Unsymmetrical Schiff Base Complexes Research Articles

Nickel(II) unsymmetrical Schiff base complex immobilized into three dimensional mesoporous silica KIT-6: a novel and efficient catalyst for selective oxidation of sulfides to sulfoxides

Nickel(II) unsymmetrical Schiff base complex immobilized into three dimensional mesoporous silica KIT-6: a novel and efficient catalyst for selective oxidation of sulfides to sulfoxides

Solvent-free selective oxidation of alcohols with tert-butyl hydroperoxide catalyzed by dioxo-molybdenum (VI) unsymmetrical Schiff base complex immobilized on CoFe2O4@SiO2 nanoparticles

Solvent-free selective oxidation of alcohols with tert-butyl hydroperoxide catalyzed by dioxo-molybdenum (VI) unsymmetrical Schiff base complex immobilized on CoFe2O4@SiO2 nanoparticles

Dioxo-molybdenum(VI) unsymmetrical Schiff base complex supported on CoFe2O4@SiO2 nanoparticles as a new magnetically recoverable nanocatalyst for selective epoxidation of alkenes

Dioxo-molybdenum(VI) unsymmetrical Schiff base complex supported on CoFe2O4@SiO2 nanoparticles as a new magnetically recoverable nanocatalyst for selective epoxidation of alkenes

Oxo‐vanadium(IV) unsymmetrical Schiff base complex immobilized on γ‐Fe2O3 nanoparticles: A novel and magnetically recoverable nanocatalyst for selective oxidation of sulfides and oxidative coupling of thiols

In this research, an unsymmetrical salen‐type oxo‐vanadium(IV) complex, [VO(salenac‐OH)] (salenac‐OH = [9‐(2′,4′‐dihydroxyphenyl)‐5,8‐diaza‐4‐methylnona‐2,4,8‐trienato](‐2)), was synthesized and covalently immobilized on the surface of magnetic γ‐Fe2O3 nanoparticles. The resulting γ‐Fe2O3@[VO(salenac‐OH)] nanoparticles were characterized by several techniques including Fourier transform infrared (FT‐IR) spectroscopy, X‐ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM), energy‐dispersive X‐ray (EDX) spectroscopy, vibrating sample magnetometry (VSM), thermal gravimetric analysis (TGA), inductively coupled plasma (ICP), and elemental analysis. The prepared γ‐Fe2O3@[VO(salenac‐OH)] nanoparticle was utilized as an efficient catalyst for selective oxidation of sulfides to sulfoxides using 30% H2O2 as oxidant and oxidative coupling of thiols into disulfides with urea/H2O2 (UHP) as an oxidizing reagent. The products were achieved with good to excellent yields at room temperature with no over‐oxidation of sulfoxides and disulfides to unexpected by‐products. This catalyst can be magnetically recovered by applying an external magnet and reused for five continuous cycles in both oxidation reactions without a significant loss in its catalytic activity. Furthermore, the FT‐IR spectrum and XRD pattern of the recovered catalyst showed no critical change to those of the fresh one.

Tin(IV) Schiff base complexes: Synthesis, thermodynamic and anti bacterial investigation, experimental and theoretical studies

A series of five coordinated diorganotin(IV) unsymmetrical Schiff base complexes have been synthesized. The structure determination and characterization of these complexes were made on the basis of UV-Vis, IR, ( 1 H and 119 Sn) NMR spectroscopy as well as elemental analysis. The binding site of the ligand was identified by IR spectroscopic measurement. Computational analyses at the level of DFT were performed to study its electronic and molecular structures. The molecular geometry, infrared vibrational frequencies, HOMO-LUMO energy gap, dipole moment, Mulliken charges, HF energies were calculated. The theoretical results were consistent with the experimental data reported. The Schiff base ligands and synthesized tin(IV) complexes were screened for their in vitro growth inhibiting activity against different strains of bacteria. Results indicated that the complexes exhibited good antibacterial activities than the ligands. Also the thermodynamic formation constants of the Schiff bases as donors with Me 2 SnCl 2 as an acceptor were measured using UV-Vis spectrophotometric titration for 1:1 complex formation at constant ionic strength (I = 0.1 M NaClO 4 ) and at 25 oC. KEY WORDS : Tin(IV) complexes, Thermodynamic parameter, Biological activity, Computational analyses Bull. Chem. Soc. Ethiop. 2019 , 33(1), 77-90 DOI: https://dx.doi.org/10.4314/bcse.v33i1.8

