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.     

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.     

Heterogenization of a molybdenum Schiff base complex as a magnetic nanocatalyst: An eco-friendly,efficient, selective and recyclable nanocatalyst for the oxidation of alkenes

A Schiff base ligand derived from 5-bromo-2-hydroxybenzaldehyde and 2,2′-dimethylpropylenediamine (H₂L) and its corresponding dioxomolybdenum(VI) complex (Mo(O)₂L) has been synthesized and characterized by spectroscopic methods. The adsorption of Mo(O)₂L on the surface of silica-coated magnetite nanoparticles via hydrogen bonding led to the formation of (α-Fe₂O₃)–MCM-41–Mo(O)₂L as a heterogeneous catalyst. FT-IR and atomic absorption spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize and investigate the new nanocatalyst. A practical catalytic method for the efficient and highly selective oxidation of a wide range of olefins with hydrogen peroxide and tert-butyl hydroperoxide in ethanol over the prepared molybdenum nanocatalyst was investigated. Under reflux conditions, the oxidation of cyclooctene with tert-butyl hydroperoxide or hydrogen peroxide led to the formation of epoxide as the sole product. The catalyst was reused at least six times without a significant decrease in catalytic activity or selectivity, and without detectable leaching of the catalyst.     

Synthesis,characterization, luminescence,antibacterial, and catalytic activities of a palladium(II) complex involving a Schiff base

A new Pd(II) complex of fluorine-containing Schiff base ligand, [Pd₂(L)₂Cl₂] (1) [L?=?N-(4-fluorobenzylidene)-2,6-diethylbenzenamine], has been synthesized using solvothermal method and characterized by elemental analysis, IR-spectroscopy, thermogravimetric analysis, powder X-ray diffraction, UV–vis absorption spectra, and single-crystal X-ray diffraction. Complex 1 is a μ-chloro-bridged dinuclear cyclometallated Pd(II) complex. Thermal analysis indicates that 1 is quite stable to heat. 1 exhibits quadruple emissions in the solid state (λ _max?=?766?nm) and possesses fluorescence lifetimes (τ ₁?=?87.20?ns, τ ₂?=?190.45?ns, and τ ₃?=?1805.10?ns at 616?nm); broad structureless bands at 690–800?nm are tentatively assigned to an excimeric ³IL transition. The Schiff base (L) and its palladium(II) compound (1) have been screened for their antibacterial activity against several bacteria, and the results are compared with the activity of penicillin. Moreover, 1 has been shown to be highly effective in the Heck reaction of 4-bromotoluene with acrylic acid.     

Schiff碱配合物模拟酶催化性能的温度效应研究

研究了新型Schiff碱双锰配合物在模拟酶催化亚碘酰苯单加氧化环已烷反应及 被亚碘酰苯氧化破坏反应中的温度效应。结果表明，在模拟酶催化反应体系中同时 存在催化环已烷单加氧反应及催化剂的氧化破坏反应；催化反应速率及氧化破坏反 应速率均随反应温度升高有规律地增大，但氧化破坏反应比催化反应对反应温度更 敏感；催化反应总产率一般随反应温度升高而降低；最适宜的反应温度为25 ℃。     

Heterogeneously catalyzed oxidation of butanediols in base free aqueous media

The oxidation of four butanediols under base-free conditions has been investigated using a set of Au, Pd and Pt catalysts prepared using sol-immobilization. The supported nanoparticles are found to be active with bimetallic alloys having much higher activity when compared with the monometallic counterparts. In general the AuPt catalysts are the most active and in all cases the corresponding C4 oxidation products were observed with high selectivity; sequential reaction of these products leads to the formation of acetic acid as an undesired by-product.     

Synthesis,characterization and crystal structure of a dioxomolybdenum(VI) complex with a N,O type bidentate Schiff base ligand as a catalyst for homogeneous oxidation of olefins

The synthesis of a Mo(VI) Schiff base complex, cis-[MoO₂{(4,6-bis(tert-butyl)-2-{(benzyl)iminomethyl}phenolate)₂}], cis-[MoO₂(L)₂] where L = 4,6-bis(tert-butyl)-2-{(benzyl)iminomethyl}phenol, derived from benzylamine and 3,5-di-tert-butylsalycilaldehyde is reported. Full characterization of this complex was accomplished with elemental analyses, spectroscopic studies (NMR, IR and electronic) and X-ray structure analysis. This complex was tested as a catalyst for the homogeneous oxidation of olefins. The Mo(VI) complex is catalytically active for the epoxidation of aliphatic substrates at 80 °C, yielding the epoxide as the sole product in yields up to 100% and turnover numbers up to 5000. Under the optimized conditions styrene was oxidized in an 81% conversion to produce styrene oxide, benzaldehyde, and acetophenone.     

