2-Arylnaphthoxazole-derived palladium(II) complexes as phosphine-free catalysts for Heck reactions

Four air- and moisture-stable new palladium(II) complexes 2a–2c and 4 have been synthesized from easily available 2-arylnaphthoxazole derivatives. The detailed structures of 2c and 4 have been determined by single-crystal X-ray analysis. The Pd–N, Pd–C bonds in palladacycle complexes 2a–2c and the Pd–N, Pd–O bonds in complex 4 form the basis for five- and six-membered chelate rings, respectively. These complexes were applied as efficient phosphine-free catalysts for Heck reactions with aryl bromides and ethyl acrylate. Typically, in the presence of two equivalent n-Bu₄NBr, using 0.01% of palladacycle complex 2c as catalyst and two equivalent of K₂CO₃ as base in DMF at 140 °C provided coupled products in moderate to high yields.     

Polymer hydrogel confined palladium nanoparticles as recyclable catalysts for Suzuki and Heck cross-coupling reactions

Reusable palladium nanoparticles highly dispersed in porous and hydrophilic interpenetrating polymer networks(IPN),i.e.,Pd@IPN hybrid gels,are employed for catalysis of Suzuki and Heck coupling reactions.Good yields are obtained with high turnover frequencies when the reactions are run with very low Pdloadings.The use of IPN gives better recyclability than that of crosslinked polyvinyl alcohol alone.The polymer networks allow the reactants to have easy access to the Pd metals.The catalysts combine high activity with the reusability offered by the heterogeneous system,without the need for strong coordination or chelating ligands.     

Palladaphosphacyclobutenes as catalysts in Heck and Suzuki reactions

Heck reactions of aryl halides with various olefins and Suzuki reactions of aryl halides with phenylboronic acid catalyzed by palladaphosphacyclobutene have been investigated. The scope of the Heck reaction has been investigated in N,N‐dimethylacetamide at 140 °C using NaOAc as base. Using 0.1% molar ratio of palladaphosphacyclobuyenes, aryl bromides were converted into 1,2‐substitutedethene products in good to high yields through coupling with both vinylarenes and acrylates. Actived aryl chloride reacted with styrene to afford 1,2‐substitutedethene products in moderate yields. The scope of the Suzuki reaction has been conducted in toluene at 110 °C using Cs₂CO₃ as base. Using 0.1% molar ratio of palladaphosphacyclobutene, aryl bromides reacted with phenylboronic acid to afford diaryl derivatives in excellent yield. Copyright © 2008 John Wiley & Sons, Ltd.     

Polystyrene-supported recyclable palladacycle catalyst for Heck, Suzuki and Sonogashira reactions

A new type of soluble polystyrene-supported palladium complex as an excellent and recyclable palladacycle catalyst was discovered for carboncarbon bond formation in Heck, Suzuki and Sonogashira reactions. Precipitation and filtration process for recycling the catalyst was also achieved.     

Hydrazinoaminocarbene–palladium complexes as easily accessible and convenient catalysts for copper-free Sonogashira reactions

Two easily accessible hydrazinoaminocarbene complexes of Pd(II) are shown to be efficient catalysts for copper-free Sonogashira cross-couplings of a variety of aryl iodides with aryl- and alkylalkynes under mild conditions, in ethanol as the solvent and using potassium carbonate as the base. The reactions were carried out with 0.05 mol % of the catalysts which demonstrated exceptional stability in the solid state and in ethanol. Protection from air is not needed. Disubstituted acetylenes were synthesized by the general procedure on up to a gram scale and the yields were 80–98%.     

New acyclic aminocarbene palladium(ii) complexes as convenient catalysts for the Sonogashira and Suzuki cross-coupling

A reaction of isocyanide complex cis-[PdCl₂(CNAr)₂] with hydrazones H₂N-N=CR¹R² proceeded at the carbon atom of one of the isocyanide groups and gave the corresponding diaminocarbene isocyanide palladium(ii) complexes. These complexes showed high catalytic activity in the Sonogashira and Suzuki cross-coupling reactions.     