Second-Order NLO Active Heterotrimetallic Schiff Base Metallopolymer

The new ionic heterotrimetallic unsymmetrically-substituted Schiff base complex [Ni{(η 5-Cp)Fe(η 5-C5H4)-C(=O)CH=C(4-HO-C6H4)NCH2CH2N=CH-(2-O-(η 6-C6H4)Ru(η 5-Cp*)}][PF6] (3; Cp = C5H5 and Cp* = C5(CH3)5) was prepared in 86% yield by a one-pot procedure by mixing equimolar amounts of 4-hydroxyphenyl functionalized ferrocenylenaminone 1, the organometallic aldehyde [(η 5-Cp*)Ru(η 6-2-HO-C6H4CHO)][PF6] (2) and nickel(II) acetate tetrahydrate in refluxing ethanol for 2 h. Its corresponding side-chain metallopolymer 4 was synthesized by reacting the organometallic-inorganic hybrid 3 with polyacrylic acid (DP = 25) in DMF at 110 °C for 48 h with an equimolar quantity of N,N′-dicyclohexylcarbodiimide and a catalytic amount of 4-dimethylaminopyridine. The new complex 3 was characterized by FT-IR and multidimensional NMR spectroscopy, elemental analysis and mass spectrometry. Single crystal X-ray diffraction analysis of 3 showed that the ferrocenyl and [(η 5-Cp*)Ru]+ units exhibit an anti-conformation and are almost coplanar with the unsymmetrical Schiff base complex fragment, while the 4-HO-C6H4 plane is almost perpendicular. The four-coordinate NiII metal ion adopts a square planar geometry, with two nitrogen and two oxygen donor atoms that are mutually trans. Size-Exclusion Chromatography established that metallopolymer 4 is formed of approximately three pendant ionic trimetallic units, while Differential Scanning Calorimetry and Thermal Gravimetric Analysis indicated that 3 and 4 are thermally stable with decomposition temperatures that exceed or border to 250 °C. Harmonic Light Scattering measurements at 1.91 µm incident wavelength showed that compounds 3 and 4 exhibit rather high second-order nonlinear responses, with hyperpolarizability β 1.91 values strongly increasing on passing from the monomeric unit 3 to its metallopolymeric counterpart 4.

Four-coordinate nickel(II) and copper(II) complex based ONO tridentate Schiff base ligands: synthesis, molecular structure, electrochemical, linear and nonlinear properties, and computational study.

We report the synthesis, characterization, crystal structures, nonlinear-optical (NLO) properties, and density functional theory (DFT) calculations of nickel(ii) and copper(ii) complex based ONO tridentate Schiff base ligands: two mononuclear compounds, [Ni(An-ONO)(NC5H5)] (5) and [Cu(An-ONO)(4-NC5H4C(CH3)3)] (6), and two heterobimetallic species, [M(Fc-ONO)(NC5H5)] (M = Ni, 7; Cu, 8), where An-ONOH2 (3) and Fc-ONOH2 (4) are the 1 : 1 condensation products of 2-aminophenol and p-anisoylacetone and ferrocenoylacetone, respectively. These compounds were characterised by microanalysis, FT-IR and X-ray crystallography in the solid state and in solution by UV-vis and (1)H and (13)C NMR spectroscopy. The crystal structures of 3-5, 7 and 8 have been determined and show for Schiff base complexes 5, 7 and 8 a four-coordinated square-planar environment for nickel and copper ions. The electrochemical behavior of all derivatives 3-8 was investigated by cyclic voltammetry in dichloromethane, and discussed on the basis of DFT-computed electronic structures of the neutral and oxidized forms of the compounds. The second-order NLO responses of 3-8 have been determined by harmonic light scattering measurements using a 10(-2) M solution of dichloromethane and working with a 1.91 μm incident wavelength, giving rather high β1.91 values of 350 and 290 × 10(-30) esu for the mononuclear species 5 and 6, respectively. The assignment and the nature of the electronic transitions observed in the UV-vis spectra were analyzed using time-dependent (TD) DFT calculations. They are dominated by LMCT, MLCT and π-π* transitions.

