Dioxomolybdenum(VI) complexes of hydrazone phenolate ligands - syntheses and activities in catalytic oxidation reactions

The new cis-dioxomolybdenum (VI) complexes [MoO₂(L²)(H₂O)] (2) and [MoO₂(L³)(H₂O)] (3) containing the tridentate hydrazone-based ligands (H₂L² = N'-(3,5-di-tert-butyl-2-hydroxybenzylidene)-4-methylbenzohydrazide and H₂L³ = N'-(2-hydroxybenzylidene)-2-(hydroxyimino)propanehydrazide) have been synthesized and characterized via IR, ¹H and ¹³C NMR spectroscopy, mass spectrometry, and single crystal X-ray diffraction analysis. The catalytic activities of complexes 2 and 3, and the analogous known complex [MoO₂(L¹)(H₂O)] (1) (H₂L¹ = N'-(2-hydroxybenzylidene)-4-methylbenzohydrazide) have been evaluated for various oxidation reactions, viz. oxygen atom transfer from dimethyl sulfoxide to triphenylphosphine, sulfoxidation of methyl-p-tolylsulfide or epoxidation of different alkenes using tert-butyl hydroperoxide as terminal oxidant. The catalytic activities were found to be comparable for all three complexes, but complexes 1 and 3 showed better catalytic performances than complex 2, which contains a more sterically demanding ligand than the other two complexes.     

Synthesis,electrochemical and antimicrobial studies of mono and binuclear iron(III) and oxovanadium(IV) complexes of [ONO] donor tridentate Schiff-base ligands

Tridentate Schiff bases (H₂L¹ or H₂L²) were derived from condensation of acetylacetone and 2-aminophenol or 2-aminobenzoic acid. Binuclear square pyramidal complexes of the type [M₂(L¹)₂]?·?nH₂O (M?=?Fe–Cl, n?=?0; M?=?VO, n?=?1) were accessed from interaction of H₂L¹ with anhydrous FeCl₃ and VOSO₄?·?5H₂O, respectively. A similar reaction with H₂L², however, produced mononuclear complexes [ML²(H₂O) _x ]?·?nH₂O (M=Fe–Cl, x?=?0, n?=?0; M=VO, x?=?1, n?=?1). The compounds were characterized using elemental analysis, FT-IR, UV-Vis, and NMR (for ligand only), and mass spectroscopies and solution electrical conductivity studies. Magnetic susceptibility measurements suggest antiferromagnetic exchange in binuclear Fe(III) and VO(IV) complexes. Thermo gravimetric analysis (TGA) provided unambiguous evidence for the presence of coordinated as well as lattice water in [VOL²(H₂O)]?·?H₂O. Cyclic voltammetric studies showed well-defined redox processes corresponding to Fe(III)/Fe(II) and VO(V)/VO(IV). In vitro antimicrobial activities of the compounds were investigated against Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas aeroginosa, Escherichia coli, Bacillus subtilis, and Proteus vulgaris. H₂L¹ and its binuclear complexes exhibited pronounced activity against all the microorganisms tested.     

Ligandenaustauschreaktionen von Bis(acetylacetonato)dioxo-molybdän(VI). Kristallstrukturen von [Salicylaldehyd-benzoylhydrazonato(2–)]dioxo-methanol-molybdän(VI) und [Benzoylaceton-benzoylhydrazonato(2–)] dioxo-triphenylphosphanoxid-molybdän(VI)

Ligand Exchange Reactions of Bis(acetylacetonato)dioxo-molybdenum(VI). Crystal Structures of [Salicylaldehyde-benzoylhydrazonato(2–)]dioxo-methanol-molybdenum(VI) and [Benzoylacetone-benzoylhydrazonato(2–)]dioxo-triphenylphosphaneoxide-molybdenum(VI) The products of ligand exchange reactions between bis(acetylacetonato)dioxo-molybdenum(VI) and tridentate diacidic ligands H₂L in the presence of triphenylphosphane were found by mass spectrometry to be complexes of the type MoO₂L. In the case of salicylaldehyde 2-hydroxyanil MoL₂ could also be identified. The compounds MoO₂L were crystallized as complexes with methanol or triphenylphosphane oxide. Crystallographic data see “Inhaltsübersicht”.     

