Non-symmetrical Schiff Base Research Articles

Polar Alkoxy Group and Pyridyl Effects on the Mesomorphic Behavior of New Non-Symmetrical Schiff Base Liquid Crystals

A series of non-symmetrical Schiff base liquid crystals were prepared and investigated. Schiff bases of p-alkyloxy aniline derivatives and 4-phenyl pyridine-4′-carbaldehyde were synthesized. The terminal alkoxy groups substituting aniline are of varied chain length, namely C6, C8, and C16. The structures of the compounds were confirmed via 1H NMR and 13C NMR spectroscopy. Different mesophases of the samples were thermally and optically characterized by differential thermal analysis (DSC) and polarized optical microscopy (POM). All samples revealed enantiotropic smectic B (SmB) and smectic A (SmA) mesophases. The results obtained were further correlated with the density functional theory (DFT) theoretical calculations. The results are compared to a series of compounds bearing biphenyl moiety in their mesogens. The thermal stabilities of the different mesophase reduced upon the increment of the alkoxy chain length. The temperature ranges of both the smectic mesophases of new compounds bearing the 4-phenyl pyridine moiety are generally expanded higher than the other series. In addition, the total mesophase range is greater in the new compounds when compared to their biphenyl analogues. The DFT results were investigated in terms of the molecular geometries and the frontier molecular orbitals as well as the charge distribution mapping to show and illustrate the difference in the mesomorphic properties.

Synthesis, Mesomorphic, and Solar Energy Characterizations of New Non-Symmetrical Schiff Base Systems.

New asymmetrical Schiff base series based on lateral methoxy group in a central core, (E)-3-methoxy-4-(((4-methoxyphenyl)imino)methyl)phenyl 4-alkoxybenzoate (An), were synthesized and their optical and mesomorphic characteristics were investigated. The lateral OCH3group was inserted in the central ring in ortho position with respect to the azomethine linkage. FT-IR, and NMR spectroscopy as well as elemental analyses were used to elucidate their molecular structures. Their mesomorphic behaviors were characterized by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). These examinations indicated that all the designed series were monomorphic and possessed nematic (N) mesophase enantiotropically, except A12 derivative which exhibited monotropic N phase. A comparative study was made between the present investigated series (An) and their corresponding isomers (Bn). The results revealed that the kind and stability of the mesophase as well as its temperature range are affected by the location and special orientation of the lateral methoxy group electric-resistance, conductance, energy-gap, and Urbach-energy were also reported for the present investigated An series. These results revealed that all electrodes exhibit Ohmic properties and electric-resistances in the GΩ range, whereas the electric resistance was decreased from 221.04 to 44.83 GΩ by lengthening the terminal alkoxy-chain to n = 12. The band gap of the An series was reduced from 3.43 to 2.89 eV by increasing the terminal chain length from n = 6 to n = 12 carbons. Therefore, controlling the length of the terminal chain can be used to improve the An series’ electric conductivity and optical absorption, making it suitable for solar energy applications.

Reaction of Non-Symmetric Schiff Base Metallo-Ligand Complexes Possessing an Oxime Function with Ln Ions

The preparation of non-symmetric Schiff base ligands possessing one oxime function that is associated to a second function such as pyrrole or phenol function is first described. These ligands, which possess inner N4 or N3O coordination sites, allow formation of cationic or neutral non-symmetric CuII or NiII metallo-ligand complexes under their mono- or di-deprotonated forms. In presence of Lanthanide ions the neutral complexes do not coordinate to the LnIII ions, the oxygen atom of the oxime function being only hydrogen-bonded to a water molecule that is linked to the LnIII ion. This surprising behavior allows for the isolation of LnIII ions by non-interacting metal complexes. Reaction of cationic NiII complexes possessing a protonated oxime function with LnIII ions leads to the formation of original and dianionic (Gd(NO3)5)2− entities that are well separated from each other. This work highlights the preparation of well isolated mononuclear LnIII entities into a matrix of diamagnetic metal complexes. These new complexes complete our previous work dealing with the complexing ability of the oxime function toward Lanthanide ions. It could open the way to the synthesis of new entities with interesting properties, such as single-ion magnets for example.

