Manganese Complexes Research Articles

The Dichotomy of Mn-H Bond Cleavage and Kinetic Hydricity of Tricarbonyl Manganese Hydride Complexes.

Acid-base characteristics (acidity, pKa, and hydricity, ΔG°H- or kH-) of metal hydride complexes could be a helpful value for forecasting their activity in various catalytic reactions. Polarity of the M-H bond may change radically at the stage of formation of a non-covalent adduct with an acidic/basic partner. This stage is responsible for subsequent hydrogen ion (hydride or proton) transfer. Here, the reaction of tricarbonyl manganese hydrides mer,trans-[L2Mn(CO)3H] (1; L = P(OPh)3, 2; L = PPh3) and fac-[(L-L')Mn(CO)3H] (3, L-L' = Ph2PCH2PPh2 (dppm); 4, L-L' = Ph2PCH2-NHC) with organic bases and Lewis acid (B(C6F5)3) was explored by spectroscopic (IR, NMR) methods to find the conditions for the Mn-H bond repolarization. Complex 1, bearing phosphite ligands, features acidic properties (pKa 21.3) but can serve also as a hydride donor (ΔG≠298K = 19.8 kcal/mol). Complex 3 with pronounced hydride character can be deprotonated with KHMDS at the CH2-bridge position in THF and at the Mn-H position in MeCN. The kinetic hydricity of manganese complexes 1-4 increases in the order mer,trans-[(P(OPh)3)2Mn(CO)3H] (1) < mer,trans-[(PPh3)2Mn(CO)3H] (2) ≈ fac-[(dppm)Mn(CO)3H] (3) < fac-[(Ph2PCH2NHC)Mn(CO)3H] (4), corresponding to the gain of the phosphorus ligand electron-donor properties.

Synthesis, spectroscopic characterization, density functional theory, molecular docking studies, antioxidant and antimicrobial potential of novel Schiff base macrocyclic complexes of bivalent manganese

The threat of antibiotic resistance to public health is becoming a major cause of mortality on a worldwide scale. It has stimulated the interest of researchers in the development of novel antibiotics. Therefore, a new series of Schiff base macrocyclic ligands (N8MacL1‐N8MacL3) and their bivalent manganese complexes were synthesized and analyzed for biological activities. Characterization of the synthesized macrocyclic compounds was done by various spectroscopic techniques like elemental analysis, infrared (IR), proton nuclear magnetic resonance (NMR), 13C NMR, ultraviolet–visible, mass, electron paramagnetic resonance (EPR), and powder X‐ray diffraction (PXRD). Based on spectral studies, an octahedral environment has been proposed around the manganese metal center in the synthesized macrocyclic complexes. Density functional theory (DFT) calculations were used to evaluate the stability and the electronic properties of the synthesized macrocyclic ligands and their Mn (II) complexes. The structures of the synthesized compounds were optimized by using the def2‐SVP basis set at B3LYP level. The synthesized compounds were evaluated against gram‐positive bacterial strains (Staphylococcus aureus and Bacillus cereus), gram‐negative bacterial strains (Escherichia coli and Xanthomonas campestris), and fungal strains (Candida albicans and Fusarium oxysporum) for their antimicrobial activity by agar well diffusion method. Among all of the newly synthesized compounds, the macrocyclic complex [Mn(N8MacL3)Cl2] exhibited high antimicrobial activity against all bacterial and fungal strains except S. aureus. The virtual screening of synthesized Schiff base ligand [L], macrocyclic ligands (N8MacL1‐N8MacL3), and their Mn (II) complex [Mn(N8MacL1)Cl2‐Mn(N8MacL3)Cl2] are performed against the receptors, which were used for in vitro antimicrobial testing, to identify the most plausible drug–ligand interactions. The scavenging activity of DPPH radicals was utilized to study the antioxidant activity of the synthesized compounds. The macrocyclic metal complex [Mn(N8MacL3)Cl2] exhibited excellent antioxidant activity.

