Imidazolium-based phosphinite ionic liquid (IL-OPPh2) as Pd ligand and solvent for selective dehalogenation or homocoupling of aryl halides

The use of an imidazolium-based phosphinite ionic liquid (IL-OPPh₂) as ligand for Pd offers an efficient reagent system for the selective dehalogenation or homocoupling of aryl halides in the presence of NaOPrⁱ or Et₃N, respectively. This ionic liquid plays a dual role as both the reaction media and also as the potential complexing agent with Pd via its phosphinite carrying group. The ionic liquid containing its corresponding Pd complex can be easily recovered and reused in several runs.     

Exploration of amino‐functionalized ionic liquids as ligand and base for Heck reaction

A kind of amino‐functionalized ionic liquid has been prepared and investigated as ligand and base for the Heck reactions between aryl iodides and bromides with olefins in the presence of a catalytic amount of Pd submicron powder in [Bmim]PF₆. The reactions generated the corresponding products in excellent yields under mild reaction conditions. The generality of this catalytic system to the different substrates also gave satisfactory results. The key feature of the reaction is that Pd species and ionic liquids were easily recovered and reused six times with constant activity. Copyright © 2010 John Wiley & Sons, Ltd.     

Cross-linked polymer supported palladium catalyzed carbonylative Sonogashira coupling reaction in water

A cross-linked polymer-supported ionic liquid immobilized palladium catalyst, which is prepared by reaction of the Pd(OAc)₂ with copolymer of 3-butyl-1-vinylimidazolium iodide and divinylbenzene, was well characterized and employed as an effective heterogeneous catalyst for carbonylative Sonogashira coupling reaction of aryl iodides with terminal alkynes in water, affording the corresponding α,β-alkynyl ketones in good to excellent yields. The catalytic system not only solves the basic problem of homogeneous palladium catalyst recovery and reuse but also avoids the use of toxic phosphine ligands. The stability of supported palladium was also discussed.     

Hydrogenation of aryl ketones using palladium nanoparticles on single-walled carbon nanotubes in an ionic liquid

Single-walled carbon nanotubes (SWNTs) are used as supporting materials for palladium (Pd) nanoparticles generated in situ in ionic liquid (IL); Pd nanocatalysts on SWNTs exhibit superior reactivity for hydrogenation of aryl ketones in IL under mild conditions (1 atm of H₂ (g) and room temperature) and can be reused above 10 times without any loss of catalytic activity.     

Palladium nanoparticles‐decorated triethanolammonium chloride ionic liquid‐modified TiO2 nanoparticles (TiO2/IL‐Pd): A highly active and recoverable catalyst for Suzuki–Miyaura cross‐coupling reaction in aqueous medium

In this work, an easily obtained procedure was successfully implemented to prepare novel palladium nanoparticles decorated on triethanolammonium chloride ionic liquid‐functionalized TiO₂ nanoparticles [TiO₂/IL‐Pd]. Different methods were carried out for characterizations of the synthesized nanocatalyst (HR‐TEM, XPS, XRD, FE‐SEM, EDX, FT‐IR and ICP). TiO₂/IL‐Pd indicated good catalytic activity for the Suzuki–Miyaura cross‐coupling reaction of arylboronic acid with different aryl halides in aqueous media at ambient temperature. The recycled catalyst was investigated with ICP to amount of Pd leaching after 6 times that had diminished slightly, Thus, was confirmed that the nanocatalyst has a good sustainability for C–C Suzuki–Miyaura coupling reaction. The catalyst can be conveniently separated by filtration of the reaction mixture and reused for 6 times without significant loss of its activity. It supplies an environmentally benign alternative path to the existing protocols for the Suzuki–Miyaura reaction.     

Mild and efficient Pd(PtBu3)2‐catalyzed aminocarbonylation of aryl halides to aryl amides with high selectivity

This work describes a mild and efficient approach for the synthesis of aryl amides via catalytic aminocarbonylation of aryl halides with alicyclic amines using a Pd(P^t Bu₃)₂/NH₄Cl catalyst system. Under mild reaction temperature of 60°C and balloon pressure of CO, 5 mol% Pd(P^t Bu₃)₂ with a cheap NH₄Cl promoter is sufficient for high yields of aryl amides. The influence of reaction parameters such as reaction temperature, ligand type and promoter on catalytic activity was investigated. This work also discusses the catalytic intermediates in detail, and provides a plausible mechanism based on an acid chloride intermediate.     

