by TiO2 photocatalysis. It should also be noted that overall net redox neutral processes would be benefited from the involvement of both reductive and oxidative electron transfers potentially enabled by excited electron and hole. In this talk, the aromatic redox tag-guided intermolecular formal [2 + 2] cycloadditions3 by TiO2 photocatalysis will be discussed in details. (1) Imada, Y.; Yamaguchi, Y.; Shida, N.; Okada, Y.; Chiba, K. Chem. Commun. 2017, 53, 3960–3963. (2) (a) Okada, Y.; Chiba, K. Chem. Rev. 2018, accepted. (b) Okada, Y.; Yamaguchi, Y.; Ozaki, A.; Chiba, K. Chem. Sci. 2016, 7, 6387–6393. (c) Okada, Y.; Nishimoto, A.; Akaba, R.; Chiba, K. J. Org. Chem. 2011, 76, 3470–3476. (3) Chiba, K.; Miura, T.; Kim, S.; Kitano, Y.; Tada, M. J. Am. Chem. Soc. 2001, 123, 11314–11315. Figure 1

Pt(IV), Pd(II), and Rh(III) complexes induced oxidative stress and cytotoxicity in the HCT-116 colon cancer cell line

The use of transition metal complexes as appropriate analogues to cisplatin and similar anticancer drugs nowadays is of utmost importance. The inertness of Pt(IV), Pd(II), and Rh(III) complexes and the choosing of convenient ligands could offer a possible advantage in comparison to Pt(II) complexes. These advantages could be attributed to the better anticancer activity and fewer possible side effects. In this paper, we have chosen three complexes of different transition metal ions, [(TLtBu)PdIICl]ClO4, [RhIII(LH2tBu)Cl3], and [PtIV(LH2tBu)Cl3]Cl (where TLtBu is 2,6-bis[(1,3-di-tert-butylimidazolin-2-imino)methyl]pyridine and LH2tBu is 2,6-bis(5-tert-butyl-1H-pyrazol-3-yl)pyridine), for biological tests. All three complexes exerted strong prooxidative and cytotoxic effects on the human colorectal colon cancer HCT-116 cell line. The Pd(II) complex showed the most significant effect, while the Rh(III) complex showed the least effect.

Cobalt Polypyridyl Complexes as Transparent Solution‐Processable Solid‐State Charge Transport Materials

Charge transport materials (CTMs) are traditionally inorganic semiconductors or metals. However, over the past few decades, new classes of solution‐processable CTMs have evolved alongside new concepts for fabricating electronic devices at low cost and with exceptional properties. The vast majority of these novel materials are organic compounds and the use of transition metal complexes in electronic applications remains largely unexplored. Here, a solution‐processable solid‐state charge transport material composed of a blend of [Co(bpyPY4)](OTf)2 and Co(bpyPY4)](OTf)3 where bpyPY4 is the hexadentate ligand 6,6′‐bis(1,1‐di(pyridin‐2‐yl)ethyl)‐2,2′‐bipyridine and OTf− is the trifluoromethanesulfonate anion is reported. Surprisingly, these films exhibit a negative temperature coefficient of conductivity (dσ/dT) and non‐Arrhenius behavior, with respectable solid‐state conductivities of 3.0 S m−1 at room temperature and 7.4 S m−1 at 4.5 K. When employed as a CTM in a solid‐state dye‐sensitized solar cell, these largely amorphous, transparent films afford impressive solar energy conversion efficiencies of up to 5.7%. Organic–inorganic hybrid materials with negative temperature coefficients of conductivity generally feature extended flat π‐systems with strong π–π interactions or high crystallinity. The lack of these features promotes [Co(bpyPY4)](OTf)2+ x films as a new class of CTMs with a unique charge transport mechanism that remains to be explored.

ChemInform Abstract: Homogeneous Metal‐Based Catalysis in Supercritical Carbon Dioxide as Reaction Medium

AbstractReview: 178 refs.

