Cu(II) Schiff base complex supported on Fe3O4 nanoparticles as an efficient nanocatalyst for the selective aerobic oxidation of alcohols

Herein, we have prepared a new Cu(II) Schiff base complex supported onto the surface of modified Fe₃O₄ nanoparticles as highly stable, heterogeneous and magnetically recyclable nanocatalyst for the selective aerobic oxidation of different alcohols. The structure, morphology, chemical composition and magnetic property of the nanocatalyst and its precursors were characterized using FT‐IR, TGA, AAS, ICP‐AES, XRD, SEM, EDS, VSM and N₂ adsorption–desorption analyses. Characterization results exhibited the uniform spherical morphology for nanocatalyst and its precursors. A promising eco‐friendly method with short reaction time and high conversion and selectivity for oxidation of various primary and secondary alcohols under O₂ atmosphere condition was achieved. The synthesized nanocatalyst could be recovered easily by applying an external magnetic field and reused for least eight subsequent reaction cycles with only negligible deterioration in catalytic performance.     

Copper-based Schiff Base Complex Immobilized on Core-shell Fe3O4@SiO2 as a magnetically recyclable and highly efficient nanocatalyst for green synthesis of 2-amino-4H-chromene derivatives

Fe₃O₄-supported copper (II) Schiff-Base complex has been synthesized through post-modification with 1,3-phenylenediamine followed by further post-modification with salicylaldehyde and coordination with Cu(II) ion. The resulted Fe₃O₄@SiO₂-imine/phenoxy-Cu(II) magnetic nanoparticles (MNPs) were characterized by various techniques including SEM, TEM, XRD, XPS, EDX, VSM, FT-IR, and ICP. The catalytic activity as a magnetically recyclable heterogeneous catalyst for one-pot, three-component synthesis of 2-amino-4H-chromene derivatives was examined. The catalyst is efficient in the reaction and can be recovered by magnetic separation and recycled several times without significant loss in the catalytic activity.     

Magnetically‐recoverable Schiff Base Complex of Pd (II) Immobilized on Fe3O4@SiO2 Nanoparticles: An Efficient Catalyst for Mizoroki‐Heck and Suzuki‐Miyaura Coupling Reactions

The activity of Pd(II)‐Schiff base complex molecules grafted on the surface of Fe₃O₄@SiO₂ particles were investigated in the palladium‐catalyzed coupling reactions of aryl halides with alkenes (Mizoroki‐Heck reaction) and phenylboronic acids (Suzuki‐Miyaura reaction) in the absence of phosphorous ligands. This method shows notable advantages such as heterogeneous nature of the catalyst, excellent yields, short reaction times, easy preparation, simplicity of operation, and cleaner reaction profiles. The catalyst can be separated from the reaction mixture by applying a permanent magnet externally and can be reused for several times without significant loss of activity. Also, the amount of palladium leaching has been determined by ICP analysis.     

A Tetranuclear Zinc(II) Complex of a [4+4] Macrocyclic Schiff Base Ligand

The cyclocondensation reaction between sodium 2,6-diformyl-4-methylphenolate(sdmp) and 1,5-diamino-3-(1-hydroxyethyl)azapentane (dhap) followed by in situ transmetallation with Zn(ClO₄)₂6H₂O produced a tetranuclear zinc(II)complex of the current biggest-sized [4+4] Schiff base macrocyclic ligand. The structure of the complex has been determined by X-ray techniques, indicating that the hydroxyethyl group of the amine, dhap, has been eliminated in the process. For comparison, the reaction of sdmp with diethylenetriamine has also been carried out. The resulting product has been characterized by its infrared and positive ion FAB mass spectra, which turned out to be a mixture of the corresponding [3+3] and [4+4] macrocyclic Schiff bases together with thecommon [2+2] mode.     

