Abstract
The development of heterogeneous metallaphotocatalysis is of great interest for sustainable organic synthesis. The rational design and controllable preparation of well-defined (site-isolated) metal/photo bifunctional solid catalysts to meet such goal remains a critical challenge. Herein, we demonstrate the incorporation of privileged homogeneous bipyridyl-based Ni-catalysts into highly ordered and crystalline potassium poly(heptazine imide) (K-PHI). A variety of PHI-supported cationic bipyridyl-based Ni-catalysts (LnNi-PHI) have been prepared and fully characterized by various techniques including NMR, ICP-OES, XPS, HAADF-STEM and XAS. The LnNi-PHI catalysts exhibit exceptional chemical stability and recyclability in diverse C−P, C−S, C−O and C−N cross-coupling reactions. The proximity and cooperativity effects in LnNi-PHI significantly enhances the photo/Ni dual catalytic activity, thus resulting in low catalyst loadings and high turnover numbers.
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Introduction
Over the past decade, homogeneous nickel catalysis has become a powerful tool for organic synthesis1,2. Merging nickel catalysis with photoredox catalysis3 enabled numerous challenging and valuable transformations. In this regard, a wide range of C–heteroatom and C−C cross-coupling reactions have been achieved, allowing for rapid access to privileged structure motifs prevalent in pharmaceuticals and functional materials (Fig. 1a)4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19. In these homogeneous Ni/photo dual catalytic systems, the highly reactive open-shell Ni(I)/Ni(III) or excited Ni(II) intermediates can be generated through photoinduced electron or energy transfer processes, allowing the transformations occur under very mild reaction conditions. Importantly, the choice of ligands plays a vital role in enhancing the nickel catalysts’ reactivity, stability, and selectivity. Despite the elegance and versatility of the existing homogeneous methods, the development of heterogeneous metallaphotocatalysis by the rational design and construction of Ni-photo bifunctional catalysts, with the advantage of facile separation and catalyst reusability, is of great interest for industrial implementation and thus in urgent demand20,21. Of note, Ni complexes featuring bidentate bipyridyl-based ligands such as 2,2’-bipyridine (bpy), 4,4’-di-tert-butyl-2,2’-bipyridine (dtbpy), and 1,10-phenanthroline (phen) have proven crucial for effective couplings in the homogenous Ni/photoredox dual catalysis3,22. These weak-field ligands lead to lower ligand field-splitting energy that promotes the formation of paramagnetic species and stabilization of open-shell Ni intermediates via metal-to-ligand charge transfer, thus significantly enhancing the reactivity of Ni center. Therefore, incorporating these privileged bipyridyl-based Ni catalysts into solid-state sensitizer materials holds great potential to furnish a novel heterogeneous platform for metallaphotoredox catalysis. The early research that employed carbon nitride (C3N4), perovskite, quantum dot (QDs) as heterogeneous photocatalyst in dual catalysis could only realize partial recycling due to the combined use of homogeneous Ni/ligand23,24,25,26,3b). The HAADF-STEM image of bpyNi-PHI (Fig. 3c) confirms the presence of single-atoms without observation of metal particles or clusters. From the Ni K-edge X-ray absorption near-edge structure (XANES) spectra (Fig. 3d), the absorption edge position and spectral line shape of bpyNi-PHI closely resemble those of Ni-O, indicating the oxidation state of the Ni single-atoms close to +2. According to the linear combination fittings on XANES profiles, the average chemical valence of Ni is calculated to be +2.03 (Supplementary Fig 15 and Supplementary Table 6), which is in good agreement with the Ni 2p XPS results. The Fourier transformation (FT) of Ni K-edge extended X-ray absorption fine structure (EXAFS) spectra of bpyNi-PHI exhibits a prominent peak centered at 1.6 Å for Ni-N/O coordination, while no Ni-Ni and Ni-O-Ni characteristic peaks are observed at 2.2 Å (Ni foil) and 2.9 Å (Ni-O-Ni structure), suggesting the atomically dispersion of Ni atoms (Fig. 3e)54,70. The EXAFS fitting results indicate that the Ni center adopts Ni-N4-O2 structure with the coordination number of ~6 (Fig. 3f and Supplementary Table 6). As the EXAFS cannot differentiate the contribution from coordinated N and O atoms due to their similar scattering factors, the existence of Ni-O bonds attributed to water cannot be excluded. Taken together, we propose Ni in bpyNi-PHI might be bonded with adjacent pyridinic nitrogen of two separated triazine units and one bipyridine molecule (inset of Fig. 3f), which is also in agreement with the structure preliminarily optimized by DFT calculation (Supplementary Fig. 16).
