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Disruption of copper homeostasis is associated with a number of severe diseases including Alzheimer’s disease (AD), Parkinson’s disease (PD), Wilson’s disease, and Menkes syndrome. Given this association, the detection and capture of Cu2+ in biological fluids and tissues may provide a new direction for the diagnosis and treatment of related disorders. The current analytical approaches, however, are challenging due to the high cost, complexity, and long time required to prepare and analyze samples. Here, we report a novel salen ligand, namely N,N’-(1,2-phenylene)bis(1-(1H-imidazol-4-yl)methanimine) (pimi), which can readily detect and concurrently capture Cu2+ from aqueous as well as biological mediums. Pimi can selectively and specifically detect Cu2+ from biofluid and cellular samples with rapid ccresponse time (

This work deals with the synthesis, spectroscopic studies and catalytic evaluation of the novel chiral salen (L1H2) and (L2H2) ligands and their chiral boronate [L1(B1-4)] and [L2(B1-4)] complexes. Initially, the reaction of 5-azidomethyl salicylaldehyde and (R)-(−)-2-amino-1-butanol in absolute ethanol afforded a new chiral salen ligand (L1H2). Then, a novel chiral salen ligand (L2H2) have been prepared from chiral salen ligand (L1H2) for the synthesis of boronate [L2(B1-4)] complexes through click reaction approach under ambient conditions. The reaction of chiral salen (L1H2) and (L2H2) ligands with various boronic acids afforded a new tetra-coordinated mononuclear chiral boronate [L1(B1-4)] and [L2(B1-4)] complexes. All the compounds are remarkably stable crystalline solids and were obtained in good yields. For the full characterization of newly synthesized chiral salen ligands and their boronate complexes, the FT-IR, UV–Vis, NMR (1H, 13C, and 11B), LC-MS, and elemental analysis techniques have been used. The well-shaped chiral boronate compounds were investigated as catalyst for the asymmetric transfer hydrogenation (ATH) of aromatic ketones under appropriate settings. Particularly, it was proved that the ferrocene-based boronate compounds can afford an efficient catalytic conversion compared to the other boronate complexes in the asymmetric transfer hydrogenation catalytic studies.

A new derivative of dioxouranium(VI) salen complex, [UO2(L)(pyridine)], where [L = N,N′-Bis(2-hydroxybenzylidene)-2,2-dimethyl-1,3-propanediamine] is synthesized and characterized by elemental analysis (C, H, N), FT-IR, ESI-MS spectrometry, UV/Vis, fluorescence, 1H and 13C NMR spectroscopy and thermal gravimetric (TG) study. Furthermore, the single crystal X-ray diffraction measurements of the complex were carried out at 100 and 273 K. The crystal structure measurements revealed that the complex has distorted pentagonal bipyramidal geometry with uranium atom located at the centre and bonded to two phenoxy oxygen and two azomethine nitrogen in tetradenate fashion and one nitrogen from pyridine making it seven coordinated. In addition, the photoluminescence property of the complex was also recorded. Keywords: Uranyl complex, Crystal structure, Photoluminescence

The H2O2 oxidation of l -cysteine and s-alkyl- l -cysteines (s-met- l -cys, s-et- l -cys & s-pro- l -cys) catalyzed by iron(III)–salen (salen = N,N′-bis(salicylidene)ethylenediaminato) complexes in aqueous CH3CN proceeds through Michaelis–Menten kinetics. The rate constant (k) values correlate well with Hammett σ constants, which gives the positive reaction constant (ρ = 1.5–1.9) value. The CV of oxoiron(IV)-salen ion shows a clear oxidation peak at 1.28 V in 0.1 M phosphate buffer (PB) solution using 0.1 M tertiary butyl ammonium perchlorate (TBAP) as supporting electrolyte at 266 K. The rate of the reaction is highly sensitive to the length of the alkyl chains present in the l -cysteines, pH and solvent composition of the medium. The calculated binding constant values (Kf) in the range of 117–613 M−1, indicate that iron(III)–salen complexes carrying electron donating substituents in the salen ligand have higher binding constant values compared to those carrying electron withdrawing substituents. Product analysis shows the conversion of l -cys to its disulfide and s-alkyl- l -cys to the corresponding sulfoxides. Based on the spectral and kinetic data the plausible mechanism has been proposed.

4-(Diethylamino) salicylaldehyde based Salen ligands were synthesized and studied using density functional theory (DFT) employing B3LYP/6-31G(d) method. These dyes exhibited intramolecular charge transfer (ICT) which were examined for their photophysical properties. They show red to deep red absorption and emission respectively in the range of 562–575 nm and 596–635 nm and exhibited positive solvatochromism which is supported by linear and multi-linear regression analysis. Oscillator strengths and transition state dipole moments are studied to understand charge transfer (CT) characteristics. These deep red emissive fluorophores showed aggregation-caused quenching (ACQ). The spectral variations were analyzed by linear solvation energy relationships proposed by Kamlet-Taft and Catalan which indicated that solvent polarizability/dipolarity influences more compared to solvent acidity or basicity. Bathochromic shift in emission and increase in dipole moment in the excited state signify ICT character. The calculated electronic spectra of dyes are elucidated on the basis of TD-DFT calculations. Spectroscopic and computational methods were used to obtain linear polarizability, hyperpolarizability of the dyes and have better NLO properties than urea. Molecular Electrostatic Potential (MEP), NBO, HOMO-LUMO analysis, global chemical reactivity descriptors are studied at same level DFT.

A dimethylformamide bound mononuclear dioxouranium(VI) salen based complex with propylene linkage is prepared from a salen ligand, H 2 L, 2,2-(1E,1E)-(2,2-dimethylpropane-1,3-diyl)bis(azanylylidene)bis(methanylylidene)diphenol. The structure of the reported uranyl complex is established by elemental analysis (C, H, N), FT-IR and NMR spectroscopic methods, and single crystal X-ray diffraction measurements. The X-ray diffraction analysis shows that the crystal is monoclinic with space group P2 1 /n (no. 14), a = 7.99198(6) A, b = 12.14896(9) A, c = 23.76987(19) A, β = 97.4163(7)°. Furthermore, to obtain insights into the structure, DFT calculations have been made employing 6-31G (d,p) and GENECP basic sets. The findings obtained from the theoretical calculations are quite close with the results obtained from the experimental data.

