Ruthenium(III) tetradentate Schiff-base complexes: spectral,catalytic, and its biocidal efficacy

New six-coordinate ruthenium(III) Schiff-base complexes of general formula [Ru(X)(PPh₃)(L)] (where X = Cl/Br and L = mononucleating bibasic tetradentate ligand derived by condensing actetoacetanilide/acetoacetotoludide with o-aminophenol/o-aminothiophenol/o-aminobenzoic acid in 1 : 2 molar ratio in ethanol) have been synthesized and characterized by physico-chemical and spectroscopic methods. The new ruthenium(III) complexes possess 2NO/2NS metal binding sites and are catalysts for the oxidation of alcohols using molecular oxygen as co-oxidant and in C–C coupling reactions. These complexes possess good biocidal (antibacterial and antifungal) activity.     

Synthesis,characterization, and in vitro antioxidant and anticancer studies of ruthenium(III) complexes of symmetric and asymmetric tetradentate Schiff bases

Ruthenium(III) complexes of three tetradentate Schiff bases with N₂O₂ donors formulated as [RuCl(LL¹)(H₂O)], [RuCl(LL²)(H₂O)] and [RuCl(LL³)(H₂O)] were synthesized and characterized by elemental analyses, molar conductance, FTIR, and electronic spectral measurements. The FTIR data showed that the tetradentate Schiff base ligands coordinate to Ru ions through the azomethine nitrogen and enolic oxygen. The antioxidant activities of the complexes were investigated through scavenging activity on 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radicals. The DPPH activity for [RuCl(LL²)(H₂O)] with IC₅₀ = 0.031 mg mL^?1 was higher than the values obtained for the other Ru(III) compounds. The study revealed that the synthesized Ru(III) complexes of the tetradentate Schiff base exhibited strong scavenging activities against DPPH and moderate against ABTS radicals. In addition, the antiproliferative studies of the complexes were also tested against human renal cancer cells (TK10), human melanoma cancer cells (UACC62), and human breast cancer cells (MCF7) using the SRB assay. The results indicated that the Ru(III) complexes showed low anticancer activities against the tested human cancer cell lines.     

Synthesis,spectroscopic characterization and catalytic activity of cis-dioxidomolybdenum (VI) complexes with chiral tetradentate Schiff bases

New chiral mononuclear cis-dioxidomolybdenum (VI) complexes, MoO ₂ L ¹ –MoO ₂ L ¹⁰ , with tetradentate Schiff bases derived from various substituted salicylaldehydes and 1S,2S-(+)-2-amino-1-(4-nitrophenyl)-1,3-propanediol were synthesized. All complexes were characterized by elemental analysis, circular dichroism, electronic and IR spectroscopy. ¹H NMR and also two-dimensional (COSY, NOESY and gHSQC) NMR measurements made for MoO ₂ L ¹ –MoO ₂ L ¹⁰ complexes show that Schiff bases are coordinated to the MoO₂²⁺ cation, creating facial (fac) and meridional (mer) types of geometrical isomers. Moreover, catalytic activity studies were also performed for all complexes in asymmetric sulfoxidation of thioanisole and epoxidation of styrene, cyclohexene and two monoterpenes, i.e. S(−)-limonene and (−)-α-pinene, using aqueous 30% H₂O₂ or tert-butyl hydroperoxide as the oxygen source.     

Syntheses,characterization and X-ray crystal structures of Ni(II) complexes of tridentate monocondensed and tetradentate dicondensed Schiff bases

Two octahedral complexes [Ni(HL¹)₂](ClO₄)₂ (1) and [Ni(HL²)₂](ClO₄)₂ (2) and a square planar complex [Ni(HL³)]ClO₄ (3) have been prepared, where [HL¹ = 3-(2-amino-ethylimino)-butan-2-one oxime, HL² = 3-(2-amino-propylimino)butan-2-one oxime] and H₂L³ = 3-[2-(3-hydroxy-1-methyl-but-2-enylideneamino)-1-methyl-ethylimino]-butan-2-one oxime. All the complexes have been characterized by elemental analyses, spectral studies and room temperature magnetic moment measurements. The molecular structures of all three compounds were elucidated on the basis of X-ray crystallography; complexes 1 and 2 are seen to be the mer isomers.     

