Electron Donor–Acceptor Complexes Without Preinstalled Sacrificial Leaving Groups: Applications in Synthesis

Various metallocenes were employed as electron donors and the activity of their electron donor acceptor (EDA) complexes with various quinones, nitro- and cyano- substituted compounds were studied. The hydrogen exchange reaction between acetylene, or molecular hydrogen, and various EDA complexes of metallocenes proceeded rapidly at room temperature but did not take place over either the metallocenes or quinones alone under the same reaction conditions. The exchange reaction proceeded over the EDA complexes via bonded hydrogen in the complexes, and the exchange rates were in the following decreasing order; nickelocene, cobaltocene and ferrocene. The cis-trans isomerization of butene was also studied over the EDA complexes. “Double-exchange” of hydrogen takes place reversibly between acetylene and the EDA complexes of 2,-6-dichloroquinone with nickelocene or cobaltocene in the following manner; C2D2+H2Z = C2H2+D2Z, where H2Z denotes the EDA complexes. The EDA complexes of metallocenes sorbed a considerable amount of ammonia at room temperature.

We report the catalytic generation of pyridyl radicals through photoexcitation of the electron donor-acceptor (EDA) complex, which enables the C2-selective heteroarylation of indole under ambient conditions. In this manifold, catalytic triarylamine and chloropyridine aggregate into an EDA complex in the presence of an inorganic base, making readily available chloropyridines good precursors for the generation of diverse pyridyl radicals. Given the broad reaction scope, this catalytic EDA complex protocol provides robust access to heterobiaryl scaffolds that are widely present in biologically important molecules.

External Photocatalyst-Free Visible Light-Promoted 1,3-Addition of Perfluoroalkyl Iodides to Vinyldiazoacetates

An efficient and operationally simple photochemical method has been demonstrated under transition metal-free, photocatalyst-free, and oxidant-free conditions. In recent times, diaryliodonium salts have become one of the most popular arylating sources under photoinduced conditions. Herein, we developed a visible light induced arylation of heterocycles using an EDA complex that is formed in situ from 2,6-lutidine and diaryliodonium triflate. Under light irradiation, the EDA complex generates the aryl radical that undergoes addition with 2-oxo-2H-chromene-3-carbonitriles via an SET process. This method serves as an effective tool to access biologically active and pharmaceutically relevant coumarin scaffolds.

This study proposes a green and efficient atom- and step-economical method for converting hazardous CS2 to dithiocarbamate derivatives under visible light irradiation and catalyst-free conditions. By the construction of novel C-S and C-N bonds, a series of β-dicarbonyl compounds and amines are incorporated into the products. Under light, CS2 and amine first form bis(dialkylaminethiocarbonyl)disulfides, which then react with K2CO3-activated β-dicarbonyl compounds to form electron donor-acceptor (EDA) complexes and subsequently generate the target products. This study confirms for the first time that bis(dialkylaminethiocarbonyl)disulfides can act as electron acceptors to form an EDA complex with β-dicarbonyl compounds, which are then coupled to form the target product under light.

Electron donor-acceptor (EDA) complex catalysis has emerged as a sustainable alternative to conventional metal- or dye-based photoredox methodologies. Sulfonylated heterocycles constitute privileged structural motifs widely found in bioactive and pharmaceutically relevant scaffolds. In this work, we describe a radical sulfonylation-cyclization (RSC) strategy for alkynes, enabled by catalytic tris(4-methoxyphenyl)amine (TMPA) and aryl sulfonyl chlorides through in situ EDA complex formation under visible-light irradiation (λ = 427 nm, 40 W Kessil) at room temperature. This protocol affords highly functionalized sulfonylated 1,2-dihydroquinoline, pyrroloindole, and chromene derivatives in good to excellent yields (60-90%) within short reaction times (≈2 h), delivering 60 examples with broad functional group compatibility under redox-neutral conditions. A detailed investigation of EDA complex formation was also carried out. Furthermore, the resulting sulfonylated 1,2-dihydroquinolines undergo photo-oxidative, catalyst, and base-free aromatization to furnish the corresponding 3-sulfonylquinolines under ambient conditions. In addition, terminal alkynes participated in EDA-mediated hydrosulfonylation, providing the corresponding (Z)-vinyl sulfones with complete stereoselectivity when tris(trimethylsilyl)silane (TTMSS) was employed as the hydride source. In total, we report a library of 94 compounds in this work.

Electron donor-acceptor (EDA) complexes are of fundamental importance and practical utility in photoactive molecules, including fluorescence probes and photoredox catalysts. However, the design guidelines for developing efficient intramolecular EDA complexes are still underdeveloped. In this study, we systematically investigate the linker structures between an indole electron donor and a dinitrobenzene electron acceptor within single-molecule EDA complexes to optimize their relative positions and efficiency of the EDA complex formation. We identify trans-1,2-cyclohexanediamine as an optimal linker with a fixed conformation, due to the presence of an intramolecular hydrogen bond. The linker produces a highly efficient EDA complex in both the solution and solid states. This study postulates a versatile core structure for the synthesis of various single-molecule EDA complexes.