Several aluminium alkyl and alkyloxide complexes supported by a thioether-bridged salen ligand were synthesized by the protonolysis reaction. Reactions of N,N’-bis(3,5-di-tert-butylsalicylidene)-2,2’-diaminophenylsulfide (H2L) with one or two equivalents of AlMe3 in toluene at 100 °C afforded the corresponding mono- and binuclear aluminium methyl complexes LAlMe (1) and L(AlMe2)2 (2). Treatment of the in situ generated complex 1 with one equivalent of ROH (R = PhCH2, iPr, CH3OCH2CH2) produced the desired aluminium alkyloxide complexes LAlOCH2Ph (3), LAl(OiPr) (4) and LAlO(CH2)2OCH3 (5). All the molecular structures were established by single crystal X-ray diffraction studies. It was found that aluminium alkyloxide complexes 3-5 showed higher catalytic activity for the homopolymerization of e-caprolactone (e-CL) than corresponding aluminium methyl complexes 1 and 2. Furthermore, these alkyloxide complexes were also efficient initiators for the copolymerization of L-lactide and e-CL to give practically random copolymers.

A series of bifunctional metal-salen complexes bearing ionic liquid substituents were investigated as catalysts for the synthesis of cyclic carbonates from carbon dioxide (CO2) and epoxides using density functional theory (DFT) and energy span model. Detailed studies reveal that the three-step mechanism involving the ring-opening of propylene oxide (PO), CO2 insertion, and ring-closure to the cyclic carbonate is kinetically more favorable than the two-step mechanism. The effect of ionic liquids, epoxide substituents and metal center of the metal-salen complexes were explored. Amino functionalized ionic liquids substituents tethered to the salen ligand of the metal-salen complexes performed well. Epoxide substituents affect the cycloaddition mainly through the electronic effect and the substituent that lowers the negative charges of the ring carbon atom to be attacked favors the cycloaddition. When the salen ligand is fixed, the catalytic activity metal-salen complexes can be measured by the interaction between the oxygen atom (O) of epoxides and the central metal (M) and there is a linear relationship between the energy span and the M-O bond length, which can be used as a descriptor to screen CO2 conversion catalysts.

A panel of stable ruthenium carbene complexes bearing a tetradentate salen ligand, with their carbene-C atom adjacent to heteroatom, were synthesized from cis-β-Ru(II)-bis(CO) complex by reacting with the corresponding carbene precursors. These carbene complexes, which were fully characterized by elemental analysis, NMR, IR spectroscopy and X-ray-crystal structure determination, all adopt a cis-β configuration; the heteroatom (N or O) adjacent to the carbene C atom contributes to the high stability of these complexes both in solution and in solid state. DFT calculations were also performed to gain insight into the Ru-Ccarbene bonds.

A Pd(II)-salen complex derived from salen ligand is reported. The reported complex is investigated by microanalyses (C, H, N), ESI-MS spectrometry, FT-IR, 1H and 13C NMR and UV/Vis spectroscopic studies. In addition, crystal structure measurement study has also been carried out in order to confirm the structure of Pd(II)-salen complex. In order to explore the insights into the structural bonding of the studied complex, computational measurements has been carried out. Combined topology and NBO studies were made to explore the nature of Pd O and Pd N bonding in the complex. The natural charges showed that the transfers of the negative charge from the ligand to palladium atom is at 1.4157–1.4312 e. Atom in a molecule (AIM) analysis showed the electron density (ρ(r) > 0.1) and its Laplacian ( ∇ 2 ρ(r) > 0). These topological parameters showed that covalent bonding interactions are dominant in Pd N and Pd O bonds. However, Pd N bonds have more covalent characters than Pd O bonds, which is further confirmed by the ratio of local electron potential energy density to the local electron kinetic energy density (|V(r)|/G(r)) found to be higher for Pd N bonds (1.1683–1.1993) as compared to Pd O bonds (1.0689–1.0926). AIM and NBO reveal that shorter Pd N and Pd O bonds have higher interaction energies (Eint) and hence higher bond covalence.

A new zinc complex based on a tetradentate N,N,O,O-type coumarin salen ligand (H2L) was prepared and characterized by elemental analysis, thermogravimetric analysis (TGA), and FT-IR, UV–vis and 1H NMR spectroscopy. The complex [Zn(L)(H2O)]·H2O was active in the ring opening polymerization (ROP) of e-caprolactone under solvent-free conditions, producing polycaprolactone (PCL) with a molecular weight up to 17,700 g mol−1 and a narrow molecular weight distribution. 1H NMR analysis showed that the PCL obtained was mainly linear, having hydroxymethylene groups in the chain ends. Differential scanning calorimetry (DSC) showed that the polymer had high crystallinity (61%) and that TGA had a decomposition temperature above 300 °C.

In this research, a simple, efficient, inexpensive, rapid and high yield method for the purification of 6 × histidine-tagged recombinant protein was developed. For this purpose, manganese ferrite magnetic nanoparticles (MNPs) were synthesized through a co-precipitation method and then they were conveniently surface-modified with tetraethyl orthosilicate (TEOS) in order to prevent oxidation and form high density of hydroxyl groups. Next, the salen ligand was prepared from condensation reaction of salicylaldehyde and 3-aminopropyl (trimethoxy) silane (APTMS) in 1:1 molar ratio; followed by complexation with Ni(OAc)2.4H2O. Finally, the prepared Ni(II)-salen complex conjugated to silica coated MNPs and MnFe2O4@SiO2@Ni-Salen complex nanoparticles were obtained. The functionalized nanoparticles were spherical with an average diameter around 70 nm. The obtained MNPs had a saturation magnetization about 54 emu/g and had super paramagnetic character. These MNPs were used efficiently to enrich recombinant histidine-tagged (His-tagged) protein-A from bacterial cell lysate. In about 45 min, highly pure His-tagged recombinant protein was obtained, as judged by SDS-PAGE analysis and silver staining. The amount of target protein in flow through and washing fractions was minimal denoting the high efficiency of purification process. The average capacity of the matrix was found to be high and about 180 ± 15 mg g−1 (protein/MnFe2O4@SiO2@Ni-Salen complex). Collectively, purification process with MnFe2O4@SiO2@Ni-Salen complex nanoparticles is rapid, efficient, selective and whole purification can be carried out in only a single tube without the need for expensive systems.

Polymeric transition metal complexes with salen-type Schiff base ligands are considered as promising materials for modification of electrical double layer capacitor electrodes. Electrochemical properties of these polymers that define their performance in supercapacitors should be influenced by the ligand structure but this influence has never been systematically investigated. This article describes results of a comparative study of capacitance and charge transfer rate in polymeric nickel complexes with six different salen-type ligands using electrochemical impedance spectroscopy, analyzes advantages and limitations of this method vs. cyclic voltammetry, and provides some insights into the structure and morphology of nickel-salen type polymers. Analysis of results obtained by different analytical techniques shows that introduction of methoxy-substituents into the phenyl rings of the salen ligand and different substituents to the diamine bridge of the ligand causes noticeable changes in electrochemical properties of corresponding polymeric nickel complexes. Experimentally obtained values of gravimetric and volumetric capacitance, as well as effective charge diffusion coefficient provide guidelines for selection of most suitable nickel-salen type polymers for application in energy storage devices, including supercapacitors.