Synthesis, structural analysis and evaluation of the catalytic activity of a non-symmetric N-(salicylidene)diethylenetriamine complex of copper(II)

A new copper(II) complex of a non-symmetric Schiff base, [Cu II (saldien)(H 2 O)] + ( 1 ), has been synthesized and characterized by elemental analysis and several other spectroscopic methods (Hsaldien = N- (salicylidene)diethylenetriamine). The crystal structure of 1 has also been determined by X-ray crystallography. The geometry of the complex cation in 1 was found to be distorted square pyramidal with the mononegative Schiff base coordinating to the copper in a tetradentate mode via the O,N,N ', and N ”-donor atoms. The remaining coordination site was occupied by the O atom of a H 2 O molecule in the axial position. The catalytic potential of 1 was tested in the oxidation reactions of cyclooctene and cyclohexene with aqueous 30% H 2 O 2 /NaHCO 3 in acetonitrile. These reactions proceeded smoothly to give the corresponding epoxides with selectivity levels greater than 99%. This catalytic system also showed high levels of activity and selectivity towards the oxidation of cyclohexane (i.e., cyclohexanol 37% and cyclohexanone 54%) in comparison with most of the other Cu-based systems reported in the literature. Synthesis and crystal structural analysis of a new copper(II) complex of a non-symmetric Schiff base have been reported. The complex showed high levels of catalytic activity and selectivity towards the oxidation of cycloalkenes and cyclohexane by H 2 O 2 and NaHCO 3 .

Asymmetric vanadium- and iron-catalyzed oxidations: new mild (R)-modafinil synthesis and formation of epoxides using aqueous H2O2 as a terminal oxidant

The enantioselective oxidation of thioanisole to methyl phenyl sulfoxide and the epoxidation of several alkenes, including terminal ones, have been realized by using new iron(III) complexes, generated in situ from primary amine-derived non-symmetrical Schiff base ligands and aqueous H2O2 as environmentally benign oxidant. Further investigations on vanadium catalysis and the application of both catalytic systems in the synthesis of enantiomerically-enriched chiral drug (R)-modafinil were undertaken. It was found that the vanadium-based catalytic system (VO(acac)2/ligand 6), is able to provide (R)-modafinil in quantitative yield and acceptable enantiomeric excess within a very short reaction time (15min).

Synthesis of 4-Substituted Styrene Compounds via Palladium-Catalyzed Suzuki Coupling Reaction Using Free Phosphine Ligand in Air

The air-stable and easy to prepare nonsymmetric Schiff base ligands have been synthesized and proven to be efficient ligands for Suzuki cross-coupling reaction between aryl bromides and arylboronic acids using PdCl2(CH3CN)2 as palladium source under aerobic conditions. The coupling reaction proceeded smoothly using N-[(3,4-dimethoxyphenyl)methylene]-1,2-benzenediamine (L3) as ligand under mild conditions to provide 4-substituted styrene compounds in good yields.

<b>Studies on some VO(IV), Ni(II) and Cu(II) complexes of non-symmetrical tetradentate Schiff-bases</b>

The coordination chemistry of VO(IV), Ni(II) and Cu(II) with unsymmetrical Schiff base ligands, [HO(OCH 3 )C 6 H 3 C(CH 3 ):N(CH 2 CH 2 )N:C(CH 3 )CH:C(C 6 H 5 )OH], H 2 L and [HO(OCH 3 )C 6 H 3 C(CH 3 ):N(CH 2 CH 2 )N:C(CH 3 )CH:C(CH 3 )OH], H 2 L 1 (derived from condensation of 1-phenyl-1,3-butanedione/2,4-pentanedione, ethylenediamine and 5-methoxy-2-hydroxy acetophenone) is discussed. The metal complexes were characterized by elemental analysis, molar conductance, magnetic susceptibility, infrared and electronic spectral measurements. They are magnetically dilute, non-electrolytes in nitromethane. The ligands are tetradentately coordinating via the imine N and enolic O atoms, resulting in 5-coordinate square-pyramidal geometry for the VO(IV) complexes and 4-coordinate square-planar geometry for the Ni(II) and Cu(II) complexes. The assignment of geometry is supported by magnetic and spectral measurements. KEY WORDS: Coordination chemistry, Magnetically dilute, Non-electrolyte, Non-symmetrical Schiff base Bull. Chem. Soc. Ethiop. 2008 , 22(2), 219-224.

