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

作者：Tang Shi ya; Yu Hai zhu; You Wan li; Guo Qing xiang^*

来源：Chinese Journal of Chemical Physics, 2013, 26(4): 415-423.

DOI：10.1063/1674-0068/26/04/415-423

• Pd catalysis
• Oxidative coupling
• C-H activation
• Mechanism
• Pentafluorobenzene

Pd-catalyzed oxidative C-H/C-H coupling reaction is an emerging type of C-H activation reaction, which attracts great interests because both reaction partners do not require 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 pentafluorobenzene 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-pentafluorophenyl silver mechanism (C-H activation of benzene and subsequent transmetalation with pentafluorophenyl silver complex), path D pentafluorophenylsilver-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. pentafluorobenzene 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 pentafluorophenylsilver complex), which is similar to path A. The calculations are consistent with the H/D exchange experiment and kinetic isotope effects. Thus the present study not only offers a deeper understanding of oxidative C-H/C-H coupling reaction, but also provides helpful insights to further development of more efficient and selective oxidative C-H/C-H coupling reactions.

• 出版日期2013-8-27
• 单位中国科学技术大学