Visible-Light Photocatalytic Direct Arylation of Arenes Using Silver Iodide Nanoparticles Supported on Magnesium-Aluminium Layered Double Hydroxide

Visible-Light Photocatalytic Direct Arylation of Arenes Using Silver Iodide Nanoparticles Supported on Magnesium-Aluminium Layered Double Hydroxide | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Visible-Light Photocatalytic Direct Arylation of Arenes Using Silver Iodide Nanoparticles Supported on Magnesium-Aluminium Layered Double Hydroxide Pengfei Han, Eric Waclawik, Steven Bottle, Xuheng Yang, Jianfang Wang, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3747453/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The direct arylation of inactive arenes with aryl halides stands as a well-established and fundamental method in organic synthesis for synthesizing biaryls. However, current direct arylation methods suffer from the generation of substantial chemical waste, reliance on moisture-sensitive reagents, and harsh reaction conditions that involve using either organic acids or potent bases. Here we report a photocatalytic system based on AgI-decorated magnesium-aluminium-layered double hydroxide (MgAl-LDH), which operates effectively under visible light, eliminating the need for base or other additives. The alignment of energy levels between catalyst components and reactant enables the system to harness visible light or sunlight irradiation for the generation of aryl and •OH radicals from aryl iodides and MgAl-LDH surface, respectively, facilitating direct C-H arylation, producing only water and iodine as by-products. Furthermore, the surface hydroxyl groups of MgAl-LDH can be readily regenerated. Our discovery provides an efficient, eco-friendly and cost-effective approach to C-H arylation. Physical sciences/Chemistry/Green chemistry/Sustainability Physical sciences/Materials science/Materials for energy and catalysis/Photocatalysis Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Carbon-carbon bond formation is a fundamental process in organic synthesis, where the creation of biaryl link between sp 2 -hybridized carbons is of particular significance, prevalent in natural products and pharmaceuticals, and in various fields of chemistry and biology 1 . Notably, biaryl motifs constitute essential substructures in many top-selling pharmaceuticals and are integral components of approximately 50% of all known drugs 2 . A promising approach for constructing biaryl frameworks involves the direct arylation of inactive arenes with haloarenes via aromatic C-H bond activation 3,4 . Various catalytic methods to achieve this have emerged, including the use of hetero-/homogeneous transition metal catalysts 5–8 , organocatalysts 9–12 , and strong reductants 13,14 . However, a common requirement in all these catalytic reactions is the use of substantial quantities of strong inorganic/organic bases, such as alkoxide, often in excess (ranging from 2 to 12 equivalents of reactant), to achieve productive catalysis. Additionally, toxic or hard-to-obtain additives/ligands are frequently employed, leading to the generation of stoichiometric waste by-products. High reaction temperatures (80–155℃) in these direct arylation processes can result in undesired dehalogenation reactions and decreased product yields. Therefore, the development of a catalytic method using catalysts that operate efficiently to drive the reaction at moderate temperatures and avoid the need for ligands, base and the removal of hazardous chemicals during product isolation is highly desirable. Several studies have identified three pivotal steps in the direct C-H arylation process: single electron transfer (SET) to convert aryl halides into aryl radicals, single electron oxidation (SEO) of biaryl radicals, and deprotonation of biaryl cations (or hydrogen abstraction as a single step instead of SEO and deprotonation) 8,9,15 . The use of a strong base has been deemed essential for obtaining biaryl product in high yields. For instance, substituting the commonly used base, potassium tert-butoxide (KO t -Bu), with other bases like NaO t -Bu, KOH, or K 3 PO 4 , resulted in only trace amounts or no desired product formation 5,12 . KOt-Bu plays a critical role in both SET and SEO processes as well as in deprotonation 15 . Although a photocatalyst composed of nickel (Ni) and gold nanoparticles (NPs) was successfully used for electron donation in the SET step 7 , Ni NPs are prone to oxidation and require substantial amounts of strong base to complete the catalytic cycle. The design of a catalytic system that enables direct C-H arylation without the need for a base or additive presents a formidable challenge, as it necessitates addressing all the three functions (i.e., SET, SEO, and deprotonation) in the catalyst itself. Here, we present a novel photocatalytic process for direct C( sp 2 )-H arylation driven by visible-light, that gives high biaryl yield without the need for additional bases or additives. As displayed in Scheme 1 , silver iodide (AgI) attached to a magnesium-aluminium layered double hydroxide (MgAl-LDH) intercalated with carbonate (CO 3 2- ) serves as an efficient photocatalyst for the arylation at 60℃, a departure from our previous work that explored supported Ag nanoparticles (NPs) for C α ( sp 3 )-H bond activation 16 . When supported Ag NPs were used to catalyse the direct C-H arylation, we observed a conversion of NPs into AgI, a key component of the actual catalyst. The catalyst design draws inspiration from prior studies that demonstrated that MgAl-LDH can serve as an alkaline support for photocatalysis, eliminating the need for additional base 17 . The hydroxyl groups and carbonate anions on the LDH surface can serve as basic sites, while the supported AgI NPs generate electron-hole pairs at the surface upon visible light irradiation 18,19 . The excited electrons facilitate the SET process, while the migration of holes to the valence band of MgAl-LDH converts surface hydroxyl groups into •OH radicals. These radicals abstract hydrogen from the biaryl radical intermediate, resulting in water as a by-product. The byproducts of the synthesis, I 2 and H 2 O, can be easily separated without environmental concerns. This unique catalyst structure harnesses visible light, including sunlight, to drive the coupling reactions between halobenzenes and arenes, offering a straightforward approach to biaryl synthesis. Thus, our process fulfils the criteria for a sustainable future 18 , combining efficiency, safety, solar energy utilisation, and environmental friendliness. Results and Discussion Catalyst Characterisation. The AgI/Mg 2 Al 1 LDH, with a silver content of 9.4 wt.% was obtained as a light-yellow powder (see Fig. 1 a), that exhibited the optimal photocatalytic performance. The results of the X-ray diffraction (XRD) analysis (Fig. 1 b), the energy-dispersive X-ray spectroscopy (EDX) elemental mappings (Fig. 1 c) and transmission electron microscopy (Fig. 1 d) show that the as-prepared Mg 2 Al 1 LDH photocatalyst was loaded with AgI nanoparticles (NPs) dispersed on LDH support. The high-resolution TEM (HR-TEM) images reveal the lattices of AgI and LDH (Figs. 1 e and f), which are in accord with the results of XRD analysis. Control experiments and performance of the catalysts. The direct arylation of benzene was chosen as a model reaction for control experiments, optimising the photocatalysts and the reaction conditions. These experiments elucidated the roles played by the catalyst components and the influence of light irradiation. Catalysts with different Mg/Al molar ratios were used for catalysing the reaction under visible light irradiation. As shown in Supplementary Table 1, the AgI/Mg 2 Al 1 LDH photocatalyst exhibits the best catalytic performance without any requirement for the addition of base or any other additives. The desired product biphenyl can be obtained and identified by mass spectrometry (Supplementary Fig. 1), with I 2 also being produced as a visibly evident byproduct (Fig. 1 a) confirmed by UV-Vis spectroscopy (Supplementary Fig. 2). A high biphenyl yield of 93% was achieved by AgI/Mg 2 Al 1 LDH catalyst under LED light irradiation at 400 nm wavelength with an intensity of 0.1 W cm -2 (Entry 1 in Table 1 ). The yield of biphenyl varies moderately with Mg/Al ratio of the catalysts (Supplementary Table 1). The absence of either the irradiation or the catalyst resulted in only a trace yield of the target product (Table 1 , entries 2 and 3). The absence of iodobenzene or benzene gave none or only a trace of biphenyl (Table 1 , entries 4 and 5), suggesting that the product is formed through a cross-coupling process. A significant discovery involves the successful utilization of natural sunlight for photocatalytic direct arylation. As shown in Supplementary Fig. 3, a 60% biphenyl yield was attained at relatively low reaction temperatures, obviating the requirement for supplementary energy input, and highlighting the system's impressive solar energy utilization efficiency. The fact that both the Mg 2 Al 1 LDH support and AgI/ZrO 2 individually exhibit low catalytic activities is worth noting (Table 1 , entries 6 and 7). The content of AgI in AgI/ZrO 2 catalyst is similar to that in AgI/Mg 2 Al 1 LDH (Supplementary Table 2, entries 1 and 2). These results indicate that there is a synergistic effect of AgI NPs and Mg 2 Al 1 LDH in the photocatalytic system. Furthermore, the addition of Na 2 CO 3 , which is the base used for preparing Mg 2 Al 1 LDH, to the system using AgI/ZrO 2 catalyst did not significantly increase the biphenyl yield (Table 1 , entry 8). This indicates that CO 3 2- anions made little contribution to the catalytic performance under these conditions. The photocatalytic system demonstrated a notable tolerance towards moisture and atmospheric oxygen, as evidenced by achievement of a moderate yield of biphenyl (56.4%, Entry 9 in Table 1 ) under an air atmosphere. Standard reaction conditions: iodobenzene (0.1 mmol), benzene (1 mL), catalyst (50 mg), Ar atmosphere, irradiated under a 400 nm wavelength LED light with 0.1 W cm -2 of intensity, the reaction was conducted at 60℃ for 20 h. Yields are determined by GC analysis. We also monitored the formation of biphenyl during the direct arylation process using the AgI/Mg 2 Al 1 LDH photocatalyst. The results, summarised in Supplementary Fig. 4a, show that the yield of biphenyl reaches 80% within the first 10 h, with 90% yield reached over 20 h. Additionally, as illustrated in Supplementary Fig. 4b, the increase in biphenyl yield does not follow a linear trend with addition of more catalyst, presumably due to screening effects within the photocatalytic system 20 . Broad substrate scope . The practicality of the AgI/Mg 2 Al 1 LDH photocatalyst in the direct arylation of arenes depends on the substrate and operation life in addition to the sustainability and environmental impact of all the products. The aryl iodides, contain electron-donating or electron-withdrawing groups, exhibited excellent reactivity towards benzene under irradiation of 400 nm light (Table 2 ). The corresponding products were obtained in good yield from 87–99%, while the reactions conducted in the dark showed negligible yields of target products. Moreover, the reactions between benzene and iodides containing heterocycles such as thiophene and pyridine afford the desired arylated heteroarenes with good yield (94% and 91%, 6–7 ), demonstrating a broad substrate scope for this photocatalytic system. It is noteworthy that iodobenzene possessing an electron-deficient nitrile substituent group exhibits a higher reactivity (99% yield) under the same conditions compared to that with an electron-donating methoxy group (91% yield), suggesting the involvement of a SET process in the reaction 9 . Importantly, direct arylation of inactive arenes beyond benzene with iodobenzene occurred using the photocatalytic system. As shown in Table 2 , good yields are obtained from arenes with substituent groups containing heteroatoms (74%-98%, 9–12 ), while moderate yields from arenes with hydrocarbon substituent group (27%-63%, 8, 13–16 ). Notably, no products related to benzylic activation were detected. This achievement is particularly challenging due to the significantly stronger C(sp 2 )-H bonds compared to the C(sp 3 )-H bond (by about 100 kJ mol − 1 ) 21 . The reaction involving toluene yielded three products (2-, 3-, and 4-methyl biphenyls) with a ratio of 62:24:14 ( 8 ), indicating potential involvement of radical intermediates in the pathway for the photocatalytic reaction 22,23 . When comparing the yields of biaryl products from the direct arylation of arenes with iodobenzene, we observed a trend of the reactant arenes: benzene > arenes with substituent groups containing heteroatoms > toluene > arenes with multiple or larger hydrocarbon substituent. The large difference in the yields reflects the heavy dependence of the arylation on the reaction between the aryl radicals and the arene. Significantly higher yields are attained from the arenes with heteroatom substituent groups compared to those with alkyl substituent groups. Reaction conditions: aryl iodide (0.1 mmol), arene (1 mL), AgI/Mg 2 Al 1 LDH catalyst (50 mg), Ar atmosphere, irradiated under a 400 nm wavelength LED light. Yields were determined by GC analysis. a Reaction was conducted at 60℃ for 20 h, and the light intensity was 0.1 W cm -2 . b Reaction was conducted at 80℃ for 20 h, and the light intensity was 0.1 W cm -2 . c Reaction was conducted at 