The syntheses, structures and photoluminescence properties are reported for two new binuclear cyclometalated iridium(III) complexes, [Ir2(ppy)4(L)] (1) and [Ir2(F2-ppy)4(L)] (2) (ppy=2-phenylpyridine, F2-ppy = 2-(2,4-difluorophenyl)pyridine, H2L=N,N′-bis(2-hydroxynaphthyl methylidene)-2-hydroxy-1,3-propanediamine. X-ray crystal diffraction shows that L ligands adopt a tetradentate mode to bridge ir(III) ions to form binuclear structures. There are π-π stacking interactions between the binuclear structures, which results in the formation of 3D supramolecular networks. UV–vis absorption spectra and photoluminescence spectra show that the introduction of F− groups in the benzene rings of ppy ligands causes blue shift.

Six new manganese(III) derivatives using the ligand H2MeOsalen: N,N′-ethylenebis(3-methoxysalicylaldiimine), have been synthesized and structurally characterized. In all cases the manganese ion is six-coordinated and occupies the internal cavity of the bicompartmental salen ligand. The manganese ion completes its coordination environment with one axial water molecule and one additional ligand, either water, ethanol or one acetate anion. The molecular unit is dimerized by the insertion of the coordinated water molecule into the external MeOsalen cavity of one neighbouring complex. This supramolecular dimer constitutes the structural basis for these compounds, the differences arising from the intermolecular hydrogen bonds involving the counter anions and crystallization solvent molecules. In this way, examples of pseudopolymorphism, cocrystallization and water/anion tapes held by the interaction with the complex dimers are described. The compound [{Mn(MeOsalen)K(H2O)0.5}2(μ-OOCMe)](PF6)3·HOCH2CH2OH is a heterometallic Mn/K derivative where the potassium ion occupies the external cavity, while the coordination of the manganese ion is completed by bridging acetate and ethyleneglycol ligands. The formation of ethyleneglycol is attributed to a stoichiometric oxidation of the ethanol solvent, attributed to the presence of the potassium ion in the complex.

Solvent selection plays a significant role in the purification process and homogeneous reaction. Solubility data is the most intuitive data to reflect the dissolution effect. The solubility of N, N′ - bis - (salicylaldehyde) ethylenediamine (1) (SalenH2) and N, N′ - ethylenebis (salicylideneiminato) methylaluminum (2) (SalenAlMe) in selected solvents was measured from 268.15 K to 318.15 K under an inert atmosphere. All the operations were carried out using standard Schlenk line techniques or in a glove box. The difference in solubility can be attributed to cohesive energy density, polarity, steric hindrance, as well as intermolecular interactions. Van't Hoff equation, Apelblat model, Polynomial equation, NRTL model, Wilson model, and UNIQUAC model were applied for correlating the experimental solubility data. These thermodynamic models were evaluated by the average relative deviation (ARD). Among those, the Apelblat model had wide applicability with an average ARD

Two major health crisis of today's world are antimicrobial drug resistance and type II diabetes. To tackle them, there is an immediate requirement for the development of new and safer drugs and the present work is one such quest for novel and efficient drug candidates. We have developed three trace metal coordination compounds tethered with a reduced salen ligand {H2(hpdbal)2-an} (L), namely, a manganese-salan complex, [MnII(H2O)2{(hpdbal)2-an}] (1), a nickel-salan complex, [NiII{(hpdbal)2-an}] (2) and a copper-salan complex, [CuII{(hpdbal)2-an}] (3). The compounds were characterized by elemental analysis, vibrational spectroscopy, electronic spectroscopy, thermogravimetric analysis, nuclear magnetic resonance and electron-paramagnetic resonance techniques. The compounds were evaluated for antimicrobial activity against seven pathogens (Escherichia coli, Klebsiella pneumonia, Acinetobacter baumannii, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Cryptococcus neoformans) and antidiabetic activity by mimicking diabetic environment on the immortal human liver cancer cells, HepG2. Complexes 1 and 2 were additionally tested for their reactivity and stability in biological media mimic conditions. The nickel(II) salan complex (2) exhibited noteworthy antifungal activity against Candida albicans and the manganese(II) salan complex (1) induced increased glucose uptake by the insulin resistant cells. Both compounds were found to be stable when solution pH conditions were varied from 3 to 9. They exhibited strong affinity of binding towards a carrier protein, bovine serum albumin which was evaluated with the aid of multi-spectroscopic techniques.

A novel binuclear phenoxo-bridged zinc complex obtained from the interaction of ligand, 2,2-(1E,1E)-(2,2-dimethylpropane-1,3-diyl)bis(azanylylidene) bis(methanylylidene)diphenol with zinc chloride is reported. The synthesized and isolated zinc complex has been characterized by FT-IR, 1H- and 13C- NMR, ESI-MS, TGA/DTA and single crystal X-ray diffraction studies. The phenoxo-bridge in this binuclear Zn(II) complex is due to the phenolic oxygen of the salen liagnd. The complex crystallizes in monoclinic P-1 space group, and different geometry has been assigned for both zinc ions in the complex.

A pair of chiral Eu(III) complexes prepared from enantiopure bis(1H-pyridin-2-one)salen ligands show strong sensitized luminescence and high circular dichroism activity in the region of π–π∗ transitions.

The catalytic activity of cobalt(III)–salen ion catalyzed selective H2O2 oxidation of organic sulfides to sulfoxides is examined using spectrophotometric technique. The catalytic reaction proceeds through Michaelis–Menten kinetics and the rate of the reaction is highly sensitive to the nature of the substituent present in the substrate as well as in the salen ligand. The product analyses show that the aryl methyl sulfides are selectively oxidized to the corresponding sulfoxides. Based on the spectral and kinetic studies two possible mechanisms have been proposed.

