A highly efficient polymer‐anchored palladium(II) complex catalyst for hydrogenation,Heck cross‐coupling and cyanation reactions

BACKGROUND: Precise architectures of steric and electronic properties of palladium species play a crucial role in designing highly functionalized catalyst systems responsible for target organic transformations. Pd catalysts supported on polymer materials have been employed extensively as catalysts not only for hydrogenation but also for coupling reactions in the production of fine chemicals. RESULTS: A new polymer‐anchored Pd(II) complex has been synthesized and characterized. The catalyst shows high catalytic activity in the hydrogenation of styrene oxide, Heck cross‐coupling and cyanation reactions of aryl halides. The effect of various reaction parameters were investigated to optimize reaction conditions. The catalytic system shows good activity in the hydrogenation of styrene oxide (conversion 98%) with a selectivity to 2‐phenylethanol (93%) which is higher than its homogeneous analogues. The catalyst also exhibits excellent catalytic activity for the Heck cross‐coupling and cyanation reactions of various substituted and non‐substituted aryl halides. CONCLUSIONS: Results demonstrate that the catalyst is robust and stable and can be recovered quantitatively by simple filtration and reused several times without loss of activity. Copyright © 2010 Society of Chemical Industry     

溶胶-凝胶法制介孔Pd/m-TiO2催化连续流Suzuki偶联反应

以PdCl2和钛酸正丁酯为原料、聚乙烯吡咯烷酮为金属保护剂、三嵌段共聚物EO96PO70EO96为模板剂,采用溶胶-凝胶法制备了一系列不同Pd负载量(质量分数0.1％～1.0％)的非均相Pd/m-TiO2催化剂.采用N2吸附-脱附等温线、XRD和TEM对其进行了表征.结果表明,催化剂具有有序介孔结构,孔径在8.7～10...     

Carboncarbon bond forming reactions: Application of covalently anchored 2,4,6-triallyloxy-1,3,5-triazine (TAT) Pd(II) complex over modified surface of SBA-15 to Heck,Suzuki, Sonogashira and Hiyama cross coupling reactions

A highly active SBA-15-TAT-Pd(II) catalyst was synthesized from organofunctionalized SBA-15 and 2,4,6-triallyloxy-1,3,5-triazine. The catalyst was employed in carrying out Heck, “copper-free” Sonogashira, Suzuki and Hiyama cross coupling reactions. Under the optimized conditions the catalyst displays excellent catalytic activity in delivering the desired products in good to excellent yields. The catalytic system exhibited superior activity regarding the time taken for the completion of reaction, isolation, Pd loading (0.62 mmol%) and yields of products as compared to the earlier reported heterogeneous SBA-15 anchored Pd catalysts. The catalyst could be recycled and reused for five times without any appreciable loss of catalytic activity.     

Facile synthesis of palladium nanoparticles supported on silica: An efficient phosphine-free heterogeneous catalyst for Suzuki coupling in aqueous media

A convenient one-step method for synthesizing highly dispersed palladium nanoparticles supported on silica, without taking assistance from any external reductant or stabilizer, has been developed. The supported nanoparticles were characterized by N₂-adsorption desorption, XRD, HRTEM, SEM-EDX, XPS, ICP analyses and applied as catalyst for Suzuki-Miyaura reactions of aryl halides. The reactions with aryl bromides were performed in neat water at room temperature; while the reactions with aryl chlorides were conducted in aqueous-ethanol at 90 °C. The catalyst could be reused at least three times without compromising with its activity, however from the fourth cycle a progressive decrease in yield was noticed. No aggregation of NPs was observed by the TEM analysis of the six-time used catalyst.     

