脯氨酸衍生的胺基吡啶四氮锰配合物催化双氧水参与的烯烃不对称环氧化反应（英文）

自然界中存在许多的金属酶,它们参与促进各种各样的氧化反应,例如羟化反应,环氧化反应等.金属酶催化的反应具有催化效率高、反应条件温和、选择性高等优点.受大自然中的金属酶结构及其性质的启发,人们提出了仿生催化氧化的理念,并开始对金属酶进行模拟,致力于发展清洁氧化的反应方式.在过去的几十年中,科学家们设计合成了一系列仿生金属配合物催化剂.例如,利用非手性的乙二胺骨架设计合成出四齿氮配体MEP(N,N'-dimethylN,N'-bis(2-pyridinylmethyl)ethane-1,2-diamine),将其制备成相应的铁配合物催化剂,该铁催化剂可以很好的实现脂肪族烯烃的环氧化,产率高达90%.2003年,Stack小组首次报道了利用手性N,N-二甲基环己二胺骨架衍生的四齿氮配体金属配合物Mn-MCP-(OTf)2(MCP=N,N-dimethyl-N,N-bis(2-pyridylmethyl)cyclohexane-trans-1,2-diamine)催化的不对称环氧化反应.该反应的对映选择性仅仅为10%.因此,发展新型手性四氮配体金属配合物,用于高产率、高对映选择性的不对称环氧化反应,值得进行深入研究.近年来发展的一些含手性二胺骨架的四齿氮配体,例如PDP(2-[[2-(1-(pyridin-2-ylmethyl)-pyrrolidin-2-yl)pyrrolidin-1-yl]methyl]pyridine),被应用到不对称环氧化反应中,但是其手性二胺骨架为联吡咯,价格昂贵,难以制备.这在很大程度上限制了其在不对称合成中的实际应用.因此,利用一些易于合成的手性二胺骨架,发展结构新颖、催化性能优良的四氮金属配合物,成为实现高效、高选择性不对称环氧化反应的关键.在之前的工作基础上,本文以简单易得、价格低廉的天然氨基酸——L-脯氨酸为起始原料,选取吡啶环和含取代基的吡啶环作为侧基氮供体,制备了三种手性四齿氮配体.随后,我们利用新发展的手性四齿氮配体,合成了相应的锰配合物,并且分别将其运用于烯烃不对称环氧化反应中,仔细评估了这些锰金属配合物的催化性能.建立了以0.2 mol%的锰配合物为催化剂,0.5当量的2,2-二甲基丁酸为添加剂,30%双氧水为氧化剂,反应温度为–30 oC,乙腈为溶剂的催化不对称环氧化反应体系.反应结果显示:该催化剂催化的不对称环氧化反应底物适用性广泛,其中苯乙烯、苯并吡喃、烯酰胺等化合物均可以被成功地转化为相应的环氧化物,得到中等至优异的对映选择性(产率最高可达95%,对映选择性最高可达99%).     

Polystyrene-supported triphenylarsines: useful ligands in palladium-catalyzed aryl halide homocoupling reactions and a catalyst for alkene epoxidation using hydrogen peroxide

The utility of both soluble (non-cross-linked) and insoluble (cross-linked) polystyrene-supported triphenylarsine reagents were examined. These reagents were prepared by standard radical polymerization methodology and used in palladium-catalyzed homocoupling reactions of aryl halides. The insoluble reagent was also used as a catalyst precursor in heterogeneous alkene epoxidation reactions in which aqueous hydrogen peroxide was the stoichiometric oxidant. For the aryl halide homocoupling reactions, both reagents worked well and afforded similar results. Unhindered aryl iodides afforded the best yields in the shortest reaction times compared to aryl bromides. The epoxidation reactions of unfunctionalized alkenes were not very efficient. This was probably due to the hydrophobicity of the polystyrene matrix, which did not swell in the reaction medium. Thus, since a microporous, gel-type polystyrene matrix was used, the majority of the arsine groups were inaccessible to the reaction components and therefore incapable of participating in catalysis.     

Synthesis of di‐nitrogen Schiff base complexes of methyltrioxorhenium(VII) and their application in epoxidation with aqueous hydrogen peroxide as oxidant

Several di‐nitrogen Schiff bases were synthesized through the condensation of 2‐pyridinecarboxaldehyde with primary amines. The Schiff bases as ligands coordinated with methyltrioxorhenium (MTO) smoothly to afford the correspondent complexes which were characterized by IR, ¹H NMR, ¹³C NMR, MS and elemental analysis. One of the complexes was analyzed by X‐ray crystallography as well. The results revealed that the complexes display distorted octahedral geometry in the solid state with a trans‐position of Schiff base. Catalytic results indicated that the complexes as catalysts increased the selectivity of epoxides remarkably compared with MTO in the epoxidation of alkenes with 30% hydrogen peroxide as oxidant and the increasing rate depended on the structure of the Schiff base ligands of the complexes. The results indicated that the stronger the donating ability of the ligand, the higher selectivity of epoxides the complex gave in the epoxidation of alkenes with 30% hydrogen peroxide as oxidant. Copyright © 2010 John Wiley & Sons, Ltd.     