60℃ for 48 h, and the light intensity was 0.1 W cm -2 . d Reaction was conducted at 85℃ for 48 h, and the light intensity was 0.2 W cm -2 . To enhance the yield of the products 1 – 7 , the catalyst was filtered out at half of the reaction time during photocatalysis, followed by the addition of 50 mg of fresh catalyst to the liquid mixture. e Reaction was conducted at 60℃ for 20 h, and the light intensity was 0.2 W cm -2 . f Reaction was conducted at 60℃ for 20 h, and the light intensity was 0.1 W cm -2 . Iodobenzene was used in producing the products 8–16 . The surface OH groups of LDH are consumed during the photocatalytic reaction to generated •OH radicals. Supplementary Fig. 5 illustrates the impact of this consumption on the biphenyl yield when using a used AgI/Mg 2 Al 1 LDH photocatalyst under 400 nm irradiation, showing a decrease from 80–48%. However, a simple regeneration method (as detailed in the Method section) involving the addition of Na 2 CO 3 aqueous solution to a sealed flask, followed by heating to 85°C with stirring for 1 hour, can effectively restore the product yield. X-ray photoelectron spectroscopy (XPS) and Zeta Potential analysis presented in Supplementary Fig. 6 indicate that the surface hydroxyl groups of LDH can be recovered by regeneration. The catalyst can be recycled multiple times. The impact of light intensity and wavelength on the catalytic performance of AgI/Mg 2 Al 1 LDH photocatalyst. Figures 2 a and 2 b demonstrate the sensitivity of the AgI/Mg 2 Al 1 LDH catalyst's performance to intensity and wavelength of the irradiation, in the context of direct benzene arylation. Higher irradiation intensity leads to increased biphenyl yield. Notably, even under the conditions of extremely low light intensity, as low as 0.01 W cm -2 , the catalyst achieves a substantial 40% biphenyl yield, indicating its efficiency. It exhibits an apparent quantum yield (AQY) of 3.3% at this low light intensity, highlighting its exceptional utilization of visible light for catalysis. Figure 2 b presents an action spectrum, which provides valuable insight into the impact of irradiation wavelength on the direct arylation using the AgI/Mg 2 Al 1 LDH catalyst. The determination of AQY involves normalising the number of target molecules generated to the incident photons within the photocatalytic system 24 . Notably, irradiation by LED light centred at 350 nm and 400 nm results in substantially elevated AQY values, while longer wavelengths (550 and 660 nm) yield negligible AQYs. This clear dependence of AQYs on the irradiation wavelengths aligns with the light absorption characteristics exhibited by the AgI/Mg 2 Al 1 LDH catalyst. This behaviour contrasts with prior research, specifically direct photolysis, where the optimal yield was achieved using deep-UV light, but a significant decrease was observed at a longer wavelength. 25 It is evident that the primary driver of the reaction is the light absorbed by AgI nanoparticles, given that the Mg 2 Al 1 LDH support has minimal absorption at wavelengths longer than 350 nm (Fig. 2 b). Consequently, the AgI nanoparticles effectively function as efficient light absorbers for the catalyst system. Photo-generated hydroxyl radicals to facilitate direct arylation. The remarkable observation that a relatively modest amount of absorbed light energy leads to a substantial biphenyl yield implies the existence of low activation energy barriers within the photocatalytic reaction pathway. An in-depth kinetic study on the reaction between iodobenzene and benzene over AgI/Mg 2 Al 1 LDH under light irradiation reveals a first-order kinetics relationship with respect to the substrate, as depicted in Supplementary Fig. 7. Employing the Arrhenius equation (raw data shown in Fig. 3 a) we estimate an apparent activation energy of 46.3 kJ mol -1 for the photocatalytic reaction, which is significantly lower than 61.7 kJ mol -1 reported for a thermally driven system 6 (as shown in Fig. 3 b). Comparison of the relative amounts of surface OH groups in the AgI/Mg 2 Al 1 LDH catalyst before and after the photocatalytic reaction, as determined from the XPS spectra of O 1s, reveals a noticeable reduction in surface hydroxyl groups during the course of the photocatalytic reaction. Within the XPS spectra (Figs. 4 a and 4 b), the O 1s peaks at 532.7, 531.4, and 530.2 eV correspond to various oxygen species in the catalyst, including metal-hydroxyl (M-OH), metal oxide (M-O), and carbonate (CO 3 2- ) of LDH, respectively 26–28 . It is noteworthy that the concentration of M-OH on the catalyst after the photocatalytic reaction is significantly lower than that on the pristine catalyst. This decline can be attributed to the transformation of surface hydroxyl groups of LDH into •OH radicals, which are consumed during the reaction, leading to the formation of sites with unpaired electron confined within oxygen vacancies. As depicted in Fig. 4 c the electron paramagnetic resonance (EPR) analysis of the AgI/Mg 2 Al 1 LDH catalyst before and after photocatalysis exhibits a prominent EPR signal characterized by a g factor of 2.004 in the used catalyst, unequivocally indicating the existence of such sites 29 . Consequently, it can be inferred that surface OH groups are consumed in the process, generating •OH radicals. The activation energy barriers in the reaction mediated by •OH radicals are notably low. The recycling experiments regenerated the surface OH groups. The •OH radicals are regarded essential for oxidation in photocatalysis 30 , being the main reactant for various fundamental processes such as SEO, double bond addition, and hydrogen abstraction 31 . Considering both SEO and hydrogen abstraction steps are involved in direct C-H arylation 9 , which •OH radicals can participate in and facilitate, LDH can serve as a reservoir for hydroxyl groups, supplying them internally to produce •OH radicals that drive the reaction without the need for any peroxide addition. This is supported by fact that Mg 2 Al 1 LDH has the maximum crystallite size, and the AgI/Mg 2 Al 1 LDH catalyst exhibits the highest biphenyl yield (Supplementary Table 3 and Supplementary Fig. 8a). The size of crystallite is directly proportional to the quantity of surface hydroxyl groups on LDH 32,33 . In contrast, other factors, such as their AgI NPs contents (represented by the silver content in Supplementary Table 2) and specific surface areas (Supplementary Fig. 9), have a lesser impact on the performance of AgI/Mg x Al y LDH photocatalysts. The presence of •OH radicals is substantiated by multiple experimental observations. Terephthalic acid (H 2 BDC) was employed as a fluorescent probe to detect •OH radicals within our photocatalytic system, following a well-documented procedure 34 . In the fluorescent experiment, a characteristic fluorescence signal at 425 nm is prominently observed (see Fig. 4 d), while the absence of any the following components: AgI NPs, Mg 2 Al 1 LDH support, H 2 BDC and irradiation, yields no discernible fluorescence peaks. The result provides direct evidence that hydroxyl can be converted to •OH radicals in the photocatalytic system. Besides, the concentration of •OH radicals varies in the order of AgI/LDH > AgI/ZrO 2 > LDH, which is consistent with their catalytic activities shown in Table 1 . The results not only provide compelling evidence for the generation of •OH radicals from LDH but also imply that the illuminated AgI NPs play a pivotal role in driving this process. The excellent performance of AgI/Mg 2 Al 1 LDH catalyst under dry conditions, as demonstrated in Table 1 , entry 1 (in the absence of moisture), further underscores the origins of •OH radicals from surface OH groups. Furthermore, the photocatalytic reaction was conducted in the presence of isopropanol (IPA) as a •OH scavenger 35 . As depicted in Fig. 4 a, the yield of biphenyl decreased from 80–57% upon addition of 1 mmol of IPA into the reaction (2nd column). These findings point to the indispensable role played by •OH radicals in the photocatalysis. In the literature, it has been reported that UV irradiation on a composite of TiO 2 and MgAl-LDH, as well as MgAl-LDH with partial Ni 2+ substitution for Mg 2+ , and zinc-tin (ZnSn)-LDH can induce the generation of •OH radicals, which can effectively eliminate environmental pollutants 36–38 . In this study, we have discovered that the visible light irradiation can induce the conversion of surface hydroxyl groups within MgAl-LDH into reactive •OH radicals, facilitating direct C-H arylation. Using visible light instead of UV irradiation enhances solar energy utilization, reduces the likelihood of generating undesired byproduct, and minimises potential safety risks. Therefore, this finding has practical implications for future sustainable chemical synthesis. The contribution of photo-generated charge carriers in the photocatalysis. As shown in Fig. 5 a, the use of KI as an effective quencher for surface-bound free radicals and a hole trapper 39 (3rd column) caused a sharp decline in yield from 80–40%, while adding Mn(Ac) 3 as an electron scavenger 40 leads to a moderate decrease in the yield (4th column). This indicates that photogenerated holes and the resultant surface-bound free radicals that form are critical for achieving high biphenyl yield. Energy level alignment of the catalyst components and reactant was investigated to understand the transport of photo-induced charge carriers. The LUMO energy level of iodobenzene was measured using cyclic voltammetry with Ag/AgCl as the reference electrode and Fc/Fc + couple used as the internal standard (Fig. 5 b). The E LUMO value of iodobenzene is calculated to be -4.32 eV relative to vacuum or -0.12 eV relative to the standard hydrogen electrode (SHE) 41 , as depicted in Fig. 5 d. Valence band X-ray photoelectron spectroscopy (VB-XPS) method was used to determine the potentials at the valence band maximum (VBM) edge of the Mg 2 Al 1 LDH and AgI, which were found to be 2.10 eV and 2.30 eV, respectively (Fig. 5 c). The E VB , SHE of Mg 2 Al 1 LDH and AgI are 1.96 and 2.16 eV, respectively (Fig. 5 d). Band gap energies (E g ) of 5.37 eV for Mg 2 Al 1 LDH and 2.85 eV for AgI were obtained from their Tauc plots, (Supplementary Fig. 10). Thus, the corresponding conduction band maximum (CBM) potentials for Mg 2 Al 1 LDH and AgI are − 3.41 and − 0.69 eV, respectively (Fig. 5 d). This data revealed that AgI NPs efficiently absorb visible light and generate electron-hole pairs. The electrons then transfer to the LUMO of the iodobenzene reactant, activating it, while the holes are captured by the surface hydroxyl groups of Mg 2 Al 1 LDH, generating •OH radicals that are crucial for the direct arylation of benzene (see discussion in Fig. 4 ). This is consistent with the result in Fig. 5 a, where the hole scavengers substantially inhibit the biphenyl yield. The influence of LDH support on the efficiency of •OH radical generation was also explored by comparing the AgI/Zn 2 Al 1 LDH catalyst with AgI/Mg 2 Al 1 LDH catalyst. The VBM difference between AgI to Zn 2 Al 1 LDH is smaller than that between AgI and Mg 2 Al 1 LDH 42 , as discussed in Supplementary Fig. 11. This leads to a slower transfer rate of photo-induced holes in AgI/Zn 2 Al 1 LDH, which, in turn, affects the biphenyl yield of this catalyst (Fig. 5 a). Mechanism of the photocatalytic system . Combining the discussions presented in Figs. 4 and 5 above, it can be concluded that the photoinduced charge carriers, •OH radicals, and oxygen vacancies play crucial roles in reducing the energy requirement for the direct C-H arylation. To confirm the conversion of iodobenzene to benzene radical, induced by the photo-excited electrons from AgI, we used time-dependent ATR-FTIR spectroscopy during visible light irradiation. Specifically, we conducted experiments using the AgI/Mg 2 Al 1 LDH catalyst and 4-chloroiodobenzene reactant as a representative sample, because the characteristic peaks of the catalyst and iodobenzene overlap. As displayed in Fig. 6 a, the intensity of the C-I bond vibration at approximately 804 cm − 1 consistently diminishes over time, while the signals originating from M-O bond at 551 cm − 1 remain unchanged. An intriguing observation is a slight red-shift at around 651 cm − 1 , which corresponds to M-OH bond in the catalyst and can be attributed to the lattice distortion resulting from increased defects, such as oxygen vacancies, within the LDH support 44 . It is important to note that our comparative analysis revealed no significant spectral changes when testing each individual sample (as demonstrated in Supplementary Fig. 12). Of particular note is the absence of any homo-coupling side products arising from the corresponding aryl halides. The remarkable selectivity towards the desired cross-coupling product can be attributed to the low concentration of aryl iodide in the system (0.1 M, molar ratio of arene to aryl iodide is about 100). To confirm this, we deliberately increased the concentration of aryl iodide in the reaction system, as evidenced in Supplementary Fig. 13, resulting in the detection of homo-coupling products. The labelling experiment is a commonly employed technique to determine whether C-H bond cleavage is the rate-determining step 9,12,45 . We determined a kinetic isotope effect (KIE) value of 1.36 through 1 H NMR analysis (see Supplementary Fig. 14), which slightly exceeds previously reported values 9,12 . This result implies that C-H activation is not the rate-determining step in the direct C-H arylation and