Syntheses, structure, redox and catalytic epoxidation properties of dioxomolybdenum(VI) complexes with Schiff base ligands derived from tris(hydroxymethyl)amino methane

Five kinds of dioxomolybdenum(VI) complexes with Schiff base ligands derived from tris(hydroxymethyl)amino methane are prepared and structurally characterized by X-ray crystallography, which reveals that these complexes adopt a distorted octahedral six-coordinate configuration formed by the tridentate Schiff base ligand, one coordinating water and two binding oxygen atoms. These complexes show good catalytic activities and selectivity in the epoxidation of cyclohexene with t-butylhydroperoxide, especially for complex 4, which could give a nearly 100% of epoxidation conversion and selectivity. Introduction of the electron-withdrawing group to the salicylidene ring of complex strongly increases the effectiveness of a catalyst, but decreases the redox stability of a complex.     

Synthesis, structure studies and electrochemistry of molybdenum(VI) Schiff base complexes in the presence of different donor solvent molecules

The reactions between bis(acetylacetonato)dioxomolybdenum(VI) and Schiff base ligands derived from 5-chlorosalicylaldehyde or 3-ethoxy-salicylaldehye, and 3-methoxy-benzoic hydrazide (m-anisic hydrazide), 2-furoic hydrazide or 2,4-dihydroxy-benzoic hydrazide in the presence of donor solvents yielded cis-dioxomolybdenum(VI) complexes with the general formula MoO₂L(D), where L = tridentate Schiff base ligand and D = dimethylsulfoxide, hexamethylphosphoramide, dimethylformamide, imidazole or methanol. The complexes were characterized by elemental analysis, electronic spectra, IR, ¹H and ¹³C NMR spectroscopies, thermogravimetric analysis, cyclic voltammetry, and the molecular structures of five of the dioxomolybdenum complexes were elucidated by single crystal X-ray diffractometion studies. In general, the complexes adopt an octahedral environment around the Mo center with a cis-oxo configuration. The other coordination sites are occupied by the imino nitrogen, phenoxyl oxygen, hydroxyl oxygen of the tridentate Schiff base and the donor atom of the solvent molecule. The structural data revealed that the labile coordination site, which is occupied by N or O atoms from the donor solvents, has a longer Mo-O or Mo-N bond distance.     

A Series of New Molybdenum(VI) Complexes with the ONS Donor Thiosemicarbazone Ligands

New dioxomolybdenum(VI) complexes were obtained by the reaction of [MoO₂(acac)₂] with 4‐phenylthiosemicarbazone ligands derived from salicylaldehyde, 2‐hydroxy‐1‐naphthaldehyde, 2‐hydroxy‐3‐methoxybenzaldehyde or from 4‐(diethylamino)salicylaldehyde. In all complexes the ligands are coordinated to molybdenum as tridentate ONS‐donors through phenolic‐oxygen, imine‐nitrogen and thiol‐sulphur. Octahedral coordination of each Mo atom is completed either by one neutral donor molecule (D) or by the oxygen atom of the Mo=O unit from the neighbouring molecule. All compounds were characterized by means of chemical analysis, IR spectroscopy, TG and in some cases by DSC measurements, some of them by X‐ray crystallography, and by one and two‐dimensional NMR method.     

