Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
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Ru Nanoparticles-Loaded Covalent Organic Framework for SolventFree One-Pot Tandem Reactions in Air Gong-Jun Chen,*,† Xiao-Bo Li,† Chen-Chen Zhao,† Hui-Chao Ma,† Jing-Lan Kan,† Yu-Bin Xin,† Cheng-Xia Chen,‡ and Yu-Bin Dong*,† †
College of Chemistry, Chemical Engineering and Materials Science, Collaborative Innovation Center of Functionalized Probes for Chemical Imaging in Universities of Shandong, Key Laboratory of Molecular and Nano Probes, Ministry of Education, Shandong Normal University, Jinan 250014, P. R. China ‡ MOE Laboratory of Bioinorganic and Synthetic Chemistry Lehn Institute of Functional Materials, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, P. R. China S Supporting Information *
ABSTRACT: Condensation of benzene-1,3,5-tricarbohydrazide with benzene-1,4dicarboxaldehyde generated a new covalent organic framework, COF-ASB (1), in which the organic units are held together via hydrazone linkage to form porous frameworks. COF-ASB (1) is highly crystalline and displays good chemical and thermal stability and is permanently porous. In addition, 1 can be an ideal support to load Ru nanoparticles (Ru NPs) to generate Ru@COF-ASB (2). The obtained composite material is able to highly promote one-pot tandem synthesis of imine products from benzyl alcohols and corresponding amines under solvent-free conditions in air.
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INTRODUCTION As an emerging class of porous crystalline solid materials, covalent organic frameworks (COFs) exhibit potential applications in gas adsorption and separation, sensing, catalysis, and proton conductivity.1 As a promising alternative to MOF materials, the robustness of COFs is improved, and they are more stable to aqueous and organic media, and even strong acidic or alkaline environment.2 These inherent advantages of COFs would make them more beneficial than MOF-based supports to upload active catalytic species, such as metal nanoparticles (MNPs), for catalysis, especially those catalytic reactions that are performed under relatively rigorous conditions. As the counterpart of MOFs,3 the study of COFsupported MNPs@COFs with heterogeneous catalytic nature, however, has received very limited investigation.4 As one important type of MNPs, ruthenium nanoparticles (Ru NPs) have attracted more attention owing to their excellent catalytic performance.5 Such highly active MNPs, however, tend to lose their catalytic activity as a consequence of the formation of aggregates due to their high surface energy.6 The alternative way for addressing such a problem is to immobilize MNPs in the porous supports which are decorated with heteroatom functionalities.7 For example, nitrogenmodified activated carbon supported Pt and Pd NPs exhibited high catalytic performance toward the alcohol oxidation.8 Notably, COFs are formed by means of reversible covalent bond formation reactions, and the heteroatom-involved © XXXX American Chemical Society
functional groups such as triazole, imine, and hydrazone could be facilely introduced into COFs during their synthetic processes. Therefore, COFs should meet the requirement at this point and are the ideal solid scaffolds to support MNPs for heterogeneous catalysis. In this contribution, we report a heteroatom-rich COF material COF-ASB (1) which is generated from benzene-1,3,5tricarbohydrazide (BTCH) and benzene-1,4-dicarboxaldehyde (TPAL) via the Schiff base condensation reaction. The obtained COF-ASB (1) can be an ideal support to upload Ru NPs to generate Ru@COF-ASB (2) composite material which can highly promote one-pot tandem synthesis of imines from alcohols and amines in heterogeneous way under solvent-free conditions.
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EXPERIMENTAL SECTION
Materials and Instrumentation. The reagents and solvents are commercially available and used without further purification. The Xray powder diffractometer (XRPD) patterns were collected by a D8 ADVANCEX-ray with Cu Kα radiation (λ = 1.5405 Å). ICP-LC was performed on an IRIS Interpid-II XSP and NU AttoM. High resolution transmission electron microscopy (HRTEM) analysis was performed on a JEOL 2100 electron microscope at an operating voltage of 200 kV. Mass spectra analysis was performed on API 200 LC/MS system (Applied Biosystems Co. Ltd.). 1H NMR and 13C Received: December 6, 2017
A
DOI: 10.1021/acs.inorgchem.7b03077 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry Scheme 1. Synthesis of 1 and 2a
a
Their photographs and SEM images are inserted. dichloromethane (3.0 mL) (3 times), and dried in vacuum at 90 °C for the next run under the same reaction conditions.
