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Bi-Functional N-Doped Co@C Catalysts for Base-Free Transfer Hydrogenations of Nitriles: Controllable Selectivity to Primary Amines vs Imines Jilan Long, Kui Shen, and Yingwei Li ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b02327 • Publication Date (Web): 27 Nov 2016 Downloaded from http://pubs.acs.org on November 28, 2016
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ACS Catalysis
Bi-Functional N-Doped Co@C Catalysts for Base-Free Transfer Hydrogenations of Nitriles: Controllable Selectivity to Primary Amines vs Imines Jilan Long,†‡ Kui Shen,†* and Yingwei Li,†* †Key Laboratory of Fuel Cell Technology of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, People’s Republic of China ‡Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, College of Chemistry and Chemical Engineering, China West Normal University, Nanchong 637000, People’s Republic of China ABSTRACT: The transfer hydrogenation of nitriles is an important and alternative strategy to produce primary amines or imines, both of which play a crucial role in the synthesis of fine chemicals and pharmaceuticals. Nevertheless, developing highly active bifunctional catalyst system with controllable selectivity for these reactions still remains a huge challenge. In this study, we presented a bi-functional N-doped Co@C catalyst system (Co@NC) for the selective transfer hydrogenation of nitriles into either primary amines or imines. The Co@NC was prepared by the direct pyrolysis of an N-containing Co-MOF in inert atmosphere, where the Ncontaining ligands could be transformed into highly graphitic N-doped carbon, endowing the catalysts with high-density special basic sites, while the Co2+ ions were reduced to uniform Co nanoparticles which were dispersed on or embedded in N-doped graphitic structures. Under base-free conditions with isopropanol as both proton-donor and solvent, the optimized Co@NC-900 (obtained at 900 oC) catalyst could convert nitriles into primary amines or imines at will with surprising selectivities (mostly higher than 90%), depending on the solvent volume added to the reaction systems. Furthermore, a possible reaction mechanism was proposed. The N-derived basic sites on Co@NC could play a similar role as the base additives which not only inhibit the formation of polyamine or prevent the products stacked on the surface of catalysts, but also effectively promote the transfer hydrogenation of nitriles. The generated corresponding primary imines could controllably attack the primary imine intermediates to form imines by adjusting the concentration of Co@NC. It is clear that this strategy offers a high-performance catalyst system for base-free transfer hydrogenations of nitriles to selectively produce primary amines vs imines.
KEYWORDS: cobalt-based catalysts, selective transfer hydrogenations, nitriles, primary amines, imines INTRODUCTION Amines and imines, as significant intermediates, play remarkable roles in the synthesis of a vast number of pharmaceuticals and agrochemicals, and thus have attracted extensive interests from both academic and industrial researchers to explore more efficient strategies to establish carbon–nitrogen bonds.1 Among the various routes, heterogeneous catalytic methods have provided numerous efficient and environmentbenign strategies towards the synthesis of amines and imines, representing a crucial technology especially for reducing environmental hazards and decreasing energy consumption as well as achieving high atom efficiency.2 To date, numerous heterogeneous catalytic systems have been developed. For instance, both amines and imines could be synthesized by hydrogenation of nitriles over a variety of heterogeneous catalysts based on noble metals, such as Pd,3 Ru,4 Rh,5 and Ir.6 In this regard, hydrogenation of nitriles established a convenient and valuable process for the preparation of both amines and imines.2 However, traditional hydrogenation of nitriles with molecular hydrogen as reductant was always characterized by an environmentally-unfriendly and harsh synthetic process, such as the use of basic additives7 and high H2 pressures, as well as noble metal catalysts, which greatly limited their industrial applications.8
As compared to the traditional hydrogenation process, transfer hydrogenation has been proposed recently as an alternative strategy, which utilizes various alternatives including phosphinicacid salts,9 aliphatic alcohols,10 hydrazines,11 formic acid salts,12 and inorganic hydride,13 as proton-donors to replace molecule hydrogen used in the traditional protocol. Among these donors, alcohols (especially isopropanol) were highly promising agents owing to the characters of non-poisonous and mild reaction conditions.14 Transfer hydrogenation of nitriles by using isopropanol as proton-donor can avoid the handling of autoclaves and hydrogen, and thus would represent a green, safe, and economic protocol.15 Nevertheless, in order to achieve high yields, most of the transfer hydrogenation of nitriles have been conducted in the presence of basic additives over noble-metal catalysts (such as Ru10a,16 or Pd17a) and some soluble non-precious metal-based catalysts (such as Fe17b, Ni 17c, Table S1). Furthermore, to our knowledge, the preparation of primary amines and imines from hydrogenation of nitriles should be carried out in separate catalytic systems. So far, there is still no report on the use of a versatile catalytic system that is able to selectively produce both primary amines and imines with an excellent switch in selectivity just by adjusting the reaction conditions. The development of highly active non-noble catalysts for the transfer hydrogenation of nitriles with controllable selectivity to
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primary amines vs imines under base-free condition is highly desirable, but remains a significant challenge. In this contribution, we report highly efficient bi-functional N-doped Co@C catalyst system (Co@NC) for the transfer hydrogenation of nitriles under base-free conditions with isopropanol as proton-donor to realize the controllable and selective synthesis of imines or amines. The Co@NC were prepared by the direct pyrolysis of an N-containing cobalt-based MOF ([Co(1,4-bdc)(ted)0.5]·2DMF·0.2H2O) in inert atmosphere. In the pyrolysis process, the Co ions of Co-MOF could be transformed into highly dispersed Co NPs which were embedded in ligand-derived N-doped graphitic carbon matrix. The N sites derived from the triethylenediamine moiety in MOF could be reserved partly after pyrolysis, which potentially endowed the catalysts with abundant Lewis basic sites. These basic sites could facilitate the proton transfer and deliver the free proton to the activated nitrile molecules to produce primary imines, which could further attack the primary imine intermediates to form imines under low