Kinetics and mechanism of the homogeneous reaction between some manganese(III)-Schiff base complexes and hydrogen peroxide in aqueous and sodium dodecyl sulphate solutions

Summary The kinetics of the reaction between H₂O₂ and some Schiff base complexes of Mn^III have been investigated in both aqueous and micellar sodium dodecyl sulphate (SDS) solution. The reaction rate is first order in both H₂O₂ and [complex], and inversely proportional to [H⁺]. The second-order rate constant increases in the sequence [Mn(salophen)(OAc)] > [Mn(salen)(OH₂)]-ClO₄ > [Mn(salen)(OAc)]H₂O, where salen = N,N-bis-(salicylidene)ethylenediamine and salophen = N,N-bis-(salicylidene)-o-phenylenediamine. At SDS concentrations below the critical micellar concentration, there is almost no effect on the rate of reaction whereas at higher concentrations the reaction rate increases slightly. A mechanism involving Mn^II and a peroxo intermediate is proposed.     

Catalytic decomposition of hydrogen peroxide in the presence ofN,N ′-bis(salicylidene)-o-phenylenediamineiron(III) sorbed on to Dowex-50W resin

Summary The tetradentate Schiff-base ligandN, N -bis(salicylidene)-o-phenylenediamine (salph) is very strongly sorbed by cation exchange materials with transition metal counter ions, forming stable complexes. The kinetics of catalytic decomposition of H₂O₂ in the presence of (salph)-Fe^III sorbed on Dowex-50W resin has been studied in aqueous medium. The reaction is first order with respect to [H₂O₂]. The rate constant, k (per g of dry resin) decreased with increasing degree of resin cross-linkage due to a salting out effect. The activation parameters were calculated and a reaction mechanism is proposed.     

Suzuki coupling reaction catalyzed heterogeneously by Pd(salen)/polyoxometalate compound: another example for synergistic effect of organic/inorganic hybrid

A hybrid compound consisting of palladium(salen) [salen = N,N′‐bis(salicylidene)ethylenediamine] complex covalently linked to a lacunary Keggin‐type polyoxometalate, K₈[SiW₁₁O₃₉](POM), was synthesized and characterized by FT‐IR, elemental analysis, inductively coupled plasma and diffuse reflectance UV–visible spectroscopic methods. The hybrid, [Pd(salen)–POM], was investigated in the Suzuki cross‐coupling in EtOH/H₂O under mild reaction conditions. In comparison to the corresponding organic and inorganic moiety, the hybrid has shown greatly improved catalytic activity, and much higher yields toward coupling products were obtained with a low catalyst loading for various aryl halides, including unreactive and sterically hindered ones. The catalyst also exhibited prominent recyclable performance and no obvious loss of activity was observed after six consecutive runs. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,spectroscopy, X-ray crystal structure,and DFT studies on a platinum(II) Schiff-base complex

[PtCl₂(SMe₂)₂] reacts with (N,N′-bis(salicylidene)-1,2-cyclohexanediamine) to give (N,N′-bis(salicylidene)cyclohexane-1,2-diamine)platinum(II). The complex has been characterized by elemental analysis, infrared (IR), UV-Vis, and single-crystal X-ray diffraction. Pt(II) is in a square-planar environment, coordinated by a chelating N₂O₂ donor. Density functional theory (DFT) calculations such as geometry optimization, vibrational frequency, electronic properties, and natural bond orbital (NBO) have been performed for the platinum compound using the OLYP method at TZP(6-311G*) basis set. The optimization calculation shows that the geometry parameters can be reproduced with the OLYP/TZP basis set. Experimental IR frequencies and calculated vibrational frequencies support each other. Time-dependent DFT has been used for absorption wavelengths and results were compared with experimental data. Moreover, NBO analysis has been performed.     

