A novel oxidation state modulation mechanism, merging oxidative quenching (IrIII-*IrIII-IrIV-IrIII) and nickel catalytic (NiII-NiI-NiIII-NiI-NiII) cycles, has been illuminated unambiguously for photoredox-mediated iridium(iii)/nickel(ii) dual catalyzed C-O cross-coupling of aryl bromide and alcohol. Quinuclidine participates in a crucial proton-coupled electron transfer process to accelerate the reaction and regulate C-O coupling selectivity.

A new type of intermolecular alkylative olefination of unactivated olefins and alkyl halides has been realized for the first time. This copper-promoted Heck-type reaction employs a directing-group strategy to efficiently produce the coupled alkyl olefin products with excellent regio- and stereoselectivity. A broad substrate scope including 1°, 2°, and 3° alkyl bromides and various nonactivated alkenes could be well tolerated. DFT calculations disclosed a dimethyl sulfoxide assisted concerted H–Br elimination process of a conformationally strained Cu­(III) cyclic transition state.

Photoredox-mediated iridium/nickel dual catalysis has successfully triggered a series of traditionally challenging carbon–heteroatom cross-coupling reactions. However, detailed mechanisms, such as the catalytic cycles for dual catalysts and the role of base additive, remain controversy in these reactions. In this study, a highly chemoselective C–S cross-coupling of thiols with heteroaryl iodides has been investigated by density functional theory (DFT) calculations and emission quenching experiments. Interestingly, the oxidation state modulation mechanism merging oxidative quenching (IrIII–*IrIII–IrIV–IrIII) and nickel catalytic cycles (NiII–NiI–NiIII–NiI–NiII) is favorable. It is consisted of four major steps: pyridine mediated proton-coupled electron transfer, oxidative addition of heteroaryl iodides with Ni­(I)–halide complex, reductive elimination, and single-electron transfer. In contrast, the radical mechanism initiated by reductive quenching of *IrIII with thiols is impractical, because oxidative addition or σ-bond metathesis from Ni­(II)–thiolate intermediate is highly energy-demanding. This study will hopefully benefit the future understanding of such photoredox-mediated dual catalytic systems.

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