concentration of basic sites, giving a perfect switch between primary amines vs imines just by adjusting the dosage of solvent. EXPERIMENTAL SECTION Chemicals. All chemicals were purchased from commercial sources and used without further treatments. All solvents were analytical grade and distilled prior to use. Synthesis of Co-MOF ([Co(1,4-bdc)(ted)0.5]·2DMF·0.2 H2O). Typically, a mixture of Co(NO)3·6H2O (0.9 mmol), 1,4benzenedicarboxylic acid (H2BDC, 0.9 mmol), triethylenediamine (TED, 0.5 mmol), and 15 ml DMF were added to a Teflon-lined autoclave and heated statically at 120 °C in an oven for 2 days (Scheme 1). The purple products were washed with DMF and methanol, and then dried under vacuum at 150 °C for 12 h. Synthesis of Co@NC catalysts. The pyrolysis of Co-MOF was carried out in a tubular furnace under argon atmosphere with a flow rate of 20 mL/min. The samples were heated at a heating rate of 2 °C/min from room temperature to 200 °C and kept at this temperature for 2 h. Then the temperature was increased to five different target temperatures (i.e. 500 °C, 600 °C, 700 °C, 800 °C, and 900 °C) with a heating rate of 2 °C/min and kept for 8 h, followed by cooling down to ambient temperature. The obtained black powders were denoted as Co@NC-500, Co@NC-600, Co@NC-700, Co@NC-800, and Co@NC-900, respectively. Owing to the easy oxidation character of metallic cobalt, the samples were preserved in pure N2 before being used as catalysts. Characterization. Powder X-ray diffraction patterns of the Co-MOF and Co@NC were recorded on a Rigaku diffractometer (D/MAX-IIIA, 3 kW) by Cu Kα radiation (40 kV, 30 mA, 0.1543 nm). BET surface areas and pore sizes were obtained from N2 adsorption/desorption isotherms at 77 K with a Micromeritics ASAP 2020M instrument. Before measurements, the samples were degassed at 150 °C for 12 h. The Co content of the Co@NC samples was measured quantitatively by atomic absorption spectroscopy (AAS) on a Hitachi Z-2300 instrument. The surface topography of Co-MOF and catalysts, as well as the element distribution of Co@NC were investigated by a Scanning Electron Microscope (SEM, MERLIN of ZEISS), the size and morphology of the Co@NC samples were determined by using a Transmission Electron Micro-
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scope (TEM, JEOL, JEM-2010HR) with energy-dispersive Xray spectroscopy (EDS) analysis. X-ray Photoelectron Spectroscopy (XPS) measurement was performed on a Kratos Axis Ultra DLD system with a base pressure of 10−9 Torr. The basic property was determined by CO2-TPD measured on a Micromeritics AutoChem II 2920 instrument equipped with a highly sensitive linear thermal conductivity detector (TCD), which was connected to a mass spectrometer (VARIAN). Typically, 70 mg of activated sample was pretreated under a flow of Helium (50 mL min-1) at 700 °C for 1 h. Then the sample was cooled to 100 °C under a flow of Helium. After adsorption of CO2, the sample was purged in Helium atmosphere at 100 °C. The TPD data were collected from 100 °C to 700 °C at a heating rate of 20 °C min-1 in a flow of Helium. Catalytic reactions. The transfer hydrogenation of nitriles was carried out in a 25 mL Schlenk tube (the large-scale synthesis (5 mmol reactant) was carried out in a 100 mL Schlenk tube). The Schlenk tube was degassed and purged several times with pure N2 to remove the air after the addition of nitrile, isopropanol and catalyst. Then the Schlenk tube was transferred into an oil bath that was preheated to 80 °C. After reaction, the mixtures were identified by GC–MS, and the conversion of nitrile and the products yields were determined by gas chromatography (GC) with nitrobenzene as an internal standard. The recyclability of the Co@NC-900 was further investigated under the above reaction conditions (0.5 mmol of 2methylbenzonitrile, 10 mol% of catalysts, 1 mL of isopropanol, 48 h, 80 oC). The detailed procedures were shown in Figure S1. Typically, the mixture containing Co@NC-900 was transformed into a clean tube after reaction. Then the reaction tube was washed by isopropanol with ultrasonic treatment for several times until the reaction tube were clean. Then the Co@NC-900 was easily separated from the reaction solution by placing a magnet close to the tube due to its good magnetic property (Figure S1). After removing the solution, the Co@NC-900 was washed with isopropanol for several times and then dried at 100 °C in an oven. In order to reduce the loss, the Co@NC-900 should be removed from the tube after drying completely. Subsequently, the Co@NC-900 was reduced by H2 flow at 400 °C for 2 h, and then reused as the catalyst in the next run. RESULTS AND DISCUSSION The powder XRD patterns of the Co-MOF (Figure S2) matched well with the published XRD patterns in literatures,18 confirming the as-synthesized MOF structure in this work. The XRD patterns of the Co@NC nanocatalysts (Figure 1) exhibited four diffraction peaks at around 44.3°, 51.6°, 76.1°, and 92.3°, respectively, which corresponded to the characteristic diffractions of (1 1 0), (2 0 0), (2 2 0) and (3 1 1) lattice planes of metallic Co (JCPDS No. 15-0806).19 This indicated Ⅱ the Co in Co-MOF have been successfully reduced to Coo by ligand-derived carbon under high temperature. The mean size of Co NPs in Co@NC-500, Co@NC-600, Co@NC-700, Co@NC-800 and Co@NC-900 was 2.15 nm, 3.83 nm, 4.79 nm, 7.19 nm and 8.63 nm respectively according to the Scherrer analysis based on the XRD results, indicating the mean size of nanoparticles increased with an increase in the calcination temperature. In addition, the Co diffraction peaks of the catalysts prepared at higher pyrolysis temperatures exhibited
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improved intensities owing to the higher crystallization degree and larger Co particles.20
formation of large nanoparticiles after pyrolysis. It was also worth to note that the pyrolysis temperature had little impact on the structural properties of the as-obtained Co@NC samples, since the BET surface areas of the samples had changed little when the pyrolysis temperatures increased. The contents of Co in the catalysts were measured by AAS, and the proportion of other elements was analyzed by element analysis. The results in Table S3 indicated that the total metal contents of Co-MOF and its derived nanocatalysts were around 20 wt% and 35-40 wt%, and the N contents were around 9 wt% and 1 wt%, respectively. The surface morphology of Co-MOF and Co@NC materials were investigated by SEM. As shown in Figure 3, all the Co@NC samples kept the similar shapes to their parent CoMOF except a more rough and porous surface. It was also worth to note that the surface of the catalysts became rougher with an increase in the pyrolysis temperature. In addition, elemental mapping pointed out that C, N, and Co were evenly distributed in the Co@NC catalysts after pyrolysis (Figure 4).
