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Dual Heterogeneous Catalyst Pd−Au@Mn(II)-MOF for One-Pot Tandem Synthesis of Imines from Alcohols and Amines Gong-Jun Chen,* Hui-Chao Ma, Wen-Ling Xin, Xiao-Bo Li, Fa-Zheng Jin, Jing-Si Wang, Ming-Yang Liu, 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 S Supporting Information *

ABSTRACT: A new Mn(II) metal−organic framework (MOF) 1 was synthesized by the combination of 4,4,4-trifluoro-1-(4-(pyridin-4-yl)phenyl)butane-1,3-dione (L) and Mn(OAc)2 in solution. 1 features a threefold-interpenetrating NbO net containing honeycomb-like channels, in which the opposite Mn(II)···Mn(II) distance is 23.5075(10) Å. Furthermore, 1 can be an ideal platform to support Pd−Au bimetallic alloy nanoparticles to generate a composite catalytic system of Pd−Au@ Mn(II)-MOF (2). 2 can be a highly active bifunctional heterogeneous catalyst for the one-pot tandem synthesis of imines from benzyl alcohols and anilines and from benzyl alcohols and benzylamines.

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INTRODUCTION It is well-known that imines are very important class of intermediates in the synthesis of various pharmaceutical, agricultural, and biological compounds. As an electrophile, the imine group is widely used in many types of organic reactions such as reduction, addition, condensation, and cycloaddition and also in multicomponent reactions.1 Imines are conventionally synthesized by the condensation of aldehydes or ketones with amines.2 The direct synthesis of imines from alcohols and amines via a one-pot tandem reaction, however, is more advantageous. Compared with aldehydes and ketones, alcohols are much more stable and readily available starting materials.3 On the other hand, tandem synthesis features cost and time savings, fewer chemicals, less energy consumption, and simplified purification processes,4 so the imine synthesis via tandem catalysis is more eco-friendly and economical. To date, some useful approaches have been developed for the direct synthesis of imines, including oxidation of secondary amines,5 selfcondensation of primary amines upon oxidation,6 and oxidative coupling of alcohols and amines.7 The catalysts for the reported direct synthesis of imines, however, are mainly homogeneous ones. Compared with homogeneous catalysts, heterogeneous catalysts are more preponderant because of their inherent merits of stability, durability, reusability, and separability.8 Very recently, heterogeneous metal−organic framework (MOF)-supported metal nanoparticle (NP) catalytic systems have been demonstrated to be highly efficient in promoting a wide variety of organic reactions.9 In comparison with MOFsupported monometallic NPs, MOF-supported bimetallic metal alloy NPs have received much less attention. On the other © XXXX American Chemical Society

hand, because of the synergistic effects between different metal NPs, heterometallic alloy NPs have proven superior to homometallic NP catalysts in some clean and energy-efficient chemical processes. Examples include vinyl acetate synthesis over a Pd−Au/SiO2 composite catalyst and other catalytic reactions with Pd−[email protected] Herein we report a new porous Mn(II) MOF, 1, which can be a platform to support Pd−Au bimetallic alloy nanoparticles to produce a composite catalytic system. The obtained Pd− Au@Mn(II)-MOF (2) can efficiently promote the synthesis of imines from alcohols and amines. 2 is heterogeneous and can be reused at least five times with retention of its high catalytic performance.

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EXPERIMENTAL SECTION

Materials and Chemicals. The reagents and solvents are commercially available and were used without further purification. The ligand 4,4,4-trifluoro-1-(4-(pyridin-4-yl)phenyl)butane-1,3-dione (L) was synthesized according to our reported procedure.11 Instrumentation. Powder X-ray diffraction (PXRD) patterns were collected on a D8 ADVANCE X-ray diffractometer with Cu Kα radiation (λ = 1.5405 Å). The total surface areas of the catalysts were measured by the Brunauer−Emmett−Teller (BET) method using carbon dioxide adsorption at 195 K on a Micromeritics ASAP 2000 sorption/desorption analyzer. ICP-LC was performed on an IRIS InterpidII XSP and NU AttoM instrument. High-resolution transmission electron microscopy (HRTEM) analysis was performed on a JEOL 2100 electron microscope at an operating voltage of 200 kV. Scanning electron microscopy (SEM) images and energy-dispersive Xray (EDX) spectra were taken on a SUB010 scanning electron Received: October 26, 2016