Facile construction of symmetric biaryls using (BeDABCO)2Pd2Cl6 as an efficient and highly active catalyst under microwave irradiation

An efficient catalytic system using (BeDABCO)₂Pd₂Cl₆ (BeDABCO, benzyl‐1,4‐diazabicyclo[2.2.2]octane) was developed for the homo‐coupling reaction of various aryl halides. Due to the combination of ionic homogeneous metal catalyst and microwave irradiation, symmetric biaryls were produced in excellent yields and short reaction times in N‐methyl‐2‐pyrrolidone at 120 °C. BeDABCO as an efficient ligand and also a quaternary ammonium salt had an efficient stabilizing effect on the Pd(0) species in this coupling reaction. Copyright © 2015 John Wiley & Sons, Ltd.     

trans-Pd(OAc)2(Cy2NH)2 catalyzed Suzuki coupling reactions and its temperature-dependent activities toward aryl bromides

A new catalytic system based on Pd-simple amines for Suzuki coupling reactions of aryl bromides is described. A well-defined air-stable complex, trans-Pd(OAc)₂(Cy₂NH)₂ effectively promotes Suzuki couplings of aryl bromides with a range of aryl boronic acids to give diaryl products in high yields. It also exhibits temperature-dependent activity toward aryl bromides bearing different electronic substituents under reaction conditions.     

Ordered Mesoporous Organosilica with Ionic‐Liquid Framework: An Efficient and Reusable Support for the Palladium‐Catalyzed Suzuki–Miyaura Coupling Reaction in Water

The preparation of a novel palladium‐supported periodic mesoporous organosilica based on alkylimidazolium ionic liquid (Pd@PMO‐IL) in which imidazoilium ionic liquid is uniformly distributed in the silica mesoporous framework is described. Both Pd@PMO‐IL and the parent PMO‐IL were characterized by N₂‐adsorption–desorption, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), TEM, and solid‐state NMR spectroscopy. We have demonstrated that Pd@PMO‐IL is an efficient and reusable catalyst for the Suzuki–Miyaura coupling reaction of various types of iodo‐, bromo‐, and even deactivated aryl chlorides in water. It was also found that although the PMO‐IL nanostructure acts as reservoir for soluble Pd species, it can also operate as a nanoscaffold to recapture the Pd nanoparticles into the mesochannels thus preventing extensive agglomeration of Pd. This observation might be attributed to the isolated ionic liquid units that effectively control the reaction mechanism by preventing Pd agglomeration and releasing and recapturing Pd nanoparticles during the reaction process. The catalyst can be recovered and reused for at least four reaction cycles without significant loss of activity.     

Efficient and ligand free palladium catalyst for Suzuki and Heck cross-coupling reactions

A simple and efficient system for Suzuki cross-coupling reactions was developed using a ligandless catalyst of Pd nanoclusters generated in situ from Pd(acac)₂. The cross-coupling reactions proceeded under mild reaction conditions with a high reaction rate (5 min) to give various biaryls in high yields. The system also exhibited catalytic potential for Heck reaction between aryl bromides and styrene.     

Synthesis of Enaminone‐Pd(II) Complexes and Their Application in Catalysing Aqueous Suzuki‐Miyaura Cross Coupling Reaction

A series of Pd(II)‐enaminone complexes, termed Pd(eao)₂, have been synthesized and characterized. The investigation on the catalytic activities of these new Pd(II)‐reagents has proved that the Pd(eao)₂‐ 1 possesses excellent catalytic activity for the Suzuki‐ Miyaura cross coupling reactions of aryl bromides/chlorides with aryl/vinyl boronic acids in the environmentally benign media of aqueous PEG400 at low loading (5 mol‰). The superiority of this Pd(II)‐reagent to those commercial Pd(II) and Pd(0) catalysts in catalyzing the reactions has been confirmed by parallel experiments. What's more, Pd(eao)₂‐ 2 has been found as a practical catalyst for the homo‐coupling reactions of aryl boronic acids.     

