A metal-organic framework material that functions as an enantioselective catalyst for olefin epoxidation

A new microporous metal-organic framework compound featuring chiral (salen)Mn struts is highly effective as an asymmetric catalyst for olefin epoxidation, yielding enantiomeric excesses that rival those of the free molecular analogue. Framework confinement of the manganese salen entity enhances catalyst stability, imparts substrate size selectivity, and permits catalyst separation and reuse.     

Two novel cyanide-bridged bimetallic magnetic chains derived from manganese(III) Schiff bases and hexacyanochromate(III) building blocks

Two novel complexes, [{Mn(salen)}(2){Mn(salen)(CH(3)OH)}{Cr(CN)(6)}](n)·2nCH(3)CN·nCH(3)OH (1) and [Mn(5-Clsalmen)(CH(3)OH)(H(2)O)](2n)[{Mn(5-Clsalmen)(μ-CN)}Cr(CN)(5)](n)·5.5nH(2)O (2) (salen(2-) = N,N'-ethylene-bis(salicylideneiminato) dianion; 5-Clsalmen(2-) = N,N'-(1-methylethylene)-bis(5-chlorosalicylideneiminato) dianion), were synthesized and structurally characterized by X-ray single-crystal diffraction. The structural analyses show that complex 1 consists of one-dimensional (1D) alternating chains formed by the [{Cr(CN)(6)}{Mn(salen)}(4){Mn(salen)(CH(3)OH)}(2)](3+) heptanuclear cations and [Cr(CN)(6)](3-) anions. While in complex 2, the hexacyanochromate(III) anion acts as a bis-monodentate ligand through two trans-cyano groups to bridge two [Mn(5-Clsalmen)](+) cations to form a straight chain. The magnetic analysis indicates that complex 1 shows three-dimensional (3D) antiferromagnetic ordering with the Ne?el temperature of 5.0 K, and it is a metamagnet displaying antiferromagnetic to ferromagnetic transition at a critical field of about 2.6 kOe at 2 K. Complex 2 behaves as a molecular magnet with Tc = 3.0 K.     

Cyano-bridged Mn(III)3M(III) (M(III) = Fe, Cr) complexes: synthesis, structure, and magnetic properties

Two cyano-bridged tetranuclear complexes composed of Mn(III) salen (salen = N,N'-ethylene bis(salicylideneiminate)) and hexacyanometalate(III) (M = Fe, Cr) in a stoichiometry of 3:1 have been selectively synthesized using {NH2(n-C12H25)2}3[M(III)(CN)6] (M(III) = Fe, Cr) starting materials: [{Mn(salen)(EtOH)}3{M(CN)6}] (M = Fe, 1; Cr, 2). Compounds 1 and 2 are isostructural with a T-shaped structure, in which [M(CN)6]3- assumes a meridional-tridentate building block to bind three [Mn(salen)(EtOH)]+ units. The strong frequency dependence and observation of hysteresis on the field dependence of the magnetization indicate that 1 is a single-molecule magnet.     

A cellulose-supported Mn(salen)Cl complex as an efficient heterogeneous catalyst for the selective oxidation of benzylic alcohols

[Mn(salen)Cl-cellulose] was synthesized by immobilization of homogeneous Mn(salen)Cl complex on cellulose and characterized by FT-IR, TGA and atomic absorption spectroscopy. The resulted catalyst exhibited moderate to high reactivity in the oxidation of benzylic alcohols into carbonyl compounds using oxone as oxidant in ambient conditions. The catalytic activity of Mn(salen)Cl and [Mn(salen)Cl-cellulose] in this reaction was investigated. The heterogeneous catalyst showed higher catalytic activity with respect to neat Mn(salen)Cl complex.     

Catalase-like catalytic reaction of the dinuclear manganese–salen complex

Catalase-like activity of a dinuclear manganese-salen (Mn–salen) complex, [Mn(salen)(H₂O)]₂(ClO₄)₂ (salen = N,N ′-bis(salicylidene)-1,2-diaminoethane), was investigated. The dinuclear Mn–salen complex exhibits higher catalase-like activity than that of the mononuclear Mn–salen compound, and its activity can be enhanced by an external base. Different reaction intermediates in the presence and absence of an external base were observed, and the catalytically active species was dimeric as evidenced by UV-Vis spectroscopic studies and mass spectrometry data.     

