Polymer bound glutamic acid salicylaldehyde Schiff‐base complex ­catalyst for oxidation of olefins with ­dioxygen

The polymer bound Schiff‐base ligand (PS‐SalGlu) has been prepared from polystyrene bound salicylaldehyde and glutamic acid, and its complex (PS‐SalGlu‐Co) has also been synthesized. The polymer ligand and its complex were characterized by infrared spectroscopy, small area X‐ray photoelectron spectroscopy, and inductively coupled plasma‐atomic emission spectro (ICP‐AFS). In the presence of the complex, cyclohexene can be effectively oxidized by molecular oxygen without reductant. The long‐chain linear aliphatic olefins, such as 1‐octene, 1‐decene, 1‐dodecene and 1‐tetradecene, can be directly oxidized by molecular oxygen catalyzed by PS‐SalGlu‐Co, which affords the 1,2‐epoxy alkane. Copyright © 2001 John Wiley & Sons, Ltd.     

Excellent Suzuki–Miyaura catalytic activity of a new Pd(II) complex with sulfonamide–Schiff base ligand

A new air‐stable Pd(II) complex containing a sulfonamide–Schiff base ligand has been synthesized, characterized and investigated as a catalyst for the Suzuki–Miyaura reactions of aryl halides with arylboronic acids. Theoretical calculations (B3LYP) and spectroscopic evidence suggest that the sulfonamide–Schiff base coordinates to the Pd centre through sulfonamide nitrogen (? SO₂NH₂) rather than imine (? CH?N). The complex shows excellent cross‐coupling activity with aryl bromides in water at room temperature and aryl chlorides in isopropanol at 60°C. Copyright © 2016 John Wiley & Sons, Ltd.     

Immobilization of a copper-Schiff base complex in a Y-zeolite matrix: Preparation,chromogenic behavior and catalytic oxidation

A new zeolite-immobilized hybrid catalyst Cu(MeO-salen)-NaY has been prepared by encapsulating [Cu(MeO-salen)(H₂O)] (1) [where MeO-salenH₂ = N,N′-(ethylene)-bis-(3-methoxysalicylaldimine)] in a NaY zeolite matrix. The hybrid material has been characterized by UV–Vis, IR and EPR spectrometry and by X-ray powder diffraction analysis. The pristine complex [Cu(MeO-salen)(H₂O)] (1) has also been synthesized and characterized by all the spectrometric methods mentioned above as well as by single crystal X-ray diffraction analysis. A brilliant color change (green to red) has been observed when the complex [Cu(MeO-salen)(H₂O)] (1) is immobilized in the zeolitic matrix. X-ray powder diffraction analysis of Cu(MeO-salen)-NaY reveals that the structural integrity of the mother zeolite in the hybrid material remains intact upon immobilization of the complex. The coordination geometry around the Cu^II ion in [Cu(MeO-salen)(H₂O)] is found to be square pyramidal. Spectroscopic studies indicate that coordination geometry of the complex undergoes a significant distortion when it is entrapped in the zeolite cavity. While Cu(MeO-salen)-NaY shows excellent catalytic activity and product selectivity in the hydroxylation of phenol and 1-naphthol, [Cu(MeO-salen)(H₂O)] (1) remains virtually catalytically inactive in these reactions.     

Synthesis, Characterization of Heterodinuclear Co-Cu Complex and Its Electrocatalytic Activity towards 02 Reduction： Implications for Cytochrome c Oxidase Active Site Modeling

A new dinudeating ligand consisting of a tetraphanylporphyrin derivative covalently linked with tris(2-benzimidazylmethyl)-amine and its homodinudear Co-Co and heterodinnelear Co-Cu complexes were synthesized and spectroscopically character-ized. The heterobimetallie cobalt-copper complex bearing three benzimidazole ligands for copper, as cytochrome c oxidase ac-tive site model, was applied to the surface of glassy carbon elec-trode to show electrocatalytie activity for O2 reduction in aque-ous solution at an addity level dose to physiological pH value.The kinetic parameters of this electrocatalytic process were ob-tained.     