Cobalt (II) Salen complex catalysts were synthesized and immobilized through covalent bonds on synthetic silica (SBA-15) and commercial supports, including silica (SiO2), alumina (Al2O3) and granular activated carbon (C). Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV–vis), diffuse reflectance ultraviolet-visible spectroscopy (DR–UV–vis) and X-ray diffraction (XRD) were used to characterize and follow the synthesis of the cobalt (II) Salen complex The UV–vis absorption spectra confirmed the formation of the Salen ligand and its coordination with the Co (II). FTIR spectra showed the incorporation of the Co Salen complex and its anchoring to the support was confirmed by DR–UV–vis. The catalytic activity was evaluated measuring the oxidation of phenol by air in a buffer solution using micellar electrokinetic chromatography (MEKC). The effects of support, initial substrate concentration, pH, oxidant (O2 vs H2O2) and temperature were investigated. The best catalytic performance was obtained when the Co Salen complex was immobilized on SBA-15 (Co Salen/SBA-15). Conversely, the results suggest that the activated carbon promoted the irreversible adsorption of the substrate. The Co Salen support was also characterized by scanning electron microscopy (SEM) to elucidate the morphology. Elemental analysis using energy dispersive X-ray spectroscopy (EDX) exhibited better Co Salen dispersion on the SiO2 and SBA-15 supports. The cobalt loading calculated from atomic absorption spectroscopy (AAS) was 0.22, 0.20, 0.14 and 0.09 mmol/g for the Co Salen supported on SiO2, SBA-15, Al2O3 and C, respectively. A specific surface area of 736.13 m2/g and a nanoporosity of 3.62 nm were obtained for SBA-15 using N2 physisorption analysis; this high specific surface area is characteristic of SBA-15 and plays a critical role in the reported activity. According to these results and the corresponding data analysis, the catalyst promoted the oxidation of phenol with a reversible first-order kinetic reaction in air, as observed from the data obtained at 3 different temperatures (25, 38 and 50 °C). These results enabled the calculation of activation energy values of 63 and 57 kJ/mol. In addition, the Co Salen/SBA-15 showed very good selectivity toward the production of catechol, which is one of the most important precursors in the chemical industry.

Two new homometallic coordination polymers 1 and 2 have been prepared by the directly one-step hydrothermal reactions of a carboxylate-functionalized salen ligand with Zn(II) and Co(II) ions, respectively. 1 exhibits a 3D open framework built by [Zn4(μ4-O)(carboxylate)8] units and double Zn-salen ligands, while 2 shows a 1D chain structure constructed by cobalt ions and the ligand derived from the hydrolysis to one C N bond of salen ligand. The preliminary fluorescence measurements of 1–2 show the influence of structure on the property.

Two new structure-related pyrazolone-type Salen ligands, N,N′-ethylamine bis[1-(4-methoxy-phenyl)-3-methyl-4-benzoylimino-2-pyrazoline-5-ol](H2LI) and N,N′-ethylamine bis[1-(4-methoxy-phenyl)-3-methyl-4-acetylimino-2-pyrazoline-5-ol](H2LII) have been designed and synthesized with the ultimate aim of self-assembling novel Zn(II) compounds with interesting fluorescence properties. Reactions of Zn(OAc)2 with the two ligands led to the formation of two new Zn(II) complexes with the formulae of [ZnLI(CH3OH)] (1) and [Zn2LII2] (2), which have been characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analysis, IR spectroscopy and thermal gravimetric analysis. Mononuclear complex 1 with the pentacoordinated zinc(II) ion hosted into the N2O3 compartment crystallized in the monoclinic space group P21/c, while the hydroxyl-bridged dinuclear [Zn2LII2] complex (2) with the pentacoordinated zinc(II) ion hosted into the N2O2 compartment crystallized in the monoclinic space group C2/c and had a Zn–O–Zn–O four-membered ring. The structure determinations show that substituted group at the 4,4′-position of the this kind of Salen ligands are important factors influencing the crystalline array. The fluorescent properties of the two compounds at ambient temperature both in solid state and solution were also investigated. The results provided interesting insights into ligand effects on the structures and fluorescent properties of zinc(II) coordination complexes.

In this work, we aim to assemble a polymeric copper(II) network by ligand modifications with carboxylic acid functional groups. A chiral, reduced salen ligand, salan R,R-H21 with pendant ester functionalities has been synthesized. Its copper(II) complex, [Cu(R,R-1)], has been isolated, and its crystal structure determined by X-ray crystallography. Hydrolysing the ester groups of R,R-H21 to carboxylic acids yields R,R-H42 as the hydrochloride salt R,R-H42·2HCl. Treatment of R,R-H42·2HCl with copper(II) acetate in the presence of triethylamine yields the complex [Cu(R,R-H22)]n and X-ray structural analysis reveals that this consists of a 2D polymeric network. Each copper(II) center is bound within the near square-planar N2O2 donor set of the Schiff base ligand [R,R-H22]2 − and pendant carboxylic acid groups of adjacent units coordinate through the CO2H carbonyl units in the axial sites of the copper ion to complete an axially distorted octahedral coordination environment. The sheets are stacked via interdigitation of the cyclohexyl domains, giving an overall porous assembly containing carboxylic acid functionalities. This has proven to be an effective strategy for adding the dimensionality of metal–organic complexes by carboxylic acid functionalization of ligands.

The one-pot reaction of (1S,2S)-(+)-1,2-diaminocyclohexane, 3-tert-butyl-2-hydroxybenzaldehyde and Zn(OAc)2·1.5H2O in methanol under reflux gives the diastereoselective formation of the first zinc(II)-salen double helicate, P-(S, S)-1, which adopts a right-handed helicity. The stereochemistry of the helicates can be readily tuned through varying the chiral diamine backbone.

A series of novel chiral salen Mn(III) complexes possessing a thermoregulated phase-transfer function was prepared for the first time. The preparation involved the introduction of the “smart” poly(N-isopropylacrylamide) (PNIPAAm) group to the framework of the chiral salen Mn(III) complex by covalently connecting to one side of the 5-position in the salen ligand (complex 1 ) or by axially grafting onto the metal center of the complex (complex 2 ). Characterization results suggested the presence of the PNIPAAm moiety and active sites in the complexes. The thermoresponsive PNIPAAm groups imparted inverse temperature-dependent water solubility to the PNIPAAm-based complexes, which allowed them to undergo thermoregulated phase-separable catalysis during oxidative kinetic resolution (OKR) in water. Excellent enantioselectivity (up to 96%) with high kinetic resolution efficacy (13.1) was achieved over complex 1 in the aqueous OKR of α -methylbenzyl alcohols, and this efficacy was significantly higher than that obtained over neat complex. The PNIPAAm-based complexes can also be easily recovered by simply regulating the temperature and be reused for four times without obvious loss of enantioselectivity and activity.