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DOI: 10.1021/acs.inorgchem.6b02592 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. Syntheses of 1 and 2. the reaction system was heated at 110 °C for 24 h to afford the desired N-benzylidenebenzylamine product (95% conversion, 99% selectivity, monitored by GC). N-Benzylideneaniline Formation from Alcohols and Amines. A toluene solution (2 mL) of benzyl alcohol (52 μL, 0.52 mmol), aniline (66 μL, 0.62 mmol), KOH (2.8 mg, 0.05 mmol), and 2 (2.0 mg, 0.75 mol %) was heated at 110 °C for 30 h to afford Nbenzylideneaniline with excellent conversion (99%) and selectivity (99%) as monitored by GC. Regeneration of 2. 2 was recovered by centrifugation, washed with ethanol (3.0 mL) and dichloromethane (3.0 mL) (three times), and dried at 90 °C in vacuum for the next run under the same reaction conditions. Leaching Test. 2 was separated from the solution by centrifugation, and the reaction solution was transferred to another reaction vial under the same conditions.

microscope with an acceleration voltage of 20 kV. Gas chromatography (GC) analysis was performed on an Agilent 7890B gas chromatograph. Electron spin resonance (ESR) spectra were obtained on a Bruker A300-10/12/S-LC spectrometer. X-ray photoelectron spectroscopy (XPS) was performed using a PHI Versaprobe II spectrometer. X-ray Crystallography. Diffraction data for the complex were collected at 293(2) K on an Agilent SuperNova single-crystal X-ray diffractometer using Cu Kα radiation (λ = 1.54178 Å) with the ω−2θ scan technique. An empirical absorption correction was applied to the raw intensities.12 The structure was solved by direct methods (SHELXS-2014) and refined by the full-matrix least-squares technique on F2 using the SHELXS-2014.13 The hydrogen atoms were added theoretically, riding on the concerned atoms and refined with fixed thermal factors. The details of crystallographic data and structure refinement parameters are summarized in Table S1. The selected bonds lengths and angles for 1 are summarized in Table S2. CCDC 1486541 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/ cif. Synthesis of Mn(II)-MOF ((MnL2)·2CH3OH, 1). A solution of Mn(OAc)2·4H2O (2.4 mg, 0.01 mmol) in MeOH (1 mL) was layered onto a solution of L (4.8 mg, 0.02 mmol) in CH2Cl2 (2 mL). The solutions were left for about 3 days at room temperature, and compound 1 was obtained as light-brown crystals. Yield: 84%. IR (KBr pellet, cm−1): 3068 (w), 1607 (s), 1569 (s), 1536 (s), 1458 (m), 1299 (m), 1250 (m), 1193 (s), 1145 (s), 1073 (m), 787 (s), 701 (s). Elemental analysis (%) calcd for C30H18F6MnN2O4 (desolvated sample): C 56.35, H 2.84, N 4.38. Found: C 56.12, H 2.88, N 4.18. Synthesis of Pd−Au@Mn(II)-MOF (2). 1 (10 mg, 0.002 mmol) was added to a CH3OH (2 mL) solution of chloroauric acid (12 mg, 0.12 mmol) and palladium nitrate (6.7 mg, 0.12 mmol). The mixture was stirred for 1 h at room temperature. The resulting solid was isolated by centrifugation and washed with CH3CN. The obtained green-yellow crystalline solid was mixed with NaBH4 (25 mg, 0.65 mmol) in water (2 mL), and the mixture was stirred for additional 5 h to afford 2 as dark-brown crystalline solids. The obtained crystalline solids were washed with CH3CN and EtOH and dried in air. ICP measurement indicated that the encapsulated amount of Pd−Au NPs in 2 is 27.7 wt % (13.4% Pd and 14.3% Au). N-Benzylidenebenzylamine Formation from Alcohols and Amines. A toluene solution (2 mL) of benzyl alcohol (52 μL, 0.52 mmol), benzylamine (66 μL, 0.62 mmol), and 2 (2.0 mg, 0.75 mol %) was stirred in vacuum. After injection of air (50 mL, 0.44 mmol of O2),

