Showing papers on "Schiff base published in 2012"
TL;DR: Two new chemically stable [acid and base] 2D crystalline covalent organic frameworks (COFs) were synthesized using combined reversible and irreversible organic reactions and showed strong resistance toward acid and boiling water and exceptional stability in base.
Abstract: Two new chemically stable [acid and base] 2D crystalline covalent organic frameworks (COFs) (TpPa-1 and TpPa-2) were synthesized using combined reversible and irreversible organic reactions. Syntheses of these COFs were done by the Schiff base reactions of 1,3,5-triformylphloroglucinol (Tp) with p-phenylenediamine (Pa-1) and 2,5-dimethyl-p-phenylenediamine (Pa-2), respectively, in 1:1 mesitylene/dioxane. The expected enol–imine (OH) form underwent irreversible proton tautomerism, and only the keto–enamine form was observed. Because of the irreversible nature of the total reaction and the absence of an imine bond in the system, TpPa-1 and TpPa-2 showed strong resistance toward acid (9 N HCl) and boiling water. Moreover, TpPa-2 showed exceptional stability in base (9 N NaOH) as well.
1,202 citations
TL;DR: This tutorial review describes the most significant advances recently made with salphen and related π-conjugated ligand systems.
Abstract: Schiff base ligands have long been successfully employed as ligands in combination with various metals to give catalysts capable of realizing a variety of synthetic transformations. One of the most widely used Schiff base ligands, the “salen” ligand, has been extensively researched. Recently, there has been increased interest in π-conjugated salen systems, known as “salphen” ligands, as a result of the differences in reactivity of the complexes in catalytic applications compared with the salen analogues. Complexes of salphen ligands display interesting photophysical and supramolecular properties which are not always observed with salen systems as a result of their π-conjugation. This tutorial review therefore describes the most significant advances recently made with salphen and related π-conjugated ligand systems.
213 citations
TL;DR: Graphene oxide was used for grafting of oxo-vanadium Schiff base via covalent attachment in this paper, which showed comparable catalytic reactivity as its homogeneous analogue with the added benefits of facile recovery and recycling of the heterogeneous catalyst.
Abstract: Graphene oxide was found to be a convenient and efficient supporting material for grafting of oxo-vanadium Schiff basevia covalent attachment. The low dimensionality and rich surface chemistry of graphene oxide play critical roles in order to achieve a good degree of such grafting. Catalytic potential of the so prepared graphene-bound oxo-vanadium Schiff base and comparison with its homogeneous analogue was studied for the oxidation of various alcohols to carbonyl compounds using tert-butylhydroperoxide as oxidant. The structural and chemical nature of the catalyst was characterized by a variety of techniques including XRD, FTIR, TGA, TEM, and ICP-AES. The immobilized complex was found to be highly efficient and showed comparable catalytic reactivity as its homogenous analogue with the added benefits of facile recovery and recycling of the heterogeneous catalyst. The graphene-bound oxo-vanadium Schiff base was successfully reused for several runs without significant loss in its catalytic activity.
179 citations
TL;DR: In this paper, the corrosion inhibition efficiency of four Schiff bases for carbon steel in 1 M HCl has been studied and the results of electrochemical impedance and Tafel polarization measurements consistently showed that both compounds are good inhibitors.
139 citations
TL;DR: In this article, a multistep method for preparing functionalized superparamagnetic Fe 3 O 4 @SiO 2 possessing high saturation magnetization was reported, which gives notable advantages such as excellent chemoselectivity, mild reaction condition, short reaction times and excellent yields.
