DFT study on synergetic Ir/Cu-metallaphotoredox catalyzed trifluoromethylation of aryl bromides

Abstract MacMillan et al. recently developed an elegant strategy for trifluoromethylation of aryl halides by merging iridium photoredox catalysis with copper catalysis [Science 360 (2018) 1010–1014]. The present work presents a complementary theoretical study to better understand the dual photoredox-copper catalysis. Calculated results confirm that the most possible photoredox catalytic cycle proceeds via a reductive quenching mechanism (IrIII/*IrIII/IrII/IrIII) with supersilanol as quencher and the CF3 reagent as oxidant. The formation of aryl radical involves three essential steps: deprotonation of the oxidized supersilanol by Na2CO3 to form the O-centered radical species, SiMe3 group migration to give the Si-centered silyl radical, bromine atom abstraction from aryl bromide. The CF3 radical can be obtained via the fragmentation process of the reduced CF3 reagent. The additions of both aryl radical and CF3 radical on the CuI center generates CuIII complex, from which the desired trifluoromethylation product is obtained via the C(sp2)−CF3 reductive elimination. All these processes were found to involve low barriers, and the highest one is only 12.7 kcal/mol, providing support of the viable trifluoromethylation strategy using copper catalysis via the radical trapping mechanism rather than the conventional oxidative addition mechanism.