Synthesis, structural investigation and kinetic studies of uranyl(VI) unsymmetrical Schiff base complexes

Uranyl(VI) complexes with unsymmetrical N2O2 Schiff base ligands were synthesized and characterized. Their characterization was performed using UV-Vis, 1H NMR, cyclic voltammetry, single-crystal X-ray crystallography, IR, TG and C.H.N. techniques. X-ray crystallography of the complexes show that beside coordination of the tetradentate Schiff base, one DMF molecule is also coordinated. In order to investigate the effect of the substitutional groups of the Schiff base on the oxidation and reduction potentials, we used the cyclic voltammetry method. Electrochemistry of these complexes showed that the presence of electron releasing groups accelerates oxidation of the complexes. The kinetics of thermal decomposition was studied using thermal gravimetric method (TG) and Coats-Redfern equation. According to Coats-Redfern plots, the kinetics of thermal decomposition of the studied complexes is first-order in all stages. Also the kinetics and mechanism of the exchange reaction of the coordinated solvent with tributylphosphine was carried out in solution, using spectrophotometric method. As a result, the second order rate constants at four temperatures and the activation parameters were calculated showing an associative mechanism for all corresponding complexes. It was concluded that the steric and the electronic properties of the complexes influence the reaction rate significantly.

Transformation of a ditopic Schiff base nickel(II) nitrate complex into an unsymmetrical Schiff base complex by partial hydrolytic degradation: structural and density functional theory studies

A new Schiff base complex [Ni(H2L1)(NO3)](NO3) (1) (H2L1 = 3-[N,N′-bis-2-(5-bromo-3-(morpholinomethyl) salicylideneamino) ethyl amine]) was synthesized from reaction of the ditopic ligand H2L1 with Ni(NO3)2 in anhydrous MeOH. Complex 1 is stable in the solid state, but prone to hydrolysis. Recrystallization of 1 from wet MeOH led to the isolation of a novel unsymmetrical complex [Ni(HL2)(NO3)](NO3) (2) (HL2 = 2-[(2-(2-aminoethylamino) ethylimino) ethyl)-5-bromo-3-(morpholino methyl) salicylidene amine]). X-ray single-crystal analysis of complex 2 showed that complex 1 had undergone partial decomposition of one imine bond. In contrast, the Schiff base complex [Ni(HL3)](NO3) (3) (H2L3 = N,N′-bis(5-methyl-salicylidene) diethylenetriamine) was stable in wet methanol, and the single-crystal structure of 3 showed that the Ni(II) center was coordinated in an unsymmetrical square planar geometry. Density functional theory calculations were performed in order to obtain a geometry-optimized model of complex 1, in which the Ni(II) center was coordinated in a similar manner as that in complex 3. The thermodynamic parameters were calculated, in order to rationalize the difference in hydrolytic reactivity between complexes 1 and 3.

A Facile Access to New Polymethylmethacrylate-Anchored Ferrocene Substituted Nickel(II) Unsymmetrical Schiff Base Complexes: Synthesis and Characterization

This paper discloses two new side-chain metallopolymers containing an unsymmetrical organometallic Schiff base complex of Ni(II) linked to a polymethylmethacrylate (PMMA) matrix. The neutral ferrocene substituted Schiff base complex 1, Ni{CpFe(η5-C5H4)-C(O)CH=C(CH3)N–o-C6H4N=CH-(2-O,5-OH-C6H3)} where (Cp = η5-C5H5), was synthesized via template reaction by condensation of the tridentate half-unit metalloligand Fc-C(O)CH=C(CH3)-N(H)-o-C6H4NH2 (Fc = ferrocenyl = CpFe(η5-C5H4)) with 2,5-dihydroxybenzaldehyde in the presence of nickel(II) acetate tetrahydrate. The binuclear Schiff base complex of Ni(II) containing an aromatic free hydroxyl group was reacted under basic conditions with PMMA to afford, upon trans-esterification reaction, metallopolymers 2 (complex 1 monomeric unit/PMMA = 1/5) and 3 (complex 1 monomeric unit/PMMA = 1/3). Elemental analysis, FT-IR, 1H and 13C NMR spectroscopies, and cyclic voltammetry were utilized to characterize the newly synthetized compounds. Surface morphology of the metallopolymer film of 2 was studied using atomic force microscopy.

