Cu2O

Subscriber access provided by - Access paid by the | UCSB Libraries

Article

Synthesis of composition tunable and (111) faceted Cu/Cu2O nanoparticles toward photocatalytic, ligandand solvent-free C-N Ullmann coupling reactions Mingming Li, Xiaofei Xing, Zhengzheng Ma, Jing Lv, Pengcheng Fu, and Zhenxing Li ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b00350 • Publication Date (Web): 22 Feb 2018 Downloaded from http://pubs.acs.org on February 23, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23 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

ACS Sustainable Chemistry & Engineering

Synthesis of composition tunable and (111) faceted Cu/Cu2O nanoparticles toward photocatalytic, ligandand solvent-free C-N Ullmann coupling reactions Mingming Li,† Xiaofei Xing,† Zhengzheng Ma,† Jing Lv,† Pengcheng Fu*,‡, and Zhenxing Li*,† †

State Key Laboratory of Heavy Oil Processing, Institute of New Energy, China

University of Petroleum (Beijing), 18 Fuxue Road, Beijing 102249, P. R. China ‡

State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan

University, 58 Renmin Road, Haikou 570228, P. R. China * Corresponding author: State Key Laboratory of Heavy Oil Processing, Institute of New Energy, China University of Petroleum (Beijing), 18 Fuxue Road, Beijing 102249, P. R. China E-mail: [email protected] (Z. Li.) State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, 58 Renmin Road, Haikou 570228, Hainan Province, P. R. China E-mail: [email protected] (P. Fu.) ABSTRACT: A novel protocol has been demonstrated for the preparation of composition tunable (111)-faceted Cu/Cu2O nanoparticles, an interesting shape evolution of nanoparticles, from octahedral, tetrahexahedron and finally to star-shaped nanostructure, was achieved by increasing the amount of glucose in the reaction. The prepared Cu/Cu2O nanoparticles can be used for the photocatalysis of the C-N Ullmann coupling reaction without the use of ligands and solvents. By the design of

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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

Page 2 of 23

the Cu/Cu2O nanoparticles with tetrahexahedron structure, the reaction productivity achieves 77%. Goals of reduction of energy consumption and environment-friendly chemical process have thus been met. As illustrative examples, these Cu/Cu2O nanoparticles are used to achieve high photocatalytic activity for both aliphatic amine and cyclic amine reacting with halogenated benzene.

KEYWORDS:

Cu/Cu2O

nanoparticle,

C-N

Ullmann

Photocatalysis


coupling

reaction,

Page 3 of 23 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


INTRODUCTION Traditional Ullmann coupling reaction is widely used in industry for near one century. However, it involves high temperature, strong alkaline, long reaction time, which results in environmental pollution and severe energy consumption. 1 In order to improve the reaction processes, many researchers have made significant efforts to enhance catalysis efficiency. For example, the copper-catalyzed Ullmann coupling reaction between aryl halides and amines has been extensively studied in recent years 2

to find efficient methods to form carbon-nitrogen (C-N) bond

3,4

since the

nitrogen-containing organic compounds have been found functionally important in the pharmaceutical, functional materials, and agricultural science areas. 5,6 Ullmann-type aryl amination is drastically hurdled by its harsh reaction conditions, Hassan et al. reported that the reaction could be conducted with high yield when the catalytic Pd(OAc)2 was used as catalyst with alkaline and isopropanol at 105 °C. 7 Furthermore, the aryl amination of either aryl bromides or aryl iodides was proven to be carried out at room temperature when phosphines were used as the ligands was used as the catalyst.

9

8

and the palladium

In consideration of the high cost of Pd catalyst and the

ligands, researchers have tried to replace them with copper due to its lower toxicity and cost for the process. 10-12 Much efforts have been made to improve the catalytic efficiency by copper in past years,

13,14

a resultant facile method for Ullmann

amination of aryl halides to be catalyzed by the copper powder at 100 °C in air was disclosed. 15 On the other hand, other catalysis and ligands have been tested for the amination process. Among them, Ma et al. have found that Ullmann-type aryl amination of aryl iodides in DMSO showed the excellent yields at 40 − 90 °C by using CuI and L-proline as the catalyst and ligand, respectively. 16 Fu et al. have shown that the C−N bond formation could be achieved at room temperature with an inexpensive catalyst (CuI). 17,18 Several shortcomings have been found when the Ullmann reactions happened in homogeneous systems,

8,19

such as the involvement of non-recyclable catalysts,

complex ligands, and environment unfriendly solvents. In response, more and more



Page 4 of 23

efforts have been made to focus on the heterogeneous catalysts for facile recyclability and industrial scale-up. Nanoparticles thus play an important role in this field for their unique physical and chemical properties: e.g., large specific surface area, high surface atomic activity, and high catalytic activity. 20 In particular, extensive researches have been done to explore homogeneous-like heterogeneous metal nanocatalysts for Ullmann coupling reactions. For example, Wang et al. have reported that their hydrotalcite-supported Pd-Au nanocatalysts were found to be efficient heterogeneous catalysts for Ullmann coupling reactions of aryl bromides or chlorides. 21 Solar energy is a green and abundant source of energy, which can be broadly utilized. 22 Photocatalysis has been widely used to prepare metals, 23,24 metal-oxides and inorganic nanocomposites. 25 However, it is rarely applied in catalytic organic coupling reactions. Although many nanoparticles have been created for the C-N Ullmann coupling reaction, photocatalysis has been somewhat underdeveloped for the same process. It is found that cuprous oxide (Cu2O) nanoparticles with controllable facets are of great significance for photocatalysis, 26 owing to their low toxicity

