Ni Schiff Base Complexes Research Articles

A novel Ni–Schiff base complex for motivating glucose electrooxidation in alkaline solutions

Many Schiff-base complexes of metal ions display enhanced catalytic activities toward redox reactions of many organic compounds; accordingly, its application in electrocatalysis is a crucial issue.

A water soluble Ni-Schiff base complex for homogeneous green catalytic C[sbnd]S cross-coupling reactions

Since the embarkation of CS cross-coupling from aryl halides with thiols a handful of works have been contemplated in aqueous medium. Herein, we report an example of a water soluble Ni-Schiff base complex as the green catalyst for the synthesis of thioethers. We have synthesized a Ni-Schiff base complex [NiL(H2O)2](ClO4)2 using N4-donor Schiff base ligand (1,3-bis(((E)-pyridin-2-ylmethylene)amino)propan-2-ol) and characterized by single crystal X-ray diffraction (SC-XRD) study along with different spectral analyses. The complex is mononuclear and cationic in nature having two perchlorate anions. Two water molecules remain coordinated with the Ni(II)-centre. The hydrogen bonding interaction through coordinated water and perchlorate anions connect the monomeric units to form 2D supramolecular structure. Based on its aqueous solubility, the complex has been used for the catalytic CS cross-coupling reaction between aryl iodide and aryl or alkyl thiols using TBAB at 60 °C in aqueous media (yield 92%). At room temperature, an isolated yield of 57% can be achieved. This environmentally benign protocol is paramount in view of the environmental sustainability.

Direct determination of monosaccharides in honey by coupling a sensitive new Schiff base Ni complex electrochemical sensor and chemometric tools

The determination and quantification of saccharides is of considerable importance in the food industry among other fields. In this work, we describe for the first time the preparation of the Schiff base Ni complex, NiII-(N,N’-bis(2,3-dihydroxybenzylidene)-1,2-diaminobenzene) (Ni(II)-2,3dhS) obtained by reaction of the tetradentate Schiff base ligand containing ortho quinone functional groups (N,N’-bis(2,3-dihydroxybenzylidene)-1,2-diaminobenzene) and Ni2+, as well as its application in the development of an electrochemical sensor. Coupled to chemometric tools, the sensor allowed the direct determination of glucose and fructose in honey, without the need of previous separation steps or chromatographic techniques. For this purpose, the new Schiff base Ni complex has been electropolymerized onto screen-printed electrodes modified with carbon nanotubes. The electropolymerization process has been exhaustively characterized by operando spectroelectrochemical techniques to confirm the generation of the desired polymer. The resulting modified electrodes present a strong electrocatalytic activity towards the oxidation of glucose and fructose in alkaline solution and have been employed in combination with partial least squares regression (PLSR) to resolve mixtures of glucose and fructose in a complex matrix, as honey. The multivariate model was based on PLSR analysis and showed good predictive capability for the two analytes in sample standard honey with an average error of 8% and relative standard deviations below 9%.

Study of Electrochemical and Electronical Properties on the Some Schiff Base Ni Complexes in DMSO Solvent by Computational Methods

Schiff bases, an aldehyde- or ketone-like compounds in which the carbonyl group is replaced by an imine or azomethine, are some of the most widely used organic compounds. In this study, the quantum mechanics calculations were performed on M(Chel) where M=Ni(II) and Chel= BAE (bis-acetylacetoneethylenediimine), BBE=bis(benzoyl acetone)ethylenediimine, BFE= bis(1,1,1-triflouroacetylacetone) ethylenediimine and BCE = bis(3-chloroacetylacetone) ethylenediimine) ligands using Gaussian 03 and hartree-fock theory (HF) at B3LYP/6-311G level in the gas phase and solution phase. The polarized continuum model (PCM) is used to calculate salvation energies. After optimizing, various parameters such as electrode potentials, energy gap, chemical hardness, chemical potential and electrophilicity in solvent (DMSO) have been calculated. It was found to be planar and four coordinate. Reduction potentials toward a given M(II) according to the Schiff base ligands changed in the trend: BAE >BCE >BFE.

2-[18F]Fluorophenylalanine: Synthesis by Nucleophilic 18F-Fluorination and Preliminary Biological Evaluation

2-[18F]Fluorophenylalanine (2-[18F]FPhe), a promising PET tracer for imaging of cerebral infarction and tumors, was efficiently prepared from an easily accessible iodonium salt precursor using Cu-mediated radiofluorination under ‘low base’ or ‘minimalist’ conditions. Whereas significant racemization was initially observed if the ‘minimalist’ protocol was applied for radiolabeling, it was completely suppressed by the careful adjustment of 18F– preprocessing. The initial biological study revealed a higher uptake of 2-[18F]FPhe in different tumor cells in comparison to that of [18F]FET. In contrast to 4-[18F]FPhe, which suffered from rapid defluorination in vivo, 2-[18F]FPhe demonstrated a sufficient in vivo stability. Conclusively, 2-[18F]FPhe is a promising PET probe that is now readily available using Cu-mediated radiofluorination under ‘minimalist’ or ‘low base’ conditions. The simplicity of the translation of the proposed procedures to automated synthesis modules allows a broad biological evaluation of 2-[18F]FPhe. Notably, a novel protocol for the preparation of N-Boc protected amino acids from the respective Ni-Schiff base complexes was developed that avoided application of strongly acidic conditions.