Scheme 1. Schematic illustration of the process used for the synthesis of Co@NC.
Figure 1. Powder XRD patterns of the Co@NC samples: (a) Co@NC-500, (b) Co@NC-600, (c) Co@NC-700, (d) Co@NC800, and Co@NC-900 before (e) and after catalytic reaction (f).
The carbonization of Co-MOF generated plentiful mesoporosity, leading to different pore structures between MOF and its derived Co@NC nanocatalysts. As shown in Figure S3, the N2 adsorption/desorption isotherms of Co-MOF exhibited a typical type-I adsorption curve, corresponding to the solely microporous structure. However, the N2 adsorption/desorption isotherms of all the Co@NC samples exhibited a type-IV adsorption with an apparent hysteresis loop in the P/P0 range of 0.5−1.0 (Figure 2a). These results indicated the presence of a large amount of mesopores in the Co@NC materials, which was confirmed by their corresponding pore distribution curves (Figure 2b). In addition, as shown in Table S2, a huge drop in BET surface area was observed after carbonization (around 100−200 m2 g-1 for the Co@NC materials prepared at different temperatures), which might be due to the collapse of main frameworks and the decrease in microporosity, as well as the
Figure 2. (a) Nitrogen adsorption/desorption isotherms of various Co@NC prepared at different temperatures and (b) the corresponding BJH pore-size distribution curves.
More structural information was further revealed by TEM characterization. The TEM images of Co@NC prepared at different pyrolysis temperatures were displayed in Figure 5. It was quite clear that higher pyrolysis temperatures could lead
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to the formation of larger Co NPs, as confirmed by their corresponding size distribution (Figure 5a-5e). In addition, the Co nanoparticles were uniformly dispersed in Co@NC-900 with an average particle size of 15.44 ± 0.56 nm (Figure 5e), and no significant aggregates were observed. Figure 5f highlighted a typical metallic Co nanoparticle with crystal lattices of 0.205 nm, which were assigned to the (1,1,1) interplanar spacing of metallic Co.21 The inserted EDS image further confirmed the coexistence of C, N and Co element in an individual particle (Inset of Figure 5f). Figure 5g and 5h clearly pointed out that the Co NPs were encapsulated by well-ordered graphitic layers with a typical distance value of graphite (0.34 nm).22 The formation of graphitic structure could efficiently prevent the aggregation of nanoparticles and facilitate the electron transferring, and thereby improved the catalytic activity.
Figure 3. SEM images of (a)Co-MOF, (b) Co@NC-500, (c) Co@NC-600, (d) Co@NC-700, (e) Co@NC-800, (f) Co@NC900.
The XPS spectra of Co@NC-900 and Co-MOF were shown in Figure 6. The Co 2p peaks of Co-MOF at around 781.25 eV and 796.75 eV could be assigned to the characteristic peaks of high-spinning Co2+.23 After pyrolysis, the Co 2p spectra of Co@NC-900 showed two distinct peaks at 778.96 eV (FWHM of 1.74 eV) and 793.54 eV (FWHM of 1.8 eV) with two obvious 2p satellite peaks (the FWHMs were 6.71 eV and 4.86 eV, respectively), which were lower than that of the Co-MOF by ~2.29 eV and ~3.21 eV, respectively, indicating that the Co(II) ions in Co-MOF were in-situ reduced to metallic Co during thermal decomposition (Figure 6a). This result was also consistent with the reported experimental regularity that if the reduction potential of centre ions of MOFs was -0.27 volts or higher (such as Co2+, Ni2+, Cu2+), the central metal ions would be reduced to metal nanoparticles by the direct pyrolysis in inert atmosphere.24 In addition, an obvious peak of Co-MOF appearing at 399.83 eV could be assigned to the N 1s of triethylenediamine coordinated with a Co mental ion (Figure
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6b).25 However, owing to the influence of magnetic metal ions (Co2+), this bonding energy was slightly higher than that of amino nitrogen (399.6 eV).26 After pyrolysis, the N 1s spectra of Co@NC-900 appeared two new peaks at 398.88 eV and 401.28 eV, which could be assigned to the pyridinic N and graphitic N, respectively, indicating that the N atoms were doped successfully into the Co/NC materials,27 which was also in accordance with the SEM-EDS results (Figure 4d, 5f). Note that these N sites might endow the catalysts with plentiful Lewis basic sites, which are believed to be able to facilitate the transfer hydrogenation reactions.28 The Co 2p and N 1s XPS spectra of the samples synthesized at other pyrolysis temperatures were also shown in Figure S4. Obviously, the intensities of graphitic N 1s peaks increased with the increase of pyrolysis temperatures, indicating that high temperature was beneficial to the graphitization of carbon. In addition, the intensities of Co 2p XPS peaks also enhanced with the increase of pyrolysis temperatures, demonstrating the crystallinity of Co nanoparticles was improved and more Co nanoparticles were exposed on the surface of catalysts. These results were also in accordance with the XRD results that more peaks corresponding to different lattice plane were appeared in the XRD patterns and the intensities of these peaks also increased at high temperatures.
Figure 4. SEM image (a) and the elemental mapping of Co@NC900: (b) C, (c) Co, (d) N.
