Manganese Schiff Base Complexes Research Articles

Rapid and efficient oxidative decarboxylation of carboxylic acids with sodium periodate catalyzed by manganese (III) Schiff base complexes

Rapid and efficient oxidative decarboxylatoin of α-aryl carboxylic acids was observed. In the chemical system containing Mn(III)-salophen complex as catalyst, carboxylic acids are converted efficiently to the corresponding carbonyl derivatives with sodium periodate. The ability of various Schiff base complexes in the oxidative decarboxylation of carboxylic acids was also investigated.

Non-planar manganese Schiff-base complexes; synthesis and molecular structures

The reactions of anhydrous sodium salts of three chiral biaryl-bridged salicylaldimine tetradentate proligands H 2L with manganese(II) chloride give the corresponding solvated complexes [Mn IIL]. The molecular structure of one chiral nonracemic example with a relatively low steric demand ligand set is shown to be composed of a homochiral dimer with bridging phenoxy groups. Both LMn units adopt the cis-β structure with Δ helicity as predetermined by the ( R)-configuration of the biaryls. Oxidation of these compounds with halogens gives manganese(III) complexes. A complex [Mn IIILI] has a trigonal bipyramidal structure with similar cis-β structure to that above. In contrast, the complex [MnL(OH 2) 2]Cl has the rather rare C 2-symmetric cis-α structure. It is thus apparent then that while the biaryl unit in these and similar compounds is able to predetermine the chirality-at-metal very efficiently, it is quite possible for conversions between diastereomeric forms cis-β and cis-α, albeit with the same helicity, to occur in response to the nature of the co-ligands.

EPR spectroscopy of copper and manganese complexes encapsulated in zeolites

The structural basis for the enhanced catalytic activities of copper and manganese Schiff base complexes encapsulated in zeolite-Y is investigated by EPR spectroscopy. The study provides an unequivocal evidence for the encapsulation of complexes inside the supercages of zeolite-Y. The EPR spectroscopy distinguishes the encapsulated complexes from the “neat” and surface-adsorbed metal complexes. Neat complexes showed broad EPR spectra corresponding to nearest neighbour spin–spin interactions whereas the zeolite-encapsulated metal complexes showed well resolved metal hyperfine features similar to the spectra in dilute frozen solutions. The spin Hamiltonian parameters reveal a distorted square pyramidal geometry and an increase in the in-plane covalency of metal–ligand bond as a consequence of encapsulation. The observed changes in the molecular electronic structure are correlated to the enhanced catalytic activity of the encapsulated metal complexes.

Structural and photolytic studies on new mononuclear and binuclear manganese complexes containing Schiff base ligands. The crystal structure of [Mn(μ-3,5-Brsalpn)(μ-O)] 2·2DMF

Mononuclear and binuclear manganese Schiff base complexes containing substituted N, N′-bis(salicylidene)propane-1,3-diamine ligands, H 2(Rsalpn) (R=5-Br, 3,5-Br and 3,5-Cl), have been prepared and characterised by elemental analyses, IR and EPR spectroscopy, FAB and LDI-TOF mass spectrometry, cyclic voltammetry and magnetic measurements. The structure of [Mn(3,5-Brsalpn)O] 2·2DMF ( 5) has been determined by X-ray diffraction techniques. The compound has a dimeric structure with μ-oxo bridges and the ligand spanning both metal centres. The capacity of the complexes to oxidise phenothiazine and their ability to catalyse the photolysis of water have also been studied.

Kinetics of oxidation of β-isophorone to keto-isophorone catalyzed by manganese Schiff base complex using molecular oxygen

Kinetic investigations were carried out on the oxidation of β-isophorone (β-IP) to keto-isophorone (KIP) catalyzed by [LMn(III)(Cl)], (where, L=bis-salicylaldehydeethylenedi-imine, salen) at temperature in the range 10–27°C and partial pressure 0.2–3 atm of molecular oxygen. β-IP gave mainly KIP as the oxidation product under the reaction conditions studied. Initial rate approach was adopted to evaluate kinetic parameters of the reaction. From the kinetic investigations, it was found that the rate of oxidation of β-IP showed a first-order dependence with respect to catalyst and substrate concentrations, and half-order dependence on the partial pressure of oxygen. The effect of temperature on the rates of oxidation was also investigated and from the Arrhenius plot of −ln rate vs. 1/ T, the activation energy estimated is 16.12 kcal mol −1. Thermodynamic activation parameters such as enthalpy, entropy and free energy of the reaction were calculated from the known thermodynamic equations. Based on the kinetic investigations, a plausible mechanism for manganese salen complex catalyzed oxidation of β-IP to KIP has been proposed.

