Activation of C-Br Bond of CBr4 and CBrCl3 Using 9-Mesityl-10-methylacridinium Perchlorate Photocatalyst

Maneuvering the Electronic State and Active Site of Assembled-Gold Nanoclusters through Polyoxometalate Implantation for Heterogeneous Green-Light Photocatalysis

Gold nanoclusters (AuNCs) exhibit unique molecule-like optical and electronic properties, making them promising candidates for photocatalysis. However, their application as primary photocatalysts in heterogeneous systems is limited by rapid electron recombination, small size, and high solubility. To overcome these limitations, we developed an approach combining AuNCs assemblies with electron trap centers to enhance charge separation and electron transfer. Using a depletion-driven assembly method, Keggin-type polyoxometalates (POMs), Na10SiW9O34 (SiW9), were uniformly embedded within spherical assemblies of glutathione-protected AuNCs, forming gold superclusters (AuSCs). The resulting AuSCs@SiW9 exhibited complete photoluminescence quenching, enhanced metallicity, and stabilized photogenerated electrons via SiW9, enabling their use as primary photocatalysts. The AuSCs@SiW9 efficiently catalyzed the functionalization of terminal aryl alkyne with N-bromosuccinimide (NBS), achieving a tribromoketones yield of 94%, significantly outperforming AuSCs with lower or higher metallicity (38 and 65%, respectively). Mechanistic studies revealed that the improved gold metallicity in AuSCs@SiW9 promotes charge transfer complex formation with NBS, while SiW9 stabilizes photogenerated electrons, enhancing electron density under light irradiation. The AuSCs@SiW9 exhibited strong visible-light absorption, photostability, and solvent dispersibility, enabling recyclability for up to five cycles and scalability for broader applications. This strategy positions gold as a viable primary photocatalyst, expanding its potential in heterogeneous photocatalysis toward synthesizing small molecules.

Selective fluorescence sensors for Cu2+ and Hg2+ ions using acridinium-polymer complexes

The photophysical properties of two acridinium derivatives, 9-phenyl-10-methylacridinium (Ph-Arc+) and 9-mesityl-10-methyl acridinium (Mes-Acr+) were investigated in aqueous solutions of poly(methacrylic acids) (PMAA) at various pH values with various polymer to dye (R/D) ratios. In acidic conditions, PMAA effectively turned on the emission of both acridinium derivatives. Micromolar concentrations of copper (II) ions can selectively turn off the emission of dye/PMAA mixtures with a linear response range from 0.50 to 10.0 µM and a detection limit as low as 0.38 µM. In near neutral conditions, Mes-Acr+ in PMAA solutions displayed extremely weak emission. However, trace amounts of Hg2+ ions can instantly turn on the emission with a low detection limit of 43.6 nM and a linear range between 1.0 to 10.0 µM. This analytical method is fast, cost-effective, and environmentally friendly, as it is conducted in 100 % aqueous solution with commercial acridinium derivatives and a biocompatible polymer.

Site-Selective γ-Trihalomethylation and γ-Dihalomethylidenation of Silyl Dienol Ethers under Organophotoredox Catalysis

We report a general remote tribromo- and trichloromethylation process using CBr4 and CBrCl3 as ready available sources of trihalomethyl radicals. This method operates under mild and metal-free photocatalyzed conditions and enables the access to γ-trihalomethylated enals with complete regioselectivity in up to 71 % isolated yield. Importantly, this protocol is easily adapted to the selective one-pot synthesis of the corresponding γ-dihalomethylidenated enals in up to 49 % overall yield. Mechanistic studies are in favor of a radical chain propagation initiated by an oxidative quenching of the photocatalyst.

Ultrasmall CsPbBr3 Nanocrystals as a Recyclable Heterogeneous Photocatalyst in 100% E- and Anti-Markovnikov Sulfinylsulfonation of Terminal Alkynes