NMR spectra were recorded on Bruker Avance 400 MHz spectrometer. Gas chromatography (GC) analysis was performed on an Agilent 7890B GC. XPS spectra were obtained from PHI Versaprobe II. Thermogravimetric analysis (TGA) was performed on TGA/SDTA851e under N2 atmosphere from 50 to 650 °C. The structural modeling was conducted with the software of Materials Studio (ver. 5.0). Synthesis of COF-ASB (1). A mixture of benzene-1,3,5tricarbohydrazide (504 mg, 2 mmol) and benzene-1,4-dicarboxaldehyde (402 mg, 3 mmol) and a drop of HOAc in DMF (3 mL) was stirred at 120 °C for 72 h to generate 1 as bright yellow crystalline solids. The obtained crystalline solids were completely washed with water and MeOH and dried in air (Yield, 85%). IR: 3200 (m), 3065 (m), 1659 (s), 1603 (w), 1550 (s), 1256 (s), 830(w), 731(w). Elemental Analysis (%) calcd for C7H5N2O: C, 63.15; N, 21.04; H, 3.79. Found (%): C, 62.76; N, 20.87; H, 4.04. Synthesis of Ru@COF-ASB (2). 1 (15 mg) and HCl (0.3 mL) was added to a CH3CN (2 mL) solution of ruthenium(III) chloride hydrate (10 mg, 0.05 mmol). The mixture was stirred for 24 h at room temperature. The resulting solid was isolated by centrifugation and washed with CH2Cl2. The obtained black crystalline solids (Scheme 1) were mixed with NaBH4 (1 mg, 0.026 mmol) in water (2 mL), and the mixture was stirred for additional 5 h to afford Ru@COF-ASB (2) as black crystalline solids. The obtained solids were completely washed with water and MeOH and dried in air. IR: 3200 (m), 3065 (m), 1659 (s), 1603 (w), 1550 (s), 1256 (s), 830(w), 731(w). ICP measurement indicated that the encapsulated amount of Ru NPs in 2 is 4.1% (mass fraction). Solvent-Free Oxidation of Benzyl Alcohols. A mixture of benzyl alcohol (1 mmol) and 2 (70 mg, 5% mol Ru) was stirred at 80 °C for 24 h to afford benzaldehydes with yield 80−93% (the products were diluted with methylene chloride and determined by GC). Leaching Test. Ru@COF-ASB (2) was separated from the reaction solution by centrifugation, and the reaction solution was transferred to another reaction vial under the same conditions. One-Pot Tandem Synthesis of Imines from Alcohols and Amines. A mixture of benzyl alcohol (1 mmol), corresponding amine (1.2 mmol), and Ru@COF-ASB (2) (70 mg, 5 mol % Ru) was stirred at 80 °C for 22 h. The yields of obtained imines were determined by GC. Recycle and Activation of Ru@COF-ASB (2). 2 was recovered by centrifugation, then was washed with ethanol (3.0 mL) and
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RESULTS AND DISCUSSION Synthesis and Structural Analysis of COF-ASB (1) and Ru@COF-ASB (2). As shown in Scheme 1, COF-ASB (1) was prepared in good yield (85%) by heating the mixture of benzene-1,3,5-tricarbohydrazide and benzene-1,4-dicarboxaldehyde with catalytic amount of HOAc in DMF at 120 °C for 72 h. 1 was obtained by filtration and successively washed with water, dichloromethane, and ethanol to afford yellow powders that were insoluble in common organic solvents and water. The morphology of the as-prepared 1 was examined by scanning electron microscopy (SEM), and their particle morphology was observed (Scheme 1). Thermogravimetric analysis (TGA) showed that no weight loss of 1 was observed until 350 °C (Figure S1, Supporting Information). Furthermore, COF-ASB (1) was characterized by Fourier transform infrared (FT-IR) and 13C cross-polarization magic angle spinning (CP-MAS) spectroscopies. The IR spectrum of 1 showed the >CO band at 1698 cm−1 of benzene-1,4dicarboxaldehyde disappeared after the condensation reaction. Meanwhile the >CN− band at 1603 cm−1 that is characteristic of the >CN− group appeared, indicating that the acylhydrazone Schiff base linkage formed9 from the condensation of benzene-1,3,5-tricarbohydrazide and benzene1,4-dicarboxaldehyde. In 1, the >CO band was observed at 1659 cm−1 while the corresponding band in the starting material of benzene-1,3,5-tricarbohydrazide was located at 1624 cm−1. This shift could be considered as a weakening of the >CO bonds as a result of resonance with the imine group, which is similar to that of molecular hydrazones.9,10 In addition, the signals at 731 and 830 cm−1 indicated that both sym-triand para-substituted phenyl moieties exist in 1. Solid-state 13C CP-MAS NMR was also used to establish the connectivity of the COF species. The existence of the phenyl (141 ppm) and acylhydrazone Schiff base (173, 158 ppm) groups in 1 was well B
DOI: 10.1021/acs.inorgchem.7b03077 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 1. (a) IR spectra of benzene-1,4-dicarboxaldehyde (purple), benzene-1,3,5-tricarbohydrazide (cyan), COF-ASB (1, blue), Ru(III)@COFASB (red), and Ru@COF-ASB (black, 2). (b) 13C NMR of 2.