Solid-Phase Immobilization of a New Epoxidation Catalyst

The heterogenization of a titanium(IV ) silsesquioxane complex in an MCM-41 molecular sieve , by tailoring the polarity of MCM-41, results in self-assembled materials (see the space-filling model on the right) that are active, truly heterogeneous, and recyclable catalysts for liquid-phase alkene epoxidation.     

Synthesis and characterization of NaY zeolite-encapsulated Mn-hydrazone Schiff base: an efficient and reusable catalyst for oxidation of olefins

The Mn-hydrazone Schiff base has been prepared, characterized, and encapsulated into NaY to prepare a new heterogeneous catalyst. Elemental analysis, UV-Vis, infrared spectroscopic analysis, diffuse reflectance spectroscopy, thermal analysis, small angle X-ray diffraction, and N₂ sorption indicate the presence of Mn-hydrazone Schiff base within the nanocavity pores of zeolite-Y. The catalysts showed excellent catalytic efficiency in epoxidation with various olefinic compounds including cyclooctene, using tert-BuOOH as oxidant. Cyclooctene showed high conversion (97%) as well as epoxide selectivity (89%) with tert-BuOOH. Moreover, the encapsulated complex showed good recoverability without significant loss of activity and selectivity within successive runs.     

SBA-15负载的Cu(Ⅱ)席夫碱配合物催化的苯乙烯氧化反应制备苯甲醛

采用一步法将原硅酸四乙酯与3-氨丙基三乙氧基硅烷在表面活性剂P123作用下,酸性共水解制备出氨基功能化的介孔分子筛SBA-15(NH2-SBA-15),再利用其中氨基与水杨醛的缩合反应制备SBA-15固载的席夫碱,该席夫碱与Cu(NO3)2溶液反应最终制成固定于SBA-15的Cu(II)席夫碱配合物多相催化剂Cu-SBA-15.采用X射线衍射、红外光谱仪、紫外可见分光光度计、场发射电镜、透射电镜、N2吸附-脱附、元素分析、原子发射光谱和热重分析对催化剂进行了表征,并将此催化剂用于无有机溶剂条件下催化氧化苯乙烯制备苯甲醛,考察了反应时间、反应温度、H2O2用量、水的用量、催化剂用量对反应的影响.当反应温度为100°C,反应时间8 h,H2O2与苯乙烯的摩尔比为2:1,不额外添加溶剂,且催化剂用量为3.8 wt%时,苯乙烯的转化率最高为84.4%,苯甲醛选择性为83.9%,催化剂的TOF值为261.1 h–1,并且重复使用3次后活性没有明显下降.规则的孔道、较大的比表面积以及分布均匀的活性中心可能是催化剂活性提高的原因.     

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。     

Synthesis,X-ray structure,DFT studies,and catalytic activity of a vanadium(V) complex containing a tridentate Schiff base

Reactions of a solution of NH₄VO₃ in H₂O₂ and water and salicylidene benzoyl hydrazine as a tridentate Schiff base (ONO) afford a six-coordinate V(V) complex [VO(ONO)(OCH₃)(CH₃OH)] with a distorted octahedral configuration. The complexes [VO(ONO)(OCH₃)(CH₃OH)] were isolated as air-stable crystalline solids and fully characterized, including by single-crystal X-ray structure analysis. DFT calculations have been performed to understand the electronic structure of the complex. Vibrational frequencies and maximum absorption wavelengths of the complex theoretically calculated are in good agreement with experimental values. [VO(ONO)(OCH₃)(CH₃OH)] shows efficient oxidation of sulfides to their corresponding sulfoxides using urea hydrogen peroxide as the oxidant at room temperature under air.     

