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A salen ligand and its derivatives salan and salalen, bearing the same substituents on the phenolate rings, have been synthesized and then used for the preparation of the corresponding Fe(iii) complexes. All complexes were characterized by MALDI ToF mass spectroscopy, Evans method, and UV-Vis and IR spectroscopy. Moreover, for the salalen-based iron complex, the X-ray structure was studied. A comparison of their behaviour in the catalysis of CO2 with benchmark epoxide substrates allowed us to individuate an order of reactivity of the different classes of complexes. A salen Fe(iii) complex was prepared with a longer bridge between the two nitrogen atoms of the ligand skeleton in order to evaluate the influence of the flexibility on the activity of the catalyst. Finally, the same complexes were tested as catalysts in the ring-opening polymerization of l-lactide and e-caprolactone.

Various metal-salen catalysts were prepared for use in the direct synthesis of diphenyl carbonate (DPC) from phenol and carbon dioxide. We found that metal-salen complexes containing titanium as central metal species retained suitable Lewis acid property for the reaction. It was revealed that the catalytic activity of Ti-salen complexes could be controlled by introducing appropriate substituents into salen ligand. Insertion of phosphonium salts into para-position of aromatic aldehyde of salen ligand enhanced solubility of the catalyst in the methanol-phenol solution, and tert-butyl substituent in the salen ligand induced selective formation of DPC due to steric effect. In addition, introduction of various bridging groups into salen ligand caused change in electronic property of central metal atom. Among the catalysts tested, Ti-(t-butyl)salphen(PPh3)Cl showed the best catalytic performance at 100 °C and 60 bar. The catalytic system utilizing Ti-(t-butyl)salphen(PPh3)Cl catalyst was then optimized by conducting the reaction at various reaction temperatures and pressures.

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.

The silicon (IV) compounds possessing SiN4O2 (6), SiN2O2C2 (7, 8), SiN2O2CCl (9) and SiN4O4 (10) coordinating frameworks have been synthesized in high yield by the reaction of the O,N,N,O- donor salen-type ligand N,N’-bis(salicylidene)ethylenediimine L with different silanes i.e. diethoxydiisocyanatosilane-(C2H5O)2Si(NCO)2 1, dichlorodiphenylsilane-Ph2SiCl2 2, dichloromethyl- phenylsilane-MePhSiCl2 3, trichlorophenylsilane-PhSiCl3 4 and silicon tetrachloride-SiCl4 5. The compounds 6–10 have been characterized by elemental analysis, IR, 1H, 13C and 29Si NMR and mass spectrometry. The decomposition reactivity of these compounds has been studied using a Thermal Gravimetric Analyzer (TGA) at a heating rate of 10°C/minute in an inert atmosphere.

Two 1-D homometallic coordination polymers 1 and 2 have been prepared by one-step hydrothermal reactions of carboxylate-functionalized salen ligands with Co(II) and Mn(II), respectively. Single-crystal X-ray diffraction analyses reveal that both the 1-D chains give 3-D supramolecular structures through intermolecular hydrogen bonds and ππ packing interactions. Magnetic investigation of 2 indicates the presence of antiferromagnetic interactions in 1-D chains.

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.

The oxovanadium(IV)-salen ion catalyzed H2O2 oxidation of N,N-dimethylaniline forms N-oxide as the product of the reaction. The reaction follows Michaelis–Menten kinetics and the rate of the reaction is accelerated by electron donating groups present in the substrate as well as in the salen ligand. This peculiar substituent effect is accounted for in terms of rate determining bond formation between peroxo bond of the oxidant and the N-atom of the substrate in the transition state. Trichloroacetic acid (TCA) shifts the λmax value of the oxidant to the red region and catalyzes reaction enormously. The cleavage of NO bond by vanadium complex leads to moderate yield of the product. But the percentage yield of the product becomes excellent in the presence of TCA.

The oxovanadium(IV)–salen-catalyzed H2O2 oxidation of phenols gives o-catechol and hydroquinone as the reaction products. The reaction follows Michaelis–Menten-type kinetics, and the rate is accelerated by electron-donating substituents on both the substrate and the salen ligand. This peculiar substituent effect is accounted for in terms of bond formation between peroxo group of the oxidant and the benzene ring of the substrate in the transition state. A suitable mechanism for the reaction is proposed.

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.

