Tri-nuclear phthalocyanine complexes carrying N/O donor ligands as hydrogen peroxide catalysts,and their bleaching activity measurements by an online spectrophotometric method

A phthalocyanine (4) with four salicylhydrazone ligating groups that are directly linked through oxygen bridges to the macrocyclic core has been synthesized by condensation of tetrakis(4-formylphenoxy)phthalocyaninato zinc(II) (3) with salicylhydrazine. Salicylhydrazine was crystallized in methanol during the synthetic procedure. The crystal structure has triclinic space group P-1 with a = 5.8292(6) Å, b = 7.3039(7) Å, c = 17.9798(18) Å, α = 84.272(8)°, β = 89.184(8)°, γ = 81.469(8)°, and Z = 4. Intramolecular O–H?O and intermolecular O–H?O, N–H?N, N–H?O hydrogen bonds were determined in the crystal structure. In addition, there is a weak C–H?π interaction. Complexation on the periphery to yield tri-nuclear Zn(II)Pcs (5–7) was performed through the reaction of a Schiff base-substituted phthalocyanine (4) with MnCl₂·4H₂O, CoCl₂·6H₂O, or Ni(OAc)₂ salts. Fourier transform infrared, ¹H NMR, ¹³C NMR, UV–Vis, ICP-OES (inductively coupled plasma optical emission spectroscopy), mass spectroscopies, and elemental analyses were applied to characterize the prepared compounds. Bleach catalyst activity of the prepared phthalocyanine complexes (5–7) was examined by the degradation of morin and curcumin, respectively. The catalysts had better activity for color removing in solutions at ambient temperature than to that of tetraacetylethylenediamine (TAED).     

Ruthenium complexes bearing bidentate Schiff base ligands as efficient catalysts for organic and polymer syntheses

A concise overview is given on mononuclear and dinuclear, bidentate Schiff base ruthenium complexes with different additional ligands and on their applications in various chemical transformations such as Kharasch addition, enol-ester synthesis, alkyne dimerization, olefin metathesis and atom transfer radical polymerization. These new ruthenium complexes, conveniently prepared from commonly available ruthenium compounds, are very stable, exhibit a good tolerance towards organic functionalities, air and moisture and display high activity and chemoselectivity in chemical transformations. Relevant features of coordination chemistry connected with the reaction mechanism and chemoselectivity are also fully described. Since the nature of Schiff bases can be changed in a variety of ways, appealing routes for designing and preparing novel ruthenium complexes can be foreseen in the future.     

双水杨醛缩环己二胺类西佛碱及其配合物的合成、性质研究

合成了两种双水杨醛缩环已二胺类西佛碱N，N’-(二羟苯次甲基)环已二胺(1)和N，N’-二(3，5-二叔丁基-2-羟苯次甲基)环已二胺(2)，以及它们的金属锌配合物(3)和(4)，通过核磁共振、元素分析和红外光谱确定了四种物质的结构，研究了它们的紫外吸收光谱、荧光光谱，测定了(3)和(4)的荧光量子效率．(4)中四个叔丁基的存在使其荧光量子效率提高．此类双西佛碱金属配合物可以应用于有机电致发光材料中．     

Synthesis and characterization of insoluble cobalt(II), nickel(II), zinc(II) and palladium(II) Schiff base complexes: Heterogeneous catalysts for oxidation of sulfides with hydrogen peroxide

