Cyclopentadienyl molybdenum dicarbonyl η-allyl complexes as catalyst precursors for olefin epoxidation. Crystal structures of Cp′Mo(CO)2(η-C3H5) (Cp′ = η-C5H4Me, η-C5Me5)

The complexes Cp′Mo(CO)₂(η³-C₃H₅) [Cp′ = η⁵-C₅H₅ (1), η⁵-C₅H₄Me (2), η⁵-C₅Me₅ (3)] have been prepared, structurally characterised by X-ray diffraction (2, 3), and tested as catalyst precursors for the epoxidation of olefins at 55 °C. Complex 1 gave a turnover frequency (TOF) of 310 mol mol_Mo⁻¹ h⁻¹ in the epoxidation of cis-cyclooctene with tert-butylhydroperoxide (TBHP, in decane) as oxidant, and 1,2-epoxycyclooctane was obtained quantitatively within 6 h. A similar result was obtained for complex 2, while the TOF for 3 was about one order of magnitude lower, suggesting a possible activity dependence on the ring substituents. For 1 the use of 1,2-dichloroethane as solvent increased the initial reaction rate to 361 mol mol_Mo⁻¹ h⁻¹, with no decrease in epoxide selectivity. Under these conditions the reaction rates for other olefins increased in the order 1-octene < trans-2-octene < cyclododecene < (R)-(+)-limonene < cis-cyclooctene, and, with the exception of limonene, the corresponding epoxide was the only product. For 1 the selective epoxidation of cis-cyclooctene could also be achieved in aqueous solution, using TBHP or H₂O₂ as oxidants, which gave epoxide yields of 99% and 27% at 24 h, respectively. The possibility of facilitating catalyst recycling by using ionic liquids as solvents was investigated.     

Synthesis,characterization and crystal structure of a dioxomolybdenum(VI) complex with a N,O type bidentate Schiff base ligand as a catalyst for homogeneous oxidation of olefins

The synthesis of a Mo(VI) Schiff base complex, cis-[MoO₂{(4,6-bis(tert-butyl)-2-{(benzyl)iminomethyl}phenolate)₂}], cis-[MoO₂(L)₂] where L = 4,6-bis(tert-butyl)-2-{(benzyl)iminomethyl}phenol, derived from benzylamine and 3,5-di-tert-butylsalycilaldehyde is reported. Full characterization of this complex was accomplished with elemental analyses, spectroscopic studies (NMR, IR and electronic) and X-ray structure analysis. This complex was tested as a catalyst for the homogeneous oxidation of olefins. The Mo(VI) complex is catalytically active for the epoxidation of aliphatic substrates at 80 °C, yielding the epoxide as the sole product in yields up to 100% and turnover numbers up to 5000. Under the optimized conditions styrene was oxidized in an 81% conversion to produce styrene oxide, benzaldehyde, and acetophenone.     

Epoxidation in ionic liquids: A comparison of rhenium(VII) and molybdenum(VI) catalysts

Complexes of the type (dimethyl-bpy)MoO₂Cl₂ and Schiff/Lewis-base complexes of methyltrioxorhenium (MTO), being efficient homogeneous catalysts for the epoxidation of olefins, have been examined with respect to their catalytic performance at 55 and 25 °C in systems employing room temperature ionic liquids (RTILs) of composition [BMIM]NTf₂, [BMIM]PF₆, [BMIM]BF₄ and [C₈MIM]PF₆ as solvents. The performance in the cyclooctene epoxidation was observed to be strongly dependent on the water content of the system and the catalyst solubility in the RTIL. MTO based systems prove to be superior with respect to lower energy consumption, higher stability and higher product yields compared to the investigated Mo(VI) system under the conditions applied.     

MCM-41 负载席夫碱催化α,β-不饱和酮的环氧化反应研究

介孔分子筛MCM-41 依次与3-氯丙基三乙氧基硅烷、环己二胺和三唑醛反应, 得到席夫碱修饰的新型介孔分子筛MCM-41 催化剂. 通过傅里叶变换红外光谱(FTIR)和X 射线多晶衍射(XRD)等方法对所得催化剂进行表征. 以过氧化氢为氧源, 介孔分子筛MCM-41 负载的席夫碱为催化剂, 研究了α,β-不饱和酮的环氧化反应, 考察了金属盐、溶剂、催化剂用量、反应时间等因素对环氧化反应的影响. 结果表明, 在室温下乙腈溶剂中, α,β-不饱和酮的环氧化反应在短时间内均以很高的产率(高达99%)得到了相应的产物. 同时, 对催化剂的重复利用进行了研究, 发现重复使用四次, 仍能以较高产率得到环氧化产物.     