Abstract: We report a new multistep method for preparing functionalized superparamagnetic Fe 3 O 4 @SiO 2 possessing high saturation magnetization. During the first step, Fe 3 O 4 @SiO 2 nanosphere core–shell is synthesized using nano-Fe 3 O 4 as the core, TEOS as the silica source and PVA as the surfactant. Then, Schiff base complex of metal is synthesized from the reaction between Schiff base and metal acetates [Co(OAc) 2 , Mn(OAc) 2 , Ni(OAc) 2 , Cu(OAc) 2 , Hg(OAc) 2 , Cr(OAc) 3 and Cd(OAc) 2 ] on the Fe 3 O 4 @SiO 2 surface. The structural and magnetic properties of functionalized magnetic silica are identified by transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) instruments. Moreover, functionalized Fe 3 O 4 @SiO 2 possessed a superparamagnetic characteristic with saturation magnetization value of about 34 emu/g. NMR, FT-IR, elemental analysis and XRD were also used for the identification of these structures. The catalytic ability of Fe 3 O 4 @SiO 2 /Schiff base complex of metal ions was found to be an efficient nanocatalyst for the conversion of aldehydes to their corresponding 1,1-diacetates compounds under mild and solvent-free conditions at room temperature. This method gives notable advantages such as excellent chemoselectivity, mild reaction condition, short reaction times and excellent yields. Also, the aforementioned nanocatalyst can be easily recovered by a magnetic field and reused for subsequent reactions for at least 5 times without noticeable deterioration in catalytic activity.
138 citations
TL;DR: In this article, the reactions of acetate salts of M(II) (Mn, Co, Ni, Cu and Zn) with N-salicylidene-o-aminophenol (saphH 2 ) in ethyl alcohol have been fully characterized by microanalysis, molar conductance, magnetic susceptibility, 1 H NMR, IR, UV-Vis, ESR, mass spectra and thermogravimetric analysis.
137 citations
TL;DR: The results demonstrated that 6, a dizinc(II) complex with potent antiproliferative activity, is able to induce caspase-dependent apoptosis in human cancer cells.
Abstract: A symmetrical macrocyclic dizinc(II) complex (1) has been synthesized by using the ligand (L1) [μ-11,24-dimethyl-4,7,16,19-tetraoxa-3,8,15,20-tetraazatricyclo-[20.3.1.110,13] heptacosa-1(25),2,7,9,11,13(27),14,20,22(26),23-decaene-26,27-diol]. A series of unsymmetrical macrocyclic dizinc(II) complexes (2–6) has been synthesized by Schiff base condensation of bicompartmental mononuclear complex [ZnL] [μ-3,16-dimethyl-8,11-dioxa-7,12-diazadicyclo-[1.114,18] heptacosa-1,3,5(20),6,12,14,16,18(19)-octacaene-19,20-diolato)zinc(II)] with various diamines like 1,2-diamino ethane (L2), 1,3-diamino propane (L3), 1,4-diamino butane (L4), 1,2-diamino benzene (L5), and 1,8-diamino naphthalene (L6). The ligand L1 and all the zinc(II) complexes were structurally characterized. To corroborate the consequence of the aromatic moiety in comparison to the aliphatic moiety present in the macrocyclic ring on the phosphate ester hydrolysis, DNA binding and cleavage properties have been studied. The observed first order rate con...
134 citations
TL;DR: A simple Schiff base type fluorescent receptor 1 was prepared and evaluated for its fluorescence response to heavy metal ions in this paper, and the selectivity of 1 for Zn 2+ is the consequence of combined effects of chelationenhanced fluorescence, C N isomerization, and inhibition of photoinduced electron transfer (PET).
130 citations
TL;DR: In this paper, a Schiff base derived from indole-3-carboxaldehyde and m-aminobenzoic acid was synthesized and characterized by elemental analysis, molar conductance, IR, UV-Vis, magnetic moment, powder XRD and SEM.
130 citations
TL;DR: Kinetic data analysis following Michaelis-Menten treatment reveals that the catecholase activity of the complexes is influenced by the flexibility of the ligand and also by the geometry around the metal ion.