Magnetic characterization, synthesis and crystal structure of a heterodinuclear CuGd Schiff base complex bridged by the two phenolic oxygen atoms

A novel heterodinuclear complex formed by the reaction of gadolinium nitrate with Schiff base complex of copper(II) has been synthesized and characterized. Preparation, crystal structure and magnetic properties of the heterodinuclear complex, LCu(Me₂CO)Gd(NO₃)₃, (L=(N,N′-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane) are reported. The complex is consisting of a deca-coordinated Gd^III ion which is bridged to four coordinated Cu^II via both phenolate oxygen atoms of the L Schiff base ligand. The average CuGd separation is 3.475(2) Å. There is also one non-coordinating acetone molecule in the crystal structure. The magnetic susceptibility of the complex was measured over the range 4.5–350 K and the observed data were successfully simulated by the equation based on the spin-Hamiltonian operator H=−JS_Cu·S_Gd. The values of the intrachain interaction parameters have been deduced from the magnetic data: exchange integral J(Cu–Gd)=7.3 cm⁻¹, g_Cu=2.17, g_Gd=2.09. This indicates a weak ferromagnetic spin exchange interaction between Cu^II and Gd^III ions. The nature of the magnetic super-exchange interaction of the title compound is compared with similar Cu^IIGd^III heterodinuclear complexes.     

Copper(II) Schiff base complexes derived from 2,2′-dimethyl-propandiamine: Synthesis, characterization and catalytic performance in the oxidation of styrene and cyclooctene

Two new mononuclear copper(II) complexes ([CuL¹]·CHCl₃ (1) and [CuL²] (2)) have been prepared by the reaction of two ONNO type Schiff base ligands, ([bis(2-hydroxy-propiophenone)2,2′-dimethylpropan-diamine] (H₂L¹) and [bis(5-bromosalicylaldehyde)2,2′-dimethyl-propandiamine] (H₂L²)) with Cu(OAc)₂·H₂O in 1:1 molar ratios. The complexes have been characterized by elemental analyses, IR and UV-Vis spectroscopy. The structures have been confirmed by X-ray single crystal analysis at 100 K. The Cu(II) atom in 1 is coordinated equatorially by a N₂O₂ donor set of the tetradentate, dinegative Schiff-base (L¹)²⁻ in a distorted square planar arrangement. While in [CuL²] (2), the Cu(II) ion possesses an additional weak intermolecular contact with one bromine atom of the ligand, thus the coordination sphere of 2 can be described as strongly distorted square pyramidal. The catalytic performance of the prepared copper complexes for the oxidation of styrene and cyclooctene with tert-butyl hydroperoxide has been evaluated.     

Polymeric complex membranes based on styrene–diene–styrene triblock copolymers for oxygen enrichment

Polymers containing a vinylpyridine, vinylimidazole or oxirane group could be used to immobilize cobalt Schiff bases (CoS), which serve as the oxygen carrier in oxygen enrichment. The graft copolymers, based on styrene–butadiene–styrene (SBS) and styrene–isoprene–styrene grafted with 4-vinylpryidine and 1-vinylimidazole, and epoxidized SBS copolymers were prepared to immobilize CoS. The equilibrium constants between CoS and polymeric materials, the oxygen coordination number and the oxygen binding constants were determined. The thermodynamic parameters of oxygen association/dissociation in various complex membranes were determined. The oxygen permeation behavior through various CoS-containing complex membranes was studied and discussed by the dual-mode facilitated transport theory. The permeation properties of oxygen and nitrogen at low pressure were also investigated.     

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.     

Palladium complex containing two sterically hindered ligands as highly efficient catalyst for Suzuki–Miyaura reaction

A new palladium(II) complex containing two sterically hindered ligands, a P,P‐bonded diphosphine and N,N‐bonded Schiff base, within the same coordination sphere has been synthesized and investigated as a catalyst for the Suzuki–Miyaura cross‐coupling reactions of aryl halides with arylboronic acids. The reaction was highly efficient with aryl bromides in water at room temperature and aryl chlorides in dimethylformamide under relatively mild conditions. Excellent yields of coupling products were obtained for a wide range of aryl halides including heteroaryl halides with a low loading of catalyst. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,characterization, crystal structure and catalytic property of [Cu(SalAHE)2] (SalAHE = salicylaldehydeimine-1-hydroxyethane) complex for the oxidation of 3,5-di-tert-butylcatechol

The crystal structure, spectroscopic properties and catalytic property of the copper(II) complex, prepared by the reaction between copper(II) diacetate with the bidentate Schiff base, SalAHE (SalAHE = salicylaldehydeimine-1-hydroxyethane), are reported. This complex is able to oxidize 3,5-di-tert-butylcatechol to the respective o-quinone. The oxidation reaction was studied in CH₃CN with molecular oxygen at 0, 5, 15 and 25 °C. The progress of the catalytic reaction was followed by gas chromatographic analyses (GC).     

