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Scientists are searching for reactive oxygen species, which have been associated with various health issues like heart problems, neurological disorders, inflammation, and aging. Salen complexes have proven to be effective in multiple oxidative stress situations and have been used as catalase and superoxide mimetics. To explore this further, three mixed complexes were synthesized using a Schiff base (salen) and a sugar (d-glucose) with Co(II), Ni(II), and Cu(II) ions. These complexes were then diagnosed by different analytical and spectral techniques. Stoichiometry, stereochemistry, some physical properties, and the method of bonding complexes were measured. Comparisons of the IR and 1HNMR spectra of the ligands with the complexes demonstrated the involvement of the azomethine group of the ligand in the chelation process. The mass spectra and TGA agree with the proposed formula of the complexes, and the conductivity and UV–Vis data supported the octahedral geometry of the complexes, and information was obtained from partial parameter calculations by molecular modeling. The metal complexes exhibited strong antimicrobial and antioxidant properties when compared to standard drugs. The like-superoxide and catalyst mimetic complexes were screened using DPPH ABTS, revealing their effectiveness. [ABSTRACT FROM AUTHOR]

A new hybrid catalyst consisting of cobalt nanoparticles immobilized onto cellulose was developed. The cellulosic matrix is derived from date palm biomass waste, which was oxidized by sodium periodate to yield dialdehyde and was further derivatized by grafting orthoaminophenol as a metal ion complexing agent. The new hybrid catalyst was characterized by FT-IR, solid-state NMR, XRD, SEM, TEM, ICP, and XPS. The catalytic potential of the nanocatalyst was then evaluated in the catalytic hydrogenation of 4-nitrophenol to 4-aminophenol under mild experimental conditions in aqueous medium in the presence of NaBH4 at room temperature. The reaction achieved complete conversion within a short period of 7 min. The rate constant was calculated to be K = 8.7 × 10−3 s−1. The catalyst was recycled for eight cycles. Furthermore, we explored the application of the same catalyst for the hydrogenation of cinnamaldehyde using dihydrogen under different reaction conditions. The results obtained were highly promising, exhibiting both high conversion and excellent selectivity in cinnamyl alcohol. [ABSTRACT FROM AUTHOR]

The low percentage of recyclability of the polymeric materials obtained by olefin transition metal (TM) polymerization catalysis has increased the interest in their substitution with more eco-friendly materials with reliable physical and mechanical properties. Among the variety of known biodegradable polymers, linear aliphatic polyesters produced by ring-opening polymerization (ROP) of cyclic esters occupy a prominent position. The polymer properties are highly dependent on the macromolecule microstructure, and the control of stereoselectivity is necessary for providing materials with precise and finely tuned properties. In this review, we aim to outline the main synthetic routes, the physical properties and also the applications of three commercially available biodegradable materials: Polylactic acid (PLA), Poly(Lactic-co-Glycolic Acid) (PLGA), and Poly(3-hydroxybutyrate) (P3HB), all of three easily accessible via ROP. In this framework, understanding the origin of enantioselectivity and the factors that determine it is then crucial for the development of materials with suitable thermal and mechanical properties. [ABSTRACT FROM AUTHOR]

The participation of both ligand and the metal center in the redox events has been recognized as one of the ways to attain the formal high valent complexes for the late 3d metals, such as Ni and Cu. Such an approach has been employed successfully to stabilize a Ni(III) bisphenoxyl diradical species in which there exist an equilibrium between the ligand and the Ni localized resultant spin. The present work, however, broadens the scope of the previously reported three oxidized equivalent species by conveying the approaches that tend to affect the reported equilibrium in CH3CN at 233 K. Various spectroscopic characterization revealed that employing exogenous N‐donor ligands like 1‐methyl imidazole and pyridine favors the formation of the Ni centered localized spin though axial binding. In contrast, due to its steric hinderance, quinoline favors an exclusive ligand localized radical species. DFT studies shed light on the novel intermediates′ complex electronic structure. Further, the three oxidized equivalent species with the Ni centered spin was examined for its hydrogen atom abstraction ability stressing their key role in alike reactions. [ABSTRACT FROM AUTHOR]

[Display omitted] Porous organic polymers are considered as excellent candidates for the electrode materials in rechargeable battery due to their desirable properties including porosity, customizable structure, and intrinsic chemical stability. Herein a Salen-based porous aromatic framework (Zn/Salen-PAF) is synthesized through a metal directed method and further used as efficient anode material for lithium-ion battery. Attributing to the stable functional skeleton, Zn/Salen-PAF delivers a reversible capacity of 631 mAh·g−1 at 50 mA·g−1, a high-rate capability of 157 mAh·g−1 at 20.0 A·g−1 and a long-term cycling capacity of 218 mAh·g−1 at 5.0 A·g−1 even after 2000 cycles. Compared to the Salen-PAF without metal ions, Zn/Salen-PAF possesses better electrical conductivity and more active sites. X-ray photoelectron spectroscopy (XPS) investigation indicates that the coordination of Zn2+ with N 2 O 2 unit not only improves the conjugation of the framework but also contributes to the in situ cross-sectional oxidation of the ligand during reaction, which results in the electron redistribution of oxygen atom and the formation of C O bonds. [ABSTRACT FROM AUTHOR]

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Reactive oxygen species are implicated in several human diseases, including neurodegenerative disorders, cardiovascular dysfunction, inflammation, hereditary diseases, and ageing. MnIII–salen complexes are superoxide dismutase (SOD) and catalase (CAT) mimetics, which have shown beneficial effects in various models for oxidative stress. These properties make them well-suited as potential therapeutic agents for oxidative stress diseases. Here, we report the synthesis of the novel glycoconjugates of salen complex, EUK-108, with glucose and galactose. We found that the complexes showed a SOD-like activity higher than EUK-108, as well as peroxidase and catalase activities. We also investigated the conjugate activities in the presence of Ricinus communis agglutinin (RCA120) lectin. The hybrid protein–galactose–EUK-108 system showed an increased SOD-like activity similar to the native SOD1. [ABSTRACT FROM AUTHOR]

