Direct oxidative C(sp3)─H/C(sp2)─H coupling reaction using recyclable Sr-doped LaCoO3 perovskite catalyst

A strontium-doped lanthanum cobaltite perovskite, La_0.6Sr_0.4CoO₃, was prepared and utilized as a recyclable heterogeneous catalyst for the direct oxidative C(sp³)─H/C(sp²)─H coupling reaction between cyclic ethers and alkenes or coumarins to achieve corresponding α-functionalized ethers. The α-functionalization of cyclic thioethers or amides with alkenes or coumarins was also achieved via this protocol. The La_0.6Sr_0.4CoO₃ catalyst exhibited better performance than a variety of homogeneous and heterogeneous catalysts. Utilizing a recyclable catalyst would offer a greener option for the direct oxidative C(sp³)─H/C(sp²)─H coupling reaction. To our best knowledge, the C(sp³)─H/C(sp²)─H coupling between olefins and ethers to generate α-functionalized ethers using a heterogeneous catalyst has not been previously reported, and the α-functionalization of cyclic thioethers or amides with alkenes or coumarins is new.     

An improved Ullmann-Ukita-Buchwald-Li conditions for CuI-catalyzed coupling reaction of 2-pyridones with aryl halides

An effective CuI-trans-N,N′-dimethylcyclohexane-1,2-diamine (DMCDA)-K₂CO₃-catalyzed coupling reaction of 2-pyridones with aryl halides is described. Under our conditions, DMCDA was found to be an effective catalyst that facilitates the coupling reactions even in toluene, a common industrial solvent. In addition, 3-bromopyridine could also be coupled effectively under these conditions, indicating that the catalytic reactivity of this system is high. The reaction could be applied for polymer modification and iterative oligo-pyridone synthesis.     

[PdCl2{8-(di-tert-butylphosphinooxy)quinoline)}]: a highly efficient catalyst for Suzuki-Miyaura reaction

The complex [PdCl₂(P-N)] containing the basic and sterically demanding 8-(di-tert-butylphosphinooxy)quinoline ligand (P-N) is a highly efficient catalyst for the coupling of phenylboronic acid with aryl bromides or aryl chlorides. The influence of solvent and base has been investigated, the highest rates being observed at 110 °C in toluene with K₂CO₃ as the base. With aryl bromides the reaction rates are almost independent on the electronic properties of the para aryl substituents, on the contrary, reduced reaction rates are observed when bulky substituents are present on the substrate. Nevertheless the coupling of 2-bromo-1,3,5-trimethylbenzene with phenylboronic acid can be carried out to completion in 2 h using a catalyst loading of 0.02 mol %. Under optimized reaction conditions, turnover frequencies as high as 1900 h⁻¹ can be obtained in the coupling of 4-chloroacetophenone with phenylboronic acid; lower reaction rates are obtained with substrates bearing EDG substituents on the aryl group.     

Guanylation of aromatic amines catalyzed by vanadium imido complexes

The reaction of formation of guanidines by coupling of carbodiimides and aromatic amines using imido vanadium complexes as catalyst have been investigated. Results demonstrate that the complex V(N-2,6-ⁱPr₂C₆H₃)Cl₃ is an effective catalyst for this process.     

Syntheses of amides via iodine-catalyzed multiple sp~3 C–H bonds oxidation of methylarenes and sequential coupling with N,N-dialkylformamides

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An efficient and simple ligand from phthalandione for palladium-catalyzed Suzuki reaction in aqueous media

An efficient and simple ligand derived from phthalandione was used for palladium catalyzed Suzuki coupling reaction in water/ethanol (V/V = 2/1) under aerobic conditions. The reaction exhibited a high catalytic efficiency even with lower Pd loading (0.002 mol %). In this work, the catalyst could be successfully used in coupling reaction between various aryl halides with phenylboronic acid in excellent yields with high turnover number (TON) (the maximal TON was up to 49,000 for the reaction of bromobenzene with phenylboronic acid). Moreover, this new ligand had been elucidated by ¹H NMR, ¹³C NMR and X-ray crystal diffraction.     

Effect of oxygen on the activity of a Pd-Fe/a-Al2O3catalyst for CO coupling to diethyl oxalate

The effect of oxygen on the activity and selectivity of a Pd-Fe/a-Al₂O₃ catalyst for CO coupling to diethyl oxalate (DEO) was studied in the range of 105 - 120^oC. The results showed that the conversion of CO and the STY (Space Time Yield) of DEO increased with increasing oxygen concentration from 5 to 10 mol% and reaction temperature, but the selectivity to DEO decreased. The role of oxygen in CO coupling is discussed on the basis of the experimental results in the present work and the XPS characterization of the catalysts. It was also found that the activity and selectivity of the catalyst could be fully recovered after removing O₂ from the reaction system.     