From the reaction between BiCl3 (1 equiv.) and LiN(SiMe3)2 (4 equiv.) and LH2 (2 equiv.), where L = a tetraphenylporphyrin, TPP, an octaethylporphyrin, OEP and phsalen in THF the title compounds have been obtained LiBiTPP2, LiBiOEP2, and LiBi(phsalen)2 and LiBi(phsalen)2·THF. Crystals grown from CH2Cl2-hexanes are colored; (green), (red-purple) and and (red-orange). The molecular structures of compound , and were determined by single-crystal X-ray crystallography and are shown to have short LiBi bonds of distance 2.8 Å involving the LiL(-)BiL(+). Compound shows a slipped structure involving Li to two oxygens and a LiBi distance of 3.1 Å. Compounds and undergo a rapid reversible exchange in toluene-d8 at 90 °C. The MALDI-MS yields weak molecular ions due to LiBiL2(+/-) with more intense ions due to BiL(+) and LiL(-) in the positive and negative modes. The short Li(+) to Bi(3+) distances are comparable to those seen in LiBi compounds, such a LiBiR2, and are comparable to those seen by Pyykkö (P. Pyykkö, J. Phys. Chem. A, 2015, 119, 2326; P. Pyykkö and M. Atsumi, Chem. - Eur. J., 2009, 15, 186; P. Pyykkö and M. Atsumi, Chem. - Eur. J., 2009, 15, 12770) for Li-Bi bonds. These can be seen to be involving Bi6s6p hybrid lone-pairs to Li(+) atoms. The lithium bis(bistrimethylsilyl)amide (2 equiv.) and phsalenH2 in THF gave a compound having Li2L·2THF, . Crystallographically compound contains two Li(+) atoms, one coordinated to five atoms LiO2N2·THF. and the other being coordinated to three atoms, LiO2·THF. By (7)Li and (1)H NMR both lithium atoms share an equivalent environment.

A chiral dimeric macrocyclic V(V) salen complex based on a chiral macrocyclic salen ligand derived from 1R, 2R-(−) diaminocyclohexane with trigol bisaldehyde was synthesized and evaluated as an efficient catalyst (5 mol%) for asymmetric addition of potassium cyanide and trimethylsilyl cyanide to various N-benzylimines at −20 °C. The dimeric chiral macrocyclic salen complex was found to be an efficient recyclable catalyst to give a high yield (91%) of α-aminonitrile and high chiral induction (ee up to 99%) in the case of 2-methoxy substituted N-benzylimines in 16 h. The catalytic system worked well with both organic and inorganic cyanide sources and the catalyst was recycled up to five cycles with retention of enantioselectivity. Based on NMR investigation and kinetics a probable mechanism was proposed for the catalytic enantioselective Strecker reaction.

CO2, being a linear and centrosymmetric molecule, is very stable, and the electrochemical reduction of CO2 requires energy. Moreover, the CO2 electroreduction proceeds at a significantly higher applied voltage than thermodynamically required. In this concern, salen ligand, H2LNO2, and its corresponding Ni(II) and Cu(II) complexes are synthesized and reported for the first time as electrocatalysts for CO2 electroreduction. Both the metal complexes are active for CO2 reduction and surprisingly result in formation of C1 and C2 hydrocarbons. The complexes are found to be very efficient to minimize overpotential required for the reaction as compared to their pure metal counterparts. Thus, the present study opens up a new class of metal complexes for the efficient electrochemical reduction of CO2 having the potential to generate hydrocarbons at lower overpotentials.

A series of neutral rare-earth metal aryloxides and amides supported by a new pentadentate (N2O3) salen ligand were synthesized, and their catalytic behaviors for the ring-opening polymerization of rac-lactide (rac-LA) were explored. The protolysis reactions of N,N′-bis(3,5-di-tert-butylsalicylidene)-2,2′-diaminodiphenyl ether (LH2) with (ArO)3Ln(THF) (ArO = 2,6-But2-4-MeC6H2O) and Ln[N(SiMe3)2]3 in a 1 : 1 molar ratio in THF gave the neutral rare-earth metal aryloxides LLn(OAr)(THF)n [n = 0, Ln = Sc (1), Yb (2); n = 1, Ln = Y (3), Sm (4) and Nd (5)] and rare-earth metal amides LLnN(SiMe3)2 [Ln = Yb (6), Y (7)], respectively. X-ray structural determination showed that complexes 1, 2, 6 and 7 have monomeric structures, in which the coordination geometry around the rare-earth metal atom can be best described as a distorted trigonal prism. Complexes 3 and 5 are THF-solvated monomers and each of the rare-earth metal atoms is seven-coordinated to form a distorted capped trigonal prism. It was found that all of these complexes can efficiently initiate the ring-opening polymerization (ROP) of rac-LA to give heterotactic-rich polylactides (PLAs). The highly heterotactic PLA (Pr up to 0.93) was obtained using complex 2 as the initiator at a polymerization temperature of 0 °C. The observed increasing order of activity of 1 < 2 < 3 < 4 ≈ 5 is in agreement with the order of their ionic radii, whereas the order of stereoselectivity is in the reverse order. The rare-earth metal salen amides can initiate rac-LA polymerization in a controlled manner, while polymerization using the rare-earth metal salen aryloxides is less controlled at room temperature.