A new hybrid catalyst consisting of cobalt nanoparticles immobilized onto cellulose was developed. The cellulosic matrix is derived from date palm biomass waste, which was oxidized by sodium periodate to yield dialdehyde and was further derivatized by grafting orthoaminophenol as a metal ion complexing agent. The new hybrid catalyst was characterized by FT-IR, solid-state NMR, XRD, SEM, TEM, ICP, and XPS. The catalytic potential of the nanocatalyst was then evaluated in the catalytic hydrogenation of 4-nitrophenol to 4-aminophenol under mild experimental conditions in aqueous medium in the presence of NaBH4 at room temperature. The reaction achieved complete conversion within a short period of 7 min. The rate constant was calculated to be K = 8.7 × 10−3 s−1. The catalyst was recycled for eight cycles. Furthermore, we explored the application of the same catalyst for the hydrogenation of cinnamaldehyde using dihydrogen under different reaction conditions. The results obtained were highly promising, exhibiting both high conversion and excellent selectivity in cinnamyl alcohol.

We report on a known Schiff base dye salen. The crystal structure of salen is in the enol–enol tautomer. Molecules are packed into a 3D supramolecular framework through C–H···π interactions. The absorption spectrum of salen in CH2Cl2 exhibits three bands in the UV region, while the spectrum in MeOH contains an additional band at 403 nm and a shoulder at 280 nm, corresponding to the cis-keto tautomer. The emission spectrum of salen in MeOH exhibits a band at 435 and 457 nm upon irradiation at 280 and 400 nm, respectively, arising from the enol–cis-keto* and/or cis-keto–cis-keto* tautomers. The solution of salen in CH2Cl2 showed dual emission with the bands at 349 and 462 nm upon irradiation at 290 nm with the low-energy emission band arising from the enol–cis-keto* and/or cis-keto–cis-keto* tautomers, while the high-energy band corresponds to the enol–enol* tautomer. The emission spectrum of salen in CH2Cl2 exhibits a single band at 464 nm upon irradiation at 380 nm, arising from the different conformers of the enol–cis-keto* and/or cis-keto–cis-keto* tautomers. The DFT calculations revealed that the enol–enol tautomer is the most favorable, followed by the enol–cis-keto tautomer. The global chemical reactivity descriptors were estimated from the HOMO and LUMO. The DFT calculations were also applied to probe salen as a potential corrosion inhibitor for some important metals used in implants. The enol–cis-keto and enol–trans-keto tautomers exhibit the best electron charge transfer from the molecule to the surface of all the studied metals, of which the most efficient electron charge transfer was established for Ni, Au, and Co. Molecular docking was applied to study interaction of tautomers of salen with a series of the SARS-CoV-2 proteins, of which the best binding affinity was found toward nsp14 (N7-MTase). [ABSTRACT FROM AUTHOR]

Salen ligands and relative metal complexes are widely used in many fields, such as catalysis, sensing, optical and electronic materials. The introduction of a wide range of substituents in different positions, both in the salen scaffold and in the diamine bridge, allows the tuning of chemical, catalytic and spectroscopic properties. In this contribution, we report the synthesis and characterization of a new salen ligand and relative Co(II) complex bearing a maleonitrile bridge and two chlorine atoms in the salen backbone. [ABSTRACT FROM AUTHOR]

A highly efficient one-step approach to the macromonomer synthesis using modified aluminum complexes as catalysts of ring-opening polymerization (ROP) of ε-caprolactone and D,L-lactide was developed. The syntheses, structures, and catalytic activities of a wide range of aluminum salen complexes, 3a-c, functionalized with unsaturated alcohol (HO(CH2)4OCH=CH2) are reported. X-Ray diffraction studies revealed a tetragonal pyramidal structure for 3c. Among the complexes 3a-c, the highest activity in bulk ROP of ε-caprolactone and D,L-lactide was displayed by 3b, affording polyesters with controlled molecular weights at low monomer to initiator ratios (Mn up to 15,000 g mol−1), relatively high polydispersities (Ð~1.8) and high number-average functionalities (Fn up to 85%). [ABSTRACT FROM AUTHOR]

Salen ligands and relative metal complexes are widely used in many fields, such as catalysis, sensing, optical and electronic materials. The introduction of a wide range of substituents in different positions, both in the salen scaffold and in the diamine bridge, allows the tuning of chemical, catalytic and spectroscopic properties. In this contribution, we report the synthesis and characterization of a new salen ligand and relative Co(II) complex bearing a maleonitrile bridge and two chlorine atoms in the salen backbone.

The low percentage of recyclability of the polymeric materials obtained by olefin transition metal (TM) polymerization catalysis has increased the interest in their substitution with more eco-friendly materials with reliable physical and mechanical properties. Among the variety of known biodegradable polymers, linear aliphatic polyesters produced by ring-opening polymerization (ROP) of cyclic esters occupy a prominent position. The polymer properties are highly dependent on the macromolecule microstructure, and the control of stereoselectivity is necessary for providing materials with precise and finely tuned properties. In this review, we aim to outline the main synthetic routes, the physical properties and also the applications of three commercially available biodegradable materials: Polylactic acid (PLA), Poly(Lactic-co-Glycolic Acid) (PLGA), and Poly(3-hydroxybutyrate) (P3HB), all of three easily accessible via ROP. In this framework, understanding the origin of enantioselectivity and the factors that determine it is then crucial for the development of materials with suitable thermal and mechanical properties.

