Mn Salen Complexes Research Articles

A magnetically recyclable Fe3O4@SiO2/Mn(iii) chiral salen complex as a highly selective and versatile heterogeneous nanocatalyst for the oxidation of olefins and sulfides

An efficient system for the selective oxidation of alkenes using TBHP and sulfides using aqueous 30% H2O2 catalyzed by a new magnetically recoverable Mn(iii) salen complex with high selectivity and excellent yields was developed.

Macrocyclic Mn(III) salen complexes as recyclable catalyst for oxidative kinetic resolution of secondary alcohols

New macrocyclic chiral Mn(III) salen complexes (C1–C4) were synthesized and were used as catalysts for oxidative kinetic resolution (OKR) of secondary alcohols with diacetoxyiodobenzene (PhI(OAc)2) and N-bromosuccinimide (NBS), in biphasic dichloromethane: water solvent mixture. Good to excellent enantioselectivities were achieved with catalyst C2 for several secondary alcohols having different steric environment. In general with catalyst C2, NBS as a co-oxidant showed better enantioselectivity than PhI(OAc)2 in OKR. The catalyst C2 was easily retrieved from the reaction mixture by the addition of hexane and recycled seven times both with NBS and PhI(OAc)2 as co-oxidants without losing its performance. Based on the experimental results a mechanism for OKR of racemic 1-phenylethanol has been proposed where (R,R)-Mn-salen preferably binds with (S)-1-phenylethanol to give (R)-1-phenylethanol in excess at the end of the reaction.

Reactivity comparison of epoxidation of unfunctionalized olefins with different oxidants catalyzed by mesoporous silica supported unsymmetric chiral Mn(III) salen complexes in heterogeneous condition

Unsymmetric Mn(III) salen complexes were synthesized through a facile method and grafted on several mesoporous silica (MCM-41, MCM-48 and SBA-15). The spectra of FT-IR and DR UV–vis indicated that the Mn(III) salen complexes were immobilized successfully and the characterization of XRD and N2 sorption proved that the mesoporous structures of supports were kept well after grafting of Mn(III) salen complexes. These heterogeneous catalysts were evaluated by the asymmetric epoxidation of unfunctionalized olefins. Comparable activity and enantioselectivity to the homogeneous catalysts were obtained. Two kinds of oxidants were employed and great difference was observed in the catalytic performance of heterogeneous epoxidation of olefins, although in homogeneous conditions m-CPBA and NaClO almost obtained the same reactivity in this reaction. The heterogenization of Mn(III) salen complexes gave different influence for two oxidation systems. Compared with m-CPBA (m-chloroperbenzoic acid), the reaction oxidated by NaClO exhibited higher conversions in heterogeneous conditions, and the reason was discussed with the aid of UV–vis spectra and reaction kinetics.

Oxidation of cycloalkanes with molecular oxygen in the presence of salen metallocomplexes in thermomorphic conditions

The oxidation of cycloalkanes with molecular oxygen, catalyzed by two groups of metallosalen complexes, was studied. The first group consisted of salen complexes with different metals such as Mn, Fe, Co, Ni, Cu, Zn, while the second group was composed of manganese salen complexes with different substituents ( t -butyl electron-donating substituents and/or electron-withdrawing perfluoroalkyl substituents). Mn, Fe and Co salen complexes are the most active catalysts, while Ni, Cu and Zn salen complexes are far less efficient. The introduction of t -butyl electron-donating substituents into Mnsalen complex increases the catalytic activity and catalysts solubility in the reaction mixture. The introduction of perfluoroalkyl electron-withdrawing substituents enhances the catalytic activity and renders the solubility of the catalyst temperature dependent (thermomorphic behaviour), thus allowing one to recover them easily after the reaction by simply cooling the system to room temperature. The synthesis of two new manganese salen complexes with perfluoroalkyl substituents was elaborated. • New strategy for recovering homogeneous catalysts–thermomorphic effect • Fluorous catalysis without fluorous solvent • Synthesis and characterization of two new perfluoroalkyl manganese complexes • Influence of substituents on physico-chemical properties of salen complexes • Influence of substituents in salen complexes on their catalytic activity

Immobilized chiral Mn(III) salen complexes on co-condensed imidazole-functionalized mesoporous materials: Effective catalysts for asymmetric epoxidation of olefins

The heterogeneous chiral Mn(III) salen catalysts with ordered hexagonal mesostructure were prepared based on mesoporous materials functionalized by imidazole groups through a co-condensation procedure. These catalysts were highly active and enantioselective for the asymmetric epoxidation of olefins. Within a short reaction time, comparable conversion and enantiomeric excess to those of the homogeneous counterpart were obtained even with a very low catalyst dosage (0.60mol%). Thus notably high turnover frequencies (up to 165h−1) were provided by these catalysts, attributed in part to the homogeneous distribution of the active centers as well as the strong electron-donating ability of imidazole groups. Comparison experiments showed that these catalysts were twice more active than the catalysts supported on the mesoporous material graft-modified with imidazole. Furthermore, the nanopore size of mesoporous hybrid supports was found to have a considerable effect on the catalytic performance.