Iron oxide modified with pyridyl‐triazole ligand for stabilization of gold nanoparticles: An efficient heterogeneous catalyst for A3 coupling reaction in water

Fe₃O₄ nanoparticles were modified with pyridyl‐triazole ligand and the new magnetic solid was applied for the stabilization of very small and uniform gold nanoparticles. The resulting magnetic material, Fe₃O₄@PT@Au, was characterized using various methods. These gold nanoparticles on a magnetic support were applied as an efficient heterogeneous catalyst for the three‐component reaction of amines, aldehydes and alkynes (A³ coupling) in neat water with 0.01 mol% Au loading. Using magnetic separation, this catalyst could be recycled for seven consecutive runs with very small decrease in activity. Characterization of the reused catalyst did not show appreciable structural modification.     

高效组合型 Pd/C 催化剂用于 Suzuki 偶联反应

 采用有机金属 Pd2(dba)3 (dba 为二亚苄基丙酮) 还原分解法制得均匀分布的 Pd 纳米颗粒 (粒径为 3~6 nm) 混合液, 并用活性炭直接吸附得到了组合型 Pd/C 纳米催化剂. 采用透射电子显微镜、X 射线光电子能谱和 X 射线衍射等手段测定了催化剂表面 Pd 颗粒大小分布、晶型和化学态等. 将该催化剂用于 Suzuki 碳-碳偶联反应, 其催化活性比浸渍法制备的 Pd/C 催化剂高 2 倍以上. 以溴代芳烃为底物时, 在 80 oC 下 0.5 h 后偶联产物收率可达 98% 以上. 以邻氯硝基苯为底物时, 在 110 oC 下 1 h 后偶联产物收率可达 64%; 延长反应时间, 产物收率可达 90% 以上.     

ipso-Fluorination of aryltrimethylsilanes using xenon difluoride

Reaction of aryltrimethylsilanes with xenon difluoride in C₆F₆/Pyrex^® at room temperature gives aryl fluorides in good yield. The reaction is inhibited when acetonitrile is used as solvent but proceeds well in CFCl₃/Pyrex^® or CH₂Cl₂/Pyrex^®. Pyrex^® appears to be a very effective heterogeneous catalyst for this ipso-fluorination. The reaction does not proceed in PTFE, quartz, soda glass or glassy-carbon flasks or Pyrex^® flasks pre-rinsed with 2 M NaOH. Aryltrimethylstannanes and arylboronic acids and their esters do not undergo ipso-fluorination under similar conditions. Plausible mechanisms involving electrophilic addition of polarised xenon difluoride [FXe^δ+?F→Pyrex^δ−] followed by ligand coupling are discussed.     

Copper(II) trans-bis-(glycinato): an efficient heterogeneous catalyst for cross coupling of phenols with aryl halides

Copper(II) trans-bis-(glycinato) complex, easily prepared by the solid state reaction of copper(II) acetate and glycine (trans-[Cu(glyo)₂·H₂O]) was found to be an efficient, recyclable, and high yielding catalyst for the Ullmann type synthesis of diaryl ethers via the cross coupling of phenols with aryl halides without using any additives at relatively low reaction temperature. The catalyst could easily be recovered by simple filtration and was reused for several runs with consistent catalytic activity.     

Sodium Cobalt Metaphosphate as an Efficient Oxygen Evolution Reaction Catalyst in Alkaline Solution

Sodium cobalt metaphosphate [NaCo(PO₃)₃] has CoO octahedra (CoO₆) and shows superior oxygen evolution reaction (OER) activity in alkaline solution, comparable with the state‐of‐the‐art precious‐metal RuO₂ catalyst. OER catalysts of this metaphosphate are prepared by combustion (Cb) and solid‐state (SS) methods. The combustion‐assisted method offers a facile synthesis and one‐step carbon composite formation. Unusually high catalytic activity was observed in NCoM‐Cb‐Ar and could be due to chemical coupling effects between NaCo(PO₃)₃ and partially graphitized carbon. This novel electrocatalyst exhibits very small overpotential of 340 mV with high mass activity of 532 A g^?1. Good charge transfer abilities and chemical coupling between NaCo(PO₃)₃ and amorphous carbon gives the OER activity in NCoM‐Cb‐Ar.     