The condensation reaction of 1,2-bis(2′-aminophenoxy)benzene with 2-pyridinecarbaldehyde in a mole ratio of 1:2 gives a new Schiff base ligand (L). Four Schiff base complexes, CoL(NO₃)₂ (1), NiLCl₂ (2), ZnL(NO₃)₂ (3) and Pd₂LCl₄ (4) have been prepared by direct reaction of the ligand (L) and appropriate metal salts. The Schiff base ligand (L) has been characterized by IR, ¹H NMR and ¹³C NMR spectroscopy and elemental analysis. Also, all complexes have been characterized by IR and XRD spectroscopy techniques and elemental analysis. The synthesized complexes have very poor solubility in all polar and non-polar solvents such as: H₂O, MeOH, EtOH, CH₃CN, DMSO, DMF, CHCl₃, CH₂Cl₂, THF, etc; therefore, they have been used as heterogeneous catalysts. Catalytic performance of the complexes was studied in oxidation of thioanisole using hydrogen peroxide (H₂O₂) as the oxidant. Various factors including the reaction temperature, amount of oxidant and catalyst amount were optimized. The palladium Schiff base complex, Pd₂LCl₄ (4), shows better catalytic activity than other complexes. Therefore, the Pd(II) Schiff base complex has been used as a catalyst for oxidation of different sulfides to their corresponding sulfones in acetonitrile with hydrogen peroxide as the oxidant. The palladium Schiff base complex, Pd₂LCl₄ (4), has shown a very good recyclability, up to five times, without any appreciable decreases in catalytic activity and selectivity.     

Synthesis of amino acid derivative Schiff base copper(II) complexes by microwave and wet mechanochemical methods

As resource- and time-saving and environmentally friendly synthetic methods than conventional one in a solution, microwave, and wet mechanochemical synthesis are tested for l-amino acid derivative Schiff base copper(II) complexes. Herein, we systematically compared efficiency (low-temperature, time, and yield (if possible to detect)) for both conventional solution method and microwave or mechanochemical methods. The wet mechanochemical synthesis promoted fast reaction (typically 20 ​min by mechanochemical vs 4 ​h by conventional) by a little amount of solvent for preparations of amino acid derivative Schiff base copper(II) complexes. New crystal structure of a five-coordinated square pyramidal copper(II) complex as one of the products of microwave method was also reported.     

Cationic palladium(II) catalysts on O-carboxymethyl chitosan Schiff base for Suzuki coupling reactions

In this study, catalytic activity of two different cationic O-Carboxymethyl chitosan Schiff base palladium (II) complexes in Suzuki coupling reactions and synthesis of biarlys having different functional groups, and reusability of the catalysts were tested. Chemical structures of the synthesized biaryls were elucidated by GC-MS and ¹H-NMR; and no by-products were observed in the spectra. Cationic palladium (II) catalysts high turnover numbers and selectivity were recorded for the reactions. Mercury test demonstrated that the reaction mechanism proceed a homogeneous route. Reusability tests of cationic biocatalysts showed that their catalytic activity were still highly efficient even after six cycles.     

Synthesis and application of new Schiff base Mn(III) complexes containing crown ether rings as catalysts for oxidation of cyclohexene and cyclooctene by Oxone

Six catalysts MnClL¹–MnClL⁶, containing two crown ether rings, were synthesised and characterised by IR spectroscopy and CHN microanalysis. A combination of Oxone, as oxidant, and these catalysts was used for the oxidation of cyclohexene and cyclooctene. Among the prepared catalysts, MnClL³ and MnClL⁴ exhibited the best catalytic efficiency. Catalysts MnClL¹, MnClL² and MnClL⁶ showed a moderate efficiency and MnClL¹ showed the lowest efficiency. Comparison of MmclL¹–MnClL⁴ and MnClL⁶ containing crown ether rings with an identical mixture of uncrowned complex MnClL⁷ [manganese N,N′-bis(salicylidene)ethylenediamine chloride] and crown ether 2 (4′-hydroxybenzo-15-crown-5), revealed a more important role for the crown ether than increasing solubility of Oxone in the organic phase. The effect on reaction times and chemical yields of temperature, pyridine as the axial base, and different alkali metal salts was also investigated.     