Crystal structures and magnetic properties of two low-dimensional materials constructed from [Mn(III)(salen)H2O]+ and [M(CN)8](3-/4-) (M = Mo or W) precursors

The syntheses, X-ray structures, and magnetic behaviors of two new cyano-bridged assemblies, the molecular [Mn(III)(salen)H2O]3[W(V)(CN)8].H2O (1) and one-dimensional [Mn(salen)(H2O)2]2[[Mn(salen)(H2O)][Mn(salen)]2[Mo(CN)(8)]].0.5ClO4.0.5OH.4.5H2O (2), are presented. Compound 1 crystallizes in the monoclinic system, has space group P2(1)/c, and has unit cell constants a = 13.7210(2) A, b = 20.6840(4) A, c = 20.6370(2) A, and Z = 4. Compound 2 crystallizes in the triclinic system, has space group P, and has unit cell dimensions a = 18.428(4) A, b = 18.521(3) A, c = 18.567(4) A, and Z = 2. The structure of 1 consists of the asymmetric V-shaped Mn-NC-W-NC-Mn-O(phenolate)-Mn molecules, where W(V) coordinates with [Mn(salen)H2O] and singly phenolate-bridged [Mn(salen)H2O]2 moieties through the neighboring cyano bridges. The [W(V)(CN)8]3- ion displays distorted square-antiprism geometry. The structure of 2 consists of the cyano-bridged [Mn3(III)Mo(IV)]n- repeating units linked by double phenolate bridges into one-dimensional zigzag chains. The Mn(III) centers are bound to Mo(IV) of square-antiprism geometry through the neighboring cyano bridges. The magnetic studies of 1 reveal the antiferromagnetic intramolecular interactions through the CN and phenolate bridges and the relatively weak intermolecular interactions. Compound 1 becomes antiferromagnetically ordered below TN = 4.6 K. The presence of the magnetic anisotropy is documented with the MH measurements carried out for both polycrystalline and single-crystal samples. At T = 1.9 K, the spin-flop transition is observed in the field of 18 kOe applied parallel to the bc plane, which is the easy plane of magnetization. Field dependence of magnetization of 1 shows field-induced metamagnetic behavior from the antiferromagnetic ground state of ST = 3/2 to the state of ST = 5/2. The magnetic properties of 2 indicate a weak antiferromagnetic interaction between Mn(III) centers in double-phenolate-bridged [Mn(III)(salen)]2 dinuclear subunits and a very weak ferromagnetic interaction between them through the diamagnetic [Mo(IV)(CN)8]4- spacer.     

Transient intermediates from Mn(salen) with sterically hindered mesityl groups: interconversion between MnIV-phenolate and MnIII-phenoxyl radicals as an origin for unique reactivity

In order to reveal structure-reactivity relationships for the high catalytic activity of the epoxidation catalyst Mn(salen), transient intermediates are investigated. Steric hindrance incorporated to the salen ligand enables highly selective generation of three related intermediates, OMnIV(salen), HO-Mn IV(salen), and H2O-MnIII(salen (+*)), each of which is thoroughly characterized using various spectroscopic techniques including UV-vis, electron paramagnetic resonance, resonance Raman, electrospray ionization mass spectrometry, 2H NMR, and X-ray absorption spectroscopy. These intermediates are all one-electron oxidized from the starting MnIII(salen) precursor but differ only in the degree of protonation. However, structural and electronic features are strikingly different: The Mn-O bond length of HO-MnIV(salen) (1.83 A) is considerably longer than that of OMnIV(salen) (1.58 A); the electronic configuration of H2O-MnIII(salen (+*)) is MnIII-phenoxyl radical, while those of OMnIV(salen) and HO-MnIV(salen) are MnIV-phenolate. Among OMnIV(salen), HO-MnIV(salen), and H2O-MnIII(salen (+*)), only the OMnIV(salen) can transfer oxygen to phosphine and sulfide substrates, as well as abstract hydrogen from weak C-H bonds, although the oxidizing power is not enough to epoxidize olefins. The high activity of Mn(salen) is a direct consequence of the favored formation of the reactive OMnIV(salen) state.     

