DFT Mechanistic Study of IrIII/NiII-Metallaphotoredox-Catalyzed Difluoromethylation of Aryl Bromides.

The work by MacMillan et al. ( Angew. Chem., Int. Ed. 2018, 57, 12543-12548) developed an IrIII/NiII-metallaphotoredox-catalyzed difluoromethylation strategy of aryl bromides using CHF2Br as the CHF2 reagent in the presence of tris(trimethylsilyl)silane. Here, we present a density functional theory (DFT)-based computational study to understand special dual catalysis promoting the C(sp2)-C(sp3) coupling. The calculated results show that the energetically more favorable pathway involves the reductive quenching of a photocatalyst (IrIII/*IrIII/IrII/IrIII) and a Ni0-initiated catalytic cycle (Ni0/NiI/NiIII/NiI/Ni0 or Ni0/NiII/NiIII/NiI/Ni0). The calculations reveal not only the mechanistic details delivering the difluoromethylarene product but also the molecular-level picture of the generation of Ni0 species from the NiII precatalyst. Moreover, the calculations also rationalize the observed stoichiometric effect of CHF2Br in the reactions of aryl bromides with different substituted groups.