Synthesis and characterization of two ruthenium(II) and osmium(II) complexes (1 and 2) having carbohydrate derived salen ligand and in situ ligand reduction are reported. The1,2-O-isopropylidene-3,5-diazido-3,5-dideoxy-α- d -xylopyranoside (L1) was reduced by catalytic hydrogenation using continuous flow hydrogen reactor in the presence of salicylaldehyde to form the corresponding bis-imino derivative H2L2. The ligand H2L2 has been transformed to H2L3 upon reduction of one of the imine bonds in consequence to the oxidation of the leaving PPh3 group to POPh3. Systematic spectroscopic characterization, 1H and 13C NMR, mass spectrometry, electronic spectra reveals the composition of the complexes. X-ray crystal structures of both the complexes are reported. Detailed electrochemical studies reveal the redox behaviour of the complexes and DFT calculations help to get the idea about the intense lowest-energy absorption for these two complexes.

The catalysis effect of [Fe(III)-salen]Cl complex on the decolorization and degradation of Malachite Green in the Fenton system was investigated in this study. A significant decolorization enhancement was observed in the presence of only trace amount of the complex without additional equipment or external energy. The effects of reaction parameters were studied and the results showed that the increase of [Fe(III)-saler]Cl complex, molar ratio of salen ligand to Fe(III) and initial concentration of H2O2 favor the increase of decolorization rate. The increase of initial concentration of the dye leads to the decrease of decolorization rate and the optimum pH was the original pH of Malachite Green solution. Under the optimal condition, the decolorization and TOC removal rates after 24 min treatment were 97.94% and 54.35% respectively. Hydroxyl radical was identified as the main active oxidant species in the [Fe(III)-salen]Cl complex catalyzed Fenton system. The degradation intermediates of Malachite Green were analyzed and a possible reaction mechanism was proposed. The decolorization of Malachite Green obeyed the pseudo-first order equation and the activation energy was calculated by the related kinetic constants, which was only 49.13% of Fe(III) Fenton system. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.

Chiral vanadium(IV)–salen complexes with variable spacer length were immobilized on polysiloxanes, which were used as catalytically active stationary phase in on-column reaction gas chromatography, on-column reaction electrophoresis, in flow-through reactors and as coating of laboratory glassware. These devices modified with the catalytically active stationary phase were employed in asymmetric sulfoxidations using hydrogen peroxide as the oxidant. The here presented approach combines catalysis and chromatographic analysis in a single step and allows to study the kinetics of reactions and to optimize reaction conditions. The initial reaction kinetics and enantioselectivity of the sulfoxidation of benzylphenylsulfide was studied in dependency of the spacer length of the immobilized salen ligand. A drastic influence of the spacer length on the enantioselectivity in the here investigated sulfoxidation was measured.

Cyclic voltammetry, controlled-potential (bulk) electrolysis, gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), and high-performance liquid chromatography–electrospray ionization–mass spectrometry (HPLC–ESI–MS) have been employed to investigate the direct reduction of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) at a carbon cathode in dimethylformamide (DMF) containing 0.10 M tetra-n-butylammonium tetrafluoroborate (TBABF4) as well as the nickel(I) salen-mediated reduction of CFC-113 in the same medium. Cyclic voltammograms for direct reduction of CFC-113 show two irreversible cathodic peaks attributable to formation of, first, 1-chloro-1,2,2-trifluoroethene (CFC-1113) and, second, trifluoroethene (HFC-1123); bulk electrolyses of CFC-113 at potentials corresponding to each of the cathodic peaks afford CFC-1113 and HFC-1123, respectively, in essentially quantitative yield. Cyclic voltammograms for reduction of nickel(II) salen in the presence of CFC-113 provide evidence for the catalytic formation of CFC-1113 and HFC-1123, and bulk electrolyses involving electrogenerated nickel(I) salen lead to mixtures of CFC-1113 and HFC-1123, although 1,1,1,2-tetrafluoroethane (HFC-134a) has been detected as a minor product. It has been determined with the aid of HPLC–ESI–MS that the salen ligand of the nickel(I) catalyst is modified during the catalytic reduction of CFC-113. A mechanistic scheme is proposed for the direct reduction of CFC-113.

Two novel compounds [Mn(salen)(dmf)2]3[Mn(salen)(dmf)(H2O)][CdCl4]2·H2O (1) and {[Mn(salen)(CH3OH)]2}[Mn(salen)(CH3OH)2]2[CdI4]2 (2) have been synthesised via interaction of manganese metal and cadmium halide with in situ generated salen ligand (salen = N,N′-ethylene-bis-salicylideneaminato) in non-aqueous (dmf, CH3OH) solutions. X-ray structure analysis reveals that in solid state 1 contains mononuclear MnIII–salen species, whilst in 2 both monomeric and out-of-plane dimeric MnIII–salen complexes are present. Moreover, in 2 the monomeric units are linked by H-bonds, forming other dimers. Equilibrium between monomeric and dimeric units in solutions of 1 and 2 was found by ESI mass-spectrometry. The magnetic measurements of 2 demonstrated antiferromagnetic interactions between MnIII centres.

A series of novel chiral salen Mn(III) complexes with inherent phase-transfer capability were prepared by covalent linkage of the limidazolium IL moieties containing various PEG chains with chiral salen ligand at two sides of 5,5′-position. Technologies of characterization well suggested the presence of polyether chain, the IL linker, and the intact active sites in the complexes. The amphipathic nature of the PEG chain allowed the PEG-based catalysts to undergo built-in phase transfer, which in turn increased the reaction rates in water/organic biphasic systems. Enantioselective epoxidation of styrene, α-methylstyrene, indene, 1,2-dihydronaphthalene, 6-cyano-2,2-dimethylchromene, and 6-nitro-2,2-dimethylchromene catalyzed by the complexes with NaOCl gave >99% conversions within 60 min. The enantiomeric excess ( ee ) for the epoxides was in the range of 68–93%, except for styrene ( ee , 35%) and α-methylstyrene ( ee , 42%). Furthermore, the PEG-based complexes were stable and could be separated from the reaction mixture by control of the solvent.

