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Showing papers on "Schiff base published in 2004"


Journal ArticleDOI
TL;DR: Practical guidelines for the preparation and use of different Schiff base metal complexes in the field of catalytic transformations are discussed in this tutorial review.
Abstract: Schiff base ligands are considered “privileged ligands” because they are easily prepared by the condensation between aldehydes and imines. Stereogenic centres or other elements of chirality (planes, axes) can be introduced in the synthetic design. Schiff base ligands are able to coordinate many different metals, and to stabilize them in various oxidation states, enabling the use of Schiff base metal complexes for a large variety of useful catalytic transformations. Practical guidelines for the preparation and use of different Schiff base metal complexes in the field of catalytic transformations are discussed in this tutorial review.

1,642 citations


Journal ArticleDOI
TL;DR: The development and application of chiral phase-transfer catalysis (PTC) for the enantioselective synthesis of optically active alpha-amino acid derivatives using achiral Schiff base esters developed in the author's laboratory and by others is reviewed.
Abstract: The development and application of chiral phase-transfer catalysis (PTC) for the enantioselective synthesis of optically active α-amino acid derivatives using achiral Schiff base esters developed in the author's laboratory and by others is reviewed. Phase-transfer catalysts derived from the Cinchona alkaloids have been exploited as inexpensive and attractive organocatalysts in the chiral PTC process. The recent evolution and use of these and other catalytic systems is described.

634 citations



Journal ArticleDOI
TL;DR: Potentiodynamic polarisation and ac impedance studies were carried out on the inhibition of carbon steel in 0.1-M hydrochloric acid solution by various Schiff bases containing heteroaromatic substituents as mentioned in this paper.

309 citations


Journal ArticleDOI
TL;DR: Generation of cis-beta metallosalen and its related complexes, their structural features, and their application to asymmetric syntheses are summarized.
Abstract: Complexes of chiral salen and its related tetradentate Schiff-base ligands adopt three different configurations, trans, cis-α and cis-β. Of these complexes, trans-complexes have been widely used as catalysts for various asymmetric reactions. However, recent studies have disclosed that cis-β metallosalen and its related complexes show unique asymmetric catalyses that cannot be achieved by trans-metallosalen complexes. The present article summarizes generation of cis-β metallosalen and its related complexes, their structural features, and their application to asymmetric syntheses.

306 citations



Journal ArticleDOI
TL;DR: In this paper, new Schiff base chelates of Cu(II), Co(II, Ni(II) and Zn(II)) derived from benzil-2,4-dinitro-phenylhydrazone with aniline have been synthesized.
Abstract: New Schiff base chelates of Cu(II), Co(II), Ni(II) and Zn(II) derived from benzil-2,4-dinitro-phenylhydrazone with aniline have been synthesised. Microanalytical data, molar conductance, and magnetic susceptibility values have been obtained, and IR,1H NMR,13C NMR, UV-Vis, CV and EPR spectral studies have been carried out to suggest tentative structures for the complexes

210 citations


Journal ArticleDOI
TL;DR: In this article, the reaction of aziridines with CO2 and epoxide with CS2 were also examined under the same reaction conditions, and it was shown that the simplest binaphthyldiamino Schiff base gave the highest yield of cyclic carbonate.

180 citations


Journal ArticleDOI
TL;DR: Tridentate/tetradentate Schiff base ligands L(1) and L(2), derived from the condensation of o-vanillin or pyridine-2-aldehyde with N,N-dimethylethylenediammine, react with nickel acetate or perchlorate salt and azide, cyanate, or thiocyanate to give rise to a series of dinuclear complexes.
Abstract: Tridentate/tetradentate Schiff base ligands L1 and L2, derived from the condensation of o-vanillin or pyridine-2-aldehyde with N,N-dimethylethylenediammine, react with nickel acetate or perchlorate salt and azide, cyanate, or thiocyanate to give rise to a series of dinuclear complexes of formulas [Ni(L1)(μ1,1-N3)Ni(L1)(N3)(OH2)]·H2O (1), {[Ni(L1)(μ1,1-NCS)Ni(L1)(NCS)(OH2)][Ni(L1)(μ-CH3COO)Ni(L1)( NCS) (OH2)]} (2) {[2A][2B]}, [Ni(L1)(μ1,1-NCO)Ni(L1)(NCO)(OH2)]·H2O (3), and [Ni(L2-OMe)(μ1,1-N3)(N3)]2 (4), where L1 = Me2N(CH2)2NCHC6H3(O-)(OCH3) and L2 = Me2N(CH2)2NCHC6H3N. We have characterized these complexes by analytical, spectroscopic, and variable-temperature magnetic susceptibility measurements. The coordination geometry around all of the Ni(II) centers is a distorted octahedron with bridging azide, thiocyanate/acetate, or cyanate in a μ1,1 mode and μ2-phenolate oxygen ion for 1−3, respectively, or with a double-bridging azide for 4. The magnetic properties of the complexes were studied by magnetic sus...