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RESULTS AND DISCUSSION Structural Analysis of 1 and 2. Mn(II)-MOF (1) was obtained as light-brown crystals by the combination of Mn(OAc)2 and L in a mixed solvent system. Single-crystal analysis indicated that 1 crystallizes in the hexagonal space group P3̅. Each Mn(II) center adopts a 4 + 2 octahedral coordination sphere (Figure 1) in which two coplanar chelating β-diketone units form the square (Mn−O distances of 2.131(4)−2.144(4) Å) and the axial positions are occupied by two pyridyl N donors (Mn−N distance of 2.244(5) Å). The solid-state packing pattern revealed that 1 is a threefoldinterpenetrating NbO framework, similar to its Cu(II) analogue.11 As indicated in Figure 1, large hexagonal channels along the crystallographic c axis exist in the structure, and the opposite Mn···Mn distance in the channel is 23.5075(10) Å (Figure S1). 1 is stable up to 150 °C, and the encapsulated MeOH molecules can be removed by heating, which is welldemonstrated by thermogravimetric analysis (TGA) and PXRD (Figure S2), indicating that 1 can be a thermally stable support to upload metal NPs and facilitate organic reactions at relatively higher temperature. Pd−Au-encapsulated Pd−Au@Mn(II)-MOF (2) was prepared by impregnation of 1 with equimolar Pd(NO3)2 and HAuCl4 in MeOH for 1 h followed by a NaBH4 reduction process (H2O, 5 h). As shown in Figure 1, the color of 1 B

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As shown in Figure 3, the one-pot synthesis of Nbenzylidenebenzylamine from benzyl alcohol and benzylamine

changed from light brown to dark after impregnation and reduction. The total uploaded Pd−Au amount, as determined by inductively coupled plasma (ICP) measurement, was up to 27.7 wt % (13.4% Pd, 14.3% Au). Thus, the formula of 2 can be described as Pd1.6Au1.0@Mn(II)-MOF. The oxidation state of the encapsulated Au and Pd after reduction was determined by X-ray photoelectron spectroscopy (XPS). The observation of Au 4f7/2 and 4f5/2 peaks at 83.86 and 87.46 eV and Pd d5/2 and d3/2 peaks at 335 and 341 eV demonstrated the existence of Au(0) and Pd(0) (Figures S3 and S4) in 2.14 In addition, the XPS spectra show that no change in valence state of the Mn(II) in 2 occurred upon treatment with NaBH4 in aqueous solution. The Mn(II) 2p1/2 and 2p3/2 peaks appeared at 653.9 and 642.3 eV with a splitting of 11.6 eV, indicating that the manganese in 2 is bivalent (Figure S5).15 Moreover, we used high-resolution transmission electron microscopy (HRTEM) to investigate the dispersion and size distribution of the Pd−Au NPs in Mn(II)-MOF. As indicated in Figure 2, the Pd−Au NPs in 2 were highly dispersed with an

Figure 3. (left) Relation of conversion/selectivity to air injection volume. (right) Reaction time examination and leaching test for the synthesis of N-benzylidenebenzylamine from alcohols and amines catalyzed by 2. Reaction conditions: 2 (2.0 mg, 0.75 wt % Pd−Au), benzyl alcohol (0.52 mmol), benzylamine (66 μL, 0.62 mmol), toluene (2 mL), and air (50 mL) at 110 °C. The solid catalyst was filtered from the reaction solution after 12 h, whereas the filtrate was transferred to a new vial and the reaction was carried out under the same conditions for an additional 24 h.

