- Importance of Two-Electron Processes in Fe-Catalyzed Aryl-(hetero)aryl Cross-Couplings: Evidence of Fe0/FeIICouple Implication
-
We demonstrate in this work that two drastically distinct mechanisms can be involved in aryl-(hetero)aryl Fe-mediated cross-couplings between Grignard reagents and organic halides, depending on the nature of the latter. (Hetero)aryl electrophiles, which easily undergo one-electron reduction, can be involved in a FeII/FeIII coupling sequence featuring an in situ generated organoiron(II) species, akin to their aliphatic analogues. On the other hand, less easily reduced substrates can be activated by transient Fe0 species formed by the reduction of the precatalyst. In this case, the coupling mechanism relies on two-electron elementary steps involving the Fe0/FeII redox couple and proceeds by an oxidative addition/reductive elimination sequence. Hammett analysis shows that both those elementary steps are faster for electrophiles substituted by electron-withdrawing groups. The two mechanisms discussed herein can be involved concomitantly for electrophiles displaying an average oxidative power. Attesting to the feasibility of the aforementioned bielectronic mechanism, high-spin organoiron(II) intermediates formed by two-electron oxidative addition onto (hetero)aryl halides in catalytically relevant conditions were also characterized for the first time. Those results are sustained by paramagnetic 1H NMR, kinetics monitoring, and density functional theory (DFT) calculations.
- Wowk, Vincent,Rousseau, Lidie,Lefèvre, Guillaume
-
supporting information
p. 3253 - 3266
(2021/10/12)
-
- The influence of the nature of phosphine ligand on palladium catalysts for cross-coupling of weakly nucleophilic potassium pentafluorophenyltrifluoroborate with ArHal and PhCH2Hal (Hal=Br, Cl)
-
The influence of the ligand nature on catalytic activity of palladium catalysts for cross-coupling of weakly nucleophilic potassium pentafluorophenyltrifluoroborate, which imitates the behavior of electron-deficient organoboron reagents, with aryl halides, ArHal (Hal=Br, Cl) was studied. The activity of the catalysts generated in situ from Pd(OAc) 2 and appropriate phosphorous containing ligands and the reaction selectivity was found to depend on the nature of bulky phosphines used as ligands. As a result, conditions for involving the electron-deficient organoboron reagent - potassium pentafluorophenyltrifluoroborate - in the palladium-catalyzed cross-coupling with aryl bromides and aryl chlorides were identified. It was demonstrated that the chosen conditions are appropriate for the reaction of K[C6F5BF3] with benzyl chloride and benzyl bromide deriving pentafluorophenylarylmethanes, C6F 5CH2Ar.
- Shabalin, Anton Yu.,Adonin, Nicolay Y.,Bardin, Vadim V.,Parmon, Valentin N.
-
p. 3720 - 3725
(2014/05/20)
-
- Palladium-catalyzed direct arylation of polyfluoroarene and facile synthesis of liquid crystal compounds
-
A convenient approach has been developed to prepare polyfluorobiphenyl by Pd(OAc)2/PCy3-catalyzed direct arylation of polyfluoroarenes with aromatic halides in the presence of Cs2CO 3 as base and toluene as solvent. In most cases, the desired arylated products of aromatic bromides were obtained in good to excellent yield at 80°C, and aryl chlorides also gave modest to good yields of arylated products at 110°C. According to this efficient C - C bondforming method, polyfluorobiphenyl liquid crystal compounds were prepared by Pd-catalyzed direct arylation reactions of polyfluoroarenes with long alkyl chain substituted aryl bromides in 62-96% yield. Copyright
- Ma, Xiaowei,Liu, Yan,Liu, Ping,Xie, Jianwei,Dai, Bin,Liu, Zhiyong
-
p. 180 - 185
(2014/03/21)
-
- Factors controlling the reactivity of heteroarenes in direct arylation with arylpalladium acetate complexes
-