An iron(III) complex of tetradentate N,N′-disubstituted bis(aminophenoxide) (designated as salan, a saturated version of the corresponding salen ligand) with a sterically hindered organic base anchored on the ligand framework, can selectively mediate the conversion of carbonyl sulfide to sulfur-containing polymers by the copolymerization with epoxides. This single-site catalyst exhibits broad substrate scope, and the resultant copolymers have completely alternating structures. In addition, this catalyst is efficient in producing diblock copolymers, suggesting a living polymerization nature.

A novel (salicylaldiminato)Pt(II) complex with two different molecular structures, one solventless ((salicylaldiminato)Pt(II)) 1 and another one solvated ((salicylaldiminato)Pt(II). C 2 H 5 OH), 1 ·C 2 H 5 OH, has been obtained by the reaction of a salen ligand with [PtCl 2 (DMSO) 2 ] in ethanol at room temperature. The asymmetric unit of solventless 1 contains 9 such complex molecules whereas 1 ·C 2 H 5 OH contains 2 complex molecules and one ethanol molecule. To get insights into the structure and bonding, DFT and TDFT calculation have been carried out. The electronic transition band at 408.0 nm (calc. 424.3 nm) is assigned to HOMO → LUMO (96%) excitation. The calculated NMR chemical shifts are interrelated with the experimental results, and a very slight effect of solvent was noticed on NMR chemical shifts. A MTT assay and the real-time cell monitoring xCELLigence system revealed that the 1 has significant potential to suppress cell viability and cell proliferation in human HT-29 and SW620 colorectal cancer cell lines.

We report here a unique example of an in situ generated aluminum initiator stabilized by a C2-symmetric salen ligand which shows a hitherto unknown high activity for the ROP of rac-lactide at room temperature. Using a simple and robust catalyst system, which is prepared from a salen complex and an onium salt, this convenient route employs readily available reagents that afford polylactide in good yields with narrow polydispersity indices, without the need for time-consuming and expensive processes that are typically required for catalyst preparation and purification. In line with the experimental evidence, DFT studies reveal that initiation and propagation proceed via an external alkoxide attack on the coordinated monomer.

Salen ligand synthesized from 2-hydroxybenzaldehyde and 2-hydroxy-1-naphthaldehyde was used as a palladium chelating ligand for the immobilization of the catalytic site. Mesoporous silica supported palladium catalysts were prepared by immobilizing Pd(OAc)2 onto a mesoporous silica gel through the coordination of the imine-functionalized mesoporous silica gel. The prepared catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), inductivity couple plasma (ICP), nitrogen adsorption-desorption, and Fourier transform infrared (FT-IR) spectroscopy. The solid catalysts showed higher activity for the hydroamination of C-(tetra-O-acetyl-β-D-galactopyranosyl)allene with aromatic amines compared with the corresponding homogenous catalyst. The heterogeneous catalytic system can be easily recovered by simple filtration and reused for up to five cycles with no significant loss of catalytic activity.

Two dinuclear aluminum alkyl complexes bearing salen ligand with alkyl backbone of different length between the nitrogen atoms (1,3-propylene (1) and 1,5-pentylene (2)) and the related hemi-salen aluminum complex (3) were tested as catalysts in the ring-opening copolymerization of cyclohexene oxide (CHO) and limonene oxide (LO) with succinic anhydride (SA) and phthalic anhydride (PA). The effects of different reaction conditions (cocatalyst and reaction solvent) on the productivity and selectivity of the reactions were evaluated. The comparison of the catalytic behavior of the dinuclear complexes bearing the aluminum reactive centers at different distances as well as of their mononuclear counterpart suggested that the copolymerization follows a monometallic pathway differently from what observed in the homopolymerization of CHO.