Spectral and computational chemistry studies for the optimization of geometry of dioxomolybdenum(VI) complexes of some unsymmetrical Schiff bases as antimicrobial agent

Abstract

This analysis highlights the design, spectroscopic characterization and quantum mechanical calculation of some new dioxomolybdenum(VI) complexes of some dibasic tetradentate Schiff bases. Ligands were derived from mono 5-bromosalicylaldehyde-orthophenylenediamine (^BrSal-OPD) and different 2-hydroxyketone derivatives. The characterization was performed by elemental analysis, FTIR, electronic, ¹H NMR and mass spectra, magnetic and molar conductance studies. Structure of the ligands and complexes were designed depending on experimental data and computational studies. According to all data, distorted octahedral geometry was proposed where oxygen atoms are in cis position. Prepared complexes exhibit moderate antimicrobial properties when evaluated against some pathogenic bacteria and fungi. Pharmacokinetic parameters were calculated to search their biological action, for example, absorption, distribution, metabolism, excretion, and toxicity.     

Organotin (IV) complexes derived from tridentate Schiff base ligands: Synthesis,spectroscopic analysis,antimicrobial and antioxidant activity

Organotin complexes of Schiff bases (derived from the condensation of hydrazides with salicylaldehyde derivatives) were prepared and their characterization was done using several spectroscopic techniques like FTIR, NMR (¹H, ¹³C, and ¹¹⁹Sn) and mass spectrometry. The spectroscopic data of the ligands and their corresponding complexes revealed that the Schiff bases chelated to the tin metal in a tridentate manner through –ONO atoms (oxygen atom of the hydroxyl group of the salicylaldehydic derivatives, the nitrogen atom of azomethine group, and the oxygen atom of enolic group present in the carboxylic acid hydrazides). Around tin atom pentacoordinated geometry was exhibited. The synthesized ligands and their complexes have been assessed for their biological potency (antibacterial, antifungal and antioxidant using Ciprofloxacin, Fluconazole and Ascorbic acid as reference compounds) and few of the compounds showed optimistic activity. The ligands having electron withdrawing group attached showed greater antimicrobial activity as compared to the other ligands. The complexes showed the better activity than the ligands. The general trend followed by the complexes was diphenyl ?> ?dibutyl ?> ?dimethyl substituted complexes. Compound 11 was the most active against microbes. The antioxidant activity increased with electron donating group. The phenyl substituted complexes showed better activity as compared to the dibutyl and dimethyl substituted complexes. Compound 20 was the best antioxidant.     

Synthesis, spectral studies, crystal structures and TDDFT studies of the rhenium(I) complexes of 2,4-dihydroxy-N′-(4-hydroxybenzilidene) benzohydrazide

The rhenium(I) carbonyl bromide complex, [ReBr(CO)₃(HL)], of the ligand derived from 2,4-dihydroxybenzaldehyde and 4-hydroxybenzoic acid hydrazide (HL), has been prepared. HL and its complex have been characterized by elemental analysis, MS, IR, UV-Vis and ¹H NMR spectroscopic methods. The structure of HL and the aqua-complex [Re(OH₂)(CO)₃(L)] where the ligands are monodeprotonated have been elucidated by X-ray diffraction. The structure of [ReBr(CO)₃(HL)] has been calculated from conformational parameters found in the aqua-complex. DFT and TDDFT calculations have been performed to obtain the IR spectra and UV-Vis absorption and emission spectra. The calculated spectra agree with the experimental results.     

Oxomolybdenum(VI) and (IV) complexes of pyrazole derived ONO donor ligands – synthesis,crystal structure studies and spectroelectrochemical correlation

Four cis-dioxomolybdenum complexes of general formula [MoO₂(Lⁿ)EtOH] (n = 1–4) and one oxomolybdenum(IV) complex [MoO(L⁴)EtOH], with potentially tridentate Schiff bases derived from 5-methyl pyrazole-3-carbohydrazide and salicylaldehyde/substituted salicylaldehyde/o-hydroxy acetophenone have been prepared. The Mo(IV) complex is derived from the Mo(VI) dioxo complex by oxotransfer reaction with PPh₃. The complexes are characterized by elemental analysis, electronic spectra, IR, ¹H NMR, and by cyclic voltammetry. All the Mo(VI) species are crystallographically characterized. The complexes have a distorted octahedral structure in which the ligand behaves as a binegative donor one, leaving the pyrazole –N uncoordinated towards the metal center. It is also revealed from the crystal structure that the Mo(VI) center enjoys an NO₅ donor environment.     