Is ferromagnetism an intrinsic property of the CuII/GdIII couple? 1. Structures and magnetic properties of two novel dinuclear complexes with a mu-phenolato-mu-oximato (Cu,Gd) core.

Two original dinuclear (Cu(II),Gd(III)) complexes (1 and 2) deriving from polydentate nonsymmetrical Schiff base ligands LiH2 have been prepared. Formally they differ by the length of the diamino chain. They crystallize in the orthorhombic Pbca (No. 61) (1) and in the monoclinic P2(1/n) (No. 14) (2) space groups. The cell parameters are a = 12.6295(7) A, b = 20.7894(9) A, c = 18.3301(13) A, and Z = 8 for 1 and a = 12.7246(16) A, b = 13.5691(17) A, c = 14.5310(19) A, beta = 94.629(16) degrees , and Z = 4 for 2. These structural studies show that in both complexes the CuII and GdIII ions are doubly bridged by a phenolato oxygen atom and an oximato (N-O) pair. The bridging network is not planar. The more important distortions are observed for the complex having the larger diamino chain. Unexpectedly the latter complex presents an antiferromagnetic interaction, but the related J value is small (J approximately equal to -0.49 cm(-1)). In the former complex the interaction is ferromagnetic (J approximately equal to 3.5 cm(-1)) as it is for complexes containing (CuO2Gd) bridging cores which yield J values varying from 1.4 to 10.1 cm(-1).

Easy synthesis of ‘half-units’: their use as ligands or as precursors of non-symmetrical Schiff base complexes

This paper is devoted to a particular reaction able to give singly condesed Schiff base derivatives of ß-diketones (called ‘half-units’) in an easy way. Indeed, 1,2-diamino-2-methylpropane, which possesses an amine function sterically hindered by two methyl groups, reacts with a diketone such as 2,4-pentanedione or 2-hydroxyacetophenone only by its non-hindered amine function, yielding a ‘half-unit’. In a following step, this terdentate ligand can react with an aldehyde function to give a non-symmetrical tetradentate Schiff base. Such a reaction can be performed on the free ‘half-unit’ or on its ‘complexed form’. Some examples of nickel and copper complexes are given. A particular interest has been given to the use of imidazole-2-carboxaldehyde which yields non-symmetrical Schiff base complexes with a free nitrogen atom not included in the N 3O coordination site. According to the procedure of ‘complexes as ligands’, it is possible to isolate bimetallic complexes with imidazole bridges. Their genuine identity has been confirmed by NMR (nickel) and also by thermal variation of the magnetic susceptibility (copper).

ChemInform Abstract: Structural Study of a New Type of B12 Model Involving a Non‐Symmetrical Equatorial Ligand; Aquaethyl(N,N′‐ethylene(acetylacetonylideneiminato)(salicylideneiminato))cobalt(III)

An X-ray crystal structure determination has been performed for a new type of B12 model involving a non-symmetrical equatorial ligand. Aquaethyl[N,N′-ethylene(acetylacetonylideneiminato)-(salicylideneiminato)]cobalt(III) crystallizes in the triclinic space group P with two formula units in a cell having the dimensions a= 9.366(1), b= 11.292(2), c= 8.009(1)A, α= 99.10(1), β= 102.48(2), and γ= 82.60(1)°. The co-ordination about the cobalt atom is that of a distorted octahedron. The equatorial co-ordination sites are occupied by the N2O2 donors from the non-symmetrical Schiff base. A water molecule occupies an axial position with a transσ-bonded ethyl group. Comparison with other types of B12 models shows that the present complex is characterized by high values of three structural parameters, i.e. the Co–O axial bond length, the dihedral angle between the two halves of the equatorial ligand, and the displacement of the cobalt atom out of the mean plane of co-ordination. These structural features are discussed in relation with other ground-state properties and with the behaviour of the Co–C bond.

