A New Catalyst System for the Heck Reaction of Unreactive Aryl Halides

A simple solution to the age-old problem of the Heck reaction of cheap but unreactive chloro- and bromoarenes [for example, reaction (1)] has been found in the catalyst [Pd(CH₃CN)₂Cl₂]⋅6 Ph₄PCl in the presence of N,N-dimethylglycine as additive. The reaction then proceeds with exceptionally high efficiency.     

Organo‐Palladium(II)‐Verbindungen mit PdC4‐Koordination: Phenylethinyl‐ und Methylphenylethinylkomplexe

Tetrakis(p‐tolyl)oxalamidinato‐bis[acetylacetonatopalladium(II)] ([Pd₂(acac)₂(oxam)]) reacted with Li–C≡C–C₆H₅ in THF with formation of [Pd(C≡C–C₆H₅)₄Li₂(thf)₄] ( 1a ). Reaction of [Pd₂(acac)₂(oxam)] with a mixture of 6 equiv. Li–C≡C–C₆H₅ and 2 equiv. LiCH₃ resulted in the formation of [Pd(CH₃)(C≡C–C₆H₅)₃Li₂(thf)₄] ( 2 ), and the dimeric complex [Pd₂(CH₃)₄(C≡C–C₆H₅)₄Li₄(thf)₆] ( 3 ) was isolated upon reaction of [Pd₂(acac)₂(oxam)] with a mixture of 4 equiv. Li–C≡C–C₆H₅ and 4 equiv. LiCH₃. 1 – 3 are extremely reactive compounds, which were isolated as white needles in good yields (60–90%). They were fully characterized by IR, ¹H‐, ¹³C‐, ⁷Li‐NMR spectroscopy, and by X‐ray crystallography of single crystals. In these compounds Li ions are bonded to the two carbon atoms of the alkinyl ligand. 1a reacted with Pd(PPh₃)₄ in the presence of oxygen to form the already known complexes trans‐[Pd(C≡C–C₆H₅)₂(PPh₃)₂] and [Pd(η²‐O₂)(PPh₃)₂]. In addition, 1a is an active catalyst for the Heck coupling reaction, but less active in the catalytic Sonogashira reaction.     

Mizoroki–Heck and Suzuki–Miyaura reactions mediated by poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid)‐stabilized magnetically separable palladium catalyst

The purpose of this work was to synthesize and characterize a new magnetic polymer nanosphere‐supported palladium(II) acetate catalyst for reactions requiring harsh conditions. In this regard, an air‐stable, moisture‐stable and highly efficient heterogenized palladium was synthesized by the coordination of palladium(II) acetate with poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid)‐grafted modified magnetic nanoparticles with a core–shell structure. The structure of the newly developed catalyst was characterized using various techniques. The catalytic activity of the resultant nano‐organometallic catalyst was evaluated in Mizoroki–Heck and Suzuki–Miyaura reactions to afford the corresponding coupling products in good to excellent yields. High selectivity as well as outstanding turnover number (14 143, 4900) and turnover frequency (28 296, 7424) values were recorded for the catalyst in Suzuki–Miyaura and Mizoroki–Heck reactions, respectively. Magnetic separation and recycling of the catalyst for at least six runs became possible without any significant loss of efficiency or any detectable palladium leaching.     

纤维素二乙烯三胺负载钯配合物的制备及对Heck反应的催化性能

通过较简单的方法合成了纤维素二乙烯三胺负载钯(0)配合物,并利用XPS、TG、DTA等手段对其进行了表征。该配合物在室温至230℃范围内有很好的稳定性,在空气氛围、DMSO中能有效地催化丙烯酸、苯乙烯与芳基碘的Heck反应,立体选择性地生成取代的反式肉桂酸、1,2-二苯乙烯,在70℃时反应6h,产率≥66%(丙烯酸、苯乙烯与带取代基芳基碘的Heck反应产率接近100%)。催化剂中起催化作用的是金属态的钯。     

Chugaev‐type bis(acyclic diaminocarbenes) as a new ligand class for the palladium‐catalyzed Mizoroki–Heck reaction