Schiff base complexes and their versatile applications as catalysts in oxidation of organic compounds: part I

Schiff bases and their complexes are good candidates as versatile compounds which are synthesized by the condensation of a primary amino compound with either aldehydes or ketones for a variety of industrial applications. They can act as catalysts in the catalytic oxidation of organic compounds. Recent researches in oxidation catalysis have focused on how to employ the metal‐catalyzed oxidation of organic substrates. This review summarizes the current developments of the last few decades for the oxidations of organic compounds that proceed through Schiff base complexes. The chemical syntheses of Schiff bases and their complexes are outlined.     

Co(II), Fe(III) or VO(II) Schiff base metal complexes immobilized on graphene oxide for styrene epoxidation

Cobalt(II), iron(III) or oxovanadium(II) Schiff base metal complexes have been covalently grafted onto graphene oxide ( GO ) previously functionalized with 3‐aminopropyltriethoxysilane. Potential catalytic behaviors were tested in the epoxidation of styrene, using air as the oxidant. The catalysts were characterized using infrared (IR) and Raman spectroscopies, thermogravimetric analyses, inductively coupled plasma atomic emission spectrometry (ICP‐AES), X‐ray diffraction, nitrogen adsorption–desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). IR spectroscopy, thermogravimetric analyses and ICP‐AES confirmed the successful incorporation of the metal Schiff base complexes onto GO . X‐ray diffraction, nitrogen adsorption–desorption, Raman spectroscopy, SEM and TEM showed the intact structure of the GO . Co-GO and Fe-GO showed high styrene conversion (90.8 versus 86.7%) and epoxide selectivity (63.7 versus 51.4%). Nevertheless, VO-GO showed poorer catalytic performance compared with Co-GO and Fe-GO . The recycling results of these heterogeneous catalysts showed good recoverability without significant loss of activity and selectivity within four successive runs. Copyright © 2015 John Wiley & Sons, Ltd.     

New chiral Schiff base–Cu(II) complexes as cyclopropanation catalysts

A series of chiral Schiff base ligands 1–4, derived from (1R,2S)-(+)-cis-1-amino-2-indanol and other chiral amines with substituted salycilaldehydes were synthesized and transformed to the corresponding Cu(II) complexes. Molecular structures of six Cu(II) complexes were determined by X-ray crystallographic studies. The structures show the metal ion in a distorted square planar geometry with dimeric or monomeric structures, depending on the ligand denticity. The potential use of these complexes in asymmetric Cyclopropanation was explored.     

Chromone-based Schiff base metal complexes as catalysts for catechol oxidation: Synthesis,kinetics and electrochemical studies

Two new Schiff base ligands with chromone moiety and their transition metal complexes were synthesized and characterized by elemental analyses, magnetic susceptibility, molar conductance and TGA analyses, FT IR, UV-Vis, NMR and mass spectroscopy. All the complexes synthesized have been investigated as functional models for catechol oxidase (catecholase) activity by employing 3,5-di-tert-butylcatechol as a model substrate. The two mononuclear copper(II) and two mononuclear iron(II) complexes show catecholase activity with turnover (k_cat) numbers lying in the range 27.2–1328.4 h^?1. According to the kinetic measurement results, the rate of catechol oxidation follows first order kinetics and iron(II) complexes were found to have higher catalytic activity than those of copper(II) complexes. Electron-donating substituent on Schiff base ligand enhanced the catalytic activity of metal complexes while the electron-withdrawing substituent led to a decrease in activity. The electrochemical properties of two Schiff bases and their metal complexes were also investigated by Cyclic Voltammetry (CV) using glassy carbon electrode (GCE) at various scan rates. Electrochemical processes of all the compounds were observed as irreversible.     

A new vanadium Schiff base complex as catalyst for oxidation of alcohols

The monoanionic bidentate Schiff base, N-(phenolyl)-benzaldimine (HL), has been employed to synthesize a new vanadium(IV) complex of general composition [VO(L)₂] (where L?=?O,?N donor of Schiff base). The ligand and complex have been fully characterized by elemental analyses, molar conductance data, FT-IR, ¹H- and ¹³C-NMR, and UV-Vis spectroscopies. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted by this complex catalyst using Oxone as oxidant under biphasic reaction conditions (CH₂Cl₂/H₂O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature.     