Figure 2. Left: The simulated (black line) and measured PXRD patterns of 1 (red line) and 2 (purple). Riveted refinement (blue line), and the difference plot between measured and Rietveld-refined PXRD patterns (dark green line). Right: HRTEM images and the electron diffraction of 1.
Figure 3. (a) Crystal packing pattern viewed down the crystallographic c axis. (b) Single hexagonal unit. (c) Crystal packing pattern viewed down the crystallographic a axis.
the optimized parameters of a = b = 31.823 Å and c = 3.700 Å, α = β = 90°, and γ = 120° (residuals wRp = 5.08% and Rp = 3.86%, Supporting Information). Its typical hexagonal crystal system is further supported by the electron diffraction (Figure 2). The calculated PXRD pattern of this hexagonal unit cell well matches with the experimental profile, including the peak location and intensity. As shown in Figure 2, 1 displays intense peaks at 5.54°, 6.40°, 8.48°, and 24.05° that correspond to the (2,−1,0), (2,0,0), (3,−2,0) and (0,0,1) planes, respectively. The observed PXRD patterns of 1 exhibited peaks with the d spacing of 15.93, 13.79, 10.41, and 3.70 Å, respectively. In
confirmed via the characteristic resonances, respectively (Figure 1b). As revealed by its powder X-ray diffraction (PXRD) pattern (Figure 2), COF-ASB (1) features a microcrystalline material with a long-range structure, and no diffraction peaks related to the substrates of benzene-1,3,5-tricarbohydrazide and benzene1,4-dicarboxaldehyde were observed, indicating the sole formation of 1. The structural modeling was then conducted with the software of Materials Studio (ver. 5.0).11 The most probable structure of 1 was simulated, analogous to that of 1 as a 2D eclipsed layered sheets using the space group of P6 with C
DOI: 10.1021/acs.inorgchem.7b03077 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 4. (a) XPS spectrum of 2. (b) HR-TEM image of 2. (c) N2 adsorption isotherms of 1 and 2 at 77 K. (d) The pore widths of 1 (black line) and 2 (red line) are centered at 2.5 and 2.0 nm, respectively.
In the full XPS spectrum of 2 (Figure 4a), the referencing of the binding energy scale is complicated by the superposition of the C(1s) and the Ru (3d) signals. The two bands at 280.2 and 284.4 eV can readily be assigned of Ru (0) 3d3/2 and 3d5/2, respectively.12 In addition, the Ru (0) 3p3/2 and 3p1/2 peaks were also observed at 461.5 and 483.5 eV in the Ru 3p region. All these measured values are comparable to those of ruthenium metal, 280, 285, 461, and 483 eV for the Ru(0) 3d5/2, 3d3/2, 3p3/2, and 3p1/2, respectively.12 In addition, we used HR-TEM to investigate the Ru NPs dispersion and size in 2. As indicated in Figure 4b, the Ru NPs in 2 were highly dispersed with particle sizes of 2−5 nm. The atomic lattice fringes with an interplanar spacing of 0.23 nm, which was corresponding to the lattice spacing of (100) plane of hcp metallic Ru.13 The porosity difference before and after Ru loading was further supported by the gas adsorption−desorption measurement. As shown in Figure 4c, N2 adsorption at 77 K revealed absorption amounts of 357.88 and 122.66 cm3/g by COF-ASB (1) and Ru@COF-ASB (2), respectively. The surface area calculated on the basis of the BET model is 233.15 m2/g for 1 and 101.92 m2/g for 2. The hysteresis in some reported microporous 2D COFs was also observed, which might be attributed to the dynamic response of the flexible framework.2c Part of the surface area loss and pore volume decrease can be attributed to the embedded Ru NPs. The pore size distribution curves, calculated from Barrett−Joyner−Halenda analysis, showed that 1 and 2 with pore widths of ca. 2.5 (1) and 2.0 nm (2), respectively (Figure 4d). The PXRD pattern after Ru NPs loading was well in agreement with that of 1 but with reduced crystallinity, indicating that the structural integrity of 1 well preserved (Figure 2). Oxidation of Benzyl Alcohol under Solvent-Free Conditions in Air. For one-pot tandem imine synthesis from alcohols and amines, we first examine the catalytic behavior of Ru@COF-ASB (2) for catalytic benzyl alcohol to benzaldehyde. The best result was observed when the benzyl