Recycling of homogeneous Pd catalysts using superparamagnetic nanoparticles as novel soluble supports for Suzuki, Heck, and Sonogashira cross-coupling reactions

Recycling of homogeneous catalysts could be achieved by using magnetic nanoparticles and solid-phase beads, but nanoparticle-supported catalysis proceeded much faster than its counterpart on resins.     

Phosphine-free Pd-salen complexes as efficient and inexpensive catalysts for Heck and Suzuki reactions under aerobic conditions

Phosphine-free palladium-salen complexes, N,N′-bis(salicylidene)-ethylenediamino-palladium and N,N′-bis(salicylidene)-1,2-phenylenediamino palladium, are found to be highly active catalysts for the Heck olefination of aryl iodides and Suzuki reaction of aryl iodides and bromides giving excellent yields (70-90%) of products under aerobic conditions, in short reaction times (10-60 min).     

Silica-supported polymeric palladium (0) complexes as catalysts for Heck reaction in organic synthesis

Silica-supported palladium (0) complexes have been prepared from γ-chloropropyl triethoxysilica and γ-aminopropyl triethoxysilica via immobilization on fumed silica, followed by reacting with ethylenediamine and salicylaldehyde, and then the reaction with palladium chloride in ethanol and reduction with KBH₄ in ethanol. They are efficient catalysts for Heck reaction of aryl iodides with alkene at 90^oC. These polymeric palladium (0) catalysts can be recovered and reused without loss in activity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis of novel palladium N‐heterocyclic‐carbene complexes as catalysts for Heck and Suzuki cross‐coupling reactions

Novel palladium‐1,3‐dialkylperhydrobenzimidazolin‐2‐ylidene (2a–c) and palladium‐1,3‐dialkylimidazolin‐2‐ylidene complexes (4a,b) have been prepared and characterized by C, H, N analysis, ¹H‐NMR and ¹³C‐NMR. Styrene or phenylboronic acid reacts with aryl halide derivatives in the presence of catalytic amounts of the new palladium‐carbene complexes, PdCl₂(1,3‐dialkylperhydrobenzimidazolin‐2‐ylidene) or PdCl₂(1,3‐dialkylimidazolin‐2‐ylidene) to give the corresponding C? C coupling products in good yields. Copyright © 2006 John Wiley & Sons, Ltd.     

Catalytic activity of palladium(II) diaminocarbene complexes in the Sonogashira and Suzuki reactions

Palladium(II) complexes with chelating and non-chelating diaminocarbene ligands were assessed as catalysts in the cross-coupling reactions of haloarenes with oct-1-yne (Sonogashira reaction) and phenylboronic acid (Suzuki reaction). Both complexes exhibited a higher catalytic activity than traditional phosphine ligandbased systems in the Sonogashira reaction, and they ensured cross-coupling not only with iodoarenes but also with bromoarenes activated by electron-withdrawing substituents. The catalytic activities of the examined complexes in the Suzuki reaction were appreciably different: the palladium(II) complex with the chelating ligand turned out to be considerably less active than the complex with the non-chelating ligand.     

Polymethyl methacrylate micro-spheres supported palladium: A new catalyst for Heck and Suzuki reactions

Polymethyl methacrylate (PMMA) micro-spheres, a kind of commercially available polymeric material was treated with PdCl₂ and formaldehyde giving a reagent with a palladium loading of 0.79 (wt.%). The Pd-PMMA catalyzed the highly efficient Heck and Suzuki reactions. The reactions can be performed under ligand-free conditions in an air atmosphere. The palladium catalyst is easily separated and can be reusable with negligible leaching of palladium.     

Suzuki and Heck coupling reactions mediated by palladium complexes bearing trans-spanning diphosphines

Palladium complexes of three trans-spanning diphosphines are examined for effecting C-C coupling reactions. Ten aryl halides of varying electron density were screened in Suzuki coupling reactions with phenylboronic acid and in Heck reactions with styrene. The results are discussed in terms of the unique flexibility and shape of the meta-terphenyl backbone upon which the diphosphine ligand is built.     