A Complete Triad of Zero-Valent 17-Electron Monoradicals of Group 7 Elements Stabilized by m-Terphenyl Isocyanides.

The first consistent series of mononuclear 17-electron complexes of three Group 7 elements has been isolated in crystalline form and studied by X-ray diffraction and spectroscopic methods. The paramagnetic compounds have a composition of [M0 (CO)(CNp-F-ArDArF2 )4 ] (M=Mn, Tc, Re; ArDArF2 =2,6-(3,5-(CF3 )2 C6 H3 )2 C6 H2 F) and are stabilized by four sterically encumbering isocyanides, which prevent the metalloradicals from dimerization. They have a square pyramidal structure with the carbonyl ligands as apexes. The frozen-solution EPR spectra of the rhenium and technetium compounds are clearly anisotropic with large 99 Tc and 185,187 Re hyperfine interactions for one component. High-field EPR (Q band and W band) has been applied for the elucidation of the EPR parameters of the manganese(0) complex.

Ein m‐Terphenylisocyanid stabilisiert 17‐Elektronen‐Monoradikale von drei Elementen der Gruppe 7

AbstractEine erste konsistente Serie einkerniger 17‐Elektronenkomplexe von drei Elementen der Gruppe 7 wurde in kristalliner Form hergestellt und durch Röntgenkristallstrukturanalyse sowie spektroskopische Methoden untersucht. Die paramagnetischen Verbindungen der Zusammensetzung [M0(CO)(CNp‐F‐ArDArF2)4] (M=Mn, Tc, Re; ArDArF2=2,6‐(3,5‐(CF3)2C6H3)2C6H2F)) werden durch jeweils vier sterisch anspruchsvolle Isocyanid‐Liganden stabilisiert, wodurch auch eine Dimerisierung der Metalloradikale verhindert wird. Die Verbindungen besitzen eine quadratisch‐pyramidale Struktur mit jeweils einem Carbonyl‐Liganden als Apex. EPR‐Spektren der Technetium‐ und Rheniumverbindungen zeigen eine deutliche Anisotropie mit großen 99Tc und 185,187Re‐Hyperfeinstrukturkopplungen für jeweils eine der Komponenten. Für die Bestimmung der EPR‐Parameter des entsprechenden Mn0‐Komplexes wurde Hochfeld‐EPR (Q‐Band und W‐Band) verwendet.

Structure and Cytotoxic Activity of the Manganese(II) Complex with 5-Methyltetrazole and 4,7-Dimethyl-1,10-Phenanthroline

Structure and Cytotoxic Activity of the Manganese(II) Complex with 5-Methyltetrazole and 4,7-Dimethyl-1,10-Phenanthroline

New Access to Nano[Mn]-Pyranopyrazole[2,3-c]dichloride Series As a Nano-Structured Schiff-Base Complex

A series of novel nano-structured manganese pyranopyrazole Schiff base complex (3a-l) has been synthesized and described. This synthetic complexation involved sequential reactions of domino four-component one-pot reaction for the template of pyranopyrazole (1), imination reaction (2) and finally completed by the complexation reaction with manganese to furnish the title compounds (3a-l). The salient of this nano-Schiff base synthetic reaction protocol is that diverse chemical functionalities were successfully incorporated, simple reaction protocol, and easy workup procedure to yield the title compounds from reasonable to moderate yield. All synthesized compounds were characterized by means of NMR, FTIR, EDX, and elemental analyzer, and by comparing the acquired spectra with the literature precedent for different manganese complexes. These findings revealed that the pyranopyrazole derivatives were successfully complexed with manganese to generate nano-Mn-Schiff base compounds. Further complexation of these derivatives generated 12 novel types of the title compounds (3a-l), which can then be subjected for future chemical applications.

