Cobalt Complexes Research Articles

Experimental and kinetic evaluation on cobalt Salen conjugated organic polymers for CO2 cycloaddition reactions and iodine vapor adsorption

The fixing reactions of carbon dioxide with epoxides will not only help to ameliorate the problem of global warming, but also facilitate the synthesis of cyclic carbonates that have a multitude of applications. Herein, a new sequence of Salen cobalt complexes adjusted with different counterions and interconnected with pyrene group were synthesized through Friedel–Crafts alkylation, which were served as conjugated organic polymers (SP-COPs) for taking advantage of catalytic CO2 fixation reactions and iodine adsorption. Further characterizations were carried out through FT-IR, UV, TGA, and SEM to comprehend the intact structure, thermal stability, morphology and other physical and chemical properties. All materials exhibited effective catalytic performance, and in particular, SP-COP-1 with co-catalyst of TBAI achieved 96.2 % conversion under ultra-mild conditions. The Ea was obtained to be 46.4 kJ·mol−1 by performing kinetic experiments at different temperatures by fitting the experimental data. The performance of iodine vapor adsorbed by these materials at ambient pressure of 75 °C reached 2.8 g·g−1, 2.2 g·g−1 and 2.6 g·g−1 respectively, and the adsorption process is describable in terms of pseudo-first-order and pseudo-second-order adsorption kinetics.

Transfer Hydrogenation of Vinyl Arenes and Aryl Acetylenes with Ammonia Borane Catalyzed by Schiff Base Cobalt(II) Complexes

A series of bench-stable Co(II) complexes containing hydrazone Schiff base ligands were evaluated in terms of their activity and selectivity in carbon-carbon multiple bond transfer hydrogenation. These cobalt complexes, especially a Co(II) precatalyst bearing pyridine-2-yl-N(Me)N=C-(1-methyl)imidazole-2-yl ligand, activated by LiHBEt3, were successfully used in the transfer hydrogenation of substituted styrenes and phenylacetylenes with ammonia borane as a hydrogen source. Key advantages of the reported catalytic system include mild reaction conditions, high selectivity and tolerance to functional groups of substrates.

Electrocatalytic Reduction of CO2 to CO by Molecular Cobalt–Polypyridine Diamine Complexes

Cobalt complexes have previously been reported to exhibit high faradaic efficiency in reducing CO2 to CO. Herein, we synthesized capsule-like cobalt–polypyridine diamine complexes [Co(L1)](BF4)2 (1) and [Co(L2) (CH3CN)](BF4)2 (2) as catalysts for the electrocatalytic reduction of CO2. Under catalytic conditions, complexes 1 and 2 demonstrated the electrocatalytic reduction of CO2 to CO in the presence or absence of CH3OH as a proton source. Experimental and computational studies revealed that complexes 1 and 2 undergo two consecutive reversible one-electron reductions on the cobalt core, followed by the addition of CO2 to form a metallocarboxylate intermediate [CoII(L)–CO22−]0. This crucial reaction intermediate, which governs the catalytic cycle, was successfully detected using high resolution mass spectrometry (HRMS). In situ Fourier-transform infrared spectrometer (FTIR) analysis showed that methanol can enhance the rate of carbon–oxygen bond cleavage of the metallocarboxylate intermediate. DFT studies on [CoII(L)–CO22−]0 have suggested that the doubly reduced species attacks CO2 on the C atom through the dz2 orbital, while the interaction with CO2 is further stabilized by the π interaction between the metal dxz or dxz orbital with p orbitals on the O atoms. Further reductions generate a metal carbonyl intermediate [CoI(L)–CO]+, which ultimately releases CO.

Polyphosphorus compounds derived from P4 conversion with sterically demanding cobalt complexes

The conversion of P4 with [CpBnCo(CO)2] (CpBn = C5(CH2C6H5)5) under thermal conditions gives almost exclusively the P10 complex [(CpBnCo)4(μ4‐η4:η4:η2:η2:η1:η1‐P10)]. However, its reaction with [CpBnCo]n, under mild conditions afforded a mixture of products including the P8 species [(CpBnCo)3(μ3‐η4:η2:η2:η1:η1‐P8)] and a rare Co3 cluster [(CpBnCo)2Co(μ3‐η5:η2:η1:η1‐C40H33)(μ‐H)(μ3‐H)]. The products were studied in solution by multinuclear NMR spectroscopy and mass spectrometry and, for some compounds in the solid state, by single crystal X‐ray diffraction.

