Trimanganese Complex Research Articles

Spectroscopic, Electrochemical, Magnetic and Structural Investigations of Dimanganese-(II/II) and Mixed-Valence-(II/III)-Tetraiminodiphenolate Complexes

Synthesis, spectroscopic [electron paramagnetic resonance (EPR), UV-Vis and Fourier transform infrared spectroscopy (FTIR)], magnetic and spectroeletrochemical properties of [MnII2(tidf)(OAc)(ClO4)(MeOH)] (tidf = a Robson type macrocyclic ligand obtained through condensation of 2,6-diformyl-4-methylphenol and 1,3-diaminopropane) are reported. Compound [MnII2(tidf)(OAc)(ClO4)(MeOH)] shows a weak antiferromagnetic behavior with exchange coupling constant J = -1.59(1) cm-1. UV-Vis and EPR spectroelectrochemical response after oxidation of complex [MnII2(tidf)(OAc)(ClO4)(MeOH)] detected the stabilization of mixed-valence Mn2(II/III) species in solution showing spectral features similar to the ones of the isolated mixedvalence [MnIIMnIII(tidf)Br3(H2O)2] compound. Crystallization of [MnII2(tidf)(OAc)(ClO4)(MeOH)] surprisingly produced the trimanganese complex [Mn3III/II/III(tidf)2(µ-OAc)2](ClO4)2, not observed in solution. It contains two pentacoordinated [MnIII(tidf)]+ units, each one connected to a central hexacoordinated MnII ion through one µ-phenolate and one µ-acetate bridge.

Syntheses, structures, and photochemical properties of (μ3-O)tris{bis(μ-carboxylato)}trimanganese complexes with naphthylacetate ligands with relevance to artificial solar energy-harvesting systems

Two new trinuclear Mn complexes containing naphthalene moieties, [Mn3(μ3-O)(μ-O2CCH2-1-naph)6(py)3] (1) and [Mn3(μ3-O)(μ-O2CCH2-2-naph)6(py)3] (2) (naph-1-CH2CO2H=1-naphthylacetic acid, naph-2-CH2CO2H=2-naphthylacetic acid, py=pyridine), were synthesized. The X-ray crystallography of 1, the EXAFS analyses of 1 and 2, and the magnetic susceptibility data for these complexes showed that they are trinuclear complexes containing a [Mn3(μ3-O)(μ-O2CR)6] core with mixed-valence Mn3(II, III, III) centers. CVs exhibited an oxidation peak ascribed to MnIII3/MnIIMnIII2 and a reduction peak ascribed to MnIIMnIII2/MnII2MnIII in CH2Cl2. In the fluorescence spectra, the fluorescence intensities of 1 and 2 were smaller than those of the naphthylacetic acids and depended on the dielectric constant of solvent. These results suggested that there is electron transfer between the manganese centers and the naphthyl moieties. The fluorescence decays of 1 and 2 in CH3CN were also faster than the decays in the toluene solutions; this result parallels the lower intensity of the static fluorescence spectra in solvents with a higher dielectric constant. The fluorescence decay curves of 1 and 2 were fitted by two lifetimes, τ1 and τ2, suggesting that electron transfer occurs from the monomer (τ1) and the excimer (τ2) of the naphthyl moieties to the manganese center.

Oxidative Atom-Transfer to a Trimanganese Complex To Form Mn6(μ6-E) (E = O, N) Clusters Featuring Interstitial Oxide and Nitride Functionalities

Utilizing a hexadentate ligand platform, a trinuclear manganese complex of the type ((H)L)Mn(3)(thf)(3) was synthesized and characterized ([(H)L](6-) = [MeC(CH(2)N(C(6)H(4)-o-NH))(3)](6-)). The pale-orange, formally divalent trimanganese complex rapidly reacts with O-atom transfer reagents to afford the μ(6)-oxo complex ((H)L)(2)Mn(6)(μ(6)-O)(NCMe)(4), where two trinuclear subunits bind the central O-atom and the ((H)L) ligands cooperatively bind both trinuclear subunits. The trimanganese complex ((H)L)Mn(3)(thf)(3) rapidly consumes inorganic azide ([N(3)]NBu(4)) to afford a dianionic hexanuclear nitride complex [((H)L)(2)Mn(6)(μ(6)-N)](NBu(4))(2), which subsequently can be oxidized with elemental iodine to ((H)L)(2)Mn(6)(μ(6)-N)(NCMe)(4). EPR and alkylation of the interstitial light atom substituent were used to distinguish the nitride from the oxo complex. The oxo and oxidized nitride complexes give rise to well-defined Mn(II) and Mn(III) sites, determined by bond valence summation, while the dianionic nitride shows a more symmetric complex, giving rise to indistinguishable ion oxidation states based on crystal structure bond metrics.