Alternating copolymerization of propylene oxide and carbon dioxide with highly efficient and selective (salen)Co(III) catalysts: Effect of ligand and cocatalyst variation

Synthetic routes to a series of new (salen)CoX (salen = N,N′-bis(salicylidene)-1,2-diaminoalkane; X = Br or pentafluorobenzoate (OBzF₅)) species are described. Several of these complexes are active for the copolymerization of propylene oxide (PO) and CO₂, yielding regioregular poly(propylene carbonate) (PPC) without the generation of propylene carbonate byproduct. Variation of the salen ligand, as well as the inclusion of organic-based ionic or Lewis basic cocatalysts, has dramatic effects on the resultant (salen) CoX catalytic activity. Highly active (R,R)-(salen- 1 )CoOBzF₅ (salen- 1 = N,N′-bis(3,5- di-tert-butylsalicylidene)-1,2-diaminocyclohexane) catalysts with [Ph₄P]Cl or [PPN]Y ([PPN] = bis(triphenylphosphine)iminium; Y = Cl or OBzF₅) cocatalysts exhibited turnover frequencies up to 720 h⁻¹ for rac-PO/CO₂ copolymerization, yielding PPC with greater than 90% head-to-tail connectivity. Additionally, the (R,R)-(salen- 1 )CoOBzF₅/[PPN]Cl catalyst system demonstrated a k_rel of 9.7 for the enchainment of (S)- over (R)-PO when the copolymerization was carried out at low temperatures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5182–5191, 2006     

The synthesis and characterization of melamine based Schiff bases and its trinuclear [salen/salophenFe(III)] and [salen/salophenCr(III)] capped complexes

Four new trinuclear Fe(III) and Cr(III) complexes involving tetradentate Schiff bases N, N′-bis(salicylidene)ethylenediamine-(salenH₂) or bis(salicylidene)-o-phenylenediamine-(salophen H₂) with 2,4,6-tris(4-carboxybenzimino)-1,3,5-triazine have been synthesized and characterized by means of elemental analysis, ¹H NMR, FT-IR spectroscopy, LC-MS, thermal analyses and magnetic susceptibility measurements. The complexes have also been characterized as low-spin distorted octahedral Fe(III) and Cr(III) bridged by COO^? group.     

Role of resin-manganese(II) complexes in hydrogen peroxide decomposition

The kinetics of hydrogen peroxide decomposition has been investigated in the presence of Wofatit KPS (4% DVB, 40–80 μm) resin in the form of mono (mea), di (dea), triethanolamine (tea), ethylenediamine (eda), and N,N′-diethylethylenediamine (deeda)- Mn(II) complexes. The rate constant k (per g dry resin) was evaluated over the temperature range 25–40°C. The reaction was first-order with respect to [H₂O₂]. The rate constant, k, with the three ethanolamines decreased in the following order mea > dea > tea which is the same order of basicity. Also, k value with deeda is lower than eda as a result of steric hindrance. The peroxo metal complex which formed at the beginning of the reaction, was found to contain the catalytic active species. The rate of reaction was proportional to [Mn-complex], [H₂O₂] and [H⁺]^?1. The activation parameters were calculated and a probable reaction mechanism is proposed. © 1994 John Wiley & Sons, Inc.     

The synthesis and characterization of 2,4,6-tris(3,4-dihydroxybenzimino)-1,3,5-triazine and its [salen/salophenFe(III)] and [salen/salophenCr(III)] capped complexes

Four new trinuclear Fe(III) and Cr(III) complexes involving tetradentate Schiff bases N,N′-bis(salicylidene)ethylenediamine-(salenH₂) or bis(salicylidene)-o-phenylenediamine-(salophenH₂) with 2,4,6-tris(3,4-dihydroxybenzimino)-1,3,5-triazine have been synthesized and characterized by means of elemental analysis, ¹H N.M.R., FT-IR spectroscopy, thermal analyses and magnetic susceptibility measurements. The complexes have also been characterized as low-spin distorted octahedral Fe(III) and Cr(III) bridged by catechol group.     

Structural and spectroscopic characterization of Cu(salen) complexes bearing long alkoxy chains

Cu(II) salen (salen?=?N,N′-ethylene-bis(salicylideneimine)) complexes bearing alkoxy chains of C₁₂ (1) and C₁₀ (2) in the salicylidene moieties were synthesized and subsequently characterized by several independent methods: single crystal X-ray diffraction, infrared spectroscopy, mass spectrometry, and UV-Vis spectroscopy. The solid state structures show that the spatial orientation and packing of the complexes are not affected by the alkyl chain length but by a coordinated solvent molecule, as demonstrated by the structure of 1 having methanol in an axial position.     

