Two-Dimensional Imine-Linked Covalent Organic Frameworks as a

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Two-Dimensional Imine-linked Covalent Organic Frameworks as A Platform for Selective Oxidation of Olefins Manman Mu, Yanwen Wang, Yutian Qin, Xilong Yan, Yang Li, and Li-Gong Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 19 Jun 2017 Downloaded from http://pubs.acs.org on June 19, 2017

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ACS Applied Materials & Interfaces

Two-Dimensional Imine-linked Covalent Organic Frameworks as A Platform for Selective Oxidation of Olefins Manman Mu a, c, Yanwen Wang b, c, Yutian Qin b, c, Xilong Yan b, c, d, Yang Li b, c, d, Ligong Chen b, c, d *

a

School of Science, Tianjin University, Tianjin, 300350, PR China

b

c

School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300350, PR China

Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin, 300072, PR China

d

Tianjin Engineering Research Center of Functional Fine Chemicals, Tianjin, PR China

Abstract Two-dimensional imine-linked covalent organic frameworks with hydroxyl groups, namely TAPT-DHTA-COFHX and TAPT-DHTA-COFDMF, were respectively constructed by the condensation of 1, 3, 5- tris- (4- aminophenyl) triazine and 2, 5dihydroxyl- terephthalaldehyde under solvothermal and reflux conditions. Both of COFs possess excellent thermal stability and the similar eclipsed stacking structure verified by XRD patterns. However, TAPT-DHTA-COFHX presented larger surface area (2238 m2/g) and higher crystallinity than TAPT-DHTA-COFDMF. Significantly, copper ions are efficiently incorporated into the pores of these two COFs via the coordination interaction with hydroxyl groups and imine linkers. The obtained copper-containing COFs (Cu-COFHX and Cu-COFDMF) were employed in the selective oxidation of styrene to benzaldehyde. Cu-COFHX with superior surface area (1886 m2/g) and pore volume (1.11 cm3/g) exhibited excellent catalytic performance and recyclability. This strategy not only provides a convenient approach to design imine-linked 2D COFs with hydroxyl groups, but also develops their novel application for catalysis.

Keywords: covalent organic framework; synthetic strategy; copper docking; 1

ACS Paragon Plus Environment


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selective oxidation of olefins; heterogenous catalysis

Corresponding Authors *E-mail:[email protected]

2


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1. Introduction Covalent organic frameworks (COFs) are an emerging class of porous crystalline materials constructed with the periodic arrangement of building blocks 1, 2, and attract intensive attention by virtue of low density, permanent porosity and structural diversity. Since the first COF materials reported in 2005 3, a number of COFs with two- (2D) or three-dimensional (3D) structures have been constructed through reversible condensation reactions such as boronic acid trimerization 4, 5, boronate ester formation

6-9

, trimerization of nitriles

10-12

, Schiff base formation

13-15

and so on.

Among them, COFs with boroxine/ boronate-ester linkages are unstable on account of the decomposition of boroxine/ boronate bonds in the presence of water or organic solvents. In contrast, the imine, hydrazone, triazine, phenazine and azine-linked COFs display improved stability. In the last decade, considerable attention was focused on their design, synthesis and promising applications in gas storage and separation, catalysis, proton conductivity, optoelectronics, chemical sensing, drug delivery and chromatography separation 16-28. In the case of 2D COFs, the framework is restricted to 2D sheets, which further stack to form a layered eclipsed structure that presents periodically aligned columns. Smith et al have proposed the mechanism of imine-based 2D COF formation, an amorphous, low surface area imine-linked network is formed through the initial rapid precipitation and subsequently this network self-assembly crystallizes to the ordered and layered 2D COF 29. The ordered 2D COFs facilitate the diffusion of reactants or charge carrier transport in the stacking direction, which implies that 2D COFs exhibit remarkable performance in the field of optoelectronics and catalysis. A series of porphyrin-containing 2D COFs with hydroxyl groups had been successively reported in recent years. It was claimed that the introduction of hydroxyl functionalities adjacent to the Schiff base centers enables the formation of intramolecular hydrogen bonds, which benefits the chemical stability, porosity and crystallinity of 2D COFs 30. In 2015, Shinde et al reported a catechol-porphyrin COF with hydroxyl groups as 3