27,28

and appropriate bandgap, 29 which can take the advantage of visible light effectively compared to conventional materials. 30 Cu2O nanoparticles have different shapes, such as, cube,

31

rod, tube, octahedral

32

etc. The (111) dominant facets are known to

possess higher photocatalytic activity than (100) and (110) facets. 33 Meanwhile, the strategy of preparing Cu/Cu2O nanostructure to eliminate the influence of low quantum efficiency of Cu2O was proposed.

34

Solvent plays an important role in

traditional reaction system, only few reports about organic solvent-free process for Ullmann amination have been mentioned in the literature. 35 In this study, we report a novel synthetic approach for Cu/Cu2O nanostructure with (111) dominant facets in octahedral and tetrahexahedrons as well as the star-shaped morphologies. The prepared Cu/Cu2O nanoparticles can be used for photocatalysis of the C-N Ullmann reaction without ligands and solvents. As illustrative examples, these Cu/Cu2O nanoparticles are used with high photocatalytic activity for both aliphatic amine and cyclic amine reacting with halogenated benzene.


Page 5 of 23 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


RESULTS AND DISCUSSION Morphology of Cu/Cu2O Nanocrystals. The composition and phase purity of the samples were measured by powder X-ray diffraction (XRD), which reveals that Cu/Cu2O nanoparticle is obtained in all samples. Figure 1 shows the representative XRD patterns of Cu/Cu2O nanoparticle in octahedral and tetrahexahedron as well as the star-shaped particles, indicating that the diffraction peaks are readily indexed to (111)-faceted Cu and Cu2O. The peak position and relative intensity of the diffraction peaks match well with standard powder diffraction data for Cu and Cu2O (JCPDS card no. 04-0836 and 05-0667). The 2θ peaks at 36.4°and 43.3°correspond to the (111) facet of Cu2O and Cu, respectively. Therefore, the nanoparticles are the combination of copper and cuprous oxide. Figure 1 indicates that the (111) peak of Cu2O and Cu is extremely high, proving that the (111) facet is mainly exposed in the crystal structure，which indicating that these Cu/Cu2O nanoparticles are in (111)-faceted orientation. Meanwhile, as shown in the XRD spectrum, the area ratio of the two peaks of (111) facet for the three different morphology nanoparticles is different. The ratio of the peak area of the (111) facet of Cu2O to the peak area of the (111) facet of Cu is 4/7, 3/4 and 1/1, respectively, corresponding to octahedral, tetrahexahedron and star-shaped, respectively, suggesting that the proportion of Cu in the Cu/Cu2O nanostructure will increase, with the increase of number of glucose in the preparation of the nanoparticles. In comparison, the relative strength of the (200) diffraction peak is much weaker than that of the diffraction peaks of (111) facet.

Figure 1. XRD patterns of octahedral, tetrahexahedron and star-shaped Cu/Cu2O nanoparticles, respectively.



The morphology and size of the obtained Cu/Cu2O nanoparticles were further analyzed by using scanning electron microscopy (SEM). The Cu/Cu2O nanoparticles with various morphologies were obtained, as shown in Figure 2. It was also observed that the morphologies were highly dependent on the amounts of glucose added. When the reaction was carried out with the glucose concentration of 0.2 g/10 ml, all the obtained particles would be in an octahedral-like morphology (Figure 2a). The size of the nanoparticles was about 3 − 4μm. In Figure 2b, tetrahexahedron patterned Cu/Cu2O nanoparticles are observed by using 0.4 g/10 ml glucose in concentration. It is clearly revealed that the nanocrystals are uniform in size. These nanoparticles have an average edge length of 3μm (Figure 2b). Finally, when the concentration of glucose is 0.5 g/10 ml or more, the star-shaped Cu/Cu2O nanoparticles were obtained. The particle size determined from the distance between two opposing vertices is about 50μm (Figure 2c).

Figure 2. SEM patterns of different shape Cu/Cu2O nanoparticles: (a) Octahedral (b) Tetrahexahedron (c) Star-shaped.

To understand the formation mechanism, Figure 3 illustrates the schematic of typical formation processes of Cu/Cu2O nanoparticles. At the initial stage, the crystals preferably tend to form thermodynamically stable octahedral morphology with the lowest surface energy. 36 Since the polyhedral particles have low-coordination surface structure on the vertex, as the reaction proceeds, it is easier to deposit copper atoms at the vertex, generating a tip at the point and growing along the vertex to form tetrahexahedron. With the increase in the amount of glucose, more copper ions are


Page 6 of 23

Page 7 of 23 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


reduced, accelerating the coordination at the vertex. And then star-shaped Cu/Cu2O nanoparticles are obtained.