177 citations


Journal ArticleDOI
TL;DR: Tetranuclear Fe(II) cubic complexes were synthesized with Schiff base ligands bridging the Fe( II) centers and revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state.
Abstract: Tetranuclear FeII cubic complexes were synthesized with Schiff base ligands bridging the FeII centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4]·2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4]·2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4]·MeOH (5), and [Fe4(3,5-Cl2-sae)4(MeOH)4] (6) (R-sap and R-sae were prepared by condensation of salicylaldehyde derivatives with aminopropyl alcohol and aminoethyl alcohol, respectively) were performed, and their magnetic properties were studied. In 1−6, the alkoxo groups of the Schiff base ligands bridge four FeII ions in a μ3-mode forming [Fe4O4] cubic cores. The FeII ions in the cubes have tetragonally elongated octahedral coordination geometries, and the equatorial coordination bond lengths in 4−6 are shorter than those in 1−3. Dc magnetic susceptibility measurements for 1−6 revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state. Analyses of the magnetization data a...

165 citations


Journal ArticleDOI
TL;DR: A number of dicopper(II) complexes of reduced Schiff base ligands have been synthesized, and the solid-state structures of 4, 5, 10 and 11 have been determined as mentioned in this paper.
Abstract: A number of dicopper(II) complexes of reduced Schiff base ligands, N-(2-hydroxybenzyl)-amino acids [Cu2L2(H2O)x]·yH2O (L = Sgly (1), D-Sala (2), L-Sala (3), DL-Sala (4), Sab2 (5), Sbal (6), Sab4 (7), Sval (8), Shis (9), Styr (10) and Stryp (11), x = 0–2 & y = 0–2) have been synthesized, and the solid-state structures of 4, 5,10 and 11 have been determined. The compounds 4 and 5 are binuclear in which the Cu(II) centres have square-pyramidal geometry with apical sites occupied by aqua ligands. In 10 and 11 one axial site is occupied by water and the other by an oxygen atom of the carboxylate group from the adjacent dimer through oxygen atoms to form 1D helical polymer. Variable temperature magnetic measurements of the dimer 4 and helical polymer 10 showed that they are typical for moderately strong antiferromagnetic coupling. All the complexes show significant catalytic activity on the oxidation of 3,5-di-tert-butylcatechol. The activity measured in terms of Kcat in the range 199–3800 h−1 has been found to follow the order: 7 > 6 > 8 > 3 > 5 ∼ 2 ∼1 > 4 > 10 >9 > 11. The catalytic activity is found to increase with increasing the length of the methylene side chain of the amino acid in the reduced Schiff base ligands.

Journal ArticleDOI
TL;DR: Thermal studies suggest a mechanism for degradation of the metal complexes as function of temperature supporting the chelation modes and show the possibility of obtaining new complexes pyrolytically in the solid state which cannot be synthesized from solution.

Journal ArticleDOI
TL;DR: A vanadyl Schiff base complex having two terminal trimethoxysilyl groups peripheral to the ligand has been used to obtain a MCM-41-like mesoporous organosilicate that has been found to catalyze efficiently the cyanosilylation of carbonyl groups.