Organic synthesis methods initiated by visible light have received increasing attention from synthetic chemists. Reactions initiated by EDA complexes do not require the use of toxic or expensive photoredox catalysts, unlike traditional photoreaction processes. However, this kind of reaction requires a particular structure for the substrate, so it is important to study the detailed and systematic reaction mechanism for its design. EDA complexes of substituted 1H-indole and substituted benzyl bromide derivatives were studied by density functional theory (DFT). The difference between EDA complexes with substituents of different kinds and locations were compared by theoretical study and a new EDA complex was predicted.

Triphenylphosphine, iodide and N-chloro-arylsulfonamides could generate amidyl radicals via EDA (Electron Donor-Acceptor) complexes under visible light irradiation, and this strategy enables the synthesis of valuable δ-chloro-arylsulfonamide and N-arylsulfonylpyrrolidine motifs in moderate yields. This blue LED-induced method utilizes more readily available reagents, providing advantages in terms of cost efficiency, broad substrate scope, and functional-group compatibility.

Electron donor-acceptor (EDA) complex photochemistry has emerged as a vibrant area in visible-light-mediated synthetic radical chemistry. However, theoretical insights into the reaction mechanisms remain limited. Our study investigates the influence of solvent polarity and halogen atom types on radical reaction pathways in EDA complexes. We demonstrate that solvent polarity modulates the charge transfer and spatial arrangement within EDA complexes, thereby influencing their stability and reaction kinetics. Iodide ions play a crucial role in facilitating free radical generation and stabilizing reaction intermediates. Different halogen atom types exhibit distinct effects on radical reactions. Variations in radical concentration and solvent environment further affect the pathway selectivity. Additionally, light conditions influence the free radical generation and pathway selectivity. Our findings enhance the understanding of EDA complex photochemistry and radical reactions, offering insights for organic synthesis and photochemistry applications.

The mechanism of the reaction between molecular hydrogen and the electron donor-acceptor complexes (A−Na+ and A=2Na+) of various aromatic hydrocarbons (A) with sodium were studied kinetically and spectroscopically. The relative activity of each electron donor-acceptor (EDA) complex for the hydrogen uptake was associated with its electronic properties, especially with the reduction potential of its anion. It was found that the hydrogen molecule reacts more readily with stronger electron-donating EDA complexes, whose anions have higher reduction potentials. It was also suggested that, on the hydrogen adsorption over the A−Na+ and A=2Na+ films (or in their solutions), the corresponding monohydroanion complexes (AH−Na+) and NaH were produced as follows : &2A^-Na^++H_2=AH^-Na^+NaH+A &A^=2Na^++H_2=AH^-Na^++NaH The behavior of AH−Na+ was closely correlated with the localization energies of electrons in the anions of the aromatic hydrocarbons.

Electron Donor-Acceptor Complexes – Key Intermediates in the Thermal and Photoinduced Reduction of Aromatic Nitro Compound in Donor Solvents

A novel and efficient photoinduced synthesis of C6-polyfunctionalized phenanthridines from three-component reactions of isocyanides, alkynes and sulfinic acids was developed. The reactions generated the corresponding products with high selectivity through the photochemical activity of the formed electron donor-acceptor (EDA) complex during the reaction via a radical tandem process under mild conditions.

Electron donor-acceptor (EDA) complex photochemistry has become a burgeoning topic in the synthetic radical chemistry mediated by visible light; however, the theoretical insights into the reaction mechanisms are limited. Herein, accurate electronic structure calculations at the CASPT2//CASSCF/PCM level of theory were performed to investigate the paradigm example of EDA complex-enabled photoreaction for visible-light-driven dearomative perfluoroalkylation of β-naphthol. The excitation energy levels of the EDA complex are controlled by noncovalent interactions because the photoinduced intermolecular charge is enhanced when the noncovalent interaction becomes weaker, leading to the broad spectra ranging from UVA (<380 nm) to visible light (>500 nm). The competitiveness of the radical-radical coupling over the radical chain pathway is also regulated due to the tunable radical concentrations varying the excitation wavelength.

An efficient synthesis of sulfone structures through selenonium salts and sodium sulfinates was developed. Under the irradiation of a blue LED lamp, the two substrates generate aryl and sulfonyl radicals through the activation of the intermediate electron donor acceptor (EDA) complex, thereby synthesizing aromatic, heteroaromatic and aliphatic sulfones in medium to good yields. The advantages of this strategy are metal-free, mild conditions and the leaving group is recycled to construct new selenonium salts.