Figure 3. The formation mechanism of Cu/Cu2O nanoparticles.

Figure 4 shows the High-resolution transmission electron microscopy (HRTEM) images of Cu/Cu2O nanoparticles with different morphology. The lattice spacing, at the border regions of those three different shaped nanoparticles, measured to be 0.244 nm, 0.256 nm and 0.245 nm, respectively, correspond to the (111) facet of Cu2O. This result indicates that the cuprous oxide is located on the surface of the Cu/Cu2O nanoparticles while copper is in the core.

Figure 4. HRTEM images of Cu/Cu2O nanoparticles: (a) Octahedral (b) Tetrahexahedron (c) Star-shaped.

According to SEM-energy dispersive X-ray (EDS) line scan profiles of a single Cu/Cu2O nanoparticle and elemental mapping images (Figure 5 and Figure 6), it is indicated that Cu is distributed throughout the nanoparticles and Cu mainly stays at the center of the particles, whereas O distributes on the surface, which is in agreement with the HRTEM results. The above analysis confirms that the successful preparation of Cu/Cu2O nanoparticles, and the Cu is in the center and Cu2O is in the outlayer of



the particle, respectively.

Figure 5. EDS line scan profiles of Cu/Cu2O nanoparticles: (a) Octahedral (b) Tetrahexahedron (c) Star-shaped.

Figure 6. EDS mapping images of Cu/Cu2O nanoparticles: (a) Octahedral (b) Tetrahexahedron (c) Star-shaped.

X-ray Photoelectron Spectroscopy (XPS) is conducted over these three different


Page 8 of 23

Page 9 of 23 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


shape Cu/Cu2O nanoparticles in order to understand the chemical structure of their surface. The representative XPS survey spectrums of Cu 2p3/2 of Cu/Cu2O nanoparticles in different shapes are shown in Figure 7. Before the curve fitting, a Shirley-type background subtraction was done and the curve fitting was set from 80% Gaussian to 20% Lorentzian function. All these spectrums can be separated into the main peak of 932.3eV, assigned to Cu2O, 37 and a small peak (about 5%) at 935.1 eV, belonged to Cu(OH)2. 38,39 This small peak exists ( 420 nm) with has no effect on the yield of the reaction (entry 2). To demonstrate the scope and applicability of this reaction for other structurally diverse amines, we investigated the reaction with other kinds of amines and the results were summarized in Table 1 (entries 1-7). Firstly, shorter chain amines was examined, such as N-propylamine and N-butylamine, the yields were respectively 68% (Table 1, entry 2) and 70% (Table 1, entry 3). As well as dodecylamine and oleylamine, the longer chain amines afforded the desired product 3d and 3e, and the yields were 76%



Page 12 of 23

and 60%, respectively (entries 4 and 5). Moreover, this coupling reaction was also carried out for cyclic amines. Morpholine and benzylamine (entries 6 and 7) have been tested and the yields were 66% and 64%, respectively. As shown in Table 1, the reaction of various amines proceeded well to afford the target product in desired yields. In addition, we explored 2-nitrobromobenzene (1b) reacted with all kinds of amines including N-octylamine, N-propylamine, N-butylamine, dodecylamine, oleylamine, morpholine and benzylamine, and the yields were 61%, 57%, 59%, 60%, 52%, 55% and 54% ,respectively (Table 1, entries 8-14). To our surprise, iodobenzene could also react with amines under this condition in the yield of 40% (Table 1, entry 15).And in the absence of light, the reactions would not proceed.

Table 1. Coupling Reaction of Aryl Halides with amines under the Catalysis of Cu/Cu2O nanoparticles.a R1

X R1 +

Y

HN

Cu/Cu2O Nanoparticles

R2

1

R2

N Y

Xenon lamp, Ar

2

3

X=I,Br; R 1or R 2=H,alkyl

Entry

1

2 NO2 NH 2

I

1

Yield (%)b

3

2a

NO 2 n-C 8H17 NH

77

3a

1a

NO 2

2

1a

NH2

N H

2b

68 3b

NO 2

3

1a

NH2

2c

70

N H

3c

NO 2

4

1a

9 NH2

2d


n-C 12H25 NH

3d

76

Page 13 of 23 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


NO2

5

1a

C 18H35 NH

8NH2

7

2e

60

3e NO 2

6

NH

O

1a

2f

O

64

3f NH2

7

N

NO2 N H

1a

60

2g

3g

2a

3a

61

NO 2 Br

8 1b

9

1b

2b

3b

57

10

1b

2c

3c

59

11

1b

2d

3d

60

12

1b

2e

3e

52

13

1b

2f

3f

55

14

1b

2g

3g

54

2c

N H

40

I

15

3h

1c

a

Reaction condition: 1 (2.5 mmol), 2 (12.5 mmol), Cu/Cu2O nanoparticles (0.5 mmol，20mol%), reaction time (12

h) under a xenon lamp in a sealed Schlenk tube in the argon atmosphere. b Isolated yield.