Synthesis,spectroscopic, electrochemical and structural characterization of Cu(II) complexes with asymmetric NN′OS coordination spheres

A set of four Cu(II) complexes, [Cu(cdnapen)], [Cu(cdnappd)], [Cu(cdMenappd)] and [Cu(cdMeMeOsalpd)], derived from Schiff base ligands with an asymmetric NN′OS coordination sphere have been synthesized. The molecular and the crystal structures have been determined by X-ray diffractometry. The structural results confirm that the complexes are tetra coordinated. The copper (II) ion coordinates to two nitrogen atoms from the imine moiety of the ligand, a sulfur atom from the methyl dithiocarboxylate moiety and a phenolic oxygen atom. The complexes show an unusual tetrahedral distortion to the square-planar geometry around the metal centre in spite of the pseudomacrocyclic skeleton of the ligand. The complexes were further characterized by cyclic voltammetry and electron paramagnetic resonance spectroscopy. The degree of tetrahedral distortion of the complexes appears to be dependent on the number of carbon atoms of the aliphatic bridge and the nature of the coordinating atoms.     

X-ray diffraction structures of two N-salicylidene tryptophananato diaquocopper(II) complexes: erythro and threo isomers

X-ray crystal structures are reported for two novel N-salicylidene tryptophanato diaquocopper(II) isomers, [Cu(Sal-Trp)(h₂O)₂, erythro (1) and hreo (2). The coordination geometry about the copper in both complexes is approximately square-pyramidal with the tridentate Sal-Trp Schiff base ligand and the oxygen atom O(W1) of one water molecule occupying the corners of a square. The coordination sphere about the copper is completed by an axial OW(2) water molecule. In 1, O(W2) [Cu---O(W2) distance 2.25(1) Å] is at the same side of the indole ring (syn disposition—“erythro” isomer), whereas in 2 the O(W2) and the α-amino acid chain are disposed anti (“threo” isomer), with a longer Cu---O(W2) distance, 2.485 Å. IR, ESR, electronic spectral data and magnetic properties are discussed and related to the copper binding mode derived from the crystal structure determination.     

Nickel(II) complexes of tridentate anthracene based Schiff bases: syntheses,properties and crystal structures

The crystal and molecular structures of Ni(II) complexes with two tridentate anthracene-containing Schiff bases are reported. The Schiff bases were prepared by condensation of 9-anthraldehyde with diethylenetriamine (adien) and with dipropylenetriamine (adipn). Complexes synthesized from Ni(O₂CCH₃)₂·4H₂O and the ligands (1?:?1 mol ratio) crystallize from methanol as [Ni(adien)(O₂CCH₃)₂(H₂O)] (1) and [Ni(adipn)(O₂CCH₃)₂]·2CH₃OH (2·2CH₃OH) in space groups P2₁/n and P2₁2₁2₁, respectively. In 1, the distorted octahedral N₃O₃ coordination sphere around the metal ion is formed by the meridional N₃-donor adien, two mutually trans unidentate acetates and one water molecule. The N₃O₃ coordination sphere constituted by the N₃-donor adipn, one unidentate acetate and one bidentate acetate in 2 can be best described as trigonal bipyramidal. The secondary amine-N of adipn, the O-atom of the unidentate acetate and the midpoint of the two O-atoms of the bidentate acetate occupy the three equatorial positions and two imine-N atoms of adipn lie in axial sites. In the crystal lattice, molecules of 1 exist as discrete dimers due to intermolecular hydrogen bonding and π–π interactions. In contrast, self-assembly of 2 via intermolecular π–π interactions leads to a one-dimensional supramolecular structure.     

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.     