Then we further performed CO2-TPD to analyze the basic property of the Co-MOF and Co@NC. The CO2 desorption temperature of Co-MOF was at around 275 oC (Figure S5), indicating a part of N atoms exposed on the surface of this MOF. As shown in Figure 7, three obvious peaks appeared at around 150 oC, 220 oC and 450 oC in the CO2-TPD curves. The total peak areas ratios of Co@NC-500, Co@NC-600, Co@NC-700, Co@NC-800, Co@NC-900 were about 1.03: 1: 1.29: 1.29: 1.18. Generally, the CO2-TPD curve can reveal efficiently the strength and the density of the basic site in the catalysts on the basis of the position and peak area of CO2desorption peaks. Therefore, it was obviously that as the pyrolysis temperature increased, the density and the strength of the basic sites in the Co@NC just changed slightly. It was worth to note that these basic sites were derived from the triethylenediamine groups in the Co-MOF.
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Figure 5. TEM images of Co@NC. (a) Co@NC-500, (b) Co@NC-600, (c) Co@NC-700, (d) Co@NC-800, (e-h) Co@NC-900. The insets in (a-e) are their corresponding size distribution of Co nanoparticles. The inset in (f) is its corresponding EDS spectrum.
Subsequently, the transfer hydrogenation of nitriles was chosen as a model reaction to investigate the activity of various Co@NC catalysts. The catalytic reaction was carried out in N2 atmosphere at 80 oC by using isopropanol as both proton-donor and solvent under base-free conditions. The conversion of 2-methylbenzonitrile and the selectivity of products over various catalysts are shown in Table 1. The blank run (without any catalysts) gave essentially no activity in this system (even using C as catalyst) after 48 h of reaction
Figure 6. XPS spectra of Co@NC-900 and as-prepared Co-MOF, (a) Co 2p and (b) N 1s.
(Table 1, entries 1-2). This result indicated the Co NPs in Co@NC were the active sites for the transfer hydrogenations of nitriles. To our delight, all the as-synthesized Co@NC catalysts were highly active for this transformation. It was quite clear that the catalysts prepared at higher pyrolysis temperatures exhibited higher catalytic activity (Table 1, entries 3-7). It can be seen that the Co@NC-500 catalyst only gave 63% conversion of 2-methylbenzonitrile with 73.7% selectivity to 2-methylbenzylamine (Table 1, entry 3). With the increase of pyrolysis temperatures, the conversion and selectivity increased dramatically. The Co@NC-900 was found to be the highest active catalyst among these catalysts investigated in this system, which could almost completely catalyse the transfer hydrogenation of 2-methylbenzonitrile, providing around 80% of selectivity to 2-methylbenzylamine (Table 1, entry 7). It was worth to note that the hydrogenation of nitriles to generate amines always proceed under alkalinity conditions, because base additives can facilitate the transfer of electrons.28
Nevertheless, there was no additional basic additive in the present system. Thus the formation of primary amine should be attributed to the special basic sites (N sites), which were derived from the partial preservation of the triethylenediamine moiety in Co-MOF during pyrolysis (Figure 7).
Figure 7. CO2-TPD profiles for Co@NC-500, Co@NC-600, Co@NC-700, Co@NC-800, and Co@NC-900.
Interestingly, the selectivities of products in our system could be efficiently controlled by simply regulating the volume of solvent (Table 1, entries 7-10). The selectivities of the corresponding primary amines was remarkably enhanced by decreasing the volume of isopropanol to 1 mL, furnishing a quantitative yield of 2-methylbenzylamine (Table 1, entry 9). Whereas increasing the volume of isopropanol to 4 mL resulted in a great decrease in the selectivity of 2methylbenzylamine, while the selectivity of N-(2methylbenzylidene)-1-(o-tolyl) soared to 95.5% (Table 1, entry 10). In addition, the functional curves with respect to the volume of isopropanol and the distribution of products were shown in Figure S6. Obviously, this high-performance catalyst system provided a perfect switch between primary amines and imines. In fact, the Co@NC-900, to the best of our knowledge, was the first example to be able to selectively produce both primary amines and imines from nitriles with an excellent
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switch in selectivity just by controlling the solvent volume (Table S1).Considering the similar reaction conditions of various parallel catalytic tests in terms of catalyst addition, substrate dosage, reaction temperature and time, we concluded that the concentration of the N-derived basic sites played the key role in controlling the product selectivities. Furthermore, the reaction also proceeded smoothly when the amount of reactant was increased to 5 mmol, affording more than 90% conversions after prolonging the reaction time to 55 h.