Synthesis of salen Mn(III) immobilized onto the ZnPS-PVPA modified by 1,2,3-triazole and their application for asymmetric epoxidation of olefins

A series of chiral salen Mn(III) complexes immobilized onto ZnPS-PVPA modified by 1,2,3-triazole through click chemistry were synthesized. High yields and comparable enantioselectivities were achieved in asymmetric epoxidation of unfunctional olefins with NaClO/PPNO and m-CPBA/NMO as well as NaIO4/imidazole as the oxidative systems. The catalytic results indicated that the catalysts were selective for oxidative systems and the additives played different roles in different oxidative systems. Moreover, the superior reusability and catalytic abilities in large-scale reactions at the same level demonstrated the potentiality for application in industry.

Thermoresponsive chiral salen Mn(III) complexes as efficient and reusable catalysts for the oxidative kinetic resolution of secondary alcohols in water

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 ANTIOXIDANT ACTIVITIES OF [5-FLUORO N, N’-BIS (SALICYLIDENE) ETHYLENEDIAMINE] AND [3, 5-FLUORO N, N’-BIS (SALICYLIDENE) ETHYLENEDIAMINE] MANGANESE (III) COMPLEXES

Antioxidants act as free radical scavengers in the oxidation processes. Thus, they will certainly play diverse roles in the biological systems and the therapy of a wide variety of diseases. Regarding this fact, in the present study, we synthesized two new salen ligand compounds by the condensation of ethylendiamine and salicylaldehyde derivatives in excellent yields. The structures of these ligands were confirmed by IR, 1 H NMR and mass spectroscopy techniques. Furthermore, we evaluated the relative dismutase, catalase and peroxidase activities of the newly synthesized complexes named as EUKs 131, 132, 141 and 142 relative to EUKs 108 and 8, as the reference compounds. The results demonstrated that all Mn-salen complexes (EUKs) illustrated significant dismutase, catalase and peroxidase activities. EUKs 131 and 8 showed the most catalase and peroxidase activities while their dismutase activities were almost the same as the other compounds. In addition, our data indicated that the biological activities of the EUKs are modulated by manganese element as well as the types and the positions of substituents on the ligand.

Immobilization of Jacobsen type catalysts on modified silica

Several immobilized Jacobsen type catalysts were covalently anchored on modified SiO2 using 3-aminopropyltriethoxysilane (3-APTES) as a reactive surface modifier. Characterization of the heterogeneous catalysts, as well as their precursors, by FTIR, DR UV-VIS, TGA and AAS confirms the successful immobilization of chiral Mn(III) salen complexes. These catalysts were examined for the diastereoselective epoxidation of R-(+)-limonene with in situ generated dimethyldioxirane (DMD) as oxidizing agent, yielding 1,2-epoxide as the main product. When compared to homogeneous catalysts, under similar experimental conditions, only a slight selectivity decrease over heterogeneous catalysts was observed. The immobilized catalysts were used three times maintaining the initial selectivity. However, after reusing them more than three times, selectivity to 1,2-epoxide decreased. FTIR results suggest partial degradation of the catalytic species. Despite the immobilization method was chosen to minimize changes in the structure of the homogeneous catalysts the diastereoselectivity (d.e.) of heterogeneous catalysts underwent a remarkable decay.

ChemInform Abstract: Studies on the Synthesis of a Chiral Salen Mn(III) Complex Immobilized onto Zirconium Aminophosphonates and Catalytic Asymmetric Epoxidation of α‐Methylstyrene.

AbstractChiral salen Mn(III) complexes anchored in the mesopores of zirconium aminophosphonates exhibit high catalytic activity and enantioselectivity in the asymmetric epoxidation of α‐methylstyrene.