The Synthesis,Characterization and Conductance Studies of New Cu(II), Ni(Ii) And Zn(II) Complexes with the Schiff Base Derived from 1,2-Bis-(o-Aminophenoxy)Ethane and Salicylaldehyde

Cu(II), Ni(II) and Zn(II) complexes with the Schiff base derived from 1,2-bis-(o-aminophenoxy)ethane with salicylaldehyde have been prepared. The complexes have been characterized by elemental analysis, magnetic measurements, ¹H NMR, ¹³C NMR, UV, visible and IR spectra as well as conductance measurements. The ligand is coordinated to the central metal as a tetradentate ONNO ligand. The four bonding sites are the central azomethine nitrogen and aldehydic OH groups. The ligand was used for complexation studies. Stability constants were measured by a conductometric method. Furthermore, the stability constants for complexation between ZnCl₂ and Cu(NO₃)₂ salts and N,N′-bis(salicylidene)-1,2-bis-(o-aminophenoxy)ethane (H₂L) in 80% dioxane/water and pure methanol were determined from conductance measurements. The magnitudes of these ion association constants are related to the nature of the solvation of the cation and the complexed cation. The mobilities of the complexes are also dependent, in part, upon solvation effects.     

Catalase-like catalytic reaction of the dinuclear manganese–salen complex

Catalase-like activity of a dinuclear manganese-salen (Mn–salen) complex, [Mn(salen)(H₂O)]₂(ClO₄)₂ (salen = N,N ′-bis(salicylidene)-1,2-diaminoethane), was investigated. The dinuclear Mn–salen complex exhibits higher catalase-like activity than that of the mononuclear Mn–salen compound, and its activity can be enhanced by an external base. Different reaction intermediates in the presence and absence of an external base were observed, and the catalytically active species was dimeric as evidenced by UV-Vis spectroscopic studies and mass spectrometry data.     

First MnIII complexes with tetradentate (N2O2) Schiff bases and tricyanomethanide: synthesis,crystal structure,and magnetic properties

The first Mn^III complexes with Schiff bases and tricyanomethanide-anion were synthesized: [Mn(salen)C(CN)₃(H₂O)] (1), [Mn(5-Brsalen)C(CN)₃(H₂O)] (2), [Mn(salpn)C(CN)₃(H₂O)] (3), [Mn(3-MeOsalen)C(CN)₃(H₂O)] (4), [Mn(5-Brsalen)(MeOH)(H₂O)][C(CN)₃] (5), and [Mn(3-MeOsalpn)(H₂O)₂][C(CN)₃] (6), where SalenH₂ is N,N′-bis(salicylidene)ethylenediamine, 5-BrsalenH₂ is N,N′-bis(5-bromosalicylidene)ethylenediamine, SalpnH₂ is N,N′-bis-(salicylidene)-1,3-diaminopropane, 3-MeOsalenH₂ is N,N′-bis(3-methoxysalicylidene)-ethylenediamine, 3-MeOsalpnH₂ — N,N′-bis(3-methoxysalicylidene)-1,3-diaminopropane. The tricyanomethanide anion in complexes 1–4 acts as a the terminal ligand, whereas in complexes 5 and 6 tricyanomethanide is not coordinated by Mn^III and acts as an out-of-sphere counterion. The structures of complexes 1–4 are characterized by the formation of dimers due to hydrogen bonds between the water molecules and oxygen atoms of the Schiff bases. The Mn...Mn distances inside the dimers are 4.69–5.41 Å. Complex 6 has a zigzag chain structure consisting of the [Mn(3-MeOsalpn)(H₂O)₂]⁺ cations bound by double bridging aqua ligands. The study of the magnetic properties of complexes 1, 3, 4, and 6 showed the existence of antiferromagnetic interactions between the Mn^III ions through the system of hydrogen bonds.     