Pd‐Catalyzed Carbonylative α‐Arylation of Aryl Bromides: Scope and Mechanistic Studies

Reaction conditions for the three‐component synthesis of aryl 1,3‐diketones are reported applying the palladium‐catalyzed carbonylative α‐arylation of ketones with aryl bromides. The optimal conditions were found by using a catalytic system derived from [Pd(dba)₂] (dba=dibenzylideneacetone) as the palladium source and 1,3‐bis(diphenylphosphino)propane (DPPP) as the bidentate ligand. These transformations were run in the two‐chamber reactor, COware, applying only 1.5 equivalents of carbon monoxide generated from the CO‐releasing compound, 9‐methylfluorene‐9‐carbonyl chloride (COgen). The methodology proved adaptable to a wide variety of aryl and heteroaryl bromides leading to a diverse range of aryl 1,3‐diketones. A mechanistic investigation of this transformation relying on ³¹P and ¹³C NMR spectroscopy was undertaken to determine the possible catalytic pathway. Our results revealed that the combination of [Pd(dba)₂] and DPPP was only reactive towards 4‐bromoanisole in the presence of the sodium enolate of propiophenone suggesting that a [Pd(dppp)(enolate)] anion was initially generated before the oxidative‐addition step. Subsequent CO insertion into an [Pd(Ar)(dppp)(enolate)] species provided the 1,3‐diketone. These results indicate that a catalytic cycle, different from the classical carbonylation mechanism proposed by Heck, is operating. To investigate the effect of the dba ligand, the Pd⁰ precursor, [Pd(η³‐1‐PhC₃H₄)(η⁵‐C₅H₅)], was examined. In the presence of DPPP, and in contrast to [Pd(dba)₂], its oxidative addition with 4‐bromoanisole occurred smoothly providing the [PdBr(Ar)(dppp)] complex. After treatment with CO, the acyl complex [Pd(CO)Br(Ar)(dppp)] was generated, however, its treatment with the sodium enolate led exclusively to the acylated enol in high yield. Nevertheless, the carbonylative α‐arylation of 4‐bromoanisole with either catalytic or stoichiometric [Pd(η³‐1‐PhC₃H₄)(η⁵‐C₅H₅)] over a short reaction time, led to the 1,3‐diketone product. Because none of the acylated enol was detected, this implied that a similar mechanistic pathway is operating as that observed for the same transformation with [Pd(dba)₂] as the Pd source.     

A PdCl2–ionic liquid brush assembly: an efficient and reusable catalyst for Mizoroki–Heck reaction in neat water

An efficient and reusable heterogeneous catalytic assembly of PdCl₂ held in ionic liquid brushes has been synthesized and an environmentally‐friendly procedure was developed for coupling aryl iodides with acrylic acid. These reactions were conducted in water under aerobic conditions with water‐insoluble or even solid aryl iodides and they proceeded smoothly and cleanly without any organic co‐solvent or other additives. A 0.5 mol% (based on Pd atom) dose of the catalyst was found to be sufficient for Mizoroki–Heck reaction. The catalyst is easily recovered post reaction, via simple filtration, and reused at least eight times without a noticeable loss of activity. The protocol has the advantages of excellent yield, environmental friendliness, and catalyst recyclability. Copyright © 2011 John Wiley & Sons, Ltd.     

负载离子液体纳米钯催化芳卤羰化反应

研究了高分散性的负载离子液体纳米钯催化剂的制备及其催化芳卤羰化反应的性能. 用XRD、HRTEM和XPS等方法对催化剂进行了表征, 结果表明, 钯组分处于高分散零价态, 其平均粒径小于5 nm, 且催化剂表面存在一厚度适中的离子液体液膜, 有利于提高催化剂的稳定性; 该催化剂对PhI、PhBr、PhCl的羰化反应的催化活性优于离子液体两相催化体系, 在优化的反应条件下, 碘苯的转化率可达99.3％, 生成苯甲酸乙酯的转化频率(TOF)可高达4926 h−1, 反应产物中苯甲酸乙酯的选择性大于99％.     

Bis(tetrazolyl)benzenes as ligands in the Suzuki reaction: Promoters or inhibitors?

The Suzuki cross-coupling with phenylboronic acid in the presence of the Pd(OAc)₂/K₃PO₄/DMF catalytic system was successful for aryl bromides and somewhat poorer for aryl chlorides. Addition of 1,3-bis(tetrazol-1-yl)benzene or its analogs lowered the yields of biaryls. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 114–118, January, 2006.     