Unusual efficiency of a non-heme iron complex as catalyst for the hydroxylation of aromatic compounds by hydrogen peroxide: comparison with iron porphyrins

The non-heme iron complex, Fe(TPAA = tris-〚N-(2-pyridylmethyl)-2-aminoethyl〛amine)(ClO₄)₂, is a bad catalyst for the epoxidation of alkenes such as cyclooctene, cyclohexene and cis-stilbene and for the hydroxylation of alkanes such as adamantane by H₂O₂, when compared to the iron porphyrin Fe〚TDCPN₅P = meso-tetra-(2,6-dichlorophenyl)-β-pentanitroporphyrin〛Cl. At the opposite, Fe(TPAA)(ClO₄)₂ is a much better catalyst for the hydroxylation of arenes by H₂O₂; in its presence, anisole, toluene, ethylbenzene, benzene and chlorobenzene are transformed into the corresponding phenols, with respective yields of 53, 17, 24, 22 and 13% based on H₂O₂. Interestingly, in Fe(TPAA)-catalysed oxidations of anisole, toluene and ethylbenzene by H₂O₂, hydroxylation of the aromatic ring is by far the major reaction, even when compared to usually favoured reactions such as benzylic oxidation and oxidative demethylation.     

Multi-wall carbon nanotube supported tungsten hexacarbonyl: an efficient and reusable catalyst for epoxidation of alkenes with hydrogen peroxide

Highly efficient epoxidation of alkenes with H₂O₂ catalyzed by tungsten hexacarbonyl supported on multi-wall carbon nanotubes (MWCNTs) modified with 1,2-diaminobenzene is reported. The prepared catalyst, [W(CO)₆@DAB-MWCNT], was characterized by elemental analysis, scanning electron microscopy, FT-IR, and diffuse reflectance UV-Vis spectroscopic methods. The prepared catalyst was applied as an efficient catalyst for green epoxidation of alkenes with hydrogen peroxide in CH₃CN. This heterogeneous metal carbonyl catalyst showed high stability and reusability in epoxidation without loss of its catalytic activity.     

Chiral imidates as a new class of nitrogen-based chiral ligands: synthesis and catalytic activity in asymmetric aziridinations and diethylzinc additions

Chiral imidates were efficiently synthesized in one step and with high yields (seven examples). These chiral imidates were used as ligands in the Cu(I)-catalyzed asymmetric aziridination of methyl cinnamate and in the asymmetric diethylzinc additions to benzaldehyde as a proof of principle. The imidate catalyst system showed high catalytic activities and induced encouraging selectivities. An X-ray structure analysis of an imidate-Cu(I) complex is included, showing a distorted tetrahedral arrangement with two bidentate ligand molecules surrounding the metal.     

Electrode modified with a composite film of ZnO nanorods and Ag nanoparticles as a sensor for hydrogen peroxide

A conducting fluorine-doped tin oxide (FTO) electrode, first modified with zinc oxide nanorods (ZnONRs) and subsequently attached with photosynthesized silver nanoparticles (AgNPs), designated as AgNPs/ZnONRs/FTO electrode, was used as an amperometric sensor for the determination of hydrogen peroxide. The first layer (ZnONRs) was obtained by chemical bath deposition (CBD), and was utilized simultaneously as the catalyst for the photoreduction of Ag ions under UV irradiation and as the matrix for the immobilization of AgNPs. The aspect ratio of ZnONRs to be deposited was optimized by controlling the number of their CBDs to render enough surface area for Ag deposition, and the amount of AgNPs to be attached was controlled by adjusting the UV-irradiation time. The immobilized AgNPs showed excellent electrocatalytic response to the reduction of hydrogen peroxide. The resultant amperometric sensor showed 10-fold enhanced sensitivity for the detection of H₂O₂, compared to that without AgNPs, i.e., only with a layer of ZnONRs. Amperometric determination of H₂O₂ at −0.55 V gave a limit of detection of 0.9 μM (S/N = 3) and a sensitivity of 152.1 mA M⁻¹ cm⁻² up to 0.983 mM, with a response time (steady-state, t₉₅) of 30-40 s. The selectivity of the sensor was investigated against ascorbic acid (AA) and uric acid (UA). Energy dispersive X-ray (EDX) analysis, transmission electron microscopic (TEM) image, X-ray diffraction (XRD) patterns, cyclic voltammetry (CV), and scanning electron microscopic (SEM) images were utilized to characterize the modified electrode. Sensing properties of the modified electrode were studied both by CV and amperometric analysis.     

Mono-substituted Keggin-polyoxometalate complexes as effective and recyclable catalyst for the oxidation of alcohols with hydrogen peroxide in biphasic system

Mono-substituted Keggin-polyoxymetalate complex Na₆ [SiW₁₁ZnH₂O₄₀]·12H₂O was demonstrated to be an effective catalyst for the selective oxidation of alcohols in the presence of hydrogen peroxide as oxidant. The reaction was carried out in an aqueous/oil biphasic system, which allowed easy recovery of catalyst, under relative mild conditions. The catalyst could be reused five times without appreciable loss of activity.     

Chiral vicinal diols as platforms for separable diastereomers in Johnson-Claisen rearrangement: a new short route to (−)-nor-canadensolide, (−)-canadensolide and (−)-sporothriolide

The chiral vicinal diols prepared by asymmetric dihydroxylation in high enantioselectivities provide an excellent platform for separable diastereomers in the Johnson-Claisen rearrangement. The separated syn-diastereomers were converted into the advanced γ-(lactone-lactol) intermediates (in six steps, 26-27% overall yields) for the synthesis of (−)-nor-canadensolide, (−)-canadensolide and (−)-sporothriolide.