N-donor ligand complexes of nickel,zinc and copper: Comparisons with tetradentate N-donor ligands derived from Schiff bases

The nickel and zinc complexes of 2-aminomethylaniline (AMA) are reported. Both metals form the octahedral complex [M(AMA)₂(ONO₂)₂] (M = Ni, Zn) where the aromatic ligands lie in the meridial plane with the anilino donors trans to one another. The remaining nitrates coordinate axially. A simple comparison with the nitrogen donor disposition (cis/trans) in nickel complexes of tetradentate N₄ donor ligands derived from symmetric Schiff base ligands is presented. The discussion is extended to interrogate the bonding motifs of the nitrate ligands viz –ONO₂ in the nickel complexes of AMA compared to the two motifs (viz O₂NO and ONO₂) that are isolated for the nickel complexes of the macrocycle hexamethyltetraazacyclotetradecane.     

Green synthesis,characterization, and DFT calculations of diorganotin (IV) complexes of Schiff bases

Diorganotin (IV) complexes (1, 2, 3, 4), of the general formula R₂Sn(L)_m have been synthesized where R = n-But, n-Oct; m = 2 when L1 = N-[(Z)-(2-hydroxy-3-methoxybenzylidene)pyrazine-2-carboxamide and m = 1 when L2 = [3,4-bis-{[(E)-(2-hydroxy-3-methoxyphenyl) methylidene]amino}phenyl](phenyl)meth-anone. The prepared Schiff bases and diorganotin complexes have been characterized by elemental analysis, FTIR, and NMR (¹H, ¹³C, and ¹¹⁹Sn) spectroscopic studies. The molecular geometry, thermochemical values, and vibrational frequencies of two complexes in the ground state were calculated using the B3LYP density functional method with LANL2DZ basis set for Sn using Gaussian 09 software. A good correlation of theoretical and experimental results shows that in both the complexes the geometry around the central tin atom is tetrahedral. The studies were further extended to test and compare the in vitro cytotoxic activity of ligands and complexes against MCF-7 cell line by MTT assay. The IC50 values show that cytotoxic activity of ligands increased on complexation with tin metal.     

Ni(II) and Cu(II) complexes with ONNO asymmetric tetradentate Schiff base ligand: synthesis,spectroscopic characterization,theoretical calculations,DNA interaction and antimicrobial studies

A novel Schiff base, namely Z ‐3‐((2‐((E )‐(2‐hydroxynaphthyl)methylene)amino)‐5‐nitrophenylimino)‐1,3‐dihydroindin‐2‐one, was synthesized from the condensation of 2‐hydroxy‐1‐naphthaldehyde and isatin with 4‐nitro‐o ‐phenylenediamine. It was structurally characterized on the basis of ¹H NMR, ¹³C NMR and infrared spectra and elemental analyses. In addition, Ni(II) and Cu(II) complexes of the Schiff base ligand were prepared. The nature of bonding and the stereochemistry of the investigated complexes were elucidated using several techniques, including elemental analysis (C, H, N), Fourier transform infrared and electronic spectroscopies and molar conductivity. The thermal behaviours of the complexes were studied and kinetic–thermodynamic parameters were determined using the Coats–Redfern method. Density functional theory calculations at the B3LYP/6‐311G++ (d, p) level of theory were carried out to explain the equilibrium geometry of the ligand. The optimized geometry parameters of the complexes were evaluated using LANL2DZ basis set. The total energy of highest occupied and lowest unoccupied molecular orbitals, Mullikan atomic charges, dipole moment and orientation are discussed. Moreover, the interaction of the metal complexes with calf thymus DNA (CT‐DNA) was explored using electronic spectra, viscosity measurements and gel electrophoresis. The experimental evidence indicated that the two complexes could strongly bind to CT‐DNA via an intercalation mechanism. The intrinsic binding constants of the investigated Ni(II) and Cu(II) complexes with CT‐DNA were 1.02 × 10⁶ and 2.15 × 10⁶ M⁻¹, respectively, which are higher than that of the standard ethidium bromide. Furthermore, the bio‐efficacy of the ligand and its complexes was examined in vitro against the growth of bacteria and fungi to evaluate the antimicrobial potential. Based on the obtained results, the prepared complexes have promise for use as drugs. Copyright © 2016 John Wiley & Sons, Ltd.     