Oxidation of Styrene to Benzaldehyde Catalyzed by Schiff Base Functionalized Triazolylidene Ni(II) Complexes

Four new Schiff base functionalized 1,2,3-triazolylidene nickel complexes, [Ni-(L₁NHC)₂](PF₆)₂; 3, [Ni-(L₂NHC)₂](PF₆)₂; 4, [Ni-(L₃NHC)](PF₆)₂; 7 and [Ni-(L₄NHC)](PF₆)₂; 8, (where L₁NHC = (E)-3-methyl-1-propyl-4-(2-(((2-(pyridin-2-yl)ethyl)imino)methyl)phenyl)-1H-1,2,3-triazol-3-ium hexafluorophosphate(V), 1, L₂NHC = (E)-3-methyl-4-(2-((phenethylimino)methyl)phenyl)-1-propyl-1H-1,2,3-triazol-3-ium hexafluorophosphate(V), 2, L₃NHC = 4,4′-(((1E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2,1-phenylene))bis(3-methyl-1-propyl-1H-1,2,3-triazol-3-ium) hexafluorophosphate(V), 5, and L₄NHC = 4,4′-(((1E)-(butane-1,4-diylbis(azanylylidene))bis(methanylylidene))bis(2,1-phenylene))bis(3-methyl-1-propyl-1H-1,2,3-triazol-3-ium) hexafluorophosphate(V), 6), were synthesised and characterised by a variety of spectroscopic methods. Square planar geometry was proposed for all the nickel complexes. The catalytic potential of the complexes was explored in the oxidation of styrene to benzaldehyde, using hydrogen peroxide as a green oxidant in the presence of acetonitrile at 80 °C. All complexes showed good catalytic activity with high selectivity to benzaldehyde. Complex 3 gave a conversion of 88% and a selectivity of 70% to benzaldehyde in 6 h. However, complexes 4 and 7–8 gave lower conversions of 48–74% but with higher (up to 90%) selectivity to benzaldehyde. Results from kinetics studies determined the activation energy for the catalytic oxidation reaction as 65 ± 3 kJ/mol, first order in catalyst and fractional order in the oxidant. Results from UV-visible and CV studies of the catalytic activity of the Ni-triazolylidene complexes on styrene oxidation did not indicate any clear possibility of generation of a Ni(II) to Ni(III) catalytic cycle.     

Studies on Phenol Oxidation with H2O2 Catalyzed by Schiff Base Cobalt(II) Complexes in Micellar Solution

The two Schiff base cobalt(II) complexes, CoL¹ and CoL², were synthesized and characterized. The metallomicelle made up of the cobalt(II) complexes and surfactants (CTAB, LSS and Brij35), as mimic peroxidase metalloenzyme, were used in the catalytic oxidation of phenol by H₂O₂. The mechanism and a kinetic mathematic model of the phenol catalytic oxidation were studied. The acid effect of reaction system, structural effect of the complexes, and effect of temperature on the rate of the phenol oxidation catalyzed by the mimetic peroxidases have been discussed. The results showed that the schiff base cobalt(II) complexes and their metallomicelles as peroxidase mimics exhibit good catalytic activity and similar catalytic character to natural enzyme.     

Synthesis and Crystal Structure of a Co(II) Complex with Schiff Base and Imidazole Ligand

1 INTRODUCTION The chemical behavior of metal complexes with Schiff base ligand has attracted much attention be- cause of their catalytic activity in some industrial[1, 2] and biochemical processes[3~5]. As some metal com- plexes have shown the catalytic activity in some polymerization reactions[2, 6], we are recently inte- rested in polymerizartion of organo-silicon com- pounds catalyzed by Schiff base complexes of tran- sition metals. A series of Schiff base complexes have been prepare…     

Selective Oxidation of Benzyl Alcohols to Aldehydes with a Salophen Copper(II) Complex and tert-Butyl Hydroperoxide at Room Temperature

An efficient and selective oxidation of benzyl alcohols has been developed using a salophen copper(II) complex as the catalyst and tert-butyl hydroperoxide (TBHP) as the oxidant in the presence of base. Moderate to excellent yields of the corresponding benzaldehydes were obtained at room temperature without the carboxylic acids being formed.     

