Oxovanadium(IV) complex of β-alanine derived ligand immobilised on polystyrene for the oxidation of various organic substrates

Tridentate Schiff base (H₂fsal-β-ala) obtained from 3-formylsalicylic acid and β-alanine has been covalently bonded to divinylbenzene cross-linked chloromethylated polystyrene. This chelating resin, abbreviated as PS-H₂fsal-β-ala (PS = polymeric support), reacts with vanadyl sulfate in DMF to give polymer bound complex, PS-[VO(fsal-β-ala) · DMF], formation of which has been confirmed by various physiochemical methods such as elemental analysis, FT-IR and diffused reflectance spectra, thermo gravimetric analysis, and scanning electron micrograph. Catalytic potential of PS-[VO(fsal-β-ala) · DMF] has been tested for the oxidation of various organic substrates such as benzene, cumene, naphthalene, cyclohexane, styrene, cyclohexene and trans-stilbene in the presence of 30% H₂O₂ as an oxidant. Oxidation products obtained from each substrate have been characterised by gas chromatography and their identities confirmed by gas chromatography–mass spectrometry.     

Oxovanadium(IV) Schiff base complexes derived from 2,2′-dimethylpropandiamine: A homogeneous catalyst for cyclooctene and styrene oxidation

Tetradentate Schiff base ligands, derived from aromatic aldehydes and aliphatic diamine (2,2′-dimethylpropandiamine), and their vanadyl complexes have been prepared and characterized. Catalytic potential of these complexes was tested for the oxidation of cyclooctene and styrene using tert-butylhydroperoxide (TBHP) as oxidant. The effects of molar ratio of oxidant to substrate, temperature and solvent have been studied. Excellent selectivity of epoxidation for cyclooctene and good selectivity for styrene were obtained. The mechanism of oxidation has also been discussed.     

Oxovanadium(IV) salicylidene Schiff base complex anchored on mesoporous silica MCM-41 as hybrid materials: a robust catalyst for the oxidation of sulfides

Oxovanadium(IV) Schiff base complex have been anchored onto the surface of purely siliceous MCM-41 and tested for its activity as catalyst for the oxidation of sulfides. This catalyst could alter this oxidation reaction extremity, exhibiting excellent yields with 100 % selectivity. The intercalation of the complex inside the silica matrix was supported by various characterization techniques like X-ray diffraction, differential thermogravimetric (TG-DTA), BET measurements, UV–Vis diffuse reflectance spectroscopy and Fourier transform infrared spectroscopy (FT-IR). The stability of the catalyst during the course of the reaction was confirmed from its post catalytic FT-IR and XRD analysis. The catalyst could be reused five times without notable loss of its catalytic activity and efficiency which indicates that the metal-Schiff base moiety is intact and the coordination environments are not altered during the reaction.     

Zeolite-encapsulated Ru(III) tetrahydro-Schiff base complex: An efficient heterogeneous catalyst for the hydrogenation of benzene under mild conditions

A series of Ru(III) tetrahydro-Schiff base complexes (denoted as Ru[H₄]-Schiff base with Schiff base = salen, salpn and salcn, see Scheme 1) were encapsulated in the supercages of zeolite Y by flexible ligand method. The prepared catalysts were characterized by X-ray diffraction, diffuse reflectance UV–Vis spectroscopy, Infrared spectroscopy, elemental analysis, as well as N₂ adsorption techniques. It was shown that upon encapsulation in zeolite Y, Ru(III) tetrahydro-Schiff base complexes exhibited higher activity for the hydrogenation of benzene than the corresponding Ru(III)-Schiff base complexes. This indicates that hydrogenation of the CN bond of the Schiff base ligands led to a modification of the coordination environment of the central Ru(III) cations. The stability of the prepared catalysts has also been confirmed against leaching of the complex molecule from the zeolite cavities, as revealed by the result that no loss of catalytic activity was observed within three successive runs with regeneration.     

Covalent anchoring of Mo(VI) Schiff base complex into SBA-15 as a novel heterogeneous catalyst for enhanced alkene epoxidation

Molybdenum(VI) Schiff base complexes modified mesoporous SBA-15 hybrid heterogeneous catalysts were synthesized by the reaction of MoO₂(acac)₂ with mesoporous SBA-15 functionalized by grafting procedures of 3-aminopropyl-triethoxysilane and salicylaldehyde, respectively. The physico-chemical properties of the as-synthesized catalysts were analyzed by ICP-AES, XRD, N₂ adsorption–desorption, FT-IR, SEM, TEM and EDX. The as-synthesized catalysts were effective in the catalytic epoxidation of cyclohexene. The catalytic activity can be further enhanced by silylation of the residual Si–OH groups using Me₃SiCl, which was largely due to the higher content of Mo active sites. The conversion and selectivity reached to 97.78 and 93.99 % using tert-butyl hydroperoxide as oxidant for Mo–CH₃–SA–NH₂–SBA-15, while 81.97 and 89.41 % in conversion and selectivity for Mo–SA–NH₂–SBA-15. At the same time, the catalytic performances of the hybrid materials were further systematically investigated under various reaction conditions (solvent, oxidants and alkenes, etc.). Mo–CH₃–SA–NH₂–SBA-15 catalyst can be recycled effectively and reused four cycles with little loss in activity. In addition, the results from hot filtration demonstrated that the catalytic activity mostly resulted from the heterogeneous catalytic process.     