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acidic sites, porphyrin rings and imine bonds as basic sites

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31

. This acid-base

bifunctional COF material was utilized as a heterogeneous catalyst in one-pot cascade reactions. In addition, several interesting works demonstrated the value of imine-linked COFs as catalyst carriers, in which the imine linkers were used to capture metallic guests

32-34

. To date, 2D imine-linked COFs bearing hydroxyl

functionalities for docking non-noble metal salts is still remained untouched. As one of the significant chemical materials, benzaldehyde has been extensively utilized in perfumes, pharmaceuticals, dyes and fine chemicals industry

35

.

Benzaldehyde is normally achieved via the oxidation of toluene or benzoyl alcohol 36, 37

, benzoic acid hydrogenolysis

38, 39

and benzoyl chloride hydrolysis. Unfortunately,

these methods still suffered from tedious procedures, harsh conditions, inefficiency and toxic waste disposal. In the view of environmental and economic points, the selective oxidation of styrene by oxygen, hydrogen peroxide and tert-butyl hydroperoxide might be a desirable process. Traditionally, the Schiff-base transition metal complexes are promising candidates for their excellent performances in the above reaction. Nevertheless, homogeneous transition metal complexes suffer from the troublesome recycling. Therefore, heterogeneous complexes by covalent anchoring of metal ion onto insoluble solid materials have attracted extensive attention

40-42

. Besides, numerous heterogeneous transition metal complexes are only

investigated in selective oxidation of alkenes to epoxides 43-46 but relative few studies focus on aldehyde compounds as the main product. It is worth mention that heterogeneous metal complexes require tedious procedures yet metal docked 2D COFs containing imine and hydroxyl units might be realized by only one-step reaction. Thereby, we envision that the design of novel 2D COFs with π-stacking and intramolecular hydrogen bonds can not only improve the stability and crystallinity, but also be served as a platform for docking metal salts which are employed in the selective oxidation of alkenes. Herein, we described the synthesis of novel 2D COFs containing imine and hydroxyl

units

(TAPT-DHTA-COF)

using

2,5-dihydroxyl-terephthalaldehyde

(DHTA, Scheme S2) as the vertices and 1,3,5-tris-(4-aminophenyl) triazine (TAPT, 4


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Scheme S1) as edges (Scheme 1). Under reflux and solvothermal conditions, 2D imine-linked COFs, TAPT-DHTA-COFDMF and TAPT-DHTA-COFHX, were achieved respectively and utilized as the platform for docking copper acetate. Next, copper-containing COFs, denoted as Cu-COFDMF and Cu-COFHX, were prepared and tested in the selective oxidation of styrene to benzaldehyde.

Scheme 1. Schematic representation of the synthesis of TAPT-DHTA-COF and Cu-COF.

