Chiral Schiff Base Research Articles

Synthesis, crystal structure, and magnetic characterization of chiral Schiff-base manganese(III) complex containing cocrystallized crown ether molecule

A chiral Schiff-base Mn(III) compound containing cocrystallized crown ether {Mn[(R,R)-Salcy]·(H2O)2}2(ClO4)2·18-Crown-6 (I), where (R,R)-Salcy = (R,R)-N, N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato) dianion, has been synthesized by the reaction of {Mn[(R,R)-Salcy](H2O)2}ClO4 with 18-crown-6 ether and K4[Mo(CN)8]. X-ray diffraction analysis revealed that the cationic mononuclear Mn(III) Schiff-base compounds were self-complementary via intermolecular O-H⋯O H-bond formed by coordinated aqua ligand of one molecule and phenolic oxygen atoms of the neighboring molecule, giving supramolecular dimeric structure. The H-bond between O atoms of the cocrystallized crown molecule and that of the mentioned above dimer supported formation of one-dimensional supramolecular chain structure which can be linked to two-dimensional supramolecular network based on intermolecular O-H⋯Cl weak interactions. Our study of its magnetic properties revealed weak antiferromagnetic coupling between the adjacent Mn(III) ions.

Synthesis, characterization, and structures of two new tetranuclear copper complexes with azido/dicyanamide bridges containing chiral Schiff base ligand

Two new copper complexes [Cu4(μ-L)2(μ1,1-N3)2(N3)2] (I) and [Cu4(μ-L)2(μ1,5-Dca)2(Dca)2] (II) (H2L = (1R,3S)-N′,N″-bis[5-methoxysalicylidene]-1,3-diamino-1,2,2-trimethylcyclopentane, Dca = dicyanamide ions) were synthesized and structurally characterized by elemental analyses, IR spectroscopy and single-crystal X-ray diffraction (CIF files CCDC nos. 1013673 (I), 1013672 (II)). The two complexes crystallize in monoclinic P21/c and triclinic $P\bar 1$ space group, respectively. Both the complexes consist of two crystallographically independent copper ions connected by a double phenoxo bridges, which are further linked to the other symmetry-related half of the molecule by two end-on azido bridges or μ1,5-dca groups.

Synthesis, X-ray structural and thermal analysis of a novel copper compound containing dissymmetric independent 5- and 6-coordinate CuL(H2O)n (n = 2, 3) units and hydrogen bond bridges.

The synthesis, thermogravimetric and X-ray structure analysis of a highly unusual copper compound prepared from a chiral tridentate Schiff base ligand is reported. The title compound [CuL(H(2)O(2)]. CuL(H(2)O(3)].H(2)O crystallizes in the orthorhombic crystal system in space group P2(1)2(1)2(1) with Z = 4. Two independent CuL(H(2)O)(n) complexes are present in the same unit cell, one five- and the other six- coordinate. The five-coordinate copper(II) centre occupies a distorted square-pyramidal geometry whereas the six-coordinate copper(II) centre has a distorted octahedral geometry. The independent copper complexes and the uncoordinated water molecule are joined together with intermolecular hydrogen bonds in a two-dimensional supramolecular network which lies parallel to the ab plane.

Enantioselective Epoxidation of Styrene by Manganese Chiral Schiff Base Complexes Immobilized on MCM-41.

Two chiral MnIII complexes synthesized and characterized by single-crystal X-ray diffraction were grafted onto mesoporous silica MCM-41. The MCM-41-immobilized solid chiral catalysts were characterized by various spectrochemical and physicochemical methods (XRD, FTIR, 29 Si NMR, TGA, UV/Vis/DRS, EPR, cyclic voltammetry, SEM, BET). Both the homogeneous and heterogeneous MnIII chiral complexes are found to be effective catalysts for epoxidation of styrene. MCM-41-supported chiral catalysts are found to retain their catalytic activity up to five cycles. When an ionic liquid was implemented to enhance the catalytic recyclability of the homogeneous catalysts, they can be recycled up to three times. However, after the third cycle the catalytic activities of the complexes were found to decrease due to rupturing of the chiral catalyst.