lends support the involvement of •OH radicals in the C-H activation. Nevertheless, it is important to note that the rate-limiting step can vary when different arenes are used as coupling partners. For instance, under identical reaction conditions, arenes with electron-withdrawing groups ( 9–12 , Table 2 ) coupled more efficiently with iodobenzene than those containing electron-donating groups ( 6 , and 13–16 , Table 2 ), highlighting the importance of C-H bond acidity in the arylation process 10,12 . The stronger electrophilic properties of •OH radicals play a crucial role in facilitating C-H bond activation and benefiting the arylation reaction compared to species generated in other catalytic systems 46,47 . Furthermore, our experiment involving an equimolar mixture of benzene and d 6 -benzene with iodobenzene resulted in a significantly lower yield of deuterated product (78%), further substantiating the above analysis. From a green chemistry perspective, radical-mediated C-H bond activation prove to be superior to transition-metal-based reactions 48 . Building upon the preceding analysis, we propose a tentative reaction mechanism for direct C-H arylation on the AgI/Mg 2 Al 1 LDH catalyst under irradiation, as depicted in Fig. 6 b. Initially, photo-excited electron from AgI NPs inject into the LUMO of aryl iodide, leading to dehalogenation and the formation of an aryl radical and iodide ion (Steps I and II). Simultaneously, the positively charged holes migrate to the LDH support, where they react with surface hydroxyl groups, generating •OH radicals while vacating surface sites to create oxygen vacancies when acquiring electrons from I − ions (Steps II and III). This effectively prevents electron-hole recombination on the AgI NPs. Subsequently, the aryl radical reacts with a neighbouring arene molecule to form a biaryl radical, favoured due to its free-radical nature. Given the high molar ratio of benzene to aryl iodide (over 100) and the increased stability of a larger conjugated radical, it is reasonable to anticipate the prevalence of biaryl radical product in the reaction system compared to the aryl radical. The process of generating •OH radicals by hole transfer, as validated in Figs. 4 d and 6 a, is counterbalanced by a SET process (C-I bond cleavage). Although it has been reported that •OH radicals can directly react with benzene, this reaction is reversible, and the •OH-benzene adduct is unstable, decomposes into •OH and benzene at temperatures exceeding 330 K 49 . Furthermore, our catalytic system was deoxygenated prior to the reaction, contrary to the conventional requirement of an oxygen atmosphere for the reaction between •OH radicals and benzene 50 . Consequently, •OH radicals abstract a hydrogen from the biaryl radical, yielding water as a byproduct, as confirmed by the water measurement test (Supplementary Table 4). Significantly, this C-H bond cleavage involved in hydrogen abstraction is a radical reaction characterized by a low activation energy barrier. Concurrently, iodide ions are oxidised at sites where •OH radicals are generated, yielding iodine and the oxygen vacancies with two electrons. It is worth noting that while molecular iodine is a recognized catalyst for many organic reactions, 51 adding a small amount of I 2 (0.1 equiv.) can completely inhibit the photocatalytic reaction. So I 2 ’s involvement in the reaction mechanism is unlikely. Moreover, the surface structure of the AgI/Mg 2 Al 1 LDH catalyst can be restored by a regeneration process (Steps III and I). In summary, the synergistic combination of AgI NPs and Mg x Al y LDH with an appropriate x/y ratio proves to be highly effective in catalysing direct C-H arylation under mild conditions. This process stands out for its elimination of the need for additives and bases, and its potential to be driven solely by solar irradiation. The excitation of electrons and holes induced by the light absorption by AgI NPs leads to the conversion of aryl halides into aryl radicals and the generation of •OH radicals on the LDH surface, which abstract hydrogen atoms from C-H bonds. Crucially, the energy alignment within the photocatalysis system allows the promotion of aryl halides conversion into aryl radicals by the excited electrons, while the holes interact with the surface hydroxyl groups on the LDH, yielding •OH radicals capable of abstracting hydrogen atoms from C-H bonds (involving the single electron oxidation of biaryl radicals). These concurrent processes are characterized by both low activation energy barriers due to their radical nature and effectively hinder electron-hole recombination within AgI nanoparticles. Consequently, the photocatalytic direct C-H arylation can proceed efficiently under visible light or solar irradiation without the need for a base and other additives. The main byproducts, water and iodine, can be conveniently separated or recovered. This synthesis approach impeccably fulfils the requirement for a sustainable future 18 , encompassing efficiency, safety, solar energy utilisation, and environmental friendliness. It opens up new avenues for catalysing C-H arylation via an eco-friendly process and the development of highly efficient catalytic systems. Methods Chemicals. The chemicals were purchased from commercial suppliers and used as provided. The supplier and purity of the chemicals are shown in the brackets. Iodobenzene (Adamas, 99%), 4-iodobenzene (Adamas, > 98%), 4-iodoanisole (Adamas, 99%), 1-chloro-4-iodobenzene (Adamas, > 98%), 4-iodobenzotrifluoride (Adamas, > 98%), 4-iodobenzonitrile (Adamas, > 98%), 3-iodothiophene (Adamas, > 98%), 3-iodopyridine (Adamas, > 98%), benzene (Greagent, ≥ 99.5%), benzene-d 6 (Adamas, 99.5%), biphenyl (Adamas, ≥ 99%), toluene (SCR, ≥ 99.5%), chlorobenzene (Greagent, ≥ 99.5%), diphenyl ether (Adamas, > 99%), acetophenone (Adamas, > 99%), 1,2-dichlorobenzene (Macklin, 99%), 1,3,5-trimethylbenzene (Macklin, 97%), m-xylene (Greagent, ≥ 99%), p-xylene (Greagent, ≥ 99%), ethylenzene (Adamas, 99%), sodium carbonate (Greagent, ≥ 99.8%), methanol (Greagent, ≥ 99.5%), sodium hydroxide (Greagent, ≥ 98%), sodium iodide (Adamas, 99.99%), potassium iodide (Adamas, 99%), terephthalic acid (Adamas, 99%), silver(I) nitrate (SCR, ≥ 99.8%), aluminium(III) nitrate nonahydrate (Greagent, ≥ 99.0%), manganese(III) acetate dihydrate (Adamas, 98%), zinc(II) nitrate hexahydrate (Keshi, ≥ 99.0%), ferrocene (TCI, 98.0%), tetra-n-butylammonium hexafluorophosphate ( n -Bu 4 NPF 6 , Adamas, ≥ 99%), acetonitrile (Greagent, ≥ 99.0%), isopropanol (TCI, 99.5%), Ar (> 99.999%). Catalyst preparation. The Mg x Al y LDH with various x/y ratios, Ni 2 Al 1 LDH, and Zn 2 Al 1 LDH were produced using a coprecipitation method. The procedure for preparing Mg 2 Al 1 LDH is shown below as a typical example. 0.0133 mol of Mg(NO 3 ) 2 6H 2 O and 0.0067 mol of Al(NO 3 ) 3 9H 2 O were added into 20 mL of deionized water to form solution A. Meanwhile, 0.02 mol of Na 2 CO 3 were dissolved in 30 mL of deionized water to form solution B. Solutions A and B were dropwise added simultaneously into a flask containing 15 mL of deionized water at 40℃ using an injection pump (with an injection rate of 2 mL min − 1 for A and 3 mL min − 1 for B). After vigorous stirring for 1 h, a 2 M NaOH aqueous solution was added dropwise to the above suspension until the final pH reached 10. The slurry was then sealed and heated to 85℃ with stirring for 3 h, followed by transfer into an oven where it was kept at 80℃ for 16 h. The resulting gel was washed with deionized water by centrifugation (at 4000 rpm) until the washings reached a pH of 7. The solid was subsequently dried in an oven at 80℃ for 48 h and ground in an agate mortar to pass through a sieve with a mesh size of 40. This process yielded approximately 1.4 g of white powder. LDHs with different metal ratios were prepared using different quantities of Mg(NO 3 ) 2 6H 2 O and Al(NO 3 ) 3 9H 2 O in a total feeding amount of 0.02 mol. AgI/LDH catalyst was prepared as follows: 200 mg of LDH powder was placed in a 100 mL beaker. Then, 18.5 mL of AgNO 3 aqueous solution (0.01 M) was added into the beaker. After sonication for 5 min, 1 mL of NaI aqueous solution (0.222 M) was dropwise added over 1 min with vigorously stirring. After of stirring, the suspension was stirred at room temperature for 24 h and then washed three times with deionized water by centrifugation (5000 rpm). Finally, it was dried at 60℃ under vacuum for 20 h. The light absorption properties of as-prepared samples are shown in Supplementary Fig. 16. Catalyst regeneration. 100 mg of the used catalyst (eg. AgI/Mg 2 Al 1 LDH) was mixed with 30 mL of deionized water in a flask and sonicated for 5 min. Then, 60 mg of Na 2 CO 3 was added to the flask, which was sealed and heated to 85℃ with stirring for 1 h. After cooling down to room temperature, the sample was washed three times with deionized water by centrifugation at 5000 rpm and dried at 60℃ under vacuum for 20 h. Photocatalytic reactions and product analysis. A 10 mL glass tube. which does not show obvious light absorption at wavelengths beyond 350 nm was used as the reaction vessel. The catalyst, reactants and a stirrer were introduced into the tube and purged with argon (100 mL min − 1 ) for 1min. before being sealed with a cap. Subsequently, the tube was placed on a magnetic stirrer and exposed to an LED light of a specific wavelength such as 400 nm while stirring at 600 rpm and a controlled temperature. The mixture was filtered through a Millipore filter (pore size 0.22 µm) after the reaction to remove the catalysts. The products in the filtrate were analysed using a Panna GC-1949 gas chromatography with an AB-5 column. An Agilent 7890A/5975C gas chromatography-mass spectrometer was used for product identification (Supplementary Figs. 17–32). All product concentrations were calibrated with an external standard method. In this photocatalytic system, yield is defined as the ratio between the amount of final product (biaryls) and added reactant (aryl iodide). The AQY value is calculated by normalizing the amount of products formed under irradiation ( N light ) to the number of photons ( n ), with subtraction of the number of the target product formed in the dark ( N dark ), as shown in the equation: $$\text{A}\text{Q}\text{Y}=\frac{{N}_{light}-{N}_{dark}}{n}\times 100\%$$ Catalyst Characterization. XRD patterns of the catalysts were recorded on a MiniFlex600-C from Rigaku Co, operated at 40 kV and 15 mA with CuKα radiation (λ = 1.541862 Å). The data were collected with a resolution of 0.01° (2θ). The morphology and elemental mapping of the catalysts were characterized using a JEOL JEM-F200 transmission electron microscope (TEM) operating at 200 kV. The DR UV-vis spectra of the samples were recorded by a Shimadzu UV-3600 plus spectrophotometer. X-ray photoelectron spectroscopy (XPS) measurements were carried out using a Shimadzu/Krayos AXIS Ultra DLD instrument. The fluorescence spectra were recorded on a F7000 FL spectrophotometer using quartz cuvettes loaded with 1 mL of sample, an excitation wavelength of 315 nm was used, and the emission was measured from 350 to 600 nm. The electron paramagnetic resonance (EPR) spectra were measured using a Bruker EMXnano spectrometer, which operated at a field modulation frequency of 100 kHz in the X-band mode. The nitrogen adsorption data were collected at -196℃ on a JW-BK2000 analyser (Beijing Jingwei Gaobo Science and Technology Co., Ltd., China) and the specific surface areas of the catalysts were calculated using the Brauner-Emmet-Teller (BET) method. The metal content in catalysts was obtained by performing inductively coupled plasma optical emission spectrometry (ICP-OES) on an Agilent 720ES. The cyclic voltammogram curves were recorded on an Autolab PGSTAT302N electrochemical workstation (Metrohm, Netherland). A three-electrode system was used, consisting of a working electrode (platinum thin-film), a counter electrode (another platinum thin-film), and an Ag/AgCl reference electrode. The analysis was conducted in an acetonitrile solution of n -Bu 4 NPF 6 (0.1 M) within the range from − 0.5 to + 1.5 V at a scan rate of 50 mV s − 1 . Absorption spectra of the liquid samples were measured using a LabTech BlueStarA UV-vis spectrophotometer with a 1 cm quartz cell. The Nuclear Magnetic Resonance (NMR) spectrum was measured using a Bruker 400 MHz spectrometer. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra were collected with a PerkinElmer Spectrum Two spectrometer. The water content measurements were carried out on an AKF-2010V Karl Fisher moisture titrator at an oven temperature of 100℃. The zeta potential measurements were recorded using a Microtrac nanotrac wave II instrument with the samples dispersed in deionized water at a concentration of 1 mg mL − 1 . The light intensity was measured by a probe coupled to a digital optical power meter (S401C, PM100D, Thorlabs). The electrochemical impedance spectroscopy (EIS) analysis was carried out in the frequency range from 10 kHz to 0.1 Hz at open circuit potential with an ac perturbation of 10 mV. Declarations Author contributions Competing interests : The authors declare no competing interests. Acknowledgements We acknowledge financial support from the National Natural Science Foundation of China (No. 22002038), the Natural Science Foundation of Hunan Province (No. 2023JJ40120), the Science and Technology Innovation Program of Hunan Province (No. 2023RC3016) and the Australian Research Council for Discovery Project DP210103357. References Hassan J, Sévignon M, Gozzi C, Schulz E, Lemaire M (2002) Aryl-aryl bond formation one century after the discovery of the ullmann reaction. Chem Rev 102:1359–1470 Yet L (2018) Privileged structures in drug discovery . 