The article presents the synthesis and properties of two new Schiff bases of resorcinarene derivatives. The Schiff bases were obtained by the reaction of formylresorcinarene with aromatic (o-aminophenol) and aliphatic (N,N-dimethyldiaminoethane) amines in chloroform. The synthesized Schiff bases exist in equilibrium of several tautomers, as evident from the IR, UV, NMR spectra and cyclic voltammetry data analysis. In DMF, methanol, and acetonitrile, the tautomeric equilibrium is shifted toward the enol-imine tautomers. [ABSTRACT FROM AUTHOR]

Reactive oxygen species are implicated in several human diseases, including neurodegenerative disorders, cardiovascular dysfunction, inflammation, hereditary diseases, and ageing. MnIII–salen complexes are superoxide dismutase (SOD) and catalase (CAT) mimetics, which have shown beneficial effects in various models for oxidative stress. These properties make them well-suited as potential therapeutic agents for oxidative stress diseases. Here, we report the synthesis of the novel glycoconjugates of salen complex, EUK-108, with glucose and galactose. We found that the complexes showed a SOD-like activity higher than EUK-108, as well as peroxidase and catalase activities. We also investigated the conjugate activities in the presence of Ricinus communis agglutinin (RCA120) lectin. The hybrid protein–galactose–EUK-108 system showed an increased SOD-like activity similar to the native SOD1.

The increasing demand for olefin polymers has prompted extensive research on catalysis, processes, and structural characterization to explore their economic potential. In this study, N,N'-bis(salicylidene)-1,2-ethylenediamine (salen) was synthesized, complexed with Fe(III) ion, and the complex was bridged by simple condensation reaction with five different dicarboxylic acids to produce dinuclear complexes. Different methods, such as 1H NMR, FT-IR, UV–Vis, and EDX elemental analysis, were used to analyze and identify the ligand and complexes. Spectroscopic results supported by molecular modeling studies, revealed that the complexes had an octahedral geometry. Structural optimization of the ligand and metal complexes was performed using Avogadro (version 1.2.0) and the Universal Force Field molecular mechanics level. Density functional theory was used to conduct computational calculations on the stability and reactivity of the zeolite-supported and unsupported complexes as catalysts for the polymerization of ethylene. Interestingly, the supported complexes were found to exhibit lower stability and higher reactivity than the neat metal complexes. As such, the synthesized complexes are promising catalysts for the production of polyethylene, and their use could significantly reduce the cost of industrial polyethylene production.

The article presents the synthesis and properties of two new Schiff bases of resorcinarene derivatives. The Schiff bases were obtained by the reaction of formylresorcinarene with aromatic (o-aminophenol) and aliphatic (N,N-dimethyldiaminoethane) amines in chloroform. The synthesized Schiff bases exist in equilibrium of several tautomers, as evident from the IR, UV, NMR spectra and cyclic voltammetry data analysis. In DMF, methanol, and acetonitrile, the tautomeric equilibrium is shifted toward the enol-imine tautomers.

A series of 4‐NEt2‐appended salen−indium complexes bridged by different diimine units (ethylene [Et, 1], phenylene [Ph, 2], and benzonitrile [PhCN, 3]) with different electronic effects were prepared in high yields by a one‐pot synthetic procedure. Among them, the solid‐state structure of 1 was identified by X‐ray crystallography, featuring a square‐pyramidal structure around the indium center. Ultraviolet–visible (UV/Vis) absorption and emission spectra of 1–3 showed typical ππ* electronic transitions centered on the salen ligands, which underwent gradual redshifts as the electron‐withdrawing ability of the bridging units increased. Such bathochromic shifts resulted from lowering the energy levels of the lowest unoccupied molecular orbital (LUMO). In addition, the full width at half maxima for the emissions of 1–4 gradually decreased with increasing electron‐accepting property of the bridging units. The observed photophysical properties were further supported by theoretical calculations. [ABSTRACT FROM AUTHOR]

Chemical recycling of polymers to their constituent monomers is the foremost challenge in building a sustainable circular plastics economy. Here, we report a strategy for highly efficient depolymerization of various CO2‐based alicyclic polycarbonates to epoxide monomers in solvent‐free conditions by a simple CrIII‐Salen complex mediated catalytic pyrolysis process. The chemical recycling of the widely studied poly(cyclohexene carbonate) exhibits excellent reactivity (TOF up to 3000 h−1, 0.1 mol % catalyst loading) and high epoxide monomer selectivity (>99 %). Mechanistic investigation reveals that the process proceeds in a sequential fashion via a trans‐carbonate intermediate. [ABSTRACT FROM AUTHOR]

Salen-based covalent organic framework (COF), constructed by salen skeleton, has great potential applications as the heterogeneous catalyst due to its unique salen-functionalized structure and uniform porous microenvironment. In this study, the mesoporous crystalline salen-COF was facile synthesized via heating salicylaldehyde and ethylenediamine in the air and characterized by fourier transform infrared, powder X-ray diffractometer, Brunauer–Emmett–Teller, and inductively coupled plasma atomic emission spectrometer. The deliberately selected macromonomer endowed salen-COF with a large pore size (2.06 nm). After metalation with cobalt, the obtained salen-COF-Co exhibited high Co(salen) crystallinity as well as the well-retained COF structure. Under the optimized reaction conditions (0.25 mol% salen-COF-Co, 120 °C, and 2.0 MPa CO2), the salen-COF-Co exhibited high reactivity and > 99% selectivity for the CO2 cycloaddition with varieties of epoxides (12 examples) to afford multifunctional cyclic carbonates. Noting that the cyclic bis- and tris-carbonates were successfully obtained with high conversions and > 99% selectivities. Moreover, the unsubstituted trimethylene oxide and hydroxyl-functionalized substituted 3-ethyl-3-methyloloxetane were successfully converted to the corresponding six-membered cyclic carbonates with moderate conversions and > 99% selectivities. In addition, during at least five recycle tests, the robust heterogeneous salen-COF-Co exhibited excellent recyclability and reusability, maintaining high crystallinity and ordered porous structure with stable reactivity. This study provides a potential heterogeneous porous catalyst for selective CO2 cycloaddition with epoxides and oxetanes. [ABSTRACT FROM AUTHOR]