Photofunctional supramolecular solution systems of chiral Schiff base nickel(II), copper(II), and zinc(II) complexes and photochromic azobenzenes

Preparations, crystal structures, electronic and CD spectra are reported for new chiral Schiff base complexes, bis(N-R-1-naphthylethyl-3,5-dichlorosalicydenaminato)nickel(II), copper(II), and zinc(II). Nickel(II) and copper(II) complexes adopt a square planar trans-[MN₂O₂] coordination geometry with Δ(R,R) configuration. While zinc(II) complex adopts a compressed tetrahedral trans-[MN₂O₂] one with Δ(R,R) configuration and exhibits an emission band around 21 000 cm⁻¹ (λ_ex = 27 000 cm⁻¹). Absorption and CD spectra were recorded in N,N′-dimethylformamide, acetone, methanol, chloroform, and toluene solutions to discuss relationships between spectral shifts of d–d and π–π^∗ bands by structural changes of the complexes and physical properties of the solvents. Moreover, we have attempted to investigate conformational changes of the complexes induced by photoisomerization of azobenzene, 4-hydroxyazobenzene, or 4-aminoazobenzene, in various solutions under different conditions. Weak intermolecular interactions between complexes and azobenzenes are important for the phenomenon by conformational changes of bulky π-conjugated moieties of the ligands.     

Synthesis and characterization of novel heteronuclear complexes of Ln(III)-Cu(II) with non-cyclic polyether Schiff base

Nine novel heteronuclear complexes of Ln(III)-Cu(II) with salicylidene tetraethylene glycol diamine (SALTTA) have been synthesized and characterized. They have the general formulae [L_nC_u2(SALTTA)₂(NO₃)₃](NO₃)₄·3H₂O (Ln=La, Pr, Nd, Sm) and [LnCu₃(SALTTA)₃(NO₃)₅]-(NO₃)₄·4H₂O (Ln=Gd, Tb, Er, Yb, Y). The IR spectra show that v_C=N in the Ln(III)-Cu(II) heteronuclear complexes are splitted up into two peaks with a far distance. It has been confirmed that oxygen atoms in oxyethylene of the ligand are not all coordinated to the central metal ions by both IR and NMR methods.     

New copper(II) and zinc(II) complexes based on azo Schiff base ligand: Synthesis,crystal structure,photoisomerization study and antibacterial activity

Newly synthesized mononuclear copper(II) and zinc(II) complexes containing an azo Schiff base ligand (L), prepared by condensation of 2-hydroxy-5-(o-tolyldiazenyl)benzaldehyde and propylamine, were obtained and then characterized using infrared and NMR spectroscopies, mass spectrometry and X-ray diffraction. Ligand L behaves as a bidentate chelate by coordinating through deprotonated phenolic oxygen and azomethine nitrogen. The copper and zinc complexes crystallize in triclinic and orthorhombic systems, respectively, with space groups P⁻1 and Pca2₁. In these complexes, the Cu(II) ion is in a square planar geometry while the Zn(II) ion is in a distorted tetrahedral environment. The photochemical behaviors of ligand L, [Cu(L)₂] and [Zn(L)₂] were investigated. The azo group in L underwent reversible trans–cis isomerization under UV and visible irradiation. This process was inhibited for the complexes. In addition, ligand L and its copper and zinc complexes were assessed for their in vitro antibacterial activities against four pathogenic strains.     