The palladium-catalyzed direct arylation of heteroarenes with aryl halides has emerged as a viable alternative to conventional cross-coupling reactions. This paper reports a detailed mechanistic study on factors controlling the reactivity of heteroarenes in direct arylation with well-defined models of the presumed intermediate [PdAr(O2CMe-κ2O)L] (1). Although recent theoretical studies have provided a reasonable description of the mechanism of C-H bond cleavage by 1, its model compounds so far tested have been evidently less reactive than that expected. We found that [PdPh(O 2CMe-κ2O)(PPh3)] (1a) and [Pd(2,6-Me 2C6H3)(O2CMe-κ2O) (PPh3)] (1c), generated in situ from isolated [PdPh(μ-O 2CMe)(PPh3)]2 (4a) and [Pd(2,6-Me 2C6H3)(μ-O2CMe)(PPh 3)]4 (4c), respectively, react with a variety of heteroarenes in almost quantitative yields. The reactivity order of heteroarenes was evaluated by competitive reactions, showing that benzothiazole (8) is significantly less reactive than 2-methylthiophene (6), despite the acidity of 8 (pKa = 27) being much higher than that of 6 (pKa = 42). This reason was examined by kinetic experiments using 1c as well as DFT calculations using the model compound [PdPh(O2CMe- κ2O)(PH3)] (1d). Both heteroarenes reacted with 1 via a sequence of three elementary processes (i.e., substrate coordination, C-H bond cleavage, and C-C reductive elimination), but their energy profiles were significantly different from each other. The reaction of 6 obeyed simple second-order kinetics, and the deuterium-labeling experiments and DFT calculations indicated the occurrence of rate-determining reductive elimination. On the other hand, the reaction of 8 displayed saturation kinetics due to the occurrence of relatively stable coordination of 8 prior to C-H bond cleavage. This coordination stability enhances the activation barrier for C-H bond cleavage, thereby causing the modest reactivity of 8. Thus, although the previous mechanistic studies on direct arylation have been focused largely on the C-H bond cleavage process, not only the C-H bond cleavage but also the substrate coordination and C-C reductive elimination must be considered.
- Wakioka, Masayuki,Nakamura, Yuki,Hihara, Yoshihiro,Ozawa, Fumiyuki,Sakaki, Shigeyoshi
-
p. 4423 - 4430
(2013/09/02)
-
- Air-stable and catalytically active phosphinous acid transition-metal complexes
-
Secondary phosphane oxides R2P(O)H are most frequently used as preligands for phosphinous acid R2POH (R = alkyl, aryl) transition-metal complexes, which are very efficient catalysts for cross-coupling reactions. To investigate the influence of electron-deficient substituents on the catalytic activity, the coordination properties of bis(trifluoromethyl)-, bis(pentafluoroethyl)-, and bis[2,4-bis(trifluoromethyl) phenyl]phosphinous acid toward catalytically relevant metals, such as palladium and platinum, are studied. The novel phosphinous acid palladium complexes reveal a high catalytic activity in Heck and Suzuki cross-coupling reactions. Because of the strong dependence of these processes on the reaction conditions, a systematic solvent and base screening with 1-bromo-3-fluorobenzene and phenyl boronic acid as model reactants is performed. The most efficient solvent/base system consists of 2-propanol and potassium phosphate, providing a full conversion and a TON of around 10 000 after 20 h at room temperature with a catalyst loading of 0.01 mol % palladium. A catalyst loading of only 0.004 mol % palladium still leads to a nearly full conversion after 20 h at room temperature. During the catalytic reaction, the formation of the corresponding phosphinic acid R2P(O)OH is observed. Further investigations lead to the conclusion that palladium nanoparticles represent the catalytically active species. We also succeeded in the generation of palladium nanoparticles, which exhibit an extremely high catalytic activity in Suzuki cross-coupling reaction with TONs over 60 000 and TOFs larger than 40 000.
