- The site-selectivity and mechanism of Pd-catalyzed C(sp2)-H arylation of simple arenes
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Control over site-selectivity is a critical challenge for practical application of catalytic C-H functionalization reactions in organic synthesis. Despite the seminal breakthrough of the Pd-catalyzed C(sp2)-H arylation of simple arenes via a concerted metalation-deprotonation (CMD) pathway in 2006, understanding the site-selectivity of the reaction still remains elusive. Here, we have comprehensively investigated the scope, site-selectivity, and mechanism of the Pd-catalyzed direct C-H arylation reaction of simple arenes. Counterintuitively, electron-rich arenes preferably undergo meta-arylation without the need for a specifically designed directing group, whereas electron-deficient arenes bearing fluoro or cyano groups exhibit high ortho-selectivity and electron-deficient arenes bearing bulky electron-withdrawing groups favor the meta-product. Comprehensive mechanistic investigations through a combination of kinetic measurements and stoichiometric experiments using arylpalladium complexes have revealed that the Pd-based catalytic system works via a cooperative bimetallic mechanism, not the originally proposed monometallic CMD mechanism, regardless of the presence of a strongly coordinating L-type ligand. Notably, the transmetalation step, which is influenced by a potassium cation, is suggested as the selectivity-determining step.
- Kim, Daeun,Choi, Geunho,Kim, Weonjeong,Kim, Dongwook,Kang, Youn K.,Hong, Soon Hyeok
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p. 363 - 373
(2021/01/14)
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- Palladium Palladium Nanoparticles Nanoparticles Supported Supported on β-cyclodextrin on β-Cyclodextrin Functionalised Functionalized Poly(amido Poly(amidoamine)s amine)s and their and Application Their Application in Suzuki-Miyaura in Suzuki-Miyaura Cross-Coupling Cross-Coupling Reactions Reactions
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Herein, the synthesis, characterization and catalytic application of an organic-inorganic, palladium (Pd)-containing hybrid material, poly(amidoamine)-cyclodextrin (Pd@PAAs-CD), is reported as an efficient catalyst for Suzuki-Miyaura coupling reactions. The structure of Pd@PAAs-CD was confirmed by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), inductively-coupled plasma atomic emission spectroscopy (ICP-AES), and 1H nuclear magnetic resonance (NMR) spectroscopy. Furthermore, an efficient protocol has been developed using Pd@PAAs-CD as the catalyst in a Suzuki-Miyaura cross-coupling reaction in an aqueous medium in high yields. By using cyclodextrin (CD) as the mediator grafted onto PAAs, the Pd nanoparticles (NPs) were dispersed and enhanced the catalytic reaction by promoting host-guest interactions with the CD. In addition, the reusability of the Pd@PAAs-CD hybrid material is demonstrated for use in multiple sequential cross-coupling reactions.
- Zhang, Wei,Yao, Zi-Jian,Deng, Wei
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p. 1667 - 1677
(2019/10/01)
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- Atom-efficient Pd-catalyzed cross-couplings of chloroarenes with triarylbismuth reagents
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Various Pd-catalyzed protocols have been developed for the atom-efficient cross-coupling of chloroarenes with triarylbismuth reagents. Using the developed protocols, an efficient synthesis of unsymmetrical biaryls in good to excellent yields was achieved by employing electron-deficient chloroarenes and a range of triarylbismuth reagents.
- Rao, Maddali L.N.,Meka, Suresh
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supporting information
(2019/07/30)
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- Pillar[5]arene-based N-heterocyclic carbene ligand for Pd-catalysed Suzuki reaction
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A pillar[5]arene-based N-heterocyclic carbene ligand was prepared by reaction of bromoethoxy pillar[5]arene with excess 1-methylimidazole at 130?°C in the absence of solvent and used as a catalyst for the Suzuki coupling reaction. Excellent yields were obtained when the Suzuki reactions were carried out under ambient atmosphere in ethanol, employing 0.2?mol% ligand, 1?mol% PdCl2(CH3CN)2 and 1.5?mmol of K2CO3. The novel pillar[5]arene-based imidazolium salt is a promising material for the construction of highly active supramolecular catalytic systems.