Three Oxidation States of Cobalt(I/II/III) Complexes by Thiaporphyrin.

Reaction of tetraphenyl-21-thiaporphyrin (HSTPP) with cobalt salt yields a pentacoordinated high-spin 3/2 [CoIICl(STTP)] (1). Through ion exchange, a roughly square-planar-geometry low-spin 1/2 CoIISTTP(BArF24) (2) complex was isolated. These two paramagnetic precursors were examined by single X-ray diffraction, nuclear magnetic resonance, electron paramagnetic resonance, superconducting quantum interference device, and density functional theory calculations. These two allowed the development of one electron reduction and oxidation to give [CoI(STTP)] (3), [CoIII(STTP)Cl(CH3CN)](BF4) (4), and [CoIII(STTP)Cl2] (5). The products of the chemical redox reactions were isolated and fully characterized. In addition, the reactivity of [CoIICl(STTP)] (1) was examined by azide (N3), cyanate (OCN), and thiocyanate (SCN) and featured a preferential N-coordination to the cobalt metal.

Cobalt complexes modulate plasmid conjugation in Escherichia coli and Klebsiella pneumoniae

Antimicrobial resistance genes (ARG), such as extended-spectrum β-lactamase (ESBL) and carbapenemase genes, are commonly carried on plasmids. Plasmids can transmit between bacteria, disseminate globally, and cause clinically important resistance. Therefore, targeting plasmids could reduce ARG prevalence, and restore the efficacy of existing antibiotics. Cobalt complexes possess diverse biological activities, including antimicrobial and anticancer properties. However, their effect on plasmid conjugation has not been explored yet. Here, we assessed the effect of four previously characterised bis(N-picolinamido)cobalt(II) complexes lacking antibacterial activity on plasmid conjugation in Escherichia coli and Klebsiella pneumoniae. Antimicrobial susceptibility testing of these cobalt complexes confirmed the lack of antibacterial activity in E. coli and K. pneumoniae. Liquid broth and solid agar conjugation assays were used to screen the activity of the complexes on four archetypical plasmids in E. coli J53. The cobalt complexes significantly reduced the conjugation of RP4, R6K, and R388 plasmids, but not pKM101, on solid agar in E. coli J53. Owing to their promising activity, the impact of cobalt complexes was tested on the conjugation of fluorescently tagged extended-spectrum β-lactamase encoding pCTgfp plasmid in E. coli and carbapenemase encoding pKpQILgfp plasmid in K. pneumoniae, using flow cytometry. The complexes significantly reduced the conjugation of pKpQILgfp in K. pneumoniae but had no impact on pCTgfp conjugation in E. coli. The cobalt complexes did not have plasmid-curing activity, suggesting that they target conjugation rather than plasmid stability. To our knowledge, this is the first study to report reduced conjugation of clinically relevant plasmids with cobalt complexes. These cobalt complexes are not cytotoxic towards mammalian cells and are not antibacterial, therefore they could be optimised and employed as inhibitors of plasmid conjugation.

Synthesis, Structure, and Antimicrobial Properties of New Cobalt(II) Complexes with 1-Propargylimidazoles

Abstract: Complexes of cobalt(II) chloride with 1-propargylimidazole, 1-propargyl-2-methylimidazole, and 1- propargylbenzimidazole ligands were synthesized and studied by FTIR spectroscopy and X-ray analysis. According to the X-ray analysis, the crystal molecules of compounds were connected by non-covalent interactions, such as halogen bonds and π-stacking. The nature and energy of coordination metal-ligand and noncovalent bonds for structures under study were estimated in the frame of QTAIM (Quantum Theory “Atoms In Molecules”). The antimicrobial activity of obtained cobalt(II) chloride complexes was evaluated in relation to microorganisms, E. durans, B. subtilis, and E. coli. Complexes of 1-propargyl-2-methylimidazole and 1- propargylbenzimidazole with cobalt(II) chloride demonstrated high activity against E. coli and E. durans relatively and could be recommended as antimicrobial drugs.