- Kurscheid, Boris,Belkoura, Lhoussaine,Hoge, Berthold
-
experimental part
p. 1329 - 1334
(2012/04/10)
-
- Carbon-carbon bond activation by 1,1-carboboration of internal alkynes
-
Internal alkynes undergo 1,1-carboboration reactions upon treatment with boranes RB(C6F5)2 (R = C6F 5, CH3) to yield trisubstituted alkenylboranes. These products can be used as substrates
- Chen, Chao,Kehr, Gerald,Froehlich, Roland,Erker, Gerhard
-
supporting information; experimental part
p. 13594 - 13595
(2010/11/18)
-
- Pentafluorophenylation of aromatic compounds with 4,5,6,7,8-pentafluoro-6- nitro-1-oxaspiro[2.5]octa-4,7-diene
-
4,5,6,7,8-Pentafluoro-6-nitro-1-oxaspiro[2.5]octa-4,7-diene reacts with arenes in the presence of AlCl3 to give pentafluorobiphenyls.
- Kovtonyuk,Kobrina,Haufe
-
experimental part
p. 1686 - 1688
(2011/04/23)
-
- Suzuki- and Heck-type cross-coupling with palladium nanoparticles immobilized on spherical polyelectrolyte brushes
-
We report on a systematic study of the use of palladium nanoparticlesimmo bilized on spherical polyelectrolyte brushes - Pd@SPB - for Heck- and Suzuki-type coupling reactions. The spherical polyelectrolyte brush particles serving as carriers for the palladium nanoparticles consist of a solid polystyrene core with a radiusof 46 nm onto which long chains of cationic polyelectrolytesare grafted. The palladium nanoparticles have directly been generated within this brush layer and the stabilization of the nanoparticlesis effected by the colloidal carriers, no further surface stabilization is necessary. We demonstrate that these composite particles present robust catalysts for the Heck- and Suzuki-type coupling reactions. This was shown by carrying out the Suzuki- and Heck-type coupling reactionsat relatively low temperatures (Suzuki reaction: 50°C, Heck reaction: 70°C). We demonstrate that the catalytic composite particles are not changed by these reaction conditions and retain their full activity for at least four runs. The yields obtained for both reactions are good to excellent. The mild operation conditions of the palladium nanoparticles are traced back to the absence of surface stabilization. Further mechanistic implications are discussed.
- Proch,Mei,Rivera Villanueva,Lu,Karpov,Ballauff,Kempe
-
experimental part
p. 493 - 500
(2009/04/06)
-
- The effect of N-heterocyclic carbene ligands in the palladium-catalyzed cross-coupling reaction of K[C6F5BF3] with aryl iodides and aryl bromides
-
The effect of N-heterocyclic carbene (NHC) ligands on the catalytic activity of in situ generated palladium complexes in the model cross-coupling reaction of K[C6F5BF3] with 4-FC6H4I was studied. Based on the obtained results, a series of pentafluorobiphenyls C6F5C6H4X were prepared from K[C6F5BF3] and XC6H4I or 4-CF3C6H4Br in high yields under aerobic conditions.
- Adonin, Nicolay Yu.,Babushkin, Dmitrii E.,Parmon, Valentin N.,Bardin, Vadim V.,Kostin, Gennadiy A.,Mashukov, Vasiliy I.,Frohn, Hermann-Josef
-
p. 5920 - 5924
(2008/09/21)
-
- Combinatorial Design of Copper-Based Mixed Nanoclusters: New Catalysts for Suzuki Cross-Coupling
-
Quantum dots (2-5 nm) of copper and copper/palladium mixtures are found to be good catalysts for Suzuki cross-coupling. The catalysts are applicable to a wide range of iodo- and bromoaryl substrates, and give moderate yields using chloroaryl substrates. Cluster activity and stability is found to depend strongly on the preparation method and the reaction conditions. The mechanism of cluster deactivation and the sensitivity of the cluster-catalysed reaction to substituent effects are studied and discussed.