Copper(II), cobalt(II), nickel(II) and zinc(II) complexes of Schiff base derived from benzil-2,4-dinitrophenylhydrazone with aniline

New Schiff base chelates of Cu(II), Co(II), Ni(II) and Zn(II) derived from benzil-2,4-dinitro-phenylhydrazone with aniline have been synthesised. Microanalytical data, molar conductance, and magnetic susceptibility values have been obtained, and IR,¹H NMR,¹³C NMR, UV-Vis, CV and EPR spectral studies have been carried out to suggest tentative structures for the complexes     

Alumina-supported metal(II) Schiff base complexes as heterogeneous catalysts in the high-regioselective cleavage of epoxides to halohydrins by using elemental halogen

A highly regioselective method for the synthesis of β-iodohydrins and β-bromohydrins through direct ring opening of epoxides with elemental halogen in the presence of alumina-supported Schiff base complexes of Mn(II), Co(II), Ni(II) and Cu(II) as new catalysts is described. This method is regioselective under mild conditions in various aprotic solvents with high yields, even when sensitive functional groups are present. The catalysts are easily recovered and can be reused several times.     

Synthesis and magnetic resonance of new heteropolynuclear Ln(III)-Cu(II) complexes with noncyclic polyether Schiff base

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Preparation and structural characterization of hetero-dinuclear Schiff base copper(II)-zinc(II) complexes and their inhibition studies on Helicobacter pylori urease

A series of hetero-dinuclear Cu^II-Zn^II complexes, [CuZnCl₂L¹] (1), [CuZnCl₂L²] (2), [CuZnBr₂L³] (3), [CuZnBr₂L⁴(DMF)] (4), [CuZnCl₂L⁴] (5), [CuZnCl₂L⁵] (6), [CuZnCl₂L³] (7) and [CuZnBr₂L¹] (8), where L¹, L², L³, L⁴ and L⁵ are the deprotonated forms of N,N′-bis(3-ethoxysalicylidene)-1,3-propanediamine (H₂L¹), N,N′-bis(2-hydroxynaphthylmethylidene)-1,3-propanediamine (H₂L²), N,N′-bis(3-methoxysalicylidene)-1,3-propanediamine (H₂L³), N,N′-bis(salicylidene)-1,3-propanediamine (H₂L⁴) and N,N′-bis(salicylidene)-1,4-butanediamine (H₂L⁵), respectively, have been synthesized and characterized by physico-chemical methods and single-crystal X-ray diffraction. The complexes were tested for their urease inhibitory activity. Complexes 1 and 8 show effective urease inhibitory activity with IC₅₀ values of 2.2 and 10.7 μM. The molecular docking study of the complexes with the Helicobacter pylori urease was performed.     

Antibacterial activity of transition metal complexes containing a tridentate NNO phenoxymethylpenicillin‐based Schiff base. An anti‐MRSA iron (II) complex

Transition metal complexes containing a phenoxymethylpenicillin‐derived Schiff base (HL) 3 obtained from the condensation of phenoxymethylpenicillin (PMP) 1 , with 1,2‐diaminobenzene 2 , were prepared. Spectroscopic and physicochemical techniques, namely, UV–Vis, FT‐IR, ¹H‐NMR, EPR, mass spectrometry, magnetic susceptibility, molar conductance, DFT studies, together with elemental and thermal analyses were used to characterize the synthesized complexes. Based on the characterization studies, the general formulae [ML (OAc)(H₂O)₂] where M = Fe 4 , Co 5 , Ni 6 , Cu 7 , and Zn 8 , were proposed for the complexes. The Schiff base ligand 3 behaved as a monoanionic tridentate NNO chelating agent. On the basis of magnetic and spectral data an octahedral geometry for all the complexes was suggested. Schiff base ligand 3 , and the metal complexes 4 – 8 were tested against G(+) or bactericidal activity by agar disc diffusion method and minimal inhibitory concentration (MIC). The results were compared with the activity of the standard drug PMP 1 . In vitro bacterial viability revealed that 3  had similar activity than 1 and exhibited modification in its bactericidal activity when formed metal complexes. It was found that the complexes 4 , 6 and 7 exhibited much better bactericidal activity than 1 against methicillin‐resistant Staphilococcus Aureus (MRSA) being complex 4 the most promising compound showing a MIC value of 0.042 μmol/ml.