Combined Electrochemical and EPR Studies of Manganese Schiff Base Complexes Encapsulated within the Cavities of Zeolite Y

Combined Electrochemical and EPR Studies of Manganese Schiff Base Complexes Encapsulated within the Cavities of Zeolite Y

Synthesis and crystal structure of manganese(III) hydroxyl-containing Schiff base complexes: [Mn(III)(Hvanpa)2]N3 (H2vanpa = 1−(3-hydroxysalicylaldeneamino)-3-hydroxypropane)

The manganese complex, [Mn(III)(Hvanpa)2]N3 has been prepared and the crystal structure determined using x-ray crystallography. The mononuclear complex has a six-coordinate octahedral geometry. The complex crystallizes in the monoclinic space group P21/c with a = 9.867(1), b = 13.316(2), c = 9.0110(1) A, β = 107.870(1)°, V = 1126.8(2) A3, and Z = 2. The Mn-O and Mn-N distances in the equatorial plane are in good agreement with those found for other manganese(III) Schiff base complexes. In the axial direction, the Mn-O distances of 2.274(2) A is about 0.3 A longer than those in the equatorial plane due to a Jahn-Teller distortion at the d4 manganese(III) center. In the crystal, each azido ion is linked through hydrogen bonding with two hydrogen atoms from the coordinate hydroxyl groups at the apical site.

Synthesis, crystal structure and properties of di-μ2-alkoxo bridged binuclear manganese(III) Schiff base complexes

Preparation and isolation of the dimeric manganese(III) complex, [Mn2(Salpa)2(H2O)2Cl2] · 2DMF, (1), was accomplished by air oxidation of a solution containing MnCl2 · 4H2O, Et3N and H2Salpa** in DMF. Complex (2), [Mn2(Salpa)2(H2O)2(N3)2] · 2EtOH was obtained by reacting (1) or [Mn2(Salpa)2(AcO)2], (3), with NaN3 in EtOH. The crystal structure of (1) was determined by X-ray crystallography. It consists of discrete six-coordinate dimeric manganese molecules with unsupported alkoxido bridges, a rare example of a chloride- and water-containing manganese model complex for the oxygen-evolution center of photosystem II. The Mn–O and Mn–N distances are in good agreement with those found for other manganese(III) Schiff base complexes. The Mn–Cl and Mn–O(water) distances of 2.5577(11) and 2.323(3) A, respectively are due to Jahn-Teller distortion at the d4 metal center. The Mn ⋯ Mn distance is 3.0077(12) A. In the crystal, the distance between the H2O molecule and the O atom of DMF of 2.692(5) A suggests hydrogen binding interactions. A t.g. study of (1) confirmed that the complex contains DMF molecules. Magnetic measurements on (1) and (2) reveal the presence of antiferromagnetic spin-exchange interactions between the manganese(III) ions.

Amino acid Schiff base complex catalyst for effective oxidation of olefins with molecular oxygen

The amino acid Schiff base manganese complex (Sal–Phe–Mn) was prepared with l-phenylalanine, salicylaldehyde and Mn(OAc) 2·4H 2O. The ligand and the complex were characterized by the infrared spectra, small area X-ray photoelectron spectroscopy, and ICP-AES. In the presence of the manganese complex, cyclohexene was effectively oxidized by molecular oxygen without reductant. The major products of the reaction were 2-cyclohexen-1-ol (–OH), 2-cyclohexen-1-one (CO) and 2-cyclohexen-1-hydroperoxide (–OOH), which was different with typical oxidation of cyclohexene. The influence of reaction temperature and additive for oxidation had been studied. The selectivity of 2-cyclohexen-1-hydroperoxide varied with reaction time and different additives. The mechanism of cyclohexene oxidation had also been discussed.

Enantioselective electrocatalytic epoxidation of olefins by chiral manganese Schiff-base complexes

Asymmetric electrocatalytic epoxidation of olefins has been achieved with chiral manganese Schiff-base complexes immobilized on a glassy carbon electrode surface using molecular dioxygen as oxidant. The electrocatalytic system gives moderate enantiomeric excess ( ee) values (65–77%) for the epoxidation of cis-stilbene, trans-stilbene and styrene. Our results indicated that the catalyst turnover number is significantly improved when the manganese complexes are immobilized on the electrode surface, which can be attributed to the suppression of the formation of inactive manganese dimer when the active metal centres are attached to the polymer network.