Superoxide dismutase activity studies of Mn(III)/Cu(II)/Ni(II) complexes with Schiff base ligands

Mimetics of superoxide dismutases would be expected to be potential new drugs because of their ability to eliminate superoxide radicals under physiological conditions. Some metal complexes with Schiff base ligand were reported to have considerable therapeutic potential. In this paper, six coordination complexes derived from water soluble chiral Schiff base ligands have been synthesized. Of these, the crystal structures of the Cu(II)/Ni(II) complexes were solved. All compounds can bind with bovine serum albumin (BSA) with non-covalent interactions. The binding constant has been determined by fluorescence spectroscopy. The SOD activity of the metal complexes and their BSA complexes have been studied. The metal ion and BSA can influence the SOD activity.

Synthesis of novel Schiff base ligands from gluco- and galactochloraloses for the Cu(II) catalyzed asymmetric Henry reaction

A series of chiral Schiff base ligands has been prepared using aminochloralose derivatives of glucose and galactose. These ligands were used as catalysts in the asymmetric Henry reaction in the presence of Cu(II) ions giving yields of up to 95%. An interesting solvent dependency on enantiomeric control was observed with the best enantiomeric excesses (up to 91%) being obtained in the presence of water.

Asymmetric synthesis of α-(1-oxoisoindolin-3-yl)glycine: synthetic and mechanistic challenges.

We report herein that the NaOMe-catalyzed reactions between the chiral glycine Schiff base (S)-4 with 2-cyanobenzaldehyde 3a provide for a convenient preparation of the novel α-(1-oxoisoindolin-3-yl)glycine 1 of high pharmaceutical potential. The reactions involve at least eight synthetic steps and can mechanistically be realized only with application of Ni(II) complexes described in this study.

Synthesis, characterization, reactivity and catalytic activity of a novel chiral manganese Schiff base complex

A new type of manganese-Schiff base complex was synthesized and used as a catalyst for the oxidation of alcohols to the carbonyl compounds.

Synthesis, Characterization, and Structures of Two New Tetranuclear Copper Complexes with Azido/Dicyanamide Bridges Containing Chiral Schiff Base Ligand

Synthesis, Characterization, and Structures of Two New Tetranuclear Copper Complexes with Azido/Dicyanamide Bridges Containing Chiral Schiff Base Ligand

A family of homochiral spin-crossover iron(II) imidazole Schiff-base complexes

Four novel homochiral mononuclear spin-crossover iron(II) complexes 1–4 have been successfully synthesized by subcomponent self-assembly of Fe(ClO4)2, 1-substituted imidazole-2-carboxaldehyde and optical phenylethylamine derivatives. X-ray crystallography revealed that the iron(II) center in 1–4 assumed an octahedral coordination environment with 6 N donor atoms from three unsymmetrical bidentate chiral Schiff-base ligands. [Fe(Ln)3]2+ components were chiral with either Λ or Δ configuration due to the screw coordination arrangement of the chiral ligands around Fe(II) center. Circular dichromism spectra confirmed the presence of non-racemic chiral metal centers in solution for 1–4. Magnetic measurements revealed that 1–4 displayed obviously spin-crossover behavior at 257, 375, 137 and 282K, respectively. The different SCO behaviors of 1–4 may result from substitution effect, packing mode, and intermolecular interactions.

Variety of Crystal Structures of Chiral Schiff Base Lu(III)-Ni(II)/ Cu(II)/Zn(II) and the Related Complexes

New mononuclear [Cu2(L1)2(H2O)]2H2O・CH3OH] (cyCu)2, multinuclear [Cu2(L1)2K2][Ni(CN)4] (cyCuKNi), and dinuclear Ni(L1)Lu(NO3)3 (cyLuNi), Cu(L1)Lu(NO3)3 (cyLuCu) and Zn(L1)Lu[(NO3)2CH3COO]CH3OH (cyLuZn) complexes incorporating chiral Schiff base ligands were prepared and characterized by various techniques such as solid-state CD spectra, diffuse reflectance electronic spectra, IR spectra, and single crystal X-ray diffraction analysis. Crystal structures were also compared with previous ones, namely [Cu(L2)](H2O) (diCu), Cu(L1)Gd(NO3)3 (cyGdCu). Interestingly, determined crystal structures exhibited drastically different structural characteristics as regards coordination numbers, crystalline solvents, features and strain condition, nevertheless with little modification in 3d metal substitution and/or modified organic ligands. In this paper, comparison of common components of structures will be discussed systematically.