Schiff base complex of Cu immobilized on MCM-41 as reusable catalyst for efficient oxidative coupling of thiols and oxidation of sulfides using hydrogen peroxide

Schiff base complex of copper-functionalized MCM-41 (Cu-complex@MCM-41) was synthesized and used as an efficient and novel heterogeneous catalyst for the oxidative coupling of thiols into corresponding disulfides and oxidation of sulfides to sulfoxides using hydrogen peroxide (H₂O₂) as the oxidant. An aliphatic and aromatic series of sulfides and thiols including various functional groups were successfully converted into corresponding products. The all products were obtained in good to excellent yields. The mesoporous catalyst is characterized by FT-IR spectroscopy, BET, XRD, SEM, EDS and TGA. Recovery of the catalyst is easily achieved by simple filtration and reused for several consecutive runs without significant loss of its catalytic efficiency.     

Synthesis of tetradentate N4 Schiff base dioxomolybdenum (VI) complex within MCM-41 as selective catalyst for epoxidation of olefins

Covalent grafting of MCM-41 with 3-chloropropyl trimethoxysilane and subsequent reactions respectively with pypr [N,N′-bis(2-pyrrolmethylidenaminopropyl)amine] and complexation with MoO₂(acac)₂ afforded MoO₂pyprMCM-41. X-ray diffraction and nitrogen sorption analyses revealed the preservation of the textural properties of the support as well as accessibility of the channel system despite sequential reduction in surface area, pore volume and pore size. Elemental analyses showed nearly complete complexation of the supported ligands and the presence of 0.24 mmol molybdenum per gram of the catalyst. Epoxidation of cyclooctene, cyclohexene, 1-hexene and 1-octene in the presence of MoO₂pyprMCM-41 with tert-butyl hydroperoxide (TBHP) were carried out with 21–98% conversion under the mild reaction conditions.     

Highly salicylate-selective membrane electrode based on a new thiomacrocyclic Schiff base complex of binuclear copper(II) as neutral carrier

New binuclear metallic complexes of thiomacrocyclic Schiff base, 3,9,13,19 -tetraphenyl-6,16-dithione-1,11-dithio-4,5,7,8,14,15,17,18-octaazacycloeicosa-3,8,13,18-tetraene binuclear metal(II) [M(II)₂-TDDOCT] (M = Cu, Co, Ni), were synthesized and their anion response characteristics were investigated. The performances of the electrodes are considerably influenced by the nature of the central metals. The Cu(II) complex-based electrode exhibited a good selectivity to salicylate anion with an anti-Hofmeister selectivity pattern: Sal⁻ > ClO₄⁻ > SCN⁻ > I⁻ > Benzoate > B_r⁻ > Acetate > F⁻ > SO₃²⁻ > NO₂⁻ > Cl⁻ > NO₃⁻ > SO₄²⁻ > H₂PO₄⁻. The electrode had an excellent linear response to Sal⁻ from 9.0 × 10^− 7 to 1.0 × 10^− 1 M with a slope of − 59.3 mV per decade,a detection limit of 5.0 × 10^− 7 M, and a fast response time within 15 s over the entire concentration series in phosphate buffer solutions of pH 5.0 at 25 °C. Spectroscopic techniques and the influence of lipophilic charged additives on the electrode behavior were used to investigate the response mechanism to Sal⁻. The electrode can be applied to the direct determination of salicylate in human urine and pharmaceutical samples and the results obtained are in accord with the results from a standard method.     