Carbonyl complexes of manganese, rhenium and molybdenum with 2-pyridylimino acid ligands

[MBr(CO)₃{κ²(N,O)-pyca}] [M = Mn(1a), Re(1b), pyca = pyridine-2-carboxaldehyde] and [MoCl(η³-C₃H₄Me-2)(CO)₂{κ²(N,O)-pyca}] (1c) react with aminoacid β-alanine to give the corresponding iminopyridine complexes 2a-2c. The same method affords the iminopyridine derivatives from γ-aminobutyric acid (GABA) (3a-3c) and 3-aminobenzoic acid (4a-4c). For complexes 2a-2c, 3a, 3c and 4a, the solid state structures have been determined by X-ray crystallography, revealing interesting differences in their hydrogen-bonding patterns in solid state.     

Synthesis of WO2pyprMCM-41 as selective and reusable catalyst for the epoxidation of alkenes

The sythesis, characterization and catalytic activity of WO₂pypr [N,N′-bis (2-pyrrolmethlidenaminopropyl) amine] complexed to MCM-41 surface in the epoxidation of some alkenes with excellent selectivity toward the corresponding epoxides is described in this presentation.     

MCM-41-supported bidentate phosphine palladium(0) complex as an efficient catalyst for the heterogeneous Stille reaction

A Stille coupling reaction of organostannanes with organic halides has been developed in the presence of a catalytic amount of MCM-41-supported bidentate phosphine palladium(0) complex (0.5 mol %) in DMF/H₂O (9:1) under air atmosphere in high yields. This polymeric palladium catalyst exhibits higher activity than Pd(PPh₃)₄ and can be reused at least 10 times without any decrease in activity.     

席夫碱修饰的MCM-41介孔分子筛与碳酸钾共同催化查尔酮的环氧化反应

将介孔分子筛MCM-41依次与3-氯丙基三乙氧基硅烷、二氨基硫脲和水杨醛反应,得到席夫碱修饰的介孔分子筛MCM-41催化剂,以过氧化氢为氧源,研究了其与K2CO3共同催化α,β-不饱和酮的环氧化反应。 化合物的结构经1H NMR和IR分析确认。 考察了金属盐、溶剂、催化剂用量、反应时间等因素对环氧化反应的影响。 结果表明,室温下α,β-不饱和酮的环氧化反应在短时间内均以较高的产率(最高达93%)得到了相应的产物。 同时,对催化剂的重复利用进行了研究,发现重复使用4次,仍能以较高产率得到环氧化产物。     

Schiff base‐functionalized boehmite nanoparticle‐supported molybdenum and vanadium complexes: efficient catalysts for the epoxidation of alkenes

Boehmite nanoparticles, with high surface area and high degree of surface hydroxyl groups, were prepared via hydrothermal‐assisted sol–gel processing of aluminium 2‐butoxide. The produced powder was covalently functionalized with 3‐(trimethoxysilyl)propylamine, and then, in order to support vanadium oxosulfate and molybdenum hexacarbonyl complexes, all the terminal amine groups were changed to Schiff bases by refluxing with salicylaldehyde. These catalysts were applied in the epoxidation of cis‐cyclooctene and other olefins with tert‐BuOOH in CCl₄. The catalytic procedures for both catalysts were optimized for various parameters such as solvent and oxidant. Recycling experiments revealed that these heterogeneous nano‐catalysts could be repeatedly applied for the epoxidation of alkenes. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,structural characterization,and catalytic reactivity of a new molybdenum(VI) complex containing 1,3,4-thiadiazole derivative as a tridentate NNO donor ligand

A new cis-dioxo molybdenum(VI) complex was obtained by reaction of 2,4-dihydroxybenzylidene(5-N,N-methylphenylamino-1,3,4-thiadiazol-2-yl)hydrazone as ligand and [MoO₂(acac)₂] in methanol and was characterized by elemental analyses, ¹H NMR, IR, and electronic spectroscopic studies. The complex was also analyzed by single-crystal X-ray diffraction. The structure determination revealed a distorted octahedral coordination geometry around molybdenum in which the tridentate NNO donor (L^2–) is bonded to [MoO₂]²⁺ through phenolic oxygen, hydrazinic nitrogen, and thiadiazole nitrogen. The sixth coordination site is occupied by a weakly bonded methanol. The complex was tested as a catalyst for homogeneous epoxidation of olefins using tert-butyl hydrogen peroxide as an oxidant. In the homogeneous catalytic system, the reactions are efficiently carried out with high yields and selectivity.     