季胺基修饰的Salen配合物的合成及性质

采用季胺基取代的水杨醛(由2,4-二羟基水杨醛、1,2-二溴乙烷、高氯酸钠等为原料合成)合成了两个新型Salen配体N,N'-二{4-[[2-(三甲胺基)乙基]氧化]水杨醛}-邻苯二胺二高氯酸盐(L¹), N-(2-羟基-5-甲基二苯甲基)-N'-{4-[[2-(三甲胺基)乙基]氧化]水杨醛}-邻苯二胺高氯酸盐(L²), 并进一步合成了8个新型Salen金属配合物[ZnL¹, NiL¹, CuL¹, ZnL², NiL², CuL², MnL², CoL²]. 用¹H NMR, ¹³C NMR, FT-IR, UV-vis, MS对配体和配合物进行了表征, 测定了金属配合物的水溶性及在水中的摩尔电导率. 结果表明, 与相应母体配合物的水溶性比较, 含有季胺基修饰的Salen金属配合物的水溶性有了较大提高.     

N,N′‐Bis(2‐hydroxybenzylidene)pentane‐1,5‐diamine

In the title potential O,N,N′,O′‐tetradentate Schiff base ligand {systematic name: 2,2′‐[pentane‐1,5‐diylbis(nitrilomethylidyne)]diphenol}, C₁₉H₂₂N₂O₂, the mutual orientation of the three planar fragments determines the conformation of the molecule. The dihedral angles between the planes of the two salicylidene groups and the plane of the central extended pentane chain are 78.4 (2) and 62.0 (3)°, and the angle between the terminal ring planes is 55.4 (1)°. Strong intramolecular O—H...N hydrogen bonds close almost‐planar six‐membered rings, and the O—H bonds are elongated as a result of hydrogen‐bond formation.     

Synthesis of 1,3,5-tris(4-(4-nitrophenyliminomethyl)phenoxymethyl)benzene as a new Schiff base and its complexation properties with the (salen and salophen)-bridged Fe/Cr(III)

In the present study, we discussed to synthesis of a new Schiff base with nitro groups and its complexation properties with Fe/Cr(III) salen/salophen capped complexes. For this, 1,3,5-tris (formylphenoxymethyl)benzene (1, TRIPOD) involving aldehyde groups was converted to the Schiff base derivative (2, TNPIM-TRIPOD) using 4-nitroaniline. The synthesized compound 2 were reacted with four new trinuclear Fe(III) and Cr(III) complexes involving tetradenta Schiff bases N,N-bis(salicylidene)ethylenediamine-(salenH₂) or bis(salicylidene)-o-phenylenediamine-(salophenH₂). Characterization of all compounds was made with elemental analysis, infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), nuclear magnetic resonance (¹H-NMR), and magnetic susceptibility measurement. The complexes can also be characterized as low-spin distorted octahedral Fe(III) and Cr(III) bridged by nitro groups.     

Trimetallic Nickel–Lanthanum and Nickel–Gadolinium Metallomesogens

Adducts were formed between a mesomorphic Ni(salen) complex [salen=2,2′-N,N′-bis(salicylidene)ethylenediamine] with six terminal alkoxy chains and a lanthanide nitrate (Ln=La, Gd). Different alkoxy chain lengths were used: OC¹²H²⁵, OC¹⁴H²⁹, OC¹⁶H³³ and OC¹⁸H³⁷. Trinuclear nickel–lanthanum and nickel–gadolinium complexes [Ln(NO³)³{Ni(salen)}²] were obtained. The compounds exhibit a wide-temperature-range hexagonal columnar mesophase (Col^H) with rather low melting points. The mesophase stability ranges of both the parent nickel complexes and the nickel–lanthanide complexes decrease with increasing chain length. A decrease in the mesophase stability range over the lanthanide series was also observed. The results are compared with those of similar copper–lanthanide complexes. A marked difference is the higher thermal stability of the nickel–lanthanide complexes in comparison with the copper–lanthanide complexes.     

Synthesis and Characterization of Nickel Oxide Nanoparticles from Ni(salen) as Precursor

Nickel oxide nanoparticles have been synthesized by thermal treatment of N,N′-(bis(salicylidene)-ethylene-1,2-diamine)Nickel(II); [Ni(salen)]; as precursor which has been synthesized via two methods: [Ni(salen)] were obtained by solid state reaction in absence solvent and co-precipitation reaction in presence of propanol as solvent, respectively. Nickel oxide nanoparticles were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy.     

