Mechanism of (Salen)manganese(III)‐Catalyzed Oxidation of Aryl Phenyl Sulfides with Sodium Hypochlorite

The oxidation of 4‐substituted phenyl phenyl sulfides was carried out with several oxo(salen)manganese(V) complexes in MeCN/H₂O 9 : 1. The kinetic data show that the reaction is first‐order each in the oxidant and sulfide. Electron‐attracting substituents in the sulfides and electron‐releasing substituents in salen of the oxo(salen)manganese(V) complexes reduce the rate of oxidation. A Hammett analysis of the rate constants for the oxidation of 4‐substituted phenyl phenyl sulfides gives a negative ρ value (ρ=?2.16) indicating an electron‐deficient transition state. The log k₂ values observed in the oxidation of each 4‐substituted phenyl phenyl sulfide by substituted oxo(salen)manganese(V) complexes also correlate with Hammett σ constants, giving a positive ρ value. The substituent‐, acid‐, and solvent‐effect studies indicate direct O‐atom transfer from the oxidant to the substrate in the rate‐determining step.     

Methyl Iodide Accelerated Asymmetric Epoxidation of Alkenes Catalyzed by Chiral Salen-Mn（Ⅲ） Complexes with Tertiary Amine Units

A series of chiral salen-Mn（Ⅲ） complexes featuring two tertiary amine units were synthesized and employed in the enantioselective epoxidation of unfunctionalized alkenes in the presence of pyridine N-oxide and 2,6-dimethylpyridine N-oxide as proximal ligands, respectively. Moderate to high enantioselectivity and acceptable yields were achieved when NaClO was used as terminal oxidant under CH2Cl2/H2O biphasic media. Methyl iodide was found to be an effective additive to accelerate the epoxidation, possibly owing to the formation of quaternary ammonium units on catalysts, which may facilitate the reaction in an oil/water biphasic medium. The subsequent stimulation experiment was carried out, and the resulting ESI-HRMS analysis revealed the formation of a novel （salen）manganese（m） intermediate featuring two quaternary ammonium units, and bearing a pyridine N-oxide and a molecule of water simultaneously axially-coordinated backbone.     

A new heterogeneous chiral (salen)manganese(III) system for enantioselective epoxidation of non‐functionalized olefins

This communication describes the design and application of a novel catalytic epoxidation system derived from the initial immobilization of a homogeneous sulfonato (salen)Mn(III) complex on two solid carriers (silica gel and siliceous earth) and subsequent dispersion of the supported manganese complexes into ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMImPF₆) and 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMImBF₄) for recycling. The performance of chiral (salen)Mn(III) system in enantioselective epoxidation of olefins was investigated systematically. Even higher enantioselectivity than that of the homogeneous counterpart was obtained with similar catalytic activity. In particular, the best catalytic result is that the combination of the silica gel‐supported (salen)Mn(III) catalyst and BMImPF₆ affords 97–100% ee for epoxidation of α‐methylstyrene, and high ee values were retained even after three cycles. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis,characterization and assessment of the cytotoxic activity of Cu(II), Fe(III) and Mn(III) complexes of camphoric acid‐derived salen ligands

Novel Cu(II), Fe(III) and Mn(III) salen‐type metal complexes from (1R,3S)‐N,N′‐bis[salicylidene]‐1,3‐diamino‐1,2,2‐trimethylcyclopentane were synthesized and screened for their in vitro cytotoxic activity against three human cancer cell lines: melanoma, colorectal and breast. In vitro experiments carried out with the three metal complexes show that the copper complex exhibits the highest cytotoxic activity towards all cell lines studied, presenting IC₅₀ values of 3.32–6.71 μM. A significant improvement in the anti‐proliferative effect, by 20‐fold, is observed with this complex when compared with conventional chemotherapy. The relationship between structure, redox characteristics and biological activity in human cancer cell lines was evaluated for the most efficient Cu(II) complex and associated with theoretical calculations. Copyright © 2015 John Wiley & Sons, Ltd.     

Asymmetric epoxidation of chromenes catalyzed by chiral pyrrolidine SalenMn(III) complexes with an anchored functional group

Chiral pyrrolidine SalenMn(III) complexes with an anchored functional group at the N_aza‐substituent in the pyrrolidine backbone were synthesized, and used as catalysts for asymmetric epoxidation of substituted chromenes. The complex 1 with an anchored imidazole as acceptor could effectively catalyze epoxidation of substituted chromenes in the absence of expensive additive 4‐phenyl pyridine N‐oxide (PPNO) by the coordination of the anchored organic base to the central manganese ion. Complexes 2 and 3 with a quaternary ammonium salt unit at the N_aza‐substituent in the pyrrolidine backbone displayed higher activities than Jacobsen catalyst and the analogous complex 4 without anchored functional group in the aforementioned reaction. Copyright © 2008 John Wiley & Sons, Ltd.     