Polymeric {TiO(salen)}n prepared from [Ti(OCHMe2)2(acac)2] and salen-H2 in MeOH and with an apparent chain structure, is mostly insoluble but dissolves when strongly heated in aromatic aldehydes or ketones, depositing the insoluble form again on cooling. p-Tolualdehyde performed differently, giving a red solution from which insoluble red crystals were deposited. X-ray crystallography showed the complex was [{Ti(salen)(O2CC6H4Me-4)-O-Ti(salen)(O2CC6H4Me-4)]. Solvent (1) (solvent = p-tolualdehyde or p-toluic acid) containing a Ti–O–Ti bridge. Reaction of {TiO(salen)}n with p-tert-butylbenzoic acid in the presence of excess p-tolualdehyde gave [{Ti(salen)(O2CC6H4CMe3-4)-O-Ti(salen)(O2CC6H4CMe3-4) ]. 4-CH3C6H4CHO (2) for which an X-ray crystal structure determination indicated similar connectivity around the metal as for (1). {TiO(salen)}n heated strongly in isobutyrophenone (PhCOCHMe2) also gave red crystals which X-ray analysis showed structural similarity to (1) and (2) but incorporating a PhCO2-ligand. {TiO(salen)}n heated in acetophenone gave a product which X-ray analysis showed was a dioxo-bridged dimer (4) in which C–C bond formation had occurred on one side of each salen ligand.

The spectroscopy, electrochemistry and electrogenerated chemiluminescence (ECL) of eight bisalicylideneethylenediamino (salen) metal complexes are reported. Two of the complexes contain an unsubstituted salen ligand and either cobalt(II) or nickel(II). The others have 1,2-cyclohexanediamonio- N , N ′-bis(3,5-di- t -butylsalicylidene) as the ligand, and chromium(III), aluminum(III), cobalt(II), cobalt(III) or manganese(II) as the metal center. The complexes have lowest energy absorption maxima between 350 and 430 nm. When excited at these wavelengths, the complexes emit between 417 and 594 nm in acetonitrile. Photoluminescence efficiencies ( ϕ em ) were between 0.0310 and 23.8 compared to Ru(bpy) 3 2+ (bpy = 2,2′-bipyridine; ϕ em = 1), with the aluminum complexes displaying the most intense photoluminescence. Both reversible and irreversible oxidative electrochemistry is displayed by the metal–salen complexes with oxidation potentials ranging between +0.152 and +1.661 V versus Ag/AgCl. The ECL intensity peaks at a potential corresponding to oxidation of both TPrA and the salen systems, indicating that both are involved in the ECL reaction sequence. ECL efficiencies ( ϕ ecl ) were between 0.0018 and 0.0086 when compared to Ru(bpy) 3 2+ ( ϕ ecl = 1) in acetonitrile (0.05 M tri- n -propylamine (TPrA) as an oxidative–reductive ECL coreactant). Also, qualitative studies using transmission filters suggest that the complexes emit ECL in approximately the same region as their photoluminescence, indicating that the same excited state is formed in both experiments.

A novel enantiopure salen ligand bearing a diphenylphosphine oxide on the 3-position of one aromatic ring was synthesized and combined with Ti(O i -Pr) 4 as a monometallic bifunctional catalyst for asymmetric cyanosilylation reaction of aldehydes with trimethylsilyl cyanide (TMSCN). The catalyst system exhibited excellent activity and moderate enantioselectivity. The addition of TMSCN to 4-nitrobenzaldehyde in the presence of 1 mol% catalyst loading could complete within 10 min at ambient temperature. An intramolecularly cooperative catalysis was observed in this system wherein the central metal Ti(IV) is suggested to play a role of Lewis acid to activate aldehydes while the appended diphenylphosphine oxide worked as Lewis base to activate TMSCN.

This brief review deals with the development of a general protocol for the synthesis of μ-oxido divanadium(V) compounds [LOV V -(μ-O)-V V O(Salen)] (L = L 1 –L 5 ) ( 1 – 5 ) incorporating coordination asymmetry. One of the vanadium centers in these compounds has an octahedral environment, completed by tetradentate Salen ligand, while the other center has a square pyramidal geometry, made up of tridentate biprotic Schiff-base ligands (H 2 L 1–5 ) with ONO ( 1 – 3 ) and ONS ( 4 , 5 ) type donor combinations. Single crystal X-ray diffraction, ESI-MS, and multi-nuclear NMR ( 1 H and 51 V) spectroscopy have been used extensively for the characterization of these compounds. The V 2 O 3 core in these compounds, save 3 , has a rare type of twist-angular structure. The V(1)⋯V(2) separations (3.7921(7)–3.3084(6) A) are by far the largest in these compounds compared to their peers containing a V 2 O 3 core. The molecules retain their unsymmetrical binuclear structures also in solution as established by NMR spectroscopy. The mixed-oxidation compound (ImH)[L 4 OV IV -(μ-O)-V V OL 5 ] 7 containing two dissimilar ligands has a V 2 O 3 core with a syn -angular structure and exhibits crystallographically imposed mirror symmetry due to static disorder. In solution of donor solvents, this angular core structure changes into a linear one ( anti -linear) by accepting solvents in to the vacant coordination site of the metal centers. Finally, the protocol for the synthesis of heterobimetallic compounds with vanadium(V) and Re(VII) combination flanked by a single μ-oxido bridge has been developed in which the precursor complexes [V IV OL 6,7 ] (H 2 L 6,7 are Salen type of ligands) are allowed to oxidize aerially in the presence of added perrhenate anion. The oxidized [V V OL 6,7 ] + species hold the ReO 4 − anion in the vacant coordination site of the metal ion, trans to the terminal oxido group, thus generating the V V –O–Re VII moiety in the heterobimetallic compounds ( 9 and 10 ). Both X-ray crystallography and 1 H NMR spectroscopy have been used to establish the identities of these compounds. In compound 9 , the Re(1)–O(11)–V(1) bridge angle is barely linear (170.2(3)°) with a Re⋯V separation of 3.9647(9) A. The redox behavior of 9 and 10 are quite interesting, each undergoing two reductions both in the positive potential range at E 1/2 = 0.59 and 0.16 V vs. Ag/AgCl reference and have single-electron stoichiometry, confirmed by constant potential coulometry.

Gas-phase equilibrium measurements have been used to determine the relative binding affinities of 18 ligands to Jacobsen's manganese salen catalyst. The group of ligands spans 5.7 kcal/mol and includes seven functional groups (alcohol, ketone, ester, acyclic ether, cyclic ether, epoxide, and amine). The data follow general trends seen in other gas-phase metal cation affinities, but are influenced to a much greater extent by steric effects. For example, a 2° amine is a stronger binder than a 1° amine (as typical for gas-phase cation binding), but a 3° amine is a much weaker binder due to excessive crowding with the bulky salen ligand. The impact of steric effects was also explored with computational modeling at the B3LYP/6-311+G(d,p)/B3LYP/6-31G(d) level. The study demonstrates the utility of using mass spectrometry to probe the ligand binding characteristics of sterically demanding, metal-centered catalysts.