Catalytic activity of LnNi-PHI
In combination with the above analyses, we speculate that the obtained LnNi-PHI materials feature site-isolated active LnNi2+ species and meanwhile retain the photocatalytic activity of the parent PHI, thus showing great potential to be served as highly effective heterogeneous metallaphotocatalysts for promoting visible-light-mediated organic transformations. In order to verify our hypothesis, five representative and synthetic useful carbon-heteroatom bond formation reactions including phosphonylation, amination, etherification, esterficiation, and thioetherification of aryl iodide with corresponding heteroatom coupling partners were investigated (Fig. 4a–e). After considerable efforts (see optimization in Supplementary Tables 7−11 of Supplementary Information), we found that LnNi-PHI (~6 wt % LnNi) including bpyNi-PHI, dtbpyNi-PHI, dOMebpyNi-PHI, dClbpyNi-PHI, and phenNi-PHI could effectively catalyze all five cross-coupling reactions, providing high yields of the desired C−P, C−N, C−O and C−S coupling products 1–5 in the presence of suitable base and solvent under blue light irradiation (Fig. 4a−e, condition A). Compared to other LnNi-PHI catalysts, dClbpyNi-PHI exhibits a relatively lower catalytic activity, requiring slightly longer reaction time (Supplementary Tables 7−11). These reactions failed to proceed in the absence of LnNi-PHI catalysts, light, or base additive, implying all were crucial for these transformations (Supplementary Tables 7−11). We further conducted a series of control experiments to probe the function of different components in LnNi-PHI and their synergy mechanism.
All reactions were conducted at 0.2 mmol scale under N2 atmosphere and blue LEDs irradiation (24 W, 460 ± 5 nm) without extra heating (at 35 ± 5 °C). Yields of products 1–5 were determined by 1H-NMR analysis using 1,3,5-trimethoxybenzene as an internal standard. a Phosphonylation. aIsolated yield in parenthesis. b Amination. c Etherification. d Esterification. e Thioetherification.
The bpyNi-PHI-based catalysts bearing lower bpyNi loadings (2.5 wt % and 1.5 wt %) delivered product 1 in decreased yields (Fig. 4a, entries 2 and 3), signifying that increasing the number of LnNi2+ active sites in LnNi-PHI is beneficial for the activity. Only trace amounts or low yields of coupled products were observed with Ni-PHI (3.2 wt % Ni, prepared from NiCl2 and K-PHI without additional bpy ligand) or a mix of both K-PHI and NiCl2 (Fig. 4a, entries 4 and 5; Fig. 4b−e, conditions B and C), verifying the bidentate nitrogen ligands (L) in LnNi-PHI play an essential role in dictating the excellent activity. Remarkably, with very low loadings of bpyNi-PHI (0.28 mol%, 0.28 mol%, 0.07 mol%, 0.07 mol%, and 0.14 mol% based on bpyNi for phosphonylation, amination, etherification, esterification and thioeserification, respectively), the reactions proceeded smoothly to afford C−P, C−N, C−O and C−S coupling products 1−5 with turnover numbers (TONs) of ~330, ~320, ~1200, ~1100 and ~680, respectively (Fig. 4a, entry 6; Fig. 4b−e, condition D). In contrast, K-PHI with separate addition of bpyNiCl2 gave low yields of coupling products (1: 13%, 2: 8%, 3: 6%, 4: 6%, and 5: 7%) at the same catalyst loading under identical conditions (Fig. 4a, entry 7; Fig. 4b−e, condition E), demonstrating that the proximity and cooperativity of the LnNi2+ active species and PHI photocatalyst carrier in LnNi-PHI might facilitate SET, and free radical transfer. In addition, other LnNi-CN catalysts exhibited much lower catalytic activities, affording coupling product 1 in low yields, due to the limited Ni-loading in these catalysts (Fig. 4a, entries 8–10).