2. Results and discussion 5



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As shown in Scheme 1, 2D imine-linked COFs with -OH functionalities (TAPT-DHTA-COF) were constructed from the monomers TAPT and DHTA under reflux or solvothermal condition. The synthesis of TAPT-DHTA-COFDMF was carried out by refluxing the mixture of TAPT (0.71 g, 2.00 mmol) and DHTA (0.42 g, 3.00 mmol) in anhydrous N, N-dimethylformamide (DMF) at 150 ℃ for 12 h under N2 atmosphere, a red powder was obtained in 86 % yield. TAPT-DHTA-COFHX was synthesized by solvothermal reaction of TAPT (10.6 mg, 0.03 mmol) and DHTA (7.47 mg, 0.045 mmol) in a 1:3 (v:v) mixture of dichlorobenzene and n-butanol in the presence of 3M acetic acid (0.2 mL) at 120 ℃ for 3 days in 83 % yield as an orange powder (S2 in details). Both of COFs were insoluble in common organic solvents such as tetrahydrofuran (THF), acetone, hexane, DMF and dimethylsulfoxide (DMSO) etc, indicating the formation of covalently cross-linked networks. Intriguingly, there is visible diversity in the morphology features of these two COFs such as color and shape. This observation inspires us to further investigate their physical and chemical properties in detail. Initially, Fourier transform infrared (FT-IR) spectra was conducted to verify the formation of TAPT-DHTA-COFHX and TAPT-DHTA-COFDMF (Figure S1). The strong adsorption bands at 1503 cm-1 and 1360 cm-1 revealed the presence of the triazine ring. The disappearance of the N-H stretching bands (3210, 3320 and 3460 cm-1) of TAPT and the C=O stretching bands (1670 cm-1) of DHTA manifested that these two starting materials were totally exhausted. Meanwhile, the appearance of the characteristic stretching bands at 1580 cm-1 might be ascribed to the formation of imine bonds which was similar to the FT-IR spectrum of reference compound 2,5-bis-(phenylimino) methylbenzene-1,4-diol (Scheme S3). This further confirmed the successful formation of imine-linked COFs via the condensation of TAPT and DHTA under reflux or solvothermal condition. The chemical structures of two imine-linked COFs were determined by

13

C

cross-polarized magic angle spinning (CP-MAS) solid-state NMR spectrum. As shown in Figure S2, the peak at 169 ppm originated from the carbon of triazine ring and the signals at ~153, 149, 134, 128, 122 ppm were assigned to the carbon atoms of 6


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the phenyl groups. Significantly, the absence of the signal for the formyl group of DHTA around 190 ppm illustrated its total consumption of start material. Furthermore, the signal at ~158 ppm assigned to the carbon atom of the C=N bond also confirmed the formation of imine-linked COFs. These conclusions were consistent with their FT-IR spectra. To further investigate their crystal structures, theoretical simulations and powder X-ray diffraction (PXRD) experiments were conducted. As described in Figure 1, TAPT-DHTA-COFHX displayed a strong peak at 2.82° corresponding to the (100) facet, indicating the high crystallinity of this material. The other minor diffraction peaks also appeared at 2θ = 4.90, 5.72, 7.54, 9.90 and 25.86°, which were assigned to (110), (200), (210), (220) and (001) facets, respectively. The π-π stacking distances were calculated as about 3.4 Å from the d spacing of 001 facet (Figure 1). The high crystallinity of TAPT-DHTA-COFHX was attributed to the presence of intramolecular O-H … N=C hydrogen bonding, which reduced structural defects and enhanced structural rigidity

47

. TAPT-DHTA-COFDMF presented the similar patterns but the

intensity was distinctly lower than that of TAPT-DHTA-COFHX. This suggested that these two materials had the similar stacking mode but TAPT-DHTA-COFDMF had lower crystallinity caused by more structural defects. To elucidate the lattice packing mode, two possible 2D modes with the eclipsed AA and staggered AB stacking were constructed for TAPT-DHTA-COF by the Materials Studio program. After geometrical energy minimization by the universal force field, the eclipsed AA stacking mode was built using space group p6/m with the optimized parameters of a = b = 36.63 Å and c = 3.38 Å, α = β = 90° and γ = 120°. It was noticeable that the experimental PXRD patterns of TAPT-DHTA-COF matched well with the simulated pattern obtained by the eclipsed AA stacking mode (Figure 1A). Furthermore, Pawley refinement was carried out to afford the refined PXRD patterns with the unit cell parameters a = b = 36.33 Å and c = 3.40 Å (Rp = 8.01 % and Rwp = 5.66 % for TAPT-DHTA-COFHX; Rp = 11.63 % and Rwp = 8.60 % for TAPT-DHTA-COFDMF). The refined XRD pattern was in good agreement with the experimental ones, as evident by their negligible difference (Figure S3). 7



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Figure 1. (A) The experimental patterns of TAPT-DHTA-COFHX (blue) and TAPT-DHTA-COFDMF (black) compared with the simulated eclipsed one (red). (B and C) Eclipsed stacking mode of TAPT-DHTA-COF.