Asymmetric reduction of aromatic ketones in pyridinium-based ionic liquids

The asymmetric reduction of aromatic ketones has been studied in pyridinium-based room temperature ionic liquids, namely, 1-ethyl-pyridinium tetrafluoroborate, [EtPy]⁺[BF₄]⁻ and 1-ethyl-pyridinium trifluoroacetate, [EtPy]⁺[CF₃COO]⁻. Ionic liquids were employed as solvents, while (R)-BINOL and (R)-BINOL-Br were used as chiral promoters. The effects of solvent, reaction time, temperature, catalyst loading and substituents were investigated. The reduction could be easily carried out in both ionic liquids with lower catalyst loading. 1-Ethyl-pyridinium tetrafluoroborate was recycled and reused efficiently.     

Lewis acid-assisted oxidative cross-coupling of 2-naphthol derivatives with copper catalysts

The oxidative coupling reactions between 2-naphthol and 3-hydroxy-2-naphthoic acid derivatives using a copper catalyst under an O₂ atmosphere in the presence of a catalytic amount of the Lewis acid, such as Yb(OTf)₃, were carried out. A highly cross-coupling selective or specific reaction effectively proceeded to give a C₁ symmetrical BINOL derivative.     

The nature of active sites and stereospecificity of their action in diene polymerization catalysed by chromium-containing systems

A study has been made of the nature of active sites, stereospecificity of their action and the regularities of diene polymerization catalysed by chromium-containing systems. All possible polymer structures with high stereospecificity can be produced for butadiene and isoprene with π-allyl chromium compounds. Tris-π-allyl chromium produces polybutadiene predominantly of 1,2-units. Cis-polybutadiene is formed when the electronegative group (Cl^?, CCl₃COO^?) is substituted for one or two π-allyl groups in Tris-allyl chromium or in the catalytic system (π-C₃H₅)₃CrAl₂O₃. A catalyst obtained through interaction of (π-C₃H₅)₃Cr with silica-alumina or silica gel produces 1,4-trans-polybutadiene and 1,4-trans-polyisoprene. The rate of butadiene polymerization in the presence of Tris-π-allyl chromium is given by k[Cr]², and in polymerization of isoprene with the catalytic system (π-C₃H₅)₃Cr-silica-alumina, by k[Cr].[M]². Polymerization of dienes catalysed by (π-C₃H₅)₃Cr-silica-alumina system or supported chromium oxide catalyst proceeds according to a type of living system. A study was made of copolymerization of butadiene and isoprene in the presence of supported chromium oxide catalyst and with that produced by the reaction of (π-C₃H₅)₃Cr with silica-alumina. The constants of copolymerization for the systems were equal. A conclusion has been drawn regarding the similar mechanisms for diene polymerization under the action of supported chromium oxide catalyst or of catalyst formed in the reaction of (π-C₃H₅)₃Cr with silica-alumina or silica gel.     

Synthesis of allylamides from allyl halides, carbon monoxide, and titanium-nitrogen complexes prepared from molecular nitrogen

4-Phenylbut-3-enamide could be synthesized from corresponding 3-chloroprop-2-enylbenzene, carbon monoxide (1 atm), and titanium-nitrogen complexes, prepared from Ti(OⁱPr)₄, Li, TMSCl, and molecular nitrogen (1 atm), using a palladium catalyst. The reaction proceeds via transmetalation of the titanium-nitrogen complex to an acylpalladium complex. P^tBu₃ as a ligand of the palladium catalyst, afforded a good result, and the amounts of Li and TMSCl affected the yield of amide. When the reaction was carried out using a bidentate ligand on the palladium complex under an atmosphere of argon instead of carbon monoxide, an allylamine derivative was obtained.     

Ionic Pd/NHC Catalytic System Enables Recoverable Homogeneous Catalysis: Mechanistic Study and Application in the Mizoroki–Heck Reaction

N-Heterocyclic carbene (NHC) ligands are ubiquitously utilized in catalysis. A common catalyst design model assumes strong M–NHC binding in this metal–ligand framework. In contrast to this common assumption, we demonstrate here that lability and controlled cleavage of the M−NHC bond (rather than its stabilization) could be more important for high-performance catalysis at low catalyst concentrations. The present study reveals a dynamic stabilization mechanism with labile metal–NHC binding and [PdX₃]⁻[NHC-R]⁺ ion pair formation. Access to reactive anionic palladium intermediates formed by dissociation of the NHC ligands and plausible stabilization of the molecular catalyst in solution by interaction with the [NHC-R]⁺ azolium ion is of particular importance for an efficient and recyclable catalyst. These ionic Pd/NHC complexes allowed for the first time the recycling of the complex in a well-defined form with isolation at each cycle. Computational investigation of the reaction mechanism confirms a facile formation of NHC-free anionic Pd in polar media through either Ph–NHC coupling or reversible H–NHC coupling. The present study formulates novel ideas for M/NHC catalyst design.     