Recyclability and leaching test
Apart from the enhanced catalytic activity, another intrinsic advantage of LnNi-PHI is potential reusability of the solid metallaphotocatalyst. Therefore, we conducted the recyclability and leaching test to probe the multinuclear catalyst deactivation and the heterogeneity of the reaction. As shown in Fig. 5a, the recovered bpyNi-PHI can be reused for further cycles to give C−P coupling product 1 and the rates of reactions over five catalytic cycles remain the same. Meanwhile, bpyNi-PHI can also at least be recycled five times without loss of activity in C−N, C−O, and C−S couplings, affording the corresponding product 2-5 with maintained yields (Fig. 5b). The recovered bpyNi-PHI after photocatalytic C−P coupling reaction was characterized by UV-vis DRS, IR, PXRD, XPS, TEM, and NMR to demonstrate the robustness of the catalyst. After catalysis, two typical diffraction peaks at 8.2° and 28.2° in XRD patterns (Fig. 5c) and the Ni 2p peak at 856 eV in XPS survey spectra (Fig. 5d and Supplementary Fig. 21) remain unchanged, indicating the structure of bpyNi-PHI was preserved during the catalysis. The FT-IR and UV-vis DRS spectra of bpyNi-PHI were also well maintained before and after the reaction (Supplementary Fig. 22). According to the statistical results of TEM images (Fig. 5e and Supplementary Fig. 23), bpyNi-PHI maintained the layered structure without formation of agglomerated Ni/Ni-O nanoparticles in the catalytic process56. Furthermore, the nickel complex in the recovered bpyNi-PHI with Ni to bpy molar ratio of ~1/1 was detected by 1H-NMR in combination with the ICP-OES results (Fig. 5f, g). Besides, slight leakage of bpyNi2+ catalytic species was observed during the recycling (Fig. 5g).
a Kinetic profile of the photocatalytic C–P coupling (0.2 mmol scale with 10 mg of bpyNi-PHI) over five catalytic cycles. b Catalyst recycling (for five catalytic cycles) of the C–N, C–O, and C–S coupling. c XRD patterns. d XPS survey spectra. e TEM images of recovered bpyNi-PHI catalyst after photocatalytic C–P coupling reaction. f 1H-NMR spectra (DMSO-d6, 400 MHz) of recovered bpyNi-PHI after treatment with 1.5 M HCl in a mixed H2O:MeOH (1:1, v-v) solvent. g Amount of nickel and ligand in recovered bpyNi-PHI determined by ICP-OES and 1H-NMR analysis.
Substrate scope of bpyNi-PHI catalyzed C−heteroatom couplings
Encouraged by the excellent catalytic activity, reliable stability, and good recyclability of LnNi-PHI, we sought to explore the scope and robustness of the bpyNi-PHI based heterogeneous metallaphotocatalyst in catalyzing diverse C−heteroatom cross-couplings. As shown in Fig. 6, a wide range of aryl/heteroaryl iodides bearing various electron-donating and electron-withdrawing substituents could undergo C−P, C−N, and C−S couplings smoothly, affording the corresponding triarylphosphine oxides (2, 6−20), biaryl/heteroaryl amines (22−34), N-aryl/heteroaryl sulfonamides (35−39), thioethers (86−93) for good to excellent yields (70−98%).