addition, the observed peak at 24.5° is correlated to the value of the interlayer distance. The d spacing of 1 was calculated to be 3.7 Å, which is well consistent with the high-resolution transmission electron microscope (TEM) characterization (Figure 2). The AA stacking model in 1 was determined by the forcefield-based molecular mechanics calculations (Figure 3a). Compared to AB-type staggered structure, the eclipsed model is more energetic preferential (Figure S2, Supporting Information). As shown in Figure 3b, the eclipsed 2D structure contains a hexagonal structural unit, in which the opposite Ocarbonyl···Ocarbonyl distance is ca. 3.1 nm. The close-packed 2D layers with an interlayer distance of 3.7 Å indicated that adjacent layers in 1 are in a weak π−π contact (Figure 3c). Ru NPs embedded Ru@COF-ASB (2) was simply prepared by the reduction (NaBH4, H2O, 5 h, r.t.) of Ru(III)@COF-ASB that was obtained by impregnating of 1 in a solution of RuCl3 in MeOH at room temperature for 1 h. The color of 1 changed from yellow to dark of 2 after the impregnation and reduction processes (Scheme 1). The total uploaded Ru amount, as determined by in inductively coupled plasma (ICP) measurement, is up to 4.1 wt %. The EDS mapping images of Ru(III)@ COF-ASB and Ru@COF-ASB (2) indicated that the Ru species homogeneously distributed in the COF matrix (Figures S3−S4, Supporting Information). The oxidation state of the Ru NPs in 2 was determined by Xray photoelectron spectroscopy (XPS, Figure 4a). Notably, if Ru(III)@COF-ASB was treated by large excess amount of NaBH4 under the given reaction conditions, the >CN- Schiff base linkage would also be reduced, and the peak at 55 ppm in solid-state 13C CP-MAS NMR spectrum clearly indicated the formation of the secondary amino group (Figure S5, Supporting Information). Therefore, the hydrazone linkage in 1 could be kept intact during the reduction process with controlled amount of NaBH4. This selective reducing approach would be very useful to construct many more new metal NPsloaded catalytic systems based on imine-linked COFs. D
DOI: 10.1021/acs.inorgchem.7b03077 Inorg. Chem. XXXX, XXX, XXX−XXX
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that the doped Ru NPs in the COF-ASB matrix are responsible for the catalytic activity (Figure S10, Supporting Information). As a heterogeneous catalyst, the recyclability of 2 was also examined. As shown in Figure 5b, 2 can be recycled five times. After each catalytic run, the solid catalyst was collected by centrifugation, washed with acetonitrile, dried at 90 °C, and reused in the next run under the same conditions. The reaction conversion was still up to 87% at the fifth catalytic run with 100% selectivity (Figure S11, Supporting Information). After five runs, XPS spectrum indicated that the valence state of Ru remains unchanged. HR-TEM image showed that the size of the Ru NPs in 2 was basically unchanged after five runs, and the PXRD pattern of 2 after recycling demonstrated that the COF structural integrity and crystallinity of 1 was preserved, so 2 was very stable during this oxidation recycling process (Figure S12, Supporting Information). With the optimized conditions in hand, we investigated the scope of the 2-catalyzed oxidation reactions utilizing different liquid benzyl alcohols. As shown in Table 1, the benzyl alcohols
alcohol oxidation reaction in air was carried out in the presence of 2 (5 mol % Ru) under solvent-free conditions at 80 °C (monitored by GC). As shown in Figure 5a, with the increase
Figure 5. Solvent-free oxidation of benzyl alcohol. (a) Reaction time examination (black line) and leaching test (red line) for solvent-free oxidation of benzyl alcohol reaction. The solid catalyst was filtrated from the reaction solution after 4 h, whereas the filtrate was transferred to a new vial, and reaction was carried out under the same conditions for an additional 16 h. (b) Catalytic cycles. After each run, the catalyst was collected by centrifugation, washed with ethanol and dichloromethane, and dried at 90 °C in vacuum for the next catalytic run under the same conditions. Reaction conditions: benzyl alcohol (104 μL, 1 mmol), 2 (70 mg, 5 mol % Ru), temperature 80 °C.