Ruthenium(II) Carbonyl Complexes Containing Unsymmetrical Schiff Bases: Synthesis, Characterization, and Catalytic Applications

Unsymmetrical Schiff base complexes of general formula [Ru(CO)(B)(L)] (B = PPh3, AsPh3, or Py; L = dianion of unsymmetrical Schiff base ligand) have been synthesized from the reaction of [RuHCl(CO)(EPh3)2(B)] (E = P or As; B = PPh3, AsPh3, or Py) with unsymmetrical Schiff bases. The new synthesized complexes were characterized by using elemental analysis, IR spectra, electronic spectra, 1H-NMR, 13C-NMR, and 31P-NMR spectra. All the complexes were tentatively assigned an octahedral geometry. The catalytic activities of the synthesized complexes have been studied and found that the complexes showed efficient catalytic activity for oxidation of alcohols and reduction of ketones.

Synthesis, characterization, antibacterial, and thermal studies of unsymmetrical Schiff-base complexes of cobalt(II)

Cobalt(II) complexes of a new series of unsymmetrical Schiff bases have been synthesized and characterized by their elemental analyses, melting points, magnetic susceptibility, thermogravimetric analysis, differential scanning calorimetry, infrared (IR), and electronic spectral measurements. The purity of the ligands and the metal complexes are confirmed by microanalysis, while the unsymmetrical nature of the ligands was further corroborated by 1H-NMR. Comparison of the IR spectra of the Schiff bases and their metal complexes confirm that the Schiff bases are tetradentate and coordinated via N2O2 chromophore. The magnetic moments and electronic spectral data support square-planar geometry for the cobalt(II) complexes. The complexes were thermally stable to 372.3°C and their thermal decomposition was generally via the partial loss of the organic moiety. The Schiff bases and their complexes were screened for in vitro antibacterial activities against 10 human pathogenic bacteria and their minimum inhibitory concentrations were determined. Both the free ligands and cobalt(II) complexes exhibit antibacterial activities against some strains of the microorganisms, which in a number of cases were comparable with, or higher than, that of chloramphenicol.

Synthesis, spectral, and catalytic studies of ruthenium(II) unsymmetrical Schiff-base complexes

Unsymmetrically-substituted ruthenium(II) Schiff-base complexes, [Ru(CO)(B)(L x )] [B = PPh3, AsPh3 or Py; L x = dianion of tetradentate unsymmetrical Schiff-base ligand; x = 4–7, L4 = salen-o-hyac, L5 = valen-o-hyac, L6 = salphen-o-hyac, L7 = valen-2-hacn], were prepared and characterized by analytical, IR, electronic, and 1H NMR spectral studies. The new complexes were tested for their catalytic activity towards the oxidation of benzylalcohol to benzaldehyde.

Synthesis, characterization and X-ray crystal structure of an allyloxo functionalized nonsymmetric nickel coordination complex based on N2O2 chelating ferrocenyl ligand

Abstract The synthesis of the new air and thermally stable orange neutral dinuclear iron–nickel unsymmetrical Schiff base complex, [8-(2-oxo,5-allyloxo-phenyl)-4,7-diaza-3-methyl-1-ferrocenyl-1-one-octa-1,3,7-trienato]nickel(II) (2), was achieved via the Williamson coupling reaction between the 2-oxo,5-hydroxyphenyl precursor 1 and allyl chloride in the presence of base. Complex 2 was isolated in 68% yield and characterized by IR, UV–Vis, 1H and 13C NMR spectroscopy, HRMS and authenticated by a single crystal X-ray diffraction analysis. The organometallic/inorganic hybrid complex 2 consists in a ferrocenyl fragment linked to a classical Werner-type complex made of an unsymmetrical quadridentate N2O2 Schiff base ligand with a pendant allyl ether functionality as a potential anchoring group. The Ni(II) center displays a square-planar geometry with the nitrogen and oxygen atoms occupying mutually trans positions. The structure of 2 · H2O shows that the water crystallization molecule interacts through two distinct intermolecular hydrogen bonds with the two oxygen atoms of the tetradentate N2O2 acyclic chelating ligand, forming in the solid state, a distorted six-membered ring.

