784-14-5Relevant academic research and scientific papers
Importance of Two-Electron Processes in Fe-Catalyzed Aryl-(hetero)aryl Cross-Couplings: Evidence of Fe0/FeIICouple Implication
Wowk, Vincent,Rousseau, Lidie,Lefèvre, Guillaume
supporting information, p. 3253 - 3266 (2021/10/12)
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.
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)
Shabalin, Anton Yu.,Adonin, Nicolay Y.,Bardin, Vadim V.,Parmon, Valentin N.
, p. 3720 - 3725 (2014/05/20)
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.
Palladium-catalyzed direct arylation of polyfluoroarene and facile synthesis of liquid crystal compounds
Ma, Xiaowei,Liu, Yan,Liu, Ping,Xie, Jianwei,Dai, Bin,Liu, Zhiyong
, p. 180 - 185 (2014/03/21)
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
Factors controlling the reactivity of heteroarenes in direct arylation with arylpalladium acetate complexes
Wakioka, Masayuki,Nakamura, Yuki,Hihara, Yoshihiro,Ozawa, Fumiyuki,Sakaki, Shigeyoshi
, p. 4423 - 4430 (2013/09/02)
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.
Air-stable and catalytically active phosphinous acid transition-metal complexes
Kurscheid, Boris,Belkoura, Lhoussaine,Hoge, Berthold
experimental part, p. 1329 - 1334 (2012/04/10)
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.
Carbon-carbon bond activation by 1,1-carboboration of internal alkynes
Chen, Chao,Kehr, Gerald,Froehlich, Roland,Erker, Gerhard
supporting information; experimental part, p. 13594 - 13595 (2010/11/18)
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
Suzuki- and Heck-type cross-coupling with palladium nanoparticles immobilized on spherical polyelectrolyte brushes
Proch,Mei,Rivera Villanueva,Lu,Karpov,Ballauff,Kempe
experimental part, p. 493 - 500 (2009/04/06)
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.
The effect of N-heterocyclic carbene ligands in the palladium-catalyzed cross-coupling reaction of K[C6F5BF3] with aryl iodides and aryl bromides
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)
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.
Pentafluorophenylation of aromatic compounds with 4,5,6,7,8-pentafluoro-6- nitro-1-oxaspiro[2.5]octa-4,7-diene
Kovtonyuk,Kobrina,Haufe
experimental part, p. 1686 - 1688 (2011/04/23)
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.
Combinatorial Design of Copper-Based Mixed Nanoclusters: New Catalysts for Suzuki Cross-Coupling
Thathagar, Mehul B.,Beckers, Jurriaan,Rothenberg, Gadi
, p. 979 - 985 (2007/10/03)
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.
