- Palladium-Catalyzed Three-Component Coupling of Ynamides
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A palladium-catalyzed regioselective three-component coupling of ynamides was developed. The reaction proceeded smoothly to furnish the desired products when carried out at 70 °C in acetonitrile/water with potassium carbonate in the presence of 2.5 mol percent Pd2(dba)3·CHCl3 without a ligand. Various iodides and boronic acids were used in this reaction, and a carbon-carbon bond was formed with satisfactory regioselectivity from the ynamides.
- Wakamatsu, Hideaki,Takahashi, Ayano,Ishii, Ayaka,Kikuchi, Youhei,Sasaki, Madoka,Saito, Yukako,Natori, Yoshihiro,Yoshimura, Yuichi
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supporting information
p. 5299 - 5303
(2020/07/08)
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- Mechanistic Studies of the Palladium-Catalyzed Desulfinative Cross-Coupling of Aryl Bromides and (Hetero)Aryl Sulfinate Salts
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Pyridine and related heterocyclic sulfinates have recently emerged as effective nucleophilic coupling partners in palladium-catalyzed cross-coupling reactions with (hetero)aryl halides. These sulfinate reagents are straightforward to prepare, stable to storage and coupling reaction conditions, and deliver efficient reactions, thus offering many advantages, compared to the corresponding boron-derived reagents. Despite the success of these reactions, there are only scant details of the reaction mechanism. In this study, we use structural and kinetic analysis to investigate the mechanism of these important coupling reactions in detail. We compare a pyridine-2-sulfinate with a carbocyclic sulfinate and establish different catalyst resting states, and turnover limiting steps, for the two classes of reagent. For the carbocyclic sulfinate, the aryl bromide oxidative addition complex is the resting state intermediate, and transmetalation is turnover-limiting. In contrast, for the pyridine sulfinate, a chelated Pd(II) sulfinate complex formed post-transmetalation is the resting-state intermediate, and loss of SO2 from this complex is turnover-limiting. We also investigated the role of the basic additive potassium carbonate, the use of which is crucial for efficient reactions, and deduced a dual function in which carbonate is responsible for the removal of free sulfur dioxide from the reaction medium, and the potassium cation plays a role in accelerating transmetalation. In addition, we show that sulfinate homocoupling is responsible for converting Pd(OAc)2 to a catalytically active Pd(0) complex. Together, these studies shed light on the challenges that must be overcome to deliver improved, lower temperature versions of these synthetically important processes.
- Davis, Christopher J.,De Gombert, Antoine,McKay, Alasdair I.,Wheelhouse, Katherine M.,Willis, Michael C.
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supporting information
(2020/02/25)
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- Oxidative Addition, Transmetalation, and Reductive Elimination at a 2,2′-Bipyridyl-Ligated Gold Center
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Three-coordinate bipyridyl complexes of gold, [(κ2-bipy)Au(η2-C2H4)][NTf2], are readily accessed by direct reaction of 2,2′-bipyridine (bipy), or its derivatives, with the homoleptic gold ethylene complex [Au(C2H4)3][NTf2]. The cheap and readily available bipyridyl ligands facilitate oxidative addition of aryl iodides to the Au(I) center to give [(κ2-bipy)Au(Ar)I][NTf2], which undergo first aryl-zinc transmetalation and second C-C reductive elimination to produce biaryl products. The products of each distinct step have been characterized. Computational techniques are used to probe the mechanism of the oxidative addition step, offering insight into both the origin of the reversibility of this process and the observation that electron-rich aryl iodides add faster than electron-poor substrates. Thus, for the first time, all steps that are characteristic of a conventional intermolecular Pd(0)-catalyzed biaryl synthesis are demonstrated from a common monometallic Au complex and in the absence of directing groups.
- Harper, Matthew J.,Arthur, Christopher J.,Crosby, John,Emmett, Edward J.,Falconer, Rosalyn L.,Fensham-Smith, Andrew J.,Gates, Paul J.,Leman, Thomas,McGrady, John E.,Bower, John F.,Russell, Christopher A.
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p. 4440 - 4445
(2018/04/05)
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- Manganese-Catalyzed Aerobic Heterocoupling of Aryl Grignard Reagents
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An improved protocol has been developed for the MnCl2-catalyzed cross-coupling reaction of two arylmagnesium bromides under dioxygen. The reaction was achieved by using the Grignard reagents in a 2:1 ratio and 20 % of MnCl2. Very good yields of the heterocoupling product were obtained when the limiting Grignard reagent underwent little homocoupling under the reaction conditions. Arylmagnesium bromides that contain p-methoxy, p-(dimethylamino), p-fluoro, and p-chloro substituents were shown to afford high product yields in the cross-coupling reactions with a variety of substituted aryl Grignard reagents. Heterocyclic Grignard reagents, on the other hand, were less effective substrates for this transformation because of the rapid homocoupling of these reagents under the reaction conditions.
- Ghaleshahi, Hajar Golshahi,Antonacci, Giuseppe,Madsen, Robert
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p. 1331 - 1336
(2017/03/23)
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- Mechanism insight and scope of PEPPSI-catalyzed cross-coupling reaction between triarylbismuth and arylbromide
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In this paper we report the first cross-coupling reaction of Ar3Bi with Ar'X mediated by Pd-NHC complexes by keeping the ability of Ar3Bi to transfer the three aryl moieties. Investigations were carried out in order to minimize the quantity of the side product Ar-Ar coming from the conversion of Ar3Bi. The results showed that PEPPSI IPr was a good catalyst precursor. Efforts were focussed on the rule of each additive such as PPh3 and the base. It was notably found that the presence of PPh3 (ratio PEPPSI IPr/PPh3: 1/1) was essential to keep the process efficient. Therefore NHC-Pd-PPh3 has been assumed as being the catalytic species. Under the optimized reaction conditions the concomitant formation of the undesired biaryl side product was restricted to its inherent formation consecutive to the reduction of the catalyst precursor to Pd(0). In a last study, the scope and the limitation of the new catalytic methodology were examined and a large range of unsymmetrical biaryl compounds Ar-Ar’ bearing various substituents from strongly electron-donating to electron-withdrawing ones have been prepared and fully characterized.