TEMPO/固载化席夫碱铜配合物共催化剂在分子氧氧化苯甲醇过程中的催化性能

通过大分子反应,将苯甲醛(BA)和邻氨基苯酚(AP)形成的双齿席夫碱配基键合在交联聚甲基丙烯酸缩水甘油酯(CPGMA)微球表面,形成固载有席夫碱配基的载体微球BAAP-CPGMA,再通过与铜盐的配位螯合反应,制备了固载有席夫碱铜配合物的微球[Cu(BAAP)2]-CPGMA.将该固载化铜配合物与均相的2,2,6,6-四甲基哌啶氮氧自由基(TEMPO)构成共催化体系TEMPO/[Cu(BAAP)2]-CPGMA,应用于分子氧氧化苯甲醇的催化氧化过程.我们考察了该共催化体系的催化性能,并探索研究了催化氧化机理.实验结果表明,共催化体系TEMPO/[Cu(BAAP)2]-CPGMA可在温和条件下(室温、常压的氧气)高效地将苯甲醇氧化为苯甲醛(选择性100%,苯甲醛产率93%),并具有良好的循环使用性能.     

呋喃甲醛缩二乙撑三胺希夫碱铜配合物的合成及结构(英)

A novel copper(Ⅱ) complex CuL(NO₃)₂(where L=N,N′-bis(furaldehyde)-diethylenetriamine) was synthesized and characterized by X-ray crystallography analysis. The crystal belongs to monoclinic, space group C2/c with cell parameters a=1.924 0(6) nm, b=0.792 8(3) nm, c=2.504 1(8) nm, β=111.163(5)°, and Z=8. The coordination geometry around Cu(Ⅱ) is a distorted trigonal-bipyramid，and one-dimensional chain is formed through intermolecular hydrogen bonds. CCDC: 255629.     

N-邻羟苄亚基苯胺Schiff碱铜配合物的合成、结构和性能表征(英)

The structure of the title compound has been determined by X-ray crystallography. Each copper atom is chelated by two N-salicylidene-aniline anion ligands with Cu-O and Cu-N distances of 0.187 6(3) and 0.200 1(4) nm, respectively. The central copper(Ⅱ) is four-coordinated and in distorted square-planar environment. The phenyl rings with salicylidene moieties form a dihedral angle of 65.40°. There are C-H…π supramolecular interactions in the crystal structure. The title compound is also examined by elemental analysis, FT-IR, UV spectra and TG-DSC analysis. CCDC: 222315.     

Synthesis,Characterization and Crystal Structures of Four Dinuclear Schiff Base Nickel(II) and Copper(II) Complexes with Versatile Bridging Groups

Four novel Schiff base nickel(II) and copper(II) complexes, derived from the end‐on (μ_1,1‐N₃) azide, end‐to‐end (μ_1,3‐NCS) thiocyanate, or phenolate oxygen bridges, have been synthesized and their crystal structures determined by X‐ray diffraction methods. They are the dinuclear double end‐on azide‐bridged [Ni₂(L1)₂(MeCN)₂(μ_1,1‐N₃)₂]·MeOH ( 1 ), the dinuclear double end‐on azide‐bridged [Ni₂(L2)₂(MeOH)₂(μ_1,1‐N₃)₂][Ni₂(L2)₂(OH₂)₂(μ_1,1‐N₃)₂]·MeOH ( 2 ), the dinuclear double end‐to‐end thiocyanate‐bridged [Cu₂(L3)₂(μ_1,3‐NCS)₂] ( 3 ), and the dinuclear double phenolate O‐bridged [Cu₂(L4)₂(NCS)₂] ( 4 ), where HL1, HL2, HL3 and HL4 are four tridentate Schiff bases obtained by the condensation of 3,5‐dibromosalicylaldehyde with N‐ethylethane‐1,2‐diamine, of 3,5‐dichlorosalicylaldehyde with N‐methylpropane‐1,3‐diamine, of 3‐bromo‐5‐chlorosalicylaldehyde with 2‐aminomethylpyridine, and of 5‐nitrosalicylaldehyde with 2‐aminomethylpyridine, respectively. Each nickel(II) atom in 1 and 2 is in an octahedral coordination, while each copper(II) atom in 3 and 4 is in a square pyramidal coordination. There exists crystallographic inversion centre symmetry in each of the complexes.     