Abstract: Three double phenoxido-bridged dinuclear nickel(II) complexes, namely [Ni2(L1)2(NCS)2] (1), [Ni2(L2)2(NCS)2] (2), and [Ni2(L3)2(NCS)2] (3) have been synthesized using the reduced tridentate Schiff-base ligands 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL1), 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL2), and 2-[1-(3-dimethylamino-propylamino)-ethyl]-phenol (HL3), respectively. The coordination compounds have been characterized by X-ray structural analyses, magnetic-susceptibility measurements, and various spectroscopic methods. In all complexes, the nickel(II) ions are penta-coordinated in a square-pyramidal environment, which is severely distorted in the case of 1 (Addison parameter τ = 0.47) and 3 (τ = 0.29), while it is almost perfect for 2 (τ = 0.03). This arrangement leads to relatively strong antiferromagnetic interactions between the Ni(II) (S = 1) metal centers as mediated by double phenoxido bridges (with J values of −23.32 (1), −35.45 (2), and −34.02 (3) cm3 K mol–1, in the conventi...
128 citations
TL;DR: In this article, a chemosensor based on a phenolic Schiff base bearing a pyrene group (sensor 1) has been synthesized and demonstrated and showed a highly selective colorimetric response to fluoride anions based on deprotonation process and fluorescent response to cyanide anions (606-fold fluorescence quantum yield enhancement) based on cyclization process.
TL;DR: The synthesis of a new highly nitrogen rich porous covalent imine network (CIN-1) material employing simple Schiff base chemistry and further grafting its surface with palladium is reported, which acts as a truly heterogeneous catalyst towards Suzuki C-C coupling reaction between aryl halides with aryalboronic acids.
Abstract: In an effort to expand the realm of possibilities of nitrogen-rich porous materials that could be used in catalysis, herein we report the synthesis of a new highly nitrogen rich (ca. 45%) porous covalent imine network (CIN-1) material employing simple Schiff base chemistry and further grafting its surface with palladium. Pd-loaded CIN-1 support acts as a truly heterogeneous catalyst towards Suzuki C–C coupling reaction between aryl halides with arylboronic acids. High surface area and excellent accessibility of the catalytic sites make it very efficient for heterogeneous catalysis. The stability of the catalyst due to intimate contact between nitrogen-rich organic support and metal allows several reuses with only a minor loss in catalytic activity.
TL;DR: A new oxido-peroxido molybdenum(VI) complex [MoO(O2)L(CH3OH)] was synthesized, using salicylidene benzoyl hydrazine as tridentate ONO donor Schiff base ligand (H2L) as discussed by the authors.
TL;DR: In this paper, a new oxovanadium(IV) Schiff base complex, VIVOL2 (1), was prepared by the reaction of a bidentate Schiff base ligand L and VO(acac)2 (L = N-salicylidin-2-chloroethylimine).
TL;DR: In this paper, the synthesis of two Mo(VI) tetradentate Schiff base complexes derived from 2,2′-dimethylpropylenediamine and aromatic aldehydes is reported.
TL;DR: The novel azomethine, 3-((3,5-dimethylphenylimino)methyl)benzene-1,2-diol (HL) was synthesized and characterized by elemental analysis, FT-IR, (1)H, (13)C NMR spectroscopy and single crystal analysis, and showed remarkable activities in each area of research.
TL;DR: The synthesis, characterization, (1)H NMR, optical absorption and fluorescent properties of a series of amphiphilic Schiff-base bis(salicylaldiminato)zinc(II) complexes are reported and the existence of aggregate species in solutions of non-coordinating solvents is indicated.
Abstract: The synthesis, characterization, 1H NMR, optical absorption and fluorescent properties of a series of amphiphilic Schiff-base bis(salicylaldiminato)zinc(II) complexes are reported. Detailed 1H NMR, DOSY NMR, optical absorption and fluorescence spectroscopy studies indicate the existence of aggregate species in solutions of non-coordinating solvents. The degree of aggregation is related to the nature of the bridging diamine. Chloroform solutions of complexes where the bridging diamine contains a naphthalene or the pyridine nucleus are always characterized by the presence of defined dimer aggregates, whereas oligomeric aggregates are likely formed by complexes where the bridging diamine contains a benzene ring. In coordinating solvents or in the presence of coordinating species, a complete deaggregation of the complexes occurs, because of the axial coordination to the ZnII ion, accompanied by considerable changes in the 1H NMR and optical absorption spectra. The effect of the alkyl chains length seems to play a minor role in the aggregation properties, as noticed by 1H NMR data, optical absorption and fluorescence spectra, which remain almost unaltered on changing the chain length.