- Thathagar, Mehul B.,Beckers, Jurriaan,Rothenberg, Gadi
-
p. 979 - 985
(2007/10/03)
-
- Copper-catalyzed Suzuki cross-coupling using mixed nanocluster catalysts
-
A small library of copper and noble metal nanoclusters is designed and synthesized. These clusters are tested as catalysts in the Suzuki cross-coupling of various aryl halides with phenylboronic acid. It is found that copper and copper/noble metal combination nanoclusters are active catalysts for this reaction, the most active being the combined copper/palladium clusters. Iodo-, bromo-, and chloroarenes can be used. In the case of p-nitrobromobenzene, a one-pot cross-coupling and selective hydrogenation is achieved. Copyright
- Thathagar, Mehul B.,Beckers, Jurriaan,Rothenberg, Gadi
-
p. 11858 - 11859
(2007/10/03)
-
- The Pd-catalyzed coupling of allyl halides and tin aryls: Why the catalytic reaction works and the stoichiometric reaction does not
-
Arylallylpalladium complexes [Pd(5-C6F5-η3-cyclohexenyl) (C6Cl2F3) -(NCMe)] (10) and [Pd2(μ-C6Cl2F3)2 (5-C6F5-1,3-η3-cyclohexenyl) 2] (13) have been synthesized. Complex 13 is an example of a rare class of metal complexes with aryl bridges and its X-ray crystal diffraction structure has been determined. These arylallylpalladium complexes are involved in the coupling of Bu3SnRf (1, Rf=dichlorotrifluorophenyl) and [Pd2(μ-Br)2(5-C6F5-1,3- η3-cyclohexenyl)2] (2); complex 10 has been detected in the course of the stoichiometric coupling reaction in acetonitrile. Decomposition experiments of 10 and 13 in different conditions, and comparison with the reactions of 1 and 2, allow us to determine that reductive elimination does not occur in the absence of additives, p-Benzoquinone coordinates to Pd to give complex 15 and promotes reductive elimination to give the coupling products selectively. The outcome of the coupling reaction is controlled by the reductive elimination step, but the overall rate is controlled by the faster preequilibrium, which determines the concentration of 10 or 13. Palladium-catalyzed coupling of allyl halides and tin aryls works better than the stoichiometric allyl-aryl reductive coupling on isolated allylarylpalladium complexes, because they benefit from the presence in the solution of substrate allylic halides acting as electron-withdrawing olefins and promoting reductive elimination. More efficient allyl-aryl couplings, whether stoichiometric or catalytic, can be achieved upon addition of p-benzoquinone to the reaction mixture in a noncoordinating solvent.
- Albeniz, Ana C.,Espinet, Pablo,Martin-Ruiz, Blanca
-
p. 2481 - 2489
(2007/10/03)
-
- Fluorinated biphenyls from aromatic arylations with pentafluorobenzenediazonium and related cations. Competition between arylation and azo coupling
-
High yields of the mixed perfluorinated biaryls (C6F5-Ar) are obtained by the catalytic dediazonlatlon of the pentafluorobenzenediazonium salt (C6F5N2+BF4-) in acetonitrile solutions containing various aromatic substrates (ArH) together with small amounts of iodide salts. Activated (electron-rich) as well as deactivated (electron-poor) arenes are successfully pentafluorophenylated by this method. The arylation is distinct from the azo coupling of the same substrates, which takes place in the absence of the iodide catalyst and yields the corresponding diazene (C6F5N=N-Ar) as product. The catalytic role of iodide, and the isomeric product distributions obtained with this procedure indicate that the arylation proceeds via the pentafluorophenyl radical in a efficient homolytic chain process. Since azo coupling involves electrophilic aromatic substitution of electron-rich ArH by C6F5N2+, the two competing pathways are distinct and do not have reactive intermediates in common.
- Kosynkin, Dmitry,Bockman, T. Michael,Kochi, Jay K.