Reaction conditions: aryl iodide (0.2 mmol), bpyNi-PHI (10 mg, 6 wt %), phosphine oxide (0.3 mmol, 1.5 eq.) or alcohol (1.0 mmol, 5.0 eq.) or amine (0.3 mmol, 1.5 eq.) or thiol (0.3 mmol, 1.5 eq). Condition A: iPr2NH (0.6 mmol, 3.0 eq.) in DMF (2 mL). Condition B: TMG (0.4 mmol, 2.0 eq.) in MeCN (2 mL). Condition C: BIPA (0.6 mmol, 3.0 eq.) in DMSO (2 mL). Condition D: iPr2NH (0.6 mmol, 3.0 eq.) in MeCN (2 mL). a42 h. bUsing methyl 4-bromobenzoate as coupling partner. c24 h. d60 h. e16 h. f36 h. g48 h. h13/1 ratio of bromo-substituted product 64 vs iodo-substituted product. iAlcohol (3.0 eq.). jUsing 10 eq. of H2O as coupling partner. k10 h. l6 h. All reactions were performed under N2 atmosphere and blue LEDs irradiation (24 W, 460 ± 5 nm) without extra heating (at 35 ± 5 °C). Isolated yields are given.
A series of synthetically useful functional groups, including ketone (6, 29, 61), aldehyde (92), ester (1, 3, 5, 28), cyano (7, 27, 62), hydroxyl (13, 90), and even unprotected NH2 groups (14, 91), are compatible with the reaction conditions. Regarding C−O couplings, this catalytic system works well with electron-deficient aryl iodides and heteroaryl iodide (3, 4, 61–63, 66), whereas substrates lacking an electron-withdrawing group exhibit low reactivity (64, 65), presumably due to the issue of oxidative addition of the corresponding aryl iodides with Ni species. Notably, the couplings could proceed selectively at the iodo-functionalized carbon atom; both aryl bromide and chloride bonds remained intact, thus providing the possibility for further synthetic elaborations (8, 9, 25, 30, 37, 86). Additionally, strong electron-deficient aryl bromide is also suitable for C–P, C–O, and C–N couplings with lower reactivity (1, 3, 28).
With respect to the heteroatom coupling partners, a wide array of other P-, N-, O-, S-containing weak nucleophiles can be effectively coupled, including dialkyl phosphite (21), aryl/heteroaryl amines (2, 40–48), primary alkyl amines (49–51), sulfonamides (54, 55), sulfoximine (56), imine (57), amide (58), carbamates (59, 60), primary alcohols (67–75), secondary alcohols (76, 77), water (78), aromatic acids (79, 80), aliphatic acids (81, 82), olefinic acids (83–85), aliphatic thiol (94), aromatic thiol (95) and thiolacids (96). However, secondary amines participated in this reaction with poor efficiency and selectivity, affording the desired C−N coupled products (52 and 53) in low yields, along with the formation of dehalogenated and phenol by-products. As in the case of aryl iodides, the coupling reactions exhibited good compatibility with functional groups such as cyclopropyl, benzyl, alkenyl, alkynyl groups (69, 70, 73, 74). In addition, high chemoselectivities for C−N and C−S coupling were observed in the presence of alcoholic functionality (46, 94).