Synthesis,In Vitro,and Computational Studies of PTP1B Phosphatase Inhibitors Based on Oxovanadium(IV) and Dioxovanadium(V) Complexes

One of the main goals of recent bioinorganic chemistry studies has been to design and synthesize novel substances to treat human diseases. The promising compounds are metal-based and metal ion binding components such as vanadium-based compounds. The potential anticancer action of vanadium-based compounds is one of area of investigation in this field. In this study, we present five oxovanadium(IV) and dioxovanadium(V) complexes as potential PTP1B inhibitors with anticancer activity against the MCF-7 breast cancer cell line, the triple negative MDA-MB-231 breast cancer cell line, and the human keratinocyte HaCaT cell line. We observed that all tested compounds were effective inhibitors of PTP1B, which correlates with anticancer activity. [VO(dipic)(dmbipy)]·2 H₂O (Compound 4) and [VOO(dipic)](2-phepyH)·H₂O (Compound 5) possessed the greatest inhibitory effect, with IC₅₀ 185.4 ± 9.8 and 167.2 ± 8.0 nM, respectively. To obtain a better understanding of the relationship between the structure of the examined compounds and their activity, we performed a computer simulation of their binding inside the active site of PTP1B. We observed a stronger binding of complexes containing dipicolinic acid with PTP1B. Based on our simulations, we suggested that the studied complexes exert their activity by stabilizing the WPD-loop in an open position and limiting access to the P-loop.     

Macrocyclic nickel(II) complex and hydrophilic polyurethane film electrodes for the electrocatalytic oxidation and selective detection of norepinephrine

Macrocyclic Ni(II) complex and hydrophilic polyurethane (PU) were used to modify activated glassy carbon (GC) electrodes for the electrocatalytic oxidation and selective detection of norepinephrine (NE). The Ni(II) complex was electropolymerized using cycling potentials, and the Ni(II) complex-modified electrode had a negatively shifted oxidation potential and increased current in phosphate buffer at pH 7.4. The linear range and detection limit were from 0.10 to 10 μM (390 nA μM⁻¹, R=0.999) and 7.7 nM (signal-to-noise ratio, S/N=3) by amperometry with flow injection, respectively. The Ni(II) complex-modified electrodes were coated with hydrophilic PU for higher selectivity. Hydrophilic anionic PU was produced by the hydrolysis of PU containing γ-benzyl l-glutamate (PUBLG) segments. The hydrophilic PU-coated electrodes increased the selectivity for NE over ascorbic acid (AA) and uric acid (UA). Moreover, NE in a human urine sample was detected with higher sensitivity, reproducibility, and stability than by using Nafion-coated electrodes. Therefore, hydrophilic PU and Ni(II) complex can be used as new electrode materials for the electrocatalysis and selective electroanalysis of NE. In particular, hydrophilic PU can be used as an alternative anionic material to Nafion for better urine compatibility.     

Synthesis and characterization of Ti(Tbse)2 and its application as a catalyst for ROP of rac‐Lactide

A novel bis(3,5‐di‐ tert‐butylsalicylaldehyde‐co‐ethanolamine) titanium(IV) complex (Ti(Tbse)₂) was synthesized and structurally characterized. The X‐ray diffraction results showed that the titanium ion was bonded with two 3,5‐di‐tert‐butylsalicylaldehyde‐co‐ethanolamine ligands (Tbse ligands) in O,N,O‐tridentate mode. Experimental results revealed that the Ti(Tbse)₂ complex could efficiently catalyze the ring‐opening polymerization (ROP) of rac‐lactide and showed a well‐controlled manner at 160 °C, and the polymers obtained had a controlled molecular weight and low polydispersity indices. Kinetic studies showed that the polymerization reaction was second order in monomer concentration and first order in catalyst concentration, and the apparent activation energy (E_a = 77.0 kJ mol^?1) and frequency factor (A = 3.3 × 10¹¹) were obtained according to the Arrhenius equation. ¹³C nuclear magnetic resonance spectra and thermogravimetric and differential scanning calorimetry analysis indicated that the polylactide was essentially a heterotactic and thermally stable polymer. Copyright © 2012 Society of Chemical Industry     

Mercapto-Functionalized MCM-41 Anchored Palladium(0) Complex as an Efficient Catalyst for the Heterogeneous Suzuki Reaction

Mercapto-functionalized MCM-41 anchored palladium(0) complex is an efficient catalyst for the heterogeneous Suzuki reaction of arylboronic acids with aryl halides. Our system not only solves the basic problems of catalyst separation and recovery but also avoids the use of phosphine ligands.     

Asymmetric Friedel–Crafts Alkylations of Indoles with Ethyl Glyoxylate Catalyzed by (S)‐BINOL‐Titanium(IV) Complex: Direct Access to Enantiomerically Enriched 3‐Indolyl(hydroxy)acetates

Enantioselective Friedel–Crafts alkylation reactions of a variety of indoles with ethyl glyoxylate, catalyzed by a chiral (S)‐BINOL‐Ti(IV) complex (10 mol %), are reported. The corresponding ethyl 3‐indolyl(hydroxy)acetates were formed in good yields and with high enantiomeric excess (up to 96 %). When methyl pyruvate or p‐chlorophenylglyoxal was used, the bisindole compound was obtained in excellent yield. A possible mechanism is proposed.     