Pentafluorophenyl imidato palladium(II) complexes: catalysts for Suzuki cross-coupling reactions

Novel N-bonded imidato complexes of general formula [Pd(N-N)(C6F5)(imidate)](imidate = maleimidate, succinimidate or phthalimidate; N-N = 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine (Me2bipy) or N,N,N',N'-tetramethylethylenediamine (tmeda)), [NBu4][Pd(C6F5)(H2O)(succinimidate)2] and [NBu4][Pd(C6F5)(L)(succinimidate)2](L = PPh3 or t-BuNC) have been synthesised. These complexes are air-, light- and moisture-stable. The crystal structures of [Pd(tmeda)(C6F5)(maleimidate)].H2O.0.5CHCl3, [NBu4][Pd(C6F5)(H2O)(succinimidate)2].H2O and [NBu4][Pd(C6F5)(t-BuNC)(succinimidate)2].2H2O have been determined by X-ray diffraction. Many of these new complexes are shown to be active phosphine-free palladium catalysts/precatalysts for the Suzuki cross-coupling reactions of aryl bromides and aryl chlorides with phenylboronic acid.     

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.     

Remarkably facile Heck and Suzuki reactions in water using a simple cationic surfactant and ligand-free palladium catalysts

A facile surfactant mediated Heck and Suzuki coupling procedure in water has been developed using ligand-free Pd-catalysts. The procedure which involves nanometric palladium colloids, is operationally simple, environmentally benign and synthetically as efficient as conventional procedures using organic solvents.     

Palladacycles bearing pendant benzamidinate ligands as catalysts for the Suzuki and Heck coupling reactions

Three pendant benzamidines [Ph-C(NC₆H₅)-{NH(CH₂)₂NMe₂}] (1), [Ph-C(NC₆H₅)-{NH(CH₂Py)}] (2) and [Ph-C(NC₆H₅)-{NH(o-C₆H₄)(oxazoline)}] (3) are described. Reactions of 1, 2 or 3 with one molar equivalent of Pd(OAc)₂ in THF give the palladacyclic complexes [Ph-C{-NH(η¹-C₆H₄)}{N(CH₂)₂NMe₂}]Pd(OAc) (4), [Ph-C{-NH(η¹-C₆H₄)}{N (CH₂Py)}]Pd(OAc) (5) and [Ph-C{-NH(η¹-C₆H₄)}{N(o-C₆H₄)(oxazoline)}]Pd(OAc) (6), respectively. Treatment of 4, 5 or 6 with excess of LiCl in chloroform affords [Ph-C{-NH(η¹-C₆H₄)}{N(CH₂)₂NMe₂}]PdCl (7), [Ph-C{-NH(η¹-C₆H₄)}{N(CH₂Py)}]PdCl (8) and [Ph-C{-NH(η¹-C₆H₄)}{N(o-C₆H₄)(oxazoline)}]PdCl (9). The crystal and molecular structures are reported for compounds 1, 3, 5, 6 and 7. The application of these palladacyclic complexes to the Suzuki and Heck coupling reactions was examined.     

Short synthesis of bis-NHC-Pd catalyst derived from caffeine and its applications to Suzuki, Heck, and Sonogashira reactions in aqueous solution

A short and efficient synthesis of a bis-NHC-palladium catalyst simply prepared from caffeine in two steps was reported. The air and moisture stable Pd catalyst can be used as a good catalyst in running Suzuki-Miyaura, Mizoroki-Heck, and Sonogashira reactions in aqueous solution.     

Synthesis of methylated resveratrol and analogues by Heck reactions in organic and aqueous solvents

The Heck reaction under phosphane free conditions using oxime-derived palladacycles or Pd(OAc)₂ as catalysts is a general methodology for the synthesis of methoxylated (E)-stilbene derivatives. Couplings can be performed either with (dicyclohexyl)methylamine as base and TBAB in aqueous DMA or in neat water and with Et₃N as base in DMA in air and under thermal and microwave conditions. The arylation of different styrenes are performed with 3,5-dimethoxyiodobenzene to afford a series of important biologically active (E)-stilbene derivatives containing the 3,5-dimethoxyphenyl moiety, including resveratrol, piceatannol and pinosilvine, which are efficiently prepared with high regioselectivity and total stereoselectivity (TON up to 10⁴).