Synthesis, characterization and biological studies on unsymmetrical Schiff-base complexes of nickel(II), copper(II) and zinc(II) and adducts with 2,2′-dipyridine and 1,10-phenanthroline

A series of metal(II) unsymmetrical Schiff-base complexes, {M(C10H6OCH:N(CH2)2N : C(CH3)CH : C(CH3)O), where M=Ni(II), Cu(II) and Zn(II)}, and their 2,2′-dipyridine (bipy) and 1,10-phenanthroline (phen) adducts are synthesized and characterized by microanalysis, magnetic susceptibility, conductance, IR and UV-Vis spectra. The ligand coordinates using the N2O2 chromophore to give a two-metal-center four-coordinate square-planar geometry. IR and UV-Vis spectra are consistent with octahedral adducts. The compounds are non-electrolytes in nitromethane and magnetic moments indicate that the complexes are magnetically dilute. The antimicrobial activity of the compounds against ten bacteria and one fungus are reported. The Cu(II) and Zn(II) complexes showed good activity against many of the organisms while their adducts are generally not sensitive. The minimum inhibitory concentrations (MICs) of the sensitive compounds are between 3.0–13.0 mg mL−1.

Organometallic–Inorganic Conjugated Unsymmetrical Schiff-Base Hybrids. Synthesis, Characterization, Electrochemistry and X-ray Crystal Structures of Functionalized Trinuclear Iron–Nickel–Ruthenium Dipolar Chromophores

The synthesis of neutral dinuclear iron–nickel unsymmetrical Schiff base complexes 3 and 4 was achieved via a template reaction involving equimolar amounts of alkyl or aryl “half-unit” precursors, respectively, Fc–C(O)CH=C(CH3)N(H)R (1: R = CH2CH2NH2; 2: R = o-C6H4NH2; Fc = CpFe(η5-C5H4); Cp = η5-C5H5), 5-bromosalicylaldehyde and nickel(II) acetate tetrahydrate in a refluxing CH2Cl2/MeOH (1:1) mixture. The ionic trinuclear unsymmetrical complex 5 was prepared by reacting its dinuclear precursor 3 with the arenophile source, [Cp*Ru(NCCH3)3]PF6 (Cp* = η5-C5(CH3)5), in refluxing CH2Cl2 for 2 h, whereas the trinuclear species 6 was formed upon regioselective π-complexation of the 5-bromosalicylidene ring of 4 by [Cp*Ru]+ at room temperature overnight. All the new compounds were adequately characterized by analytical and spectroscopic techniques and, in addition, the crystal and molecular structures of the “half-unit” 1, the binuclear complex 4 and its hemisolvate adduct 4 · 0.5CH3OH, the trinuclear Schiff base compound 5 · 2(CH3)2CO, and the mixed sandwich metalloligand 7 have been determined by X-ray crystallography. Both organometallic–inorganic hybrids 5 and 6 contain the neutral electron-releasing ferrocenyl group, and the cationic electron-withdrawing ruthenium mixed sandwich, linked through the unsymmetrical tetradentate Schiff base complex {Ni(ONNO)}. UV–vis, 1H and 13C NMR as well as electrochemical data clearly indicate a mutual donor–acceptor electronic influence between the organometallic termini. Furthermore, X-ray crystal structure analysis of 5 · 2(CH3)2CO reveals the partial delocalization of bonding electron density throughout the dinucleating nickel Schiff base ligand.