was chosen as the model reaction to examine the catalytic activity of 2. When the reaction was carried out in toluene at 110 °C in vacuum, no expected N-benzylidenebenzylamine was obtained because no alcohol oxidation could occur without oxygen. On the other hand, the reaction also failed to afford the expected imine product once it was performed in toluene at 110 °C in air. This could have been caused by the poor stability of the oxidizable benzylamine under the reaction conditions. Thus, the oxygen amount could be the key factor for this onepot tandem synthesis. A series of control experiments with different amounts of air were performed (air volumes: 20, 30, 40, 50, and 60 mL). As shown in Figure 3, the best conversion (>95%) and selectivity (∼100%) were observed when 50 mL of air (0.62 mmol of O2) was used for the reaction under the reaction conditions (110 °C, toluene; Figure S7). Having determined the optimal amount of air, we also examined the reaction time. Figure 3 shows that the initial conversion of N-benzylidenebenzylamine continuously increased as time went on, and the maximum yield (>95%) appeared at 24 h (Figure S8). The conversion and especially the selectivity for the desired product began to decrease after 24 h. The turnover number (TON) and turnover frequency (TOF) at 24 h for N-benzylidenebenzylamine formation from alcohols and amines were 126.7 and 5.28 h−1, respectively, under the optimized conditions (Figure 3). In order to gain insight into the heterogeneous nature of 2, a hot leaching test was carried out. As indicated in Figure 3, no further reaction took place without 2 after ignition of the reaction at 12 h, indicating that 2 exhibits a typical heterogeneous catalyst nature in this reaction. The recyclability of 2 was also examined. After each 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 conversion was still at 90% even after five catalytic cycles (Figure S9). The size of the Pd−Au NPs in 2 slightly increased (5−20 nm), and the atomic lattice fringes

Figure 2. HRTEM and SEM-EDS images of 2 and PXRD patterns simulated for 1 and measured for 1 and 2.

average particle size of 2−5 nm. Atomic lattice fringes with a spacing of 0.231 nm were observed, corresponding to (111) planes.16 SEM-EDS elemental mapping of 2 further supported the above observation (Figure 2). The PXRD pattern of 2 is in good agreement with that of pristine 1, demonstrating that the crystallinity and structural integrity of 1 is well-maintained during the Pd−Au loading and reducing processes. In addition, the porosity before and after Pd−Au loading was confirmed by gas adsorption−desorption experiments. CO2 adsorption by 1 and 2 at 195 K revealed absorption amounts of 56.7 and 53.6 m3/g by Mn(II)-MOF and Pd1.6Au1.0@ Mn(II)-MOF, respectively. The pore size distribution curve, calculated from Barrett−Joyner−Halenda analysis, shows that the narrow pore diameter distributions for 1 and 2 have widths of 1.80 and 0.63 nm, respectively (Figure S6). N-Benzylidenebenzylamine Formation from Alcohols and Amines. On the basis of above observations, we next examined the catalytic behavior of 2 for the one-pot synthesis of imine species, an important class of compounds in organic synthesis, biomedicine, and materials science, from amines and alcohols. The direct synthesis of −RCN− from amines and alcohols by a one-pot tandem reaction is challenging because the optimal reaction conditions for the first aerobic alcohol oxidation step and the following anaerobic condensation step largely differ from each other. C

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Inorganic Chemistry Table 1. Summary of the Tandem Reactions Based on Substituted Benzyl Alcohols and Benzylaminesa

a

The reactions were carried out under the optimized conditions: toluene, 110 °C, 2 (0.75% Pa−Au alloy), 24 h.