Journal ArticleDOI
TL;DR: In this paper, the efficiency of N-(2-hydroxyphenyl)salicyaldimine (1), N,N′-bis-(salicyaldehyde)-1,3-diaminopropane (2), derived from the reduction of N.N.bis.1, 3diamine (3), as corrosion inhibitors has been studied.

Journal ArticleDOI
TL;DR: In this article, a family of chromium complexes bearing tridentate pyridine-based ligands is disclosed as highly active precatalysts for the oligomerization of ethylene.
Abstract: A family of chromium complexes bearing tridentate pyridine-based ligands are disclosed as highly active precatalysts for the oligomerization of ethylene. The ligands are comprised of two distinct types: Type 1, in which both ketone groups of 2,6-diacetylpyridine are converted to imines to produce pyridine bisimine NNN ligands; and Type 2, in which only one ketone group of 2,6-diacetylpyridine is condensed with an aniline derivative to give monoimine NNO coordination sets. Ligands of either type are coordinated to chromium(II) or chromium(III) chlorides, and activation of the resultant complexes with methylaluminoxane (MAO) produces highly active ethylene oligomerization and polymerization catalysts. Catalysts of Type 1 (NNN set) generally produce 1-butene when only two ortho alkyl substituents are present but switch to making waxes or polyethylene when the size and/or number of ortho substituents are increased. Catalysts of Type 2 (NNO set) produce waxes and polyethylene under all of the substitution pat...

Journal ArticleDOI
TL;DR: In this article, neutral complexes of CuII have been synthesised from the Schiff bases derived from salicylidene-4-aminoantipyrine and PhNH2/substituted anilines.
Abstract: Neutral complexes of CuII have been synthesised from the Schiff bases derived from salicylidene-4-aminoantipyrine and PhNH2/substituted anilines. The structural features have been determined from their microanalytical, i.r., u.v.–vis., 1H-, 13C-n.m.r., mass and e.s.r. spectral data. All the complexes exhibit square-planar geometry. Their magnetic susceptibility measurements and low conductance data provide evidence for the monomeric and non-electrolytic natures of the complexes respectively. The electrochemical behaviour of the complexes in MeCN at 298 K was studied. The kinetic parameters were determined and are discussed. The X-band e.s.r. spectra of the complexes in DMSO at 300 and 77 K were recorded and their salient features are reported. The powder XRD diffraction patterns for all the complexes are found to be similar. The antimicrobial activity of the ligands and their copper complexes against the bacteria Staphylococcus aureus, Klebsiella pneumoniae, Salmonella typhi, Pseudomonas aerugenosa and Bacillus subtilis are also reported. The complexes have higher activities than those of the free Schiff bases. Moreover, they have higher activity than the control (ampicillin) except for Klebsiella pneumoniae and Pseudomonas aerugenosa.

Journal ArticleDOI
TL;DR: An octahedral structure has been confirmed for the complexes that were characterized by elemental analyses, Infra red, electronic, electron paramagnetic resonance spectroscopy and cyclic voltammetry and screened for their antibacterial properties.