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.     

Dioxomolybdenum(VI) complexes of hydrazone phenolate ligands - syntheses and activities in catalytic oxidation reactions

The new cis-dioxomolybdenum (VI) complexes [MoO₂(L²)(H₂O)] (2) and [MoO₂(L³)(H₂O)] (3) containing the tridentate hydrazone-based ligands (H₂L² = N'-(3,5-di-tert-butyl-2-hydroxybenzylidene)-4-methylbenzohydrazide and H₂L³ = N'-(2-hydroxybenzylidene)-2-(hydroxyimino)propanehydrazide) have been synthesized and characterized via IR, ¹H and ¹³C NMR spectroscopy, mass spectrometry, and single crystal X-ray diffraction analysis. The catalytic activities of complexes 2 and 3, and the analogous known complex [MoO₂(L¹)(H₂O)] (1) (H₂L¹ = N'-(2-hydroxybenzylidene)-4-methylbenzohydrazide) have been evaluated for various oxidation reactions, viz. oxygen atom transfer from dimethyl sulfoxide to triphenylphosphine, sulfoxidation of methyl-p-tolylsulfide or epoxidation of different alkenes using tert-butyl hydroperoxide as terminal oxidant. The catalytic activities were found to be comparable for all three complexes, but complexes 1 and 3 showed better catalytic performances than complex 2, which contains a more sterically demanding ligand than the other two complexes.     

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.     

Inorganic–organic hybrid chitosan‐based Schiff base–Ni complex as a novel,highly efficient and recyclable heterogeneous catalyst for synthesis of pyrazolophthalazinediones

A Schiff base based on chitosan was synthesized through treatment of chitosan and p ‐dimethylaminobenzaldehyde in methanol solution. This biopolymeric Schiff base was used to prepare a new first row transition metal complex of Ni(II). The biopolymeric Schiff base and the synthesized tetra‐coordinated complex were characterized using Fourier transform infrared, ¹H NMR and ¹³C NMR techniques. Then, an efficient synthetic method for functionalized 1H –pyrazolo[1,2‐b ]phthalazine‐5,10‐diones was successfully developed using one‐pot domino reaction of ninhydrin and malononitrile with 3‐arylamino‐5,5‐dimethyl‐2‐cyclohexenones catalysed by the chitosan‐based Schiff base complex of Ni(II) at room temperature. The advantages of this protocol are easy work‐up, short reaction times and high yield of products and also the catalyst can be readily isolated from the reaction mixture and recycled without loss of catalytic activity.     

Effect of ligand structure of Schiff base oxovanadium(IV) complexes on their catalytic activity in aerobic oxidation of alcohols

Two kinds of immobilized bidentate Schiff base oxovanadium(IV) complexes are prepared via polymer reactions and coordination reactions with chloromethylated cross-linked polystyrene (CMCPS) microspheres as matrix. Benzaldehyde (BA)-functionalized CPS microspheres, BA-CPS microspheres, were prepared through nucleophilic substitution with CMCPS microsphere as precursor and p-hydroxy benzaldehyde as reagent, and then Schiff base reactions were carried out with 3-aminopyridine (AP) and glycine (GL) as reagents, respectively, obtaining two kinds of bidentate Schiff base ligand-bonded microspheres, BAAP-CPS microspheres and BAGL-CPS microspheres. Finally, through coordination reactions with vanadyl sulfate (VOSO₄) as reagent, the two kinds of immobilized bidentate Schiff base oxovanadium(IV) complex microspheres, CPS-[VO(BAAP)₂] and CPS-[VO(BAGL)₂], were obtained. The two immobilized complexes, VO(BAAP)₂ and VO(BAGL)₂, are N,N- and N,O-type bidentate Schiff base oxovanadium(IV) complexes and their ligands have different chemical structures. The two catalyst microspheres were used in oxidation of cyclohexanol and benzyl alcohol with molecular oxygen as oxidant and their catalytic activities are compared. The experimental results show that both solid catalysts can catalyze the transformation reactions of cyclohexanol and benzyl alcohol to their corresponding carbonyl compounds under mild conditions. However, CPS-[VO(BAAP)₂] microspheres have much higher catalytic activity and better stability than CPS-[VO(BAGL)₂] microspheres. For the immobilized bidentate Schiff base oxovanadium(IV) catalysts, the catalytic property is closely related to the chemical structures of the ligands, and for this, a theoretical explanation is given.     