Manganese Salan Complexes as Catalysts for Hydrosilylation of Aldehydes and Ketones

Manganese has attracted significant recent attention due to its abundance, low toxicity, and versatility in catalysis. In the present study, a series of manganese (III) complexes supported by salan ligands have been synthesized and characterized, and their activity as catalysts in the hydrosilylation of carbonyl compounds was examined. While manganese (III) chloride complexes exhibited minimal catalytic efficacy without activation of silver perchlorate, manganese (III) azide complexes showed good activity in the hydrosilylation of carbonyl compounds. Under optimized reaction conditions, several types of aldehydes and ketones could be reduced with good yields and tolerance to a variety of functional groups. The possible mechanisms of silane activation and hydrosilylation were discussed in light of relevant experimental observations.

Highly Luminescent Nonclassical Binuclear Manganese(II) Complex Scintillators for Efficient X-ray Imaging.

Scintillators can be widely applied to the fields of radioactivity detection, space exploration, and medical diagnosis and have attracted great attention. Recently, manganese(II) complexes with high-efficiency phosphorescent emission are expected to be good candidates for new scintillator materials. Herein, we design and synthesize a series of novel nonclassical binuclear neutral manganese(II) complexes with unique coordination modes, in which the crystal structures of CP1 and CP2 contain both four-coordinated and six-coordinated manganese(II) centers and CP3 is formed as a binuclear five-coordinated dichloro-bridged dimer. The single crystals of CP1-CP3 exhibit excellent stability, which can be attributed to their nonionic structures. They all exhibit intense red emission under UV and X-ray irradiation. Among the three manganese(II) complexes, CP1 demonstrates the best luminescence efficiency and X-ray scintillation performance with a high photoluminescence quantum yield (PLQY) of 91.9%, a relative light yield of 21037 photons MeV-1, and a detection limit of 34.45 nGyair s-1. Moreover, X-ray imaging based on CP1 scintillator screen demonstrates a spatial resolution of nearly 6 lp mm-1. As far as we know, this is the first report about stable binuclear neutral manganese(II) complexes for X-ray imaging and opens a new avenue for exploring novel scintillator materials.

Physicochemical insight into the metal atom effect on magnetocaloric behavior of paramagnetic metalloporphyrins

To reveal the effect of coordinated organic and inorganic σπ-ligands on the magnetocaloric properties of metal ions at room temperature, we have synthesized paramagnetic (5,10,15,20-tetraphenylporphinato)cobalt(II), (chloro)(2,3,7,8,12,13,17,18-octaethylporphinato))manganese(III), their coordination complexes with 1-methyl-2-(pyridin-4′-yl)-3,4-fullero[60]pyrrolidine (1:3 and 1:2, respectively), and (ethoxy)(oxo)(5,10,15,20-tetraphenylporphinato)molybdenum(V) and have fully characterized their chemical structure by UV–vis, IR, 1H NMR, MALDI TOF spectral methods. Using the direct microcalorimetric method and DSC we have obtained, respectively, magnetocaloric effect, heat, change of enthalpy/entropy during the magnetization over the temperature range of 285 – 338 K in magnetic fields from zero to 1 T and the specific heat capacities in the temperature range from 270 to 400 К in zero fields for paramagnets synthesized. Involving the results of DFT calculations, we have shown that the electron structure of a central metal atom is the determining factor in the positive magnetocaloric effect in the complexes studied. The decrease in the MCE value is observed in the case of the intramolecular antiferromagnetic interactions in external magnetic fields (manganese(III) complexes) and additional axial bonding of the bulk fullerene-containing base.

Manganese(II) Bromide Coordination toward the Target Product and By-Product of the Condensation Reaction between 2-Picolylamine and Acenaphthenequinone

A heteroleptic binuclear manganese complex was obtained and characterized by single-crystal X-ray diffraction. Manganese ions coordinate with the target product and by-product of the condensation reaction between 2-picolylamine and acenaphthenequinone are characterized by different geometries in the resulting complex.

DFT Method Used for Prediction of Molecular and Electronic Structures of Mn(VI) Macrocyclic Complexes with Porhyrazine/Phthalocyanine and Two Oxo Ligands.