Copolymers are valuable supports for obtaining heterogeneous catalysts that allow their recycling and therefore substantial savings, particularly in the field of asymmetric catalysis. This contribution reports the use of two comonomers: Azido-3-propylmethacrylate (AZMA) bearing a reactive azide function was associated with 2-methoxyethyl methacrylate (MEMA), used as a spacer, for the ATRP synthesis of copolymers, and then post-functionalized with a propargyl chromium salen complex. The controlled homopolymerization of MEMA by ATRP was firstly described and proved to be more controlled in molar mass than that of AZMA for conversions up to 63%. The ATRP copolymerization of both monomers made it possible to control the molar masses and the composition, with nevertheless a slight increase in the dispersity (from 1.05 to 1.3) when the incorporation ratio of AZMA increased from 10 to 50 mol%. These copolymers were post-functionalized with chromium salen units by click chemistry and their activity was evaluated in the asymmetric ring opening of cyclohexene oxide with trimethylsilyl azide. At an equal catalytic ratio, a significant increase in enantioselectivity was obtained by using the copolymer containing the largest part of salen units, probably allowing, in this case, the more favorable bimetallic activation of both the engaged nucleophile and electrophile. Moreover, the catalytic polymer was recovered by simple filtration and re-engaged in subsequent catalytic runs, up to seven times, without loss of activity or selectivity. [ABSTRACT FROM AUTHOR]

Enantioselective addition of trimethylsilyl cyanide (TMSCN) to aldehydes is one of the most extensively studied organic reactions in asymmetric catalysis. Herein, we report our intensive kinetic investigation on the asymmetric addition of TMSCN to benzaldehyde, catalyzed by a covalently bridged dinuclear (salen)titanium complex 2, which has been one of the most efficient artificial chiral catalysts reported so far for this reaction. It was found that the method of initial rates for kinetic investigation is not appropriate in this case because of the presence of a significant incubation period in the catalysis, while the method of progress rates proved to be more reliable and efficient for judging the kinetic orders of this catalytic system. The kinetic results revealed that the reaction follows first order with respect to the catalyst and is nearly independent of concentrations of both benzaldehyde and TMSCN. A detailed catalytic mechanism for cyanosilylation of benzaldehyde in the presence of 2 was proposed, wherein the key active dinuclear species works in a cooperative manner for dual activation of both reactants. [ABSTRACT FROM AUTHOR]

In this work, (3,5-bis((4,6-dichloro-1,3,5-triazine-2-yl)oxy)phenyl)methanol was obtained by reacting cyanuric chloride with 3,5-dihydroxybenzyl alcohol at 0 °C. Then, s-triazine bridged calixarene codded as L1 was obtained by reacting the compounds with 3,5-dihydroxybenzyl alcohol. Targed ligands, which we code as L2 and L3, were obtained from the reaction of the L1 coded compound with 4-aminobenzoic acid or 4-hydroxybenzoic acid, respectively. [MSalen/Saloph] capped s-triazine bridged calixarene complexes were obtained from the reaction of the L2 or L3 codded ligand and the [(MSalen/Saloph)2O] (M = Cr3+, Fe3+, Co3+) starting complexes in 1,4-dioxane media. The ligands and complexes were characterized by using 1H-NMR, FT-IR spectroscopy, UV-Vis spectroscopies, magnetic susceptibility, TGA-DTA and elemental analysis techniques. Metal contents of the complexes were determined by using ICP-AES spectroscopy. Calixarenes can be used in many areas such as chiral phase transfer catalyst, recognition of enantiomers, stationary phase in chromatography, recovery of heavy and precious metals molecules or ions from environmental wastes. [ABSTRACT FROM AUTHOR]

The complexation reaction between salen (Bis(salicylidene)ethylenediamine) and Cu(II) cations in methanol (MeOH), 2-propanol (2-PrOH), acetonitrile (AN), tetrahydrofuran (THF), and chloroform (CHCl3) as nonaqueous solvents at 25º C has been investigated. The stoichiometry and formation constants of complexes have been determined spectrophotometrically and conductometrically by method of continuous variations and mole ration method. The stoichiometry of Cu(II)-salen complexes in all solvents were 1:1 (ML) type using the two methods. By method of continuous variation, chloroform > 2-propanol > methanol ~ acetonitrile ~ tetrahydrofuran. However, by mole ratio method, the order of stability was as follows: chloroform ~ tetrahydrofuran > 2-propanol > methanol ~ acetonitrile. The resulting average of pKf values in each solvent using the two spectrophotometric methods was as follows: 7.40, 6.89, 6.8, 6.22, and 6.18 for chloroform, 2-propanol, tetrahydrofuran, acetonitrile, and methanol, respectively. The Cu(II) cation formed a more stable complex with salen in chloroform. However, the less stable complex was in methanol.

A highly efficient one-step approach to the macromonomer synthesis using modified aluminum complexes as catalysts of ring-opening polymerization (ROP) of ε-caprolactone and D,L-lactide was developed. The syntheses, structures, and catalytic activities of a wide range of aluminum salen complexes, 3a-c, functionalized with unsaturated alcohol (HO(CH2)4OCH=CH2) are reported. X-Ray diffraction studies revealed a tetragonal pyramidal structure for 3c. Among the complexes 3a-c, the highest activity in bulk ROP of ε-caprolactone and D,L-lactide was displayed by 3b, affording polyesters with controlled molecular weights at low monomer to initiator ratios (Mn up to 15,000 g mol−1), relatively high polydispersities (Ð~1.8) and high number-average functionalities (Fn up to 85%).