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with all of the conversions of 2-methylbenzonitrile less than 5% (Table 2, entries 1-4), due to the absent of N-derived basic sites over Co@C-900 or basic additive.28 Furthermore, the 2methylbenzylamine could be hardly detected in these systems, which was attributed to the lack of basic sites to control the selectivity (Table 2, entries 1-4). Table 2. Transfer hydrogenation of 2-methylbenzonitrilea
Table 1. Transfer hydrogenation of 2-methylbenzonitrile over different catalystsa
Ent ry Entry 1 2
Sol. Catalyst (mL) -
b
3
C Co@NC-500
4
Co@NC-600
5
Co@NC-700
2 2 2 2 2
Con. (%) Trace 99
4.5
95.5
0
11
c
Co@NC-900
10
93.0
>99
0
0
12
c
Co@NC-900
40
91.3
3.7
96.3
0
a
Reaction condition: 2-methylbenzonitrile (0.5 mmol), catalyst (Co 10 mol%), 80 oC, 48 h. bThe C was obtained by using aqua regia to remove the Co from the Co@NC-900. c2methylbenzonitrile (5 mmol), catalyst (Co 10 mol%), 80 oC, 55 h. To elucidate the significance of basic sites, two different MOFs were also applied as sacrificial templates to prepare other two Co-based catalysts for this reaction. MOF-7129 (Co(1,4-bdc)(DMF), 1,4-bdc=1,4-benzenedicarboxylic acid, DMF = N,N'-dimethyl formamide ) was firstly employed as sacrificial template to prepare the catalyst (denoted as Co@C900) by using the same pyrolysis conditions. It was worth to point out that there were no basic sites detected in Co@C-900 due to the N-free feature of the parental MOF-71 (DMF molecules have been removed before pyrolysis). As expected, Co@C-900 exhibited poor catalytic activities for this reaction
a
Reaction condition: 2-methylbenzonitrile (0.5 mmol), catalyst (Co 10 mol%), 80 oC, 48 h. bCo-MOF-71 as sacrificial template, catalyst (Co 10 mol%). cZIF-67 as sacrificial template, catalyst (Co 10 mol%). Subsequently, another N-containing ZIF-6730 (Co(mim)2, mim = 2-methylimidazole) was also employed as sacrificial template to prepare another Co-based catalyst (denoted as Co@NC-900(67)). ZIF-67 employed a fully saturated coordination model for both Co and N sites in structure, which was greatly different from the Co-MOF structure (unsaturated coordination for both Co and N sites). As a result, the strength of basic sites of Co@NC-900(67) was much lower than that of Co@NC-900, as was confirmed by its low desorption temperature in CO2-TPD profile (lower than 450 oC, Figure S7), although the N-content of both catalysts was almost the same. As shown in Table 2, Co@NC-900(67) only possessed a moderate reaction activity and low selectivity for this reaction, probably due to the lack of strong basic sites. These results indicated that the conversion of 2-methylbenzonitrile and the selectivity of 2-methylbenzonitrile and N-(2methylbenzylidene)-1-(o-tolyl) were greatly influenced by the concentration and strength of basic sites, as well as the structure of catalysts. It was of importance to certify that the heterogeneous catalyst was stable enough and could be reused. Firstly, the chemical state of Co nanoparticles after reaction was confirmed by XPS spectrum (Figure S8). The bonding energy of 778.5 eV and 793.4 eV could be assigned to the character of Co (0), while the bonding energy of 781.0 eV and 796.5 eV matched well with the character of Co (II). This indicated that
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Table 3. Transfer hydrogenation various nitriles to primary aminesa
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Entry 1
1 mL i-PrOH
4 mL i-PrOH
Substrate t (h) 48
Con. (%) >99
Sel. (%)
t (h)
Con. (%)
48
>99
45
>99
40
>99
50
>99
60
>99
60
>99
60
>99
72
>99
Sel. (%)
>99 2
50
>99
95.5 95.0
>99 3
46
>99
4
40
>99
>99 >99
5b
48
>99 97.0
6b
48
>99 96.0
7b
48
>99
8b
46
>99
95.0 >99
9b
55
>99
10b
24
>99
11c
48
>99
>99 90.0
As expected, the Co@NC-900 could catalyse smoothly the transfer hydrogenations of a broad scope of nitriles to selectively produce their corresponding primary amines or imines with a perfect switch only by adjusting the volume of solvent (Table 3). Specifically, the electron-donating group substrates, such as 2-methylbenzonitrile, 3-methylbenzonitrile, 4methylbenzonitrile and 4-methoxybenzonitrile were firstly
>99 97.5 >99 98.1 91.0
72
>99
24
>99
72 >99 90.0 a Reaction condition: nitirles 0.5 mmol, Co@NC-900 catalyst (Co 10 mol%), i-PrOH solvent; b100 oC; c120 oC. the CoII and Co0 co-existed in the used catalysts. Therefore, the catalysts should be reduced at H2 flow for 2 h at 400 oC before reuses. Subsequently, we investigated the recyclability of the Co@NC-900 catalyst under the conditions of 80 oC and 1 mL isopropanol. Results were exhibited in Figure S9, where no apparent loss in conversion and selectivity was observed even up to four runs, indicating its excellent recyclability. Further investigation of the general applicability of this system was performed under the optimum reaction conditions.
98.0
85.9 80.5
91.0
