Dual-Role Halogen-Bonding-Assisted EDA-SET/HAT Photoreaction System with Phenol Catalyst and Aryl Iodide: Visible-Light-Driven Carbon–Carbon Bond Formation

Abstract

Electron donor–acceptor (EDA) complex-mediated single-electron transfer (SET) is a crucial method for generating carbon radicals. Hydrogen atom transfer (HAT) enables the direct generation of alkyl radicals. We report a dual-role EDA-SET/HAT photoreaction system for carbon–carbon bond formation using a phenol catalyst and aryl iodide. This system facilitates addition of alkyl radicals generated from ethers, amide, sulfide, and cycloalkane to arenes. Mechanistic studies revealed that EDA complex formation is mediated by halogen bonding between phenoxide and aryl iodide. Irradiation of the EDA complex with visible light generates an aryl radical, which abstracts a hydrogen atom from an sp3 carbon to form an alkyl radical.

Halogen-Bonding-Promoted Photoinduced C–X Borylation of Aryl Halide Using Phenol Derivatives

“…Moreover, we observed the formation of a 1:1 complex between 2-naphtoxide and 1a with a binding constant ( K a ) of 0.49 M –1 in DMSO- d 6 using a 1 H NMR titration method and Job’s plot analysis (Scheme c; see Supporting Information (SI), Figures S1–S4). Since these results are similar to the previous results , and are sufficient to rule out the formation of EDA complexes by π–π* interaction, such as the independent reporting by Miyake and Melchiorre, , we hypothesize that the formation of EDA complexes by XB interactions is the key to initiating the reaction.…”

“…Since the photochemical activation of the EDA complex through XB interaction is the aggregation between the organic halide and the electron donor, selective activation of the organic halide and generation of a carbon-centered radical only by fragmentation of the anion radical species generated are possible (Figure b) . Very recently, a novel method for photoactivation of organic halides by XB has been developed that utilizes Lewis bases such as phenol instead of well-known halogen-bonding acceptors such as amines …”

Photoinduced Cascade Reactions of 2-Allylphenol Derivatives toward the Production of 2,3-Dihydrobenzofurans

“…Interestingly, suitable phenolate anions may be also employed as photo-organocatalysts to drive the synthesis of relevant molecules. ,, As examples, Shang and co-workers have described the use of o -phosphinophenolates as photocatalysts for the defluoroalkylation and hydrodefluorination of trifluoromethyl groups and for the borylation of aryl halides. , Recently, employing a similar approach, our group developed a novel phenolate-based photocatalytic system capable of driving the production of valuable alkyl iodides (Figure a) . An alternative mechanistic manifold is represented by the ability of phenolate derivatives to form electron donor–acceptor (EDA) complexes with electron-poor radical precursors (Figure a). ,, An intriguing aspect of these ground-state molecular aggregates is that, generally, their absorption profiles show a bathochromic shift . Thus, when the EDA complex is irradiated with light of an appropriate wavelength, an electron transfer can occur, resulting in the formation of reactive radicals that can be used to initiate organic transformations .…”

“…10c An alternative mechanistic manifold is represented by the ability of phenolate derivatives to form electron donor–acceptor (EDA) complexes with electron-poor radical precursors ( Figure 1 a). 7 , 9d , 12 An intriguing aspect of these ground-state molecular aggregates is that, generally, their absorption profiles show a bathochromic shift. 13 Thus, when the EDA complex is irradiated with light of an appropriate wavelength, an electron transfer can occur, resulting in the formation of reactive radicals that can be used to initiate organic transformations.…”

Binaphthol derivatives as catalysts for visible light induced aryl halide derivatizations

“…30,31 So, it is promising to use phenols for photocatalytic reduction reactions due to their reversible gain and loss of electrons under alkaline conditions. [32][33][34][35][36][37][38][39] Binaphthol (BINOL) is a common compound constructed of two β-naphthols bonded at the 1-position, exhibiting fine stability and diversified derivation. The conjugated structure of the naphthalene ring also endows it with a notable photoresponse.…”