Table 1. Summary of the Liquid Benzyl Alcohols Oxidation Catalyzed by 2
in time from 2 to 25 h, the yield of benzaldehyde significantly enhanced. It should be noted that an excellent yield of 90% was achieved at 24 h (conversion 90%, selectivity 100%). However, no more changes in the yield can be observed after extending the reaction time (Figure S6, Supporting Information). In addition, when the reactions were performed at 90 and 100 °C, the oxidation product yields were 90 and 91%, respectively. Also, when benzyl alcohol oxidation was carried out at 60 and 70 °C, benzaldehyde was obtained in lower 49 and 69% yields, respectively. In view of the following condensation reaction between amine and the in situ generated benzaldehyde, the optimum reaction temperature of 80 °C was adopted (Figure S7, Supporting Information). It is known that the direct synthesis of −RCN− from amines and alcohols via one-pot tandem reaction is challenging because the optimal reaction conditions for the first aerobic alcohol oxidation step and the second anaerobic condensation step largely differ from each other. The higher temperature would be beneficial to the aerobic alcohol oxidation but detrimental to the stability of the co-existing amine substrate (Figure S8, Supporting Information). It therefore, appears that 24 h and 80 °C are the optimum reaction time and temperature for the maximum yield of benzaldehyde under solvent free conditions. The total number (TON) is 18 h−1, and turnover frequency (TOF) is 0.75 h−1 under the optimized conditions. In order to show the heterogeneous nature of 2, the hot leaching test was examined. As shown in Figure 5a, the yield did not increase without 2 after ignition of the oxidation reaction at 6 h (Figure S9, Supporting Information), indicating 2 exhibited a typical heterogeneous catalyst nature. In addition, only tiny amounts of benzaldehyde (Yield, 2%) was generated when the oxidation reaction was performed in the presence of 1 under the optimized conditions, indicating
with electron-withdrawing nitro group showed less reactivity and gave a relatively lower conversion (80%), whereas the electron-donating group of methoxy-substituted benzyl alcohols proved to be more active and furnished the desired products in 93% conversion. Notably, the reaction selectivity toward benzaldehydes is 100% in all cases (Figure S13, Supporting Information). Comparing this work with other catalysts for the solvent-free selective oxidation of benzyl alcohol (Table S1, Supporting Information), 2 exhibits excellent catalytic activity and selectivity for benzyl alcohol oxidation. One-Pot Tandem Synthesis of Imines from Benzyl Alcohols and Amines. As known, imine is a very important class of compounds in organic synthesis, biomedicine, and materials science. As shown above, 2 is a highly efficient and stable catalyst for benzyl alcohol oxidation under solvent-free conditions in air. Thus, we wondered if the imine species could be one-pot synthesized from alcohols and amines in the presence of 2 under reaction conditions. For this, benzyl alcohol and phenylamine amine were chosen as model substrates. To our delight, when the mixture of benzyl alcohol (1 mmol) and phenylamine (1.2 mmol) was stirred at 80 °C in the presence of 2 (5 mol % Ru) for 22 h (monitored by TLC) under solvent-free conditions, the corresponding imine product was generated in 90% yield (conversion 90%, selectivity 100%) (Figure S14, Supporting Information). As shown in Figure 6, the conversion began to decrease after 22 h. The TON and TOF at 22 h for N-benzylideneaniline formation from alcohol and amine were 18 and 0.82 h−1, respectively, E
DOI: 10.1021/acs.inorgchem.7b03077 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 6. Solvent-free one-pot tandem reaction from benzyl alcohol. (a) Reaction time examination (black line) and leaching test (red line) for solvent free one-pot tandem synthesis of imine. The solid catalyst was filtrated from the reaction solution after 6 h, whereas the filtrate was transferred to a new vial, and reaction was carried out under the same conditions for an additional 12 h. (b) Catalytic cycles. After each run, the catalyst was collected by centrifugation, washed with ethanol and dichloromethane, and dried at 90 °C in vacuum for the next catalytic run under the same conditions. Reaction conditions: Ru@COF-ASB (2) (70 mg, 5 mol % Ru), benzyl alcohol (104 μL, 1 mmol), phenylamine (109 μL, 1.2 mmol), and 80 °C.
