Mechanistic Study of Pd/Ag Dual-Catalyzed Cross-Dehydrogenative Coupling of Perfluoroarenes with Thiophenes

The mechanism of the Pd/Ag dual-catalyzed cross-dehydrogenative coupling (CDC) between perfluoroarenes and thiophenes was clarified. The exact role of the catalytic resting state of the homo-biaryl-Pd(II) complex, which was previously overlooked in Pd/Ag dual-catalyzed CDC, was carefully investigated. Detailed experimental studies indicated that a homo-biaryl-Pd(II) complex occurred in the catalytic off-cycle as a resting state and prevented the homocoupling of perfluoroarenes. In addition, these studies indicated that the C-H bond activation steps of perfluoroarenes and thiophenes proceeded by different mechanisms. While the C-H bond of perfluoroarenes was immediately activated by Ag(I) salts, the C-H bond of thiophenes was activated by the Pd(II) catalyst. Kinetic studies revealed that the Pd(II)-C-H activation of thiophenes is most likely the rate-determining step.