83–154 Bowman WR, Storey JM (2007) D. 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Bioorgan Med Chem 10:2283–2290 Wu F et al (2020) Making base-assisted C-H bond activation by Cp*Co(III) effective: a noncovalent interaction-inclusive theoretical insight and experimental validation. Organometallics 39:2609–2629 Li JJ (2015) CH bond activation in organic synthesis. CRC press He YZ, Mallard WG, Tsang W (1988) Kinetics of hydrogen and hydroxyl radical attack on phenol at high temperatures. J Phys Chem 92:2196–2201 Eberhardt MK (1981) Reaction of benzene radical cation with water. Evidence for the reversibility of hydroxyl radical addition to benzene. J Am Chem Soc 103:3876–3878 Breugst M, von der Heiden D (2018) Mechanisms in iodine catalysis. Chem -Eur J 24:9187–9199 Tables Table 1 and 2 are available in the Supplementary Files section. Schemes Scheme 1 is available in the Supplementary Files section Additional Declarations There is NO Competing Interest. Supplementary Files CHarylationSINat.Sustain.submittedversion.docx Scheme1.png Scheme 1. Direct arylation of inactive arenes with haloarenes using AgI/Mg 2 Al 1 LDH as an efficient visible light photocatalyst. Mg 2 Al 1 LDH exhibits layered hydroxide sheets consisting of octahedrally coordinated Mg 2+ and Al 3+ ions surrounded by hydroxyl groups. These hydroxide sheets possess positive charges, which are balanced by the presence of CO 3 2- anions between the host layers and on the external surface. Tables.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3747453","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":266011130,"identity":"5ee5dc20-12e5-471f-b073-d5fef2e25ec2","order_by":0,"name":"Pengfei Han","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8ElEQVRIiWNgGAWjYLCCCgaJBAYG5mMQ3gFitJwBa2FLI0kLA1ALjxlxWszZew+/OFBhkcc/u+fb48I2Bjm+GwmMnwvwaLHsOZdmceCMRLHEnbPbjWe2MRhL3khglp6BR4vBjRwz449tEokNN3K3SfO2MSRuuJHAxsyDT8v9N2YGB/9JJM6/kfMMpKWesJYbPMYPDjZIAA3PYQNpSTAgpMWyJ8eM4cAxicSNN9LMpHnOSRjOPPOwWRqfFnP2M8YfDtTUJc67kfxMmqfMRp7vePLBz3gdBoxCCSQ+iM3YgEcDWAvzB7wqRsEoGAWjYBQAABvoT4aJN9TjAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-9482-7903","institution":"Changsha Institute of Technology","correspondingAuthor":true,"prefix":"","firstName":"Pengfei","middleName":"","lastName":"Han","suffix":""},{"id":266011131,"identity":"a2230251-f124-48c3-8b69-921691b9eeb6","order_by":1,"name":"Eric Waclawik","email":"","orcid":"","institution":"Queensland University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Eric","middleName":"","lastName":"Waclawik","suffix":""},{"id":266011132,"identity":"e8ad418e-9888-49c0-a146-259e393217a3","order_by":2,"name":"Steven Bottle","email":"","orcid":"https://orcid.org/0000-0003-0436-2044","institution":"Queensland University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Steven","middleName":"","lastName":"Bottle","suffix":""},{"id":266011133,"identity":"bdf0cb0f-0564-4640-a0bb-719c0b5a0556","order_by":3,"name":"Xuheng Yang","email":"","orcid":"","institution":"Changsha Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Xuheng","middleName":"","lastName":"Yang","suffix":""},{"id":266011134,"identity":"1eab7d46-5e78-421c-8dc9-065c22e2a3cd","order_by":4,"name":"Jianfang Wang","email":"","orcid":"","institution":"Changsha Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Jianfang","middleName":"","lastName":"Wang","suffix":""},{"id":266011135,"identity":"5d5a00a6-e681-4cc3-81d9-8c4a4b78776b","order_by":5,"name":"Cheng-an Tao","email":"","orcid":"","institution":"Changsha Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Cheng-an","middleName":"","lastName":"Tao","suffix":""},{"id":266011136,"identity":"dd816357-d9d2-4448-a067-8cecfb6e8310","order_by":6,"name":"Huai Yong Zhu","email":"","orcid":"https://orcid.org/0000-0002-1790-1599","institution":"Queensland University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Huai","middleName":"Yong","lastName":"Zhu","suffix":""}],"badges":[],"createdAt":"2023-12-13 08:49:00","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3747453/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3747453/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":49452431,"identity":"0cb6a404-ab56-4902-be12-57eef27b1a82","added_by":"auto","created_at":"2024-01-11 05:16:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":856493,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePhotograph of the photoreaction system and characterisation of the photocatalyst. a\u003c/strong\u003e Photographs of the catalyst, the reactant, and the product. \u003cstrong\u003eb\u003c/strong\u003e The XRD patterns of the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst. \u003cstrong\u003ec\u003c/strong\u003e HADDF-STEM and the corresponding elemental mappings of the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst. The white islands in the HADDF-STEM image are AgI particles as the elemental mappings shown. \u003cstrong\u003ed\u003c/strong\u003e,\u003cstrong\u003e \u003c/strong\u003eTEM image of the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst. The scale bars represent 1 μM. The TEM images in \u003cstrong\u003ec\u003c/strong\u003e and \u003cstrong\u003ed\u003c/strong\u003e indicate the structure of AgI nanoparticles on LDH support.\u003cstrong\u003e e\u003c/strong\u003e,\u003cstrong\u003e f\u003c/strong\u003e HRTEM images of the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst, showing the Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH and AgI lattice features, respectively.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3747453/v1/3f189d708fa6f8eb77708ea7.png"},{"id":49452432,"identity":"f1cbbe64-4b07-41e2-8686-edc664095f9c","added_by":"auto","created_at":"2024-01-11 05:16:24","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":186909,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe light intensity and wavelength-dependent photocatalytic performance of AgI/Mg\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eAl\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eLDH catalyst. a \u003c/strong\u003eThe dependence of the catalytic performance of the light intensity. The coloured diamond-shaped symbols associated with biphenyl yield were obtained from three independent tests, the solid lines represent the averaged data and the red dashed line is guide for the eye. \u003cstrong\u003eb\u003c/strong\u003e UV-Vis spectra of the catalyst and Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003e-LDH support, and dependence of the photocatalyst’s activity for direct arylation of benzene with iodobenzene on the light irradiation wavelength. The light intensity was 0.1 W cm\u003csup\u003e-2\u003c/sup\u003e for all wavelengths. Error bars associated with AQY are the standard error of three sets of unique measurements. Ultraviolet (UV) and light emission diode (LED) lamps with four peak wavelengths (350±5 nm, 400±5 nm, 450±5 nm, 550±5 nm, 660±5 nm) were used to drive the reaction.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3747453/v1/132d138e4d8a2ed71db94903.png"},{"id":49452494,"identity":"a7cacf80-522b-46ea-8672-32884eb553c7","added_by":"auto","created_at":"2024-01-11 05:24:24","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":216354,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe kinetic study of direct arylation of benzene with iodobenzene. a \u003c/strong\u003eThe kinetic study of the reaction under irradiation using AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst. Reaction conditions: iodobenzene (0.1 mmol), benzene (1 mL), AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst (50 mg), Ar atmosphere, irradiated under a 400 nm wavelength LED light at 0.1 W cm\u003csup\u003e-2 \u003c/sup\u003eof intensity. \u003cstrong\u003eb \u003c/strong\u003eThe comparison of the calculated activation energy and that in a previous reference\u003csup\u003e6\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3747453/v1/46d7cc6bc3ddc68449875628.png"},{"id":49452433,"identity":"0800e387-19fd-4cd6-8e3c-90a8052c195e","added_by":"auto","created_at":"2024-01-11 05:16:24","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":332917,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIdentification of photo-generated hydroxyl radicals in AgI/Mg\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eAl\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ey\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eLDH photocatalyst for direct arylation. a and b \u003c/strong\u003eO 1s spectra of AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH photocatalyst before and after the arylation reaction. \u003cstrong\u003ec \u003c/strong\u003eEPR spectra of AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH photocatalyst before and after the arylation reaction. \u003cstrong\u003ed\u003c/strong\u003e Fluorescence spectra of different reaction systems: AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH+terephthalic acid (H\u003csub\u003e2\u003c/sub\u003eBDC)+irradiation, AgI/ZrO\u003csub\u003e2\u003c/sub\u003e+H\u003csub\u003e2\u003c/sub\u003eBDC+irradiation, Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH+H\u003csub\u003e2\u003c/sub\u003eBDC+irradiation, H\u003csub\u003e2\u003c/sub\u003eBDC+irradiation, AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH+H\u003csub\u003e2\u003c/sub\u003eBDC+heating, AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003e-LDH+irradiation.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3747453/v1/7d9246aeb64c1635278dee1a.png"},{"id":49452436,"identity":"135c837c-1db1-4ddd-9810-2e51d9db3339","added_by":"auto","created_at":"2024-01-11 05:16:24","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":273163,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffects of the addition of various scavengers and the support on the photocatalysis, and the energy alignment. a \u003c/strong\u003eSupport and additive effect on yield of biphenyl in the direct arylation of benzene by AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst. Error bars associated with biphenyl yield are the standard error of three sets of unique measurements. \u003cstrong\u003eb\u003c/strong\u003e Cyclic voltammogram (CV) of iodobenzene. The inset shows the CV of the ferrocene/ferrocenium (Fc/Fc\u003csup\u003e+\u003c/sup\u003e) couple used as an internal reference. \u003cstrong\u003ec \u003c/strong\u003eValence band XPS analysis of Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH support and AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst. \u003cstrong\u003ed\u003c/strong\u003e Energy positions of the conduction and valence band of AgI and Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH, and the LUMO energy level of the iodobenzene reactant The E\u003csub\u003eVB\u003c/sub\u003e,\u003csub\u003eSHE \u003c/sub\u003eof Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH and AgI was calculated using the equation: E\u003csub\u003eVB\u003c/sub\u003e,\u003csub\u003eSHE\u003c/sub\u003e = φ + E\u003csub\u003eVB\u003c/sub\u003e,\u003csub\u003eXPS \u003c/sub\u003e– 4.44, where φ is the work function of the instrument (4.3 eV)\u003csup\u003e43\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3747453/v1/9eae55b2f1815c5b80c70523.png"},{"id":49452712,"identity":"50fee5d2-4967-4b51-95a2-1051dfd11010","added_by":"auto","created_at":"2024-01-11 05:32:24","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":543941,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eProposed tentative photocatalysis mechanism. a \u003c/strong\u003eChanges with time of FTIR spectra of the mixture of aryl iodide and AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst, the setup can be found in Supplementary Fig. 15. \u003cstrong\u003eb\u003c/strong\u003e Proposed mechanism for the photocatalysis.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3747453/v1/3ef14d0f51be6b9d207d26fe.png"},{"id":49482791,"identity":"f9a5176a-9076-4130-b314-c15e2157bd92","added_by":"auto","created_at":"2024-01-11 15:33:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2696704,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3747453/v1/5e25f6f1-db66-4383-8c7e-2160e1ec992f.pdf"},{"id":49452437,"identity":"8a703af1-3665-400b-b80e-920cfc7d64dc","added_by":"auto","created_at":"2024-01-11 05:16:24","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":3811526,"visible":true,"origin":"","legend":"","description":"","filename":"CHarylationSINat.Sustain.submittedversion.docx","url":"https://assets-eu.researchsquare.com/files/rs-3747453/v1/ddbbb61dd3e7639fda41c224.docx"},{"id":49452439,"identity":"5511fcca-4e49-40a4-bda9-9d56f268a311","added_by":"auto","created_at":"2024-01-11 05:16:24","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":305197,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScheme 1. \u003c/strong\u003eDirect arylation of inactive arenes with haloarenes using AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH as an efficient visible light photocatalyst. Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH exhibits layered hydroxide sheets consisting of octahedrally coordinated Mg\u003csup\u003e2+\u003c/sup\u003e and Al\u003csup\u003e3+\u003c/sup\u003e ions surrounded by hydroxyl groups. These hydroxide sheets possess positive charges, which are balanced by the presence of CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e anions between the host layers and on the external surface.