Late-stage diversification and gram-scale synthesis
The applicability of bpyNi-PHI-based heterogeneous metallaphotocatalytic C−heteroatom bond formation was further explored for the late-stage diversification of bioactive and pharmaceutical molecules. As shown in Fig. 7a, complex aryl iodides derived from natural molecules including L-menthol and L-phenylalanine could undergo diverse C−heteroatom couplings smoothly, delivering the corresponding ether (97), ester (98, 99), phenol (100), amine (101), sulfonamide (102), phosphine oxide (103, 105) and thiolether (104) in satisfactory yields. A series of natural α-amino acid derivatives such as L-alanine, L-phenylalanine, L-proline, L-serine, L-cysteine were amenable to the C−O and C−S couplings to form the corresponding esterification, etherification, and thioletherification products (106–108, 109, 110) with high efficiency. The carbohydrate alcohols derived from D-fructose and D-glucose worked well under current catalytic system to produce the desired O-arylated products (111, 112) in good yields. Elaborated phenol (estrone) and (S)-styralyl alcohol also proved to be suitable O-containing coupling partners (113, 114). To further illustrate the potential practicality, we successfully applied the developed protocol to the preparation of antifungal phosphonate (115), derivatives of anti-inflammatory drug celecoxib (116), and antigout drug probenecid (117) as well as antidepressant drug fluoxetine (118). Moreover, the scalability of our protocol was demonstrated by gram-scale synthesis of triarylphosphine oxide 1 and antidepressant drug fluoxetine 118. As shown in Fig. 7b, the reaction scale was increased 20-fold in batches to produce the coupling product with only a minimal decrease in yield.
a Late-stage functionalization of bioactive and drug molecules. a16 h. b12 h. c36 h. dAlcohol (0.3 mmol, 1.5 eq.). eUsing elaborate phenol (estrone) as coupling partner. f72 h. gAlcohol (0.6 mmol, 3.0 eq.). h60 h. Isolated yields are given. b Gram-scale synthesis. See Fig. 6 and Supplementary Information for detailed reaction conditions and procedures.
In summary, we have developed a facile cation exchange strategy to incorporate a series of privileged bipyridyl-based Ni catalysts into highly ordered and crystalline K-PHI. A variety of PHI-supported cationic bipyridyl-based Ni catalysts have been successfully constructed and fully characterized by NMR, ICP-OES, XPS, HAADF-STEM and XAS. The obtained LnNi-PHI solid catalysts, featuring high dosage (~6 wt %) of site-isolated bipyridyl-Ni active species with Ni to bpy molar ratio of ~1/1, can be served as highly effective and recyclable metallaphotocatalysts for diverse C−heteroatom cross-coupling reactions with broad substrate scope and good functional group tolerance. The practicability of these heterogeneous protocols has also been demonstrated in the late-stage diversification of various bioactive compounds and pharmaceutical molecules. Notably, the proximity between Ni and photocatalytic centers in LnNi-PHI significantly enhances the photo/Ni dual catalytic activity, thus dramatic increasing the TONs (300−1200 for Ni). Additionally, the heterogeneous LnNi-PHI catalysts exhibit exceptional chemical stability with low Ni leaching during the reaction and thus can be recycled. We anticipate the ligand exchange strategy report here will provide the basis for develo** other novel PHI-supported metallaphotocatalysts.
Methods
Preparation of LnNi-PHI
To a 20 mL oven-dried sealed tube equipped with a magnetic stir bar was added (bpy)NiCl2(H2O)n (40 mg) and K-PHI (200 mg). It was capped with a rubber septum, evacuated, and backfilled with nitrogen three times. Then, DMF (5 mL) was added via syringe. The mixture was stirred under nitrogen at room temperature for 72 h and centrifuged. The resulting solid was successively washed with DMF (2 × 5 mL) with sonication and separation by centrifugation, deionized water (2 × 5 mL) with sonication and separation by centrifugation, and MeCN (2 × 5 mL) with sonication and separation by centrifugation. The resulting powder was dried at 50 °C under vacuum for 12 h to yield bpyNi-PHI as dark yellow powder. (average yield per batch: ~202 mg). Other LnNi-PHI catalysts including dtbpyNi-PHI, dOMebpyNi-PHI, dClbpyNi-PHI and phenNi-PHI were prepared using the corresponding bipyridyl-Ni(II) complexes instead of (bpy)NiCl2(H2O)n via the same procedure as bpyNi-PHI. According to the ICP-OES results, the content of Ni in LnNi-PHI was determined to be 0.29 mmol/g (1.68 wt %) for bpyNi-PHI, 0.18 mmol/g (1.04 wt %) for dtbpyNi-PHI, 0.24 mmol/g (1.39 wt %) for dOMebpyNi-PHI, 0.21 mmol/g (1.22 wt %) for dClbpyNi-PHI, 0.25 mmol/g (1.45 wt %) for phenNi-PHI, respectively. The scale-up synthesis was also performed using 2.0 g of K-PHI and 0.4 g of (bpy)NiCl2(H2O)n in DMF (50 mL) to produce 2.1 g of bpyNi-PHI with 1.53 wt % Ni content.