TL;DR: In this article, three transition metal coordination complexes, Cu(C18H16N3O2)2·2CH3OH (1), Zn(c18H 16N 3O2), 2·2 CH3CH2O2 (2) and Cd(C16N 3 O2) 2· 2CH3HO (3), were synthesized and characterized by IR, UV, elemental analysis, and X-ray diffraction single crystal analysis.
TL;DR: The synthesis of cationic and anionic species of heavier low-valent group 14 elements of germanium( II) and tin(II) by using the substituted Schiff base 2,6-diacetylpyridinebis(2, 6-diisopropylanil) as Lewis base (LB).
Abstract: Cationic and anionic species of heavier low-valent group 14 elements are intriguing targets in main group chemistry due to their synthetic potential and industrial applications. In the present study, we describe the synthesis of cationic (MCl+) and anionic (MCl3–) species of heavier low-valent group 14 elements of germanium(II) and tin(II) by using the substituted Schiff base 2,6-diacetylpyridinebis(2,6-diisopropylanil) as Lewis base (LB). Treatment of LB with 2 equiv of GeCl2·dioxane and SnCl2 in toluene gives compounds [(LB)GeIICl]+[GeIICl3]− (1) and [(LB)SnIICl]+[SnIICl3]− (2), respectively, which possess each a low-valent cation and an anion. Compounds 1 and 2 are well characterized with various spectroscopic methods and single crystal X-ray structural analysis.
TL;DR: Experiments prove that the addition of n-butyl methyl ether as intermolecular donor per se has no influence on the selectivity of molybdenum dioxo complexes, which prove to be very active and selective in the challenging epoxidation of styrene.
Abstract: Reaction of [MoO(2)(η(2)-tBu(2)pz)(2)] with Schiff base ligands HL(X) (X = 1-5) gave molybdenum(VI) dioxo complexes of the type cis-[MoO(2)(L(X))(2)] as yellow to light brown solids in moderate to good yields. All ligands coordinate via its phenolic O atom and the imine N atom in a bidentate manner to the metal center. The third donor atom (R(2) = OMe or NMe(2)) in the side chain in complexes 1-4 is not involved in coordination and remains pendant. This was confirmed by X-ray diffraction analyses of complexes 1 and 3. Complexes 1, 3, and 5 exist as a mixture of two isomers in solution, whereas complexes 2 and 4 with sterically less demanding substituents on the aromatics only show one isomer in solution. All complexes are active catalysts in the epoxidation of various internal and terminal alkenes, and epoxides in moderate to good yields with high selectivities are obtained. In the challenging epoxidation of styrene, complexes 1 and 2 prove to be very active and selective. The selectivity seems to be influenced by the pendant donor arm, as complex 5 without additional donor in the side chain is less selective. Experiments prove that the addition of n-butyl methyl ether as intermolecular donor per se has no influence on the selectivity. The basic conditions induced by the NMe(2) groups in complexes 3 and 4 lead to lower activity.
TL;DR: Two new copper(I) hydrazone complexes have been synthesised from bivalent copper precursor [CuCl(2)(PPh(3))(2)] and ferrocene containing bidentate hydraz one ligands HL(1) or HL(2) (2) based on the elemental analyses and spectroscopic data.
Abstract: Two new copper(I) hydrazone complexes have been synthesised from bivalent copper precursor [CuCl2(PPh3)2] and ferrocene containing bidentate hydrazone ligands HL1 (1) or HL2 (2). Based on the elemental analyses and spectroscopic data, the complexes are best formulated as [CuL1(PPh3)2] (3) and [CuL2(PPh3)2] (4) of the monovalent copper ion. Solid state structures of ligand 2 and its corresponding complex 4 were also determined. The DNA/albumin interactions of all the synthesised compounds were investigated using absorption, emission and synchronous fluorescence studies. Further, antioxidant properties of all the compounds have also been checked against ABTS, O2− and OH radicals. Additionally, the in vitro cytotoxic activity of compounds 1–4 was assessed using tumour (HeLa, A431) and non-tumour (NIH 3T3) cell lines.