Oxidation of styrene over polymer‐ and nonpolymer‐anchored Cu(II) and Mn(II) complex catalysts

Catalytic oxidation of styrene was investigated over polymer‐ and nonpolymer‐anchored Cu(II) and Mn(II) complex catalysts prepared by schiff base tridentate ligands. The effect of temperature, styrene to H₂O₂ mole ratio and catalyst amount on the catalytic activity and product selectivity was investigated. Further, the catalysts were characterized by various techniques, such as elemental analysis, atomic absorption spectroscopy (AAS), FTIR, FE‐SEM, EDAX, TGA, and UV–vis spectrophotometer. The elemental analysis, EDAX and AAS results confirmed the formation of Cu(II) and Mn(II) complexes, and it was found that the metal loading in the polymer‐anchored complex catalysts were in the range of 0.53–3.74 %. FTIR results showed the co‐ordination bond formation between the polymer ligands and metal ion. The catalytic data showed that, over all the catalysts, the main reaction products were benzaldehyde, styrene oxide, and benzoic acid. The polymer‐anchored complex catalysts were found to be much more active when compared with nonpolymer‐anchored catalysts. The maximum conversion of styrene (92.3%) was obtained over PS‐[Cu(Hfsal‐aepy)Cl] catalyst with benzaldehyde selectivity to 69% at the styrene to H₂O₂ mole ratio of 1 : 4 at 75°C. Although the PS‐[Mn(Hfsal‐aepy)Cl] catalyst was less active, it was highly selective to benzaldehyde. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

New application of an anchored Ru(II)-N-heterocyclic carbene complex

A new, heterogenized Ru(II)-N-heterocyclic carbene complex was prepared via the method developed by Augustine. The anchored catalyst was characterized by spectros-copic methods and was applied in the hydrogenation of different olefins, aldehydes and ketones. The hydrogenations were performed both in alcohol and in aqueous media on homogeneous and heterogenized complexes. The immobilized complex had a reasonable activity in both conditions and at the same time it was possible to filter out from the reaction mixture and to recycle in several subsequent runs.     

Tethering of Cu(II) Schiff base metal complex on mesoporous material MCM-41: catalyst for Ullmann-type coupling reactions

The siloxane-functioned Cu(II) complex derived from 3-aminopropyltrimethoxysilane, terephthaldehyde and 2-aminophenol was anchored on hexagonal mesoporous silica MCM-41. The MCM-41 and its Schiff base MCM-41 complex was characterized by FTIR, small-angle X-ray diffraction, SEM-EDX, N₂ adsorption and desorption analysis and TGA. The synthesized Cu-Schiff base MCM-41 catalyst has been successfully applied as a catalyst for Ullmann-type coupling reaction of the aryl halides with aryl halides, phenols, amines and N-heterocyclic amines. In the coupling reaction the yields of the products were good and the catalyst was recovered by simple filtration method and can be reused.     

Diethanol amine‐functionalized polymer‐supported palladium (0) complex as catalyst for Suzuki cross‐coupling reaction in water

Diethanol amine‐functionalized polymer‐supported palladium (0) complex as catalyst for Suzuki cross‐coupling reaction in water was synthesized and characterized. The catalyst exhibits excellent catalytic activity and stability in the Suzuki cross‐coupling reaction. Various aryl bromides were coupled with aryl boronic acids in water, under air, and in the presence of 0.5 mol % of the catalyst to afford corresponding cross‐coupled products in high yields at 100°C. Furthermore, the heterogeneous catalyst can be readily recovered by simple filtration and reused for several times only with a slight decrease in its activity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and catalytic properties of a new dioxomolybdenum(VI) complex covalently anchored to mesoporous MCM-48

Reaction of the solvent adduct MoO₂Cl₂(THF)₂ with the 1,4-diazabutadiene ligands RNC(Ph)C(Ph)NR [R = (CH₂)₂CH₃, (CH₂)₃Si(OMe)₃] leads to complexes of the type MoO₂Cl₂(LL) in good yields at room temperature within a few minutes. The complex bearing the trimethoxysilyl groups was immobilized in the ordered mesoporous silica MCM-48 by covalent bonding. Solid state MAS NMR spectroscopy (¹³C, ²⁹Si) confirms that the structural integrity of the complex was retained during immobilization, except for loss of methoxide groups due to the reaction with surface silanols. Powder X-ray diffraction (XRD) and N₂ adsorption studies of the derivatized material indicate that the textural properties of the support were preserved during the grafting experiment and that the channels remained accessible. The modified material is active and selective in the epoxidation of cyclooctene at 55 °C using tert-butyl hydroperoxide as the oxidant. Stability was checked by recycling the solid catalyst several times. Some activity is lost from the first to second runs, but thereafter stabilizes. The catalytic behavior of the heterogenized catalyst was also compared with that observed in homogeneous phase for the complex with R=(CH₂)₂CH₃.     