Thermogravimetric analysis (TGA) demonstrated that TAPT-DHTA-COFHX exhibited the excellent thermal stability up to 450℃ without decomposition. However, owing to more structural defects, TAPT-DHTA-COFDMF began to decompose above 300℃ (Figure S4). Even so, both imine-linked COFs displayed excellent thermal behavior. The morphologies of TAPT-DHTA-COFHX and TAPT-DHTA-COFDMF were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As indicated in Figure 2, TAPT-DHTA-COFHX revealed a uniform morphology with particle size of about 0.3 µm but TAPT-DHTA-COFDMF presented a relative random distribution of particle size and aggregation. This indicated that the COF materials prepared by solvothermal method possessed more uniform crystalline structure for self-healing process. In addition, TEM study demonstrated that two materials were planar extended and aligned in parallel to form the platelike structures (Figure S5).

8


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Figure 2. SEM images of (a) TAPT-DHTA-COFDMF and (b) TAPT-DHTA-COFHX

The porosity of two COFs was then evaluated by nitrogen adsorption isothermal analysis (Figure 3, Table S1) and type IV adsorption isotherms were found. The sharp increases at low relative pressure manifested their permanent microporosity. The gradual increase at relative high pressure and the sharp increase above P/P0 = 0.9 were presumably caused by the voids in the loose stacking material

33

. However,

TAPT-DHTA-COFHX presented a larger specific surface area (SBET) of 2238 m2/g and pore volume of 1.29 cm3/g than those of TAPT-DHTA-COFDMF (SBET of 660 m2/g and pore volume of 0.56 cm3/g), which indicated that the synthetic method indeed affects the crystal structure of COF materials, leading to the diversity of porosity.

Figure 3. N2 adsorption/ desorption isotherms for (a) TAPT-DHTA-COFHX and (b) TAPT-DHTA-COFDMF

9



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As mentioned above, we successfully synthesized two imine-linked COFs bearing hydroxyl units with the 2D eclipsed structure. It was expected that these COFs could serve as a promising support for non-noble metal salts to form heterogeneous metal complexes, thus enhanced catalytic performance might be envisioned for the selective oxidation of alkenes. Therefore, two copper(II)-containing TAPT-DHTA-COF (Scheme 1), denoted as Cu-COFDMF and Cu-COFHX, were prepared by a simple post-treatment of TAPT-DHTA-COF with copper acetate (see S-5 for details). FT-IR spectra of Cu-COFDMF and Cu-COFHX showed the preservation of characteristic peaks for C=N, O-H and triazine ring. This confirmed that copper loadings were not disturbed the COF architecture after incorporation of copper salts into the TAPT-DHTA-COF matrix (Figure S6). PXRD analysis for Cu-COFHX and Cu-COFDMF suggested that the diffraction peaks remained compared to TAPT-DHTA-COF, but their intensity were decreased after Cu(OAc)2 docking, which also demonstrated that the framework integrity was maintained but the crystallinity of Cu-COF was relative lower than that of TAPT-DHTA-COF (Figure 4). TGA curves indicated that Cu-COF displayed the similar thermal behavior as TAPT-DHTA-COF. Meanwhile, Cu-COFDMF and Cu-COFHX were stable up to 300 and 450 ℃ respectively (Figure S7).

Figure 4. XRD patterns of (a) TAPT-DHTA-COFHX, (b) Cu-COFHX and (c) Cu-COFDMF

To gain further insight into the interactions between Cu and COF material, X-ray 10