Homogeneous Metal-Based Catalysis in Supercritical Carbon Dioxide as Reaction Medium

Above 31.1 °C and 73.8 bar, carbon dioxide reaches the supercritical state, being transformed into a fluid (scCO2) that has attracted interest in the last few decades as reaction medium for several transition-metal-catalyzed organic transformations. The main feature of this fluid rests on its capability to dissolve large amounts of other gases such as hydrogen, carbon monoxide, ethylene, or even methane and light alkanes. In this manner, very high concentrations of these reactants are available for catalysis. In this contribution a review of the main achievements of the use of transition-metal complexes as catalysts in scCO2 is presented.

ChemInform Abstract: Photoredox α‐Allylation of α‐Halocarbonyls with Allylboron Compounds Accelerated by Fluoride Salts under Visible Light Irradiation.

Organic dyes are an attractive alternative to the use of transition-metal complexes in photoredox catalysis. Herein, we report an inexpensive organic dye (eosin Y)-catalyzed radical coupling of α-bromocarbonyl compounds with allyltrifluoroborates under visible light irradiation. This reaction was accelerated by either Bu4NF or CsF. Based on mechanistic studies, the cation exchange between potassium allyltrifluoroborate and Bu4NF proceeded to generate KF. The generated KF or CsF acts as a Lewis acid to promote a single electron transfer (SET) from eosin Y to α-halocarbonyls. The protocol was applied to bromoesters, bromoketones, and bromoamides to give the coupling products in high yields.

Luminescent Rhenium(I) and Iridium(III) Polypyridine Complexes as Biological Probes, Imaging Reagents, and Photocytotoxic Agents.

Although the interactions of transition metal complexes with biological molecules have been extensively studied, the use of luminescent transition metal complexes as intracellular sensors and bioimaging reagents has not been a focus of research until recently. The main advantages of luminescent transition metal complexes are their high photostability, long-lived phosphorescence that allows time-resolved detection, and large Stokes shifts that can minimize the possible self-quenching effect. Also, by the use of transition metal complexes, the degree of cellular uptake can be readily determined using inductively coupled plasma mass spectrometry. For more than a decade, we have been interested in the development of luminescent transition metal complexes as covalent labels and noncovalent probes for biological molecules. We argue that many transition metal polypyridine complexes display triplet charge transfer ((3)CT) emission that is highly sensitive to the local environment of the complexes. Hence, the biological labeling and binding interactions can be readily reflected by changes in the photophysical properties of the complexes. In this laboratory, we have modified luminescent tricarbonylrhenium(I) and bis-cyclometalated iridium(III) polypyridine complexes of general formula [Re(bpy-R(1))(CO)3(py-R(2))](+) and [Ir(ppy-R(3))2(bpy-R(4))](+), respectively, with reactive functional groups and used them to label the amine and sulfhydryl groups of biomolecules such as oligonucleotides, amino acids, peptides, and proteins. Additionally, using a range of biological substrates such as biotin, estradiol, and indole, we have designed luminescent rhenium(I) and iridium(III) polypyridine complexes as noncovalent probes for biological receptors. The interesting results generated from these studies have prompted us to investigate the possible applications of luminescent transition metal complexes in intracellular systems. Thus, in the past few years, we have developed an interest in the cytotoxic activity, cellular uptake, and bioimaging applications of these complexes. Additionally, we and other research groups have demonstrated that many transition metal complexes have facile cellular uptake and organelle-localization properties and that their cytotoxic activity can be readily controlled. For example, complexes that can target the nucleus, nucleolus, mitochondria, lysosomes, endoplasmic reticulum, and Golgi apparatus have been identified. We anticipate that this selective localization property can be utilized in the development of intracellular sensors and bioimaging reagents. Thus, we have functionalized luminescent rhenium(I) and iridium(III) polypyridine complexes with various pendants, including molecule-binding moieties, sugar molecules, bioorthogonal functional groups, and polymeric chains such as poly(ethylene glycol) and polyethylenimine, and examined their potentials as biological reagents. This Account describes our design of luminescent rhenium(I) and iridium(III) polypyridine complexes and explains how they can serve as a new generation of biological reagents for diagnostic and therapeutic applications.