Synthesis and Characterization of Two Mononuclear Mn~Ⅲ Compounds with Mixed Schiff Base Ligands

Two mononuclear Mn compounds of Mn III (salen)(L 1) and Mn III (salen)(L 2) (H 2 salen=N,N-ethylenebis-(salicylideneaminato),L 1=4-(2-hydroxybenzylideneamino)benzoic acid and L 2=4-(2-hydroxybenzylideneamino)-2-hydroxybenzoic acid) have been prepared and characterized by X-ray crystallography.Both compounds crystallize in the monoclinic system,space group P2 1 /c with a=14.351(4),b=14.955(3),c=11.869(3) and β=91.529(3)° for 1;and those for 2:a=14.439(9),b=15.217(9),c=11.660(7) and β=91.648(1)°.The compounds have similar structures,in which the Mn III center adopts a distorted square-pyramidal geometry with the basal plane constructed by two N and two O atoms from the salen ligand and the apical position occupied by the carboxylate O atom from L 1 or L 2 ligand.The voltammetric behavior of the compounds is examined,which shows quasi-reversible one-electron reduction of Mn(Ⅲ) to Mn(Ⅱ).The reduction potentials of both compounds fall between-0.33 V [E 0 (O 2 /O 2 ·)] and 0.65 V [E 0 (1 O 2 /O 2 ·)],which suggest that 1 and 2 could be potential mimics of Mn-SOD.     

Probing the reactivity of oxomanganese-salen complexes: an electrospray tandem mass spectrometric study of highly reactive intermediates

Electrospray ionization in combination with tandem mass spectrometric techniques has been employed to study the formation of oxomanganese-salen complexes upon oxidation of [Mn(III)(salen)]+ cations as well as the properties and reactions of the oxidized species in the gas phase. Two species could be characterized as the principal oxidation products: the oxomanganese(v) complex, [Mn=O(salen)]+, which is the actual oxygen-transfer agent in epoxidation reactions, and the dinuclear, mu-oxo bridged [L(salen)Mn-O-Mn(salen)L]2+ with two terminal ligands L; the latter acts as a reservoir species. The effects of various substituents in the 5- and 5'-positions, respectively, of the salen ligand on the reactivity of the epoxidation catalyst were determined quantitatively from CID (collision-induced dissociation) experiments and B3LYP density functional calculations. Accordingly, the effect of axial donor ligands on the reactivity of the epoxidation catalyst was studied. Electron-withdrawing substitutents on the salen ligand and additional axial ligands decrease the stability and thus enhance the reactivity of the Mn=O moiety, while electron-donating salen substituents have a strong stabilizing effect.     

Synthesis, structure, magnetic properties and DFT calculations of two hydroxo-bridged complexes based on Mn(III)(Schiff-Bases)

Two hydroxo-bridged complexes, {[Mn(III)(3-CH(3)O)salen](2)[Cr(III)(salen)(OH)(2)]}ClO(4)·6H(2)O (1) and {[Mn(III)(5-CH(3))salen](2)(OH)}ClO(4)·3H(2)O (2) [salen = N,N'-ethylenebis(salicylideneiminato) dianion], have been synthesized by the hydrolysis of the corresponding Mn(III)(Schiff-Bases) derivatives and [Cr(salen)(H(2)O)(2)]Cl precursors. X-Ray structure characterization reveals the discrete linear arched trinuclear structure of 1 and the 1D chain arrangement of 2. Magnetic experimental data and density functional theory (DFT) calculations both indicate the dominant antiferromagnetic interaction mediated by the hydroxo-bridges in both 1 and 2. Frequency-dependent AC susceptibilities reveal slow relaxation of 1 in low temperature. It is worth noting that the structure and magnetic properties of 1 is comparable to a reported cyano-bridged SMM, K[(5-Brsalen)(2)(H(2)O)(2)Mn(2)Cr(CN)(6)]·2H(2)O.     

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.     

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。     

Structure and magnetic properties of an unprecedented syn-anti μ-nitrito-1κO:2κO' bridged Mn(III)-salen complex and its isoelectronic and isostructural formate analogue

The preparation, crystal structures and magnetic properties of two new isoelectronic and isomorphous formate- and nitrite-bridged 1D chains of Mn(III)-salen complexes, [Mn(salen)(HCOO)](n) (1) and [Mn(salen)(NO(2))](n) (2), where salen is the dianion of N,N'-bis(salicylidene)-1,2-diaminoethane, are presented. The structures show that the salen ligand coordinates to the four equatorial sites of the metal ion and the formate or nitrite ions coordinate to the axial positions to bridge the Mn(III)-salen units through a syn-antiμ-1κO:2κO' coordination mode. Such a bridging mode is unprecedented in Mn(III) for formate and in any transition metal ion for nitrite. Variable-temperature magnetic susceptibility measurements of complexes 1 and 2 indicate the presence of ferromagnetic exchange interactions with J values of 0.0607 cm(-1) (for 1) and 0.0883 cm(-1) (for 2). The ac measurements indicate negligible frequency dependence for 1 whereas compound 2 exhibits a decrease of χ(ac)' and a concomitant increase of χ(ac)' on elevating frequency around 2 K. This finding is an indication of slow magnetization reversal characteristic of single-chain magnets or spin-glasses. The μ-nitrito-1κO:2κO' bridge seems to be a potentially superior magnetic coupler to the formate bridge for the construction of single-molecule/-chain magnets as its coupling constant is greater and the χ(ac)' and χ(ac)' show frequency dependence.     