- Xiao, Xue-Dong,Liu, Jia-Qi,Bai, Ya-Li,Wang, Rui-Hua,Wang, Jun-Wen
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- CuPd nanoparticles as a catalyst in carbon-carbon cross-coupling reactions by a facile oleylamine synthesis
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CuPd bi-metallic nanoparticles were synthesized in oleylamine without the use of additional surfactants, ligands, or reducing agents. The alloyed nanoparticles showed high catalytic activity in Suzuki cross-coupling reactions with excellent turnover number (6000) and turnover frequency of 72:000 h-1 under microwave irradiation. These nanoparticles were successfully utilized in a Suzuki coupling reaction with a diverse range of functionalized substrates. The catalyst also demonstrated multiple recyclability for Suzuki coupling reactions. The CuPd nanoparticles have also probed the utility in other cross-coupling reactions such as Heck and Sonogashira coupling reactions. According to the XPS data, two oxidation states of each metal exist on the surface of the nanoparticle. This is advantageous especially for Sonogashira cross-coupling reactions because having Cu+ present on the surface of the catalyst eliminates the need for a copper salt to stabilize the alkyne during the reaction.
- Smith, Sarah E.,Siamaki, Ali R.,Gupton, B. Frank,Carpenter, Everett E.
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p. 91541 - 91545
(2016/10/11)
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- Palladium nanoparticles supported on carbon nanotubes from solventless preparations: Versatile catalysts for ligand-free Suzuki cross coupling reactions
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Palladium nanoparticles supported on single- or multi-walled carbon nanotubes (Pd/SWCNT and Pd/MWCNT) were prepared by a rapid, solventless method that does not require reducing agents or electric current. The method involves a straightforward process using dry mixing of a precursor Pd salt (e.g., palladium acetate) with carbon nanotubes at ambient temperature by ball-milling (mechanochemical route) or with subsequent annealing at 300°C (thermal route) in an inert atmosphere. The Pd/MWCNT sample with Pd nanoparticle size of 1-3 nm and uniform dispersion prepared by mechanochemical ball-milling at room temperature [designated as (Pd/MWCNT)M] displayed remarkable catalytic activity towards Suzuki cross coupling reactions with a high turn over number (TON) of 7250 and turn over frequency (TOF) of 217-500 h-1. These nanoparticles were characterized by a variety of techniques including transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Additionally, the (Pd/MWCNT)M sample was successfully employed in Suzuki cross coupling reactions with a wide variety of functionalized substrates.
- Siamaki, Ali R.,Lin, Yi,Woodberry, Kendra,Connell, John W.,Gupton, B. Frank
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p. 12909 - 12918
(2013/10/22)
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- An enthalpic basis of additivity in biphenyl hydroxamic acid ligands for stromelysin-1
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Fragment based drug discovery remains a successful tool for pharmaceutical lead discovery. Although based upon the principle of thermodynamic additivity, the underlying thermodynamic basis is poorly understood. A thermodynamic additivity analysis was performed using stromelysin-1 and a series of biphenyl hydroxamate ligands identified through fragment additivity. Our studies suggest that, in this instance, additivity arises from enthalpic effects, while interaction entropies are unfavorable; this thermodynamic behavior is masked by proton transfer. Evaluation of the changes in constant pressure heat capacities during binding suggest that solvent exclusion from the binding site does not account for the dramatic affinity enhancements observed.
- Wilfong, Erin M.,Du, Yu,Toone, Eric J.
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supporting information
p. 6521 - 6524
(2012/11/07)
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- SYNTHESIS OF 4-ALKOXY-4'-CYANOBIPHENYLS
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A preparative method was developed for the synthesis of liquid crystals of the 4-alkoxy-4'-cyanobiphenyl group.It involves the nitration of 4-cyanobiphenyl to 4-nitro-4'-cyanobiphenyl, reduction of the latter, diazotization of the obtained 4-amino-4'-cyanobiphenyl, and alkylation of the 4-hydroxy-4'-cyanobiphenyl formed during decomposition of the diazonium salt.
- Ruolene, Yu. I.,Adomenas, P. V.,Adomenene, O. K.,Denis, G. I.
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p. 1192 - 1195
(2007/10/02)
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