Furthermore, in order to illustrate the recycling performance of the Cu/Cu2O nanoparticle catalyst, the model reaction of 2-nitroiodobenzene (1a) and N-octylamine (2a) were chosen to investigate the reusability of the Cu/Cu2O nanoparticle catalyst. The catalyst after each run was centrifuged and washed with ethyl acetate and ethanol, followed by drying to remove the residues from the surface of the Cu/Cu2O nanoparticles, which showed great reusability. Moreover, the reuses of the catalyst indicated that such the Cu/Cu2O nanoparticles are quite stable and still maintain high catalytic activity of 75% after fifth reuse (Figure 10). The isolated yields from first to fifth catalytic reaction are 77%, 77%, 76%, 76% and 75%, respectively. The slight decrease of the catalytic activity is because of the partial coverage of organic compounds on the surface of the Cu/Cu2O nanoparticles. In addition, as suggested by the SEM image of the Cu/Cu2O nanoparticles after the catalytic reaction, the particle size of the Cu/Cu2O nanoparticles does not exhibit any appreciable aggregation (Figure S1), confirming the good stability of Cu/Cu2O nanoparticles during the reaction process.

Figure 10. The reuses of tetrahexahedron shaped Cu/Cu2O nanoparticles on the C-N Ullmann coupling reaction of 2-nitroiodobenzene with N-octylamine.

We turned our attention to elucidating the reaction mechanism, a plausible mechanism for the C-N Ullmann coupling reaction of amines with aryl halides catalyzed by Cu/Cu2O nanoparticles was depicted in Scheme 2. First, we assume that Cu/Cu2O nanoparticles can be coordinated with the amines to form Cu(NHCH2R) (1)


Page 14 of 23

Page 15 of 23 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


and then with light irradiation it may induce charge transfer of Cu(NHCH2R) (1) to the formation of photoexcited state [Cu(NHCH2R)]* (2). Next, 2-nitroiodobenzene (1a) and excited state 2 generate its corresponding [Cu (NHCH2R)] +X- (3) and radical ion 2a via single electron transfer (SET). Last, the target product 3a generates and the copper catalysis cycle is closed. It needs to be emphasized that no ligand or additive is required in this reaction system. Cu/Cu2O nanoparticles exhibit an excellent catalytic activity.

Scheme 2. Possible mechanism for the C-N Ullmann coupling reaction.

To verify this plausible mechanism, the FTIR comparison of N-octylamine, N-octylamine and 2-nitroiodobenzene mixture, and N-octylamine, 2-nitroiodobenzene and Cu/Cu2O catalyst mixture was commenced and the results were shown in Figure 11. It was found that the infrared absorption of N-H of N-octylamine at 3390 cm–1 was disappeared when the Cu/Cu2O catalyst was added to the mixture, which indicates that the coordination between n-octylamine and Cu/Cu2O nanoparticles.



Figure 11. FTIR comparison of N-octylamine, N-octylamine and 2-nitroiodobenzene mixture, and N-octylamine, 2-nitroiodobenzene and Cu/Cu2O catalyst mixture.

Experimental section Synthesis method Synthesis of (111)-faceted octahedral shaped Cu/Cu2O Nanoparticles.

All chemicals used in this experiment were used without further purification. Cu/Cu2O nanoparticles were synthesized using the hydrothermal method. In a typical procedure, Cu(OAc)2 (0.1579g, 0.8mmol), PVP (1.5g) and glucose (0.2g) were dissolved in 10 mL of ultrapure water and stirred for 2 hours at room temperature. Then, the solution was transferred to a 20 mL Teflon-lined stainless steel autoclave. The autoclave was sealed and heated to 140°C for 4 h and then cooled to room temperature naturally. The obtained Cu/Cu2O nanoparticles were washed and precipitated for three times at room temperature through the addition of 5ml ethanol. Synthesis of (111)-faceted twenty-four tetrahedrons shaped Cu/Cu2O Nanoparticles.

In a typical procedure, Cu(OAc)2 (0.1579g, 0.8mmol), PVP (1.5g) and glucose (0.3g) were dissolved in 10 mL of ultrapure water and stirred for 2 hours at room temperature. And the other steps are all the same as 3.1.1. Synthesis of (111)-faceted star-shaped Cu/Cu2O Nanoparticles.

In a typical procedure, Cu(OAc)2 (0.1579g, 0.8mmol), PVP (1.5g) and glucose (0.5g) were dissolved in 10 mL of ultrapure water and stirred for 2 hours at room temperature. And the other steps are all the same as 3.1.1. Characterization.


Page 16 of 23

Page 17 of 23 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


The morphology and size of the nanoparticles were observed by Hitachi SU8010 scanning electron microscopy (SEM, Japan) at 200 kV. The energy-dispersive X-ray analysis (EDS) were recorded on a Hitachi SU8010 scanning electron microscopy under a working voltage of 200 kV. HRTEM images were taken on a JEM 2100 LaB6 with an accelerating voltage of 200 kV. The X-ray diffraction (XRD) patterns of samples were determined on a Burker D8-advance X-ray power diffractometer operated at 40kV and current of 40mA with Cu-K radiation ( =1.5406 Å). NMR spectra were recorded with a JNM-ECA600 spectrometer at 600 MHz for 1H NMR. The UV-visible absorption spectrum was recorded on a Hitachi U-3010 spectrometer. X-ray photoelectron spectrometer (XPS) were measured in an ion-pumped chamber (evacuated to 2 ×10-9 Torr) of an Escalad5 spectrometer, employing Mg KR radiation (BE) 1253.6 eV). Representative procedure for catalytic reactions.