By using the data of the DFT quantum chemical calculation in the OPBE/TZVP and B3PW91/TZVP levels, the possibility of the existence of a manganese(VI) heteroligand complex containing porphyrazine or its tetra[benzo] derivative (phthalocyanine) and two oxygen (O2-) ligands, which is still unknown for this element, is shown. The parameters of the molecular structure, multiplicity of the ground state, NBO analysis data and standard thermodynamic parameters (enthalpy ΔH0f, entropy S0f and Gibbs's energy ΔG0f of formation) of each of these metal macrocyclic compounds are presented. Additionally, it is noted that, based on the totality of structural data obtained by the above versions of the DFT method, the existence of a similar complex of manganese with di[benzo] derivative of porhyrazine and two oxygen (O2-) ligands seems doubtful.

Effect of Supplementing Vitamin E, Selenium, Copper, Zinc, and Manganese during the Transition Period on Dairy Cow Reproductive Performance and Immune Function.

The transition dairy cows are challenged by various stresses such as decreased dry matter intake, liver dysfunction, increased inflammation, and oxidative stress, particularly in subtropical regions. These might increase the requirement for vitamin E and trace elements. To examine whether supplementation of vitamin E, selenium or copper, zinc, and manganese complex would help transition dairy cows to achieve greater reproduction performance by overcoming the immune function and postpartum disorders in subtropical Taiwan. A total of 24 Holstein Friesian dairy cows were enrolled in this study and divided into three groups (n = 8 cows/group): treatment 1 supplemented with organic selenium and vitamin E (SeE), treatment 2 supplemented with organic copper, zinc, and manganese complex (CZM) and control (CON). The results showed SeE supplementation improved immune function, reproductive performance, and milk yield, but not negative energy balance status. Supplementation of CZM improved milk yield and energy regulation through antioxidative capacity and immune function, but had no influence on reproductive performance.

Corrosion inhibition of Schiff base and their metal complexes with [Mn (II), Co (II) and Zn (II)]: Experimental and quantum chemical studies

The synthesis, characterization, and examination of anti-corrosion performance of 2-furaldehyde semicarbazone Schiff base (FSC) complexes of cobalt (II), zinc (II), and manganese (II) on XC38 carbon steel immersed in 1 M HCl solution are performed using experimental investigations and quantum chemical simulation approaches. The theoretical approach used were DFT calculations and MC simulation. The inhibition effect was also studied by electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP). Electrochemical testing results show that these chemical compounds are particularly powerful inhibitors, which FSC-Mn provides a considerable inhibition of 91.48%at 500 ppm. The results also demonstrate that the inhibition effect of the four inhibitors increased with increasing inhibitor concentration, revealing that these compounds adsorb significantly to the steel surface. The scanning electron microscopy (SEM) analyses indicated that FSC and its complexes adsorbed onto the surface of XC38 carbon steel by forming a barrier between the inhibitors and the vacant d-orbital of iron. Quantum investigations were consistent with experimental findings on the four inhibitors’ capacity to prevent XC38 carbon steel from corroding in 1 M HCl, which were also proven effective as cathodic and anodic type inhibitors, displacing water molecules from mild steel, and producing heterogeneous coatings on the XC38 carbon steel surface to defend against corrosion.

Silver(I) 1,10-Phenanthroline Complexes Are Active against Fonsecaea pedrosoi Viability and Negatively Modulate Its Potential Virulence Attributes.