TL;DR: The new selenated Schiff bases L1-L4 which differ in the chain lengths of non-coordinating substituents and their square planar complexes have been synthesized and characterized by multinuclei NMR and the activity of 4 which has ligand L4 has been found highest.
Abstract: The new selenated Schiff bases L1–L4 which differ in the chain lengths (longest in L4) of non-coordinating substituents and their square planar complexes [Pd(L–H)Cl] (1–4) [L = L1–L4, behaving as (Se, N, O−) ligand] have been synthesized and characterized by multinuclei NMR. The molecular structure of 1 has been elucidated by X-ray diffraction on its single crystal [Pd–Se = 2.3965(9) A]. All the complexes 1–4 (0.5 mol%) have been found suitable to catalyze Suzuki–Miyaura coupling reactions under mild conditions. The activity of 4 which has ligand L4 has been found highest. The formation of palladium(0) nano-particles (NPs) stablilized by organoselenium species appears to be the catalytic pathway. The length of the pendent alkyl chain present in the complex molecule unprecedentedly controls the dispersion and composition of these particles and consequently the catalytic activity.
TL;DR: Biological studies, carried out in vitro against selected bacteria, fungi, and K562 leukaemia cell line, have shown that different substituted groups attached at the dithiocarbazate moieties and metals showed distinctive differences in the biological property.
TL;DR: New amphiphilic gelators that contained both Schiff base and L-glutamide moieties were synthesized and their self-assembly in various organic solvents in the absence and presence of metal ions was investigated, showing a chiral recognition ability.
Abstract: New amphiphilic gelators that contained both Schiff base and L-glutamide moieties, abbreviated as o-SLG and p-SLG, were synthesized and their self-assembly in various organic solvents in the absence and presence of metal ions was investigated. Gelation test revealed that o-SLG formed a thermotropic gel in many organic solvents, whilst p-SLG did not. When metal ions, such as Cu(2+), Zn(2+), Mg(2+), Ni(2+), were added, different behaviors were observed. The addition of Cu(2+) induced p-SLG to from an organogel. In the case of o-SLG, the addition of Cu(2+) and Mg(2+) ions maintained the gelating ability of the compound, whilst Zn(2+) and Ni(2+) ions destroyed the gel. In addition, the introduction of Cu(2+) ions caused the nanofiber gel to perform a chiral twist, whilst the Mg(2+) ions enhanced the fluorescence of the gel. More interestingly, the Mg(2+)-ion-mediated organogel showed differences in the fluorescence quenching by D- and L-tartaric acid, thus showing a chiral recognition ability.
TL;DR: Since their fluorescence is selectively quenched by Cu(2+), the sulfonato-Salen-type ligands can be used as highly selective and sensitive turn-off fluorescence sensors for the detection of Cu( 2+) in water and fluorescence imaging in living cells.
24 Apr 2012
TL;DR: In this article, a simple approach to the synthesis of macrocyclic Schiff base ligand resulted from the condensation of bisaldehyde and ethylenediamine was prepared and its complexes were synthesized and characterized using different physicochemical studies as elemental analysis, FT-IR, 1H NMR, conductivity, magnetic properties, thermal analysis, and their biological activities.
Abstract: A novel, simple approach to the synthesis of macrocyclic Schiff base ligand resulted from the condensation of bisaldehyde and ethylenediamine was prepared (7, 8, 15, 16, 17, 18-hexahydrodibenzo (a, g) (14) annulene) (L) and its complexes were synthesized and characterized using different physicochemical studies as elemental analysis, FT-IR, 1H NMR, conductivity, magnetic properties, thermal analysis, and their biological activities. The spectroscopic data of the complexes suggest their 1:1 complexe structures which are investigated by elemental analysis, FT-IR, 1H NMR, conductivity, magnetic properties, thermal analysis, and their biological activities. The spectroscopic studies suggested the octahedral structure for the all complexes. The spectroscopic data of the complexes suggest their structure in which (N2O2) group act as a tetradentate ligand and two chlorides as monodentate ligands. Also electronic spectra and magnetic susceptibility measurements indicate octahedral structure of these complexes. The synthesized Schiff base and its metal complexes also were screened for their antibacterial and antifungal activity. Here we report the effect of a neutral chelating ligand on the complexation with iron to determine it in different types of natural water using recovery test. The activity data show that the metal complexes to be more potent/ antibacterial than the parent Schiff base ligand against one or more bacterial species.