The electrochemical oxidation of HMF (5-hydroxymethylfurfural) to DMF (2,5-furandicarboxaldehyde) catalysed by a salen-manganese homogeneous catalyst is reported. DMF is a versatile precursor in the synthesis of functional polymers, pharmaceuticals, antifungal agents, and furan-urea resins. A manganese(III)-Schiff base complex 1 was synthetized and characterized by different analytical and spectroscopic techniques. Complex 1 behaved as an efficient catalyst of the electrochemical oxidation of HMF to DMF. The conversion of HMF to DFF was performed under mild conditions. The oxidation of DFF to HMF with a conversion rate of 75% was achieved at pH 8.5, using sodium chloride as the electrolyte to increase the conductivity and to reduce the power dissipation.

Main observation and conclusion: Supramolecular polymer networks (SPNs) have always been the focus of research due to their novel features of good processability, stimuli‐responsiveness, self‐healing, and recyclability. Herein, we report the preparation of a metallacycle‐linked supramolecular gel via orthogonal metal‐ligand interactions and host‐guest interactions. A triangular metallacycle with three appended 21‐crown‐7 (21C7) units was obtained by the metal coordination of nickel(II)‐salen‐based dipyridyl ligands and platinum(II) acceptors. The integration of this metallacycle and traditional copolymer bearing secondary ammonium salts constructed a SPN via host‐guest recognition between 21C7 units and ammonium salts, and a supramolecular gel further formed at high concentration. Multiple stimulus responsiveness and self‐healing properties of gel were observed. The gel exhibited better stretchability compared to relative gel formed by copolymer alone owing to the synergistic effect of covalent bonds and supramolecular interactions. Moreover, compared to the model gel without metallacycles, the gel showed higher storage and loss moduli, and exhibited stronger stiffness in the self‐healing tests performed with rheometer, indicating the metallacycle played an important role in improving the stiffness and self‐healing of the gel. Therefore, the feasible approach to the formation of SPNs by the marriage of covalent polymers and metallacycles is expected to open a new way to design novel SPNs. [ABSTRACT FROM AUTHOR]

The creation of molecular components for use as electronic devices has made enormous progress. In order to advance the field further toward realistic electronic concepts, methods for the controlled modification of the conducting properties of the molecules contacted by metallic electrodes need to be further developed. Here a comprehensive study of charge transport in a class of molecules that allows modifications by introducing metal centers into organic structures is presented. Single molecules are electrically contacted and characterized in order to understand the role of the metal centers in the conductance mechanism through the molecular junctions. It is shown that the presence of single metal ions modifies the energy levels and the coupling of the molecules to the electrical contacts, and that these modifications lead to systematic variations in the statistical behavior of transport properties of the molecular junctions. A rigorous statistical analysis of thousands of junctions is performed to reveal this correlation. The understanding of the role of the metal ion in the resulting conductance properties is an essential step toward the development of molecular electronic circuits. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: Supramolecular polymer networks (SPNs) have always been the focus of research due to their novel features of good processability, stimuli‐responsiveness, self‐healing, and recyclability. Herein, we report the preparation of a metallacycle‐linked supramolecular gel via orthogonal metal‐ligand interactions and host‐guest interactions. A triangular metallacycle with three appended 21‐crown‐7 (21C7) units was obtained by the metal coordination of nickel(II)‐salen‐based dipyridyl ligands and platinum(II) acceptors. The integration of this metallacycle and traditional copolymer bearing secondary ammonium salts constructed a SPN via host‐guest recognition between 21C7 units and ammonium salts, and a supramolecular gel further formed at high concentration. Multiple stimulus responsiveness and self‐healing properties of gel were observed. The gel exhibited better stretchability compared to relative gel formed by copolymer alone owing to the synergistic effect of covalent bonds and supramolecular interactions. Moreover, compared to the model gel without metallacycles, the gel showed higher storage and loss moduli, and exhibited stronger stiffness in the self‐healing tests performed with rheometer, indicating the metallacycle played an important role in improving the stiffness and self‐healing of the gel. Therefore, the feasible approach to the formation of SPNs by the marriage of covalent polymers and metallacycles is expected to open a new way to design novel SPNs. [ABSTRACT FROM AUTHOR]

Salen-type ligands with electron-accepting substituents on the aromatic ring were synthesized. These ligands were used as extractant agents in polymeric inclusion membranes for the extraction of metal ions from aqueous solutions. Measurements of the membrane potential indicated selectivity of the membrane, which was confirmed by the quantification of the extracted metal. Ten types of metal ions were studied to establish the selectivity of each membrane. Salen-type ligands had higher selectivity to gold than to other metals and allowed for the extraction of acceptable percentages of this metal. The results showed that the percentage of extracted gold depends on the type of substituent present in the ligand's aromatic ring, the pH of the working solution and the area of the membrane. There was no effect of membrane thickness on the metal extracted. The time required to reach a certain extraction percentage decreased considerably as the membrane area increased. [ABSTRACT FROM AUTHOR]

Using adamantane-1,3-diamine and 3,5-di-tert-butylsalicylic aldehyde as raw materials, the generated salen aluminum complex was characterized by 1H, 13C NMR spectroscopy and elemental analysis. After isopropyl alcohol activation treatment, the complex has good activity (70.3-95.6%), which can provide poly(D,L-lactide) with a Pm of 0.87 for rac-lactide. [ABSTRACT FROM AUTHOR]

