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 Ir-III/Ni-II-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(sp(2))-C(sp(3)) coupling. The calculated results show that the energetically more favorable pathway involves the reductive quenching of a photocatalyst (Ir-III/*Ir-III/Ir-II/Ir-III) and a Ni-0-initiated catalytic cycle (Ni-0/Ni-I/Ni-III/Ni-I/Ni-0 or Ni-0/Ni-II/Ni-III/Ni-I/Ni-0). The calculations reveal not only the mechanistic details delivering the difluoromethylarene product but also the molecular-level picture of the generation of Ni-0 species from the Ni-II precatalyst. Moreover, the calculations also rationalize the observed stoichiometric effect of CHF2Br in the reactions of aryl bromides with different substituted groups.

Automated summary

The study developed an Ir-III/Ni-II metallaphotoredox-catalyzed difluoromethylation strategy and used CHF2Br as the reagent. The computational calculations showed that a special dual catalysis mechanism promoted the coupling of C(sp(2))-C(sp(3)), and rationalized the stoichiometric effect of CHF2Br in reactions with aryl bromides containing different substituents.