Journal ArticleDOI
TL;DR: The DFT calculations indicate that for almost all complexes the presence of a sixth equatorial or axial H(2)O ligand leads to much more stable compounds.
Abstract: The Schiff base N,N'-ethylenebis(pyridoxylideneiminato) (H(2)pyr(2)en, 1) was synthesized by reaction of pyridoxal with ethylenediamine; reduction of H(2)pyr(2)en with NaBH(4) yielded the reduced Schiff base N,N'-ethylenebis(pyridoxylaminato) (H(2)Rpyr(2)en, 2); their crystal structures were determined by X-ray diffraction The totally protonated forms of 1 and 2 correspond to H(6)L(4+), and all protonation constants were determined by pH-potentiometric and (1)H NMR titrations Several vanadium(IV) and vanadium(V) complexes of these and other related ligands were prepared and characterized in solution and in the solid state The X-ray crystal structure of [V(V)O(2)(HRpyr(2)en)] shows the metal in a distorted octahedral geometry, with the ligand coordinated through the N-amine and O-phenolato moieties, with one of the pyridine-N atoms protonated Crystals of [(V(V)O(2))(2)(pyren)(2)]2 H(2)O were obtained from solutions containing H(2)pyr(2)en and oxovanadium(IV), where Hpyren is the "half" Schiff base of pyridoxal and ethylenediamine The complexation of V(IV)O(2+) and V(V)O(2) (+) with H(2)pyr(2)en, H(2)Rpyr(2)en and pyridoxamine in aqueous solution were studied by pH-potentiometry, UV/Vis absorption spectrophotometry, as well as by EPR spectroscopy for the V(IV)O systems and (1)H and (51)V NMR spectroscopy for the V(V)O(2) systems Very significant differences in the metal-binding abilities of the ligands were found Both 1 and 2 act as tetradentate ligands H(2)Rpyr(2)en is stable to hydrolysis and several isomers form in solution, namely cis-trans type complexes with V(IV)O, and alpha-cis- and beta-cis-type complexes with V(V)O(2) The pyridinium-N atoms of the pyridoxal rings do not take part in the coordination but are involved in acid-base reactions that affect the number, type, and relative amount of the isomers of the V(IV)O-H(2)Rpyr(2)en and V(V)O(2)-H(2)Rpyr(2)en complexes present in solution DFT calculations were carried out and support the formation and identification of the isomers detected by EPR or NMR spectroscopy, and the strong equatorial and axial binding of the O-phenolato in V(IV)O and V(V)O(2) complexes Moreover, the DFT calculations done for the [V(IV)O(H(2)Rpyr(2)en)] system indicate that for almost all complexes the presence of a sixth equatorial or axial H(2)O ligand leads to much more stable compounds

Journal ArticleDOI
TL;DR: A series of neutral nickel complexes with Schiff-base ligands was synthesized and characterized by X-ray single-crystal analyses in this article, which showed high catalytic activities of up to 3.16 x 10(7) g PNB mol(-1) Ni h(-1), for the addition polymerization of norbornene in the presence of modified methylaluminoxane (MMAO) as cocatalyst.

Journal ArticleDOI
TL;DR: A reliable procedure has been established by use of a catalytic amount of 1% NaOH (aq) and ammonium chloride, which tolerates a wide range of aldehydes to afford the corresponding anti-beta-hydroxy-alpha-amino esters almost exclusively in an essentially optically pure form.
Abstract: A highly efficient direct asymmetric aldol reaction of a glycinate Schiff base with aldehydes has been achieved under mild organic/aqueous biphasic conditions with excellent stereochemical control, using chiral quaternary ammonium salt 1b as a phase-transfer catalyst. The initially developed reaction conditions, using 2 equiv of aqueous base (1% NaOH (aq)), exhibited inexplicably limited general applicability in terms of aldehyde acceptors. The mechanistic investigation revealed the intervention of an unfavorable yet inevitable retro aldol process involving the chiral catalyst. On the basis of this information, a reliable procedure has been established by use of a catalytic amount of 1% NaOH (aq) and ammonium chloride, which tolerates a wide range of aldehydes to afford the corresponding anti-β-hydroxy-α-amino esters almost exclusively in an essentially optically pure form.

Journal ArticleDOI
TL;DR: The obtained results are a contribution to the knowledge of copper(II) Schiff base complexes with ligands of aldimine or ketimine type and form the basis for further preclinical tests of these bioactive agents in biological models of oxidative stress.

Journal ArticleDOI
TL;DR: Variable-temperature magnetic susceptibility measurements and magnetization measurements at 2 K reveal that complexes and have antiferromagnetic coupling while has ferrom electromagnetic coupling which is also confirmed by EPR spectra at 4-300 K.
Abstract: Three new basal–apical, μ2-1,1-azide bridged complexes, [CuL1(N3)]2 (1), [CuL2(N3)]2 (2) and [CuL3(N3)]2 (3) with very similar tridentate Schiff base blocking ligands [L1 = N-(3-aminopropyl)salicylaldimine, L2 = 7-amino-4-methyl-5-azahept-3-en-2-one and L3 = 8-amino-4-methyl-5-azaoct-3-en-2-one) have been synthesised and their molecular structures determined by X-ray crystallography. In complex 1, there is no inter-dimer H-bonding. However, complexes 2 and 3 form two different supramolecular structures in which the dinuclear entities are linked by strong H-bonds giving one-dimensional systems. Variable-temperature (300–2 K) magnetic susceptibility measurements and magnetization measurements at 2 K reveal that complexes 1 and 2 have antiferromagnetic coupling while 3 has ferromagnetic coupling which is also confirmed by EPR spectra at 4–300 K. Magnetostructural correlations have been made taking into consideration both the azido bridging ligands and the existence of intermolecular hydrogen bonds in complexes 2 and 3.