Engineered mesoporous ionic‐modified γ‐Fe2O3@hydroxyapatite decorated with palladium nanoparticles and its catalytic properties in water

A new mesoporous organic–inorganic nanocomposite was formulated and then used as stabilizer and support for the preparation of palladium nanoparticles (Pd NPs). The properties and structure of Pd NPs immobilized on prepared 1,4‐diazabicyclo[2.2.2]octane (DABCO) chemically tagged on mesoporous γ‐Fe₂O₃@hydroxyapatite (ionic modified (IM)‐MHA) were investigated using various techniques. The synergistic effects of the combined properties of MHA, DABCO and Pd NPs, and catalytic activity of γ‐Fe₂O₃@hydroxyapatite‐DABCO‐Pd (IM‐MHA‐Pd) were investigated for the Heck cross‐coupling reaction in aqueous media. The appropriate surface area and pore size of mesoporous IM‐MHA nanocomposite can provide a favourable hard template for immobilization of Pd NPs. The loading level of Pd in the nanocatalyst was 0.51 mmol g^?1. DABCO bonded to the MHA surface acts as a Pd NP stabilizer and can also lead to colloidal stability of the nanocomposite in aqueous solution. The results reveal that IM‐MHA‐Pd is highly efficient for coupling reactions of a wide range of aryl halides with olefins under green conditions. The superparamagnetic nature of the nanocomposite means that the catalyst to be easily separated from solution through magnetic decantation, and the catalytic activity of the recycled IM‐MHA‐Pd showed almost no appreciable loss even after six consecutive runs.     

A General Palladium‐Catalyzed Hiyama Cross‐Coupling Reaction of Aryl and Heteroaryl Chlorides

A general palladium‐catalyzed Hiyama cross‐coupling reaction of aryl and heteroaryl chlorides with aryl and heteroaryl trialkoxysilanes by a Pd(OAc)₂/ L2 catalytic system is presented. A newly developed water addition protocol can dramatically improve the product yields. The conjugation of the Pd/ L2 system and the water addition protocol can efficiently catalyze a broad range of electron‐rich, ‐neutral, ‐deficient, and sterically hindered aryl chlorides and heteroaryl chlorides with excellent yields within three hours and the catalyst loading can be down to 0.05 mol % Pd for the first time. Hiyama coupling of heteroaryl chlorides with heteroaryl silanes is also reported for the first time. The reaction can be easily scaled up 200 times (100 mmol) without any degasification and purification of reactants; this facilitates the practical application in routine synthesis.     

Silicon containing new salicylaldimine Pd(II) and Co(II) metal complexes as efficient catalysts in transformation of carbon dioxide (CO2) to cyclic carbonates

A new series of metal complexes of salicyladimine ligands with Pd(II) and Co(II) have been prepared and characterized by different techniques (elemental analysis, UV-vis, FT-IR, ¹H NMR spectra, magnetic susceptibility measurements). Electronic spectra and magnetic susceptibility measurements reveal square planar geometry for Pd(II) metal complex and tetrahedral geometry for Co(II) metal complex. The synthesized Pd(II) and Co(II) complexes were also tested as catalysts for the formation of cyclic organic carbonates from carbon dioxide and liquid epoxides which served as both reactant and solvent. The results showed that the [M(L₃)₂] (M = Pd or Co) complexes bearing 5-methyl substituent on the aryl ring are more efficient than the other Pd(II) and Co(II) metal complexes for the formation of cyclic organic carbonates from carbon dioxide. These catalysts, [Pd(L₃)₂] and [Co(L₃)₂] complexes and location (p-position of phenoxy) of electron donating methyl substituent in particular, effectively promote the of carbon dioxide activation with liquid epoxides under solvent-free homogeneous conditions. Furthermore, [Pd(L₃)₂] can be reused more than eight times with a minimal loss of its original catalytic activities.     

PEG-modified N-heterocyclic carbene ligands for highly efficient and recyclable Pd-catalyzed Heck reaction in water

A water-soluble and air-stable Pd(OAc)₂/mPEG _n MeImI system was found to be a highly efficient and reusable catalyst for the coupling of aryl halides and styrene in neat water using K₂CO₃ as base. After extraction, the catalytic system could be reused several times with only a slight decrease in its activity.     

Highly Active Heterogeneous PdCl2/MOF Catalyst for Suzuki–Miyaura Cross-Coupling Reactions of Aryl Chloride

The exploration of highly efficient Pd/MOF heterogeneous catalyst system for the Suzuki–Miyaura cross-coupling (SMC) reactions of aryl chlorides is still challenging. Herein, a PdCl₂/UiO-67-bpydc was successfully synthesized by immobilizing a low amount of PdCl₂ onto the zirconium-based MOF (UiO-67-bpydc). PdCl₂/UiO-67-bpydc showed excellent catalytic performance and good recycle ability for the SMC reaction of aryl chlorides under an ambient condition. Furthermore, PdCl₂/UiO-67-bpydc retains the high catalytic activity even after five cycles, and exhibited excellent substrate size selectivity.