A mixture of 2-nitrobromobenzene (2.5mmol), amine (12.5mmol, 5eq) and Cu/Cu2O nanoparticles (20mol %) was stirred in the argon atmosphere for 12 h under a xenon lamp in a sealed Schlenk tube. The reaction mixture was extracted with ethyl acetate when the reaction was completed (monitored by Thin Layer Chromatography (TLC)). The crude product was purified by column chromatography using ethyl acetate/petroleum ether as the eluent. The resulting products were characterized by 1H NMR. 1. N-Octyl-2-nitroaniline (Table 1, entry 1). 1H NMR (600 MHz, DMSO-d6) δ 8.06 (d, J = 8.6 Hz, 1H), 7.53 (t, J = 7.8 Hz, 1H), 7.04 (d, J = 8.7 Hz, 1H), 6.67 (t, J = 7.2 Hz, 1H), 3.34 (d, J = 6.5 Hz, 2H), 1.63 (t, 2H), 1.39-1.21(d, J = 5.9 Hz, 10H), 1.10(m, 1H), 0.85(d, 3H) 2. N-Propyl-2-nitroaniline (Table 1, entry 2).1H NMR (600 MHz, DMSO-d6) δ 8.12 (d, J = 7.9 Hz, 1H), 8.06 (d, J = 8.6Hz, 1H), 7.53 (t, J = 7.8 Hz, 1H), 7.05 (d, J = 8.1 Hz, 1H), 6.67 (d, J = 6.4 Hz, 1H), 3.32 (d, J = 5.9 Hz, 2H), 1.65 (d, 2H), 0.95 (t, J = 7.4 Hz, 3H). 3. N-Butyl -2-nitroaniline (Table 1, entry 3).1H NMR (600 MHz, DMSO-d6) δ 8.10 (s, 1H), 8.06 (d, J =1.6 Hz, 1H), 7.53 (t, J = 7.8 Hz, 1H), 7.05 (d, J = 8.7 Hz, 1H), 6.71 (m, 1H), 3.35 (d, J = 9.3 Hz, 2H), 1.69-1.57 (m, 2H), 1.46-1.34 (m, 2H), 0.93 (t, J = 7.4 Hz, 3H). 4. N-Dodecyl-2-nitroaniline (Table 1, entry 4). 1H NMR (600 MHz, DMSO-d6) δ 8.06 (d, J = 1.6 Hz, 1H), 7.53 (t, J = 7.0 Hz, 1H), 7.04 (d, J = 9.4 Hz, 1H), 6.70 (m, 1H), 3.34 (d, J = 6.2 Hz, 2H), 1.62 (s, 1H), 1.36 (d, J = 7.8 Hz, 2H), 1.27 (d, J = 4.0 Hz, 2H), 1.17-1.08 (m, 16H), 0.91-0.82 (m, 3H).



