Theoretical Mechanistic Study of C(sp³)−C(sp²) Cross‐Coupling by Photoredox‐Mediated Iridium(III)/Nickel(II)/Quinuclidine Triple Catalysis

Abstract

The photoredox-mediated iridium(III)/nickel(II)/3acetoxyquinuclidine triple-synergistic catalysis was comprehensively investigated by taking a C(sp 3 )À C(sp 2 ) bond crosscoupling as a reaction model using density functional theory (DFT) calculations. The synergistic mechanism of the triple catalytic system includes a reductive quenching cycle (Ir III À *Ir III À Ir II À Ir III ), an organocatalytic cycle, and a nickel catalytic cycle (Ni II À Ni I À Ni III À [Ni III ] ⊖ À Ni II ). Electronic process analysis shows that 3-acetoxyquinuclidine acts as a hydrogen atom transfer (HAT) catalyst to regioselectively provide αcarbon centered radical. Due to more favorable oxidative addition of CÀ Br to Ni(I) than HAT to avoid the formation of stable Ni(II) species, the generated α-carbon centered radical prefers to be captured by oxidative addition product Ni(III) to form an unusual [Ni III ] ⊖ C ⊕ species when 3-acetoxyquinuclidine was employed. These theoretical insights not only provide deep electronic process understanding of the photoredoxmediated iridium(III)/nickel(II) synergistic catalysis, but also clarify the electron-withdrawing group effect of quinuclidine, which has a potential guiding role for further development of new cross-coupling reactions.

Direct C(sp3)–H Acylation by Mechanistically Controlled Ni/Ir Photoredox Catalysis

“…Furthermore, it represents an acyl version of the well-described photochemical reactivity of N -alkylpyridinium salts, which many chemists have highlighted to perform novel transformations with many reviews published on this topic . This study provides insight into the thermodynamics of nickel oxidation and reduction while demonstrating the versatility of the nickel catalyst and how it can be manipulated to enable new mechanisms and transformations . Overall, this study could serve as a valuable starting point for developing new nickellaphotoredox reactions by proposing concrete mechanistic hypotheses and designs.…”