A facile preparation of palladium Schiff base complex supported into MCM-41 mesoporous and its catalytic application in Suzuki and Heck reactions

A simple and efficient method for phosphine-free C–C coupling reactions such as Heck and Suzuki reactions in the presence of pyrrole Schiff base complex of palladium immobilized on mesoporous mesoporous of MCM-41 (Pd-Py-MCM-41) has been reported. The Suzuki reaction was carried out in PEG-400 using phenylboronic acid (PhB(OH)₂). Pd-Py-MCM-41 has been found as a promising catalyst for Heck reaction of butyl acrylate with aryl halides (including Cl, Br and I). The catalyst was characterized by FT-IR, TEM, XRD, SEM, BET and ICP-OES techniques. The protocol proves to be efficient and environmentally benign in terms of high yield, easy of recovery and reusability of catalyst.     

Activation of aryl chlorides in water for Suzuki coupling with a hydrophilic salen-Pd(II) catalyst

For exploiting aqueous condition, we have designed a simple water-soluble palladium Schiff-base catalyst for Suzuki-Miyaura reactions of aryl halides with arylboronic acids. The reactions could be performed in neat water with aryl bromides and iodides at room temperature and with aryl chlorides at 100 °C. Good-to-excellent yields of cross-coupling products were obtained with a diverse range of aryl halides including heteroaryl halides. Interestingly, the homogeneous catalyst could be conveniently recycled with aryl bromides or chlorides for at least four times, although a progressive decrease in the product yields were noticed.     

Hydrogenation of olefins over palladium(II) complexes supported on a modified macroporous polymer bead

Gellular and macroporous polymer supports have been prepared. A modified polymer support has also been prepared by coating the internal pore wall of macroporous poly(styrene-co-divinylbenzene) with lightly crosslinked polymer containing functional groups. The supports were phosphinated and PdCl₂ was supported on them. The supports and catalysts were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy. The polymer-supported Pd catalysts were used in the hydrogenation of olefins. The effects of the support structure and solvent were also studied. ©1997 SCI     

Facile synthesis of water-soluble luminescent mesoporous Tb(OH)3@SiO2 core-shell nanospheres

Luminescent mesoporous Tb(OH)₃@SiO₂ core-shell nanospheres were synthesized through W/O microemulsion process at ambient temperature. The negatively charged silica favors a coating of the positively charged Tb³⁺ composite. Thus, silicon layer was adsorbed on the surface of Tb(OH)₃ groups to form Tb-O-Si through electrostatic interaction. X-ray diffraction, field emission transmission electron microscopy (FE-TEM), energy-dispersive X-ray spectrometry, and Fourier transform infrared, UV/Visible, and photoluminescence spectroscopies were applied to examine the phase purity, crystallinity, surface morphology, and optical properties of the core-shell nanospheres. The FE-TEM results have revealed typically ordered mesoporous characteristics of the material with monodisperse spherical morphology in a narrow size distribution. The luminescent mesoporous core-shell nanospheres exposed remarkable splitting with broadening in the emission transition ⁵D₄ → ⁷F₅ (543 nm). In addition, the luminescent mesoporous core-shell nanospheres emit strong green fluorescence (from Tb³⁺) in the middle of the visible region under 325 nm (3.8) excitation. The luminescent mesoporous Tb(OH)₃@SiO₂ core-shell nanospheres can therefore be exploited as fluorescent probes in biomarkers or biolabeling, optical sensing, and drug delivery system. Further, these nanospheres could have potential use as scattering layers in dye-sensitized solar cells.     

Synthesis,characterisation and catalytic activity of styrene–divinylbenzene copolymer (XAD-2) bound palladium (II) complex

Polymer-anchored Pd(II) complex catalyst was sythesised by sequential attachment of 1,2-diaminopropane as a ligand to the chloromethylated commercially available styrene-divinylbenzene copolymer (XAD-2). The catalyst was characterised using techniques such as FTIR, SEM, EPR, and UV-VIS reflectance spectroscopy. Other physicochemical properties, such as bulk density, moisture content, swelling and surface area by the BET method at low temperature by nitrogen adsorption, were also studied. The catalyst was tested for the rate of hydrogenation of cyclohexene. The influence of various factors such as temperature, concentration of catalyst, substrate, and quantity of solvent have been determined. The results are compared with the homogeneous analogue. The recycling efficiency of the catalyst was also studied.     