Transition metal complexes of a Schiff base: synthesis,characterization, and antibacterial studies

Synthesis of a new Schiff base derived from 2-hydroxy-5-methylacetophenone and glycine and its coordination with compounds Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and UO₂(VI) are described. The ligand and complexes have been characterized on the basis of analytical, electrical conductance, infrared, ESR and electronic spectra, magnetic susceptibility measurements, and thermogravimetric analysis. The ligand is a dibasic tridentate (ONO) donor in all the complexes except Zn(II), where it is a monobasic bidentate (OO) donor. The solid state DC electrical conductivity of ligand and its complexes have been measured over 313–398 K, and the complexes were semiconducting. Antibacterial activities of ligand and its metal complexes have been determined by screening the compounds against various Gram (+) and Gram (?) bacterial strains.     

Aluminum complexes of sterically hindered tetradentate Schiff bases: Synthesis, structure, and reactivity toward -caprolactone

The sterically hindered Schiff bases tbmSalenH₂ [tbmSalen = N,N′-1,2-ethylenebis(3-tert-butyl-5-methylsalicylideneimine)] and tbmSalcenH₂ [tbmSalcen = N,N′-trans-1,2-cyclohexanediyl-bis(3-tert-butyl-5-methylsalicylideneimine)] afforded a series of aluminum complexes of the general formulae [Al(tbmSalen)X] and [Al(tbmSalcen)X] (X = Cl, Me, Et). The molecular structure of [Al(tbmSalcen)Cl] was determined by single-crystal X-ray structural analysis which revealed a five-coordinate aluminum center with a distorted square pyramidal geometry. The alkyl complexes were found to oligomerize -caprolactone.     

氯取代二苯基苯甲酰基吡唑酮席夫碱的合成与抑菌活性

酰基吡唑啉酮及其席夫碱是一类杂环β─二酮螯合剂。其活性的双酮配位基可以同多种金属或稀土离子形成大量的配合物,是金属和稀土离子良好的萃取剂和螯合剂[1~5],是一类优良的荧光材料中间体,同时表现出一定的抗菌、抗病毒性能[6~11],目前在药理、生物活性试剂、冶金、染料、发     

Synthesis,characterization and biocidal studies of ruthenium(II) carbonyl complexes containing tetradentate Schiff bases

Stable ruthenium(II) complexes of Schiff bases have been prepared by reacting [RuHCl(CO)(PPh₃)₂(B)] (B = PPh₃, pyridine or piperidine) with bis(o-vanillin)ethylenediimine (valen), bis(o-vanillin)propylene-diimine (valpn), bis(o-vanillin)tetramethylenediimine (valtn), bis(o-vanillin)o-phenylenediimine (valphn), bis(salicylaldehyde)tetramethylenediimine (saltn) and bis(salicylaldehyde)o-phenylenediimine (salphn). These complexes have been characterised by elemental analyses, i.r., electronic, ¹H- and ³¹P{¹H}-n.m.r. spectral studies. In all the above reactions, the Schiff bases replace two molecules of Ph₃P, a hydride and a halide ion from the starting complexes, indicating that the Ru–N bonds present in the complexes containing heterocyclic nitrogen bases are stronger than the Ru–P bond to Ph₃P. The new complexes of the general formula [Ru(CO)(B)(L)] (B = PPh₃, py or pip; L = tetradentate Schiff bases) have been assigned an octahedral structure. Some of the Schiff bases and the new complexes have been tested against the pathogenic fungus Fusarium sp.     

