Visible‐Light‐Induced Vicinal Dichlorination of Alkenes through LMCT Excitation of CuCl 2

CuCl2 -Catalyzed α-Chloroketonation of Aromatic Alkenes via Visible-Light-Induced LMCT

Here we report a copper-catalyzed protocol for the synthesis of α-chloroketones from aromatic alkenes including electron-deficient olefins under visible-light irradiation. Preliminary mechanistic studies show that the peroxo Cu(II) species is the key intermediate and hydroperoxyl (HOO⋅) and chlorine (Cl⋅) radicals can be generated by ligand-to-metal charge transfer (LMCT).

Visible-Light-Induced Oxidative α-keto-Dichlorination of Arylalkynes by CuCl2 at Room Temperature

A visible light-induced oxidative α-keto-dichlorination of terminal and internal aryl alkynes was developed to form dichloroacetophenones (DCAPs) and dichlorophenyl-acetophenones (DCPAPs), respectively, by using CuCl₂ as a photoredox catalyst in the presence of air at room temperature (without using any exogenous photocatalyst). Here, photoexcited CuCl₂ underwent ligand-to-metal charge transfer to generate a Cl radical, which readily added to the alkynes to form DCAPs or DCPAPs in the presence of O₂ . This α-keto-dichlorination reaction is a green and mild protocol as it produced water as the only by-product. Moreover, the evaluation of green chemistry metrics indicated that the E-factor (mass of wastes/mass of products) of the current α-keto-chlorination method is around 10.1 times lower than that of a literature-reported photochemical method. The Eco Scale value (score 55, which on a scale of 0-100 indicates an acceptable synthesis) signifies that this process is simple, highly efficient, eco-friendly, and cost-effective.

HCl-Catalyzed Aerobic Oxidation of Alkylarenes to Carbonyls

The construction of C-O bonds through C-H bond functionalization remains fundamentally challenging. Here, a practical chlorine radical-mediated aerobic oxidation of alkylarenes to carbonyls was developed. This protocol employed commercially available HCl as a hydrogen atom transfer (HAT) reagent and air as a sustainable oxidant. In addition, this process exhibited excellent functional group tolerance and a broad substrate scope without the requirement for external metal and oxidants. The mechanistic hypothesis was supported by radical trapping, ¹⁸ O labeling, and control experiments.

Visible-Light-Induced Homolysis of Earth-Abundant Metal-Substrate Complexes: A Complementary Activation Strategy in Photoredox Catalysis

The mainstream applications of visible-light photoredox catalysis predominately involve outer-sphere single-electron transfer (SET) or energy transfer (EnT) processes of precious metal RuII or IrIII complexes or of organic dyes with low photostability. Earth-abundant metal-based Mn Ln -type (M=metal, Ln =polydentate ligands) complexes are rapidly evolving as alternative photocatalysts as they offer not only economic and ecological advantages but also access to the complementary inner-sphere mechanistic modes, thereby transcending their inherent limitations of ultrashort excited-state lifetimes for use as effective photocatalysts. The generic process, termed visible-light-induced homolysis (VLIH), entails the formation of suitable light-absorbing ligated metal-substrate complexes (Mn Ln -Z; Z=substrate) that can undergo homolytic cleavage to generate Mn-1 Ln and Z. for further transformations.