Carboxylate Bridged Binuclear Cobalt(II) Complexes Catalyze the Hydrolysis of Thiolates to Alcohols

A binuclear Co(II) complex, [Co2(PhBIMP)(μ‐O2CPh)(MeCN)]2+ (1) ((PhBIMP is the anion of 2,6 bis[(bis((N‐1‐methyl‐4,5‐diphenylimidazoylmethyl) amino)methyl]‐4‐methylphenol)) catalyzes the hydrolysis of thiolates to the corresponding alcohols/phenols at room temperature. Hydrolysis of 11 different thiolates has been investigated with a catalyst loading of 4 ‐ 6.7 mol% and with the highest TON values reaching 22. Furthermore, the effects of electron donating and electron withdrawing groups on the bridging benzoate of 1 have been investigated. The intermediates, products, and fate of the catalyst have been identified by mass spectrometric, gas chromatographic and gravimetric methods, and based on that, a mechanism for the catalytic cycle has been proposed.

Cover: Journal of the Chinese Chemical Society 04/2024

This study achieves successful synthesis of organ‐ometallic Cp* cobalt complexes with 1,4‐diisocyanobenzene as a linear bridging ligand, over‐coming solubility challenges. Investigating stepwise and self‐assembly pathways, it results in characterized rectangular tetranuclear Cp*Co/1,4‐diisocyanobenzene complexes using X‐ray diffraction and various spectro‐scopic techniques. More details about this figure will be discussed by Dr. Sodio C. N. Hsu and his co‐workers on page 376–384 in this issue.image

Thermodynamic studies on the formation of ion-pair cobalt complexes in acetone–water mixtures

Dicarboxylic acids are stronoger acids than moncraboxylic acids and more soluble in water due to the presence of two carboxylic (–COOH) groups which are industrially important in producing polyester, polyamides, and polyols and as a pioneer to pharmaceutical additives. Succinic acid is one of the most prosperous chemicals that can be generated from renewable resources which can be used in the industries of antiseptics, cosmetics, sutures, drugs, solvents, detergents, herbicides, fungicides, synthetic resins, and inks. The ion–pair formation is very important in diferent applications, used widely for inorganic analysis by liquid chromatography and used for the heavy metal removal from waste water, so studing the ion-pair association constant (KA) formed between chloropentamminecobalt(III) cation [CpX2+] and a different ligands of dicarboxylate anions (AC2-), have been determined by EMF technique in different compositions of acetone aqueous media (0–44.20 wt% acetone) for succinic acid and for the other dicarboxylic acids (Maleic, Malonic and Malic) in the same solvent composition (40 wt% acetone) with in temperature range (30 – 60 °C). The thermodynamic association properties (ΔGA°, ΔHA° and ΔSA°) have been estimated and discussed. Extra thermodynamic correlations like ΔHA°- ΔSA° and ΔGA°- ΔGI(orII)° (where I and II are mentioned for the first and second dissociation constant of the dicarboxylic acids) in different compositions of acetone aqueous media for succinic acid and in fixed solvent composition for the other dicarboxylic acids were examined in order to give more information about the behavior of solvent molecules and its effect on formation of the ion-pair molecules. In addition, The Gibbs free energy of transfer for the association process ΔGA°(t) from water to acetone mixed solvents were calculated for succinic acid in order to indicate the spontaneous nature and the stabilization of the ion-pair by increasing the acetone weight percent in the mixed acetone – aqueous media. The linear correlation between pKD values and the relative permittivity of acetone aqueous medium is in accordance to Born’s equation.