Kinetics and mechanism of the decomposition of hydrogen peroxide catalyzed by Mn(II)-bis-salicylaldimine complexes

Summary The tetradentateSchiff bases N,N-bis(salicylidene) ethylenediamine (salen), N,N-bis-(salicylidene) hexylenediamine (salhex), and N,N-bis(salicylidene)-o-phenylenediamine (sal-o-phen) are very strongly adsorbed by cation exchange resins (Dowex-50W) with manganese(II) as a counter ion, forming stable complexes. The kinetics of the catalytic decomposition of H₂O₂ in presence of these complexes has been studied in aqueous medium. The decomposition reaction is first order with respect to H₂O₂ in the case ofsalen andsal-o-phen and third order in the case ofsalhex. The greater the ligand methylene chain length or the greater the steric effect of the ligand, the greater will be the rate of reaction. The reaction is governed by the entropy of activation. A reaction mechanism is proposed.

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Kinetik und Mechanismus der von Mn(II)-bis-Salicylaldimin — Komplexen katalysierten Zersetzung von Wasserstoffperoxid

Zusammenfassung Die teradentatenSchiffschen Basen N,N-bis-Salicyliden-ethylendiamin (salen), N,N-bis-Salicyliden-Hexylendiamin (salhex) und N,N-bis-Salicyliden-o-phenylendiamin (sal-o-phen) werden von Kationenaustauschen (Dowex-50W) mit Mangan(II) als Gegenion unter der Bildung stabiler Komplexe adsorbiert. Die Kinetik der katalytischen Zersetzung von H₂O₂ in Gegenwart dieser Komplexe wurde in wäßrigem Medium untersucht. Die Zersetzungsreaktion ist erster Ordnung bezüglich H₂O₂ in den Fällensalen undsal-o-phen und dritter Ordnung im Fall vonsalhex. Die Reaktionsgeschwindigkeit steigt mit der Länge der Methylenkette des Liganden und mit dessen Raumbedarf und wird von der Aktivierungsentropie bestimmt. Ein Reaktionsmechanismus wird vorgeschlagen.

     

The first 3-D supramolecular Mn(III) salen complex with 4,4-dicarboxy-2,2-bipyridine: structure and magnetic properties

The Mn(III) salen complex [Mn(salen)(H₂O)₂](dcbp)_0.5 · H₂O (dcbp = 4,4-dicarboxy-2,2-bipyridine, salen = N,N′-ethylenebis-salicylideneaminato) has been isolated under hydrothermal conditions and is structurally characterized. The complex is formed by three independent units, one [Mn(salen)(H₂O)₂], one H₂dcbp, and one guest water molecule, which are further interconnected by hydrogen-bond interactions to form a 3-D supramolecular architecture. IR spectra, UV-Vis spectra, and variable temperature magnetic susceptibility of the complex have been studied. The magnetic study indicated a weak antiferromagnetic interaction between the [Mn(salen)(H₂O)₂] molecules.     

Syntheses of polyfluorophenylcobalt(III) schiff base complexes using organothallium reagents

The complexes RCo(acacen) [R = C₆F₅, p-HC₆F₄, or o-HC₆F₄; H₂acacen = N,N′-ethylenebis(acetylacetonimine)] and RCo(salen) [R = C₆F₅ or p-HC₆F₄; H₂salen = N,N′-ethylenebis(salicylaldimine)] have been prepared by reaction between Co(acacen) or Co(salen) and the appropriate bromobis(polyfluorophenyl)thallium(III) compounds, and have been isolated as pyridinates. Spectroscopic evidence for formation of C₆F₅Co(salophen) [H₂salophen = _N,N′-o-phenylenebis(salicylaldimine)] has also been obtained. The reactivity of the thallium compounds increased in the sequence Ph₂TlBr ? (o-HC₆F₄)2TlBr < (p-HC₆F₄)₂TlBr < (C₆F₅)₂TlBr, and of the cobalt complexes in the sequence Co(salophen) < Co(salen) < Co(acacen). Possible mechanisms are discussed.