5. N-Oleyl-2-nitroaniline (Table 1, entry 5). 1H NMR (600 MHz, DMSO-d6) δ 8.02 (d, J = 8.6 Hz, 1H), 7.65 (s, 1H), 6.99 (s, 1H), 6.63 (s, 1H), 5.28 (s, 2H), 3.29 (d, J = 12.5 Hz, 2H), 1.95 (d, J = 6.7 Hz, 4H), 1.57 (s, 2H), 1.54-1.09 (m, 22H), 0.80 (t, J = 8.5 Hz, 3H). 6. N-Morpholinyl-2-nitroaniline (Table 1, entry 6). 1H NMR (600 MHz, DMSO-d6) δ 7.81 (s, 1H), 7.61 (s, 1H), 7.35 (s, 1H), 7.16 (s, 1H), 3.72-3.67 (m, 4H), 3.01-2.95 (m, 4H). 7. N-Benzyl-2-nitroaniline (Table 1, entry 7). 1H NMR (600 MHz, DMSO-d6) δ 8.08 (d, J = 10.2 Hz, 1H), 7.48 (m, 2H), 7.35-7.26 (t, J = 7.1 Hz, 6H), 6.91 (d, J = 8.7 Hz, 1H), 4.62 (s, 2H). 8. N-Octyl-2-nitroaniline (Table 1, entry 8). 1H NMR (600 MHz, DMSO-d6) δ 8.06 (d, J = 8.6 Hz, 1H), 7.53 (s, 1H), 7.04 (d, J = 8.1 Hz, 1H), 6.67 (s, 1H), 3.37 (m, 2H), 1.61 (s, 2H), 1.37-1.30 (d, J = 4.7 Hz, 10H), 1.08 (m, 1H), 0.86 (s, 3H). 9. N-Propyl-2-nitroaniline (Table 1, entry 9). 1H NMR (600 MHz, DMSO-d6) δ 8.12 (d, J = 7.9 Hz, 1H), 8.06 (d, J = 8.6 Hz, 1H), 7.53 (s, 1H), 7.05 (d, J = 8.7 Hz, 1H), 6.67 (s, 1H), 3.32 (s, 2H), 1.64 (s, 2H), 0.95 (s, 3H). 10. N-Butyl -2-nitroaniline (Table 1, entry 10). 1H NMR (600 MHz, DMSO-d6) δ 8.06 (d, J = 7.0 Hz, 1H), 7.53 (t, J = 7.8 Hz, 1H), 7.05 (d, J = 5.0 Hz, 1H), 6.70 (m, 1H), 6.64 (d, J = 6.5 Hz, 1H), 3.38 (m, 2H), 1.62 (s, 2H), 1.39 (s, 2H), 0.93 (s, 3H). 11. N-Dodecyl-2-nitroaniline (Table 1, entry 11). 1H NMR (600 MHz, DMSO-d6) δ 8.06 (d, J = 10.2 Hz, 1H), 7.53 (s, 1H), 7.04 (d, J = 8.7 Hz, 1H), 6.67 (s, 1H), 3.33 (s, 2H), 1.99 (s, 1H), 1.62 (s, 2H), 1.36 (s, 2H), 1.27-1.18 (d, J = 12.2 Hz, 16H), 0.85 (s, 3H). 12. N-Oleyl-2-nitroaniline (Table 1, entry 12). 1H NMR (600 MHz, DMSO-d6) δ 8.06 (d, J = 10.2 Hz, 1H), 7.53 (s, 1H), 7.04 (d, J = 8.7 Hz, 1H), 6.67 (s, 1H), 5.32 (s, 2H), 4.03 (s, 2H), 3.33 (s, 1H), 1.99 (d, J = 5.5 Hz, 4H), 1.62 (s, 2H), 1.35-1.09 (m, 22H), 0.84 (s, 3H). 13. N-Morpholinyl-2-nitroaniline (Table 1, entry 13). 1H NMR (600 MHz, DMSO-d6) δ 7.81 (d, J = 8.1 Hz, 1H), 7.61 (s, 1H), 7.34 (d, J = 7.2 Hz, 1H), 7.16 (s, 1H), 3.69 (s, 4H), 2.98 (s, 4H). 14. N-Benzyl-2-nitroaniline (Table 1, entry 14). 1H NMR (600 MHz, DMSO-d6) δ 8.08 (d, J = 8.6 Hz, 1H), 7.45 (s, 1H), 7.35 (d, J = 7.4 Hz, 6H), 6.91 (d, J = 8.7 Hz, 1H), 4.62 (s, 2H). 15. N-Butylaniline (Table 1, entry 15). 1H NMR (600 MHz, DMSO-d6) δ 7.04 (s, 2H), 6.54 (s, 1H), 6.49 (s, 2H), 3.32 (s, 1H), 2.97 (s, 2H), 1.52 (s, 2H), 1.38 (s, 2H), 0.91 (s, 3H).

CONCLUSION In summary, we have successfully synthesized (111)-faceted Cu/Cu2O nanoparticles of various architectures using a facile hydrothermal method in this work. A series of morphologies, such as octahedron, tetrahexahedron, and star-shaped particles, were obtained through the delicate manipulation of the amount of glucose. With the increase in the amount of glucose, the shape of the nanoparticles would change from the octahedron, through tetrahexahedron to star-shape gradually. Cu mainly stayed at the center of the Cu/Cu2O nanoparticles, whereas Cu2O would be distributed on the surface. The Cu/Cu2O nanoparticles were then used as a effective catalyst in the C-N Ullmann coupling reactions under light irradiation without the aid of any ligands and solvents, which demonstrated high photocatalytic activity for both


Page 18 of 23

Page 19 of 23 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


aliphatic amine and cyclic amine reacting with halogenated benzene. The study has shown that nanotechnology, photocatalysis and optics can be synergised to upgrate industrial chemical processes for elimination of environmental pollution by ligand and solvent free reactions, for reduction of energy consumption by utilization of solar energy and for enhancement of catalytic efficiency by introduction of nanomaterials.

Supporting Information The optimization of the reaction conditions, the SEM image of the Cu/Cu2O nanoparticles after the catalytic reaction and the NMR spectrums for all photocatalytic C-N Ullmann coupling products. This material is available free of charge via the Internet at http://pubs.acs.org.

ACKNOWLEDGEMENTS We gratefully acknowledge the financial support from the National Natural Science Foundation of China (NSFC) (Grant Nos. 21501197) and Beijing Natural Science Foundation (Grant No. 2182061). REFERENCES (1) Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M. Aryl−aryl bond formation one century after the discovery of the Ullmann reaction. Chem. Rev. 2002, 102, 1359–1470. (2) Yoo, W. J.; Tsukamoto, T.; Kobayashi S. Visible light-mediated Ullmann-type C–N coupling reactions of carbazole derivatives and aryl iodides. Org. Lett. 2015, 17, 3640−3642. (3) Hermann, W. A. N-Heterocyclic Carbenes: A new concept in organometallic catalysis. Angew. Chem., Int. Ed. 2002, 41, 1290−1309. (4) Sambiagio, C.; Marsden, S. P.; Blacker, A. J.; McGowan, P. C. Copper catalysed Ullmann type chemistry: from mechanistic aspects to modern development. Chem. Soc. Rev. 2014, 43, 3525−3550. (5) Son, S. U.; Park, I. K.; Park, J.; Hyeon, T. Synthesis of Cu2O coated Cu nanoparticles and their successful applications to Ullmann-type amination coupling reactions of aryl chlorides .Chem. Commun. 2004, 778−779. (6) Nandwana, N.; Dhiman, S.; Shelke, G.; Kumar, A. Copper-catalyzed tandem Ullmann type C–N coupling and dehydrative cyclization: synthesis of imidazo [1, 2-c] quinazolines. Org. Biomol. Chem. 2016, 14, 1736−1741.