Synthesis and Crystal Structure of a Copper(II) Complex with 2,4-Dihydroxybenzylidene Benzoylhydrazone Ligand

1 INTRODUCTION The chemical properties of acylhydrazones Schiff bases and their complexes with some transition metal ions have been intensively investigated in several re- search areas because of their chelating capability and pharmacological applications[1～10]. Intriguingly, the copper(II) complexes are shown to be signifycantly more potent than the metal free chelate, suggesting that the metal complex is the biologically active species. Owing to the biological interest in these types …     

Symmetric and Unsymmetric Nickel(II) Schiff Base Complexes; Metal-Localized Versus Ligand-Localized Oxidation

The oxidation of symmetric and unsymmetric nickel(II) Schiff base complexes was examined in acetonitrile by cyclic voltammetry. Unlike nickel(II) bis(salicylaldimine) complexes which undergo oxidative polymerization at the electrode surface, the complexes examined in this study contain at least one β-ketoimine chelate and are irreversibly oxidized at the electrode surface. The mixed chelate complexes are oxidized at potentials midway between those of the symmetric bis(salicylaldimine) and bis(β-ketoimine) complexes, suggesting a metal-localized rather than a ligand-localized oxidation. Oxidation of nickel(II) to nickel(III) followed by rapid intramolecular electron transfer to give reactive ligand-radical species is proposed to explain the irreversible oxidation of the nickel(II) Schiff base complexes.     

Functionalization of superparamagnetic Fe3O4@SiO2 nanoparticles with a Cu(II) binuclear Schiff base complex as an efficient and reusable nanomagnetic catalyst for N‐arylation of α‐amino acids and nitrogen‐containing heterocycles with aryl halides

Fe₃O₄@SiO₂ nanoparticles was functionalized with a binuclear Schiff base Cu(II)‐complex (Fe₃O₄@SiO₂/Schiff base‐Cu(II) NPs) and used as an effective magnetic hetereogeneous nanocatalyst for the N‐arylation of α‐amino acids and nitrogen‐containig heterocycles. The catalyst, Fe₃O₄@SiO₂/Schiff base‐Cu(II) NPs, was characterized by Fourier transform infrared (FTIR) and ultraviolet‐visible (UV‐vis) analyses step by step. Size, morphology, and size distribution of the nanocatalyst were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and dynamic light scatterings (DLS) analyses, respectively. The structure of Fe₃O₄ nanoparticles was checked by X‐ray diffraction (XRD) technique. Furthermore, the magnetic properties of the nanocatalyst were investigated by vibrating sample magnetometer (VSM) analysis. Loading content as well as leaching amounts of copper supported by the catalyst was measured by inductive coupled plasma (ICP) analysis. Also, thermal studies of the nanocatalyst was studied by thermal gravimetric analysis (TGA) instrument. X‐ray photoelectron spectroscopy (XPS) analysis of the catalyst revealed that the copper sites are in +2 oxidation state. The Fe₃O₄@SiO₂/Schiff base‐Cu(II) complex was found to be an effective catalyst for C–N cross‐coupling reactions, which high to excellent yields were achieved for α‐amino acids as well as N‐hetereocyclic compounds. Easy recoverability of the catalyst by an external magnet, reusability up to eight runs without significant loss of activity, and its well stability during the reaction are among the other highlights of this catalyst.     