Synthesis,characterization, and antioxidant activity of heterocyclic Schiff bases

Schiff base derivatives have gained great importance due to revealing a great number of biological properties. Schiff bases were synthesized by treatment of 4-amino-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one ( 1 ) with various aldehydes in methanol at reflux. In addition, diamine was reacted with an aldehyde to yield the corresponding Schiff bases. The structures of synthesized Schiff bases were elucidated by spectroscopic methods such as microanalysis, ¹H-NMR, ¹³C-NMR, and FTIR. Antioxidant activities of synthesized Schiff bases were carried out using different antioxidant assays such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH^•) scavenging, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging, and reducing power activity. (E)-4-((1H-indol-3-yl)methyleneamino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one ( 3 ), (E)-1,5-dimethyl-4-((2-methyl-1H-indol-3-yl)methyleneamino)-2-phenyl-1H-pyrazol-3(2H)-one ( 5 ), (E)-1,5-dimethyl-2-phenyl-4-(thiophen-2-ylmethyleneamino)-1H-pyrazol-3(2H)-one ( 7 ), (E)-1,5-dimethyl-2-phenyl-4-(quinolin-2-ylmethyleneamino)-1H-pyrazol-3(2H)-one ( 9 ), (1S,2S,N1,N2)-N1,N2-bis((1H-indol-3-yl)methylene)cyclohexane-1,2-diamine ( 11 ), and (1S,2S,N1,N2)-N1,N2-bis((2-methyl-1H-indol-3-yl)methylene)cyclohexane-1,2-diamine ( 12 ) were synthesized in high yields. Compound 5 displayed a good ABTS^•+ activity. Compound 3 revealed the outstanding activity in all assays. Compound 7 has the best-reducing power ability in comparison to other synthesized compounds. Although compounds 5, 11, 12 are new, compounds 3, 7, 9 are known. Due to revealing a good antioxidant activity, the synthesized compounds ( 3, 5, 7 ) have the potential to be used as synthetic antioxidant agents.     

Nickel(II) complex with an asymmetric tetradentate Schiff base ligand: synthesis,characterization, crystal structure,and DFT studies

Abstract

A new asymmetric tetradentate Schiff base, bis(5-methoxysalicylidene)-4-methylbenzene-1,2-diamine), H₂L, and its Ni(II) complex were prepared and characterized using elemental analyses (CHN), FTIR, UV–Vis, ¹H NMR, and ¹³C{¹H} NMR spectroscopic techniques, and crystal structures of both were determined by X-ray crystallography. For both ligand and Ni(II) complex, density functional theory calculations to find geometry parameters, IR frequencies, electronic properties, and natural bond orbital analysis (NBO) were done with M062X method and Def2-TZVP basis set. All calculated data are consistent with the experiments. NBO data for the Ni(II) complex show that the main type of transition in UV-Vis is interligand charge-transfer, which is assigned as π-π*.     

Synthesis,characterization and antioxidant activities of dioxomolybdenum(VI) complexes of new Schiff bases derived from substituted benzophenones

Abstract

Five novel ONS donor Schiff base ligands were synthesized by the reaction of 2-hydroxybenzophenone (L1), 2-hydroxy-4-methoxybenzophenone (L2), 2-hydroxy-4-octyloxybenzophenone (L3), 2-hydroxy-4-methoxy-4′-methylbenzophenone (L4), and 2-hydroxy-4-allyloxybenzophenone (L5) with thiocarbohydrazide. Neutral solvate dioxomolybdenum(VI) complexes with the general formula [MoO₂L(ROH)], [C1–C5] (L?=?L1, L2, L3, L4, L5 and R?=?CH₃, C₂H₅, or C₄H₉), were prepared from these Schiff bases. Characterization of all compounds was carried out by means of elemental analysis, conductivity measurements, ¹H-NMR, FT-IR, UV-Vis spectroscopy and mass spectrometry (for L1, C2, and C4) techniques. The crystal structures of ligand (L5) and complex (C1) were determined by single-crystal X-ray crystallography. Spectroscopic data and X-ray diffraction studies confirmed that the ligand is coordinated to the cis-MoO₂²⁺ core through ONS, while the sixth coordination site is occupied by solvent (ROH). The ligands and complexes were tested for in vitro antioxidant capacities. The TEAC coefficients of the ligands and complexes were found higher than reference compound. DPPH radical scavenging activities of these compounds were also investigated.     