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photoelectron spectroscopy (XPS) studies of TAPT-DHTA-COFHX and Cu-COFHX were conducted (Figure 5, Figure S8A and S8B). The N 1s XPS spectrum provided in Fig. 5A revealed that the C=N band shifts from 398.8 eV to 399.8 eV, which should be caused by the donor-acceptor interaction between nitrogen atom and copper ions. As shown in Fig. 5C, the main peak at 532.5 eV presented by the O 1s spectrum of TAPT-DHTA-COFHX was assigned to the C-O (phenolic hydroxyl). After the incorporation of copper ions, the molar ratio of the C-O decreased from 90.44% to 79.82% and the peak at 535.0 eV emerged (Fig. 5D), which might be attributed to the interaction of copper (II) with oxygen to form metal complexes. Furthermore, the Cu 2p XPS spectrum of Cu-COFHX was deconvoluted into three typical bands at 934.5, 945.5 and 954.2 eV (Figure 5B). Among them, the signals at 934.5 and 954.2 eV were corresponding to the binding energy of Cu 2p3/2 and Cu 2p1/2, respectively. The appearance of a Cu 2p3/2 satellite peak at 945.5 eV might be attributed to the coordination interaction between the salicylaldehyde analogous ligand and the copper center

48

, which was consistent with the N and O XPS spectra. In addition, XPS

studies of TAPT-DHTA-COFDMF and Cu-COFDMF were also conducted (Figure S8C and S8D) and the Cu 2p XPS spectrum of Cu-COFDMF was analogous to that of Cu-COFHX (Figure S9B). After the incorporation of copper ions, the characteristic peak attributed to N elemental basically maintain unchanged but the main peak attributed to O elemental moved compared with ones of TAPT-DHTA-COFDMF (Figure S9A and Figure S9C). This indicated that the Cu ions only interacted with oxygen to form metal complexes since the structure of TAPT-DHTA-COFDMF was more disorderly than that of TAPT-DHTA-COFHX.

11



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Figure 5. (A) N 1s XPS spectra of (a) TAPT-DHTA-COFHX and (b) Cu-COFHX; (B) Cu 2p XPS spectrum of Cu-COFHX; O 1s XPS spectra of (C) TAPT-DHTA-COFHX and (D) Cu-COFHX

Nitrogen adsorption isotherms were also recorded to investigate the porosity of Cu-COF (Figure S10). The BET surface areas and pore volumes of Cu-COFHX were confirmed to be 1886 m2/g and 1.11 cm3/g, lower than ones of TAPT-DHTA-COFHX, possibly due to the partial blockage of the channels during the incorporation of copper. Moreover, the BET surface areas and pore volumes of Cu-COFDMF were 366 m2/g and 0.41 cm3/g, also much lower than ones of Cu-COFHX, possibly attributed to its more unordered skeleton structure. Next, these copper-containing COFs were explored as the heterogeneous catalyst for the selective oxidation of alkenes. Firstly, styrene was used as the substrate. As shown in Table 1, the blank experiment in the absence of catalyst revealed a negligible conversion of styrene while a relative low styrene conversion (19.90 %) was obtained in the presence of TAPT-DHTA-COFHX. Encouragingly, the conversion of styrene with Cu-COFDMF as a catalyst increased to 44.33 %, indicating that Cu incorporated in the framework of COFs plays a key role in promoting the 12


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catalytic oxidation of styrene. Significantly, the styrene conversion and benzaldehyde selectivity in the case of Cu-COFHX as catalyst further increased to 76.13 % and 76.20 %. This might be attributed to its superior crystallinity, highly ordered structure, larger surface area and pore volume, which facilitated the adsorption and diffusion of reactants.

Table 1. Selective oxidation of styrene over various COFs Selectivity (%) Catalyst

Conversion (%) Benzaldehyde

Styrene oxide

Other

no

-

-

-

-

TAPT-DHTA-COFHX

19.90

81.88

-

18.12

Cu-COFDMF

44.33

71.96

15.74

13.40

Cu-COFHX

76.13

76.20

14.05

9.74

Reaction conditions: styrene (1 mmol), 70% TBHP (3 mmol), catalyst (3 mg), CH3CN (1 mL) at 40℃ for 5h.