(0.231 nm) were still clearly observed after five runs (Figure S10). No valence change for Pd and Au species was detected by XPS (Figures S11 and S12). The PXRD patterns of 2 after reuse for five cycles indicated that the structural integrity of 2 was well-preserved (Figure S13). After five catalytic runs, the filtrate was examined by ICP-AES. The results showed the total amount of Pd and Au was 25.4 wt % (10.6 wt % Pd, 14.8 wt % Au), indicating that only tiny amounts of Au (2.8 wt %) and Pd (0.5 wt %) were lost during the catalytic cycles. Thus, Mn(II)MOF is an ideal platform to support Pd−Au alloy NPs for this tandem reaction. It is noteworthy that the yield of the benzyl alcohol oxidation step is 71% (Figure S14). It was expected that amine addition would significantly shift the reaction equilibrium to the right and thus that more N-benzylidenebenzylamine would be formed. A control experiment indicated that the yield of Nbenzylidenebenzylamine in the presence of Mn(II)-MOF 1 (5 mol %) was only 2%. In addition, the tandem reaction catalyzed by monometallic Au@Mn(II)-MOF or Pd@Mn(II)-MOF resulted in much lower conversion (48%; Figure S15). After that, we examined the substrate scope of the tandem reaction (Figure S16). As shown in Table 1, compared with alcohols bearing electron-donating groups (48−75%), benzyl alcohols with electron-withdrawing groups led to imines in much higher conversions (93−99%). On the other hand, amine substrates with electron-withdrawing groups resulted in excellent yields (93−99%) that were significantly better than those for amines possessing electron-donating groups (59− 93%). N-Benzylideneaniline Formation from Alcohols and Amines. To further investigate the catalytic efficiency of 2, the tandem reaction was expanded to benzyl alcohols and aromatic amines. As shown in Figure 4, benzyl alcohol and phenylamine were chosen as model substrates, and the reaction was performed in air under alkaline conditions (Figure 4). To our delight, the corresponding imine was obtained in 99% yield

Figure 4. (top left) Leaching test. Reaction conditions: 2 (2.0 mg, 0.75 wt % Pd−Au), toluene solution (2 mL), benzyl alcohol (52 μL, 0.52 mmol), phenylamine (66 μL, 0.62 mmol), and KOH (2.8 mg, 0.05 mmol) at 110 °C for 30 h. The solid catalyst was filtered from the reaction solution after 15 h, whereas the filtrate was transferred to a new vial and the reaction was carried out under the same conditions for an additional 15 h. (top right) Catalytic cycles. (bottom left) PXRD patterns of 2 after each catalytic run. (bottom right) TEM images of 2 after five catalytic runs.

after 30 h (Figures 4 and S17). The TON and TOF values for N-benzylideneaniline formation from alcohols and phenylamine D

DOI: 10.1021/acs.inorgchem.6b02592 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 2. Summary of the Tandem Reactions Based on Substituted Benzyl Alcohols and Phenylaminesa

a

The reactions were carried out under the optimized conditions: toluene, 110 °C, 2 (0.75% Pd−Au alloy), 30 h.

Figure 5. (left) N-Benzylidenebenzylamine formation from benzaldehyde−benzylamine condensation. Reaction conditions: benzaldehyde (0.52 mmol), benzylamine (0.62 mmol), toluene (2 mL), air (50 mL), 2 (2.0 mg, 0.75 wt % Pd−Au), 1 (4 mg), T = 110 °C. (right) N-Benzylideneaniline formation from benzaldehyde−phenylamine condensation. Reaction conditions: benzaldehyde (0.52 mmol), phenylamine (0.50 mmol), toluene (2 mL), 2 (2.0 mg, 0.75 wt % Pd−Au), 1 (4 mg), T = 110 °C.

were 132 and 4.4 h−1, respectively. The hot leaching test confirmed that 2 in this reaction is the heterogeneous catalyst, and it could be reused for five catalytic cycles without significant loss its activity (yields of 93% over five catalytic cycles) (Figures 4 and S18). The PXRD patterns of 2 after reuse for five cycles indicated that the structural integrity of 2 was well-preserved (Figure 4). The Pd−Au NPs were slightly agglomerated, and the size of the Pd−Au NPs in 2 increased from 2−5 nm to 5−20 nm after the fifth run; the atomic lattice fringes for the Pd−Au NPs, however, were still clearly observed