离子液体功能化手性salen Mn(Ⅲ)配合物不对称催化仲醇氧化动力学拆分反应

采用共价键联法,将亲水性咪唑类离子液体结构引入手性salen Mn(Ⅲ)配合物的C5位,制备了离子液体功能化手性salen Mn(Ⅲ)配合物.傅里叶变换红外光谱、紫外光谱和旋光分析等结果表明,咪唑类离子液体结构已嫁接到手性salen Mn(Ⅲ)配合物结构中,且嫁接过程未破坏催化活性中心.在以PhI(OAc)2为氧化剂,H2O/CH2Cl2为溶剂的(+/-)-α-甲基苯甲醇不对称氧化动力学拆分反应中,该催化剂表现出比传统手性salen Mn(Ⅲ)催化剂更高的催化活性,仲醇的转化率达到63%以上,对映选择性为99%,拆分效率为18.3%.可通过调变溶剂实现催化剂的分离并重复使用3次以上.实验结果表明,亲水性咪唑离子液体可改善水相反应传质问题且有利于稳定催化活性中间体,从而提高催化活性及稳定性.     

Aggregate manganese Schiff base moieties by terephthalate or acetate: dinuclear manganese and trinuclear mixed metal Mn2/Na complexes

A reaction system consisting of terephthalic acid, NaOH, inorganic Mn(II) or Mn(III) salt, and salicylidene alkylimine resulted in dinuclear manganese complexes (salpn)(2)Mn(2)(mu-phth)(CH(3)OH)(2) (1, salpn = N,N'-1,3-propylene-bis(salicylideneiminato); phth = terephthalate dianion), (salen)(2)Mn(2)(mu-phth)(CH(3)OH)(2) (2, salen = N,N'-ethylene-bis(salicylideneiminato)), (salen)(2)Mn(2)(mu-phth)(CH(3)OH)(H(2)O) (3), and (salen)(2)Mn(2)(mu-phth) (4), while the absence of NaOH in the reaction led to a mononuclear Mn complex (salph)Mn(CH(3)OH)(NO(3)) (5, salph = N,N'-1,2-phenylene-bis(salicylideneiminato)). In addition, a trinuclear mixed metal complex H[Mn(2)Na(salpn)(2)(mu-OAc)(2)(H(2)O)(2)](OAc)(2) (6) was obtained from the reaction system by using maleic acid instead of terephthalic acid. Five-coordinate Mn ions were found in 4 giving rise to an intermolecular interaction and constructing a one-dimensional linear structure. Antiferromagnetic exchange interactions were observed for 1-3, and a total ferromagnetic exchange of 4 was considered to stem from intermolecular magnetic coupling. (1)H NMR signals of phenolate ring and alkylene (or phenylene) backbone of the diamine are similar to those reported in the literature, and the phth protons are at -2.3 to -10.1 ppm. Studies on structure, bond valence sum analysis, and magnetic properties indicate the oxidation states of the Mn ions in 6 to be +3, which are also indicated by ESR spectra in dual mode. Ferromagnetic exchange interaction between the Mn(III) sites was observed with J = 1.74 cm(-1). A quasireversible redox pair at -0.29V/-0.12V has been assigned to the redox of Mn(2)(III)/Mn(III)Mn(II), implying the intactness of the complex backbone in solution.     

2D warp-and-woof interwoven networks constructed by helical chains with different chirality

Two unprecedented 2D entangled layers of warp-and-woof threads interwoven by left- and right-handed helical chains, {[Mn(salen)Au(CN)2]4(H2O)}n (salen = N,N'-ethylenebis(salicylideneaminato)) and {Mn(acacen)Ag(CN)2}n (acacen = N,N'-ethylenebis(acetylacetonylideneiminate)) 2, have been synthesized and characterized.     