Catalytic Oxidation of Benzyl Alcohol Using Nanosized Cu/Ni Schiff-Base Complexes and Their Metal Oxide Nanoparticles

In this work, nanosized Cu and Ni Schiff-base complexes, namely ahpvCu, ahpnbCu, and ahpvNi, incorporating imine ligands derived from the condensation of 2-amino-3-hydroxypyridine, with either 3-methoxysalicylaldehyde (ahpv) or 4-nitrobenzaldehyde (ahpnb), were synthesized using sonochemical approach. The structure and properties of the new ligands and their complexes with Ni(II) and Cu(II) were determined via infrared (IR), nuclear magnetic resonance (NMR), electronic spectra (UV-Vis), elemental analysis (CHN), thermal gravimetric analysis (TGA), molar conductivity (Λm), and magnetic moment (μeff). The combined results revealed the formation of 1:1 (metal: ligand) complexes for ahpvCu and ahpvNi and 1:2 for ahpnbCu. Additionally, CuO and NiO nanoparticles were prepared by calcination of the respective nanosized Cu/Ni complexes at 500 °C, and characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Significantly, the as-prepared nanosized Schiff-base Cu/Ni complexes and their oxides showed remarkable catalytic activity towards the selective oxidation of benzyl alcohol (BzOH) in aqueous H2O2/ dimethylsulfoxide (DMSO) solution. Thus, catalytic oxidation of BzOH to benzaldehyde (BzH) using both ahpvCu complex and CuO nanoparticles in H2O2/DMSO media at 70 °C for 2 h yielded 94% and 98% BzH, respectively, with 100% selectivity.

Synthesis of polymer supported Ni (II)-Schiff Base complex and its usage as a catalyst in sodium borohydride hydrolysis

Influence of using as catalysis, Ni-Schiff Base complex which we previously synthesized [1] used to support with amberzyme oxirane resin (A.O.R.) polymer for increasing the catalytic activity in NaBH4 hydrolysis reaction, to hydrogen generation was studied. The prepared catalyst was characterized by using SEM, XRD, BET, FT-IR analyze technique. Polymer supported Ni-Schiff Base complex catalyzed NaBH4 hydrolysis reaction was investigated depending on concentration of NaBH4, concentration of NaOH, temperature, percentage of Ni complex in total polymer supported Ni-Schiff Base complex and amount of catalyst factors. The maximum hydrogen production rate from hydrolysis of sodium borohydride with nickel-based complex catalyst compared to the pure nickel catalyst is increased from 772 mL H2·g−1 cat.·min−1 to 2240 mL H2 g−1 cat.·min−1 [1], and with supported amberzyme oxirane resin polymer this nickel based complex catalyst was increased to 13000 mL H2·g−1 cat.·min−1 at 30 °C. The activation energy of complex catalyzed NaBH4 hydrolysis reaction was found as 25.377 kJ/mol. This work also includes kinetic information for the hydrolysis of NaBH4.

Hydrolysis of a Ni-Schiff-Base Complex Using Conditions Suitable for Retention of Acid-labile Protecting Groups

Unnatural amino acids, amino acids containing side-chain functionalities not commonly seen in nature, are increasingly found in synthetic peptide sequences. Synthesis of some unnatural amino acids often includes the use of a precursor consisting of a Schiff-base stabilized by a nickel cation. Unnatural side-chains can be installed on an amino acid backbone found in this Schiff-base complex. The resulting unnatural amino acid can then be isolated from this complex using hydrolysis of the Schiff-base, typically by employing reflux in strongly acidic solution. These highly acidic conditions may remove acid-labile side-chain protecting groups necessary for the unnatural amino acids to be used in microwave-assisted solid-phase peptide synthesis. In this work, we present an efficient hydrolysis and subsequent Fmoc protection of an amino acid isolated from a Ni-Schiff base complex. Hydrolysis conditions presented in this work are suitable for retention of acid-labile side-chain protecting groups and may be adaptable to a variety of unnatural amino acid substrates.

Hydrolysis of a Ni-Schiff-Base Complex Using Conditions Suitable for Retention of Acid-labile Protecting Groups.

Unnatural amino acids, amino acids containing side-chain functionalities not commonly seen in nature, are increasingly found in synthetic peptide sequences. Synthesis of some unnatural amino acids often includes the use of a precursor consisting of a Schiff-base stabilized by a nickel cation. Unnatural side-chains can be installed on an amino acid backbone found in this Schiff-base complex. The resulting unnatural amino acid can then be isolated from this complex using hydrolysis of the Schiff-base, typically by employing reflux in strongly acidic solution. These highly acidic conditions may remove acid-labile side-chain protecting groups necessary for the unnatural amino acids to be used in microwave-assisted solid-phase peptide synthesis. In this work, we present an efficient hydrolysis and subsequent Fmoc protection of an amino acid isolated from a Ni-Schiff base complex. Hydrolysis conditions presented in this work are suitable for retention of acid-labile side-chain protecting groups and may be adaptable to a variety of unnatural amino acid substrates.