- Cassirame, Bénédicte,Condon, Sylvie,Pichon, Christophe
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- Ligand-Assisted Gold-Catalyzed Cross-Coupling with Aryldiazonium Salts: Redox Gold Catalysis without an External Oxidant
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Gold-catalyzed C(sp)-C(sp2) and C(sp2)-C(sp2) cross-coupling reactions are accomplished with aryldiazonium salts as the coupling partner. With the assistance of bpy ligand, gold(I) species were oxidized to gold(III) by diazonium without any external oxidants. Monitoring the reaction with NMR and ESI-MS provided strong evidence for the nitrogen extrusion followed by AuIII reductive elimination as the key step.
- Cai, Rong,Lu, Mei,Aguilera, Ellen Y.,Xi, Yumeng,Akhmedov, Novruz G.,Petersen, Jeffrey L.,Chen, Hao,Shi, Xiaodong
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p. 8772 - 8776
(2015/11/27)
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- Palladium nanoparticles supported on SiO2 by chemical vapor deposition (CVD) technique as efficient catalyst for Suzuki-Miyaura coupling of aryl bromides and iodides: Selective coupling of halophenols
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Nanoparticles of palladium were supported on SiO2 by chemical vapor deposition technique. The obtained Pd nanocatalyst was characterized by various techniques. This catalyst was found to be very efficient for the selective cross-coupling of hydroxyl-substituted aryl iodides and bromide with arylboronic acids in water at room temperature to produce the corresponding hydroxyl-substituted biaryls. Coupling of phenylboronic acid with aryl iodides and bromides carrying substituents other than hydroxy group was also performed efficiently in refluxing ethanol. Copyright 2012 John Wiley & Sons, Ltd. Palladium nanoparticles supported on SiO2 as an efficient heterogeneous catalyst was prepared by CVD technique and applied in Suzuki coupling reaction mild conditions. The Suzuki reaction of halophenols was conducted at room temperature in the presence of this catalyst. Copyright
- Iranpoor, Nasser,Firouzabadi, Habib,Safavi, Afsaneh,Motevalli, Somayeh,Doroodmand, Mohammad M.
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experimental part
p. 417 - 424
(2012/09/22)
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- Assessment of the intermediacy of arylpalladium carboxylate complexes in the direct arylation of benzene: Evidence for C-H bond cleavage by "ligandless" species
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Palladium-catalyzed direct arylations of benzene have been proposed to occur by the generation of a phosphine-ligated arylpalladium pivalate complex LPd(Ar)(OPiv) and reaction of this complex with benzene. We have isolated an example of the proposed intermediate and evaluated whether this complex does react with benzene to form the biaryl products of direct arylation. In contrast to the proposed mechanism, no biaryl product was formed from cleavage of the benzene C-H bond by LPd(Ar)(OPiv). However, reactions of LPd(Ar)(OPiv) with benzene and additives that displace or consume the phosphine ligand formed the arylated products in good yield, suggesting that a "ligandless" arylpalladium(II) carboxylate complex undergoes the C-H cleavage step. Consistent with this conclusion, we found that reactions catalyzed by Pd(OAc)2 without a ligand occur faster than, and with comparable selectivities to, reactions catalyzed by Pd(OAc)2 and a phosphine ligand.
- Tan, Yichen,Hartwig, John F.
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supporting information; experimental part
p. 3308 - 3311
(2011/05/04)
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- Abnormal N-heterocyclic carbene promoted Suzuki-Miyaura coupling reaction: A comparative study
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A C2-protected imidazolium salt that generates an abnormal N-heterocyclic carbene (NHC) was applied for the palladium-catalyzed Suzuki-Miyaura coupling reactions. The abnormal NHC precursor promoted the reactions while suppressing homocoupling of aryl boronic acid, which was observed with the corresponding normal NHC precursor. The related well-defined abnormal NHC-based palladium complexes also showed better activity than the normal NHC-based analogues, exhibiting faster reaction rates especially at the initial stage of the reaction.
- Xu, Xiangya,Xu, Baochang,Li, Yongxin,Hong, Soon Hyeok
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scheme or table
p. 6343 - 6349
(2011/02/17)
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- Structure-reactivity relationships in negishi cross-coupling reactions
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Competition experiments have been performed to determine the relative reactivities of substituted bromobenzenes and of different arylzinc reagents in the [Pd(PPh3)4]-catalyzed Negishi cross-coupling reaction in THF at 25 °C. The crosscoupling reactions are accelerated by electron acceptors in the bromobenzenes, the effect of which increases in the order ortho a larger effect than substituent variations in the arylzinc halides (ρ = -0.98).
- Dong, Zhi-Bing,Manolikakes, Georg,Shi, Lei,Knochel, Paul,Mayr, Herbert
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supporting information; experimental part
p. 248 - 253
(2010/03/30)
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- PALLADIUM-CATALYZED CARBON-CARBON COUPLING REACTIONS WITH TETRAARYLBORATES
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A simple synthetic method is described, based on the use of a palladium(0) catalyst, to obtain carbon-carbon coupling reactions of aromatic bromides with sodium tetraaryl borates.
- Catellani, Marta,Chiusoli, Gian Paolo,Fornasari, Vilma
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p. 779 - 781
(2007/10/02)
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