Iron(III) [bond] Salen complexes as enzyme models: mechanistic study of oxo(salen)iron complexes oxygenation of organic sulfides

The oxidation of a series of para-substituted phenyl methyl sulfides was carried out with several oxo(salen)iron (salen = N,N'-bis(salicylidine)ethylenediaminato) complexes in acetonitrile. The oxo complex [O=Fe(IV)(salen)](*+), generated from an iron(III) [bond] salen complex and iodosylbenzene, effectively oxidizes the organic sulfides to the corresponding sulfoxides. The formation of [O [double bond] Fe(IV)(salen)](*+) as the active oxidant is supported by resonance Raman studies. The kinetic data indicate that the reaction is first-order in the oxidant and fractional-order with respect to sulfide. The observed saturation kinetics of the reaction and spectral data indicate that the substrate binds to the oxidant before the rate-controlling step. The rate constant (k) values for the product formation step determined using Michaelis-Menten kinetics correlate well with Hammett sigma constants, giving reaction constant (rho) values in the range of -0.65 to -1.54 for different oxo(salen)iron complexes. The log k values observed in the oxidation of each aryl methyl sulfide by substituted oxo(salen)iron complexes also correlate with Hammett sigma constants, giving positive rho values. The substituent effect, UV-vis absorption, and EPR spectral studies indicate oxygen atom transfer from the oxidant to the substrate in the rate-determining step.     

Synthesis of new binol based [1+1] macrocyclic chiral manganese(III) Schiff bases as catalysts for asymmetric epoxidation

A series of new chiral binol based [1+1] macrocyclic Schiff bases have been synthesized in high yields in short reaction times via cyclo-condensation of dialdehydes with long tethers and chiral diamines. Macrocyclic Mn(salen) complexes containing N₂O₂ salen units incorporated with spacers of increased tether lengths were synthesized and characterized. The newly synthesized catalyst system was successfully employed for the enantioselective epoxidation of unfunctionalized olefins with high yields and good enantioselectivity.     

大位阻手性吡咯烷(salen)Mn(III)配合物在烯烃不对称环氧化反应中的应用

设计合成了具有大位阻的手性吡咯烷(salen)Mn(III)配合物Mn3,并研究了其在NaClO水/有机两相氧化体系中催化烯烃的不对称环氧化反应性能。 具有叔胺基团的配合物Mn3具有比Jacobsen催化剂更高的反应活性、以及近似的产率和略高的对映选择性。 尤其是过量CH₃I的加入可以极大地缩短环氧化反应的时间,而高产率和高对映选择性依然保持。     

Influence of the built-in pyridinium salt on asymmetric epoxidation of substituted chromenes catalysed by chiral (pyrrolidine salen)Mn(III) complexes

Chiral (pyrrolidine salen)Mn(III) complexes 1 with an N-benzoyl group and 2 with an N-isonicotinoyl group as well as the corresponding N-methyl (3) and N-benzyl (4) pyridinium salts of 2 were synthesized. The catalytic properties of 1–4 and 2 with excess CH₃I were explored to figure out the influence of the internal pyridinium salt in the catalyst on asymmetric epoxidation of substituted chromenes with NaClO/PPNO as an oxidant system in the aqueous/organic biphasic medium. The (pyrrolidine salen)Mn(III) complexes with an internal pyridinium salt, either formed in situ or isolated, displayed higher activities than analogous complexes 1, 2 and Jacobsen's catalyst in the aforementioned reaction, with comparable high yields and ee values. The acceleration of the reaction rate is attributed to the phase transfer capability of the built-in pyridinium salt of the (salen)Mn(III) catalyst. The effect of the internal pyridinium salt on the epoxidation of substituted chromenes is similar to that of the external pyridinium salts and ammonium halides.     