Complexation of N,N′-ethylene- and N,N′-butylene-bis(salicylideneiminato)cobalt(II) (Co(salen)) with nitrogen-containing heterocyclic ligands (pyridine, imidazole) and investigation into the mechanism responsible for the spin crossover behavior of these complexes have been computationally studied using the DFT B3LYP*/6-311++G(d,p) method. The results of calculations of geometric characteristics and energy parameters are in good agreement with an available experimental data. An addition of a base molecule to Co(salen) has been shown to be accompanied by the narrowing of the energy gap between the high-spin and the low-spin electronic states up to the values typical for spin crossover cobalt complexes. According to the calculations, the energy barrier of spin-forbidden rearrangement of a monoadduct of N,N′-butylene-bis(salicylideneiminato) Co(II) with pyridine does not exceed of 6 kcal/mol. This finding allows one to consider the adducts of Co(salen) with nitrogen-centered ligands as the prospective spin crossover systems. The computational investigation into the spatial and electronic structure of N,N′-butylene-bis(salicylideneiminato) Co(II) dimer predicts the simultaneous existence in a crystal cell of two types of molecules with different metal spin states.

We have examined the effects of environmental perturbations, specifically solvents and concentrations, on axial chirality of a recently synthesized axially chiral binaphthyl fluorene based salen ligand, named AFX-155, {[2,2'-(1E,1'E)-(R)-1,1'-binaphthyl-2,2'-diylbis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)bis(4-((7-(diphenylamino)-9,9-dihexyl-9H-fluoren-2-l)ethynyl)-phenol)]}. Chirality and dominant conformations of AFX-155 in CDCl3 solvent have been characterized using vibrational absorption (VA) and vibrational circular dichroism (VCD) spectroscopy in combination with DFT calculations. AFX-155 exhibits triple axial chirality: one is at the binaphthyl ring and the other two are related to the axes of chirality along the -C-N bonds where Cs are part of the binaphthyl group. To evaluate solvent and concentration dependence, complementary VA and VCD experiments in both THF-d8 and CDCl3 have been performed, as well as the optical rotatory dispersion (ORD) and electronic CD (ECD) measurements in CDCl3 under much diluted conditions. While the binaphthyl chirality is determined by the synthetic route, the results show that the latter two axial chirality labels of the dominant diastereomers are concentration dependent. Under much diluted conditions, R-binaphthyl, R_intra_HB//R_extra_HB (R-RR) is favoured, whereas R-binaphthyl, S_intra_HB//S_extra_HB (R-SS) is the dominant species in a concentrated solution. This diastereomeric interconversion is found to be independent of the two solvents used. To provide insights into this interesting finding, conformational searches and the related spectral simulations have been carried out at the DFT/B3LYP/6-31G(d) level.

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.

We report our systematic studies of novel, simple, selective, and sensitive optical (both colorimetric and fluorescent) chemosensors for detecting Al(3+) based on transmetalation reactions (metal displacement or exchange reactions) of a series of K(I), Ca(II), Zn(II), Cu(II), and Pt(II) complexes containing different ligands of salen-based Schiff bases. Both the chemical structure of the salen ligand and the identity of the central metal ion have a tremendous impact on the sensing performance, which is mainly determined by the stability constant of the complex. Moreover, the selectivities of the salen-complex-based chemosensors are much better than those of the corresponding free salen ligands because of the shielding function of the filled-in metal ion in the complex. Therefore, the present work potentially provides a new and simple way to design optical probes via complex-based transmetalation reactions.

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.

Nitrogen functional groups are found in many biologically active compounds and their stereochemistry has a profound effect on biological activity. Nitrene transfer reactions such as aziridination, C-H bond amination, and sulfimidation are useful methods for introducing nitrogen functional groups, and the enantiocontrol of the reactions has been extensively investigated. Although high enantioselectivity has been achieved, most of the reactions use (N-arylsulfonylimino)phenyliodinane, which co-produces iodobenzene, as a nitrene precursor and have a low atom economy. Azide compounds, which give nitrene species by releasing nitrogen, are ideal precursors but rather stable. Their decomposition needs UV irradiation, heating in the presence of a metal complex, or Lewis acid treatment. The examples of previous azide decomposition prompted us to examine Lewis acid and low-valent transition-metal complexes as catalysts for azide decomposition. Thus, we designed new ruthenium complexes that are composed of a low-valent Ru(II) ion, apical CO ligand, and an asymmetry-inducing salen ligand. With these ruthenium complexes and azides, we have achieved highly enantioselective nitrene transfer reactions under mild conditions. Recently, iridium-salen complexes were added to our toolbox.