-
p. 2003 - 2012
(2007/10/03)
-
- Thermal (iodide) and photoinduced electron-transfer catalysis in biaryl synthesis via aromatic arylations with diazonium salts
-
The dediazoniative arylation of various aromatic hydrocarbons (Ar'H) with diazonium salts (ArN2+) in acetonitrile can be readily effected to biaryls (Ar-Ar') in high yields, simply by the addition of small (catalytic) amounts of sodium iodide. [In the absence of Ar'H, the competitive iodination to ArI is nearly quantitative.] Iodide catalysis of biaryl formation is efficiently mediated by aryl radicals (Ar') that participate in an efficient homolytic chain process in which ArN2+ acts as a 1-electron oxidant. The complex kinetics of such an electron-transfer chain or ETC process (Scheme I) is quantitatively verified by computer simulation of the Ar'H-dependent (a) competition between arylation vs iodination and (b) catalytic efficiency of iodide. using the GEAR algorithms. ETC catalysis also pertains to the alternative photochemical procedure for arylation (in the absence of iodide), in which the deliberate irradiation of the charge-transfer band of the precursor complex (ArN2+, Ar'H) initiates the same homolytic chain arylation. The latter underscores the mechanistic generality of the ETC formulation for various types of catalytic dediazoniations of aromatic diazonium salts.
- Kosynkin,Bockman,Kochi
-
p. 4846 - 4855
(2007/10/03)
-
- Reactions of pentafluorophenylxenon(II) hexafluoroarsenate (+)(-) with aromatic compounds
-
Pentafluorophenylxenon(II) hexafluoroarsenate (+)(-) reacts (MeCN, 20 deg C) with aromatic compounds C6H5X (X=CH3, F, CF3, NO2 and CN), yielding isomeric mixtures of polyfluorinated biphenyls XC6H4C6F5.When X=I, iodopentafluorobenzene is formed in addition, whereas trimethylsilylbenzene (X=SiMe3) is only converted to C6H5C6F5 and C6F5H.These results are compared with the data for the radical pentafluorophenylation and fluorination reactions of the corresponding aromatic compounds with XeF2.Polyfluoroaromatic compounds C6F6, C6F5H, C6F5I, C6F5CN and C6F5SiMe3 do not react with (+)(-) under the same conditions.
- Frohn, H. J.,Klose, A.,Bardin, V. V.
-
p. 201 - 216
(2007/10/02)
-
- Diazotization of pentafluoroaniline by means of anion-catalyzed phase transfer catalysis in a hydrophobic organic solvent
-
Anion-catalyzed phase-transfer catalysis was successfully applied to diazotization of pentafluoroaniline in a dichloromethane-aqueous sulfuric acid two-phase system.The resulting diazonium group was coupled in situ with anisole, 1-methoxynaphthalene, and mesitylene, and replaced in situ with bromo, hydryl, and phenyl substituents under a two-phase condition.
- Iwamoto, Hidetoshi,Sonoda, Takaaki,Kobayashi, Hiroshi
-
p. 535 - 537
(2007/10/02)
-
- Homolytic Reactions of Polyfluoroaromatic Compounds. Part 16. Competitive Phenylation of Polyfluorobenzenes
-
Pairs of polyfluorobenzenes were allowed to compete for phenyl radicals generated by thermolysis of benzoyl peroxide at 80 deg C.From the relative yields of biaryl, and the yields of each biaryl formed upon arylation of each arene individually, the relative rates of attack of each site in each arene were deduced.Neither iron(III) benzoate nor trichloroacetic acid uniformly improved yields of biaryl, although in some cases the isomer distribution altered, when decomposition of benzoyl peroxide was carried out in the presence of such additives, to favour products of aryldehydrogenation or of aryldefluorination, respectively.Competition did not usually affect the distribution of attack of a particular arene, except when hexafluorobenzene was used, in which case greater selectivity of attack of the second arene occured.This suggested the formation of a 'stabilised' phenyl radical, and supported an earlier suggestion of species such as >; other evidence also supported the postulate.
- Allen, Kim J.,Bolton, Roger,Williams, Gareth H.
-
p. 691 - 696
(2007/10/02)
-