SYNTHESIS, CHARACTERIZATION, PREPARATION AND EVALUATION OF THE BACTERICIDAL POTENTIAL OF TWO Co+2 COMPLEXES USING LIGANDS 4-AMINOPYRIDINE AND 2,2'-BIPYRIDINE

Background: The growing interest in organic-inorganic compounds is motivated by the unique advantages these materials offer. Combining organic and inorganic elements enables the creation of structures with varied geometries, paving the way for a wide range of coordination possibilities and directed self-assembly. Aims: To synthesize and characterize by spectroscopic techniques and thermal analysis new Co+3 compounds coordinated with 4-aminopyridine; 2,2'-bipyridine and evaluate their bactericidal potential against two distinct bacterial strains: Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Method: In this study, we report the synthesis route and characterization of the complexes by FTIRmed spectroscopy and TG/DSC thermal analysis, and the obtained complexes have the stoichiometry [Co(NH3)4(bipy)]Cl3.½H2O and [Co(NH3)4(4-apy)] Cl3.½ H2O. Results: The synthesis methodology of cobalt complexes with the ligands 4-aminopyridine and 2,2’-bipyridine proved effective, resulting in the formation of desired precipitates. The thermogravimetric analysis provided insights into the thermal properties of the complexes, indicating stability within certain temperature ranges. Mid-infrared spectroscopy allowed for the structural characterization of the complexes, highlighting characteristic shifts in the bonds of the coordinated ligands. Discussions: Evaluation of the bactericidal activity of the complexes yielded promising results, underscoring the importance of compound solubility. The complex [Co(NH3)4(bipy)]Cl.½H2O exhibited efficacy in bactericidal inhibition, particularly against the S. aureus strain. These findings emphasize the relevance of solubility and chemical composition in the antimicrobial activity of the complexes. Furthermore, the results contribute to the advancement of coordination chemistry and its potential applications, particularly in pharmacology. Conclusions: These biological activity tests revealed significant activity of the complexes against both bacterial strains. This suggests that these complexes have the potential to inhibit the growth and proliferation of these bacteria, indicating their usefulness as effective antimicrobial agents.

Synthesis, Characterisation, Hirshfeld surface analysis, Magnetic susceptibility, DFT calculations, pkCSM profile, and Biological activities of Novel mono‐, di‐, and multinuclear Cobalt (II) complexes

This study explores the synthesis and diverse properties of newly synthesised water‐soluble cobalt (II) complexes (1‐3). Analysis of the complexes through various methods, including Hirshfeld surface analysis, reveals distinctive intermolecular interactions, particularly robust H‐bonding contributions to crystal packing. 2D fingerprint plots provide quantitative insights into supramolecular interactions, while TGA‐DSC analysis elucidates multi‐step decomposition processes, mainly involving organic moieties. FT‐IR and SCXRD confirm the structures of the complexes. Magnetic susceptibility measurements show paramagnetic behaviour in all complexes. FMO calculations expose HOMO‐LUMO gaps and charge transfer processes, with NBO analysis emphasizing the significance of chloride, nitrogen, and oxygen atoms in coordination. In addition, pkCSM profile was carried out. The biological properties of the complexes reveal potent antibacterial activity for 2 and 3 against Gram‐positive and Gram‐negative bacteria. Despite lower antibacterial efficacy compared to standard antibiotics, their water solubility suggests potential human pharmacological applications. In terms of anti‐inflammatory activity, all three complexes exhibit concentration‐dependent prevention of ovalbumin denaturation, with 2 being the most effective. Compound 3, despite having seven carboxyl groups, exhibits the weakest anti‐inflammatory effect, potentially attributed to complex formation obscuring these groups. Furthermore, all complexes display antioxidant activities; 1 and 2 are greater than BHT in the ferric thiocyanate assay.