TL;DR: The metal complexes have a promising biological activity comparable with the parent Schiff base ligand against bacterial and fungal species and the NLO properties of the ligand are expected to result in the realization of advanced optical devices in optical fiber communication (OFC) and optical computing.
TL;DR: In this paper, three trinuclear heterometallic nickel(II)manganese (II) complexes were synthesized by using [NiL] as the so-called ligand complex, where H2L = N,N-bis(salicylidene)-1,3-propanediamine.
Abstract: Three new trinuclear heterometallic nickel(II)manganese(II) complexes, [(NiL)2Mn(NCS)2] (1), [(NiL)2Mn(NCO)2] (2), and [{NiL(EtOH)}2Mn(NO2)2]center dot 2EtOH (3), have been synthesized by using [NiL] as the so-called ligand complex [where H2L = N,N'-bis(salicylidene)-1,3-propanediamine] and have been structurally characterized. Crystal structure analyses revealed that complexes 1 and 2 are angular trinuclear species, in which two terminal four-coordinate square planar [NiL] moieties are coordinated to a central MnII through double phenoxido bridges. The MnII is in a six-coordinate distorted octahedral environment that is bonded additionally to two mutually cis nitrogen atoms of terminal thiocyanate (in 1) and cyanate (in 2). In complex 3, in addition to the double phenoxo bridge, the two terminal NiII ions are linked to the central MnII by means of a nitrite bridge (1?N:2?O) that, together with a coordinated ethanol molecule, gives rise to an octahedral environment around the NiII ions and consequently the structure becomes linear. Catecholase activity of these three complexes was examined by using 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate. All three complexes mimic catecholase activity and the rate of catechol oxidation follows saturation kinetics with respect to the substrate and first-order kinetics with respect to the catalyst. The EPR spectra of the complexes exhibit characteristic six line spectra, which indicate the presence of high-spin octahedral MnII species in solution state. The ESI-MS positive spectrum of 1 in the presence of 3,5-DTBC has been recorded to investigate possible complexsubstrate intermediates.
TL;DR: Iron(III) Schiff-base complexes of general formula [Fe(L)(2)Cl]·2H(2)O, where L = N,Ń-bis(salicylidene)ethylenediamine and N,€1,2-phenylenedienine have been encapsulated within various alkali exchanged zeolites and are found to be catalytically active toward the oxidative coupling of 2-napthol.
Abstract: Iron(III) Schiff-base complexes of general formula [Fe(L)2Cl]·2H2O, where L = N,Ń-bis(salicylidene)ethylenediamine and N,N-disalicylidene-1,2-phenylenediamine have been encapsulated within various alkali exchanged zeolites viz. LiY, NaY, and KY by flexible ligand method. The encapsulated complexes are characterized by EDX, scanning electron microscopy (SEM), powder X-ray diffraction (XRD), FT-IR, UV–vis, diffuse reflectance spectroscopy (DRS), electron spin resonance spectroscopy (ESR) and cyclic voltammetry studies. The diffuse reflectance UV–vis spectra of encapsulated complexes show a dramatic red shift of the charge transfer band with increasing electropositivity of the exchangeable cations. The electrochemical analysis predicts the shifting of the reduction potential toward negative values with increasing size of the alkali exchanged cations. The zeolite encapsulated Schiff-base complexes of iron are found to be catalytically active toward the oxidative coupling of 2-napthol. Metal complexes incorpo...
TL;DR: A series of NNO tridentate Schiff base ligands were used to prepare zinc amide and zinc phenoxide complexes that were shown to be efficient l-lactide ring-opening polymerization (ROP) catalysts as discussed by the authors.