A New Methodology for Synthesis of 1,2-Epoxy Alkane with the Linear Aliphatic Olefins in Presence of Molecular Oxygen

The linear aliphatic olefins, such as 1-octene, 1-decene, 1-dodecene and 1-tetradecene, were effectively epoxidized with molecular oxygen catalyzed by the amino acid Schiffbase manganese complex (Sal-Phe-Mn). The products of the reaction was 1, 2-epoxy alkane

Crystal structure of [Mn2(III)(salpa)2Cl2(H2O)2] (H2salpa = 1-(salicylaldeneamino)-3-hydroxypropane)

The manganese complex, (Mn2(III)(salpa)2Cl2(H2O)2], has been prepared and its structure determined using x-ray crystallography. The dimer is a di-μ2-alkoxo complex which is a six-coordinate manganese dimer with unsupported alkoxide bridges and a rare example of a chloride- and water-containing manganese dimer. The complex crystallizes in the monoclinic space group P21/c with a = 9.315(5), b = 11.130(4), c = 11.637(5) A, β = 104.33(3)°, V = 1169.0(9) A3, and Z = 2. The structure comprises discrete binuclear clusters in which the metal atoms are bridged by two alkoxo oxygens of the salpa2− ligands. The Mn—O and Mn—N distances are in good agreement with those found for other manganese(III) Schiff base complexes. The Mn—Cl and Mn—O3 distances are 2.585(2) and 2.371(2) A, respectively, and the Mn ··· Mn distance is 3.001(1) A. In the crystal, there are two types of hydrogen bonding between the H2O molecule and the Cl atom with Cl ··· H(H2O) distance of 2.33(6) (intramolecule: −1 + x, y, −1 + z) and 2.68(6) A (intermolecule: −1 + x, 0.5−y, −0.5 + z).

Synthesis of catalytically active polymer‐bound Schiff base manganese complexes for selective epoxidation of unfunctionalized olefins

A polymerizable unsymmetric tetradentate Schiff base with one vinyl group 3 was synthesized and copolymerized with styrene in toluene. Mn(III) ion was quantitatively incorporated into the copolymers by the functional moieties. The resulting linear polymer-bound manganese complexes (4a′ and 4b′) were used as catalyst under homogeneous condition for selective epoxidation of unfunctionalized olefins (i.e. styrene, α-methylstyrene and cyclohexene) at room temperature in the presence of iodosylbenzene (PhIO) as the terminal oxidant. The efficacy of epoxidation using the polymeric catalysts was comparable to that of the monomolecular analog. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3249–3254, 1997

Synthesis of catalytically active polymer-bound Schiff base manganese complexes for selective epoxidation of unfunctionalized olefins

A polymerizable unsymmetric tetradentate Schiff base with one vinyl group 3 was synthesized and copolymerized with styrene in toluene. Mn(III) ion was quantitatively incorporated into the copolymers by the functional moieties. The resulting linear polymer-bound manganese complexes (4a′ and 4b′) were used as catalyst under homogeneous condition for selective epoxidation of unfunctionalized olefins (i.e. styrene, α-methylstyrene and cyclohexene) at room temperature in the presence of iodosylbenzene (PhIO) as the terminal oxidant. The efficacy of epoxidation using the polymeric catalysts was comparable to that of the monomolecular analog. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3249–3254, 1997

DNA photocleavage by cationic schiff base complexes of manganese(III)

DNA photocleavage by cationic schiff base complexes of manganese(III)

Oxidation of alkanes by tert-butyl hydroperoxide catalyzed by polynuclear manganese Schiff base complexes

The polynuclear manganese(III) Schiff base complexes 1– 7 containing μ-alkoxo and μ-acetato bridging and a variety of structural features were employed as catalysts for oxidation of cyclohexane by tert-butyl hydroperoxide in acetonitrile solution at room temperature. Oxidation of cyclohexane using complexes 1 to 5 gave cyclohexanol and cyclohexanone in moderate to high yields. However, the complexes 6 and 7 possessing chloride ligands, were inactive as catalysts. The complexes 1 and 2 were further employed as catalysts for oxidation of other substrates viz. adamantane, toluene, ethylbenzene, cumene, cis-cyclooctene, trans-stilbene and cyclohexanol. Dual mechanistic pathways involving predominantly a metal based oxidant proceeding in a heterolytic manner and a simultaneous free radical autoxidation are proposed for the oxyfunctionalization of alkanes.