The genus Fonsecaea is one of the etiological agents of chromoblastomycosis (CBM), a chronic subcutaneous disease that is difficult to treat. This work aimed to evaluate the effects of copper(II), manganese(II) and silver(I) complexes coordinated with 1,10-phenanthroline (phen)/1,10-phenanthroline-5,6-dione (phendione) on Fonsecaea spp. Our results revealed that most of these complexes were able to inhibit F. pedrosoi, F. monophora and F. nubica conidial viability with minimum inhibitory concentration (MIC) values ranging from 0.6 to 100 µM. The most effective complexes against F. pedrosoi planktonic conidial cells, the main etiologic agent of CBM, were [Ag(phen)2]ClO4 and [Ag2(3,6,9-tdda)(phen)4].EtOH, (tdda: 3,6,9-trioxaundecanedioate), displaying MIC values equal to 1.2 and 0.6 µM, respectively. These complexes were effective in reducing the viability of F. pedrosoi biofilm formation and maturation. Silver(I)-tdda-phen, combined with itraconazole, reduced the viability and extracellular matrix during F. pedrosoi biofilm development. Moreover, both silver(I) complexes inhibited either metallo- or aspartic-type peptidase activities of F. pedrosoi as well as its conidia into mycelia transformation and melanin production. In addition, the complexes induced the production of intracellular reactive oxygen species in F. pedrosoi. Taken together, our data corroborate the antifungal action of metal-phen complexes, showing they represent a therapeutic option for fungal infections, including CBM.

Study of Cyclohexane and Methylcyclohexane Functionalization Promoted by Manganese(III) Compounds

Alkane functionalization using safe and low-energy processes is of great interest to industry and academia. Aiming to contribute to the process of saturated hydrocarbon functionalization, we have studied a set of three manganese(III) complexes as catalysts for promoting the oxidation of saturated hydrocarbons (cyclohexane and methylcyclohexane) in the presence of hydrogen peroxide or trichloroisocyanuric acid (TCCA). The mononuclear manganese(III) compounds were prepared using the ligands H2LMet4 (6,6’-((1,4-diazepane-1,4-diyl)bis(methylene))bis(2,4-dimethylphenol), H2salen (2,2’-((1E,1’E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))diphenol) and H2salan (2,2’-((ethane-1,2-diylbis(azanediyl))bis(methylene))diphenol). The catalytic processes were carried out in acetonitrile at 25 and 50 °C for 24 h. The increase in the temperature was important to get a better conversion. The compounds did not promote cyclohexane oxidation in the presence of H2O2. However, they were active in the presence of TCCA, employing a ratio of 1000:333:1 equivalents of the substrate:TCCA:catalyst. The best catalytic activity was shown by the compound [Mn(salen)Cl], reaching conversions of 14.5 ± 0.3% (25 °C) and 26.3 ± 1.1% (50 °C) (yield for chlorocyclohexane) and up to 12.1 ± 0.5% (25 °C) and 29.8 ± 2.2% (50 °C) (total yield for the mixture of the products 1-chloro-4-methylcyclohexane, 3-methylcyclohexene and 1-methylcyclohexene). The interaction of the catalysts with TCCA was studied using electron paramagnetic resonance (EPR), suggesting that the catalysts [Mn(LMet4)Cl] and [Mn(salan)Cl] act via a different mechanism from that observed for [Mn(salen)Cl].

A Low-cost Manganese Complex Catalyst for Phenolic Coupling and Further Oxidation of Phenols

A Low-cost Manganese Complex Catalyst for Phenolic Coupling and Further Oxidation of Phenols

Characterization and Antibacterial Evaluation of New Complexes of Nicotinamide semicarbazon Manganese (II), Zinc (II), Silver (I) Synthesizes

The purpose of this research article is to explore the coordination chemistry and antibacterial activity of six new mononuclear complexes formed via reacting Ag(I), Zn(II), and Mn(II) ions with the Schiff base as a ligand (Nicotinamide- semicarbazone) in a (1:2) ratio in both acidic and basic medium., the six complexes are characterized by elemental analysis(CHN), atomic absorption spectroscopy, Infrared spectroscopy, (1H NMR). and different Technique such as melting point, conductivity measurements, Molar refraction The suggested formula of the complexes were [M(NASC)2] Xn in natural medium and [M(NASC)2] in basic medium, M = Ag n=1, M= Zn, Mn n=2, X=NO3 NASC = Nicotinamide- semicarbazone. It was a tridentate ligand it coordinated onto metal ions via three nitrogen atoms, producing off white or yellow complexes with only an octahedral geometry. These complexes and their ligands were evaluated as antibiotics against a series of medically significant bacteria, and both were found to be very effective.