Heterometallic MIIRuIII2 compounds constructed from trans-[Ru(Salen)(CN)2]- and trans-[Ru(Acac)2(CN)2]-. Synthesis, structures, magnetic properties, and density functional theoretical study

The synthesis, structures, and magnetic properties of four cyano-bridged M(II)Ru(III)2 compounds prepared from the paramagnetic Ru(III) building blocks, trans-[Ru(salen)(CN)2]- 1 [H2salen = N,N'-ethylenebis(salicylideneimine)] and trans-[Ru(acac)2(CN)2]- (Hacac = acetylacetone), are described. Compound 2, {Mn(CH3OH)4[Ru(salen)(CN)2]2}.6CH3OH.2H2O, is a trinuclear complex that exhibits antiferromagnetic coupling between Mn(II) and Ru(III) centers. Compound 3, {Mn(H2O)2[Ru(salen)(CN)2]2.H2O}n, has a 2-D sheetlike structure that exhibits antiferromagnetic coupling between Mn and Ru, leading to ferrimagnetic-like behavior. Compound 4, {Ni(cyclam)[Ru(acac)2(CN)2]2}.2CH3OH.2H2O (cyclam = 1,4,8,11-tetraazacyclotetradecane), is a trinuclear complex that exhibits ferromagnetic coupling. Compound 5, {Co[Ru(acac)2(CN)2]2}n, has a 3-D diamond-like interpenetrating network that exhibits ferromagnetic ordering below 4.6 K. The density functional theory (DFT) method was used to calculate the molecular magnetic orbitals and the magnetic exchange interaction between Ru(III) and M(II) (Mn(II), Ni(II)) ions.     

Monodisperse crosslinked pHEMA particle‐supported chiral Mn(III)salen catalyst for asymmetric epoxidation of olefin

Monodisperse crosslinked poly(hydroxyethyl methacrylate) particles (pHEMA) were synthesized for immobilization of the chiral Mn(III)salen homogeneous catalyst by axial coordination. The pHEMA‐Mn(III)salen catalyst was subsequently characterized by FT‐IR, UV and scanning electron microscopy. The results showed that, the heterogeneous Mn(III)salen catalysts also exhibited high activity and enantioselectivity compared to the homogeneous catalyst for the disubstituted cyclic indene and 6‐cyano‐2,2‐dimethylchromene. Moreover, the catalysts were easily separated from the reaction systems and could be renewed several times without significant loss of catalytic activity. Meanwhile, the enantiomeric excess (ee) value remained at 80% in the eighth cycle. The pHEMA support, immobilized by Mn(III)salen, probably acted as a mediator of the reaction between the substrate and the oxidant, and enhanced the stability of the Mn(III)salen compound. Copyright © 2012 John Wiley & Sons, Ltd.     

水、氯配位的Shiff碱单核及双核锰化合物的合成与结构表征

在水杨醛与二元胺形成的Schiff碱与Mn盐的反应体系中分离出两个单核Mn化合 物,(salen)Mn(H_2O)Cl(1)和[(salpr)Mn(H_2O)_2]Cl(2),并测定了结构。应用对 苯二甲酸在碱性条件下拉接两个单核Mn的Schiff碱配位单元,生成(salen)_2Mn_2 [μ-p-C_6H_4(COO)_2](H_2O)(CH_3OH)(3)并进行了结构表征。讨论了这些化合物 的红外及~1HNMR谱,揭示了Mn中心对配体信号的影响。     

Synthesis,Crystal Structure and Magnetic Properties of a Two-Dimensional Heterometallic Assembly ∣[Mn(salen)]∣2∣[Ni(CN)4∣·1/2H2O

A heterometallic assembly, [Mn(salen)]₂[Ni(CN)₄ ]·1/2H₂O (where salen=N, N'-ethylene-bis(salicylideneiminato)-dianion), has been prepared from the reaction of [Mn(salen)H₂O]ClO₄ ·H₂O with K₂ [Ni(CN)₄ ]·H₂O in methanol/water. The compound crystallizes in the tetragonal space group P 4/ncc with the cell dimensions of a =14.604(2) Å, c =16.949(3) Å, and Z=4. The compound assumes a two-dimensional distorted square network structure, formed from Ni―CN―Mn(salen)―NC―Ni linkages with dimensions of Ni―C = 1.867(7)Å, Mn―N - 2.312(6) Å, Mn―N―C - 163.8(6)° Ni―C―N = 178.4(6)°. The two metal atoms Ni(II) and MN(III) have square and slightly distorted octahedral arrangements, respectively. Magnetic susceptibility measurements indicate the presence of an intramolecular antiferro-magnetic interaction and gives a Mn―Mn exchange integral of ?3.2cm^?1.