\u003c/p\u003e","description":"","filename":"Scheme1.png","url":"https://assets-eu.researchsquare.com/files/rs-3747453/v1/e31f2cc7048597820c3d20ef.png"},{"id":49452496,"identity":"0a29649d-4e57-484d-a3b6-7d62d2a7a950","added_by":"auto","created_at":"2024-01-11 05:24:24","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":146740,"visible":true,"origin":"","legend":"","description":"","filename":"Tables.docx","url":"https://assets-eu.researchsquare.com/files/rs-3747453/v1/28e8c6cba7f73d5354029e29.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Visible-Light Photocatalytic Direct Arylation of Arenes Using Silver Iodide Nanoparticles Supported on Magnesium-Aluminium Layered Double Hydroxide","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCarbon-carbon bond formation is a fundamental process in organic synthesis, where the creation of biaryl link between \u003cem\u003esp\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e-hybridized carbons is of particular significance, prevalent in natural products and pharmaceuticals, and in various fields of chemistry and biology\u003csup\u003e1\u003c/sup\u003e. Notably, biaryl motifs constitute essential substructures in many top-selling pharmaceuticals and are integral components of approximately 50% of all known drugs\u003csup\u003e2\u003c/sup\u003e. A promising approach for constructing biaryl frameworks involves the direct arylation of inactive arenes with haloarenes via aromatic C-H bond activation\u003csup\u003e3,4\u003c/sup\u003e. Various catalytic methods to achieve this have emerged, including the use of hetero-/homogeneous transition metal catalysts\u003csup\u003e5\u0026ndash;8\u003c/sup\u003e, organocatalysts\u003csup\u003e9\u0026ndash;12\u003c/sup\u003e, and strong reductants\u003csup\u003e13,14\u003c/sup\u003e. However, a common requirement in all these catalytic reactions is the use of substantial quantities of strong inorganic/organic bases, such as alkoxide, often in excess (ranging from 2 to 12 equivalents of reactant), to achieve productive catalysis. Additionally, toxic or hard-to-obtain additives/ligands are frequently employed, leading to the generation of stoichiometric waste by-products. High reaction temperatures (80\u0026ndash;155℃) in these direct arylation processes can result in undesired dehalogenation reactions and decreased product yields. Therefore, the development of a catalytic method using catalysts that operate efficiently to drive the reaction at moderate temperatures and avoid the need for ligands, base and the removal of hazardous chemicals during product isolation is highly desirable.\u003c/p\u003e \u003cp\u003eSeveral studies have identified three pivotal steps in the direct C-H arylation process: single electron transfer (SET) to convert aryl halides into aryl radicals, single electron oxidation (SEO) of biaryl radicals, and deprotonation of biaryl cations (or hydrogen abstraction as a single step instead of SEO and deprotonation)\u003csup\u003e8,9,15\u003c/sup\u003e. The use of a strong base has been deemed essential for obtaining biaryl product in high yields. For instance, substituting the commonly used base, potassium tert-butoxide (KO\u003cem\u003et\u003c/em\u003e-Bu), with other bases like NaO\u003cem\u003et\u003c/em\u003e-Bu, KOH, or K\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, resulted in only trace amounts or no desired product formation\u003csup\u003e5,12\u003c/sup\u003e. KOt-Bu plays a critical role in both SET and SEO processes as well as in deprotonation\u003csup\u003e15\u003c/sup\u003e. Although a photocatalyst composed of nickel (Ni) and gold nanoparticles (NPs) was successfully used for electron donation in the SET step\u003csup\u003e7\u003c/sup\u003e, Ni NPs are prone to oxidation and require substantial amounts of strong base to complete the catalytic cycle. The design of a catalytic system that enables direct C-H arylation without the need for a base or additive presents a formidable challenge, as it necessitates addressing all the three functions (i.e., SET, SEO, and deprotonation) in the catalyst itself.\u003c/p\u003e \u003cp\u003eHere, we present a novel photocatalytic process for direct C(\u003cem\u003esp\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e)-H arylation driven by visible-light, that gives high biaryl yield without the need for additional bases or additives. As displayed in Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, silver iodide (AgI) attached to a magnesium-aluminium layered double hydroxide (MgAl-LDH) intercalated with carbonate (CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e) serves as an efficient photocatalyst for the arylation at 60℃, a departure from our previous work that explored supported Ag nanoparticles (NPs) for C\u003csub\u003eα\u003c/sub\u003e(\u003cem\u003esp\u003c/em\u003e\u003csup\u003e3\u003c/sup\u003e)-H bond activation\u003csup\u003e16\u003c/sup\u003e. When supported Ag NPs were used to catalyse the direct C-H arylation, we observed a conversion of NPs into AgI, a key component of the actual catalyst.\u003c/p\u003e \u003cp\u003eThe catalyst design draws inspiration from prior studies that demonstrated that MgAl-LDH can serve as an alkaline support for photocatalysis, eliminating the need for additional base\u003csup\u003e17\u003c/sup\u003e. The hydroxyl groups and carbonate anions on the LDH surface can serve as basic sites, while the supported AgI NPs generate electron-hole pairs at the surface upon visible light irradiation\u003csup\u003e18,19\u003c/sup\u003e. The excited electrons facilitate the SET process, while the migration of holes to the valence band of MgAl-LDH converts surface hydroxyl groups into \u0026bull;OH radicals. These radicals abstract hydrogen from the biaryl radical intermediate, resulting in water as a by-product. The byproducts of the synthesis, I\u003csub\u003e2\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eO, can be easily separated without environmental concerns.\u003c/p\u003e \u003cp\u003eThis unique catalyst structure harnesses visible light, including sunlight, to drive the coupling reactions between halobenzenes and arenes, offering a straightforward approach to biaryl synthesis. Thus, our process fulfils the criteria for a sustainable future\u003csup\u003e18\u003c/sup\u003e, combining efficiency, safety, solar energy utilisation, and environmental friendliness.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003eCatalyst Characterisation.\u003c/strong\u003e The AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH, with a silver content of 9.4 wt.% was obtained as a light-yellow powder (see Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea), that exhibited the optimal photocatalytic performance. The results of the X-ray diffraction (XRD) analysis (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb), the energy-dispersive X-ray spectroscopy (EDX) elemental mappings (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec) and transmission electron microscopy (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ed) show that the as-prepared Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH photocatalyst was loaded with AgI nanoparticles (NPs) dispersed on LDH support. The high-resolution TEM (HR-TEM) images reveal the lattices of AgI and LDH (Figs. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ee and f), which are in accord with the results of XRD analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eControl experiments and performance of the catalysts.\u003c/strong\u003e The direct arylation of benzene was chosen as a model reaction for control experiments, optimising the photocatalysts and the reaction conditions. These experiments elucidated the roles played by the catalyst components and the influence of light irradiation. Catalysts with different Mg/Al molar ratios were used for catalysing the reaction under visible light irradiation. As shown in Supplementary Table 1, the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH photocatalyst exhibits the best catalytic performance without any requirement for the addition of base or any other additives. The desired product biphenyl can be obtained and identified by mass spectrometry (Supplementary Fig.\u0026nbsp;1), with I\u003csub\u003e2\u003c/sub\u003e also being produced as a visibly evident byproduct (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea) confirmed by UV-Vis spectroscopy (Supplementary Fig.\u0026nbsp;2). A high biphenyl yield of 93% was achieved by AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst under LED light irradiation at 400 nm wavelength with an intensity of 0.1 W cm\u003csup\u003e-2\u003c/sup\u003e (Entry 1 in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). The yield of biphenyl varies moderately with Mg/Al ratio of the catalysts (Supplementary Table 1). The absence of either the irradiation or the catalyst resulted in only a trace yield of the target product (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, entries 2 and 3). The absence of iodobenzene or benzene gave none or only a trace of biphenyl (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, entries 4 and 5), suggesting that the product is formed through a cross-coupling process.\u003c/p\u003e\n\u003cp\u003eA significant discovery involves the successful utilization of natural sunlight for photocatalytic direct arylation. As shown in Supplementary Fig.\u0026nbsp;3, a 60% biphenyl yield was attained at relatively low reaction temperatures, obviating the requirement for supplementary energy input, and highlighting the system\u0026apos;s impressive solar energy utilization efficiency.\u003c/p\u003e\n\u003cp\u003eThe fact that both the Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH support and AgI/ZrO\u003csub\u003e2\u003c/sub\u003e individually exhibit low catalytic activities is worth noting (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, entries 6 and 7). The content of AgI in AgI/ZrO\u003csub\u003e2\u003c/sub\u003e catalyst is similar to that in AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH (Supplementary Table\u0026nbsp;2, entries 1 and 2). These results indicate that there is a synergistic effect of AgI NPs and Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH in the photocatalytic system. Furthermore, the addition of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, which is the base used for preparing Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH, to the system using AgI/ZrO\u003csub\u003e2\u003c/sub\u003e catalyst did not significantly increase the biphenyl yield (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, entry 8). This indicates that CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e anions made little contribution to the catalytic performance under these conditions. The photocatalytic system demonstrated a notable tolerance towards moisture and atmospheric oxygen, as evidenced by achievement of a moderate yield of biphenyl (56.4%, Entry 9 in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) under an air atmosphere.\u003c/p\u003e\n\u003cp\u003eStandard reaction conditions: iodobenzene (0.1 mmol), benzene (1 mL), catalyst (50 mg), Ar atmosphere, irradiated under a 400 nm wavelength LED light with 0.1 W cm\u003csup\u003e-2\u003c/sup\u003e of intensity, the reaction was conducted at 60℃ for 20 h. Yields are determined by GC analysis.\u003c/p\u003e\n\u003cp\u003eWe also monitored the formation of biphenyl during the direct arylation process using the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH photocatalyst. The results, summarised in Supplementary Fig.\u0026nbsp;4a, show that the yield of biphenyl reaches 80% within the first 10 h, with 90% yield reached over 20 h. Additionally, as illustrated in Supplementary Fig.\u0026nbsp;4b, the increase in biphenyl yield does not follow a linear trend with addition of more catalyst, presumably due to screening effects within the photocatalytic system\u003csup\u003e20\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eBroad substrate scope\u003c/strong\u003e. The practicality of the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH photocatalyst in the direct arylation of arenes depends on the substrate and operation life in addition to the sustainability and environmental impact of all the products. The aryl iodides, contain electron-donating or electron-withdrawing groups, exhibited excellent reactivity towards benzene under irradiation of 400 nm light (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). The corresponding products were obtained in good yield from 87\u0026ndash;99%, while the reactions conducted in the dark showed negligible yields of target products. Moreover, the reactions between benzene and iodides containing heterocycles such as thiophene and pyridine afford the desired arylated heteroarenes with good yield (94% and 91%, \u003cstrong\u003e6\u0026ndash;7\u003c/strong\u003e), demonstrating a broad substrate scope for this photocatalytic system. It is noteworthy that iodobenzene possessing an electron-deficient nitrile substituent group exhibits a higher reactivity (99% yield) under the same conditions compared to that with an electron-donating methoxy group (91% yield), suggesting the involvement of a SET process in the reaction\u003csup\u003e9\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eImportantly, direct arylation of inactive arenes beyond benzene with iodobenzene occurred using the photocatalytic system. As shown in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, good yields are obtained from arenes with substituent groups containing heteroatoms (74%-98%, \u003cstrong\u003e9\u0026ndash;12\u003c/strong\u003e), while moderate yields from arenes with hydrocarbon substituent group (27%-63%, \u003cstrong\u003e8, 13\u0026ndash;16\u003c/strong\u003e). Notably, no products related to benzylic activation were detected. This achievement is particularly challenging due to the significantly stronger C(sp\u003csup\u003e2\u003c/sup\u003e)-H bonds compared to the C(sp\u003csup\u003e3\u003c/sup\u003e)-H bond (by about 100 kJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e21\u003c/sup\u003e. The reaction involving toluene yielded three products (2-, 3-, and 4-methyl biphenyls) with a ratio of 62:24:14 (\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e), indicating potential involvement of radical intermediates in the pathway for the photocatalytic reaction\u003csup\u003e22,23\u003c/sup\u003e. When comparing the yields of biaryl products from the direct arylation of arenes with iodobenzene, we observed a trend of the reactant arenes: benzene\u0026thinsp;\u0026gt;\u0026thinsp;arenes with substituent groups containing heteroatoms\u0026thinsp;\u0026gt;\u0026thinsp;toluene\u0026thinsp;\u0026gt;\u0026thinsp;arenes with multiple or larger hydrocarbon substituent. The large difference in the yields reflects the heavy dependence of the arylation on the reaction between the aryl radicals and the arene. Significantly higher yields are attained from the arenes with heteroatom substituent groups compared to those with alkyl substituent groups.