The charge and spin distribution in manganese-salen complexes were analyzed using different basis sets and density functionals. Five population analysis methods [Mulliken, Lowdin, Natural population analysis (NPA), atoms in molecules (AIM), and CHelpG] were used to characterize the charge distribution. Results show that NPA and AIM were the only methods capable of giving charges with the correct sign for all cases under study. According to the analysis of the natural charge and spin distributions, the salen ligand shows a complex behavior, counteracting the effect of the chloro and oxo ligands on the metal center. Furthermore, the presence of a chloride counter ion increases the oxo-radical character of Oxo-Mn(salen) complexes, which may play an important role in the rationalization of the catalytic properties of Mn(salen) complexes. © 2014 Wiley Periodicals, Inc.

A series of monometallic salen aluminum complexes were prepared by covalent linkage of the imidazolium-based ionic liquid moieties containing various polyether chains with the salen ligand at the two sides of the 5,5′-position. The salen aluminum complexes proved to be efficient and recyclable homogeneous catalysts towards the organic solvent-free synthesis of cyclic carbonates from epoxides and CO2 in the absence of a co-catalyst. The catalysts presented excellent “CO2 capture” capability due to the molecules containing polyether chains and the metal aluminum center, in which >90% yield of cyclic carbonate could be obtained under mild conditions. The catalysts can be easily recovered and six times reused without significant loss of activity and selectivity. Moreover, based on experimental and previous work, the “CO2 capture and activation” cycloaddition reaction mechanisms by monometallic or bimetallic salen aluminum complexes were both proposed.

A salen ligand based on a chiral cis-2,5-diaminobicyclo[2.2.2]octane scaffold forms an iron(III) complex with ferric chloride which catalyzes asymmetric addition of thiols to α,β-unsaturated ketones under mild conditions. The reaction (sulfa-Michael addition) produces β-thioketones in excellent yield and high enantiomeric excess from a wide range of aliphatic and aromatic thiols using chalcones and other conjugated enones as Michael acceptors. With α-substituted α,β-unsaturated ketones as acceptors, the addition shows strong preference (typically >50:1) for the syn diastereomer over the anti product. An asymmetric synthesis of (R)-Montelukast, the sodium salt of which is the commercial anti-asthma drug Singulair®, was devised using conjugate addition of a thiol catalyzed by our iron(III)–salen complex to an α,β-unsaturated ketone synthesized in a four-component, one-pot tandem Michael-aldol condensation. The reaction sequence to (R)-Montelukast proceeded in 72% overall yield over four steps from commercially available materials. A mechanism for our catalyzed asymmetric sulfa-Michael addition is advanced which coordinates the enone acceptor to the metal centre of the iron–salen complex in an open lower quadrant under the bicyclic scaffold, thereby exposing only the si face of the double bond to attack by the external nucleophilic thiol. Prior internal coordination of the thiol to the metal centre of the complex is proposed based on spectroscopic and chemical evidence and leads to activation of the catalyst through a trans ligand effect.

International audience; A new chiral uranyl(VI) complex incorporating a tetradenate salen ligand is reported. Thesynthesized uranyl complex is studied by microanalyses, spectroscopic and X–ray diffractionstudies. The structural studies reveal a slightly distorted pentagonal bipyramid coordinationenvironment around uranyl ion. Interestingly, the uranyl complex was found to be potentialvisible light active catalyst for C–H bond functionalization of dialkylanilines, and affordedmoderate to excellent yield of corresponding –aminonitriles when exposed to visible light for 8hours in the presence of NaCN and acetic acid as cyanide source, and H2O2 as oxidant.