Copolymers are valuable supports for obtaining heterogeneous catalysts that allow their recycling and therefore substantial savings, particularly in the field of asymmetric catalysis. This contribution reports the use of two comonomers: Azido-3-propylmethacrylate (AZMA) bearing a reactive azide function was associated with 2-methoxyethyl methacrylate (MEMA), used as a spacer, for the ATRP synthesis of copolymers, and then post-functionalized with a propargyl chromium salen complex. The controlled homopolymerization of MEMA by ATRP was firstly described and proved to be more controlled in molar mass than that of AZMA for conversions up to 63%. The ATRP copolymerization of both monomers made it possible to control the molar masses and the composition, with nevertheless a slight increase in the dispersity (from 1.05 to 1.3) when the incorporation ratio of AZMA increased from 10 to 50 mol%. These copolymers were post-functionalized with chromium salen units by click chemistry and their activity was evaluated in the asymmetric ring opening of cyclohexene oxide with trimethylsilyl azide. At an equal catalytic ratio, a significant increase in enantioselectivity was obtained by using the copolymer containing the largest part of salen units, probably allowing, in this case, the more favorable bimetallic activation of both the engaged nucleophile and electrophile. Moreover, the catalytic polymer was recovered by simple filtration and re-engaged in subsequent catalytic runs, up to seven times, without loss of activity or selectivity.

Three cobalt(II)-salen complexes (CoL1, CoL2 and CoL3) were synthesized via the reaction of the three tetradentate ligands as N,N′-ethylenebis(salicylimine) L1, N,N′-ethylenebis(3-tert-butylsalicylimine) L2 and N,N′-ethylenebis(3,5-di-tert-butylsalicylimine) L3, with a stoichiometric amount of cobalt(II) acetate tetrahydrate, respectively. All the three complexes were studied as oxidative desulfurization catalyst on dibenzothiophene taken in model fuel oil n-dodecane. The acetonitrile used as an extracting solvent and H2O2 as an oxidant. Comparatively CoL3 proved to be the best catalyst which showed the 76% DBT removal at the optimized conditions. The nth-order kinetic model is the best way to represent oxidation kinetics of complexes. This cobalt(II) Schiffs base complexes were studied as catalyst for oxidative desulfurization of dibenzothiphene (DBT) taken as model sulphur compounds in fuel model oil (n-dodecane) using H2O2 as oxidant and acetonitrile as extracting solvent for DBT sulfone in a batch experiment. [ABSTRACT FROM AUTHOR]

The synthesis of three complex series of the form [AnCl2(salen)(Pyx)2] (H2salen=N,N′‐bis(salicylidene)ethylenediamine; Pyx=pyridine, 4‐methylpyridine, 3,5‐dimethylpyridine) with tetravalent early actinides (An=Th, U, Np, Pu) is reported with the goal to elucidate the affinity of these heavy elements for small neutral N‐donor molecules. Structure determination by single‐crystal XRD and characterization of bulk powders with infrared spectroscopy reveals isostructurality within each respective series and the same complex conformation in all reported structures. Although the trend of interatomic distances for An−Cl and An−N (imine nitrogen of salen or pyridyl nitrogen of Pyx) was found to reflect an ionic behavior, the trend of the An−O distances can only be described with additional covalent interactions for all elements heavier than thorium. All experimental results are supported by quantum chemical calculations, which confirm the mostly ionic character in the An−N and An−Cl bonds, as well as the highest degree of covalency of the An−O bonds. Structurally, the calculations indicate just minor electronic or steric effects of the additional Pyx substituents on the complex properties. [ABSTRACT FROM AUTHOR]

Although salens and imidazoles are well‐studied motifs among bioactive and therapeutic agents, their properties when combined in transition metal complexes are not well developed. To explore the structure/reactivity of this class of compounds, a salen‐based ligand, namely (2,2′‐{1,2‐ethanediylbis[nitrilo(E)methylylidene]}diphenol, S), and its binary (MS) and ternary (MSI) complexes (I = imidazole; M = Co (II), Ni (II), Cu (II), Cd (II), Al (III), and La (III)) have been synthesized and fully characterized by standard physicochemical and theoretical methods. Evidence from structural analysis tools along with DFT modeling revealed an unusual monobasic tridentate salen binding mode, involving the phenolic oxygen, the nitrogen of the azomethine group, and NH group formed via phenol‐to‐cyclohexadienone tautomerization, giving rise to a general molecular formula of MSI complexes as [M(S)(I)2(Cl)] for M (II) = Co, Ni, Cu and Cd or [M(S)(I)(Cl)2] for M (III) = Al and La, respectively. The antimicrobial activities of S, MS, and MSI were screened against several bacterial and fungal strains. Of all tested complexes, CdS and CuSI were the most effective antimicrobials, giving larger inhibition zones than the reference antibiotics. The antimicrobial efficacy for the MS complexes follows the order: CdS > gentamicin > CuS > NiS > CoS > LaS > AlS > S, whereas MSI complex, potencies are ordered as CuSI > gentamicin > CdSI >NiSI > CoSI > LaSI > AlSI > S. In vitro cytotoxicity screening of MSI complexes disclosed that both CuSI and CdSI exhibited higher activity against human liver (Hep‐G2) and breast (MDA‐MB231) carcinoma cell lines than the reference (cisplatin) drug. The satisfactory bioactivities observed for several of these compounds supports the underlying design idea for combining important bioactive motifs for possible therapeutic benefit. [ABSTRACT FROM AUTHOR]

Platinum electrodes were modified with polymers of the (±)-trans-N,N′-bis(salicylidene)-1,2-cyclohexanediaminenickel(II) ([Ni(salcn)]) and (±)-trans-N,N′-bis(3,3′-tert-Bu-salicylidene)-1,2-cyclohexanediaminenickel(II) ([Ni(salcn(Bu))]) complexes to study their electrocatalytic and electroanalytical properties. Poly[Ni(salcn)] and poly[Ni(salcn(Bu))]) modified electrodes catalyze the oxidation of catechol, aspartic acid and NO2−. In the case of poly[Ni(salcn)] modified electrodes, the electrocatalysis process depends on the electroactive surface coverage. The films with low electroactive surface coverage are only a barrier in the path of the reducer to the electrode surface. The films with more electroactive surface coverage ensure both electrocatalysis inside the film and oxidation of the reducer directly on the electrode surface. In the films with the most electroactive surface coverage, electrocatalysis occurs only at the polymer–solution interface. The analysis was based on cyclic voltammetry, EQCM (electrochemical quartz crystal microbalance) and rotating disc electrode method.