Journal ArticleDOI
TL;DR: The complexes from H(2)L(4) show different stoichiometry ratio and with a variable grade of deprotonation in the ligand, depending upon the salt used and working conditions.

Journal ArticleDOI
TL;DR: In this paper, a phase-transfer-catalyzed direct Mannich reaction of glycinate Schiff base 3 with α-imino ester 4 has been accomplished with high enantioselectivity by the utilization of N-spiro C2-symmetric chiral quaternary ammonium bromide 2 as a catalyst.

Journal ArticleDOI
TL;DR: In this paper, the physicochemical properties of new metal complexes with salicylidine-2-aminobenzimidazole (SABI) were investigated using elemental and thermal analyses, IR, conductometric, solid reflectance and magnetic susceptibility measurements.
Abstract: New metal complexes of Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with salicylidine-2-aminobenzimidazole (SABI) are synthesized and their physicochemical properties are investigated using elemental and thermal analyses, IR, conductometric, solid reflectance and magnetic susceptibility measurements. The base reacts with these metal ions to give 1:1 (Metal:SABI) complexes; in cases of Fe(III), Co(II), Cu(II), Zn(II) and Cd(II) ions; and 1:2 (Metal:SABI) complexes; in case of Ni(II) ion. The conductance data reveal that Fe(III) complex is 2:1 electrolyte, Co(II) is 1:2 electrolyte, Cu(II), Zn(II) and Cd(II) complexes are 1:1 electrolytes while Ni(II) is non-electrolyte. IR spectra showed that the ligand is coordinated to the metal ions in a terdentate mannar with O, N, N donor sites of the phenloic -OH, azomethine -N and benzimidazole -N3. Magnetic and solid reflectance spectra are used to infer the coordinating capacity of the ligand and the geometrical structure of these complexes. The thermal decomposition of the complexes is studied and indicates that not only the coordinated and/or crystallization water is lost but also that the decomposition of the ligand from the complexes is necessary to interpret the successive mass loss. Different thermodynamic activation parameters are also reported, using Coats-Redfern method.

Journal ArticleDOI
TL;DR: It is argued that the vertical movement of a water molecule in the K-to-L transition is a key event determining the directionality of proton translocation in the protein.

Journal ArticleDOI
TL;DR: In this article, a widely applicable approach for the preparation of Pd-complexes supported on silica-based mesoporous and laminar inorganic solids (silica gel, purely siliceous and acidic MCM-41, and delaminated zeolites ITQ-2 and ITQs6) is presented.
Abstract: We present a widely applicable approach for the preparation of Pd-complexes supported on silica-based mesoporous and laminar inorganic solids (silica gel, purely siliceous and acidic MCM-41, and delaminated zeolites ITQ-2 and ITQ-6) which involves the use of the Schiff bases 2-tert-butyl-4-methyl-6{(E)-[(2S)-1-(1-arylmethyl)pyrrolidinyl]imino}methylphenol (aryl=phenyl, 1-naphthyl, 2-naphthyl) as anchored ligands. As an extension of our research in “recyclable catalytic systems” we report results demonstrating the reactivity and recyclability of these systems for the Heck reaction (in a biphasic mode using ethylene glycol and toluene) and Suzuki coupling under phosphine-free conditions. The complexes are insensitive to oxygen or moisture, and no change of their activity was observed when exposed to an open system during the usual operation. No palladium black was observed after an extended reaction time and no residual palladium was detected from the filtrate at the end of the reaction.