Tetranuclear group 7/8 mixed-metal and open trinuclear group 7 metal carbonyl clusters bearing bridging 2-mercapto-1-methylimidazole ligands

The reactivity of group 7 metal dinuclear carbonyl complexes [M(2)(CO)(6)(mu-SN(2)C(4)H(5))(2)] (1, M = Re; 2, M = Mn) toward group 8 metal trinuclear carbonyl clusters were examined. Reactions of 1 and 2 with [Os(3)(CO)(10)(NCMe)(2)] in refluxing benzene furnished the tetranuclear mixed-metal clusters [Os(3)Re(CO)(13)(mu(3)-SN(2)C(4)H(5))] (3) and [Os(3)Mn(CO)(13)(mu(3)-SN(2)C(4)H(5))] (4), respectively. Similar treatment of 1 and 2 with Ru(3)(CO)(12) yielded the ruthenium analogs [Ru(3)Re(CO)(13)(mu(3)-SN(2)C(4)H(5))] (5), and [Ru(3)Mn(CO)(13)(mu(3)-SN(2)C(4)H(5))] (6), but in the case of 2 a secondary product [Mn(3)(CO)(10)(mu-Cl)(mu(3)-SN(2)C(4)H(5))(2)] (7) was also formed. Compounds have a butterfly core of four metal atoms with the M (Mn or Re) at a wingtip of the butterfly and containing a noncrystallographic mirror plane of symmetry. This result provides a potential method for the synthesis of a series of new group 7/8 mixed metal complexes containing a bifunctional heterocyclic ligand. Compound 7 is a unique example of a 54-electron trimanganese complex having bridging 2-mercapto-1-methylimidazolate and chloride ligands. Interestingly, the reaction of 1 with Fe(3)(CO)(12) at 70-75 degrees C furnished the tri- and dirhenium complexes [Re(3)(CO)(10)(mu-H)(mu(3)-SN(2)C(4)H(5))(2)] (8) and [Re(2)(CO)(6)(N(2)C(4)H(5))(mu-SN(2)C(4)H(5))(2)] (9), respectively instead of the expected formation of the mixed-metal clusters. The former is an interesting example of a 52-electron trirhenium-hydridic complex containing bridging 2-mercapto-1-methylimidazolate ligand, while the latter can be viewed as a 1-methylimidazole adduct of 1 . No mixed Fe-Re complexes were produced in this reaction. The molecular structures of the new compounds and were established by single-crystal X-ray diffraction analyses and the DFT studies of compounds , and are reported.

Trimanganese Complexes Bearing Bidentate Nitrogen Ligands as a Highly Efficient Catalyst Precursor in the Epoxidation of Alkenes.

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Trimanganese Complexes Bearing Bidentate Nitrogen Ligands as a Highly Efficient Catalyst Precursor in the Epoxidation of Alkenes

A series of trinuclear manganese complexes coordinated with neutral bidentate nitrogen ligands, [Mn3L2(OAc)6], were prepared from manganese acetate and the corresponding ligands. Using peracetic acid as the oxidant, the air- and moisture-stable manganese clusters exhibited excellent catalytic activity and selectivity in the epoxidation of olefins under mild conditions. The highest activity was observed with a trinuclear complex containing a 2-pyridylimino ligand, [Mn3(ppei)2(OAc)6] (ppei = 2-pyridinal-1-phenylethylimine). With this system, the substrate scope was extremely wide to include terminal and electron-deficient double bonds of both aliphatic and aromatic alkenes. The high activity was undiminished under the reaction conditions even directly using a mixture of the pyridylimino ligands and manganese acetates, making this process more convenient. It was also observed that analogous trinuclear complexes, such as [Mn3(bipy)2(OAc)6] and [Mn3(phen)2(OAc)6], displayed excellent activities. While radical intermediacy was inferred from the product distribution, kinetic data revealed that the epoxidation is roughly first-order in manganese cluster precursor and oxidant, respectively, and zero-order in olefin. These results led us to propose that the trinuclear complexes [Mn3L2(OAc)6] serve as catalyst precursors that dissociate into monomeric species with the formulation of [MnL2(OAc)2] under the reaction conditions.

Electron Localization and Delocalization in Mixed-Valence Transition Metal Clusters: Structural and Spectroscopic Studies of Oxo-Centered Trinuclear Complexes [Fe3O(OOCCMe3)6(py)3]+/0and [Mn3O(OOCCMe3)6(py)3]+/0