The precise synthesis of ultrasmall, monodisperse CsPbBr3 nanocrystals is crucial due to their enhanced photophysical properties resulting from strong quantum confinement effects. Traditional methods struggle with size control, complicating synthesis. Although CsPbBr3 nanocrystals find applications in LEDs and photovoltaics, their use in photocatalysis for organic reactions remains limited. Our study introduces ultrasmall TBIA-CsPbBr3 nanocrystals (∼5.6 nm), synthesized via a three-precursor hot injection method using tribromoisocyanuric acid (TBIA) as a bromine precursor for the first time. These nanocrystals exhibit a near-unity photoluminescence quantum yield (PLQY) of 0.99 and an elevated oxidation potential of +1.80 V. We demonstrate their efficacy as recyclable heterogeneous photocatalysts in a one-pot, 100% E-selective, anti-Markovnikov sulfinylsulfonation of terminal alkynes under visible light, achieving a high product conversion rate (PCR) of 62,500 μmol g-1 h-1 and recyclability for up to five cycles. Density functional theory (DFT) calculations support the exclusive formation of the E-isomer. TBIA-CsPbBr3 outperforms other CsPbBr3 perovskites in photocatalysis, with superior efficiency attributed to their extended excited-state lifetime and higher surface area, which accelerates the organic transformation process.

Pioneering Metal-Free Late-Stage C-H Functionalization Using Acridinium Salt Photocatalysis

Using organic dyes as photocatalysts is an innovative approach to photocatalytic organic transformations. These dyes offer advantages such as widespread availability, adaptable absorption properties, and diverse chemical structures. Recent progress has led to the development of organic photocatalysts that can utilize visible light to modify chemically inert C-H bonds. These catalysts are sustainable, selective, and versatile, enabling mild reactions, late-stage functionalization, and various transformations in line with green chemistry principles. As catalysts in photoredox chemistry, they contribute to the development of efficient and environmentally friendly synthetic pathways. Acridinium-based organic photocatalysts have proved valuable in late-stage C-H functionalization, enabling transformative reactions under mild conditions. This review emphasizes their innovative features, such as organic frameworks, efficient light absorption properties, and their applications in modifying complex molecules. It provides an overview of recent advancements in the use of acridinium-based organic photocatalysts for late-stage C-H bond functionalization without the need for transition metals, showcasing their potential to expedite the development of new molecules and igniting excitement about the prospects of this research in the field.

Base-promoted triple cleavage of CCl2Br: a direct one-pot synthesis of unsymmetrical oxalamide derivatives

We present a novel, eco-friendly and one-pot approach for synthesizing unsymmetrical oxalamides with the aid of dichloroacetamide and amine/amides in the presence of CBr4 in a basic medium. The use of water as a potent supplement for the oxygen atom source and the detailed mechanism have been disclosed. Moreover, the protocol involves triple cleavage of CCl2Br and the formation of new C-O/C-N bonds, with the advantage of achieving selective bromination using CBr4 with good to excellent yield under mild conditions. The method also demonstrates promise for industrial use, as proven by its effective implementation in gram-scale synthesis conducted in a batch process, along with its utilization in a continuous-flow system.

Photocatalytic Multicomponent Annulation of Amide-Anchored 1,7-Diynes Enabled by Deconstruction of Bromotrichloromethane

We present the first example of visible-light-mediated multicomponent annulation of 1,7-diynes by taking advantage of quadruple cleavage olf carbon-halogen bonds of BrCCl3 to generate a C1 synthon, which was adeptly applied to the preparation of skeletally diverse 3-benzoyl-quinolin-2(1H)-one acetates in moderate to good yields. Controlled experiments demonstrated that H2O acted as both oxygen and hydrogen sources, and gem-dichlorovinyl carbonyl compound exhibited as a critical intermediate in this process. The mechanistic pathway involves Kharasch-type addition/6-exo-dig cyclization/1,5-(SN")-substitution/elimination/binucleophilic 1,6-addition/proton transfer/tautomerization sequence.

Atom Transfer Radical Addition Reactions of Quinoxalin-2(1H)-ones with CBr4 and Styrenes Using Mes-Acr-MeClO4 Photocatalyst

The atom transfer radical addition (ATRA) reaction is defined as a method for introducing halogenated compounds into alkenes via a radical mechanism. In this study, we present an ATRA approach for achieving regioselective functionalization of quinoxalin-2(1H)-ones by activating C-Br bonds of CBr4 and subsequent trihaloalkyl-carbofunctionalization of styrenes employing the 9-mesityl-10-methylacridinium perchlorate (Fukuzumi) photocatalyst under 3W blue LED (450-470 nm) irradiation. This three-component radical cascade process demonstrates remarkable efficiency in the synthesis of 1-methyl-3-(3,3,3-tribromo-1-(4-chlorophenyl)propyl)quinoxalin-2(1H)-one derivatives.