Synthesis,X-ray studies,and catalytic activity of tridentate Schiff base dioxo-molybdenum(VI)

The reaction of a solution of MoO₂(acac)₂ in CH₃OH and salicylidene 2-picoloyl hydrazone as a tridentate ONO donor Schiff base (ONO) afford a six-coordinated Mo(VI) complex [MoO₂(ONO)(CH₃OH)], with a distorted octahedral configuration. [MoO₂(ONO)(CH₃OH)] was isolated as an air-stable crystalline solid and fully characterized by single-crystal X-ray structure analysis. [MoO₂(ONO)(CH₃OH)] shows reactivity in the oxidation of sulfides to their corresponding sulfoxides using urea hydrogen peroxide as the oxidant at room temperature under air.     

Dioxomolybdenum(VI) complexes of hydrazones of two substituted salicylaldehydes: synthesis,structures, and catalytic properties

Dioxomolybdenum(VI) complexes [MoO₂L(CH₃OH)] (L?=?L¹?=?N′-(2-hydroxy-5nitrobenzylidene)isonicotinoylhydrazide for 1, L?=?L²?=?N′-(4-diethylamino-2-hydroxybenzylidene)-4-methylbenzohydrazide for 2) were prepared and structurally characterized by physicochemical and spectroscopic methods and single-crystal X-ray determination. Mo in the complexes is octahedrally coordinated. Both complexes show effective catalysis in oxidation of cyclohexene, vinylbenzene, 1-butylene, and 1-pentene, to their corresponding epoxides. In general, high epoxide yields (over 89%) and selectivity (100%) were observed for all aliphatic and aromatic substrates.     

Synthesis,crystal structure and fluorescence properties of two dinuclear zinc(II) complexes incorporating tridentate (NNO) Schiff bases

Reactions of hydrated zinc(II) trifluoroacetate and sodium azide with two tridentate Schiff bases HL¹ (2-((E)-(2-(dimethylamino)ethylimino)methyl)-4-chlorophenol) and HL² (2-((E)-(2-(dimethylamino)ethylimino)methyl)-4-bromophenol) under the same reaction conditions yielded two dinuclear isostructural zinc(II) complexes, [Zn(L¹)(N₃)]₂ (1) and [Zn(L²)(N₃)]₂ (2), respectively. The complexes were characterized systematically by elemental analysis, UV–Vis, FT-IR, and ¹H NMR spectroscopic methods. Single-crystal X-ray diffraction studies reveal that each of the dinuclear complexes consists of two crystallographically independent zinc(II) ions connected by double bridging phenoxides. All zinc(II) ions in 1 and 2 are surrounded by similar donor sets and display distorted square–pyramidal coordination geometries. The ligands and complexes reveal intraligand ¹(π → π*) flourescence. The enhancement of the fluorescence intensities for the complexes compared to the ligands indicates their potential to serve as photoactive materials.     

Synthesis, X-ray crystal structures, spectroscopic and cyclic voltammetric studies of Cu(II) Schiff base complexes of pyridoxal

Two mononuclear Cu(II) complexes, [Cu(L¹H₂)](ClO₄)_1.25Cl_0.75·1.25H₂O (1) and [Cu(L²H₂)](ClO₄)₂ (2), of the pyridoxal Schiff base ligands N,N′-dipyridoxylethylenediimine (L¹H₂) and N,N′-dipyridoxyl-1,3-propanediimine (L²H₂) are reported. X-ray crystal structures of both complexes are also reported. In both complexes the pyridoxal nitrogen atoms remain protonated. In the solid state, the tetradentate Schiff base ligand is virtually planar in 1, while in 2 the ligand conformation is like an inverted umbrella. In cyclic voltammetry experiments it is found that in these complexes the Cu(III) and Cu(I) states are more easily accessible than in their salen type analogs. The pyridoxal Schiff base complexes are also found to be resistant to oxidative electro-polymerization, unlike their corresponding salicyl aldehyde Schiff base complexes.