investigated, affording the corresponding benzylamines in quantitative yields in 1 mL isopropanol (Table 3, entries 1-4), while providing the corresponding imine products with more than 95% selectivities in 4 mL isopropanol (Table 3, entries 14). Likewise, the electron-withdrawing substrates, including 4bromobenzonitrile, 4-chlorobenzonitrile and 4fluorobenzonitrile, should carry out the transfer hydrogenation at a higher temperature, giving the desired benzylamine products with more than 95% selectivities (Table 3, entries 5-7), or generating the corresponding imines with more than 97% selectivities (Table 3, entries 5-7), respectively. Furthermore, it is necessary to point out that the transfer hydrogenation of aliphatic nitriles is always a big challenge, because the transfer hydrogenation of the C≡N group in aliphatic nitriles could easily result in the formation of the corresponded methyl group.31 However, in the present system, aliphatic nitriles such
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Figure 8. The proposed mechanism for transfer hydrogenation of nitriles to primary amines and imines
as 2-phenylacetonitrile and n-pentanenitrile, even 2-(4chlorophenyl) acetonitrile underwent the transfer hydrogenation successfully, affording the desired benzylamine products in excellent yields (Table 3, entries 8-10). Similarly, these aliphatic nitriles could also be hydrogenated to produce the corresponding imines with more than 80% selectivities (Table 3, entries 8-10). Interestingly, the Co@NC-900 only catalyzed the transfer hydrogenation of one C≡N group in terephthalonitrile, giving the corresponding benzylamine and imine product in 90% and 91% selectivities, respectively (Table 3, entry 11). On the basis of the above results, we proposed a possible reaction mechanism with respect to the transfer hydrogenation of nitriles to controllably produce amines and imines. In this system, no base additive was added. So we speculated that the N-derived basic sites (confirmed by CO2-TPD) on the catalysts played a similar role as the reported base additives, which could facilitate the proton transfer to control the conversion of transfer hydrogenation reaction.28 Moreover, these N-derived basic sites were not only responsible for protecting the catalyst from deactivation by inhibiting the formation of polyamine or preventing the product stack on the surface of catalysts,32-33 but also in charge of adjusting the concentrations of intermediates and thus controlling the selectivities of amines and imines.28 The plausible reaction mechanism is exhibited in Figure 8. Firstly, the nitriles and isopropanol were adsorbed on the catalysts. Then the basic sites of the catalysts helped to release the protons from isopropanol and deliver the free protons to the activated nitrile molecules (Figure 8, II), generating the corresponding primary imine intermediate III (Figure 8, III), which was very active and could be further hydrogenated to produce a primary amine V (Figure 8, IV-V). 34 At this moment, if the concentration of basic sites was high enough, no other products would be produced, and thus the main products were the primary amines. Nevertheless, if the concentration of basic sites was too low to control the concentration of the intermediate, imines would be the main product as we mentioned above.33 In the present system, the concentra-
tion of basic sites was decreased with an increase in isopropanol volume, so the as-generated primary amine V could controllably attack the primary imine intermediate III to form the intermediate VI (Figure 8, VI), followed by liberating a diamine (Figure 8, VII) with the regeneration of the catalysts (Figure 8, I). Finally, NH3 was liberated from the diamine to generate the desired imine products (Figure 8, VIII).[34b-d, 35] CONCLUSION In summary, we have developed an efficient MOF-derived Co@NC catalyst system for the controllable transfer hydrogenation of nitriles to generate primary amines or imines with a perfect switch. The Co@NC catalysts, which were prepared by employing an N-containing Co-MOF as the sacrificial template, were proved to be highly active in the base-free transfer hydrogenation of a variety of nitriles to generate their corresponding primary amines or imines with highly controllable selectivities by using isopropanol as proton-donor. Further, the catalysts exhibited good recyclability without any loss in conversion and selectivity even up to four runs. Moreover, the proposed mechanism indicated the concentration of the Nderived basic sites played the key role in giving the catalysts a perfect switch of the selectivity by controlling the concentration of the primary imine intermediate. The controllable selectivity, combining with the high efficiency, good compatibility and recyclability as well as mild reaction conditions, makes this system an attractive alternative pathway for transfer hydrogenations of nitriles to produce primary amines vs imines, showing potential application in chemical industry.
ASSOCIATED CONTENT Additional XRD pattern, nitrogen adsorption/desorption isotherms and CO2-TPD profile, etc. This material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION Corresponding Author
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*E-mail:
[email protected] (K. Shen). *E-mail:
[email protected] (Y. Li).
Notes The authors declare no competing financial interest
ACKNOWLEDGMENT We thank the Scientific Research Fund of Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province (CSPC2015-1-2), and Scientific Research Fund of China West Normal University (412553), National Natural Science Foundation of China (21322606, 21436005, and 21576095), China Postdoctoral Science Foundation (2015M572323, 2016T90785), Fundamental Research Funds for the Central Universities (2015ZM045, 2015ZP002, and 2015PT004) and Guangdong Natural Science Foundation (2014A030310445, 2016A050502004 and 2013B090500027) for financial support.
REFERENCES (1) (a) Hayes, K. Appl. Catal. A, 2001, 221, 187-195. (b) Rueping, M.; Sugiono, E.; Schoepke, F. R. Synlett, 2010, 852-865. (c) Müller, T. E.; Beller, M. Chem. Rev. 1998, 98, 675-703. (d) Seayad, J.; Tillack, A.; Hartung, C. G.; Beller, M. Adv. Synth. Catal. 2002, 344, 795-813. (e) Tang, W.; Zhang, X. Chem. Rev. 2003, 103, 3029-3069. (f) Pohlki, F.; Doye, S. Chem. Soc. Rev. 2003, 32, 104114. (g) Blaser, H. U.; Spindler, F. Handbook of Homogeneous Hydrogenation, Wiley-VCH, Weinheim, 2007. (h) Severin, R.; Doye, S. Chem. Soc. Rev. 2007, 36, 1407-1420. (i) Müller, T. E.; Hultzsch, K. C.; Yus, M.; Foubelo, F.; Tada, M. Chem. Soc. Rev. 2008, 108, 3795-3892. (j) Nugent, T. C.; EI-Shazly, M. Adv. Synth. Catal. 2010, 352, 753-819. (2) (a) Enthaler, S.; Junge, K.; Addis, D.; Erre, G.; Beller, M. ChemSusChem 2008, 1, 1006-1010. (b) Enthaler, S.; Addis, D.; Junge, K.; Erre, G.; Beller, M. Chem. Eur. J. 2008, 14, 9491-9494; (c) Li, X.; Zeeland, R. V.; Maligal-Ganesh, R. V.; Pei, Y.; Power, G.; Stanley, L.; Huang W. ACS Catal., 2016, 6 , 6324; (d) Choi, K. M.; Na, K.; Somorjai, G. A.; Yaghi O. M. J. Am. Chem. Soc., 2015, 137, 7810; (e) Li, X.; Goh, T. W.; Li, L.; Xiao, C., Guo, Z.; Zeng, X. C.; Huang, W. ACS Catal., 2016, 6, 3461; (f) Li, X.; Guo, Z.; Xiao, C.; Goh, T. W.; Tesfagaber, D.; Huang, W. ACS Catal., 2014, 4, 3490. (3) (a) Huang, Y.; Sachtler, W. M. H. J. Catal. 1999, 188, 215225. (b) Hegedús, L.; Máthe, T. Appl. Catal. A: Gen. 2005, 296, 209-215. (c) Hegedűs, L.; Máthé, T.; Kárpáti, T. Appl. Catal. A: Gen. 2008, 349, 40-45. (d) Maki, S.; Okawa, M.; Makii, T.; Hirano, T.; Niwa, H. Tetrahedron Lett. 2003, 44, 3717-3721. (e) Ikawa, T.; Fujita, Y.; Mizusaki, T.; Betsuin, S.; Takamatsu, H.; Maegawa, T.; Monguchi, Y.; Sajiki, H. Org. Biomol. Chem. 2012, 10, 293-304. (f) Chatterjee, M.; Kawanami, H.; Sato, M.; Ishizaka, T.; Yokoyama, T.; Suzuki, T. Green Chem. 2010, 12, 87-93. (g) Maegawa, T.; Fujita, Y.; Sakurai, A.; Akashi, A.; Sato, M.; Oono, K.; Sajiki, H. Chem. Pharm. Bull. 2007, 55, 837-839. (4) (a) Toti, A.; Frediani, P.; Salvini, A.; Rosi, L.; Giolli, C.; Giannelli, C. Comptes Rendus Chimie 2004, 7, 769-772. (b) Li, T.; Bergner, I.; Nipa, F. H.; Zimmer-De, M. I.; Song, D.; Morris, R. H. Organometallics, 2007, 26, 5940-5949. (c) Grey, R. A.; Pez, G. P.; Wallo, A. J. Am. Chem. Soc. 1981, 103, 7536-7542. (d) Pez, G. P.; Grey, R. A.; Corsi, J. J. Am. Chem. Soc. 1981, 103, 7520-7528. (e) Takemoto, S.; Kawamura, H.; Yamada, Y.; Okada, T.; Ono, A.; Yoshikawa, E.; Mizobe, Y.; Hidai, M. Organometallics, 2002, 21, 3897-3904. (f) Xie, X.; Liotta, C. L.; Eckert, C. A. Ind. Eng. Chem. Res. 2004, 43, 7907-7911. (g) Werkmeister, S.; Junge, K.; Beller, M. Org. Process Res. Dev. 2014, 18, 289-302. (h) Kusaka, H.; Hara, Y.; Onuki, M.; Akai, T.; Okuda, M. J. Catal. 1996, 161, 96-106. (5) (a) Rajesh, K.; Dudle, B.; Blacque, O.; Berke, H. Adv. Synth. Catal. 2011, 353, 1479-1484. (b) Giannandrea, R.; Mastrorilli, P.; Zaccaria, G.; Nobile, C. F. J. Mol. Catal. A: Chem. 1996, 109,
113-117. (c) Huang, Y.; Sachtler, W. M. H. Appl. Catal. A: Gen. 1999, 182, 365-378. (6) (a) Zerecero-Silva, P.; Jimenez-Solar, I.; Crestani, M. G.; Arévalo, A.; Barrios-Francisco, R.; García. J. J. Appl Catal A: Gen. 2009, 363, 230-234. (b) Srimani, D.; Feller, M.; Ben-David, Y.; Milstein, D. Chem. Commun. 2012, 48, 11853-11855. (c) RaseroAlmansa, A. M.; Corma, A.; lglesias, M.; Sánchez, F. Green Chem. 2014, 16, 3522-3527. (7) Werkmeister, S.; Junge, K.; Wendt, B.; Spannenberg, A.; Jiao, H.; Bornschein, C.; Beller, M. Chem. Eur. J. 2014, 20, 4227-4231. (8) (a) Addis, D.; Enthaler, S.; Junge, K.; Wendt, B.; Beller, M. Tetrahedron Lett. 2009, 50, 3654-3656. (b) Ortiz- Cervantes, C.; Iyañez, I.; García, J. J. J. Phys. Org. Chem. 2012, 25, 902-907. (c) Huang, Y.; Adeeva, V.; Sachtler, W. M. H. Appl. Catal. A: Gen. 2000, 196, 73-85. (d) Werkmeister, S.; Junge, K.; Beller, M. Org. Process Res. Dev. 2014, 18, 289-302. (e) Segobia, D. J.; Trasarti, A. F.; Apesteguía, C. R. Appl. Catal. A: Gen. 2012, 445, 69-75. (9) Zoran, A., Khodzhaev, O.; Sasson, Y. J. Chem. Soc. 1994, 2239-2240. (10) (a) Horn, S.; Gandolfi, C.; Albrecht, M. Eur. J. Inorg. Chem. 2011, 18, 2863-2868. (b) Palmer, M. J.; Wills, M. Tetrahedron: Asymmetry 1999, 10, 2045-2061. (11) (a) Kumbhar, P. S.; Sanchez-Valente, J.; Millet, J. M. M.; Figueras, F. J. Catal. 