\u003c/p\u003e\n\u003cp\u003eReaction conditions: aryl iodide (0.1 mmol), arene (1 mL), AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst (50 mg), Ar atmosphere, irradiated under a 400 nm wavelength LED light. Yields were determined by GC analysis. \u003csup\u003ea\u003c/sup\u003eReaction was conducted at 60℃ for 20 h, and the light intensity was 0.1 W cm\u003csup\u003e-2\u003c/sup\u003e. \u003csup\u003eb\u003c/sup\u003eReaction was conducted at 80℃ for 20 h, and the light intensity was 0.1 W cm\u003csup\u003e-2\u003c/sup\u003e. \u003csup\u003ec\u003c/sup\u003eReaction was conducted at 60℃ for 48 h, and the light intensity was 0.1 W cm\u003csup\u003e-2\u003c/sup\u003e. \u003csup\u003ed\u003c/sup\u003eReaction was conducted at 85℃ for 48 h, and the light intensity was 0.2 W cm\u003csup\u003e-2\u003c/sup\u003e. To enhance the yield of the products \u003cstrong\u003e1\u003c/strong\u003e\u0026ndash;\u003cstrong\u003e7\u003c/strong\u003e, the catalyst was filtered out at half of the reaction time during photocatalysis, followed by the addition of 50 mg of fresh catalyst to the liquid mixture. \u003csup\u003ee\u003c/sup\u003eReaction was conducted at 60℃ for 20 h, and the light intensity was 0.2 W cm\u003csup\u003e-2\u003c/sup\u003e. \u003csup\u003ef\u003c/sup\u003eReaction was conducted at 60℃ for 20 h, and the light intensity was 0.1 W cm\u003csup\u003e-2\u003c/sup\u003e. Iodobenzene was used in producing the products \u003cstrong\u003e8\u0026ndash;16\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003eThe surface OH groups of LDH are consumed during the photocatalytic reaction to generated \u0026bull;OH radicals. Supplementary Fig.\u0026nbsp;5 illustrates the impact of this consumption on the biphenyl yield when using a used AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH photocatalyst under 400 nm irradiation, showing a decrease from 80\u0026ndash;48%. However, a simple regeneration method (as detailed in the Method section) involving the addition of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e aqueous solution to a sealed flask, followed by heating to 85\u0026deg;C with stirring for 1 hour, can effectively restore the product yield. X-ray photoelectron spectroscopy (XPS) and Zeta Potential analysis presented in Supplementary Fig. 6 indicate that the surface hydroxyl groups of LDH can be recovered by regeneration. The catalyst can be recycled multiple times.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe impact of light intensity and wavelength on the catalytic performance of AgI/Mg\u003c/strong\u003e \u003csub\u003e\u0026nbsp;\u003cstrong\u003e2\u003c/strong\u003e\u0026nbsp;\u003c/sub\u003e \u003cstrong\u003eAl\u003c/strong\u003e \u003csub\u003e\u0026nbsp;\u003cstrong\u003e1\u003c/strong\u003e\u0026nbsp;\u003c/sub\u003e \u003cstrong\u003eLDH photocatalyst.\u003c/strong\u003e Figures \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb demonstrate the sensitivity of the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst\u0026apos;s performance to intensity and wavelength of the irradiation, in the context of direct benzene arylation. Higher irradiation intensity leads to increased biphenyl yield. Notably, even under the conditions of extremely low light intensity, as low as 0.01 W cm\u003csup\u003e-2\u003c/sup\u003e, the catalyst achieves a substantial 40% biphenyl yield, indicating its efficiency. It exhibits an apparent quantum yield (AQY) of 3.3% at this low light intensity, highlighting its exceptional utilization of visible light for catalysis.\u003c/p\u003e\n\u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb presents an action spectrum, which provides valuable insight into the impact of irradiation wavelength on the direct arylation using the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst. The determination of AQY involves normalising the number of target molecules generated to the incident photons within the photocatalytic system\u003csup\u003e24\u003c/sup\u003e. Notably, irradiation by LED light centred at 350 nm and 400 nm results in substantially elevated AQY values, while longer wavelengths (550 and 660 nm) yield negligible AQYs. This clear dependence of AQYs on the irradiation wavelengths aligns with the light absorption characteristics exhibited by the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst. This behaviour contrasts with prior research, specifically direct photolysis, where the optimal yield was achieved using deep-UV light, but a significant decrease was observed at a longer wavelength.\u003csup\u003e25\u003c/sup\u003e It is evident that the primary driver of the reaction is the light absorbed by AgI nanoparticles, given that the Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH support has minimal absorption at wavelengths longer than 350 nm (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb). Consequently, the AgI nanoparticles effectively function as efficient light absorbers for the catalyst system.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePhoto-generated hydroxyl radicals to facilitate direct arylation.\u003c/strong\u003e The remarkable observation that a relatively modest amount of absorbed light energy leads to a substantial biphenyl yield implies the existence of low activation energy barriers within the photocatalytic reaction pathway. An in-depth kinetic study on the reaction between iodobenzene and benzene over AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH under light irradiation reveals a first-order kinetics relationship with respect to the substrate, as depicted in Supplementary Fig. 7. Employing the Arrhenius equation (raw data shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea) we estimate an apparent activation energy of 46.3 kJ mol\u003csup\u003e-1\u003c/sup\u003e for the photocatalytic reaction, which is significantly lower than 61.7 kJ mol\u003csup\u003e-1\u003c/sup\u003e reported for a thermally driven system \u003csup\u003e6\u003c/sup\u003e (as shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb).\u003c/p\u003e\n\u003cp\u003eComparison of the relative amounts of surface OH groups in the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst before and after the photocatalytic reaction, as determined from the XPS spectra of O 1s, reveals a noticeable reduction in surface hydroxyl groups during the course of the photocatalytic reaction. Within the XPS spectra (Figs. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb), the O 1s peaks at 532.7, 531.4, and 530.2 eV correspond to various oxygen species in the catalyst, including metal-hydroxyl (M-OH), metal oxide (M-O), and carbonate (CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e) of LDH, respectively\u003csup\u003e26\u0026ndash;28\u003c/sup\u003e. It is noteworthy that the concentration of M-OH on the catalyst after the photocatalytic reaction is significantly lower than that on the pristine catalyst. This decline can be attributed to the transformation of surface hydroxyl groups of LDH into \u0026bull;OH radicals, which are consumed during the reaction, leading to the formation of sites with unpaired electron confined within oxygen vacancies. As depicted in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec the electron paramagnetic resonance (EPR) analysis of the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst before and after photocatalysis exhibits a prominent EPR signal characterized by a g factor of 2.004 in the used catalyst, unequivocally indicating the existence of such sites\u003csup\u003e29\u003c/sup\u003e. Consequently, it can be inferred that surface OH groups are consumed in the process, generating \u0026bull;OH radicals. The activation energy barriers in the reaction mediated by \u0026bull;OH radicals are notably low. The recycling experiments regenerated the surface OH groups.\u003c/p\u003e\n\u003cp\u003eThe \u0026bull;OH radicals are regarded essential for oxidation in photocatalysis\u003csup\u003e30\u003c/sup\u003e, being the main reactant for various fundamental processes such as SEO, double bond addition, and hydrogen abstraction\u003csup\u003e31\u003c/sup\u003e. Considering both SEO and hydrogen abstraction steps are involved in direct C-H arylation\u003csup\u003e9\u003c/sup\u003e, which \u0026bull;OH radicals can participate in and facilitate, LDH can serve as a reservoir for hydroxyl groups, supplying them internally to produce \u0026bull;OH radicals that drive the reaction without the need for any peroxide addition. This is supported by fact that Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH has the maximum crystallite size, and the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst exhibits the highest biphenyl yield (Supplementary Table\u0026nbsp;3 and Supplementary Fig.\u0026nbsp;8a). The size of crystallite is directly proportional to the quantity of surface hydroxyl groups on LDH\u003csup\u003e32,33\u003c/sup\u003e. In contrast, other factors, such as their AgI NPs contents (represented by the silver content in Supplementary Table\u0026nbsp;2) and specific surface areas (Supplementary Fig.\u0026nbsp;9), have a lesser impact on the performance of AgI/Mg\u003csub\u003ex\u003c/sub\u003eAl\u003csub\u003ey\u003c/sub\u003eLDH photocatalysts.\u003c/p\u003e\n\u003cp\u003eThe presence of \u0026bull;OH radicals is substantiated by multiple experimental observations. Terephthalic acid (H\u003csub\u003e2\u003c/sub\u003eBDC) was employed as a fluorescent probe to detect \u0026bull;OH radicals within our photocatalytic system, following a well-documented procedure\u003csup\u003e34\u003c/sup\u003e. In the fluorescent experiment, a characteristic fluorescence signal at 425 nm is prominently observed (see Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed), while the absence of any the following components: AgI NPs, Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH support, H\u003csub\u003e2\u003c/sub\u003eBDC and irradiation, yields no discernible fluorescence peaks. The result provides direct evidence that hydroxyl can be converted to \u0026bull;OH radicals in the photocatalytic system. Besides, the concentration of \u0026bull;OH radicals varies in the order of AgI/LDH\u0026thinsp;\u0026gt;\u0026thinsp;AgI/ZrO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;LDH, which is consistent with their catalytic activities shown in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The results not only provide compelling evidence for the generation of \u0026bull;OH radicals from LDH but also imply that the illuminated AgI NPs play a pivotal role in driving this process.\u003c/p\u003e\n\u003cp\u003eThe excellent performance of AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst under dry conditions, as demonstrated in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, entry 1 (in the absence of moisture), further underscores the origins of \u0026bull;OH radicals from surface OH groups. Furthermore, the photocatalytic reaction was conducted in the presence of isopropanol (IPA) as a \u0026bull;OH scavenger\u003csup\u003e35\u003c/sup\u003e. As depicted in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea, the yield of biphenyl decreased from 80\u0026ndash;57% upon addition of 1 mmol of IPA into the reaction (2nd column). These findings point to the indispensable role played by \u0026bull;OH radicals in the photocatalysis.\u003c/p\u003e\n\u003cp\u003eIn the literature, it has been reported that UV irradiation on a composite of TiO\u003csub\u003e2\u003c/sub\u003e and MgAl-LDH, as well as MgAl-LDH with partial Ni\u003csup\u003e2+\u003c/sup\u003e substitution for Mg\u003csup\u003e2+\u003c/sup\u003e, and zinc-tin (ZnSn)-LDH can induce the generation of \u0026bull;OH radicals, which can effectively eliminate environmental pollutants\u003csup\u003e36\u0026ndash;38\u003c/sup\u003e. In this study, we have discovered that the visible light irradiation can induce the conversion of surface hydroxyl groups within MgAl-LDH into reactive \u0026bull;OH radicals, facilitating direct C-H arylation. Using visible light instead of UV irradiation enhances solar energy utilization, reduces the likelihood of generating undesired byproduct, and minimises potential safety risks. Therefore, this finding has practical implications for future sustainable chemical synthesis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe contribution of photo-generated charge carriers in the photocatalysis.