A new type of multifunctional single ionic dysprosium complex based on chiral salen-type Schiff base ligand

A new type of multifunctional single ionic chiral dysprosium complex (DyL) was obtained by the reaction of Dy(NO3)3 and salen-type Schiff base ligand N,N′-bis(3,5-dichlorosalicylidene)-(1R,2R)-1,2-cyclohexylenediamine. In the synthesis reaction, Dy(III) was found not only to be the central metal to coordinate with two Schiff base ligands, but also the Lewis acid catalyst to promote the partial decomposition of salen-type Schiff base ligand. Complex DyL crystallizes in a chiral and polar space group P21. The central metal Dy(III) adopts eight-coordinated square antiprism geometry with Δ absolute configuration. Complex DyL exhibits good SHG and ferroelectric properties. The single-crystal sample of DyL displays an obvious ferroelectric behavior with a remnant polarization (Pr) of ca. 4.51μCcm−2 and Ec of ca. 28.11kVcm−1. The solid luminescent spectrum of DyL presents characteristic emission 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy(III).

Base-induced self-assembly for one-dimensional coordination polymers via chiral pendant-armed Schiff base mononuclear Pb(II) macrocycles.

A pair of 18-membered [1 + 1] chiral pendant-armed Schiff base macrocyclic mononuclear Pb(II) complexes with an unusual N1O2 coordination mode, synthesized from two chiral isomeric dialdehyde components, can be further self-assembled to one-dimensional ribbon coordination polymers by adding NaOH as a base to remove two phenolic protons.

X-ray structure analysis, electronic and vibrational circular dichroism of chiral-at-metal dioxidovanadium(V) complexes with amino acids derived Schiff base ligands

Five new chiral dioxidovanadium Schiff base complexes derived from l-valine, l-leucine, l-histidine, l-threonine and d-threonine were synthesized and characterized by elemental analysis, 1H and 51V NMR and IR spectra. The absolute configurations of the complexes were determined by X-ray single crystal analysis in solid state and by electronic and vibrational circular dichroism in CH3CN solution. The l-threoninato complex, which contains two stereogenic centers in the amino acid site, does not show epimerization of the amino acid, in contrast with the analogical isoleucine-derived complexes reported recently. Conglomerate crystallization was observed in racemic dl-valine- and dl-threonine-derived complexes.

Effect of steric congestion and non-covalent interaction on the self-organization of two isostructural 1D chiral coordination polymers

Two isostructural 1D chiral coordination polymers namely, [M(L)(N(CN)2)]n have been synthesized using a racemic mixture of chiral tridentate Schiff base ligand, LH (LH=2-((phenyl(2-pyridyl)methylimino)methyl)phenol), M(II) ions (M=Cu (1), Zn (2)) and dicyanamide ion. Structural characterization reveals that dicyanamide ion links two mononuclear units having same enantiomer of ligand L (either R or S) though it’s end-on-end bridging mode and extends further towards the formation of 1D homochiral self-assembly in a chiral self-recognition manner. The effects of different non-covalent interactions on the arrangement of 1D chiral coordination polymers into 2D sheet have been studied. The results demonstrate the effect of dicyanamide ion, steric congestion and non-covalent interactions on the homochiral self-assembly of the synthesized complexes.

Synthesis, characterization and catalytic activity of chiral binaphthyl Schiff-base manganese complexes for the epoxidation of styrene

Chiral binaphthyl Schiff base ligands were prepared by condensation of 2,2′-diamino-1,1′-binaphthalene with various salicylaldehydes. Ligands were coordinated with Mn(III) as catalysts. The catalytic efficiency of the complexes was tested on the epoxidation of styrene. The influences of the parameters such as reaction time, position of substituents with various oxidants on the epoxidation reactions were investigated.