Organometallic diaqua complexes of palladium(II)

The protonation of [(C₆F₅)LPd(μ-OH)₂PdL(C₆F₅)] by triflic acid (CF₃SO₃H) results in the formation of the diaqua complexes [Pd(C₆F₅)L(H₂O)₂][CF₃SO₃] (L=PPh₃ (1) or AsPh₃ (2)). The crystal structure of 2 was elucidated by X-ray diffraction analysis revealing the presence of tetrameric units involving hydrogen bonds.     

Bidentate salen Cu(II) complex functionalized on mesoporous MCM-41 as novel nano catalyst for the oxidative coupling of thiols into disulfides using urea hydrogen peroxide (UHP)

Functionalized Copper(II) complex into nano dimensional mesoreactor was successfully prepared. The Copper(II) complex with N–O donor Schiff base ligand was readily trapped into mesoporous silica MCM-41 through the post grafting method. N–O Chelating Schiff-base-MCM-41 has been derived from 5-bromo-salicylaldehyde and 3-aminopropyltriethoxysilane which was functionalized on MCM-41 via silicon alkoxide route. This compound was characterized by FT-IR, TGA, small angle X-ray diffraction patterns, ICP/MS analysis and N₂ sorption–desorption analysis. The catalytic property of Cu–salen–MCM-41 was considered for the preparation of disulfides using urea hydrogen peroxide as oxidant. The reaction progress is simple and proceeds under mild and heterogeneous conditions in acetonitrile at the ambient of temperature. The corresponding disulfides have been achieved with high purity and good to excellent yields; also, no over oxidation to sulfoxide or sulfone was observed in all cases. The catalyst can be recovered and reused several times without significant loss of stability and activity.     

聚酰胺-胺为模板的钯纳米簇催化的Suzuki偶联反应

以不同代数、不同端基和不同程度端基桥联的聚酰胺-胺(PAMAM)树状大分子为模板,制备出稳定的钯纳米金属簇催化剂,通过催化Suzuki偶联反应考察了其应用效果。结果发现以4.5GPAMAM-OCH3为模板制备的钯纳米簇催化剂,反应条件温和,产品易于分离提纯,产率可达96%。将4.5GPAMAM-OCH3端基用乙二胺部分桥联后作为模板制备钯纳米金属簇催化剂,以防止纳米粒子团聚失活,初探结果表现出优异的重复使用性能。     

Diphosphino-functionalized MCM-41 anchored palladium(0) complex as an efficient catalyst for Heck arylation of conjugated alkenes with aryl halides

Diphosphino-functionalized MCM-41 anchored palladium(0) complex (denoted as MCM-41-2P-Pd(0)) was conveniently synthesized from commercially available and cheap γ-aminopropyltriethoxysilane via immobilization on MCM-41, followed by reacting with diphenylphosphinomethanol and palladium chloride and then the reduction with hydrazine hydrate. XRD and XPS spectroscopies were employed to characterize the title palladium complex. It was found that this complex is a highly active and stereoselective catalyst for Heck arylation of conjugated alkenes with aryl halides and can be reused many times without loss of activity.     

Suzuki cross-coupling reaction over a palladium–pyridine complex immobilized on hydrotalcite

A catalyst consisting of a Pd(II) complex immobilized on the surface of a layered double hydroxide (LDH) was prepared. The Pd–LDH complex proved effective in the Suzuki cross-coupling reaction under very mild conditions (viz. a temperature of 55 °C and atmospheric pressure); in fact, it provided conversion and selectivity results surpassing those of existing heterogeneous phase catalysts and most homogeneous phase catalysts for the same purpose. The support and the active phase of the catalyst were characterized by using various instrumental techniques including X-ray diffraction and NMR spectroscopy. Of the inorganic bases used in combination with the catalyst, potassium carbonate was found to provide the best results in the reaction.