(7) Hassan, J.; Penalva, V.; Lavenot, L.; Gozzi, C.; Lemaire, M. Catalytic alternative of the Ullmann reaction. Tetrahedron 1998, 54, 13793−13804. (8) Zhou, F. T.; Guo, J. J.; Liu, J. G.; Ding, K.; Yu, S. Y.; Ca, Q. Copper-catalyzed desymmetric intramolecular Ullmann C–N coupling: an enantioselective preparation of indolines. J. Am. Chem. Soc. 2012, 134, 14326−14329. (9) Zhang, L. L.; Wang, A. Q.; Miller, J. T.; Liu, X. Y.; Yang, X. F.; Wang, W. T.; Li, L.; Huang, Y. Q.; Mou, C. Y.; Zhang, T. Efficient and durable Au alloyed Pd single-atom catalyst for the Ullmann reaction of aryl chlorides in water. ACS Catal. 2014, 4, 1546−1553. (10) Maejima, T.; Ueda, M.; Nakano, J.; Sawama, Y.; Monguchi, Y.; Sajiki, H. Mechanism study of copper-mediated one-pot reductive amination of aryl halides using trimethylsilyl azide. J. Org. Chem. 2013, 78, 8980−8985. (11) Ye, S. R.; Rathmell, A. R.; Stewart, I. E.; Ha, Y. C.; Wilson, A. R.; Chen Z. f.; Wiley, B. J. A rapid synthesis of high aspect ratio copper nanowires for high-performance transparent conducting films. Chem. Commun. 2014, 2562−2564. (12) Bariwal, J.; Van der Eycken, E. C–N bond forming cross-coupling reactions: an overview. Chem. Soc. Rev. 2013, 42, 9283–9303. (13) Monnier, F.; Taillefer, M. Catalytic C-C, C-N, and C-O Ullmann-type coupling reactions: copper makes a difference. Angew. Chem., Int. Ed. 2008, 47, 3096−3099. (14) Marcoux, J. F.; Doye, S.; Buchwald, S. L. A general copper-catalyzed synthesis of diaryl ethers. J. Am. Chem. Soc. 1997, 119, 10539−10540. (15) Jiao, J.; Zhang, X. R.; Chang, N. H.; Wang, J.; Wei, J. F.; Shi, X. Y.; Chen, Z. G. A facile and practical copper powder-catalyzed, organic solvent- and ligand-free Ullmann amination of aryl halides. J. Org. Chem. 2011, 76, 1180–1183. (16) Ma, D. W.; Cai, Q.; Zhang, H. Mild method for Ullmann coupling reaction of amines and aryl halides. Org. Lett. 2003, 5, 2453−2455. (17) Ziegler, D. T.; Choi, J.; Muñoz-Molina, J. M.; Bissember, A. C.; Peters, J. C.; Fu, G. C. A versatile approach to Ullmann C–N couplings at room temperature: new families of nucleophiles and electrophiles for photoinduced, copper-catalyzed processes. J. Am. Chem. Soc. 2013, 135, 13107−13112. (18) Creutz1, S. E.; Lotito1, K. J.; Fu1, G. C.; Peters, J. C. Photoinduced Ullmann C–N coupling: demonstrating the viability of a radical pathway. Science 2012, 338, 647-651. (19) Zeng, M. F.; Du, Y. J.; Shao, L. J.; Qi, C. Z.; Zhang, X. M. Palladium-catalyzed eeductive homocoupling of