At this point, we performed a series of experiments in order to optimize the reaction conditions. The screening of solvent was accomplished by using Cu-COFHX as a catalyst at 50 ℃ for 5h. Acetonitrile was the suitable solvent for this reaction to afford a relative high conversion of styrene (76.27 %) and selectivity of benzaldehyde (70.50 %; Table 2, entries 1-3). Decreasing the molar ratio of styrene/TBHP from 1:3 to 1:6 lead to the decline of the benzaldehyde selectivity due to the overoxidation of styrene. However, with the increase of molar ratio to 1:1, the benzaldehyde selectivity still dropped, resulting from incomplete oxidation of styrene (Table 2, entries 4 and 5). Moreover, it was observed that increasing the catalyst dosage and extending the reaction time played tiny influences on the catalytic oxidation (Table 2, entries 6 and 7). In terms of reaction temperature, 40 ℃ was the best choice to achieve high conversion of styrene (76.13 %) and selectivity of benzaldehyde (76.20 %; Table 2, entries 8 and 9). 13



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Table 2. Selective oxidation of styrene under various reaction conditions

n(Styrene):

Temperture

Entry

Conversion

Selectivityb (%)

a

Solvent n(TBHP)

(℃)

(%)

Styrene Benzaldehyde

Othere

oxide

a

1

1:3

50

CH3CN

76.27±0.20

70.50

26.22

3.27

2

1:3

50

CCl4

98.60

45.08

3.23

51.69

3

1:3

50

1,2-DCM

100

46.62

5.02

48.36

4

1:6

50

CH3CN

100

39.33

25.66

35.01

5

1:1

50

CH3CN

63.05±0.20

66.79

33.21

-

6c

1:3

50

CH3CN

82.43±0.10

63.81

21.92

14.27

7d

1:3

50

CH3CN

76.79±0.20

65.17

25.48

9.35

8

1:3

40

CH3CN

76.13±0.30

76.20

14.05

9.74

9

1:3

60

CH3CN

100

38.85

7.08

54.08

Reaction conditions: styrene (1 mmol), solvent (1 mL), catalyst dosage (3 mg),

reaction time (5 h); b

Determined by GC;

c

Catalyst dosage = 5 mg;

d

Reaction time = 8 h;

e

Other: including benzoic acid, phenyl-acetadehyde and 1-phenylethane-1,2-diol;

With the optimized experimental conditions in hand, we explored the substrate scope, including aromatic, aliphatic and cyclo-olefins. As summarized in Table 3, a satisfactory conversion of α-methyl styrene (98.77%) and yield of acetophenone (93.01%) were presented. The oxidation of (E)-1, 2-stilbene proceeded smoothly but the poor selectivity of benzaldehyde was observed. For the oxidation of aliphatic 1-hexene, the conversion and yield of the corresponding aldehyde were 44.87% and 39.88% respectively. Besides, cyclooctene received only 21.55% conversion but the main product was epoxide. The poor catalytic efficiency might be attributed to the 14


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larger steric hindrance from cyclo- and chain olefins which made it difficult for reactants to access the pores of Cu-COFHX. Finally, the recyclability of Cu-COFHX for the selective oxidation of styrene was investigated. This material could be easily recovered from the reaction mixture by centrifugation and reuses three times without significant loss of catalytic activity (Figure S11). It was clearly verified that copper was robustly immobilized onto TAPT-DHTA-COFHX, resulting in the remarkable reusability and stability of Cu-COFHX. Moreover, the leaching experiment of Cu-COFHX was also examined by a hot filtration test to further confirm the heterogeneity of this material. This material was removed from the reaction mixture by filtration after 2 h of reaction and the filtrate was kept under the same conditions (Figure S12). The above reaction should proceed further if some catalysts left. Obviously, the reaction was interrupted immediately and no further reaction was detected after the removal of Cu-COFHX, verifying the heterogeneity of this material.