A novel functional nitronyl nitroxide and its copper and cobalt complexes: Synthesis, structures and magnetic properties

Four new metal complexes derived from a functional nitronyl nitroxide ligand, 2-(6-bromo-3-pyridyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (NIT-6Br-3Py) and M(hfac)2+ (M2+ = Cu2+, Co2+; hfac = hexafluoroacetylacetonate), [(Cu(hfac)2)3(NIT-6Br-3Py)2] (1), [Cu(hfac)2NIT-6Br-3Py]n (2), [Co(hfac)2(H2O)NIT-6Br-3Py] (3) and [(Co(hfac)2)2(NIT-6Br-3Py)2] (4) have been synthesized and characterized. In complex 1, the NIT-6Br-3Py ligand acts as bridging ligand to link three Cu(II) ions leading to {Cu3} complex while complex 2 displays a 1D-chain structure. Complex 3 possesses mono-nuclear structure and 4 is a four-spin complex with a dimeric structure, where the NIT-6Br-3Py ligand links Co ions via the oxygen atom of NO group and the nitrogen atom from pyridine ring. Magnetic studies show that the antiferromagnetic interactions are dominated in complexes 1, 3 and 4, while there exist strong ferromagnetic interactions between CuII and coordinated nitronyl nitroxide radical ligand in complex 2.

Dehydrogenative N‐N Coupling and Facile Synthesis of Cobalt Complexes Supported by Tetrazene Based Ligand: Synthesis of Quinolines and Quinazolinones via Activation of Alcohols

Herein we first report the unprecedented synthesis of tetrazene‐based cobalt complexes using unusual coupling of amines via dehydrogenation. These cobalt complexes were employed for dehydrogenative coupling reactions to synthesize N‐heterocycles (quinoline, and quinazolinone). Based on control experiments and IR identification of intermediates, we proposed a plausible reaction mechanism. Synthesis protocols were utilized for preparative scale synthesis and biologically active molecule (±)‐galipinine synthesis.

Photocatalytic Hydrogen Production with A Molecular Cobalt Complex in Alkaline Aqueous Solutions.

The thermodynamic favorability of an alkaline solution for the oxidation of water suggests the need for developing hydrogen evolution reaction (HER) catalysts that can function in basic aqueous solutions so that both of the half reactions in overall water splitting can occur in mutually compatible solutions. Although photocatalytic HERs have been reported mostly in acidic solutions and a few at basic pHs in mixed organic aqueous solutions, visible-light driven HER catalyzed by molecular metal complexes in purely alkaline aqueous solutions remains largely unexplored. Here, we report a new cobalt complex with a tetrapyridylamine ligand that catalyzes photolytic HER with turnover number up to 218 000 in purely aqueous solutions at pH 9.0. Density functional theory (DFT) calculations suggested a modified electron transfer (E)-proton transfer (C)-electron transfer (E)-proton transfer (C) (mod-ECEC) pathway for hydrogen production from the protonation of CoII-H species. The remarkable catalytic activity resulting from subtle structural changes of the ligand scaffold highlights the importance of studying structure-function relationships in molecular catalyst design. Our present work significantly advances the development of a molecular metal catalyst for visible-light driven HER in more challenging alkaline aqueous solutions that holds substantial promise in solar-driven water-splitting systems.

Promoting a Cobalt Complex of Qingzhuan Dark Tea Polysaccharides on Fracture Healing in Rats.

Fractures occur commonly with multiple injuries, and their incidence has increased in recent years. Trace amounts of cobalt are necessary for many living organisms as it stimulates hematopoiesis and improves bone health. However, cobalt is also toxic, as it might cause allergic reactions and tissue destruction. These factors limit the application of cobalt in some medical fields. We studied the tea polysaccode-cobalt complex (TPS-Co) prepared from Qingzhuan Dark Tea polysaccharides. We used 6-week-old Sprague-Dawley rats to establish a femoral fracture model and evaluated the effects of CoCl2 and TPS-Co on the healing of femoral fractures. In this study, treatment with TPS-Co for the same content of cobalt intake decreased the side effects associated with CoCl2 treatment and accelerated the healing of femoral fractures in rats. This treatment method promoted angiogenesis by upregulating the expression of vascular endothelial growth factor and hypoxia-inducible factor. Bone formation was promoted via the upregulation of the expression of bone morphogenetic protein 2 and serum bone alkaline phosphatase. TPS-Co was found to actively regulate bone and vascular systems, resulting in significant bone regeneration effects. Therefore, the Qingzhuan Dark Tea polysaccharide cobalt complex might be used as an additive or drug to promote fracture healing, and thus, it might have a huge market value.