\u003c/strong\u003e As shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea, the use of KI as an effective quencher for surface-bound free radicals and a hole trapper\u003csup\u003e39\u003c/sup\u003e (3rd column) caused a sharp decline in yield from 80\u0026ndash;40%, while adding Mn(Ac)\u003csub\u003e3\u003c/sub\u003e as an electron scavenger\u003csup\u003e40\u003c/sup\u003e leads to a moderate decrease in the yield (4th column). This indicates that photogenerated holes and the resultant surface-bound free radicals that form are critical for achieving high biphenyl yield.\u003c/p\u003e\n\u003cp\u003eEnergy level alignment of the catalyst components and reactant was investigated to understand the transport of photo-induced charge carriers. The LUMO energy level of iodobenzene was measured using cyclic voltammetry with Ag/AgCl as the reference electrode and Fc/Fc\u003csup\u003e+\u003c/sup\u003e couple used as the internal standard (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb). The \u003cem\u003eE\u003c/em\u003e\u003csub\u003eLUMO\u003c/sub\u003e value of iodobenzene is calculated to be -4.32 eV relative to vacuum or -0.12 eV relative to the standard hydrogen electrode (SHE)\u003csup\u003e41\u003c/sup\u003e, as depicted in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ed. Valence band X-ray photoelectron spectroscopy (VB-XPS) method was used to determine the potentials at the valence band maximum (VBM) edge of the Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH and AgI, which were found to be 2.10 eV and 2.30 eV, respectively (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ec). The E\u003csub\u003eVB\u003c/sub\u003e,\u003csub\u003eSHE\u003c/sub\u003e of Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH and AgI are 1.96 and 2.16 eV, respectively (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ed). Band gap energies (E\u003csub\u003eg\u003c/sub\u003e) of 5.37 eV for Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH and 2.85 eV for AgI were obtained from their Tauc plots, (Supplementary Fig.\u0026nbsp;10). Thus, the corresponding conduction band maximum (CBM) potentials for Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH and AgI are \u0026minus;\u0026thinsp;3.41 and \u0026minus;\u0026thinsp;0.69 eV, respectively (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ed). This data revealed that AgI NPs efficiently absorb visible light and generate electron-hole pairs. The electrons then transfer to the LUMO of the iodobenzene reactant, activating it, while the holes are captured by the surface hydroxyl groups of Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH, generating \u0026bull;OH radicals that are crucial for the direct arylation of benzene (see discussion in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). This is consistent with the result in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea, where the hole scavengers substantially inhibit the biphenyl yield.\u003c/p\u003e\n\u003cp\u003eThe influence of LDH support on the efficiency of \u0026bull;OH radical generation was also explored by comparing the AgI/Zn\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst with AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst. The VBM difference between AgI to Zn\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH is smaller than that between AgI and Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH\u003csup\u003e42\u003c/sup\u003e, as discussed in Supplementary Fig.\u0026nbsp;11. This leads to a slower transfer rate of photo-induced holes in AgI/Zn\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH, which, in turn, affects the biphenyl yield of this catalyst (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMechanism of the photocatalytic system\u003c/strong\u003e. Combining the discussions presented in Figs. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e above, it can be concluded that the photoinduced charge carriers, \u0026bull;OH radicals, and oxygen vacancies play crucial roles in reducing the energy requirement for the direct C-H arylation.\u003c/p\u003e\n\u003cp\u003eTo confirm the conversion of iodobenzene to benzene radical, induced by the photo-excited electrons from AgI, we used time-dependent ATR-FTIR spectroscopy during visible light irradiation. Specifically, we conducted experiments using the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst and 4-chloroiodobenzene reactant as a representative sample, because the characteristic peaks of the catalyst and iodobenzene overlap. As displayed in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea, the intensity of the C-I bond vibration at approximately 804 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e consistently diminishes over time, while the signals originating from M-O bond at 551 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e remain unchanged. An intriguing observation is a slight red-shift at around 651 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which corresponds to M-OH bond in the catalyst and can be attributed to the lattice distortion resulting from increased defects, such as oxygen vacancies, within the LDH support\u003csup\u003e44\u003c/sup\u003e. It is important to note that our comparative analysis revealed no significant spectral changes when testing each individual sample (as demonstrated in Supplementary Fig.\u0026nbsp;12).\u003c/p\u003e\n\u003cp\u003eOf particular note is the absence of any homo-coupling side products arising from the corresponding aryl halides. The remarkable selectivity towards the desired cross-coupling product can be attributed to the low concentration of aryl iodide in the system (0.1 M, molar ratio of arene to aryl iodide is about 100). To confirm this, we deliberately increased the concentration of aryl iodide in the reaction system, as evidenced in Supplementary Fig.\u0026nbsp;13, resulting in the detection of homo-coupling products.\u003c/p\u003e\n\u003cp\u003eThe labelling experiment is a commonly employed technique to determine whether C-H bond cleavage is the rate-determining step\u003csup\u003e9,12,45\u003c/sup\u003e. We determined a kinetic isotope effect (KIE) value of 1.36 through \u003csup\u003e1\u003c/sup\u003eH NMR analysis (see Supplementary Fig.\u0026nbsp;14), which slightly exceeds previously reported values\u003csup\u003e9,12\u003c/sup\u003e. This result implies that C-H activation is not the rate-determining step in the direct C-H arylation and lends support the involvement of \u0026bull;OH radicals in the C-H activation. Nevertheless, it is important to note that the rate-limiting step can vary when different arenes are used as coupling partners. For instance, under identical reaction conditions, arenes with electron-withdrawing groups (\u003cstrong\u003e9\u0026ndash;12\u003c/strong\u003e, Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) coupled more efficiently with iodobenzene than those containing electron-donating groups (\u003cstrong\u003e6\u003c/strong\u003e, and \u003cstrong\u003e13\u0026ndash;16\u003c/strong\u003e, Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e), highlighting the importance of C-H bond acidity in the arylation process\u003csup\u003e10,12\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe stronger electrophilic properties of \u0026bull;OH radicals play a crucial role in facilitating C-H bond activation and benefiting the arylation reaction compared to species generated in other catalytic systems\u003csup\u003e46,47\u003c/sup\u003e. Furthermore, our experiment involving an equimolar mixture of benzene and d\u003csub\u003e6\u003c/sub\u003e-benzene with iodobenzene resulted in a significantly lower yield of deuterated product (78%), further substantiating the above analysis. From a green chemistry perspective, radical-mediated C-H bond activation prove to be superior to transition-metal-based reactions\u003csup\u003e48\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eBuilding upon the preceding analysis, we propose a tentative reaction mechanism for direct C-H arylation on the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst under irradiation, as depicted in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb. Initially, photo-excited electron from AgI NPs inject into the LUMO of aryl iodide, leading to dehalogenation and the formation of an aryl radical and iodide ion (Steps I and II). Simultaneously, the positively charged holes migrate to the LDH support, where they react with surface hydroxyl groups, generating \u0026bull;OH radicals while vacating surface sites to create oxygen vacancies when acquiring electrons from I\u003csup\u003e\u0026minus;\u003c/sup\u003e ions (Steps II and III). This effectively prevents electron-hole recombination on the AgI NPs. Subsequently, the aryl radical reacts with a neighbouring arene molecule to form a biaryl radical, favoured due to its free-radical nature. Given the high molar ratio of benzene to aryl iodide (over 100) and the increased stability of a larger conjugated radical, it is reasonable to anticipate the prevalence of biaryl radical product in the reaction system compared to the aryl radical. The process of generating \u0026bull;OH radicals by hole transfer, as validated in Figs. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed and \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea, is counterbalanced by a SET process (C-I bond cleavage). Although it has been reported that \u0026bull;OH radicals can directly react with benzene, this reaction is reversible, and the \u0026bull;OH-benzene adduct is unstable, decomposes into \u0026bull;OH and benzene at temperatures exceeding 330 K\u003csup\u003e49\u003c/sup\u003e. Furthermore, our catalytic system was deoxygenated prior to the reaction, contrary to the conventional requirement of an oxygen atmosphere for the reaction between \u0026bull;OH radicals and benzene\u003csup\u003e50\u003c/sup\u003e. Consequently, \u0026bull;OH radicals abstract a hydrogen from the biaryl radical, yielding water as a byproduct, as confirmed by the water measurement test (Supplementary Table\u0026nbsp;4). Significantly, this C-H bond cleavage involved in hydrogen abstraction is a radical reaction characterized by a low activation energy barrier.\u003c/p\u003e\n\u003cp\u003eConcurrently, iodide ions are oxidised at sites where \u0026bull;OH radicals are generated, yielding iodine and the oxygen vacancies with two electrons. It is worth noting that while molecular iodine is a recognized catalyst for many organic reactions,\u003csup\u003e51\u003c/sup\u003e adding a small amount of I\u003csub\u003e2\u003c/sub\u003e (0.1 equiv.) can completely inhibit the photocatalytic reaction. So I\u003csub\u003e2\u003c/sub\u003e\u0026rsquo;s involvement in the reaction mechanism is unlikely. Moreover, the surface structure of the AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH catalyst can be restored by a regeneration process (Steps III and I).\u003c/p\u003e\n\u003cp\u003eIn summary, the synergistic combination of AgI NPs and Mg\u003csub\u003ex\u003c/sub\u003eAl\u003csub\u003ey\u003c/sub\u003eLDH with an appropriate x/y ratio proves to be highly effective in catalysing direct C-H arylation under mild conditions. This process stands out for its elimination of the need for additives and bases, and its potential to be driven solely by solar irradiation. The excitation of electrons and holes induced by the light absorption by AgI NPs leads to the conversion of aryl halides into aryl radicals and the generation of \u0026bull;OH radicals on the LDH surface, which abstract hydrogen atoms from C-H bonds. Crucially, the energy alignment within the photocatalysis system allows the promotion of aryl halides conversion into aryl radicals by the excited electrons, while the holes interact with the surface hydroxyl groups on the LDH, yielding \u0026bull;OH radicals capable of abstracting hydrogen atoms from C-H bonds (involving the single electron oxidation of biaryl radicals). These concurrent processes are characterized by both low activation energy barriers due to their radical nature and effectively hinder electron-hole recombination within AgI nanoparticles. Consequently, the photocatalytic direct C-H arylation can proceed efficiently under visible light or solar irradiation without the need for a base and other additives. The main byproducts, water and iodine, can be conveniently separated or recovered. This synthesis approach impeccably fulfils the requirement for a sustainable future\u003csup\u003e18\u003c/sup\u003e, encompassing efficiency, safety, solar energy utilisation, and environmental friendliness. It opens up new avenues for catalysing C-H arylation via an eco-friendly process and the development of highly efficient catalytic systems.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cb\u003eChemicals.