This paper presents the results of the first application of N,N'-bis(salicylidene)ethylenediamine (salen) as an extractant in classical liquid–liquid extraction and as a carrier in membrane processes designed for the recovery of noble metal ions (Pd2+, Ag+, Pt2+, and Au3+) from aqueous solutions. In the case of the utilization of membranes, both sorption and desorption were investigated. Salen has not been used so far in the sorption processes of precious metal ions. Recovery experiments were performed on single-component solutions (containing only one type of metal ions) and polymetallic solutions (containing ions of all four metals). The stability constants of the obtained complexes were determined spectrophotometrically. In contrast, electrospray ionization high-resolution mass spectrometry (ESI-HRMS) was applied to examine the elemental composition and charge of the generated complexes of chosen noble metal ions and salen molecules. The results show the great potential of N,N'-bis(salicylidene)ethylenediamine as both an extractant and a carrier. In the case of single-component solutions, the extraction percentage was over 99% for all noble metal ions (molar ratio M:L of 1:1), and in the case of a polymetallic solution, it was the lowest, but over 94% for platinum ions and the highest value (over 99%) for gold ions. The percentages of sorption (%Rs) of metal ions from single-component solutions using polymer membranes containing N,N'-bis(salicylidene)ethylenediamine as a carrier were highest after 24 h of the process (93.23% for silver(I) ions, 74.99% for gold(III) ions, 69.11% and 66.13% for palladium(II) and platinum(II) ions, respectively), similar to the values obtained for the membrane process conducted in multi-metal solutions (92.96%, 84.26%, 80.94%, and 48.36% for Pd(II), Au(III), Ag(I), and Pt(II) ions, respectively). The percentage of desorption (%Rdes) was very high for single-component solutions (the highest, i.e., 99%, for palladium solution and the lowest, i.e., 88%, for silver solution), while for polymetallic solutions, these values were slightly lower (for Pt(II), it was the lowest at 63.25%).

The formation of plastic or brittle organic crystals of salen derivatives that depend on the solvents employed for crystallization is demonstrated. Large yellow crystals (ranging from mm to cm size) of ten different salen derivatives were obtained and investigated. Among them, (bis(2‐hydroxyacetophenone)ethylenediimine) 2, which was recrystallized from dichloromethane, tetrahydrofuran or chloroform, exhibited plastic deformation behaviour when mechanical force was applied to the (001) face. In contrast, when 2 was recrystallized from benzene, brittle crystals were obtained. Face indexing confirmed that different crystal faces were obtained by depending on the solvent employed for recrystallization, which leads to either flexible (plastic) or brittle crystals. Photoluminescence with a band maximum at 510 nm and thermochromism related to tautomerism between OH and NH forms were also investigated, and indicate that 2 is a flexible organic single‐crystal material with multifunctional properties. [ABSTRACT FROM AUTHOR]

Herein, to elucidate the effect of substituent electronic properties on the photophysical properties of indium‐based organometallic luminophores, we prepare a series of indium complexes (1–5) with salen ligands bridged by an electron‐withdrawing 4,5‐dichlorophenylene (Cl2Ph) unit. The structures of all the complexes are fully confirmed by 1H and 13C NMR spectroscopy as well as elemental analysis. In particular, the molecular structure of 3, confirmed by X‐ray crystallography, is monomeric and the central indium atom adopts a square‐pyramidal geometry. The UV/Vis and fluorescence spectra of 1–5 show typically salen‐centered intramolecular charge transfer transitions with gradual bathochromic shifts as the electron‐donating ability of the substituents increases. This feature is further supported by electrochimical studies. Furthermore, the lowest unoccupied molecular orbital energy levels of 1–5 are considerably lower (approximately −3.70 eV) than those of salen‐based indium complexes with other aryl‐bridging units owing to the reduced electron‐donating effect of the (Cl2Ph)salen group. [ABSTRACT FROM AUTHOR]

Two novel Salen‐DPCPs metal complexes (Salen‐DPCP‐1 and Salen‐DPCP‐2), containing both Salen‐Schiff base (Salen), phenyl phosphate structures (DPCP) and nickel component, were prepared to reduce fire hazards of epoxy resin (EP). The results showed that 5 wt % addition of Salen‐DPCP‐1 brought a higher flame‐retardant efficiency to the EP, where the V‐0 rating in UL‐94 burning test and 31.5% of limiting oxygen index (LOI) were achieved. Meanwhile, total heat release, total smoke production, and total CO yield dramatically decreased by 28.1, 23.6, and 21.4%. In addition, these results basically reappeared when Salen‐DPCP‐2 were introduced into EP to obtain Salen‐DPCP‐2/EP composites. Chemical structure and morphology characterization of the carbon residue confirmed that Salen‐DPCPs improved the catalytic charring ability and the noncombustible gas releasing ability by the Fourier transform infrared, X‐ray photoelectron spectroscopy, and Scanning electron microscopy technology. Therefore, it is an efficient strategy to develop novel Salen composites modified by flame‐retardant groups to improve the fire rating of polymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48734. [ABSTRACT FROM AUTHOR]