General procedure 1 for bpyNi-PHI based heterogeneous photocatalytic C−P couplings
To a 10 mL oven-dried sealed tube equipped with a magnetic stir bar was added the corresponding aryl iodide (0.2 mmol, 1.0 eq.), H-phosphine oxide (0.3 mmol, 1.5 eq.) and bpyNi-PHI (10 mg, 6.0 wt % Nibpy). Then, dry DMF (2 mL) and iPr2NH (0.6 mmol, 3.0 eq.) were added. The tube was closed with a rubber septum and the reaction mixture was degassed by three cycles vacuum/N2 of “freeze-pump-thaw”. The reaction mixture was stirred and irradiated by blue LEDs (24 W, 460 ± 5 nm) without extra heating (35 ± 5 °C) for the indicated time. In each case, the blue LEDs was placed 3 cm from the reaction tube (Supplementary Fig. 19a). An independent fan was used to maintain the temperature inside the irradiation reaction system. Upon completion, the reaction mixture was diluted with deionized water (5 mL) and extracted with ethyl acetate (3 × 5 mL). The combined organic layer was washed with brine, dried over anhydrous Na2SO4, and concentrated. Finally, the crude residue was purified by silica gel column chromatography. For comparison, two 40 W Kessil PR lamp (50% power, 456 nm) were used as alternative light sources (Supplementary Fig. 19b), similar yield of methyl 4-(diphenylphosphoryl)benzoate (1, 48 h, 63.2 mg, 94%,) as obtained.
General procedure 2 for bpyNi-PHI based heterogeneous photocatalytic C−N couplings
To a 10 mL oven-dried sealed tube equipped with a magnetic stir bar was added the corresponding aryl iodide (0.2 mmol, 1.0 eq.), amine (0.3 mmol, 1.5 eq.), and bpyNi-PHI (10 mg, 6.0 wt % Nibpy). Then, dry MeCN (2 mL) and TMG (0.4 mmol, 2.0 eq.) were added. The tube was closed with a rubber septum and the reaction mixture was degassed by three cycles vacuum/N2 of “freeze-pump-thaw”. After that the reaction mixture was stirred and irradiated by blue LEDs (24 W, 460 ± 5 nm) without extra heating (35 ± 5 °C) for the indicated time. An independent fan was used to maintain the temperature inside the irradiation reaction system. In each case, the blue LEDs was placed 3 cm from the reaction tube (Supplementary Fig. 19a). Upon completion, the reaction mixture was concentrated under reduced pressure to evaporate the solvent, and the crude residue was purified by silica gel column chromatography.
General procedure 3 for bpyNi-PHI based heterogeneous photocatalytic C−O couplings
To a 10 mL oven-dried sealed tube equipped with a magnetic stir bar was added the corresponding aryl iodide (0.2 mmol, 1.0 eq.), alcohol (1.0 mmol, 5.0 eq.), and bpyNi-PHI (10 mg, 6.0 wt % Nibpy). Then, dry MeCN (2 mL) and TMG (0.4 mmol, 2.0 eq.) were added. The tube was closed with a rubber septum and the reaction mixture was degassed by three cycles vacuum/N2 of “freeze-pump-thaw”. The reaction mixture was stirred and irradiated by blue LEDs (24 W, 460 ± 5 nm) without extra heating (35 ± 5 °C) for the indicated time. In each case, the blue LEDs was placed 3 cm from the reaction tube (Supplementary Fig. 19a). An independent fan was used to maintain the temperature inside the irradiation reaction system. Upon completion, the reaction mixture was concentrated under reduced pressure to evaporate the solvent, and the crude residue was purified by silica gel column chromatography.