A variety of transition metal tetrahydro-salen complexes M-[H 4 ]Salen (M = Cu, Co and Fe) and the corresponding metal salen complexes M-Salen were firstly tethered onto amino-functionalized mesoporous SBA-15 and screened as heterogeneous catalysts for aerobic epoxidation of styrene. The mesoporous structural integrity throughout the tethering procedure, the successful tethering of the organometallic complexes, the loadings of metal ions and organic ligands as well as the catalyst surface constitution and location of active organometallic species on the SBA-15 support were determined by comprehensive characterization techniques such as XRD, N 2 adsorption/desorption, TEM, FT-IR, UV–vis spectroscopy, ICP-AES, XPS and TG/DSC. The tethered catalyst M-[H 4 ]Salen-SBA (M = Cu or Co) exhibits improved reactivity than the corresponding M-Salen-SBA catalyst due to the incorporation of a modified coordination environment of the central metal cations by C N bond hydrogenation. However, Fe-[H 4 ]Salen-SBA shows lower reactivity as compared to Fe-Salen-SBA possibly due to the easy formation of relatively inactive dinuclear iron(III) tetrahydro-salen complexes, verified by XPS and ESR. The recycling results of these heterogeneous catalysts exemplified by Co-Salen-SBA, Co-[H 4 ]Salen-SBA and Fe-Salen-SBA, show good recoverability without significant loss of activity and selectivity within successive runs. Heterogeneity tests of three sample catalysts confirm the high stability of cobalt catalysts against leaching of active species into solution.

A dimeric salen ligand derived from L-tartaric acid was synthesized through linking two salen units with 1,6-dibromohexane. The corresponding Ti complex was proved to be an efficient catalyst for asymmetric addition of trimethylsilyl cyanide to aldehydes, providing the corresponding optically active trimethylsilyl ether of cyanohydrins with moderate to good enantiomeric excesses and excellent yields under relatively low catalyst loading condition.

A new chiral salen ligand based on two ferrocenyl groups is designed. Unlike known salen ligands, of which chirality originates from central and axial chiral centers, the chirality of this ligand comes from the planar chiral ferrocenyl groups. The ligand is synthesized stereoselectively using a novel aromatization strategy starting from a ferrocene derivative, which was readily prepared using a known chiral auxiliary approach.

Two dinuclear cobalt/copper compounds have been isolated from the reaction between N,N′-ethylenebis(salicylideniminato)cobalt(II), [Co(salen)], and copper(II) chloride in different conditions. The first one is a dinuclear cobalt(III)/copper(II) derivative, [Co(salen)Cl2Cu(EtOH)2Cl], 1, that have the cobalt atom six-coordinated to the four donor atoms of the salen ligand and to two chlorine atoms in a slightly distorted octahedral environment and the copper atom five-coordinated to the two bridging oxygen atoms of the salen ligand, two ethanol molecules and one extra chlorine atom. This compound is the only reported example of a cobalt/copper derivative with the cobalt maintaining the salen coordinative site, since the usual reaction takes place by a transmetalation process. This reaction is observed in the second derivative, [Cu(salen)CoCl2], 2, where the copper atom displaces the cobalt from the salen cavity. The copper atom adopts a square-planar coordinative environment, while the cobalt is tetrahedrically coordinated to the two bridging oxygen and two chlorine atoms. Both compounds present several intermolecular contacts that increase the dimensionality in the crystal and some of which can transmit magnetic interactions. The magnetic properties confirm the structural picture, with isolated copper(II) centres in 1, where the cobalt(III) is in the low spin form, and with antiferromagnetically coupled S = 1/2 and S = 3/2 centres in 2.

[Iron(III)–salen] complexes (salen = N,N′bis(salicylidene)ethylenediaminato) efficiently catalyze the H2O2 oxidation of organic sulfides and sulfoxides. The spectrophotometric kinetic studies show that these reactions follow Michaelis–Menten kinetics. The rate of the reaction is highly sensitive to the nature of the substituent present in the aryl moiety of ArSMe or ArS(O)Me and phenolic moiety of salen ligand. The plot of log k values of p-XC6H4SMe and p-XC6H4S(O)Me with Hammett σ constant give the reaction constant (ρ) values in the range of −0.7 to −1.5 and −0.7 to −1.0, respectively, for different iron(III)–salen complexes But the plot of log k values with σ gives positive ρ value when we introduce substituents in the phenolic moiety of iron(III)–salen complexes. The binding of the substrates with iron(III)–salen complexes is more pronounced with the sulfoxides. The product analyses show the selective oxidation of sulfides to sulfoxides and sulfoxides to sulfones. Based on the spectral and kinetic studies the possible mechanisms have been proposed.

Mononuclear and heterodinuclear complexes of the salen-type ligand H2LH2 [H2LH2 = 2,2′-[1,2-dihydroxybenzene-4,5-diylbis(nitrilomethylidine)]bis(3,5-di-tert-butylphenol)] were prepared, whereof [{Mn(CH3OH)2}LH2]Cl, [ML( ZrCp 2 ∗ )] (M = Ni, Cu, CrCl(py); py = pyridine, Cp∗ = pentamethylcyclopentadienyl) were characterized by X-ray analysis. Additionally, cyclic voltammetric investigations were performed to ascertain the influence of the second transition metal complex fragment [ ZrCp 2 ∗ ]2+ on the metallo salen ligand. Moreover, the complexes were tested in the catalytic epoxidation of styrene. Although the complexes are quite sensitive towards oxidants, monometallic complex [{Mn(CH3OH)2}LH2]Cl exhibited a conversion of 70.6% with styrene oxide selectivity of 88% over 1 h at room temperature.

A polymeric ionic liquid (IL)-functionalized chiral salen ligand (PICL) was synthesized by covalent polymerization between amino ( NH2) group of 1,3-dipropylamineimidazolium bromide with chloromethyl ( CH2Cl) group at two sides of 5,5′ positions in the typical chiral salen ligand. Treatment of the synthesized PICL with Mn(OAc)2⋅4H2O and LiCl under aerobic oxidation yielded the corresponding polymeric IL-functionalized chiral salen Mn(III) complex (PICC). The typical IR bands at 1613, 1540, 570, and 412 cm−1, as well as the maximum UV–vis absorbed peaks around 433 nm of the PICC were proposed as characteristics of the monomeric salen Mn(III) complex. The PICC was used as a catalyst in the enantioselective epoxidation of styrene. Comparable catalytic activity and enantioselectivity relative to the monomeric chiral salen Mn(III) complex were observed. Furthermore, recovery of the polymeric catalyst was readily accomplished by simple precipitation in n-hexane, and subsequently reused (10 times) without significant loss of reactivity and enantioselectivity.