Studies on the Phenol Oxidation by H2O2 Catalyzed by Metallomicelle Made from Crowned Schiff Base Co(II) Complexes Containing Benzoaza-15-crown-5

Three novel cobalt(II) complexes of the benzoaza-15-crown-5 Schiff base, CoL¹, CoL², and CoL³ were synthesized and characterized. Metallomicelles made from CoL and surfactants (CTAB, LSS, and Brij35) were used as mimetic peroxidase in the catalytic oxidation of phenol by H₂O₂. For comparison, the catalytic activity of the complexes (CoL¹, CoL², and CoL³) were also investigated. The mechanism and a kinetic mathematic model of the phenol catalytic oxidation were studied. The acid effect of reaction system, structural effect of the complexes, and effect of temperature on the rate of the phenol catalytic oxidation by the mimetic peroxidase were discussed. The results show that the Schiff base cobalt(II) complexes and their metallomicelles as peroxidase mimics exhibit good catalytic activity and similar catalytic character to natural enzyme.     

Synthesis and Characterization of Nickel(II) and Copper(II) Complexes with Schiff Base (1R,2R)-(-)-Diaminocyclohexane-N,N'-bis(3-tert-butyl-5-(4'-benzoic acid)-salicylidene)

Two homochiral metallosalen complexes, Ni(salen) (salen = (1R,2R)-(-)-diaminocyclohexane-N,N'-bis(3-tert-butyl-5-(4'-benzoic acid)-salicylidene) 1 and Cu(salen) 2, have been synthesized and characterized by IR, microanalysis, TGA, powder and single-crystal X-ray crystallography. Both 1 and 2 crystallize in orthorhombic space group P21212 with Z = 4. For 1, a = 12.082(2), b = 15.447(3), c = 18.784(4) , V = 3505.7(12) 3, Mr = 731.50, Dc = 1.386 g/cm3, μ = 0.606 mm–1, F(000) = 1544, the final GOOF = 1.043, R = 0.0496 and wR = 0.1248 for 4791 observed reflections with I > 2σ(I). For 2, a = 12.181(2), b = 15.501(3), c = 18.877(4) , V = 3564.3(12) 3, Mr = 736.33, Dc = 1.372 g/cm3, μ = 0.665 mm–1, F(000) = 1548, the final GOOF = 1.062, R = 0.0575 and wR = 0.1508 for 4562 observed reflections with I > 2σ(I). The crystal structures of 1 and 2 are isostructural with very similar supramolecular structures. An infinite two-dimensional network is generated by hydrogen bonding interactions and intermolecular π···π interactions.     

Synthesis and Crystal Structure of a Mononuclear Zn(II) Complex with Tridentate Schiff Base,Zn(C_(12)H_(18)N_2O)(NCS)_2

1 INTRODUCTION In recent years there has been considerable and increasing interest in the synthesis of transition metal complexes with multidentate Schiff base ligands[1~4] because such ligands can accommodate one, two or more metal centers and may synthesize homo and/or heteronuclear metal complexes with interesting ste- reochemistry[5, 6]. In addition, these metal complexes can be used for biological modeling applications, catalysis, design of molecular ferromagnet and mate- rials chemis…     

Co(II) Schiff碱载氧载氮性能研究

运用INDO－UHF计算方法研究了CO(Ⅱ) Schiff碱的载氧特性，结果表明，Co(Ⅱ)与O_2的作用是通过σ键组合，并具有较明显的反铁磁性耦合作用, 论证了作为第五轴向配体在可逆载氧过程中的必要性，对比研究了Co－N_2的相互作用. 计算表明，CO(Ⅱ)的Schiff碱络合物可能作为氧氮分离的活性物质，从而具有一定的、潜在的工业应用价值.     

Dioxygen Affinity and Catalytic Performance of Bis-(furaldehyde) Schiff Bases Co(II) Complexes in Cyclohexene Oxidation

As mimetic oxygen carrier or oxidation catalyst, Schiff base cobalt complexes such as Co (II) salen have been widely studied1-4. However their high-price greatly limited their application. The synthesis of cheap furaldehyde Schiff bases and their complexes with Co (II), as well as the dioxygen affinity and biomimetic catalytic oxidation performance of these complexes are worth trying to study. In this paper, the saturated dioxygen uptake of cobalt complexes with different bis-(furaldehyd…