Asymmetric Manganese Research Articles

Construction of a new double phenoxo bridged asymmetric manganese(III) Schiff base complex: Observation of ferromagnetic interaction within the dimer and antiferromagnetic interaction between dimers

A dimeric phenoxo bridged manganese(III) complex, [Mn2L2(OH2)(CH3OH)](ClO4)2 [H2L = N,N′-bis((2-hydroxy-1-phenyl)ethylidene)ethane-1,2-diamine] has been synthesized and characterized. The structure has been confirmed by single crystal X-ray crystallography. The χMT value at room temperature is slightly higher than that expected for two non-interacting species with S = 2 (g = 2), that corresponds to two high spin manganese(III) centers. That χMT value increases gradually with lowering temperature to reach a maximum and then an abrupt decrease of χMT value is observed at lower temperature. A ferromagnetic interaction (J = 1.44 cm−1) between the manganese(III) centers within the dimer is counter balanced by the presence of zero-field splitting (ZFS, D = −2.03 cm−1) at very low temperature and possibly also by antiferromagnetic interaction between dimers (zJ = -0.06 cm−1). In order to investigate the single-molecule magnet (SMM) nature of the complex, alternating current (ac) magnetic measurements were carried out from 2 to 7 K under a 3.5 Oe ac field between 1 and 1000 Hz.

Optimisation of an asymmetric manganese oxide/activated carbon capacitor working at 2 V in aqueous medium

The charge storage mechanism of manganese oxide and activated carbon has been studied in aqueous medium in order to optimise an asymmetric (or hybrid) supercapacitor based on these two materials as positive and negative electrode, respectively. Amorphous manganese oxide can be polarised up to potentials of 1.2 V in neutral medium. Under negative polarisation, a pseudocapacitive behaviour of activated carbon has been demonstrated, that is related with reversible hydrogen adsorption in the pores. It allows carbon to be polarised at potential values far from the thermodynamic decomposition of the electrolyte. Balancing the mass of these two materials with pseudocapacitive properties results in a practical cell voltage of 2 V in aqueous medium, with energy densities close to the values obtained with electric double layer capacitors working in organic electrolytes, while avoiding their disadvantages.

Manganese(II)/(III) glycolates: preparation, X-ray crystallographic study, and application in radical cycloaddition reactions

Alternative methods for stereoselective synthesis of the chiral racemic manganese(II) glycolate have been developed. Its geometry is proven to be independent of the nature of the starting material (Mn(Gly) 3 and Mn(OAc) 3) and reaction conditions (temperature, solvent). The single-crystal X-ray analysis shows that a chiral environment around the manganese atom is created by glycolate units lying in the perpendicular planes and water molecules disposed cis to each other. By its thermodynamic stability, the isolated complex ranks as second most unstable among five alternative isomeric structures. Manganese(III) glycolate has been suggested as a novel mediator for radical cycloadditions of β-dicarbonyl compounds to alkenes. It is the first time that an α-hydroxycarboxylic acid is used as a spectator ligand thus providing a possibility for using this class of compounds in asymmetric manganese(III)-mediated radical processes.

Intrazeolite assembly of a chiral manganese salen epoxidation catalyst

Asymmetric manganese salen epoxidation catalysts are assembled and trapped in a multistep synthesis in the cages of zeolite EMT; these heterogeneous catalysts produce high enantiomeric excess in the epoxidation of aromatic alkenes with NaOCl.

Contribution a l'etude des metaux asymetriques : V. Substitution photochimique des carbonyles du greffon Mn(CO) 3 dans des complexes cymantreniques; incidence sur la force des liaisons metal—ligand, diastereotopie et diastereoisomerie inherentes a la chiralite du manganese. Etude RMN

Various studies by p K a measurements, v (CO) frequencies and NMR data on the photochemical replacement of CO by various phosphines or phosphites provide information on the metal—ligand bond strength in the derivatives of cymantrene. For pseudo-tetrahedral complexes with an asymmetric manganese atom, the chirality at the metal atom and the consequent diastereotopy are shown by NMR. Several general NMR data bearing relation to 31P are also discussed.

Optisch aktive Übergangsmetall-Komplexe, IX

The enantiomeric complexes ( + ) - and ( - )-C5H5Mn(COOCH3) (NO)P(C6H5)3 were prepared, firstly by a transesterification of the diastereomeric menthyl derivates ( + )- and (-) -C5H5Mn (COOC10H19) (NO)P(C6H5)3, secondly by OCH3⊖-addition to the cations of ( + )-and (-) - [C5H5Mn (CO) (NO) P (C6H5)3] [PF6]. The kinetics of the exchange of triphenylphosphine in C5H5Mn (COOCH3) (NO) P(CeH5) 3 were investigated by deuteration and monitored by IR spectroscopy. The rate of this exchange in benzene solution is equal to the rate of racemisation of (+) - and (-)-C5H5Mn (COOCH3) (NO) P(C6H5)3 in the same solvent. It is concluded that the rate determining step for the change in configuration at the asymmetric manganese atom is the dissociation of triphenylphosphine. In this reaction an achiral intermediate of relatively high stability is formed.

Über nitrosyl-metall-komplexe X. Substitutionsreaktionen an [C 5H 5Mn(CO) 2NO] +[PF 6] − mit neutralen donorliganden

In order to further investigate the optical activity of the asymmetric manganese atom, a large number of complexes of the type [C 5H 5Mn(CO)(NO)L] + [PF 6] − is needed. These compounds were prepared by the reaction of [C 5H 5Mn(CO) 2NO] +[PF 6] − with several neutral donors. According to the equation [C 5H 5Mn(CO) 2NO] +[PF 6] − + L → [C 5H 5Mn(CO)(NO)L] + [PF 6] − + CO monosubstituted products were formed with L = P(C 4H 9) 3, P(C 6H 11) 3, P(CH 2C 6H 5) 3, P(OC 6H 5) 3, P(OC 2H 5) 3, As(C 6H 5) 3 and CNC 6H 11. In acetone the reactions proceed at room temperature. When L = Sb(C 6H 5) 3, S(C 6H 5) 2, C 5H 8 and C 6H 10 a reaction was also observed, but the corresponding monosubstitution products could not be isolated. PCl 3 did not react with [C 5H 5Mn(CO) 2NO] +[PF 6] −. The new compounds were investigated by IR and 1H NMR spectroscopy.