Journal ArticleDOI
TL;DR: The ternary copper(II) complexes [Cu(salgly)L] (L = phen, 1, 10-phenanthroline; dpq, dipyridoquinoxaline), where salgly, salala and salphe are tridentate Schiff-base ligands derived from the condensation of salicylaldehyde with glycine, L-alanine and L-phenylalanine, respectively, are prepared and their nuclease activity studied as mentioned in this paper.
Abstract: The ternary copper(II) complexes [Cu(salgly)L] (L = phen, 1; dpq, 2), [Cu(salala)L] (L = phen, 3; dpq, 4) and [Cu(salphe)L] (L = phen, 5; dpq, 6), where salgly, salala and salphe are tridentate Schiff-base ligands derived from the condensation of salicylaldehyde with glycine, L-alanine and L-phenylalanine, respectively, are prepared and their nuclease activity studied (phen, 1,10-phenanthroline; dpq, dipyridoquinoxaline). The crystal structure of 3 displays a distorted square-pyramidal (4+1) coordination geometry in which the ONO-donor Schiff base is bonded to the metal atom in the basal plane. The chelating phen ligand displays an axial-equatorial mode of bonding. The complexes exhibit a d-d band near 670nm and a charge transfer band near 370nm in methanol. The one-electron paramagnetic complexes display axial EPR spectra in DMF glass at 77K, indicating a ${d_{x2-y2}} ^1$ ground state. The complexes are redox-active and exhibit a quasi-reversible CuII/CuI couple in DMF at approximately -0.6 V vs. SCE. They show catalytic activity in the oxidation of ascorbic acid by molecular oxygen. The ability of the complexes to bind calf thymus (CT) DNA follows the order: 2 \approx 4 \approx 6 > 1 \approx 3 \approx 5. Complexes 1-6 show oxidative DNA cleavage activity in the presence of mercaptopropionic acid as a reducing agent. All the complexes show hydrolytic cleavage activity in the absence of light or any reducing agent. The oxidative and hydrolytic DNA cleavage efficiencies follow the order: 2 \approx 4 \approx 6 > 1 \approx 3 \approx 5. The dpq complexes, which have a greater DNA binding ability, display enhanced nuclease activity than their phen analogues. The hydrolytic DNA cleavage rate of 1.8 h-1, observed for 2, is significantly high relative to most of the known copper-based synthetic hydrolases. Mechanistic pathways involved in the nuclease activity of the complexes are discussed.

Journal ArticleDOI
TL;DR: A series of new 3d-4f heterobimetallic Schiff base complexes of the general formula [Zn(μ-L2)Ln(NO3)3(H2O)n] were synthesized and characterized by X-ray crystallography.

Journal ArticleDOI
TL;DR: In this paper, the photochromic and thermochromic properties of trans - N, N "-bis(salicylidene)-1,2-cyclohexanediamine (1), trans - n, N ''-bis (3,5-dichloro-salicidene)1, 2-cycloencoderamide (CBE), trans- n, n ''-isomerization in the excited state.
Abstract: The photochromic and thermochromic properties of trans - N , N ′-bis(salicylidene)-1,2-cyclohexanediamine ( 1 ), trans - N , N ′-bis(3,5-dichloro-salicylidene)-1,2-cyclohexanediamine ( 2 ), trans - N , N ′-bis(3,5-di- t -butyl-salicylidene)-1,2-cyclohexanediamine ( 3 ) and trans - N , N ′-bis(2-hydroxy-naphylidene)-1,2-cyclohexanediamine ( 4 ) were investigated by UV and fluorescence spectroscopies in the crystalline state at various temperatures and the molecular structures of 2 and 4 were determined by single-crystal X-ray diffraction. The existence of the two Schiff base groups on a single molecule does not seem to differentiate the chromobehavior of the present compounds (except possibly for 3 ) with respect to the usual Schiff bases of salicylaldehyde. It is suggested that for this class of compounds also, what determines the thermochromic behavior is the enhanced basicity of the nitrogen atom, due the absence of π,π- and n ,π-conjugation with an aryl ring bound to it. The role of the crystal structure in this case is important only in so far as it affects the electron density on the nitrogen atom. Photochromism, however, is structure dependent and requires space for the generation of the photoproduct that involves cis to trans isomerization in the excited state.