A series of differently substituted Chugaev‐type palladium bis(acyclic diaminocarbene) complexes was screened to identify the most active catalyst for Mizoroki–Heck coupling reactions of aryl bromides with styrene. The best catalyst, which contains three methyl groups on the bis(carbene) ligand, gives excellent coupling yields at 120 °C for both activated and deactivated aryl bromides. However, activity with aryl chlorides is limited to electron‐deficient examples. The optimized catalyst demonstrates limited air and moisture stability, giving reduced yields in couplings of activated aryl bromides in open‐flask conditions. The modular synthesis of this class of catalysts should allow further fine‐tuning of activity in Mizoroki–Heck and related coupling reactions. Copyright © 2012 John Wiley & Sons, Ltd.     

Palladium–S‐propyl‐2‐aminobenzothioate immobilized on Fe3O4 magnetic nanoparticles as catalyst for Suzuki and Heck reactions in water or poly(ethylene glycol)

A moisture‐ and air‐stable heterogenized palladium catalyst was synthesized by coordination of palladium with S‐propyl‐2‐aminothiobenzamide supported on Fe₃O₄ magnetic nanoparticles. The prepared nanocatalyst was characterized using Fourier transform infrared, energy‐dispersive X‐ray and inductively coupled plasma atomic emission spectroscopies, X‐ray diffraction, vibrating sample magnetometry, transmission and scanning electron microscopies, dynamic laser scattering and thermogravimetric analysis. This catalyst could be dispersed homogeneously in water or poly(ethylene glycol) and further applied as an excellent nano‐organometal catalyst for Suzuki and Heck reactions. The catalyst was easily separated with the assistance of an external magnet from the reaction mixture and reused for several consecutive runs without significant loss of its catalytic efficiency or palladium leaching. The leaching of catalyst was examined using hot filtration and inductively coupled plasma atomic emission spectroscopy. Also, the effects of various reaction parameters on the Suzuki and Heck reactions are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Palladium(II) complexes bearing N‐alkylpiperidoimidazolin‐2‐ylidene derivatives: Effect of alkyl chain length of ligands on catalytic activity

A series of piperidoimidazolinium salts which differ in the chain lengths (butyl, octyl, dodecyl, octadecyl) and their Pd–N‐heterocyclic carbene complexes with pyridine were synthesized and characterized using elemental analysis and spectroscopic methods. The effects of these ligands on catalyst activation and the performance of the complexes were studied in Suzuki–Miyaura reactions of arylboronic acid with aryl chlorides. The complex with the ligand having the longest chain length was found to be most active. The results demonstrated that the length of the alkyl chain of the piperidoimidazolin‐2‐ylidene controlled the dispersion and composition of the nanoparticles and it affected the catalytic activity. The impact of alkyl chain length of piperidoimidazolin‐2‐ylidene on the Suzuki–Miyaura reactions of arylboronic acid with aryl halides was systematically investigated.     

偕胺肟纤维-钯(II)配合物的制备及对Heck反应的催化性能研究

以聚丙烯腈纤维为基体,通过较简单的方法获得了偕胺肟纤维- 钯(II)配合物,采用FTIR、XPS等技术对其结构和性能进行了表征。本研究考察了该配合物在不同反应条件下对碘苯与苯乙烯的Heck反应的催化性能,结果显示：该配合物在较温和的条件下即可很好的催化Heck反应,经重复使用5次后,1,2-二苯乙烯的产率仍达90%以上,并且反应结束后催化剂易于从反应体系中分离。对于其他不同底物之间的Heck反应,偕胺肟纤维- 钯(II)配合物同样显示较好的催化性能。     

Catalytic activity of Pd(II) and Pd(II)/DAB-R systems for the Heck arylation of olefins