(Figure 4), and their good dispersity was further confirmed by SEM-EDS measurements (Figure S19). In addition, ICP-AES analysis indicated that the Pd−Au amount decreased to 15.8 wt % (5.9% Pd, 9.9% Au) which might have resulted from the presence of strong base. The zero-valent oxidation states of Au and Pd species in 2 after 5 runs were still maintained (Figures S20 and S21). In the absence of base, the desired imine product was obtained even with an enhanced amount of 2. Again, the scope of this tandem reaction was explored by the use of various substituted benzyl alcohols and phenylamines. As E

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2013CB933800), and the Taishan Scholar’s Construction Project.

indicated in Table 2, benzyl alcohols with electron-donating groups (e.g., CH3, OCH3) afforded the desired products in higher yields (87−98%) than those with electron-withdrawing groups (49−81%). On the other hand, aromatic amines with electron-withdrawing groups (such as halogen and NO2) provided excellent yields (99%) compared with those bearing electron-donating groups (Figure S22). It is well-known that Pd−Au alloys are effective species to catalyze alcohol oxidation to the corresponding aldehydes by activation of oxygen on the Pd−Au alloy.17 For example, 1O2 species were detected during the course of the first oxidation step (Figures S23 and S24).18 To demonstrate the catalytic activity of 2 for the second step of aldehyde−amine condensation, a series of control experiments of benzaldehyde−benzylamine and benzaldehyde−phenylamine condensationg reactions were performed (Figure 5). For benzaldehyde− benzylamine condensation, the results indicated that the reaction time lies in a wide time range of 12−21 h. Meanwhile, the reaction time for benzaldehyde−phenylamine condensation reaction is in a range of 12−24 h. As shown in Figure 5, the catalytic activities obey the sequence 2 > 1 > catalyst-free on the basis of the reaction times. Thus, we concluded that 2 catalyzes both steps of the imine synthesis from benzyl alcohol and benzylamine or phenylamine.