Nickel(II), copper(II), cobalt(II), and palladium(II) complexes with a Schiff base: crystal structure,DFT study and copper complex catalyzed aerobic oxidation of alcohol to aldehyde

Ni(II), Cu(II), Co(II), and Pd(II) complexes were synthesized with a Schiff base containing thioether with ONS donors chelating to the metal center. The ligand and complexes were characterized by elemental analysis, FT-IR, ¹H-NMR, UV–visible spectroscopy and magnetic studies. The crystal structures of the ligand and its Ni(II) and Pd(II) complexes were determined by single-crystal X-ray diffraction analysis. Structures revealed that the ligand chelated with Ni(II) and Pd(II) center in slightly distorted octahedral and slightly distorted square planar fashion, respectively. DFT studies of the Pd(II) complex revealed that the calculated structural parameters are very close with the experimentally observed data. The Cu(II) complex shows very good catalytic activity toward the conversion of alcohol to aldehyde under aerobic oxidation with ammonium persulfate.     

Heterogeneous catalytic aerobic oxidation behavior of Co–Na heterodinuclear polymeric complex of Salen-crown ether

A new kind of Co–Na heterodinuclear polymer complex based on Salen Schiff base and crown ether has been successfully prepared by condensation polymerization. Its catalytic behavior for aerobic oxidation of cyclohexene, alkylbenzenes and linear aliphatic olefins was studied in the absence of any solvents or reducing agents under mild conditions. The oxidation of cyclohexene catalyzed by the above catalyst proved to be a simple and efficient method for obtaining 2-cyclohexen-1-one (CO) and 2-cyclohexen-ol (OH) in a high selectivity. Kinetics of the oxidation was also investigated. The results showed that the aerobic oxidation of cyclohexene catalyzed by Salen-crown ether heterodinuclear polymer complex follows a radical chain aerobic oxidation mechanism. This oxidation system is also efficient in the oxidation of alkylbenzenes and linear aliphatic olefins, which afforded corresponding benzylic oxidation products and epoxides, respectively.     

Dinuclear Zn(II) and tetranuclear Co(II) complexes of a tetradentate N2O2 Schiff base ligand: Synthesis,crystal structure,characterization, DFT studies,cytotoxicity evaluation,and catalytic activity toward benzyl alcohol oxidation

Two novel dinuclear Zn(II) and tetranuclear Co(II) complexes of a tetradentate N₂O₂ Schiff base ligand (H₂ L = N,N′-bis-(4-hydroxysalicylidene)-1,3-diaminopropane) were prepared. The structures of the H₂ L ligand, [4(Zn₂ L (μ-O₂CCH₃)(O₂CCH₃)(H₂O))]⋅4CH₃OH⋅3H₂O (complex 1 ) and [Co₄ L ₂(μ-O₂CCH₃)₂(O₂CCH₃)₂]⋅2H₂O (complex 2 ) were unambiguously characterized by elemental analysis, mass spectrometry, Fourier-transform infrared spectroscopy (FT-IR), ¹H nuclear magnetic resonance (NMR), and UV–Vis spectroscopy. Single crystal X-ray diffraction studies revealed that two Zn(II) nuclei of 1 were connected through μ-phenolato and μ-acetato bridges and had distorted square pyramidal and distorted octahedral coordination geometries. Four Co(II) nuclei of 2 , on the contrary, showed a Co₄O₄ cubane-like configuration in which Co(II) cations and O atoms were located at alternating corners of a distorted cube. Density functional theory studies at the B3LYP/6–31 G(d) level were carried out to gain an insight into the thermodynamic stability of the complexes. in vitro cytotoxicity of the ligand and the complexes were evaluated using the MTT assay against breast cancer MCF7 cells, melanoma cancer A375 cells, and prostate cancer PC3 cells as representative human cancer cell lines. Complex 1 showed a remarkable activity against A375 and PC3 cancer cell lines. In addition, 1 and 2 were used as precursors to produce zinc and cobalt oxide nanoparticles via pyrolysis technique. The resulting ZnO and Co₃O₄ nanoparticles were characterized using FT-IR spectroscopy, UV–Vis diffuse reflectance spectroscopy, powder X-ray diffraction, and field emission scanning electron microscopy. Then, these nanoparticles were used as heterogeneous catalysts in the oxidation of benzyl alcohol with hydrogen peroxide at room temperature. Both catalysts showed good recyclability with a negligible decrease in their efficiency during four catalytic cycles. The results of theoretical calculations showed that the most stable product was benzaldehyde, which is in good agreement with the obtained experimental results.     