Structural study of a new type of B12model involving a non-symmetrical equatorial ligand; aquaethyl[N,N′-ethylene(acetylacetonylideneiminato)-(salicylideneiminato)]cobalt(III)

An X-ray crystal structure determination has been performed for a new type of B12 model involving a non-symmetrical equatorial ligand. Aquaethyl[N,N′-ethylene(acetylacetonylideneiminato)-(salicylideneiminato)]cobalt(III) crystallizes in the triclinic space group P with two formula units in a cell having the dimensions a= 9.366(1), b= 11.292(2), c= 8.009(1)A, α= 99.10(1), β= 102.48(2), and γ= 82.60(1)°. The co-ordination about the cobalt atom is that of a distorted octahedron. The equatorial co-ordination sites are occupied by the N2O2 donors from the non-symmetrical Schiff base. A water molecule occupies an axial position with a transσ-bonded ethyl group. Comparison with other types of B12 models shows that the present complex is characterized by high values of three structural parameters, i.e. the Co–O axial bond length, the dihedral angle between the two halves of the equatorial ligand, and the displacement of the cobalt atom out of the mean plane of co-ordination. These structural features are discussed in relation with other ground-state properties and with the behaviour of the Co–C bond.

Non-symmetric Schiff base Co(II) complexes. Synthesis and catalytic activity in the oxidation of 2,6-Di-tert-butylphenol by molecular oxygen

We report the synthesis of a series of unsymmetrical tetradentate Schiff base ligands. In the reaction of o-phenylenediamines with aromatic aldehydes, use of chloroform as a solvent allows a kinetic control of the formation of mono-Schiff base. Further condensation of the half-unit with 5-formyl 1,3-dimethyl barbituric acid leads to the non- symmetric Schiff base. Cobalt(II) complexes of these ligands have been prepared and the influence of the structure of the ligands on half-wave Co(II)/Co(III) potential values and the catalytic activation of O 2 has been investigated.

ChemInform Abstract: NON‐SYMMETRICAL SCHIFF BASE COMPLEXES. EXPERIMENTAL SUPPORT TO AN INTRAMOLECULAR, NON‐SYMMETRICAL ACTIVATION PROCESS AND SYNTHESIS OF A NEW TYPE OF TETRAAZA MACROCYCLIC COMPLEXES

Chemischer InformationsdienstVolume 16, Issue 25 Organoelement Compounds ChemInform Abstract: NON-SYMMETRICAL SCHIFF BASE COMPLEXES. EXPERIMENTAL SUPPORT TO AN INTRAMOLECULAR, NON-SYMMETRICAL ACTIVATION PROCESS AND SYNTHESIS OF A NEW TYPE OF TETRAAZA MACROCYCLIC COMPLEXES J.-P. COSTES, J.-P. COSTESSearch for more papers by this authorG. CROS, G. CROSSearch for more papers by this authorJ.-P. LAURENT, J.-P. LAURENTSearch for more papers by this author J.-P. COSTES, J.-P. COSTESSearch for more papers by this authorG. CROS, G. CROSSearch for more papers by this authorJ.-P. LAURENT, J.-P. LAURENTSearch for more papers by this author First published: June 25, 1985 https://doi.org/10.1002/chin.198525325Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume16, Issue25June 25, 1985 RelatedInformation

The syntheses, properties and crystal and molecular structures of the copper(II) and nickel(II) complexes of the non-symmetric schiff bases, derived from 1,2-diaminoethane, pentane-2,4-dione and 2-pyrollecarboxaldehyde

The synthesis of a non-symmetric Schiff base derived from 1,2-diaminoethane, pentane-2,4-dione and 2-pyrollecarboxaldehyde is described and the copper(II) and nickel(II) complexes are reported. The crystal structure of the nickel(II) complex is monoclinic, R = 0.0368, 1451 reflections: the crystal structure of the copper(II) complex is isomorphous, ( R = 0.0387, 1239 reflections). In both structures, the metals adopt square-planar coordination geometries and long intermolecular contacts lead to weak oligomerisation. The EPR spectra of the copper(II) complex is discussed and related to the structure.

A new example of ligand-to-metal electron-transfer process : one-electron reduction products of nickel(II)-tetradentate schiff base complexes

The reduction of three nickel(III) complexes involving two symmetrical N,N′-ethylenebis (acetylacetoneiminato) and N,N′-ethylenebis (salicylideneiminato) and one non-symmetrical N,N′-ethylene (acetylacetoneiminatosalicylideneiminato) and Schiff bases has been investigated by electrochemistry and ESR spectroscopy. In all cases, exhaustive reduction results in the formation of nickel(I) complexes. However, ESR data support the formation of a nickel(II)-stabilized ligand radical species at the early stage of the reduction of the non-symmetrical Schiff base complex.