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe chemicals were purchased from commercial suppliers and used as provided. The supplier and purity of the chemicals are shown in the brackets. Iodobenzene (Adamas, 99%), 4-iodobenzene (Adamas, \u0026gt;\u0026thinsp;98%), 4-iodoanisole (Adamas, 99%), 1-chloro-4-iodobenzene (Adamas, \u0026gt;\u0026thinsp;98%), 4-iodobenzotrifluoride (Adamas, \u0026gt;\u0026thinsp;98%), 4-iodobenzonitrile (Adamas, \u0026gt;\u0026thinsp;98%), 3-iodothiophene (Adamas, \u0026gt;\u0026thinsp;98%), 3-iodopyridine (Adamas, \u0026gt;\u0026thinsp;98%), benzene (Greagent, \u0026ge;\u0026thinsp;99.5%), benzene-d\u003csub\u003e6\u003c/sub\u003e (Adamas, 99.5%), biphenyl (Adamas, \u0026ge;\u0026thinsp;99%), toluene (SCR, \u0026ge;\u0026thinsp;99.5%), chlorobenzene (Greagent, \u0026ge;\u0026thinsp;99.5%), diphenyl ether (Adamas, \u0026gt;\u0026thinsp;99%), acetophenone (Adamas, \u0026gt;\u0026thinsp;99%), 1,2-dichlorobenzene (Macklin, 99%), 1,3,5-trimethylbenzene (Macklin, 97%), m-xylene (Greagent, \u0026ge;\u0026thinsp;99%), p-xylene (Greagent, \u0026ge;\u0026thinsp;99%), ethylenzene (Adamas, 99%), sodium carbonate (Greagent, \u0026ge;\u0026thinsp;99.8%), methanol (Greagent, \u0026ge;\u0026thinsp;99.5%), sodium hydroxide (Greagent, \u0026ge;\u0026thinsp;98%), sodium iodide (Adamas, 99.99%), potassium iodide (Adamas, 99%), terephthalic acid (Adamas, 99%), silver(I) nitrate (SCR, \u0026ge;\u0026thinsp;99.8%), aluminium(III) nitrate nonahydrate (Greagent, \u0026ge;\u0026thinsp;99.0%), manganese(III) acetate dihydrate (Adamas, 98%), zinc(II) nitrate hexahydrate (Keshi, \u0026ge;\u0026thinsp;99.0%), ferrocene (TCI, 98.0%), tetra-n-butylammonium hexafluorophosphate (\u003cem\u003en\u003c/em\u003e-Bu\u003csub\u003e4\u003c/sub\u003eNPF\u003csub\u003e6\u003c/sub\u003e, Adamas, \u0026ge;\u0026thinsp;99%), acetonitrile (Greagent, \u0026ge;\u0026thinsp;99.0%), isopropanol (TCI, 99.5%), Ar (\u0026gt;\u0026thinsp;99.999%).\u003c/p\u003e \u003cp\u003e \u003cb\u003eCatalyst preparation.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe Mg\u003csub\u003ex\u003c/sub\u003eAl\u003csub\u003ey\u003c/sub\u003eLDH with various x/y ratios, Ni\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH, and Zn\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH were produced using a coprecipitation method. The procedure for preparing Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH is shown below as a typical example. 0.0133 mol of Mg(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e 6H\u003csub\u003e2\u003c/sub\u003eO and 0.0067 mol of Al(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e 9H\u003csub\u003e2\u003c/sub\u003eO were added into 20 mL of deionized water to form solution A. Meanwhile, 0.02 mol of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e were dissolved in 30 mL of deionized water to form solution B. Solutions A and B were dropwise added simultaneously into a flask containing 15 mL of deionized water at 40℃ using an injection pump (with an injection rate of 2 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for A and 3 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for B). After vigorous stirring for 1 h, a 2 M NaOH aqueous solution was added dropwise to the above suspension until the final pH reached 10. The slurry was then sealed and heated to 85℃ with stirring for 3 h, followed by transfer into an oven where it was kept at 80℃ for 16 h. The resulting gel was washed with deionized water by centrifugation (at 4000 rpm) until the washings reached a pH of 7. The solid was subsequently dried in an oven at 80℃ for 48 h and ground in an agate mortar to pass through a sieve with a mesh size of 40. This process yielded approximately 1.4 g of white powder. LDHs with different metal ratios were prepared using different quantities of Mg(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e 6H\u003csub\u003e2\u003c/sub\u003eO and Al(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e 9H\u003csub\u003e2\u003c/sub\u003eO in a total feeding amount of 0.02 mol.\u003c/p\u003e \u003cp\u003eAgI/LDH catalyst was prepared as follows: 200 mg of LDH powder was placed in a 100 mL beaker. Then, 18.5 mL of AgNO\u003csub\u003e3\u003c/sub\u003e aqueous solution (0.01 M) was added into the beaker. After sonication for 5 min, 1 mL of NaI aqueous solution (0.222 M) was dropwise added over 1 min with vigorously stirring. After of stirring, the suspension was stirred at room temperature for 24 h and then washed three times with deionized water by centrifugation (5000 rpm). Finally, it was dried at 60℃ under vacuum for 20 h. The light absorption properties of as-prepared samples are shown in Supplementary Fig.\u0026nbsp;16.\u003c/p\u003e \u003cp\u003e \u003cb\u003eCatalyst regeneration.\u003c/b\u003e \u003c/p\u003e \u003cp\u003e100 mg of the used catalyst (eg. AgI/Mg\u003csub\u003e2\u003c/sub\u003eAl\u003csub\u003e1\u003c/sub\u003eLDH) was mixed with 30 mL of deionized water in a flask and sonicated for 5 min. Then, 60 mg of Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e was added to the flask, which was sealed and heated to 85℃ with stirring for 1 h. After cooling down to room temperature, the sample was washed three times with deionized water by centrifugation at 5000 rpm and dried at 60℃ under vacuum for 20 h.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePhotocatalytic reactions and product analysis.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eA 10 mL glass tube. which does not show obvious light absorption at wavelengths beyond 350 nm was used as the reaction vessel. The catalyst, reactants and a stirrer were introduced into the tube and purged with argon (100 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) for 1min. before being sealed with a cap. Subsequently, the tube was placed on a magnetic stirrer and exposed to an LED light of a specific wavelength such as 400 nm while stirring at 600 rpm and a controlled temperature.\u003c/p\u003e \u003cp\u003eThe mixture was filtered through a Millipore filter (pore size 0.22 \u0026micro;m) after the reaction to remove the catalysts. The products in the filtrate were analysed using a Panna GC-1949 gas chromatography with an AB-5 column. An Agilent 7890A/5975C gas chromatography-mass spectrometer was used for product identification (Supplementary Figs.\u0026nbsp;17\u0026ndash;32). All product concentrations were calibrated with an external standard method.\u003c/p\u003e \u003cp\u003eIn this photocatalytic system, \u003cem\u003eyield\u003c/em\u003e is defined as the ratio between the amount of final product (biaryls) and added reactant (aryl iodide). The AQY value is calculated by normalizing the amount of products formed under irradiation (\u003cem\u003eN\u003c/em\u003e\u003csub\u003elight\u003c/sub\u003e) to the number of photons (\u003cem\u003en\u003c/em\u003e), with subtraction of the number of the target product formed in the dark (\u003cem\u003eN\u003c/em\u003e\u003csub\u003edark\u003c/sub\u003e), as shown in the equation:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\text{A}\\text{Q}\\text{Y}=\\frac{{N}_{light}-{N}_{dark}}{n}\\times 100\\%$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cb\u003eCatalyst Characterization.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eXRD patterns of the catalysts were recorded on a MiniFlex600-C from Rigaku Co, operated at 40 kV and 15 mA with CuKα radiation (λ\u0026thinsp;=\u0026thinsp;1.541862 \u0026Aring;). The data were collected with a resolution of 0.01\u0026deg; (2θ). The morphology and elemental mapping of the catalysts were characterized using a JEOL JEM-F200 transmission electron microscope (TEM) operating at 200 kV. The DR UV-vis spectra of the samples were recorded by a Shimadzu UV-3600 plus spectrophotometer. X-ray photoelectron spectroscopy (XPS) measurements were carried out using a Shimadzu/Krayos AXIS Ultra DLD instrument. The fluorescence spectra were recorded on a F7000 FL spectrophotometer using quartz cuvettes loaded with 1 mL of sample, an excitation wavelength of 315 nm was used, and the emission was measured from 350 to 600 nm. The electron paramagnetic resonance (EPR) spectra were measured using a Bruker EMXnano spectrometer, which operated at a field modulation frequency of 100 kHz in the X-band mode. The nitrogen adsorption data were collected at -196℃ on a JW-BK2000 analyser (Beijing Jingwei Gaobo Science and Technology Co., Ltd., China) and the specific surface areas of the catalysts were calculated using the Brauner-Emmet-Teller (BET) method. The metal content in catalysts was obtained by performing inductively coupled plasma optical emission spectrometry (ICP-OES) on an Agilent 720ES. The cyclic voltammogram curves were recorded on an Autolab PGSTAT302N electrochemical workstation (Metrohm, Netherland). A three-electrode system was used, consisting of a working electrode (platinum thin-film), a counter electrode (another platinum thin-film), and an Ag/AgCl reference electrode. The analysis was conducted in an acetonitrile solution of \u003cem\u003en\u003c/em\u003e-Bu\u003csub\u003e4\u003c/sub\u003eNPF\u003csub\u003e6\u003c/sub\u003e (0.1 M) within the range from \u0026minus;\u0026thinsp;0.5 to +\u0026thinsp;1.5 V at a scan rate of 50 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Absorption spectra of the liquid samples were measured using a LabTech BlueStarA UV-vis spectrophotometer with a 1 cm quartz cell. The Nuclear Magnetic Resonance (NMR) spectrum was measured using a Bruker 400 MHz spectrometer. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra were collected with a PerkinElmer Spectrum Two spectrometer. The water content measurements were carried out on an AKF-2010V Karl Fisher moisture titrator at an oven temperature of 100℃. The zeta potential measurements were recorded using a Microtrac nanotrac wave II instrument with the samples dispersed in deionized water at a concentration of 1 mg mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The light intensity was measured by a probe coupled to a digital optical power meter (S401C, PM100D, Thorlabs). The electrochemical impedance spectroscopy (EIS) analysis was carried out in the frequency range from 10 kHz to 0.1 Hz at open circuit potential with an ac perturbation of 10 mV.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003e \u003cb\u003eCompeting interests\u003c/b\u003e: The authors declare no competing interests.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eWe acknowledge financial support from the National Natural Science Foundation of China (No. 22002038), the Natural Science Foundation of Hunan Province (No. 2023JJ40120), the Science and Technology Innovation Program of Hunan Province (No. 2023RC3016) and the Australian Research Council for Discovery Project DP210103357.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHassan J, S\u0026eacute;vignon M, Gozzi C, Schulz E, Lemaire M (2002) Aryl-aryl bond formation one century after the discovery of the ullmann reaction. 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Evidence for the reversibility of hydroxyl radical addition to benzene. J Am Chem Soc 103:3876\u0026ndash;3878\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBreugst M, von der Heiden D (2018) Mechanisms in iodine catalysis. Chem -Eur J 24:9187\u0026ndash;9199\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1 and 2 are available in the Supplementary Files section.\u003c/p\u003e"},{"header":"Schemes","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-3747453/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3747453/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe direct arylation of inactive arenes with aryl halides stands as a well-established and fundamental method in organic synthesis for synthesizing biaryls. However, current direct arylation methods suffer from the generation of substantial chemical waste, reliance on moisture-sensitive reagents, and harsh reaction conditions that involve using either organic acids or potent bases. Here we report a photocatalytic system based on AgI-decorated magnesium-aluminium-layered double hydroxide (MgAl-LDH), which operates effectively under visible light, eliminating the need for base or other additives. The alignment of energy levels between catalyst components and reactant enables the system to harness visible light or sunlight irradiation for the generation of aryl and \u0026bull;OH radicals from aryl iodides and MgAl-LDH surface, respectively, facilitating direct C-H arylation, producing only water and iodine as by-products. Furthermore, the surface hydroxyl groups of MgAl-LDH can be readily regenerated. Our discovery provides an efficient, eco-friendly and cost-effective approach to C-H arylation.\u003c/p\u003e","manuscriptTitle":"Visible-Light Photocatalytic Direct Arylation of Arenes Using Silver Iodide Nanoparticles Supported on Magnesium-Aluminium Layered Double Hydroxide","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-11 05:16:19","doi":"10.21203/rs.3.rs-3747453/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4fec9164-f6a4-4954-a216-953d96718784","owner":[],"postedDate":"January 11th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":28025044,"name":"Physical sciences/Chemistry/Green chemistry/Sustainability"},{"id":28025045,"name":"Physical sciences/Materials science/Materials for energy and catalysis/Photocatalysis"}],"tags":[],"updatedAt":"2024-12-16T15:30:09+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-11 05:16:19","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3747453","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3747453","identity":"rs-3747453","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}