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(1) (a) Kobayashi, S.; Ishitani, H. Catalytic Enantioselective Addition to Imines. Chem. Rev. 1999, 99, 1069−1094. (b) Ma, J. A. Catalytic asymmetric synthesis of α- and β-amino phosphonic acid derivatives. Chem. Soc. Rev. 2006, 35, 630−636. (c) Kobayashi, S.; Mori, Y.; Fossey, J. S.; Salter, M. M. Catalytic Enantioselective Formation of C− C Bonds by Addition to Imines and Hydrazones: A Ten-Year Update. Chem. Rev. 2011, 111, 2626−2704. (2) (a) Patil, R. D.; Adimurthy, S. Catalytic Methods for Imine Synthesis. Asian J. Org. Chem. 2013, 2, 726−744. (b) Largeron, M.; Fleury, M. B. Bioinspired Oxidation Catalysts. Science 2013, 339, 43− 44. (3) Sithambaram, S.; Kumar, R.; Son, Y. C.; Suib, S. L. Tandem catalysis: Direct catalytic synthesis of imines from alcohols using manganese octahedral molecular sieves. J. Catal. 2008, 253, 269−277. (4) Chen, B.; Shang, S.; Wang, L. Y.; Zhang, Y.; Gao, S. Mesoporous carbon derived from vitamin B12: a high-performance bifunctional catalyst for imine formation. Chem. Commun. 2016, 52, 481−484. (5) (a) Jiang, G.; Chen, J.; Huang, J. S.; Che, C. M. Highly Efficient Oxidation of Amines to Imines by Singlet Oxygen and Its Application in Ugi-Type Reactions. Org. Lett. 2009, 11, 4568−4571. (b) Yuan, H.; Yoo, W. J.; Miyamura, H.; Kobayashi, S. Discovery of a Metalloenzyme-like Cooperative Catalytic System of Metal Nanoclusters and Catechol Derivatives for the Aerobic Oxidation of Amines. J. Am. Chem. Soc. 2012, 134, 13970−13973. (c) Choi, H.; Doyle, M. P. Oxidation of secondary amines catalyzed by dirhodium caprolactamate. Chem. Commun. 2007, 23, 745−747. (6) (a) Gu, X. Q.; Chen, W.; Morales-Morales, D.; Jensen, C. M. Dehydrogenation of secondary amines to imines catalyzed by an iridium PCP pincer complex: initial aliphatic or direct amino dehydrogenation? J. Mol. Catal. A: Chem. 2002, 189, 119−124. (b) Su, C. L.; Tandiana, R.; Tian, B. B.; Sengupta, A.; Tang, W.; Su, J.; Loh, P. Visible-Light Photocatalysis of Aerobic Oxidation Reactions Using Carbazolic Conjugated Microporous Polymers. ACS Catal. 2016, 6, 3594−3599. (7) (a) Taylor, R. J. K.; Reid, M.; Foot, J.; Raw, S. A. Tandem Oxidation Processes Using Manganese Dioxide: Discovery, Applications, and Current Studies. Acc. Chem. Res. 2005, 38, 851−869. (b) Blackburn, L.; Taylor, R. J. K. In Situ Oxidation−Imine Formation−Reduction Routes from Alcohols to Amines. Org. Lett. 2001, 3, 1637−1639. (8) (a) Mizuno, N.; Misono, M. Heterogeneous Catalysis. Chem. Rev. 1998, 98, 199−218. (b) Royer, S.; Duprez, D.; Can, F.; Courtois, X.; Batiot-Dupeyrat, C.; Laassiri, S.; Alamdari, H. Perovskites as Substitutes of Noble Metals for Heterogeneous Catalysis: Dream or Reality. Chem. Rev. 2014, 114, 10292−10368. (9) Falcaro, P.; Ricco, R.; Yazdi, A.; Imaz, I.; Furukawa, S.; Maspoch, D.; Ameloot, R.; Evans, J. D.; Doonan, C. J. Application of metal and metal oxide nanoparticles@MOFs. Coord. Chem. Rev. 2016, 307, 237− 254. (10) (a) Han, Y. F.; Wang, J. H.; Kumar, D.; Yan, Z.; Goodman, D. W. A kinetic study of vinyl acetate synthesis over Pd-based catalysts: kinetics of vinyl acetate synthesis over Pd-Au/SiO2 and Pd/SiO2 catalysts. J. Catal. 2005, 232, 467−475. (b) Gu, X. J.; Lu, Z. H.; Jiang, H. L.; Akita, T.; Xu, Q. Synergistic Catalysis of Metal−Organic Framework-Immobilized Au-Pd Nanoparticles in Dehydrogenation of Formic Acid for Chemical Hydrogen Storage. J. Am. Chem. Soc. 2011, 133, 11822−11825. (c) Liu, H. l.; Li, Y. W.; Jiang, H. F.; Vargas, C.; Luque, R. Significant Promoting Effects of Lewis Acidity on Au−Pd Systems in The Selective Oxidation of Aromatic Hydrocarbons. Chem. Commun. 2012, 48, 8431−8433. (d) Vilhelmsen, L. B.; Walton, K. S.; Sholl, D. S. Structure and Mobility of Metal Clusters in MOFs: Au, Pd, and Au Pd Clusters in MOF-74. J. Am. Chem. Soc. 2012, 134, 12807− 12816. (e) Long, J. L.; Liu, H. L.; Wu, S. J.; Liao, S. J.; Li, Y. W. Selective Oxidation of Saturated Hydrocarbons Using Au-Pd Alloy

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CONCLUSION We successfully synthesized a Mn(II)-MOF (1)-supported Pd−Au alloy NP catalyst 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 to be viable for the construction of many more new and interesting MOF-supported metal alloy NPs catalysts, and studies toward the preparation of new mixed-metal alloy-loaded MOF catalytic 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.6b02592. Single-crystal data of 1 and its thermal stability, additional characterization of 2, GC results for the onepot syntheses of N-benzylidenebenzylamine and Nbenzylideneaniline, and singlet oxygen detection (PDF) Crystallographic data for 1 (CIF)

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REFERENCES

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 the National Natural Science Foundation of China (Grants 21671122, 21475078, 21301109, and 21271120), the 973 Program (Grant F

DOI: 10.1021/acs.inorgchem.6b02592 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/acs.inorgchem.6b02592 Inorg. Chem. XXXX, XXX, XXX−XXX