Effects of copper ions on DNA binding and cytotoxic activity of a chiral salicylidene Schiff base

A chiral Schiff base HL N-(5-bromo-salicylaldehyde)dehydroabietylamine (1) and its chiral dinuclear copper complex [Cu2L4]·4DMF (2) have been synthesized and fully characterized. The interactions of 1 and 2 with salmon sperm DNA have been investigated by viscosity measurements, UV, fluorescence and circular dichroism (CD) spectroscopic techniques. Absorption spectral (Kb=3.30×105M−1 (1), 6.63×105M−1(2)), emission spectral (Ksv=7.58×103M−1 (1), 1.52×104M−1 (2)), and viscosity measurements reveal that 1 and 2 interact with DNA through intercalation and 2 exhibits a higher DNA binding ability. In addition, CD study indicates 2 cause a more evident perturbation on the base stacking and helicity of B-DNA upon binding to it. In fluorimetric studies, the enthalpy (ΔH>0) and entropy (ΔS>0) changes of the reactions between the compounds with DNA demonstrate hydrophobic interactions. 1 and 2 were also screened for their cytotoxic ability and 2 demonstrates higher growth inhibition of the selected cancer cells at concentration of 50μM, this result is identical with their DNA binding ability order. All the experimental results show that the involvement of Cu (II) centers has some interesting effect on DNA binding ability and cytotoxicity of the chiral Schiff base.

Effect of Nanospace Confinement on the Catalytic Activity and Stability of a Chiral Schiff Base Complex (CuL; L=C22 H24 N2 O4 ): A Combined Experimental and Theoretical Study.

Emerging trends in recyclable homogeneous chiral catalysts and their application in asymmetric synthesis are prompting a renewed interest in the field of catalysis as well as in industry. However, owing to fatal disadvantages of the homogeneous catalyst, they are not easily recoverable and recyclable. Herein, a comparison is made of the recyclability and stability of a homogeneous chiral CuII Schiff base complex of general formula CuL, in which L=C22 H24 N2 O4 , with that of a zeolite-Y-confined heterogeneous catalyst. On the basis of our experimental evidence, we demonstrate how self-decomposition and bimetallic formation disrupt the catalytic activity of a homogeneous catalyst. By exploiting the special structure of faujasite zeolite, self-decomposition of the chiral catalyst is fully controlled and efficiently used for the asymmetric nitroaldol reaction. The use of ionic liquid results in catalytic enhancement and provides a convenient way to recycle the homogeneous catalyst up to three cycles. When encapsulated in a cavity of faujasite by means of the "ship-in-a-bottle" synthesis method, it shows much better catalytic activity with enhanced enantioselectivity, recyclability, and stability. The heterogeneous catalyst is recycled up to nine cycles and retains the catalytic activity for a longer period of time relative to its homogeneous counterpart. The synthesized heterogeneous CuII complex provides the nitroaldol product with a maximum of 84 % yield and 87 % enantiomeric excess (ee; R isomer). Structural and reactivity differences between the homogeneous and heterogeneous chiral complexes are substantiated by density functional theory (DFT) calculations.

Synthese und Koordinationsverhalten neuer Schiffscher Basen aus 3-Formylacetylaceton und natürlichenL-Aminosäuren

Three novel chiral Schiff Base ligands (H2L) were prepared from the condensation reaction of 3-formyl acetylacetone with the amino acids L-alanine, L-phenylalanine, and L-threonine. X-ray single crystal analyses revealed that the Schiff Base compounds exist as enamine tautomers in the solid state. The molecular structure of the compounds is stabilized by an intramolecular hydrogen bridge between the enamine NH function and a carbonyl oxygen atom of the pentandione residue. Treatment of the ligands H2L with copper(II) actetate in the presence of pyridine led to the formation of copper complexes [CuL(py)]. In each of the complexes the copper atoms adopt a distorted square-pyramidal coordination. Three of the basal coordination sites are occupied by the doubly deprotonated Schiff Bases L2– which act as tridentate chelating O, N, O-ligands. The remaining coordination sites are occupied by a pyridine ligand at the base and a carboxyl oxygen atom of a neighboring complex at the apical position. The latter coordination is responsible for a catenation of the complexes in the solid state.

Polarized UV light induced molecular arrangement depending on flexibility of chiral Schiff Base Ni(II), Cu(II), and Zn(II) complexes by Azobenzene in PMMA matrix

Polarized UV light induced molecular arrangement depending on flexibility of chiral Schiff Base Ni(II), Cu(II), and Zn(II) complexes by Azobenzene in PMMA matrix