Porous organic polymers (POPs) represent interesting candidate materials for carbon dioxide (CO2) adsorption applications owing to the permanently porous nature of the structures and the ability to vary metalloligand centres that can be incorporated as a potential means of property tuning. This work reports the synthesis and characterisation of four transition metal complexes (using M=Mn, Ni, Fe, and Pd) of the bis-bromo salen ligand, and the incorporation of these complexes into POPs with tris-(p-ethynyl)-triphenylamine to yield metallated polymers (POPMn, POPNi, POPFe, and POPPd). The POPs were shown to possess Brunauer–Emmett–Teller (BET) surface areas of up to 650m2g−1. Overall, this work provides further insight into the potential of permanently porous polymeric materials in post-combustion capture applications.

The structure of (BeSalen)2 is reported. The incompatibility of the geometry of the beryllium with the inflexibility of the Salen ligand gives rise to a rare dimeric bis-didentate motif.

The reactions between a salen ligand N,N'-bis(3-methoxysalicylidene)-1,2-cyclohexanediamine (H2L) and different metal salts lead to the formation of four 3d-4f [MDy] and [MDy]2 (M = Zn/Cu) compounds, where the [MDy]2 can be considered as resulting from the assembly of two [MDy] building blocks. Field-induced single molecule magnet (SMM) behavior was observed in [ZnDy] and [CuDy] compounds with the effective suppression of fast quantum tunneling under a dc field. Moreover, the [ZnDy]2 compound demonstrates typical SMM behavior, which may originate from the high axial anisotropy of Dy ions correlating to the change of coordination geometry and enhanced ferromagnetic interactions between Dy ions via the coupling of two [DyZn] units. The result suggests the positive effects of coupling blocking units to enhance their SMM behavior, presenting a promising strategy for constructing efficient heterometallic SMMs.

A two-photon fluorescent probe has become a critical tool in biology and medicine owing to its capability of imaging intact tissue for a long period of time, such as in two-photon fluorescence microscopy (TPM). In this context, a series of Salen-based zinc-ion bioimaging reagents that were designed based on an intramolecular charge-transfer mechanism were studied through the quantum-chemical method. The increase of one-photon absorption and fluorescence emission wavelength and the reduction of the oscillator strength upon coordination with a zinc ion reveal that they are fluorescent bioimaging reagents used for ratiometric detection. When the Salen ligand is incorporated with Zn(2+), the value of the two-photon absorption (TPA) cross-section (δmax) will decrease, and most of the ligands and complexes exhibit a TPA peak in the near-infrared spectral region. That is, a substituent at the end of the ligand can influence the luminescence property, besides increasing solubility. In addition, the effect of an end-substituted position on the TPA property was considered, such as ortho and meta substitution. The detailed investigations will provide a theoretical basis to synthesize zinc-ion-responsive two-photon fluorescent bioimaging reagents as powerful tools for TPM and biological detection in vivo.

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.

Adsorption isotherm of N,N′-bis(2,4,6-trihydroxyacetophenone)-2,2-dimethylpropandiimine (THAPDP) as an environmentally friendly Salen Ligand corrosion inhibitor on mild steel was studied in alkaline solution (pH=10) containing 3% NaCl. Measurements were carried out using electrochemical and surface techniques. Potentiodynamic polarization curves suggested that this compound was an effective corrosion inhibitor for mild steel and the protection efficiency was increased with the increase in inhibitor concentration. The experimental results indicated that this organic compound was a mixed-type inhibitor. Adsorption on the mild steel surface followed the Langmuir isotherm model. Activation parameters and thermodynamic adsorption parameters of the corrosion process such as E a , Δ H , Δ S , K ads , and Δ G ads were calculated at different temperatures.Keywords: Corrosion, Inhibitor, Adsorption isotherm, Langmuir, Salen ligand. 1. INTRODUCTION Carbon steel has been widely used under different conditions in various industries [1]. One of the known applications of mild steel is to being used in the steam boiler of the power plants [2]. The corrosion rate of mild steel is remarkably dependent on the chemical composition of the aqueous media in which the metal surface is exposed. Feedwater pH is one of the chemistry parameters that affects corrosion, and for an all-steel feedwater system, typically the more alkaline solution, pH > 9.2 up to about 10, is convenient. In practice corrosion can never be stopped but hindered to a reasonable level. Corrosion prevention systems favor the use of corrosion inhibitors with low or zero environmental impacts. A corrosion inhibitor is a chemical substance that, upon addition to a corrosive environment, results in the decrease of corrosion rate to an acceptable level. Most of the well-known inhibitors are organic compounds which mainly contain heteroatoms such as oxygen, nitrogen or sulphur, and multiple bonds, which allow an adsorption on the metal surface [3-8]. The resultant film of chemisorbed inhibitor is responsible for protection either by physically blocking the surface from the corrosion environment or by retarding the electrochemical processes. These compounds are often simultaneously affected on both anodic and cathodic corrosion reactions. Therefore, they are sometimes referred to as mixed-type corrosion inhibitors [8-11]. The planarity and the lone electron pairs in the heteroatoms, are important features that determine the adsorption of these molecules on the metallic surface [12].The aim of this work is to investigate the use of THAPDP as an environmentally friendly inhibitor for the corrosion of mild steel in alkaline solution (pH=10) containing 3% NaCl evaluated by Tafel polarization data. The effect of temperature and concentration on corrosion inhibition were studied. Thermodynamic parameters were calculated from experimental data of the inhibition process at different temperatures.