Table 3. Selective oxidation of olefins by Cu-COFHX a Conversion (%)

Yield (%)b

TOF (h-1)c

1d

76.13±0.20

58.01±0.14

19.77

2d

98.77±0.10

93.01±0.09

25.65

3d

74.56±0.10

17.92±0.02

19.36

44.87±0.20

39.88±0.18

11.65

21.55±0.20

10.51±0.10

5.60

Entry

4d

Substrate

Product

O

5e a

Reaction conditions: Substrate (1 mmol), 70% TBHP (3 mmol), acetonitrile (1mL), 15



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catalyst dosage (3 mg), 40℃, 5h; b

Determined by GC;

c

TOF, h-1: (turnover frequency) moles of substrate converted per mole metal ion per

hour; d

Main by-products: the corresponding epoxides;

e

Main by-product: 2-cycloocten-1-one;

3. Conclusions In summary, two novel imine-linked two-dimensional COFs bearing hydroxyl groups were synthesized via solvothermal and reflux strategies. Both of these two COFs displayed excellent thermal stability and similar crystal structures verified by XRD patterns, but TAPT-DHTA-COFHX owned a larger surface area, higher crystallinity as well as porosity than TAPT-DHTA-COFDMF. These two COFs could function as an outstanding platform for docking copper acetate, which was coordinated with imine and hydroxyl units of COFs. Such copper loading together with superior surface area and pore volume of the imine-linked carrier could also provide Cu-COFHX with excellent catalytic performance and recyclability towards selective oxidation of styrene to benzaldehyde. Thus, this strategy not only provides an alternative way for the synthesis of novel imine-linked 2D COFs with hydroxyl units, which facilitates the coordination of metal ions with COFs, also open up a new approach for designing non-noble metal docked COFs for diverse practical applications.

Acknowledgements We are grateful to the supports from the National Natural Science Foundation of China. All the authors received funding from the National Natural Science Foundation of China (No.21576194).

Supporting Information 16


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Synthetic procedures of COFs and Cu docking COFs, FT-IR, TGA, 13C CP MAS NMR spectra, HR-TEM of TAPT-DHTA-COFDMF and TAPT-DHTA-COFHX, FT-IR, TGA, XPS, N2 adsorption-desorption isotherms of Cu-COFDMF and Cu-COFHX, Recycling tests with Cu-COFHX, BET data of TAPT-DHTA-COF and Cu-COF.

References: 1.

Hunt, J. R.; Doonan, C. J.; LeVangie, J. D.; Côté, A. P.; Yaghi, O. M. Reticular Synthesis of Covalent Organic Borosilicate Frameworks. J. Am. Chem. Soc. 2008, 130, 11872-11873.

2.

Kuhn, P.; Antonietti, M.; Thomas, A. Porous, Covalent Triazine-Based Frameworks Prepared by Ionothermal Synthesis. Angew. Chem., Int. Ed. 2008, 47, 3450-3453.

3.

Côté, P.; Benin, A. I.; Ockwig, N. W.; Matzger, A. J.; O’Keeffe, M.; Yaghi, O. M. Porous, Crystalline, Covalent Organic Frameworks. Science 2005, 310, 1166-1170.

4.

El-Kaderi, H. M.; Hunt, J. R.; Mendoza-Cortés, J. L.; Côté, A. P.; Taylor, R. E.; O’Keeffe, M.; Yaghi, O. M. Designed Synthesis of 3D Covalent Organic Frameworks. Science 2007, 316, 268-272.

5.

Bunch, D. N.; Dichtel, W. R. Internal Functionalization of Three-Dimensional Covalent Organic Frameworks. Angew. Chem. Int. Ed. 2012, 51, 1885 –1889.

6.

Wan, S.; Guo, J.; Kim, J.; Ihee, H.; Jiang, D. A Belt-Shaped, Blue Luminescent, and Semiconducting Covalent Organic Framework. Angew. Chem. Int. Ed. 2008, 47, 8826-8830.

7.

Spitler, E. L.; Koo, B. T.; Novotney, J. L.; Colson, J.W.; Uribe-Romo, F. J.; Gutierrez, G. D.; Clancy, P.; Dichtel W. R.; A 2D Covalent Organic Framework with 4.7-nm Pores and Insight into Its Interlayer Stacking. J. Am. Chem. Soc. 2011, 133, 19416-19421.

8.

