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.