under the optimized reaction conditions (Figure S15, Supporting Information). Again, the heterogeneous catalytic nature of 2 was confirmed by the hot leaching test. As shown in Figure 6, no further reaction occurred in the absence of 2 after ignition of the reaction at 6 h, indicating that 2 is a heterogeneous catalyst for this one-pot tandem reaction (Figure S16, Supporting Information). In addition, the second condensation step between benzaldehyde and phenylamine was very fast, and the reaction could be finished in several minutes under the given reaction conditions with or without 2. For example, the desired Nbenzylideneaniline was obtained in 94% yield after 3 min with 2 under solvent-free condition at 80 °C, meanwhile high reaction efficiency (3 min, 93%) was also observed in the absence of 2 under the same reaction conditions (Figure S17, Supporting Information). Therefore, 2, as an alcohol oxidation catalyst, did not affect and inhibit the second step of the condensation reaction under the reaction conditions. The recyclability of 2 was examined for this one-pot tandem reaction. After each catalytic run, the solid catalyst of 2 was collected by centrifugation, washed with acetonitrile, dried at 90 °C, and reused in the next run under the same conditions. As shown in Figure 6, the conversion was still up to 88% with 100% selectivity for the fifth catalytic run (Figure S18, Supporting Information). Notably, the size and valence of the Ru NPs in 2 remain unchanged after five runs (Figure S19, Supporting Information). In addition, the amount of Ru species in 2 was examined by ICP. The result showed the amount of Ru is 4.0%, indicating that basically no Ru species loss occurred after five catalytic cycles. Moreover, the PXRD pattern of 2 after reused for five cycles demonstrated that the structural integrity of 2 was well preserved (Figure S19, Supporting Information). Therefore, 2 herein is able to tolerate relatively rigorous reaction conditions, such as higher temperature, air atmosphere, and relatively long reaction time. So COF-ASB (1) is an ideal platform to support Ru NPs for this tandem reaction. After that, we examined the scope of this one-pot tandem reaction under the optimized reaction conditions. Table 2 summarized the results of these tandem reactions. We found that the combination of benzyl alcohols without substituted
Table 2. Summary of the One-Pot Tandem Reactions Based on Substituted Benzyl Alcohols and Phenylamines and Benzylaminesa
a
Reaction conditions: Ru@COF-ASB (2) (70 mg, 5 mol % Ru), benzyl alcohol (1 mmol), amine (1.2 mmol), 80 °C, solvent-free, in air, 22 h. Yields were determined by GC (Figure S20, Supporting Information).
group or electron-donating groups with aminobenzenes without substituent group or with electron-withdrawing groups generally afforded the desired products in higher yields (80− 91%). However, a combination of the aminobenzene bearing electron-withdrawing group such as −Cl with either electrondonating or electron-withdrawing groups attached benzyl F
DOI: 10.1021/acs.inorgchem.7b03077 Inorg. Chem. XXXX, XXX, XXX−XXX
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alcohols gave relatively lower yields (75−81%). In addition, the one-pot tandem reaction was expanded to benzyl alcohols and benzylamines. As shown in Table 2, N-benzylidenebenzylamines were successfully prepared under the reaction conditions. It seems that the substituted group type on benzylamines did not significantly affect the product yield. On the other hand, the benzyl alcohols with electron-donating groups or without substituted groups afforded the corresponding imine products in higher yields (89−92%) than those with electron-withdrawing groups (70−75%) (Figure S20, Supporting Information).
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CONCLUSION In summary, we successfully prepared a new porous COF-ASB (1)-supported Ru NPs catalytic composite system that was demonstrated to be a highly efficient heterogeneous catalyst for the one-pot tandem synthesis of imines from benzyl alcohols and anilines and from benzyl alcohols and benzylamines. We expect this approach will be useful for the fabrication of many more new and attractive COF-supported meal NPs heterogeneous catalysts, and studies toward the synthesis of new metal NPs-loaded COF composite catalytic heterogeneous systems are underway.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b03077. Additional characterization of 1 and 2, GC results for the benzyl alcohols oxidation and one-pot syntheses of Nbenzylidenebenzylamine and N-benzylideneaniline, and the characterization of 2 after catalysis (PDF)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Yu-Bin Dong: 0000-0002-9698-8863 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We are grateful for financial support from NSFC (grant nos. 21671122, 21475078, 21301109, 21501111) and Taishan scholar’s construction project.
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REFERENCES
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DOI: 10.1021/acs.inorgchem.7b03077 Inorg. Chem. XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.inorgchem.7b03077 Inorg. Chem. XXXX, XXX, XXX−XXX