Palladium-catalyzed reactions of aryl bromides with various olefins involving Pd(II)/diazabutadiene (DAB-R) systems have been investigated. The scope of a coupling process using Pd(II) sources and an α-diimine as ligand in the presence of Cs₂CO₃ as base was tested using various substrates. The Pd(OAc)₂/DAB-Cy (1, DAB-Cy=1,4-dicyclohexyl-diazabutadiene) system presents the highest activity with respect to electron-neutral and electron-deficient aryl bromides in coupling with electron rich olefins. The synthesis and X-ray characterization of a Pd(II)-diazabutadiene ligand is reported. Extensive optimization experiments showed that another Pd(II) source, Pd(acac)₂ (acac=acetylacetonate), proved to activate aryl bromides at high temperatures, low catalyst loadings when the appropriate concentration of ⁿBu₄NBr additive was employed. The effect of the DAB-Cy ligand is important at very low catalyst loadings and high temperatures. Pd(acac)₂ and Pd(acac)₂/DAB-Cy precatalysts were very effective for the arylation of various olefins with aryl bromides with respect to reaction rate, catalyst loadings, and functional group tolerance.     

Pd(II) complexes of Schiff bases and their application as catalysts in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions

Schiff bases of 2‐(phenylthio)aniline, (C₆H₅)SC₆H₄N?CR (R = (o‐CH₃)(C₆H₅), (o‐OCH₃)(C₆H₅) or (o‐CF₃)(C₆H₅)), and their palladium complexes (PdLCl₂) were synthesized. The compounds were characterized using ¹H NMR and ¹³C NMR spectroscopy and micro analysis. Also, electrochemical properties of the ligands and Pd(II) complexes were investigated in dimethylformamide–LiClO₄ solution with cyclic and square wave voltammetry techniques. The Pd(II) complexes showed both reversible and quasi‐reversible processes in the ?1.5 to 0.3 V potential range. The synthesized Pd(II) complexes were evaluated as catalysts in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions. Copyright © 2015 John Wiley & Sons, Ltd.     

The Synthesis of (η3‐C3H5)Pd{Si[N(tBu)CH]2}Cl and the Catalytic Property for Heck Reaction

Treatment of N‐heterocyclic silylene Si[N(^tBu)CH]₂ ( 1 ) and [(η³‐C₃H₅)PdCl]₂ in toluene led to the formation of the mononuclear complex (η³‐C₃H₅)Pd{Si[N(^tBu)CH]₂}Cl ( 3 ), the silicon analogue to N‐heterocyclic carbene complex (η³‐C₃H₅)Pd{C[N(^tBu)CH]₂}Cl ( 2 ). Complex 3 was characterized with ¹H NMR and ¹³C NMR. Investigation shows that (η³‐C₃H₅)Pd{Si[N(^tBu)CH]₂}Cl is an active catalyst for Heck coupling reaction of styrene with aryl bromides.     

Pd(II) salen complex covalently anchored to multi‐walled carbon nanotubes as a heterogeneous and reusable precatalyst for Mizoroki–Heck and Hiyama cross‐coupling reactions

A Pd(II) salen complex anchored to multi‐walled carbon nanotubes showed excellent catalytic activity and stability for the Mizoroki–Heck and Hiyama cross‐couplings of aryl halides with olefins and phenylsiloxanes. Furthermore, the heterogeneous catalyst could be reused up to four times with the catalytic activity being recovered easily after simple manipulations. Copyright © 2014 John Wiley & Sons, Ltd.     

Cobalt supported on dendronized magnetic nanoparticles: A new highly efficient and recyclable catalyst for the Mizoroki–Heck cross‐coupling reaction

Polyamidoamine (PAMAM) is one of the most interesting types of hyperbranched polymers that carry a large number of amino groups on its surface. PAMAM has gained significant attention from synthetic organic chemists due to its structural characteristics, controllable structure, inner porosity, and ability to trap a wide range of ions and molecules. So, in this work, the PAMAM dendrimer was synthesized, grafted onto the surface of magnetite nanoparticles, and the resulting hybrid nanoparticles were then employed as suitable host for immobilizing cobalt nanoparticles. The newly developed catalyst was well characterized by Fourier transform‐infrared, X‐ray diffraction, thermogravimetric analysis, field emission‐scanning electron microscopy, transmission electron microscopy, atomic absorption spectroscopy, element mapping and energy‐dispersive X‐ray analysis. The efficiency of the as‐prepared nanocatalyst was evaluated for the Mizoroki–Heck cross‐coupling reactions. The MNP@PAMAM‐Co represented perfect catalytic efficiency and high selectivity for the Mizoroki–Heck cross‐coupling reaction compared with previously reported catalysts. The catalyst separation from the reaction mixture was easily achieved with the assistance of an external magnetic field, and its recycling was also investigated for five consecutive runs. Hot filtration confirmed no leaching of the active metal during the Heck coupling.     

