Mechanistic Study of Palladium-Catalyzed Oxidative C-H/C-H Coupling of Polyfluoroarenes with Simple Arenes  

钯催化多氟代芳烃与简单芳烃的氧化C—H／C—H偶联反应机理

作　　者：唐诗雅[1] 于海珠[1] 尤万里[1] 郭庆祥[1] 

机构地区：[1]中国科学技术大学化学系,合肥230026

出　　处：《Chinese Journal of Chemical Physics》2013年第4期415-423,J0001,共10页化学物理学报（英文）

摘　　要：Pd-catalyzed oxidative C-H/C-H coupling reaction is an emerging type of C-H acti- vation reaction, which attracts great interests because both reaction partners do not re- quire pre-functionalization. In the present study, we employed DFT methods to investigate the mechanism of Pd（OAc）2-catalyzed oxidative C-H/C-H coupling of pentafluoroben-zene with benzene. Four possible pathways were examined in the C-H activation part： path A benzene-pentafluorobenzene mechanism （C-H activation of benzene occurs before the C-H activation of pentafluorobenzene）, path B pentafluorobenzene-benzene mechanism （C-H activation of benzene occurs after the C-H activation of pentafluorobenzene）, path C benzene-pentafluorophenylsilver mechanism （C-H activation of benzene and subsequent transmetalation with pentafiuorophenyl silver complex）, path D pentafiuorophenylsilver- benzene mechanism （transmetalation with pentafluorophenyl silver complex and subsequent C-H activation of benzene）. Based on the calculations, the sequences of two C-H activation steps are found to be different in the oxidative couplings of same substrates （i. e. pentafiu- orobenzene and benzene） in different catalytic systems, where the additive Ag salts played a determinant role. In the absence of Ag salts, the energetically favored pathway is path B （i.e. the C-H activation of pentafluorobenzene takes place before the C-H cleavage of benzene）. In contrast, with the aid of Ag salts, the coordination of pentafluorophenylsilver to Pd center could occur easily with a subsequent C-H activation of benzene in the second step, and the second step significantly raises the whole reaction barrier. Alternatively, in the presence of Ag salts, the kinetically preferred mechanism is path C （i. e. the C-H activation of benzene takes place in the first step followed by transmetalation with pentafluorophenyl- silver complex）, which is similar to path A. The calculations are consistent with the H/D exchange experiment and kinetic isotope effects. Thus

关 键 词：Pd catalysis Oxidative coupling C-H activation Mechanism Pentafluo-robenzene 

分 类 号：O[理学]