Synthesis, Spectroscopy, X-ray Structures, DNA Binding and Photocatalytic Properties of Two Ni(II) and Co(II) Complexes of a Pyrazolyl Schiff-base Ligand

Two new nickel(II) and cobalt(II) complexes, [Ni(MPAFA)3](BF4)2 (I) and [Co(MPAFA)3](BF4)2 (II) were synthesized from a pyrazole containing ‘NN’ bidentate Schiff-base ligand, N-(furan-2-ylmethyl)-1-(5-methyl-1H-pyrazol-3-yl)methanimine, (MPAFA) (L). The complexes I and II were characterized by various physico-chemical and spectral parameters. Both I and II were 1:3 (M:L) coordination complexes and behaving as 1:2 electrolytes. Single crystal X-ray diffraction studies revealed that both of them were distorted octahedral in nature with a N6 donor set. The binding interactions of the complexes with CT-DNA were studied by UV-Vis and fluorescence spectroscopic methods. I was found to bind with CT-DNA in a partial intercalative mode, whereas II bound via the groove-like manner in solutions. The ligand and the complexes were shown to have potential photocatalytic activity in degrading methylene-blue (MB) under UV-Vis light irradiation.

Exploiting Co(III)-Cyclopentadienyl Complexes To Develop Anticancer Agents.

In recent years, organometallic complexes have attracted much attention as anticancer therapeutics aiming at overcoming the limitations of platinum drugs that are currently marketed. Still, the development of half-sandwich organometallic cobalt complexes remains scarcely explored. Four new cobalt(III)-cyclopentadienyl complexes containing N,N-heteroaromatic bidentate, and phosphane ligands were synthesized and fully characterized by elemental analysis, spectroscopic techniques, and DFT methods. The cytotoxicity of all complexes was determined in vitro by the MTS assay in colorectal (HCT116), ovarian (A2780), and breast (MDA-MB-231 and MCF-7) human cancer cell lines and in a healthy human cell line (fibroblasts). The complexes showed high cytotoxicity in cancer cell lines, mostly due to ROS production, apoptosis, autophagy induction, and disruption of the mitochondrial membrane. Also, these complexes were shown to be nontoxic in vivo in an ex ovo chick embryo yolk sac membrane (YSM) assay.

Engineered Metal‐Loaded Biohybrids to Promote the Attachment and Electron‐Shuttling between Enzymes and Carbon Electrodes

AbstractThe inorganic content and the catalytic performance pose metal‐loaded enzyme nanoflowers as promising candidates for developing bioelectrodes capable of functioning without the external addition of a redox mediator. However, these protein‐inorganic hybrids have yet to be successfully applied in combination with electrode materials. Herein, the synthesis procedure of these bionanomaterials is reproposed to precisely control the morphology, composition, and performance of this particular protein‐mineral hybrid, formed by glucose oxidase and cobalt phosphate. This approach aims to enhance the adherence and electron mobility between the enzyme and a carbon electrode. The strategy relies on dressing the protein in a tailored thin nanogel with multivalent chemical motifs. The functional groups of the polymer facilitate the fast protein sequence‐independent biomineralization. Furthermore, the engineered enzymes enable the fabrication of robust cobalt‐loaded enzyme inorganic hybrids with exceptional protein loads, exceeding 90% immobilization yields. Notably, these engineered biohybrids can be readily deposited onto flat electrode surfaces without requiring chemical pre‐treatment. The resulting bioelectrodes are robust and exhibit electrochemical responses even without the addition of a redox mediator, suggesting that cobalt complexes promote electron wiring between the active site of the enzyme and the electrode.

Manganese, Cobalt, and Cadmium Complexes of Quinazoline Schiff Base Ligand and Methionine: Synthesis, Characterization, DFT, Docking studies and biomedical application

Manganese, Cobalt, and Cadmium Complexes of Quinazoline Schiff Base Ligand and Methionine: Synthesis, Characterization, DFT, Docking studies and biomedical application