Two Lewis acid–base bifunctional monometallic aluminum–salen complexes were prepared based on a new type of salen ligand with two N-methylhomopiperazine moieties at the 3,3′-position. The Al(salen) complexes proved to be efficient and recyclable homogeneous catalysts towards the organic solvent-free synthesis of cyclic carbonates from epoxides and CO2 in the absence of a co-catalyst, in which >90% yield of cyclic carbonate could be obtained under relatively mild conditions. The catalysts can be easily recovered and reused five times without significant loss of activity and selectivity. Furthermore, the Lewis acid–base cooperative activation mechanism by the bifunctional Al(salen) complexes was proposed according to experimental data.

The synthesis and characterization of aluminum alkyl and alkoxide complexes bearing racemic 6,6′-dimethylbiphenyl-bridged salen-type ligands, and their catalysis in the ring-opening polymerization (ROP) of rac-lactide are reported. Reactions of AlMe3 with various amounts of the proligands L1−4H2 (6,6′-[(6,6′-dimethyl-[1,1′-biphenyl]-2,2′-diyl)bis(nitrylomethilidyne)]-bis(2-R1-4-R2-phenol): L1H2, R1 = R2 = Me; L2H2, R1 = tBu, R2 = Me; L3H2, R1 = R2 = cumyl; L4H2, R1 = Br, R2 = tBu) afforded the corresponding mono- and dinuclear aluminum methyl complexes [L1−3AlMe (1–3), L1−4Al2Me4 (4–7)]. Aluminum alkoxide complexes L2AlOiPr (8), L2AlOBn (9), and α-alkoxy ester complexes L2Al(OCMe2CO2Me) (10), L2Al[(S)-OCHMeCO2Me] (11) were prepared via in situ alcoholysis of the parent aluminum methyl complex 2 with the corresponding alcohols. The molecular structures of mononuclear complexes 1–3, dinuclear complex 6, alkoxide complexes 8–9 and α-alkoxy ester complexes 10–11 were established by single-crystal X-ray diffraction studies. Two broad resonances at about 69–70 ppm and 25–41 ppm were observed in the 27Al NMR spectra of complexes 10 and 11, indicating the existence of both four- and five-coordinate aluminum centers in solution, which results from the dissociation of one N donor of the salen ligand, accompanied by an association and dissociation equilibrium of the carbonyl group of the α-alkoxy ester ligand to the aluminum center. Complex 11 is also a rare example of an O-lactate model complex that mimics the first insertion of L-LA. All complexes were investigated for the ROP of rac-LA at 110 °C in toluene. The polymerization initiated by complexes 1–3 in the presence of iPrOH showed living features, affording PLAs with narrow molecular weight distributions (PDIs = 1.03–1.05) and 65–73% isotacticities. Particularly, complex 8 showed an “immortal” behavior for the polymerization of rac-LA in the presence of excess alcohol. Compared with the mononuclear counterparts, the tetra-coordinate dinuclear aluminum complexes enabled a few fold boosts in activity, but gave atactic PLAs with broadened PDIs.

A chiral dimeric macrocyclic V(V) salen complex based on a chiral macrocyclic salen ligand derived from 1R, 2R-(−) diaminocyclohexane with trigol bisaldehyde was synthesized and evaluated as an efficient catalyst (5 mol%) for asymmetric addition of potassium cyanide and trimethylsilyl cyanide to various N-benzylimines at −20 °C. The dimeric chiral macrocyclic salen complex was found to be an efficient recyclable catalyst to give a high yield (91%) of α-aminonitrile and high chiral induction (ee up to 99%) in the case of 2-methoxy substituted N-benzylimines in 16 h. The catalytic system worked well with both organic and inorganic cyanide sources and the catalyst was recycled up to five cycles with retention of enantioselectivity. Based on NMR investigation and kinetics a probable mechanism was proposed for the catalytic enantioselective Strecker reaction.