The first 3-D supramolecular Mn(III) salen complex with 4,4-dicarboxy-2,2-bipyridine: structure and magnetic properties

The Mn(III) salen complex [Mn(salen)(H₂O)₂](dcbp)_0.5 · H₂O (dcbp = 4,4-dicarboxy-2,2-bipyridine, salen = N,N′-ethylenebis-salicylideneaminato) has been isolated under hydrothermal conditions and is structurally characterized. The complex is formed by three independent units, one [Mn(salen)(H₂O)₂], one H₂dcbp, and one guest water molecule, which are further interconnected by hydrogen-bond interactions to form a 3-D supramolecular architecture. IR spectra, UV-Vis spectra, and variable temperature magnetic susceptibility of the complex have been studied. The magnetic study indicated a weak antiferromagnetic interaction between the [Mn(salen)(H₂O)₂] molecules.     

DNA-binding and cleavage studies of chiral Mn(III) salen complexes

Chiral bridge-substituted manganese(III) complexes of N,N′-bis-(2-hydroxynaphthalene-1-carbaldehyde)-(1R,2R)-(−)-diaminocyclohexane and N,N′-bis-(2-hydroxynaphthalene-1-carbaldehyde)-(1S,2S)-(+)-diaminocyclohexane have been synthesized. The interaction of these complexes with calf thymus DNA(CT-DNA) was investigated by spectroscopic, thermal denaturation studies, circular dichroism (CD), and viscosity measurements. Results of spectroscopic and viscosity measurements suggest that the two complexes bind to DNA via an intercalative mode and display enantioselectivity. These Mn(III) complexes have been found to promote the cleavage of plasmid DNA pBR322 in the presence of H₂O₂.     

Oxovanadium(IV)‐Salen Ion Catalyzed H2O2 Oxidation of Tertiary Amines to N‐Oxides– Critical Role of Acetate Ion as External Axial Ligand

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 λ_max value of the oxidant to the red region and catalyzes reaction enormously. The cleavage of N? O 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.     

Asymmetric,regio‐ and stereo‐selective alternating copolymerization of CO2 and propylene oxide catalyzed by chiral chromium Salan complexes

Chiral chromium complexes of tetradentate N,N′‐disubstituted bis(aminophenoxide) (designated as Salan, a saturated version of Schiff‐base Salen ligand) in conjunction with an ionic quaternary ammonium salt can efficiently catalyze the copolymerization of CO₂ with racemic propylene oxide (rac‐PO) at mild conditions to selectively afford completely alternating poly(propylene carbonate) (PPC) with ～ 95% head‐to‐tail linkages and moderate enantioselectivity. These new catalyst systems predominantly exceed the previously much‐studied SalenCr(III) systems in catalytic activity, polymer enantioselectivity, and stereochemistry control. The chiral diamine backbone, sterically hindered substitute groups on the aromatic rings, and the presence of sp³‐hydridized amino donors and its N,N′‐disubstituted groups in chiral SalanCr(III) complexes all play significant roles in controlling polymer stereochemistry and enantioselectivity. Furthermore, a relationship between polycarbonate enantioselectivity and its head‐to‐tail linkages in relation to regioselective ring‐opening of the epoxide was also discussed on the basis of stereochemical studies of PPCs derived from the copolymerization of CO₂ with chiral PO at various conditions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6102–6113, 2008     

Synthesis of chiral salen Mn(III) complexes covalently linked to Re(I)-based photosensitizers

Two Mn(III)Re(I) binuclear complexes were prepared as catalyst-photosensitizer models, in which the chiral pyrrolidine salen Mn(III) unit was covalently bonded to an Re(I) bipyridyl carbonyl moiety via a carboxamide linkage. The spectral and electrochemical properties of the Mn(III)Re(I) complexes were studied.     

Heterogeneous chiral Mn(III) salen catalysts for the epoxidation of unfunctionalized olefins immobilized on mesoporous materials with different pore sizes

Two chiral Mn(III) salen complexes were immobilized onto a series of mesoporous MCM-41 and MCM-48 materials with different pore sizes and the as-synthesized catalysts were active and enantioselective for the asymmetric epoxidation of styrene and indene. The results of XRD, FTIR, DR UV-vis, and N₂ sorption showed that the chiral Mn(III) salen complexes were anchored in the channels of mesoporous materials. The influence of organic silicane dosage on the catalytic performance was studied and the optimum dosage of organic silicane for preparing heterogeneous catalysts was determined. Furthermore, the effect of the fine-tuning of pore size on the performance of heterogeneous catalysts was discussed. In general, larger pore size of the supports could lead to higher conversions and the compatible pore size with substrate may be responsible for the improved enantiomeric excess (ee) values.     