Activation of Molecular Oxygen by Biomimetic Schiff Base Complexes of Manganese, Iron, and Cobalt

AbstractThe metal complexes (E,E)‐[{diethyl 2,2′‐[1,2‐phenylenebis(iminomethylidyne)]bis[3‐oxobutanoato]}(2–)‐N,N′,O3,O3′]manganese (Mn1a), [3,3′]‐[1,2‐phenylenebis(iminomethylidyne)bis(2,4‐pentanedionato)(2–)‐N,N′,O2,O2′]manganese (Mn1b), and (Z,Z)‐[diethyl 3,3′‐(1,2‐phenylenediimino)bis(2‐cyano‐2‐propenoato)](2–)‐N3,N3′,O1,O1′]manganese (Mn1c) were sythesised and the oxygenation of these complexes was investigated by gas volumetry. All complexes except Mn1c are able to take up oxygen but with different magnitudes. The catalytic activity of the Mn, Co, and Fe complexes of the ligands 1a and 1c and (E,E)‐[{diethyl 2,2′‐[1,2‐ethylenebis(iminomethylidyne)]bis[3‐oxobutanoato]} (2–)N,N′,O3,O3′] iron (Fe1d) and [diethyl (all‐E)‐5,14‐dihydro‐6,17‐dimethyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine‐7,16‐dicarboxylato)(2–)‐N5,N9,N14,N18]iron (Fe2a) has been compared with respect to the oxidation of hydroquinone by molecular oxygen. The results are interpreted with the aid of electrochemical properties, Lewis acidities, and other relevant factors. However, no simple relationship between the catalytic activity and the other factors could be found.

Synthesis of catalytically active polymer‐bound schiff base manganese complexes for selective epoxidation of unfunctional olefins

AbstractAn unsymmetric tetradentate Schiff base with one vinyl group was first synthesized and copolymerized with styrene in toluene. Metalation of the copolymer with Mn(OAc)2 ·4H2O and LiCl‐H2O was quantitatively incorporated by the functional moiety determined by ICP‐AES technology The linear polymer‐bound manganese complexes were used in homogeneous condition as catalysts in acetonitrile for selective epoxidation of unfunctional olefins(i.e. styrene, α ‐methylstyrene and cyclohexene) at room temperature in the presence of iodosylbenzene (PhIO) as the terminal oxidant. The efficacy of epoxidation using the polymeric catalysts was comparable to the monomolecular analogs. Polymer effect was discussed.

Electronic and steric effects in manganese Schiff-base complexes as models for the water oxidation complex in photosystem II. The isolation of manganese-(II) and -(III) complexes of 3- and 3,5-substituted N,N′-bis(salicylidene)ethane-1,2-diamine (H2salen) ligands

Manganese-(II) and -(III) complexes of substituted N,N′-bis(salicylidene)ethane-1,2-diamine (H2salen) ligands H2L (substituents are in the 3, 5 or 3,5 positions of the phenyl rings of the salen moiety) have been prepared and thoroughly characterised. The reaction of Mn(ClO4)2·6H2O with H2L in ethanol in air normally leads to manganese(III) complexes ligated by both the N2O2 ligand and water molecule(s). However, by employing electron-withdrawing substituents on the ligand, e.g. 3-Br,5-NO2, a manganese(II) complex can be obtained. A ‘borderline’ ligand is represented by the 5-NO2 derivative (nsalen), which produces a manganese(II) complex contaminated with a small amount of a manganese(III) species. Using a more rigorous oxidising agent in the synthesis, [Fe(η-C5H5)2][FeCl4], drives the reaction totally to a manganese(III) complex [Mn(nsalen)Cl(H2O)]. In addition to magnetic susceptibility studies, cyclic voltammetry has been employed. All the complexes exhibit an oxidation and reduction peak, the reversible character being confirmed by pulse voltammetry. Pulse voltammetry also confirmed the nature of the manganese(II) species [Mn(bnsalen)(H2O)2·2H2O [H2bnsalen =N,N′-bis(3-bromo-5-nitrosalicylidene)ethane-1,2-diamine] and that a slight amount of a manganese(III) species is present in [Mn(nsalen)(H2O)2]·2H2O. Six complexes have been crystallographically characterised. Despite the retention of an octahedral manganese environment in all of them, the supramolecular structures exhibit a wide diversity. The 3,5-dichloro and 5-bromo salen complexes containing co-ordinated water display combined π and hydrogen bonding, as well as dimerisation. The complex [{Mn(µ-dbsalen)(µ-O)}2](dbsalen = 3,5-dibromo derivative) offers an alternative bridging arrangement, and [Mn(bsalen)(MeOH)(OClO3)]·H2O (bsalen = 5-bromo derivative) highlights the versatility of the manganese centre in these systems where, unexpectedly, perchlorate is co-ordinated in place of a lattice water. A more subtle rearrangement of supramolecular structure is obtained in [Mn(nsalen)Cl(H2O)] where the usual combination of π- or hydrogen-bonding interaction is modified by the corresponding ability of the 5-NO2 substituent.

Oxyfunctionalization of cyclohexane catalyzed by oxo-bridged manganese Schiff base complexes

Oxo-bridged polynuclear manganese Schiff base complexes catalyzed the oxidation of cyclohexane to cyclohexanol and cyclohexanone In the presence of tert-butyl hydroperoxide or hydrogen peroxide.