Trinuclear π-conjugated chromophores formed by a neutral ferrocenyl group and a cationic mixed ruthenium sandwich linked through an unsymmetrical Schiff-base complex spacer

The synthesis of neutral dinuclear unsymmetrical Schiff base complexes 1 and 2 was carried out in an one-pot two-step reaction sequence that involves the reaction of 1-ferrocenyl-1,3-butanedione with an excess of ethylenediamine in refluxing CH2Cl2, to generate the intermediate “half-unit” Fc–C(O)CH2C(CH3)NCH2CH2NH2, Fc = (η5-Cp)Fe(η5-C5H4), Cp = C5H5), followed by its in situ templated reaction with salicylaldehyde and nickel(II) or copper(II) acetate in refluxing CH2Cl2–EtOH (3 : 1) mixture. On the other hand, ionic trinuclear unsymmetrical complexes [3]+PF6− and [4]+PF6− were synthesized by reacting dinuclear precursors 1 and 2, respectively, with [(η5-Cp*)Ru(CH3CN)3]+PF6−, Cp* = C5Me5, in refluxing CH2Cl2. Both complexes contain the neutral electron-releasing ferrocenyl group and the cationic electron-withdrawal sandwich, [(η5-Cp*)Ru(η6-arene)]+, connected by a tetradentate {M(ONNO)} chelate (M = Ni, Cu). The new unsymmetrical organometallic Schiff base compounds were characterized by elemental analysis, IR, UV-Vis, 1H NMR and EPR spectroscopy. In addition, the Ni(II) containing complexes 1 and [3]+PF6− were authenticated by X-ray diffraction analysis. Solvatochromic and electrochemical properties were also studied. The organometallic–inorganic hybrid unsymmetrical Schiff base complexes [3]+PF6− and [4]+PF6− can be defined as type I non-rod-shaped dipolar chromophores.

Synthetic Study of Symmetrical and Unsymmetrical Schiff Base Complexes of VO(IV) and Mn(III) Derived from 2,2′‐Diaminobiphenyl

The symmetrical and unsymmetrical Schiff base complexes of VO(IV) and Mn(III) derived from 2,2′‐diaminobiphenyl and derivatives of salicylaldehyde and 1‐hydroxy‐2‐naphthaldehyde have been synthesized and characterized by elemental analysis, NMR, infrared and electronic absorption spectroscopies, and conductivity measurements. The reaction of the ligands with oxovanadium(IV) was found to be kinetically unfavored, probably due to the small ionic radius of the metal ion, which is not in accordance with the cavity size of the ligands.

Catalytic and antimicrobial activities of new ruthenium(II) unsymmetrical Schiff base complexes

Hexa-coordinated ruthenium(II) complexes of the type [Ru(CO)(PPh3)(Z)(L)] [Z = PPh3, pyridine (py) or piperidine (pip); L = anion of the Schiff base] have been prepared by reacting [RuHCl(CO)(PPh3)2(Z)] with tridentate Schiff bases derived by condensing anthranilic acid with acetylacetone, salicylaldehyde, o-vanillin and o-hydroxyacetophenone. The complexes were characterised by analytical and spectral (i.r., electronic, 1H- and 31P-n.m.r.) data, and were found to be effective catalysts for oxidising primary alcohols to aldehydes in the presence of N-methylmorpholine-N-oxide (NMO) as co-oxidant. The Schiff bases and their ruthenium(II) complexes show growth inhibitory activity against pathogenic fungi Aspergillus flavus, Fusarium oxysporium and Rhizoctonia solani.

Synthesis and characterisation of manganese(III) unsymmetrical Schiff-base complexes: a unique example of a cocrystallised manganese(III) unsymmetrical Schiff-base complex, and a symmetric Schiff-base complex arising from rearrangement of the former

Some manganese(III) complexes with unsymmetrical Schiff bases have been prepared and characterised. The ligands were prepared by condensation of 7-amino-4-methyl-5-azahept-3-en-2-one with salicylaldehyde, 2-hydroxyacetophenone or substituted salicylaldehydes (5-chloro, 5-methoxy, 3-ethoxy or 3,5-dibromo). On reaction with manganese(II) perchlorate in air, manganese(III) Schiff-base complexes are obtained. The crystal structures of two of these have been determined, one being cocrystallised with [{Mn(salen)(H2O)}2][ClO4]2 containing the symmetrical salen ligand [N,N′-ethane-1,2-diylbis-(salicylideneiminate)]. Unlike the dimeric structures previously found for similar complexes, the two structures are monomeric with octahedral MnN2O4 co-ordination spheres.