Carbamoyl manganese complexes for epoxidation of alkenes and cycloaddition of epoxides to carbon dioxide

There is no precedent for the usage of transition metal carbamoyl complexes (typical hydrogenase models) as pre-catalysts for oxidation or CO2 utilization purposes. In this work, we describe that carbamoyl-Mn(I) complexes are capable of selectively catalyzing both epoxidation of olefins and epoxides with carbon dioxide to form cyclic carbonates. The dual-role catalytic system was well adapted to a wide range of aromatic olefins, and the desired cyclic carbonates were obtained in moderate to excellent yields. Mechanistic investigations indicated that active Mn(II)-oxo and Mn(III)-oxo species were involved in the oxidation process.

Hydrogen Bonding-Assisted and Nonheme Manganese-Catalyzed Remote Hydroxylation of C-H Bonds in Nitrogen-Containing Molecules.

The development of catalytic systems capable of oxygenating unactivated C-H bonds with excellent site-selectivity and functional group tolerance under mild conditions remains a challenge. Inspired by the secondary coordination sphere (SCS) hydrogen bonding in metallooxygenases, reported herein is an SCS solvent hydrogen bonding strategy that employs 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) as a strong hydrogen bond donor solvent to enable remote C-H hydroxylation in the presence of basic aza-heteroaromatic rings with a low loading of a readily available and inexpensive manganese complex as a catalyst and hydrogen peroxide as a terminal oxidant. We demonstrate that this strategy represents a promising compliment to the current state-of-the-art protection approaches that rely on precomplexation with strong Lewis and/or Brønsted acids. Mechanistic studies with experimental and theoretical approaches reveal the existence of a strong hydrogen bonding between the nitrogen-containing substrate and HFIP, which prevents the catalyst deactivation by nitrogen binding and deactivates the basic nitrogen atom toward oxygen atom transfer and the α-C-H bonds adjacent to the nitrogen center toward H-atom abstraction. Moreover, the hydrogen bonding exerted by HFIP has also been demonstrated not only to facilitate the O-O bond heterolytic cleavage of a putative MnIII-OOH precursor to generate MnV(O)(OC(O)CH2Br) as an active oxidant but also to affect the stability and the activity of MnV(O)(OC(O)CH2Br).

Manganese(III) complexes with tetradentate O^C^C^O ligands: Synthesis, characterization and catalytic studies on the CO2 cycloaddition with epoxides

A novel class of manganese(III) complexes bearing bis(NHC)-bis(phenolate) (O^C^C^O) type ligands was successfully synthesized. Three differently substituted imidazolium salts (with 2-hydroxyphenyl, (H4L1)Br2, 5‑tert‑butyl‑2-hydroxyphenyl, (H4L2)Br2, and 3,5-di‑tert‑butyl‑2-hydroxyphenyl, (H4L3)Br2, groups) were prepared as precursors of the (O^C^C^O) ligands and a convenient high-yield complexation reaction using manganese(III) acetate was developed. Electrospray ionization mass spectrometry (ESI-MS) and single-crystal X-ray diffraction (SC-XRD) data confirm the formation of the complexes of general formula [MnBrL1–3] and clarify their coordination geometry. The complexes were studied as homogeneous catalysts in the cycloaddition of CO2 to benzyl glycidyl ether (BGE) to form the corresponding cyclic carbonate, using tetrabutylammonium bromide (TBAB) or bis(triphenylphosphine)iminium bromide (PPNBr) as co-catalysts. The complex [MnBrL3] shows the highest activity, and kinetic investigations revealed a pseudo-first order dependence with respect to BGE under neat conditions. The temperature effect was also investigated using the Eyring and Arrhenius equations and the activation parameters for the neat reaction using [MnBrL3] and TBAB were experimentally determined (ΔH‡ = 11.2 kcal·mol-1 and ΔS‡ = -50 cal·mol-1·K-1). On the basis of the performed mechanistic studies and DFT investigations, a catalytic cycle which involves the CO2 1,2-insertion as the rate determining step is proposed.