Crystal structures are reported for the following complexes [Fe3O(OOCCMe3)6(py)3]ClO4·0.5py, 1; [Mn3O(OOCCMe3)6(py)3]ClO4·MeCN, 2; [Mn3O(OOCCMe3)6(py)3], 4; [Fe3O(OOCCMe3)6(py)3], 5. Crystal data are as follows: 1, system monoclinic, space group P21/n, a = 11.658(5) Å, b = 35.450(5) Å, c = 14.084(5) Å, β = 100.10(1)°, V = 5730(3) Å3, Z = 4; 2, orthorhombic, P212121, a = 18.592(11) Å, b = 25.924(11) Å, c = 13.290(5) Å, V = 6405(3) Å3, Z = 4; 4, monoclinic, P21/c, a = 17.941(4) Å, b = 14.945(3) Å, c = 21.655(4) Å, β = 96.50(3)°, V = 5769(2) Å3, Z = 4; 5, monoclinic, P21, a = 11.800(3) Å, b = 20.238(7) Å, c = 12.003(2) Å, β = 106.97(2)°, V = 2741.6(13) Å3, Z = 2. In 1 and 2, the triangular metal ion clusters are close to equilateral geometry, but the coordination polyhedra of the metal ions are significantly different. Those of the fully oxidized triiron(III) cluster are close to the ideal tetragonal symmetry. Those of the trimanganese(III) cluster show strong Jahn−Teller distortions, the four Mn−carboxylate bonds defining a long and a short O−Mn−O axis and these axes around the three Mn centers being correlated so as to define an approximate 3-fold screw axis for the whole cluster. In the mixed-valence trimanganese complex 4 the coordination implies localized valence states close to (2Mn3+ + Mn2+) but in the triiron complex 5 the bond distances are close to those expected for a partially averaged state (2Fe2.5++ Fe3+). Mössbauer spectra of the mixed-valence iron complex indicate a phase transition to a localized (2Fe3+ + Fe2+) state below T = 96 K. In the high-temperature phase, IR spectra support a model in which the electron transfer takes place between two adjacent iron centers at a rate which remains lower than that of the infrared time scale up to room temperature.

Trimanganese complexes with a linear MnIIMnIIIMnII assemblage bridged by carbohydrates

Reaction of manganese(II) salts (MnX 2 ·nH 2 O, X = Cl, Br, NO 3 ) with tris[(N-aldosyl)aminoethyl]amines L n , prepared by the reaction between tris(aminoethyl)amine (tren) with aldose [D-mannose (D-man) (L 1 )] or L-rhamnose [L-rha = 6-deoxy-L-man) (L 2 )] in situ, affords red–orange crystals formulated as [(MnL n ) 2 Mn(H 2 O)]X 3 (n = 2, X = Cl 1; n = 2, X = Br 2; n = 2, X = NO 3 3; n = 1, X = Cl 4), complexes 3 and 4 are characterized by X-ray crystallography.

The reaction of a bridged vinylidenedi-iron complex with cobalt, iron, and manganese carbonyl species; X-ray crystal structures of the complexes [Fe3(µ3-CMe)(µ-CO)2(CO)6(η-C5H5)] and [Co3Fe(µ4-CCH2)(µ-CO)2(CO)7(η-C5H5)

Treatment of trans-[Fe2(µ-CCH2)(µ-CO)(CO)2(η-C5H5)2] with [Fe2(CO)9] in diethyl ether affords [Fe3(µ3-CMe)(µ-CO)2(CO)6(η-C5H5)](1), which was characterised by X-ray crystallography, and shown to contain a tetrahedral CFe3 core which has near, but not exact, mirror symmetry. The Fe3 triangle has two nearly equal sides [2.519(1) and 2.509(1)A] and one longer side [2.602(1)A], the two former being bridged approximately symmetrically by carbonyl ligands. The Fe3 triangle is triply bridged by the µ3-CMe ligand, but with the C atom significantly closer to the unique iron atom, which also carries the cyclopentadienyl ligand. The C-Me vector is perpendicular to the Fe3 plane, and the terminal carbonyl ligands form two mutually orthogonal sets of three on each of the ‘basal’ iron atoms. Crystals of (1) are monoclinic, space group P21/c with four molecules in a unit cell of dimensions a= 8.943(4), b= 12.156(4), c= 15.904(8)A, and β= 103.57(4)°; R= 0.026 for 2 771 intensities [I 3.0σ(I)]. Reaction of compound (1) with C5H6 in toluene, or thermolysis of the complex trans-[Fe2(µ-CCH2)(µ-CO)(CO)2(η-C5H5)2], gives [Fe3(µ3-CMe)(µ-CO)3(η-C5H5)3]. Treatment of trans-[Fe2(µ-CCH2)(µ-CO)(CO)2(η-C5H5)2] with [Co2(CO)8] in diethyl ether yields as the principal product [Co3Fe(µ4-CCH2)(µ-CO)2(CO)7(η-C5H5)](3). The latter complex was shown by X-ray crystallography to have a Co3Fe core arranged as a ‘butterfly’(interplanar angle 124°) with the iron atom occupying one of the ‘wingtips’ and carrying the cyclopentadienyl ligand. The molecule has overall CS symmetry (required crystallographically), the mirror being defined as the perpendicular bisector of the body of the butterfly. The µ4-C atom bridges the four metal atoms on the concave side, and the –CCH2 moiety is η2-bonded to the wingtip cobalt atom. Two of the nine carbonyl ligands bridge the Co–Fe edges, approximately symmetrically; the other seven are terminal and form orthogonal sets (2 + 2 + 3). Crystals of (3) are orthorhombic, space group Pcam, with four molecules in a unit cell of dimensions a= 18.135(16), b= 8.194(9), and c= 12.711(10)A; R= 0.054 for 1 772 intensities [I 2.0σ(/)]. The trimanganese complex [Mn3(µ-H)3(CO)12] reacts with trans-[Fe2(µ-CCH2)(µ-CO)(CO)2(η-C5H5)2] in benzene to form the mixed-metal cluster [Fe2Mn(µ3-CMe)(µ-CO)3(CO)3(η-C5H5)2].