784-14-5Relevant articles and documents
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.
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
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.