As part of our ongoing interest in the supramolecular chemistry of fluorinated organomercurials, we have investigated the interaction of bis(pentafluorophenyl)mercury ((C6F5)2Hg), and trimeric (perfluoro-o-phenylene)mercury ([o-C6F4Hg]3), with nickel(II) N,N'-bis(salicylidene)ethylenediamine) (Ni(salen)). While solution studies monitored by UV-VIS spectroscopy suggest that Ni(salen) interacts with the trinuclear mercury complex in solution, the 1 : 1 adduct (Ni(salen)-(C6F5)2Hg) and the 1 : 1 adducts Ni(salen)-[o-C6F4Hg]3 and [Ni(salen)-[o-C6F4Hg]3-THF-H2O] can be obtained by slow evaporation of solutions containing the two building blocks. While arene-fluoroarene and hydrogen bonding interactions, as well as interactions between mercury and the salen ligand are the predominant forces responsible for the formation of these adducts, Ni(salen)-[o-C6F4Hg]3 and [Ni(salen)-[o-C6F4Hg]3-THF-H2O] also display short Ni-Hg separations consistent with the presence of metallophilic interactions. Quantum theory of atoms in molecules (QTAIM) analyses of the Ni-Hg interactions in these adducts finds that these interactions are dominated by electrostatic and dispersion forces, despite featuring non-negligible covalent contributions.

A series of conjugated multi-structured fluorescent probe molecules based on a salen ligand were designed and investigated in dimethyl sulfoxide solvent using a quantum-chemical method. The results indicate that the one-photon absorption and fluorescence emission spectra (λ (O) and λ (EM)) of these molecules generally show redshifts (of 23.1-74.5 and 22.7-116.6 nm, respectively) upon the coordination of the molecules to Zn(2+). Large Stokes shifts (1511.2-11744.1 cm(-1)) were found for the molecules, meaning that interference between λ (O) and λ (EM) can be avoided for these molecules. The two-photon absorption spectra of the molecules usually present blueshifts, but the two-photon absorption cross-section (δ) greatly increases (by 221.5-868.0 GM) upon the coordination of the molecules with Zn(2+). Most of the molecules show strong two-photon absorption peaks in the range 678.2-824.4 nm, i.e., in the near-infrared region. In a word, the expanded π-conjugated frameworks of these molecules lead to redshifted λ (O) and λ (EM) and enhanced δ values. Moreover, (L-phenyl)​2 and (L-phenyl-ethynyl)2 are the most suitable of the multi-structured molecules examined in this work for use as two-photon fluorescent probes for zinc ion detection in vivo. Graphical Abstract Scheme of the calculated transition energies (E0k and E0n) and the transition dipole moments (M0k and Mkn). NTO 109, NTO 197 and NTO 228 of Zn(L-phenyl-ethynyl), Zn2(L-phenyl-ethynyl)2 and Zn3(L-phenyl)3 for one-photon absorption, respectively.

Three dinuclear aluminum alkyl complexes of the general formula LAl2Me4, where L are salen ligands with an alkyl backbone of different lengths between the nitrogen atoms (1,3-propylene (1), 1,5-pentylene (2) and 1,12-dodecaylene (3)), have been prepared through alkane elimination reactions between each ligand and two equivalents of AlMe3. The related hemi-salen aluminum complex 4 was prepared by an analogous reaction between a phenoxy–imine ligand and a single equivalent of AlMe3. The activities of these aluminum complexes in the ring-opening polymerization (ROP) of rac-lactide and of several epoxides have been investigated and compared. The dinuclear complex 1, bearing the salen ligand with the shortest alkyl bridge, was the most active in the ROP of LA producing isotactic enriched PLA. Otherwise, the other complexes (2 and 3), in which the metal centers are remote, produced atactic PLA with inferior activity. Analogous differences in terms of activity emerged in the ROP of epoxides. The comparison of the catalytic behavior of the dinuclear complexes as well as their mononuclear counterparts suggests the cooperation between the two aluminum metal centers of the dinuclear species in which these are close enough.

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.