A highly efficient and recyclable catalyst—dendrimer supported chiral salen Mn(iii) complexes for asymmetric epoxidation

A novel series of PAMAM dendrimer-supported chiral salen Mn(III) complexes has been synthesized and applied to the enantioselective epoxidation of unfunctionalized olefins. Technologies of characterization clearly suggested the axial grafting of the chiral salen Mn(III) complex on the surface of PAMAM dendrimers through a phenoxy group spacer. It was found that the peripherally modified dendrimers benefited from the cooperativity between neighboring sites confined to the surface of the dendrimers, thereby enhancing the asymmetric induction of the catalyst. Higher enantioselectivity for PAMAM dendrimer-supported chiral salen Mn(III) complexes over the homogeneous counterpart was observed in the enantioselective epoxidation of unfunctionalized olefins. Furthermore, the dendritic supports imparted selective solubility properties to the catalysts. These catalysts could be easily recovered from the reaction solution by using solvent precipitation, and could be reused for several times without loss of activity and enantioselectivity.

Mn-salen@MIL101(Al): a heterogeneous, enantioselective catalyst synthesized using a ‘bottle around the ship’ approach

An enantioselective catalyst, consisting of a chiral Mn(III)salen complex entrapped in the MIL-101 metal organic framework, is reported. For the first time, we assemble a robust MOF-cage around a chiral complex. The heterogeneous catalyst shows the same selectivity as the homogeneous complex and is fully recyclable. Theoretical calculations provide insight into this retention of selectivity.

Chiral salen Mn(iii) complexes immobilized onto crystalline aluminium oligo-styrenyl phosphonate-hydrogen phosphate (AlSPP) for heterogeneous asymmetric epoxidation

A novel type of organic polymer–inorganic hybrid material layered crystalline aluminium oligo-styrenyl phosphonate-hydrogen phosphate (AlSPP) was designed and prepared in the absence of any template. The chiral salen Mn(III) complex immobilized onto alkoxy-modified AlSPP was synthesized and characterized by FT-IR, diffusion reflection UV-vis, AAS, N2 volumetric adsorption, SEM, TEM, XRD, TG and AFM. The supported catalysts displayed superior catalytic activities in the asymmetric epoxidation of α-methylstyrene and indene with m-CPBA as an oxidant. Delightfully, the heterogeneous catalysts afforded a remarkable increase in conversion and ee values without the expensive O-coordinating axial bases for the asymmetric epoxidation of olefins. The catalysts can be easily recovered and reused with a slight decrease in activity and enantioselectivity after ten cycles. Furthermore, they could also be efficiently used in large-scale reactions with the enantioselectivity being maintained at the same level, which provided the potentiality for application in industry.

Salen‐Based Coordination Polymers of Manganese and the Rare‐Earth Elements: Synthesis and Catalytic Aerobic Epoxidation of Olefins

Treatment of N,N'-bis(4carboxysalicylidene)ethylenediamine (H(4)L), with MnCl(2)⋅(H(2)O)(4), and Ln(NO(3))(3)⋅(H(2)O)(m) (Ln = Nd, Eu, Gd, Dy, Tb), in the presence of N,N-dimethylformamide (DMF)/pyridine at elevated temperature resulted (after work up) in the formation of 1D coordination polymers {[Ln(2)(MnLCl)(2)(NO(3))(2)(dmf)(5)]⋅4 DMF}(n) (1-5). In these coordination polymers the rare earth ions are connected through carboxylate groups from Mn-salen units in a 1D chain structure. Thus, the Mn-salen complex acts as a "metalloligand" with open coordination sites. All compounds were used as catalysts in the liquid-phase epoxidation of trans-stilbene with molecular oxygen, which resulted in the formation of stilbene oxide. Since the choice of the lanthanide had virtually no influence on the performance of the catalyst, only the manganese-gadolinium was studied in detail. The influence of solvent, catalyst concentration, reaction temperature, oxidant, and oxidant flow rate on conversion, yield, and selectivity was analyzed. A conversion of up to 70%, the formation of 61% stilbene oxide (88% selectivity), and a TON of 84 were observed after 24 h. A hot filtration test confirmed that the reaction is mainly catalyzed through a heterogeneous pathway, although a minor contribution of homogeneous species could not be completely excluded. The catalyst could be reused without significant loss of activity.