Synthesis and characterizations of N,N′‐bis(diphenylphosphino)‐2‐(aminomethyl)aniline derivatives: application of a palladium(II) complex as pre‐catalyst in Heck and Suzuki cross‐coupling reactions

The reaction of 2‐(aminomethyl)aniline with 2 equivalents of PPh₂Cl in the presence of Et₃N, proceeds in CH₂Cl₂ to give N,N′‐bis(diphenylphosphino)‐2‐(aminomethyl)aniline 1 in good yield. Oxidation of 1 with aqueous H₂O₂, elemental sulfur or gray selenium gave the corresponding oxide, sulfide and selenide dichalcogenides [Ph₂P(E)NHC₆H₄CH₂NHP(E)Ph₂] (E: O, 2a; S, 2b; Se, 2c), respectively. The reaction of [Ph₂PNHC₆H₄CH₂NHPPh₂] with PdCl₂(cod), PtCl₂(cod) and [Cu(MeCN)₄]PF₆ gave the corresponding chelate complexes, PdCl₂1, PtCl₂1 and [Cu(1)₂]PF₆. The new compounds were fully characterized by NMR, IR spectroscopy and elemental analysis. The catalytic activity of the Pd(II) complex was tested in the Suzuki coupling and Heck reactions. The Pd(II) complex catalyzes the Suzuki coupling and Heck reaction, affording biphenyls and stilbenes respectively, in good yields. Copyright © 2009 John Wiley & Sons, Ltd.     

An improved preparation of mesoporous silica‐supported Pd as sustainable catalysts for phosphine‐free Suzuki–Miyaura and Heck coupling reactions

An improved and eco‐friendly procedure has been developed to generate mesoporous silica‐supported palladium nanoparticles (SiO₂@PdNP) that could be used as a sustainable heterogeneous Pd catalyst for phosphine‐free Suzuki–Miyaura and Heck coupling reactions with excellent turnover number and turnover frequency. The presence of Pd on the silica surface was detected by X‐ray diffraction and the structural morphology of SiO₂@PdNP was obtained by transmission electron microscopy. The heterogeneous catalytic system is recyclable and leaching of the metal after the reaction is not apparently observed. Copyright © 2013 John Wiley & Sons, Ltd.     

Kryptofix 5 as an inexpensive and efficient ligand for the palladium‐catalyzed Mizoroki‐Heck reaction

A novel complex of PdCl₂ with a multidentate cryptand ligand, Kryptofix 5, has been prepared and characterized by various techniques including ¹H‐ and ¹³C NMR spectroscopy, Fourier transform infrared (FT‐IR), Raman, ultraviolet and visible (UV‐VIS) spectroscopy, inductively coupled plasma (ICP), CHN elemental and energy dispersive X‐ray analysis (EDX). This heat‐ and air‐stable complex was utilized as a highly active catalyst for the Mizoroki‐Heck reaction of aryl halides with various olefins. Interestingly, it was found that aryl bromides as well as aryl iodides were efficiently cross‐coupled with terminal alkenes at 130 °C in 10 min. Furthermore, the least reactive aryl chlorides reacted with styrene to obtain the desired products in acceptable yields.     

Synthesis,Structure, and Application of Self‐Assembled Copper(II) Aqua Complex by H‐Bonding for Acceleration of the Nitroaldol Reaction on Water

Simple addition : Copper(II) aqua complex 1 can be prepared in a one‐pot synthesis and is self‐assembled by H‐bond interactions. Complex 1 is shown to accelerate the nitroaldol reaction on water, which is a heterogeneous process, requiring no additive or base, and 1 can be recycled without loss of activity.