Synthesis, structure and spectral characterisation of a hydrogen-bonded polymeric manganese(III) Schiff base complex

A new hydrogen-bonded polymeric Mn(III) complex C₁₉H₂₀Mn₁N₃O₃S₁ (1) has been synthesised by conventional procedure with a new Schiff base ligand (2Z,3Z)-N ¹,N ²-bis(1-(2-hydroxyphenyl)ethylidene)ethane-1,2-diamine (H ₂ L) bearing a tetradentate N₂O₂ donor site. The complex has been characterised with several spectroscopic techniques like FT-IR, UV/Vis and EPR and also well supported by variable temperature magnetic susceptibility study. The structure of the co-ordination complex has been unequivocally confirmed from single crystal X-ray diffraction study. The redox stability of the metal chelate complex has been investigated with a slow scan cyclic voltammetry.     

Synthesis, structure, and magnetic properties of two 1-D helical coordination polymeric Cu(II) complexes

Two helical coordination polymeric copper(II) complexes bearing amino acid Schiff bases HL or HL′, which are condensed from 2-hydroxy-1-naphthaldehyde with 2-aminobenzoic acid or l-valine, respectively, have been prepared and characterised by X-ray crystallography. In [CuL]_n (1) the copper(II) atoms are bridged by syn-anti carboxylate groups giving infinite 1-D right-handed helical chains which are further connected by weak C-H?Cu interactions to build a 2-D network. While in [CuL′]_n (2) the carboxylate group acts as a rare monatomic bridge to connect the adjacent copper(II) atoms leading to the formation of a left-handed helical chain. Magnetic susceptibility measurements indicate that 1 exhibits weak ferromagnetic interactions whereas an antiferromagnetic coupling is established for 2. The magnetic behavior can be satisfactorily explained on the basis of the structural data.     

Synthesis and structure of tetranuclear copper(Ⅱ) complex containing μ4-oxo bridge

A new dinucleating Schiff base ligand HL(L=C13H17N2O3) has been synthesised and characterized.The single crystal structure of its complex [L2Cu4O(AcO4)]·2H2O has beendetermined by X-ray diffraction methods.The result indicates that every Cu atom has its square pyramidal coordination polyhedron and there is a tetrahedral Cu4O core in the complex molecule.Its active sites where catalytic oxidation of dioxygen occurs have been inferred.     

Immobilization of dioxomolybdenum(VI) Schiff base complex on graphene oxide nanosheets and its catalytic activity for oxidation of sulfides

Graphene oxide was an effective supporting material for immobilizing a dioxomolybdenum Schiff base complex via covalent interaction. The large surface of graphene oxide plays important roles to obtain a good degree of catalytic reaction. Catalytic capacity of the graphene-bound dioxomolybdenum Schiff base complex was investigated for the oxidation of various sulfides to sulfoxide compounds using hydrogen peroxide urea as an oxidant. The catalyst was characterized by various techniques including XRD, FTIR, TGA, SEM, UV–vis, and ICP-AES. The immobilized complex was very efficient with the extra benefits of easy recovery and recycling of the heterogeneous catalyst. The graphene oxide bound dioxomolybdenum Schiff base complex was reused for several runs without meaningful loss in catalytic activity.     

轴向有机配体对Schiff碱配合物模拟酶催化性能的影响

研究了13种轴向有机中性配体(咪唑、嘧啶、吡唑、吡嗪、哌啶、4-甲基吡啶、3-甲基吡啶、2-甲基吡啶、2,6-二甲基吡啶、三苯基膦、噻吩、呋喃、吡咯)对Schiff碱双锰配合物在模拟酶催化PhIO单加氧化环己烷反应中催化性能的影响。结果表明,这些轴向有机配体均能提高Schiff碱金属配合物的催化活性;一般轴向配体碱性愈强,催化剂的催化活性愈高。