镍(II)配合物官能化的MCM-41催化分子氧环氧化苯乙烯

制备了镍(II)席夫碱配合物官能化的MCM-41多相催化剂MCM-41-Ni.利用X射线粉末衍射、氮气物理吸附脱附、红外光谱、热重、电感耦合等离子体原子发射光谱、元素分析和透射电镜等方法对催化剂进行了表征.以氧气为氧化剂,MCM-41-Ni在催化环氧化苯乙烯的反应中表现出较高的催化活性;苯乙烯的转化率为95.2%,环氧苯乙烷的选择性为66.7%.系统地研究了反应温度、催化剂用量、溶剂以及反应时间对反应性能的影响.催化剂经过4次循环仍然表现出较好的稳定性和催化活性.     

The use of Cu and Zn salicylaldimine complexes as catalyst precursors in ring opening polymerization of lactides: ligand effects on polymer characteristics

A range of monomeric tetra‐coordinate copper (II) and zinc (II) complexes based on N,O‐bidentate salicylaldimine Schiff base ligands has been synthesized and characterized using various spectroscopic techniques. These complexes were then evaluated as initiators in ring‐opening polymerization of lactides at both 70 °C and 110 °C. The effect of structural changes in the complexes on the ability of these compounds to initiate lactide polymerization as well as the impact on the chemical and physical characteristics of the polymers obtained indicate that the coordination geometry of the metal complex, M? O bond length and substituents on the Schiff base ligand all play a role in the catalyst activity. Electronic factors were dominant in the case of the copper complexes while steric factors prevailed in the case of Zn initiators. Both the Zn and Cu complexes exhibit characteristics of living ring opening polymerization. Copyright © 2010 John Wiley & Sons, Ltd.     

MCM-41固载Co席夫碱配合物的制备及其催化烯烃环氧化的研究

环氧化合物作为有机合成中间体具有广泛应用,催化烯烃环氧化一直是催化化学中的一个重要课题[1～2].尽管已经报道了以过酸、过氧化氢、烷基过氧化物、或分子氧为氧化剂,以金属配合物(通常为钌、钼、钛的配合物)为催化剂的反应体系,但对环氧化物的选择性却很低[3].另外,除了需探索具有高选择性的催化体系外,应用分子氧或空气作为氧化剂更适宜于经济和安全的要求.目前,在以分子氧作为氧化剂,均相催化烯烃环氧化的研究中,应用醛类化合物作为氧转移试剂是一种有效的和方便的促进烯烃环氧化的方法[4].但是,均相催化剂难于分离和重复使用,因此…     

Synthesis of titanium–triazine based MCM-41 hybrid materials as catalyst for the asymmetric epoxidation of cinammyl alcohol

A molecular precursor approach involving tethering procedures was used to produce site isolated titanium-supported asymmetric epoxidation catalysts. This was done by first modifying the support in one step with a mixture of silanes: the synthesized triazine propyl triethoxysilane as functional linker and hexamethyldisilizane as capped agent, to increase the hydrophobicity of the support and mask the remaining silanol groups. In addition, [Ti(OPrⁱ)₄] and [{Ti(OPrⁱ)₃(OMent)}₂] (MentO = 1R,2S,5R-(−)-menthoxo) complexes were heterogenized by reaction with the modified MCM-41. Finally, after [Ti(OPrⁱ)₄] immobilization on to the organomodified support the reaction with the chiral auxiliary (+)-diethyl-l-tartrate was accomplished. All the materials were characterized by elemental analysis, X-ray diffraction, nitrogen adsorption techniques, FT-IR, ICP-MS, DR-UV–vis, ²⁹Si and ¹³C MAS NMR and TGA. The different systems were tested in the asymmetric epoxidation of cinnamyl alcohol in order to evaluate their catalytic activity and enantioselectivity.     

Synthesis,characterization and biological screening studies of mixed ligand complexes using flavonoids as precursors

Flavonoids are a group of plant phenolics that provide various health benefits through cell signalling pathways and antioxidant effects. In the present study, a new series of mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) were synthesized by incorporating curcumin and quercetin flavonoid precursors. The structural features of the synthesized complexes were explored using elemental analysis, thermogravimetric analysis, UV–visible, infrared, NMR, mass and electron paramagnetic resonance spectral analyses and conductivity measurements. These data support an octahedral geometry of the synthesized complexes. In silico biological activity score for the ligand was predicted using PASS online software. ADMET properties were studied using VLS3D online software. Anti‐inflammatory and antioxidant activities were experimentally validated which prove that theoretical predictions are in agreement with the experimental results. Interestingly the synthesized complexes interact with calf thymus DNA through groove binding mode. Moreover, they have good potential to cleave pUC19 DNA. Minimum inhibitory concentration values of the synthesized complexes reveal that they have better antimicrobial efficacy than the ligands.     