2000, 191, 467-473. (b) Auer, S. M.; Grunwaldt, J. D.; Köppel, R. A.; Baiker, A. J. Mol. Catal. A: Chem. 1999, 139, 305-313. (12) Kadyrov, R.; Riermeier, T. H. Angew. Chem., Int. ed. 2003, 42, 5472-5474. (13) (a) Uematsu, N.; Fujii, A.; Hashiguchi, S.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1996, 118, 4916-4917. (b) Haddenham, D.; Pasumansky, L.; DeSoto, J.; Singaram, S. E. B. J. Org. Chem. 2009, 74, 1964-1970. (c) Bornschein, C.; Werkmeister, S.; Junge, K.; Beller, M. New J. Chem. 2013, 37, 2061-2065. (d) Das, S.; Wendt, B.; Mçller, K.; Junge, K.; Beller, M. Angew. Chem., Int. Ed. 2012, 51, 1662-1666. (e) Khurana, J. M.; Kukreja, G. Synthetic Commun. 2002, 32, 1265-1269. (f) Saavedra, J. Z.; Resendez, A.; Rovira, A.; Eagon, S.; Haddenham, D.; Singaram, B. J. Org. Chem. 2012, 77, 221-228. (14) (a) Wang, F.; Shi, R.; Liu, Z. Q.; Shang, P. J.; Pang, X.; Shen, S.; Feng, Z.; Li, C.; Shen, W. ACS Catal. 2013, 3, 890-894; (b) Salam, N.; Kundu, S. K.; Roy, A. S.; Mondal, P.; Ghosh, K.; Bhaumik, A.; Islam, S. M. Dalton Trans. 2014, 43, 7057-7068. (15) (a) Watanabe, Y.; Ohta, T.; Tsuji, Y.; Hiyoshi, T.; Tsuji, Y. Bull. Chem. Soc. Jpn. 1984, 57, 2440-2446. (b) Imai, H.; Nishiguchi, T.; Fukuzumi, K. Chem. Lett. 1976, 655-660. (c) Shen, K.; Chen, X.; Chen, J.; Li, Y. ACS Catal., 2016, 6, 5887-5903. (16) Mizushima, E.; Yamaguchi, M.; Yamagishi, T. J. Mol. Catal. A: Chem. 1999, 148, 69-75. (17) (a)Vilches-Herrera, M.; Werkmeister, S.; Junge, K.; Börner, A.; Beller, M. Catal. Sci. Technol. 2014, 4, 629-632; (b) Das, S.; Wendt, B.; Mçller, K.; Junge, K.; Beller; M. Angew. Chem. Int. Ed. 2012, 51, 1662–1666. (c) Khurana, J. M.; Kukreja, G. Synthetic Commu., 2002, 32, 1265-1269. (18) (a) Lee, J. Y.; Olson, D. H.; Pan, L.; Emge, T. J.; Li, J. Adv. Funct. Mater. 2007, 17, 1255-1262. (b) Tan, K., Nijem, N.; Canepa, P.; Gong, Q.; Li, J.; Thonhauser, T.; Chabal, Y. J. Chem. Mater. 2012, 24, 3153-3170. (c) Dybtsev, D. N.; Chun, H.; Kim, K. Angew. Chem., Int. Ed. 2004, 43, 5033-5036. (19) Shen, K.; Chen, L.; Long, J.; Zhong, W.; Li, Y. ACS Catal. 2015, 5, 5264-5271. (20) (a) Long, J.; Zhou, Y.; Li, Y. Chem. Commun. 2015, 51, 2331-2334. (b) Long, J.; Zhou, Y.; Li, Y. Chinese J. Catal. 2016, 37, 955–962. (21) Nam, K. M.; Shim, J. H.; Ki, H.; Choi, S. I.; Lee, G.; Jang, J. K.; Jo, Y.; Jung, M. H.; Song, H.; Park, J. T. Angew. Chem., Int. Ed. 2008, 47, 9504-9508. (22) Tang, J.; Salunkhe, R. R.; Liu, J.; Torad, N. L.; Imura, M.; Furukawa, S.; Yamauchi, Y. J. Am. Chem. Soc. 2015, 137, 15721580.
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(23) Biesingera, M. C.; Payne, B. P.; Grosvenor, A. P.; Lau, L. W. M.; Gerson, A. R.; Smart, R. C. Appl. Surf. Sci. 2011, 257, 27172730. (24) (a) Das, R.; Pachfule, P.; Banerjee, R.; Poddar, P. Nanoscale 2012, 4, 591-599. (b) Zhong, W.; Liu, H.; Bai, C.; Liao, S.; Li, Y. ACS Catal. 2015, 5, 1850-1856. (25) (a) Souza, F. G.; Richa, P.; Siervo, A.; Oliveira, G. E.; Rodrigues, C. H. M.; Nele, M.; Pinto, J. C. Macromol. Mater. Eng. 2008, 239, 675-683. (b) Long, J.; Shen, K.; Chen, L.; Li, Y. J. Mater. Chem. A, 2016, 4, 10254-10262. (26) (a) Stevens, J. S.; Byard, S. J.; Muryn, C. A.; Schroeder, S. L. M. J. Phys. Chem. B, 2010, 114, 13961-13969. (b) Stevens, J. S.; Byard, S. J.; Schroeder, S. L. M. J. Pharm. Sci. 2010, 99, 44534457. (c) Shibata, M.; Kimura, Y.; Yaginuma, D. Polymer 2004, 45, 7571-7577. (27) (a) Li, X. L.; Wang, H. L.; Robinson, J. T.; Sanchez, H.; Diankov, G.; Dai, H. J. J. Am. Chem. Soc. 2009, 131, 15939-15944. (b) Chen, L.; Xu, C.; Du, R.; Mao, Y.; Xue, C.; Chen, L.; Qu, L.; Zhang, J.; Yi, T. J. Mater. Chem. A 2015, 3, 5617-5627. (c) Lefevre, M.; Proietti, E.; Jaouen, F.; Dodelet, J. P. Science 2009, 324, 71-74. (28) (a) Dong, Z. R.; Li, Y. Y.; Chen, J. S.; Li, B. Z.; Xing, Y.; Gao, J. X. Org. Lett. 2005, 7, 1043-1045. (b) Noyori, R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97-102. (c) Long, J.; Yin, B.; Li, Y.; Zhang, L. AIChE J. 2014, 60, 3565-3576. (d) Noyori, R.; Yamakawa, M.; Hashiguchi, S. J. Org. Chem. 2001, 66, 79317944. (29) (a)Rosi, N. L.; Kim, J.; Eddaoudi, M.; Chen, B.; O’Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2005, 127, 1504-1518. (b) Miles, D. O.; Jiang, D.; Burrows, A. D.; Halls, J. E.; Marken, F. Electrochem. Commun. 2013, 27, 9–13 (30) (a) Banerjee, R.; Phan, A.; Wang, B.; Knobler, C.; Furukawa, H.; O'Keeffe, M. Science 2008, 319, 939-943. (b) Qian, J.; Sun, F.; Qin, L. Mater. Lett. 2012, 82, 220-223. (31) Brieger, G.; Nestrick, T. J. Chem. Rev. 1974, 74, 567-580. (32) Allgeier, A. M.; Duch, M. W. Chemical industries, Dekker, 2001, Vol. 82, pp. 229. (33)Thomas-Pryor, S. N.; Manz, T. A.; Liu, Z.; Koch, T. A.; Sengupta, S. K.; Delgass, W. N. Chemical Industries, Dekker, New York, 1998, Vol. 75, pp. 195. (34) (a) Srimani, D.; Feller, M.; David, Y. B.; Milstein, D. Chem. Commun. 2012, 48, 11853-11855. (b) Al-Hmoud, L.; Jones, C. W. J. Catal. 2013, 301, 116-124. (c) Reguillo, R.; Grellier, M.; Vautravers, N.; Vendier, L. J. Am. Chem. Soc. 2010, 132, 7854-7855. (35) Gnanaprakasam, B.; Zhang, J.; Milstein, D. Angew. Chem., Int. Ed. 2010, 49, 1468-1471.
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