100-10-7 Use of "homeopathic" ligand-free palladium as catalyst for aryl-aryl coupling reactions

We have previously shown that the use of ligand-free palladium employing Pd(OAc)2 as catalyst precursor in the Heck reaction of aryl bromides is possible if low catalyst loadings, typically between 0.01-0.1 mol % are used. We have now tested this phenomenon, which we have dubbed " homeopathic" palladium, in biaryl formation using the Suzuki, the Negishi and the Kumada cross-coupling reactions. The Suzuki reaction of aryl bromides, both activated and deactivated, is possible using 0.02-0.05 mol % of Pd(OAc)2. In this reaction turnover frequencies up to 30,000 have been reached with activated substrates. Even aryl chlorides could be reacted if strongly electron-withdrawing substituents were present. The Negishi coupling with a variety of arylzinc halides was possible on aryl bromides containing electron-withdrawing substituents. The Kumada reaction only gave low yields of products under "homeopathic' conditions. https://www.lookchem.com/CASDataBase_100-10-7.htm

评论

发表评论

此博客中的热门博文

100-48-1 In situ immobilized palladium nanoparticles on surface of poly-methyldopa coated-magnetic nanoparticles (Fe3O4@PMDA/Pd): A magnetically recyclable nanocatalyst for cyanation of aryl halides with K4[Fe(CN)6]

Poly-methyldopa (PMDP)-coated Fe 3 O 4 nanoparticles (Fe 3 O 4 @PMDP) have been synthesized through a simple and green procedure. In the present study, for the first time, Pd nanoparticles were successfully deposited using Fe 3 O 4 @PMDP as a core-shell magnetic coordinator and stabilizer agent. In this protocol, Pd ions were adsorbed on surfaces of Fe 3 O 4 @PMDP through immersion of the PMDP-coated Fe 3 O 4 nanoparticles into a palladium plating bath. Next, they were reduced in situ to palladium nanoparticles using PMDP's N-containing groups and reducing ability. The structure, morphology and physicochemical properties of the synthesized nanoparticles were characterized by different analytical techniques such as energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscope (FESEM), Fourier-transform infrared spectroscopy (FT-IR) spectroscopy, high resolution transmission electron microscopy (HR-TEM), inductively coupled plasma (ICP), thermo gravimetric...
阅读全文

767-58-8 The Photochemistry of Conformationally Rigid Benzylic Esters: 2,2-Dimethyl-1-indanyl Acetates and Pivalates

The photochemistry, in methanol, of substituted 2,2-dimethyl-1-indanyl acetates 9a-c and pivalates 10a-c has been studied.In agreement with previous studies on benzylic esters, the results show that the substituents change the yield of products derived from the ion pair.The mechanistic conclusion reached is that the substituents change the oxidation potential of the indanyl radicals and thus the rate constant of electron transfer for converting the radical pair to the ion pair.The results also reveal two other substituent effects.First, substituents can increase the overall efficiency of the photoreaction by enhancing homolytic cleavage.The second effect is conformational.In compounds where the bond that is cleaving is conformationally mobile, such as the C-O bond in benzylic esters, substituents on the ring can change the population of the reactive conformer and thus the overall efficiency of the reaction.For the indanyl acetate esters, the difference in excited-state reaction rate be...
阅读全文

75-09-2 Catalytic dechlorination of carbon tetrachloride in liquid phase with methanol as H-donor over AG/C catalyst

Catalytic hydrodechlorination of carbon tetrachloride (CCl 4 ) is an effective measure to remove CCl 4 due to its pollutant character. The dechlorination of CCl 4 to dichloromethane (CH 2 Cl 2 ) and chloroform (CHCl 3 ) with a molar ratio of 3:2 was catalyzed by carbon-supported silver (Ag/C) catalyst in methanol solution. It was proposed from the catalytic results and characterization (X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy) data that, the chloride ion is abstracted from adsorbed CCl 4 by Ag to form CCl 3 and CCl 2 radicals and silver chloride (AgCl), and meanwhile the dehydrogenation of methanol over Ag domains intrigues initial active Ag-H species and formaldehyde (HCHO): then the CCl 3 and CCl 2 radicals are combined with Ag-H to generate reaction products (CHCl 3 , and CH 2 Cl 2 ) and Ag, and the dehydrogenated product HCHO facilitates the regeneration of formed AgCl to Ag with formation of carbon monoxide and hydrogen chloride. Th...
阅读全文