Page 20 of 23

Page 21 of 23 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


aromatic halides and oxidation of alcohols. J. Org. Chem. 2010, 75, 2556−2563. (20) Carrettin, S.; Blanco, M.C.; Corma, A.; Hashmi, A.S. Heterogeneous gold-catalysed synthesis of phenols. Adv Synth Catal. 2006, 348, 1283–1288. (21) Wang, J.; Xu, A. j.; Jia, M. l.; Bai, S.; Cheng X. D.; Zhaorigetu, B. Hydrotalcite-Ssupported Pd–Au nanocatalysts for Ullmann homocoupling reactions at low temperature. New J. Chem. 2017, 41, 1905−1908 (22) Xuan, J.; Xiao, W. J. Visible-light photoredox catalysis. Angew. Chem., Int. Ed. 2012, 51, 6828−6838. (23) Cargnelloa, M.; Montinid, T.; Smoline, S. Y.; Priebef, J. B. Engineering titania nanostructure to tune and improve its photocatalytic activity. P. Natl. Acad. Sci. USA 2016, 113, 3966-3971. (24) Gordon, T. R.; Cargnello, M.; Paik, T.; Mangolini, F.; Weber, R. T.; Fornasiero, P. ; Murray, C. B. Nonaqueous synthesis of TiO2 nanocrystals using TiF4 to engineer morphology, oxygen vacancy concentration, and photocatalytic activity. J. Am. Chem. Soc. 2012, 134, 6751–6761. (25) Zhou, Z.; Wang, J.; Yu, J.; Shen, Y.; Li, Y.; Liu, A.; Liu, S.; Zhang, Y. Dissolution and liquid crystals phase of 2D polymeric carbon nitride. J. Am. Chem. Soc. 2015, 137, 2179−2182. (26) Tan, C. S.; Hsu, S. C.; Ke, W. H.; Chen, L. J.; Huang, M. H. Facet-dependent electrical conductivity properties of Cu2O crystals. Nano Lett. 2015, 15, 2155−2160. (27) Zheng, Z.; Huang, B.; Wang, Z.; Guo, M.; Qin, X.; Zhang, X.; Wang, P.; Dai, Y. Crystal faces of Cu2O and their stabilities in photocatalytic reactions. J. Phys. Chem. C. 2009, 113, 14448−14453. (28) Paracchino, A.; Laporte, V.; Sivula, K.; Grätzel, M.; Thimsen, E. Highly active oxide photocathode for photoelectrochemical water reduction. Nat. Mater. 2011, 10, 456−461. (29) Filipic, G.; Cvelbar, U. In situ measurements of ultimate bending strength of CuO and ZnO nanowires. Nanotechnology 2012, 23, 194001. (30) Su, Y.; Li, H. F.; Ma, H. B.; Robertson, J.; Nathan A. Controlling surface termination and facet orientation in Cu2O nanoparticles for high photocatalytic activity: a combined experimental and density functional theory study. ACS Appl. Mater. Interfaces. 2017, 9, 8100−8106. (31) Kuo, C. H.; Chen, C. H.; Huang, M. H. Seed-mediated synthesis of monodispersed Cu2O nanocubes with five different size ranges from 40 to 420 nm. Adv. Funct. Mater. 2007, 17, 3773−3780. (32) Xu, Y.; Wang, H.; Yu, Y. F.; Tian, L.; Zhao, W. W.; Zhang, B. Cu2O nanocrystals: surfactant-free room-temperature morphology-modulated synthesis and shape-dependent heterogeneous organic catalytic activities. J. Phys. Chem. C. 2011, 115, 15288–15296. (33) Kwon, Y.; Soon, A.; Han, H.; Lee, H. Shape effects of cuprous oxide particles on stability in water and



photocatalytic water splitting. J. Mater. Chem. A. 2015, 3, 156–162. (34) Chen, W.; Fan, Z. L.; Lai, Z. P. Synthesis of core–shell heterostructured Cu/Cu2O nanowires monitored by in situ XRD as efficient visible-light photocatalysts. J. Mater. Chem. A. 2013, 1, 13862–13868. (35) Xu, H. J.; Zheng, F. Y.; Liang, Y. F.; Cai, Z. Y.; Feng, Y. S.; Che, D. Q. Ligand-free CuCl-catalyzed C–N bond formation in aqueous media. Tetrahedron Lett. 2010, 51, 669–671. (36) Xie, J.; Yan, C.Z.; Zhang, Y.; Gu, N. Shape evolution of “multibranched” Mn–Zn ferrite nanostructures with high performance: a transformation of nanocrystals into nanoclusters. Chem. Mater. 2013, 25, 3702−3709. (37) Wang, M.; Sun, L.; Lin, Z.; Cai, J.; Xie, K.; Lin, C. p–n heterojunction photoelectrodes composed of Cu2O-loaded TiO2 nanotube arrays with enhanced photoelectrochemical and photoelectrocatalytic activities. Energy Environ. Sci. 2013, 6, 1211−1220. (38) Platzman, I.; Brener, R.; Haick, H.; Tannenbaum, R. Oxidation of polycrystalline copper thin films at ambient conditions. J. Phys. Chem. C. 2008, 112, 1101−1108. (39) Zuo, Z. J.; Li, J.; Han, P.D.; Huang, W. XPS and DFT studies on the autoxidation process of Cu sheet at room temperature. J. Phys. Chem. C. 2014, 118, 20332−20345. (40) Sui, Y. M.; Fu, W. Y.; Yang, H. B.; Zeng, Y.; Zhang, Y.Y.; Zhao, Q.; Li, Y.; Zhou, X.M.; Leng, Y.; Li, M.H.; Zou, G.T. Low temperature synthesis of Cu2O crystals: shape evolution and growth mechanism. Cryst. Growth Des. 2010, 10, 99−108.


Page 22 of 23

Page 23 of 23 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


A facile and efficient protocol has been demonstrated for the preparation of (111)-faceted Cu/Cu2O nanoparticles, using for catalyzing C-N Ullmann reaction by photocatalysis without ligand and solvent.


Cu2O

Recommend Documents