Synthetic and catalytic investigations of ruthenium(III) complexes with triphenylphosphine/triphenylarsine and tridentate Schiff base

The synthesis and characterization of several hexa‐coordinated ruthenium(III) complexes of the type [RuCl(PPh₃)₂(L)] (L = dibasic tridentate ligand derived by the condensation of salicylaldehyde/o‐vanillin with o‐aminophenol/o‐aminothiophenol) are reported. IR, electronic, EPR spectral data and redox bahaviour of the complexes are discussed. An octahedral geometry has been tentatively proposed for all the complexes. The new complexes were found to be effective catalysts for the oxidation of benzyl alcohol and cyclohexanol to benzaldehyde and cyclohexanone respectively using N‐methylmorpholine‐N‐oxide as a co‐oxidant. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis,spectral, electrochemical and catalytic studies of new Ru(III) tetradentate Schiff base complexes

The synthesis and characterization of several hexa‐coordinated ruthenium(III) Schiff base complexes of the type [RuX(EPh₃)(L)] (X = Cl or Br; E = P or As; L = dianion of the tetradentate Schiff base) are reported. IR, EPR, electronic spectra and cyclic voltammetric data of the complexes are discussed. An octahedral geometry has been tentatively proposed for all of these complexes. The new complexes have been subjected to catalytic activity in the reaction of oxidation of alcohols in the presence of N‐methylmorpholine‐N‐oxide. Copyright © 2007 John Wiley & Sons, Ltd.     

Electron transfer reactions of tris(polypyridine)ruthenium(III) complexes with organic sulfides: importance of hydrophobic interaction

Ruthenium(III)-polypyridyl complexes, generated from the photochemical oxidation of Ru(II) complexes with molecular oxygen, undergo facile electron transfer reaction with dialkyl and aryl methyl sulfides. The rate controlling electron transfer process is confirmed from the absorption spectrum of the transient sulfide radical cation. The spectrophotometric kinetic study shows that the reaction is of total second order, first order in Ru(III) complex and in the organic sulfide. The reaction rate is susceptible to the change of ligand in [Ru(NN)₃]³⁺ and the structure of organic sulfide.     

Effect of added donor ligands on the selective oxygenation of organic sulfides by oxo(salen)chromium(V) complexes

Oxo(salen)chromium(V) complexes, [(salen)Cr^VO]⁺, oxidize organic sulfides selectively to sulfoxides in high yield. This oxygenation reaction is catalyzed by ligand oxides (LO's), pyridine N-oxide, 4-picoline N-oxide, 4-phenyl pyridine N-oxide and triphenylphosphine oxide. The rate is accelerated by 10-20 times with an increase in yield of sulfoxide in less reaction time. This catalytic activity is highly sensitive to the nature of the substituent in the phenyl ring of ArSMe and in the 3- and 5-position of the salen ligand. The reaction constant (ρ) value obtained with the ligand oxide catalyzed reaction is low compared to the value in the absence of LO. The strong binding and catalytic activity of ligand oxides on the oxo(salen)chromium(V) ion oxygenation is explained in terms of binding constants and a mechanism involving the electrophilic attack of [(salen)Cr^VO]⁺-LO adduct on the sulfur centre of phenyl methyl sulfide.     

Asymmetric Epoxidation of cis/trans‐β‐Methylstyrene Catalysed by Immobilised Mn(Salen) with Different Linkages: Heterogenisation of Homogeneous Asymmetric Catalysis

Immobilised Mn(salen) catalysts with two different linkages were studied in the asymmetric epoxidation of cis/trans‐β‐methylstyrene using NaClO as oxidant. The immobilised Mn(salen) complexes inside nanopores can lead to different catalytic behaviour compared with that of homogeneous Jacobsen catalyst. The rigidity of the linkage was found to be a key factor affecting the catalytic performance of immobilised catalysts. The immobilised catalyst with a rigid linkage exhibited comparable chemical selectivity, enantioselectivity and cis/trans ratio of product formation to that obtained with homogeneous Jacobsen catalysts. In contrast, the immobilised catalyst with a flexible linkage gave remarkably lower chemical selectivity, enantioselectivity and inverted cis/trans ratio compared with the results obtained with the homogeneous Jacobsen catalyst and the immobilised catalyst with rigid linkage. Thus, for immobilised Mn(salen) catalysts, a rigid linkage connecting active centres to the support is essential to obtain activity and enantioselectivity as high as those obtained in homogeneous systems.