Synthesis of layered crystalline AlSPP and its immobilized chiral salen Mn(III) catalysts applicated in the large scale asymmetric epoxidation of olefins

Chiral salen Mn(III) complex was axially immobilized onto phenoxy-modified organic polymer-inorganic hybrid material layered crystalline aluminium oligo-styrenyl phosphonate-hydrogen phosphate. The prepared catalysts exhibited excellent activities and enantioselectivities for asymmetric epoxidation of unfunctionalized olefins with m-chloroperbenzoic acid as oxidant, especially for the epoxidation of α-methylstyrene (conversion: up to 99 %; ee: exceed 99 %). A point worth emphasizing is that the heterogeneous catalysts afforded remarkable increases of conversions and ee values without adding axial base N-methylmorpholine N-oxide for the asymmetric epoxidation of olefins. The catalyst can be easily recovered and reused with slightly decrease of activity and enantioselectivity after seven cycles. Delightedly, this novel heterogeneous catalyst could also be efficiently used in large-scale reactions with the enantioselectivity being maintained at the same level, which provided the potentiality for application in industry.

Organic carbonates as solvents in macrocyclic Mn(III) salen catalyzed asymmetric epoxidation of non-functionalized olefins

Organic carbonates, e.g., dimethyl carbonate and propylene carbonate were used as reaction media in enantioselective epoxidation of non-functionalized alkenes by using a series of chiral macrocyclic Mn(III) salen complexes (5mol%) as catalyst with pyridine N-oxide as an axial base. This protocol worked effectively with urea hydrogen peroxide, as well as sodium hypochlorite as oxidants to give respective epoxides in high yields and ee (up to >91% in selected cases). Furthermore kinetic studies of the catalytic epoxidation reaction in dimethyl carbonate:methanol (optimized solvent mixture) with urea hydrogen peroxide as an oxidant showed first order dependence on catalyst and oxidant whereas it is zero order for the substrate, styrene.

DNA Binding, Antioxidant Activity, and DNA Damage Protection of Chiral Macrocyclic Mn(III) Salen Complexes

We are reporting the synthesis, characterization, and calf thymus DNA binding studies of novel chiral macrocyclic Mn(III) salen complexes S-1, R-1, S-2, and R-2. These chiral complexes showed ability to bind with DNA, where complex S-1 exhibits the highest DNA binding constant 1.20 × 10(6) M(-1). All the compounds were screened for superoxide and hydroxyl radical scavenging activities; among them, complex S-1 exhibited significant activity with IC(50) 1.36 and 2.37 μM, respectively. Further, comet assay was used to evaluate the DNA damage protection in white blood cells against the reactive oxygen species wherein complex S-1 was found effective in protecting the hydroxyl radicals mediated plasmid and white blood cells DNA damage.

Chiral Mn(III) salen complexes immobilized directly on pyrolytic waste tire char for asymmetric epoxidation of unfunctionalized olefins

Two kinds of chiral Mn(III) salen complexes were synthesized and directly immobilized on pyrolytic waste tire char (PWTC) without modification of any organosilicon, which was an economic support, having rich oxy functionalized groups inherently. The as-prepared heterogeneous catalysts were characterized by X-ray photoelectron spectra (XPS), N2 sorption, Fourier transform infrared spectra (FT-IR) and thermogravimetric analysis (TG), and possessed of good catalytic performance in asymmetric epoxidation of unfunctionalized olefins. They obtained higher enantiomeric excess (ee) values than that of homogeneous catalysts for asymmetric epoxidation of 1-phenylcyclehexene and could be recycled three times.

Studies on the Synthesis of a Chiral Salen Mn (III) Complex Immobilised onto Zirconium Aminophosphonates and Catalytic Asymmetric Epoxidation of α–methylstyrene

A chiral salen Mn (III) complex has been immobilised onto zirconium aminophosphonates by axial coordination with different linkage arm lengths (CH2) n ( n = 2–6), to give a series of heterogeneous catalysts. The catalysts exhibited good to excellent catalytic efficiency in the asymmetric epoxidation of α–methylstyrene. One heterogeneous catalyst, with n = 6, gave higher catalytic properties than the original chiral salen Mn (III) complex in the NaClO/PPNO system. It can be easily recovered and reused several times without significant loss of activity.

Structure-control in assembly of nanosheets: Novel chiral catalysts for the asymmetric epoxidation of α-methylstyrene without axial base

Abstract Heterogeneous chiral catalysts with different structure, surface character and location of active species were assembled by salen Mn(III) complex and α-Zr(HPO4)2 nanosheets. The bumpy edge-accumulated surfaces of nanosheets lead the catalyst to have a high ee value without axial base in the asymmetric epoxidation of α-methylstyrene.