Mild and Efficient Ni-Catalyzed Biaryl Synthesis with Polyfluoroaryl Magnesium Species: Verification of the Arrest State, Uncovering the Hidden Competitive Second Transmetalation and Ligand-Accelerated Highly Selective Monoarylation

Employing a nickel catalyst and electron-deficient polyfluoroaryl magnesium species, a highly selective monoarylation of polyfluoroarenes containing multiple identical coupling sites has been achieved for the first time, which represents a long-standing problem due to the competitive reactivity between the desired products and the starting polyfluoroarenes. Because of the negative fluorine effect, a surprisingly stable cis [Ni­(ArF4)2(DPEPhos)] species 4 (ArF4 = 2,3,5,6-tetrafluorophenyl) confirmed by X-ray crystallography is isolated, which acts as catalyst arrest state as proven by a thermal decomposition test. Further retro-transmetalation experiments uncover a hidden secondary transmetalation between ArF4-Ni-Ph and excess ArF4-MgCl that competes with the desired but reluctant reductive elimination at the high-valent nickel center. Accordingly, through the cooperation of newly developed DMM-DPEPhos, and a dioxane-mediated Schlenk equilibrium with Grignard reagent, the formation of the corresponding arrest state is remarkably inhibited. An excellent coupling efficiency and an excellent monoarylation selectivity are therefore generally accomplished with a widespread electrophile scope and good functional group tolerance under mild conditions. Importantly, our novel method shows great power in the gram-scale synthesis of thienyl-2,3,5,6-tetrafluorophenyl units that represent key components in materials science.