Organotin(IV) complexes of dibasic tridentate Schiff bases containing ONO donor atoms

Organotin(IV) Schiff base complexes of the type (L)SnR₂ [where R?CH₃, C₆H₅ or CH₂CH₂CO₂ CH₃], (LH)Sn(C₆H₅)₃ and (L)SnCl(CH₂CH₂CO₂ CH₃) [where LH₂?2-N-salicylideneimino-2-methyl-1-propanol, derived from the condensation of salicylaldehyde and 2-amino-2-methyl-1-propanol] have been prepared and characterized on the basis of their elemental analyses, IR, ¹H, ¹³C and ¹¹⁹Sn NMR studies. In these mononuclear complexes the Schiff base acts either as a dianionic tridentate or as a monobasic bidentate moiety by coordinating through an alkoxy group, an azomethine nitrogen and a phenoxide ion to tin. Sulphur dioxide inserts in the tin–methyl/–phenyl bond in the above Schiff base complexes to give tin–O–sulphinates of formulae (L)RSn(SO₂R) and (LH)(C₆H₅)₂Sn(SO₂C₆H₅).     

Systematic studies on mechanochemical synthesis: Schiff bases from solid aromatic primary amines and aldehydes

A versatile and robust mechanochemical route to Aldehyde–Schiff base conversions has been established for a broad range of aldehydes via a simple cogrinding in mortar with a pestle under a solvent‐free, as well as solvent‐assisted, environment. The extent of amines reactivity under these conditions has also been explored, along with an examination of the possible connection between reactivity and electronic substituent effects. Results obtained demonstrated that the solvent‐free mechanochemical conversion of p‐toluidine and aromatic aldehydes to the corresponding Schiff bases proceeded more smoothly than the corresponding synthesis with 4‐aminobenzonitrile. The present approach not only provides good to excellent yields but also eliminates the disadvantages of the traditional synthesis of Schiff bases, such as the use of hazardous solvents, more or less demand of expensive catalysts, and looking for optimization on reaction conditions.     

Thermal and spectral studies on complexes derived from tetradentate Schiff bases

Several new complexes of Schiff bases ligands H₄La and H₄Lb with transition metal ions such as Cr(III), Fe(III), Co(II) and Zn(II) are synthesized. Elemental analysis, infrared, UV–Vis and thermal analysis, as well as conductivity and magnetic susceptibility measurements are used to elucidate the structure of the newly prepared metal complexes. A square planar geometry is suggested for Zn(II) complexes, while an octahedral geometry suggested for the Cr(III), Fe(III) and Co(II) complexes. The thermal decomposition of complexes was found to be first order reaction and the thermodynamic parameters corresponding to the different decomposition steps were reported.     

Synthesis,characterization and evaluation of antidengue activity of enantiomeric Schiff bases derived from S-substituted dithiocarbazate

A series of Schiff bases have been successfully synthesized through the acid-catalyzed condensation of S-substituted dithiocarbazates and three enantiomerically pure monoterpenes, (1 R )-(+)-camphor, (1 S )-(-)-camphor, (1 R )-(-)-camphorquinone, (1 S )-(+)-camphorquinone, ( R )-(-)-carvone and ( S )-(+)-carvone. Spectroscopic results revealed that the Schiff bases containing camphor or carvone likely adopted an E -configuration along the characteristic imine bond while those containing camphorquinone assumed a Z -configuration. The antidengue potential of these compounds was evaluated based on DENV 2 caused cytopathic effect (CPE) reduction-based in vitro evaluation. The compounds were validated through secondary foci forming unit reduction assay (FFURA). Compounds were also tested for their cytotoxicity against Vero cells. The compounds showed variable degrees of antiviral activity with the camphor compounds displaying the highest antidengue potential. The enantiomers of the compounds behaved almost similarly during the antiviral evaluation.