PS负载acac系列钼配合物的合成、表征及其催化性能

以二乙烯苯交联的大孔聚苯乙烯树脂(PS)为载体,首次制备了高分子配体PS-(OCH2CH2)n-acac(n=0,1,2),并在其上组装入了Mo活性中心而成为催化剂--PS-(OCH2CH2)n-acac-Mo(n=0,1,2);用红外光谱分别对高分子配体及催化剂的结构进行了表征.XPS表征证实催化剂中钼以Mo(Ⅵ)价态存在,此外还对催化剂可能存在的结构进行了分析.实验检测了PS-(OCH2CH2)n-acac-Mo (n=0,1,2)在以n(t-BuOOH)=0.1 mol计,n( (◇)):n(t-BuOOH)=3:1,溶剂用量～10 mL,反应温度～80℃,时间～60 min条件下的催化性能.结果表明,在大孔PS载体上,活性组分与载体间增加2个-(OCH2CH2)-距离的臂长,对催化剂催化性能无明显影响;PS-(OCH2CH2)n-acac-Mo催化剂(n=0,1,2)催化环己烯环氧化活性和选择性优异,其中以PS-acac-Mo催化剂最优,环氧环己烷收率在99.5%以上.用于环己烯环氧化反应经循环使用5次后,t-BuOOH转化率仍高达99%以上,催化选择性并未发现明显减低,仍保持在99%以上.     

C3‐Symmetric Titanium(IV) Triphenolate Amino Complexes for a Fast and Effective Oxidation of Secondary Amines to Nitrones with Hydrogen Peroxide

The efficient catalytic oxidation of secondary amines to nitrones using hydrogen peroxide as primary oxidant is described. The titanium(IV) complex 2 bearing a C₃‐symmetrical triphenolate amino ligand has proved to be an air‐ and water‐tolerant complex that efficiently catalyzes secondary amine oxidations at 60 °C without previous activation [catalyst loading as low as 0.01%, yields up to 99%, turnover numbers (TONs) up to 8000 and turnover frequencies (TOFs) up to 11000 h⁻¹).     

Electrogenerated chemiluminescence of ruthenium (II) bipyridyl complex directly immobilized on glassy carbon electrodes

Ru(bpy)₃Cl₂ was used to modify the glass carbon electrodes (GCE) by oxidation and co-deposition on the electrode surface. The modified electrodes were characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). About 2.2 × 10⁻⁹ mol Ru(bpy)₃ ²⁺ was immobilized on the GCE surface (ϕ = 4 mm). The modified GC electrodes showed stable electrochemiluminescence with tripropylamine (TPrA) as the co-reactant with a linear range from 10 to 500 μM (R ² = 0.999). Among the 10 amino acids tested, the modified electrode system showed selective response to arginine and lysine, indicating that the molecular structure played an important role as co-reactant. This simple and sensitive electrode modifying method when combined with flow-injection or liquid chromatography systems has the potential for amino acid analyses.     

Boehmite-supported CuO as a catalyst for catalytic transfer hydrogenation of 5-hydroxymethylfurfural to 2,5-bis(hydroxymethyl)furan

2,5-bis(hydroxymethyl)furan (BHMF) is an important monomer of polyester. Its oxygen-containing rigid ring structure and symmetrical diol functional group establish it as an alternative to petroleum-based monomer with unique advantages for the prodution of the degradable bio-based polyester materials. Herein, we prepared a boehmite-supported copper-oxide catalyst for the selective hydrogenation of 5-hydroxymethylfurfural into BHMF via catalytic transfer hydrogenation (CTH). Further, ethanol successfully replaced conventional high-pressure hydrogen as the hydrogen donor, with up to 96.9% BHMF selectivity achieved under suitable conditions. Through characterization and factor investigations, it was noted that CuO is crucial for high BHMF selectivity. Furthermore, kinetic studies revealed a higher by-product activation energy compared to that of BHMF, which explained the influence of reaction temperature on product distribution. To establish the catalyst structure-activity correlation, a possible mechanism was proposed. The copper-oxide catalyst deactivated following CTH because ethanol reduced the CuO, which consequently decreased the active sites. Finally, calcination of the catalyst in air recovered its activity. These results will have a positive impact on hydrogenation processes in the biomass industry.     

Diethanol amine‐functionalized polymer‐supported palladium (0) complex as catalyst for Suzuki cross‐coupling reaction in water

Diethanol amine‐functionalized polymer‐supported palladium (0) complex as catalyst for Suzuki cross‐coupling reaction in water was synthesized and characterized. The catalyst exhibits excellent catalytic activity and stability in the Suzuki cross‐coupling reaction. Various aryl bromides were coupled with aryl boronic acids in water, under air, and in the presence of 0.5 mol % of the catalyst to afford corresponding cross‐coupled products in high yields at 100°C. Furthermore, the heterogeneous catalyst can be readily recovered by simple filtration and reused for several times only with a slight decrease in its activity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011