Synthesis and application of new Schiff base Mn(III) complexes containing crown ether rings as catalysts for oxidation of cyclohexene and cyclooctene by Oxone

Six catalysts MnClL¹–MnClL⁶, containing two crown ether rings, were synthesised and characterised by IR spectroscopy and CHN microanalysis. A combination of Oxone, as oxidant, and these catalysts was used for the oxidation of cyclohexene and cyclooctene. Among the prepared catalysts, MnClL³ and MnClL⁴ exhibited the best catalytic efficiency. Catalysts MnClL¹, MnClL² and MnClL⁶ showed a moderate efficiency and MnClL¹ showed the lowest efficiency. Comparison of MmclL¹–MnClL⁴ and MnClL⁶ containing crown ether rings with an identical mixture of uncrowned complex MnClL⁷ [manganese N,N′-bis(salicylidene)ethylenediamine chloride] and crown ether 2 (4′-hydroxybenzo-15-crown-5), revealed a more important role for the crown ether than increasing solubility of Oxone in the organic phase. The effect on reaction times and chemical yields of temperature, pyridine as the axial base, and different alkali metal salts was also investigated.     

Highly efficient and excellent reusable catalysts of molybdenum(VI) complexes grafted on ZPS‐PVPA for epoxidation of olefins with tert‐BuOOH

Four new kinds of heterogeneous catalysts for olefins epoxidation were obtained by grafting diamines on organic polymer–inorganic hybrid material, zirconium poly (styrene‐phenylvinylphosphonate)‐phosphate (ZPS‐PVPA), and subsequently coordinating with Schiff base Mo(VI) complexes. The catalysts were characterized by IR, XPS, SEM and TEM. All catalysts were evaluated through the epoxidation of olefins using tert‐BuOOH as oxidant. The heterogeneous catalysts possess the advantages of high conversion, selectivity and excellent reusability. The catalysts were easily separated from the reaction systems and could be reused 13 times without significant loss of catalytic activity. Copyright © 2010 John Wiley & Sons, Ltd.     

The first MCM-41-supported thioether palladium(0) complex: A highly active and stereoselective catalyst for Heck arylation of olefins with aryl halides

The first MCM-41-supported thioether palladium(0) complex has been synthesized from 3-(2-cyanoethylsulfanyl)propyltriethoxysilane via immobilization on MCM-41, followed by reacting with palladium chloride, and then the reduction with hydrazine hydrate. It was found that this complex has not only high activity and stereoselectivity for arylation reaction of conjugated alkenes with aryl iodides or activated aryl bromides, but also can efficiently catalyze the arylation reaction of conjugated alkenes with unactivated bromoarenes. This polymeric palladium catalyst can be easily recovered from the products and reused at least 10 times without loss of activity.     

Covalent supporting of novel dioxo‐molybdenum tetradentate pyrrole‐imine complex on Fe3O4 as high‐efficiency nanocatalyst for selective epoxidation of olefins

A novel Mo(VI) tetradentate Schiff base complex based on two pyrrole‐imine donors was anchored covalently on Fe₃O₄ nanoparticles and characterized using physicochemical techniques. The catalytic epoxidation process was optimized in terms of the effects of solvent, reaction temperature, kind of oxidant and amount of oxidant and catalyst. Then the novel heterogeneous nanocatalyst was used for the efficient and selective catalytic epoxidation of internal alkenes (cyclohexene, cyclooctene, α‐pinene, indene and trans ‐1,2‐diphenylethene) and terminal alkenes (n ‐heptene, n ‐octene, n ‐dodecene and styrene) using tert ‐butyl hydroperoxide (70% in water) as oxidant in 1,2‐dichloroethane as solvent. The prepared nanocatalyst is very effective for the selective epoxidation of cis ‐cyclooctene with 100% conversion, 100% selectivity and turnover frequency of 1098 h⁻¹ in just 30 min. The magnetic nanocatalyst was easily recovered using an external magnetic field and was used subsequently at least six times without significant decrease in conversion.     

Epoxidation of cyclooctene by host (nanocavity of zeolite-Y) guest (copper(II) complexes with 16- and 17-membered diaza dioxa macrocyclic Schiff bases) nanocomposite materials

This work reports the synthesis and characterization of macrocyclic copper(II) complexes encapsulated within the nanopores of zeolite-Y. The obtained nanoparticles entrapped in the nanopores of zeolite have been characterized by FT-IR, UV–Vis, Diffuse reflectance spectra, spectroscopic techniques, molar conductance, magnetic moment data, XRD, thermal, and elemental analysis. The complexes (neat and encapsulated) were used for the oxidation of cyclooctene with tert-butyl hydroperoxide as oxidant in different solvents. The supported Cu[L₁]²⁺-Y exhibited a moderate 81.9% selectivity for epoxidation with 84.2% conversion. The catalytic activity and selectivity of the heterogeneous catalysts do not change after recycling five times.