The development of a team‐based approach to research‐led transnational practical chemistry teaching is described in which a team of five Chinese students on an articulated transnational degree programme, supported by a team of academic and technical staff, carried out a study examining the structural chemistry of a series of manganese(III) salen complexes. A series of four crystallographically characterized manganese(III) salen complexes with ancillary carboxylate ligands are reported here. The carboxylate coordination modes range from the bridging syn‐anti μ2‐κO : κO′ mode observed in the predominant cyclohexanoate and isobutyrate species, to a capping terminal monodentate mode for the adamantanoate species, and an unusual mixture of bridging and terminal coordination modes observed in a second minor phase of the cyclohexanoate species. The variation on extended structures based on the weakly interacting aliphatic backbones may provide a useful basis for further structural studies. [ABSTRACT FROM AUTHOR]

Three novel phosphorus‐containing Salen‐based derivatives (Salen‐DPCP‐M: M = Ni, Zn, and Mn), which include both phenyl phosphate structures (DPCP) and Salen‐metal complexes, were prepared for enhancing the fire safety of thermoplastic polyurethane (TPU). Thermogravimetric analysis (TGA) showed that Salen‐DPCP‐M altered the thermal degradation pathways of TPU probably due to the phosphorus‐containing structure of Salen‐DPCP‐M. The cone calorimeter test showed that the addition of 3 wt% of Salen‐DPCP‐Ni, Salen‐DPCP‐Zn, and Salen‐DPCP‐Mn lowered the peak of heat release rate (PHRR) from 1495 kW/m2 for neat TPU to 690, 875, and 813 kW/m2, respectively, for the TPU composites, which demonstrated that Salen‐DPCP‐M improved the fire safety of TPU. In addition, the release of toxic CO gas from the Salen‐DPCP‐Ni/TPU and Salen‐DPCP‐Zn/TPU composites was reduced by 78.2% and 80.0%, respectively. The results of TGA/infrared spectrometry (TG‐FTIR) showed that the incorporation of Salen‐DPCP‐Ni promoted the release CO2, while reducing the formation of harmful gases. Laser Raman spectroscopy (LRS) and scanning electron microscopy (SEM) showed that Salen‐DPCP‐Ni/TPU and Salen‐DPCP‐Zn/TPU composites formed a dense and stable char layer. Herein, the mechanism of these flame retardants containing novel phosphorus‐containing Salen‐metal complexes is also proposed. [ABSTRACT FROM AUTHOR]

In a recent paper, the Lewis acidic character of a series of Zn-Sal(ph)en complexes was reviewed, using conceptual density functional theory descriptors to assess the acidic character. It was shown that the nature of the bridging diamine link in the Schiff base ligand controls this character that is mainly responsible for the coordination of the Zn2+, hence for the geometry of these complexes. However, the usual dual descriptor did exhibit significant weaknesses to retrieve the electrophilic part on the metal cation of the Zn-sal(ph)en complexes. Indeed, it is necessary to include the densities of the electronic excited states through the so-called state-specific dual descriptor. This procedure will allow us to recover successfully the appropriate reactivity of the studied complexes holding diamine bridges differing by flexible to semi-rigid and to rigid ranges. Nevertheless, the selection of the excited state allowing a meaningful description of the Lewis acidic is not a priori obtained from a direct identification of the Kohn–Sham (KS) orbitals involved in the excitation. The present work reports an analysis of the relaxation of the KS orbitals when a fraction of charge is added to a virtual orbital, and when an excitation is considered, while a fractional charge is transferred from an occupied orbital toward a virtual orbital. [ABSTRACT FROM AUTHOR]

The complexation reaction between salen (Bis(salicylidene)ethylenediamine) and Cu(II) cations in methanol (MeOH), 2-propanol (2-PrOH), acetonitrile (AN), tetrahydrofuran (THF), and chloroform (CHCl3) as nonaqueous solvents at 25º C has been investigated. The stoichiometry and formation constants of complexes have been determined spectrophotometrically and conductometrically by method of continuous variations and mole ration method. The stoichiometry of Cu(II)-salen complexes in all solvents were 1:1 (ML) type using the two methods. By method of continuous variation, chloroform > 2-propanol > methanol ~ acetonitrile ~ tetrahydrofuran. However, by mole ratio method, the order of stability was as follows: chloroform ~ tetrahydrofuran > 2-propanol > methanol ~ acetonitrile. The resulting average of pKf values in each solvent using the two spectrophotometric methods was as follows: 7.40, 6.89, 6.8, 6.22, and 6.18 for chloroform, 2-propanol, tetrahydrofuran, acetonitrile, and methanol, respectively. The Cu(II) cation formed a more stable complex with salen in chloroform. However, the less stable complex was in methanol. [ABSTRACT FROM AUTHOR]

A salen type ligand of 2-hydroxy 1-napthaldehyde with ethylene diamine was synthesized by sonochemical process. The synthetic process is simple yet efficient using environmentally benign water as a solvent. The synthesized salen ligand was characterized by physical constant, ¹H NMR, FT-IR, HRMS, and UV-visible spectroscopy. The ligand was then coupled with various transition metals (Cu, Co, Ni, and Fe) under sonication and metal complexes were prepared. The metal complexes are obtained in excellent yield under sonication within short period of time. The metal complexes are identified by FT-IR, HRMS and UV-visible spectroscopic analysis. The developed protocol is simple, clean, high yielding, green, and with reduced reaction times by application of sonication. The products are purified by simple filtration followed by washing with water/alcohol and drying processes. [ABSTRACT FROM AUTHOR]