Inorganic–organic hybrid chitosan‐based Schiff base–Ni complex as a novel, highly efficient and recyclable heterogeneous catalyst for synthesis of pyrazolophthalazinediones

A Schiff base based on chitosan was synthesized through treatment of chitosan and p‐dimethylaminobenzaldehyde in methanol solution. This biopolymeric Schiff base was used to prepare a new first row transition metal complex of Ni(II). The biopolymeric Schiff base and the synthesized tetra‐coordinated complex were characterized using Fourier transform infrared, 1H NMR and 13C NMR techniques. Then, an efficient synthetic method for functionalized 1H–pyrazolo[1,2‐b]phthalazine‐5,10‐diones was successfully developed using one‐pot domino reaction of ninhydrin and malononitrile with 3‐arylamino‐5,5‐dimethyl‐2‐cyclohexenones catalysed by the chitosan‐based Schiff base complex of Ni(II) at room temperature. The advantages of this protocol are easy work‐up, short reaction times and high yield of products and also the catalyst can be readily isolated from the reaction mixture and recycled without loss of catalytic activity.

Chiral Ni-Schiff Base Complexes inside Zeolite-Y and Their Application in Asymmetric Henry Reaction: Effect of Initial Activation with Microwave Irradiation

Chiral Ni(II)-Schiff base complexes synthesized inside the cavity of zeolite-Y were used as heterogeneous chiral catalyst for asymmetric Henry reaction. Synthesized catalysts were characterized using various spectrochemical and physicochemical techniques. Solid state NMR analysis has been used to confirm the internal location of the metal complexes. To the best of our knowledge MAS NMR has not been used to characterize chiral diamagnetic Ni2+-Schiff base complex inside zeolite-Y. The catalytic activities of the materials were dependent on temperature, solvent, and amount of catalyst. High catalytic transformation of aldehydes with nitromethane to nitro-aldol product (92% yield and 83% ee, S-isomer) was achieved at −10 °C. Initial activation of the reaction with microwave irradiation for 15 min leads to a substantial decrease in the reaction time in comparison to normal stirring. Heterogeneous catalysts were found to be advantageous over the homogeneous counterparts in terms of recyclability of the catalys...

A novel Ni-Schiff base complex derived electrocatalyst for oxygen evolution reaction

Efficient electrocatalysts for the oxygen evolution reaction (OER) are critical for various energy conversion devices such as metal-air batteries, rechargeable fuel cell, and water splitting for hydrogen production. In this work, a novel non-precious-metal OER catalyst was prepared from the pyrolysis of a Ni-Schiff base complex with thiourea. The derived catalyst is composed of nickel oxide coupled with nickel sulfide loaded on nitrogen-doped carbon matrix (NiO-NiS/N-C), which manifested excellent OER electrocatalytic activity, and an onset potential of 1.54 V vs reversible hydrogen electrode was achieved in alkaline electrolyte. The high performance of as-obtained electrocatalyst was illustrated by fully dispersed active components of NiO coupled with NiS nanoparticles, as well as the strong interaction between NiS, NiO particles, and N-doped carbon substrate. Our findings supply an easier path to fabricate the active catalyst through one-step metal organic framework transformation way and are promising for use in energy conversion systems and also yield new impetus for exploring other non-noble metal catalysts.

Synthesis, molecular docking, and inhibitory activity of a Ni Schiff-base complex against urease

A Ni(II) Schiff-base complex, Ni(C14H10NOBr2)2, was synthesized and structurally characterized by single-crystal X-ray analysis. Its inhibitory activity against Helicobacter pylori urease was evaluated in vitro and showed strong inhibitory activity against H. pylori urease compared with acetohydroxamic acid (IC50 = 42.12 µmol L−1), which is a positive reference. A docking analysis using the autodock 4.0 program could explain the inhibitory activity of the complex against urease.

Solvent-Assisted Formation of Vesicles by a Self-Assembling Ni3−Schiff Base Complex

A linear trinuclear Ni-Schiff base complex [Ni(3)(salpen)(2)(PhCH(2)COO)(2)(EtOH)] has been synthesized by combining Ni(ClO(4))(2).6H(2)O, phenyl acetic acid (C(6)H(5)CH(2)COOH), and the Schiff base ligand, N,N'-bis(salicylidene)-1,3-pentanediamine (H(2)salpen). This complex is self-assembled through hydrogen bonding and C-H-pi interaction in the solid state to generate a sheet-like architecture, while in organic solvent (CH(2)Cl(2)), it forms vesicles with a mean diameter of 290 nm and fused vesicles, depending upon the concentration of the solution. These vesicles act as an excellent carrier of dye molecules in CH(2)Cl(2). The morphology of the complex has been determined by scanning electron microscopy and transmission electron microscopy experiments, and the encapsulation of dye has been examined by confocal microscopic image and electronic absorption spectra.