Hollow nanoshell-sphere Fe@Fe/Pd reactors: a magnetically recoverable catalyst for the C<Subscript>sp</Subscript>–S cross-coupling reactions in water

The hollow Pd–PVP–Fe nanosphere and Fe–PVP nanoparticle catalysts were synthesized by thermal method. Mixing of two metallic nanocatalysts was applied in the C_sp–S cross-coupling reactions between diphenyl disulfide and phenylacetylene under mild conditions in water. Results show that bi-catalytic system has higher catalytic efficiencies than their monocatalytic systems due to synergy between two catalysts. Order of adding two metallic catalysts were adjusted into the coupling reaction medium. Therefore, various bi-catalytic systems were obtained and characterized by XRD, SEM, EBSD, EDX, UV–Vis spectra, and particle size analyzer. Under special order of adding, the obtained hollow nanoshell-sphere Fe@Fe/Pd reactor showed higher catalytic activity in the coupling reaction compared to other bi-catalytic systems. The C_sp–S coupling products obtained of various diaryl disulfides and phenylacetylene at presence Fe@Fe/Pd (only 7.3?×?10^?5 mmol Pd) catalyst with moderate to high yields in water solvent and mild reaction conditions. After the reaction, the catalyst/product(s) separation could be easily achieved with an external magnet and more than 95% of catalyst could be recovered. The recovered catalyst was characterized by XRD, SEM, EBSD, EDX, and UV–Vis spectra. The Fe@Fe/Pd was reused at least six repeating cycles without any loss of its high catalytic activity. Tuning morphology and chemical composition of bi-catalytic system are key mainstays of high activity of Fe@Fe/Pd in repeating cycles of cross-coupling reactions.     

Highly efficient copper(0)-catalyzed Suzuki-Miyaura cross-coupling reactions in reusable PEG-400

Readily available copper powder with K₂CO₃ as the base was extremely effective catalyst for Suzuki-Miyaura coupling reaction performed in PEG-400, which afforded almost quantitative coupling products of aryl iodides. Using iodine as additive, coupling products of aryl bromides or chlorides could be obtained with moderate to good yields.     

Carbon nanotubes decorated α-Al2O3 containing cobalt nanoparticles for Fischer-Tropsch reaction

A new hierarchical composite consisted of multi-walled carbon nanotubes (CNTs) layer anchored on macroscopic α-Al₂O₃ host matrix was synthesized and used as support for Fischer-Tropsch synthesis (FTS). The composite constituted by a thin shell of a homogeneous, highly entangled and structure-opened carbon nanotubes network and it exhibited a relatively high and fully accessible specific surface area of 76 m²·g^?1, compared with that of 5 m²·g^?1 of the original α-Al₂O₃ support. The metal-support interaction between carbon nanotubes surface and cobalt precursor and high effective surface area led to a relatively high dispersion of cobalt nanoparticles. This hierarchically supported cobalt catalyst exhibited a high FTS activity along with an extremely high selectivity towards liquid hydrocarbons compared with the cobalt-based catalyst supported on pristine α-Al2O₃ or on CNTs carriers. This improvement can attribute to the high accessibility of composite surface area comparing with the macroscopic host structure alone or to the bulk CNTs where the nanoscopic dimension induced a dense packing with low mass transfer which favoured the problem of reactants competitive diffusion towards the cobalt active site. In addition, intrinsic thermal conductivity of decorated CNTs could help the heat dissipating throughout the catalyst body, thus avoiding the formation of local hot spots which appeared in high CO conversion under pure syngas feed in FTS reaction. Cobalt supported on CNTs decorated α-Al₂O₃ catalyst also exhibited satisfied high stability during more than 200 h on stream under relatively severe conditions compared with other catalysts reported in the literature. Finally, the macroscopic shape of such composite easily rendered its usage as catalyst support in a fixed-bed configuration without facing problems of transport and pressure drop as encountered with the bulk CNTs.