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.