The reaction of uranyl acetate with (2,2′-(1E,1′E)-(2-benzyl-3-hydroxyquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene) diphenol) (H2L1) at room temperature in methanol and chloroform yields the UO2L1 complex. Crystals were grown through solvent diffusion of the ligand–metal complex in dimethyl formamide with diethyl ether to prepare: UO2L1 · DMF (1). Complexes with 2,2′-(1E,1′E)-(2-benzyl-3-hydroxyquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dibenzene-1,4-diol (H2L2) and 2,2′-(1E,1′E)-(2-hydroxy-3-isopropylquinoxaline-6,7-diyl)bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)diphenol (H2L3) were also prepared, and crystals of the uranyl complexes (UO2L2 · DMF (2) and (3)) grown from DMF/ether. A fourth complex UO2L4 · H2O (4) was prepared through layering a solution of the tetra-tert-butyl substituted 2-quinoxalinol salen ligand H2L4 in acetone with an aqueous solution containing uranyl acetate. The complexes exhibit a symmetric core featuring a slightly distorted bicapped pentagonal geometry around the uranium center with two oxo-groups and two imine groups from the ligand chelating the ligand and the fifth site in the coordination plane of the ligand occupied by a solvent molecule. These compounds have been characterized using solution (NMR and UV–Vis) and solid-state (IR, X-ray crystallography) techniques. Complexes of H2L4 with early transition metals; Mn2+, Co2+, Ni2+, and Cu2+ are also prepared and characterized for comparison of solution and spectroscopic characteristics.

Reaction of silver nitrite with Ru(salen)(PPh(3))(Cl) (salen(2-)=N,N'-ethylenebis(salicylideneiminato dianion) using [NEt(4)]OH as a phase transfer agent led to the formation of a stable, N-coordinated nitrite ion complex (Ru(III)-NO(2)) that was characterized by single crystal X-ray diffraction. This reaction also resulted in nitration of the two phenolic rings of the salen ligand, which was unexpected given the basic conditions. With sodium nitrite, the Ru(III)-nitro complex was formed, but no ring nitration was observed. Thus, in a non-acidic medium, the combination of nitrite with redox active metal centers may provide a route to the nitration of phenolic derivatives. Possible mechanisms of this unusual reaction having potential relevance to aromatic nitrations in biological systems are discussed. This is also the first report of the crystal structure of a Ru(III)-nitro complex, a species that has been suggested to be unstable and prone to rapid disproportionation.

In situ X-ray absorption spectroscopy at the Mn K- and Br K-edge was employed to study the cycloaddition of carbon dioxide to propylene oxide and styrene oxide, catalyzed by Mn(III) salen bromide complexes. Three homogeneous complexes with varying salen ligand structure and one complex immobilized on silica were used and compared. Ex situ X-ray absorption spectroscopy showed that in all cases octahedral complexes in a distorted symmetry were present and that the bromide ligand was coordinated to the Mn central atom. Under reaction conditions the structure of the catalysts strongly changed. In order to investigate this change, a special spectroscopic batch reactor cell was designed that allowed continuous monitoring of catalyst structure under cycloaddition conditions directly at the synchrotron radiation source, i.e. while maintaining the demanding conditions of elevated pressure and temperature. Complementary XAS investigations on the two key elements of the catalyst, the manganese central atom and the bromide ligand, showed that the coordination sphere of the hexacoordinated manganese central atom changed due to the replacement of the bromo-ligand probably by an epoxide molecule under reaction conditions. This was the case for all three homogeneous catalysts with varying salen ligand structure as well as for the heterogeneous catalyst. In case of the heterogeneous catalyst bromide also went into the solution whereas most of the manganese remained on the solid support. The loss of the direct coordination of the bromine neighbors to the Mn central atom was also evidenced by EXAFS spectra, e.g. loss of Br backscattering in the Mn K-EXAFS spectra and the Mn-backscattering in the Br K-edge spectra. In the catalytic studies it was observed that propylene oxide usually reacted much faster than styrene oxide. This seems to be related to a faster coordination of propylene oxide to the Mn atom, which could be followed in a time-resolved manner at the Br K-edge. On the basis of the analysis of the XANES and EXAFS data together with observations from literature a reaction mechanism is proposed.

The new tetra dentate dianionic H2PS (N,N'-dipyridoxyl (1,3-propylenediamine)) Schiff-base ligand and its octahedral Co(III) salen complex [Co(PS)(H2O)(CH3OH)]+CH3COO(-) were synthesized, where coordinating atoms of H2PS (N,N,O(-),O(-)) occupied equatorial positions with H2O and CH3OH as axial ligands. The nature of the H2PS and its complex were determined by elemental and spectrochemical (IR, UV-vis, 1H NMR and Mass) analysis. Also, the fully optimized geometries and vibrational frequencies of them together with the 1H NMR chemical shifts of H2PS have been calculated using density functional theory (B3LYP) method. Obtained structural parameters are in good agreement with the experimental data reported for similar compounds. The calculated and experimental results confirmed the suggested structures for the ligand and complex.

Salen ligand synthesized from ( 1R , 2R )-(-)-1,2-diaminocyclohexane and 2-hydroxy-3(3-triethoxysilyl-propyl)-benzaldehyde has been used as manganese chelate for the immobilization of the catalytic site. Sol–gel hydrolysis and polycondensation of this chelate with ten equivalents of tetraethyl orthosilicate produced the heterogeneous catalyst. This catalyst is active in enantioselective epoxidations of alkenes in 61–76% yield and 54–86% e.e., using sodium hypochlorite as the primary oxidant. Additionally the immobilized catalyst shows an improvement in the enantioselectivity when compared to the homogeneous Mn(III)–salen analog.

A series of novel chiral salen Mn(III) complexes functionalized by ionic liquid (IL) of 1-propylamine-3-methylimidazolium tetrafluoroborate were synthesized through the reaction of amino group (–NH2) of the IL with chloromethyl (–CH2Cl) in the salen ligand at one side of the 5 position (complex 2) and at two sides of the 5, 5 � position (complex 3), as well as by direct axial coordination between –NH2 of the IL and metal center of the salen Mn(III) complex (complex 4). All of the synthesized complexes were well characterized, and their performance in the enantioselective epoxidation of styrene was investigated systematically. Under optimum reaction conditions, a 99% styrene epoxide yield with 50% enantiometric excess (ee) could be obtained over the complex 2. Furthermore, the IL-functionalized chiral salen Mn(III) complexes of 2 and 3 could be conveniently separated from the reaction system by simple precipitation in hexane and subsequently used without significant loss of activity and enantioselectivity.