A new magnetic nanoparticle‐supported Schiff base complex of manganese: an efficient and recyclable catalyst for selective oxidation of alcohols

A new magnetic nanoparticle‐supported Schiff base complex of manganese was prepared via the copper‐catalyzed ‘click’ reaction of an aminosalicylidene manganese complex bearing terminal alkynyl with azide‐functionalized shell–core magnetic nanoparticles. The as‐prepared catalyst was applied in the oxidation of alcohols to corresponding aldehydes or ketones with high yield and selectivity when the reaction was carried out in dimethylsulfoxide at 110°C for 4 h using tert‐butyl hydroperoxide as oxidant. Moreover, the catalyst can be easily separated from the reaction mixture using an external magnet and reused five times with no significant loss of catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

NaY分子筛固载席夫碱钴配合物的制备、表征及其催化性能研究

利用“瓶中造船”（ship-in-a-bottle） 技术将双水杨醛缩乙二胺合钴（Cosalen）配合物封装于Y型沸石分子筛的超笼中,制备出固载型席夫碱钴金属配合物Cosalen/Y（SB）。同时采用浸渍方法将Cosalen负载于Y型分子筛的表面,制备了浸渍型的负载物Cosalen/Y（IM）。采用原子吸收、红外光谱、紫外光谱、X射线衍射、热重 差热和电镜扫描等方法对两者进行了表征。 结果表明 ,固载物Cosalen/Y（SB）中Cosalen已成功地进入了分子筛的孔道内。以分子氧为氧源,考察了Cosalen/Y（SB）对环己烷的催化氧化性能以及催化剂用量、溶剂、氧气压力对反应的影响。结果表明,Cosalen/Y（SB）具有较高的催化氧化活性和对环己醇、环己酮以及己二酸的选择性,有一步氧化环己烷生成己二酸的潜力。重复实验表明,催化剂稳定性较好,没有明显的活性组分流失。     

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, characterization, and sorption properties of silica gel-immobilized Schiff base derivative

Silica gel was derivatized with benzophenone 4-aminobenzoylhydrazone (BAH), a Schiff base derivative, after silanization of silica by 3-chloropropyltrimethoxysilane (CPTS) by using a reported method. Characterization of the surface modification was confirmed through infrared spectroscopy, thermogravimetry, and elemental analysis. The immobilized surface was used for Cu(II), Ni(II), Zn(II), and Co(II) sorption from aqueous solutions. The influence of the amount of sorbent, ion concentration, pH, and temperature was investigated. The sorption data followed Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms. The mean sorption energy (E) of benzophenone 4-aminobenzoylhydrazone (BAH) immobilization onto silica gel was calculated from D-R isotherms, indicating a chemical sorption mode for four cations. Thermodynamic parameters, i.e., DeltaG, DeltaS, and DeltaH, were also calculated for the system. From these parameters, DeltaH values were found to be endothermic: 27.0, 22.7, 32.6, and 34.6 kJ mol(-1) for Cu(II), Ni(II), Co(II), and Zn(II) metal ions, respectively. DeltaS values were calculated to be positive for the sorption of the same sequence of divalent cations onto sorbent. Negative DeltaG values indicated that the sorption process for these three metal ions onto immobilized silica gel is spontaneous.     

Synthesis,X-ray studies,and catalytic activity of tridentate Schiff base dioxo-molybdenum(VI)

The reaction of a solution of MoO₂(acac)₂ in CH₃OH and salicylidene 2-picoloyl hydrazone as a tridentate ONO donor Schiff base (ONO) afford a six-coordinated Mo(VI) complex [MoO₂(ONO)(CH₃OH)], with a distorted octahedral configuration. [MoO₂(ONO)(CH₃OH)] was isolated as an air-stable crystalline solid and fully characterized by single-crystal X-ray structure analysis. [MoO₂(ONO)(CH₃OH)] shows reactivity in the oxidation of sulfides to their corresponding sulfoxides using urea hydrogen peroxide as the oxidant at room temperature under air.