General procedure 4 for bpyNi-PHI-based heterogeneous photocatalytic C−O couplings
To a 10 mL oven-dried sealed tube equipped with a magnetic stir bar was added the corresponding aryl iodide (0.2 mmol, 1.0 eq., if solid), carboxylic acid (0.3 mmol, 1.5 eq., if solid), and bpyNi-PHI (10 mg, 6.0 wt % Nibpy). Then, dry DMSO (2 mL) and BIPA (0.6 mmol, 3.0 eq.) were added. The tube was closed with a rubber septum and the reaction mixture was degassed by three cycles vacuum/N2 of “freeze-pump-thaw”. After that the reaction mixture was stirred and irradiated by blue LEDs (24 W, 460 ± 5 nm) without extra heating (35 ± 5 °C) for the indicated time. In each case, the blue LEDs was placed 3 cm from the reaction tube (Supplementary Fig. 19a). An independent fan was used to maintain the temperature inside the irradiation reaction system. Upon completion, the reaction mixture was diluted with deionized water (5 mL) and extracted with ethyl acetate (3 × 5 mL). The combined organic layer was washed with brine, dried over anhydrous Na2SO4, and concentrated. Finally, the crude residue was purified by silica gel column chromatography.
General procedure 5 for bpyNi-PHI-based heterogeneous photocatalytic C−S couplings
To a 10 mL oven-dried sealed tube equipped with a magnetic stir bar was added the corresponding aryl iodide (0.2 mmol, 1.0 eq.), thiol or thiolacid (0.3 mmol, 1.5 eq.), and bpyNi-PHI (10 mg, 6.0 wt % Nibpy). Then, dry MeCN (2 mL) and iPr2NH (0.6 mmol, 3.0 eq.) were added. The tube was closed with a rubber septum and the reaction mixture was degassed by three cycles vacuum/N2 of “freeze-pump-thaw”. After that the reaction mixture was stirred and irradiated by blue LEDs (24 W, 460 ± 5 nm) without extra heating (35 ± 5 °C) for the indicated time. In each case, the blue LEDs was placed 3 cm from the reaction tube (Supplementary Fig. 19a). An independent fan was used to maintain the temperature inside the irradiation reaction system. Upon completion, the reaction mixture was concentrated under reduced pressure to evaporate the solvent, and the crude residue was purified by silica gel column chromatography.
Data availability
The authors declare that all data generated in this study are available within the article and the Supplementary Information. Any additional detail can be requested from the corresponding authors.
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Acknowledgements
This work is supported by funding from the Natural Science Foundation of Chongqing (CSTB2022NSCQ-MSX1105 to Y.C., CSTB2022NSCQ-MSX1032 to Y.T.), the National Natural Science Foundation of China (Grant no. 21801030 to Y.C.), the King Abdullah University of Science and Technology (KAUST), Saudi Arabia, Office of Sponsored Research (URF/1/4025 to C.Z. and M.R.). We thank the Analytical and Testing Center of Chongqing University for assistance with NMR spectrum analysis.
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L.X and Q.Y. performed photocatalytic experiments; Q.Y. and Y.B. synthesized and characterized LnNi-PHI catalysts; C.Z. checked data and carried out DFT calculation; Y.T., M.R., and Y.C. conceived and supervised the research study. Y.C., C.Z., and M.R. wrote the paper with input from all authors. All authors discussed the results. L.X., Q.Y., and C.Z. contributed equally.
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**ng, L., Yang, Q., Zhu, C. et al. Poly(heptazine imide) ligand exchange enables remarkable low catalyst loadings in heterogeneous metallaphotocatalysis. Nat Commun 14, 1501 (2023). https://doi.org/10.1038/s41467-023-37113-8
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DOI: https://doi.org/10.1038/s41467-023-37113-8
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