Chen, L.; Furukawa, K.; Gao, J.; Nagai, A.; Nakamura, T.; Dong, Y.; Jiang, D. Photoelectric Covalent Organic Frameworks: Converting Open Lattices into 17



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 18 of 23

Ordered Donor–Acceptor Heterojunctions. J. Am. Chem. Soc. 2014, 136, 9806−9809. 9.

Medina, D. D.; Rotter, J. M.; Hu, Y.; Dogru, M.; Werner, V.; Auras, F.; Markiewicz, J. T.; Knochel, P.; Bein, T. Room Temperature Synthesis of Covalent–Organic Framework Films through Vapor-Assisted Conversion. J. Am. Chem. Soc. 2015, 137, 1016−1019.

10. Roeser, J.; Kailasam, K.; Thomas, A. Covalent Triazine Frameworks as Heterogeneous Catalysts for the Synthesis of Cyclic and Linear Carbonates from Carbon Dioxide and Epoxides. ChemSumChem 2012, 5, 1793-1799. 11.

Katekomol, P.; Roeser, J.; Bojdys, M.; Weber, J.; Thomas, A. Covalent Triazine Frameworks Prepared from 1,3,5-Tricyanobenzene. Chem. Mater. 2013, 25, 1542-1548.

12. Hao, L.; Ning, J.; Luo, B.; Wang, B.; Zhang, Y.; Tang, Z.; Yang, J. A. Thomas, L. Zhi, Structural Evolution of 2D Microporous Covalent Triazine-Based Framework toward the Study of High-Performance Supercapacitors. J. Am. Chem. Soc. 2015, 137, 219−225. 13. Uribe-Romo, F. J.; Hunt, J. R.; Furukawa, H.; Klöck, C.; O’Keeffe, M.; Yaghi, O. M. A Crystalline Imine-Linked 3-D Porous Covalent Organic Framework. J. Am. Chem. Soc. 2009, 131, 4570–4571. 14. Biswal, B. P.; Chandra, S.uman; Kandambeth, S.; Lukose, B.; Heine, T.; Banerjee, R. Mechanochemical Synthesis of Chemically Stable Isoreticular Covalent Organic Frameworks. J. Am. Chem. Soc. 2013, 135, 5328−5331. 15. Zhou, T.-Y.; Xu, S.-Q.; Wen, Q.; Pang, Z.-F.; Zhao, X. One-Step Construction of Two Different Kinds of Pores in a 2D Covalent Organic Framework. J. Am. Chem. Soc. 2014, 136, 15885-15888. 16. Ma, S.; Sun, D.; Simmons, J. M.; Collier, C. D.; Yuan, D.; Zhou, H.-C.; Metal-Organic

Framework

from

an

Anthracene

Derivative

Containing

Nanoscopic Cages Exhibiting High Methane Uptake. J. Am. Chem. Soc. 2008, 130, 1012-1016. 17. Cao, D.; Lan, J.; Wang, W.; Smit, B. Lithium-Doped 3D Covalent Organic 18


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


Frameworks: High-Capacity Hydrogen Storage Materials. Angew. Chem., Int. Ed. 2009, 48, 4730-4733. 18. Doonan, C. J.; Tranchemontagne, D. J.; Glover, T. G.; Hunt, J. R.; Yaghi, O. M. Exceptional Ammonia Uptake by a Covalent Organic Framework. Nat. Chem. 2010, 2, 235-238. 19. Ding, S.-Y.; Gao, J.; Wang, Q.; Zhang, Y.; Song, W.-G.; Su, C.-Y.; Wang, W. Construction of Covalent Organic Framework for Catalysis: Pd/COF-LZU1 in Suzuki–Miyaura Coupling Reaction. J. Am. Chem. Soc. 2011, 133, 19816-19822. 20. Fang, Q.; Gu, S.; Zheng, J.; Zhuang, Z.; Qiu, S.; Yan, Y. 3D Microporous Base-Functionalized Covalent Organic Frameworks for Size-Selective Catalysis. Angew. Chem. Int. Ed. 2014, 53, 2878-2882. 21. Xu, H.; Gao, J.; Jiang, D. Stable, Crystalline, porous, Covalent Organic Frameworks as a Platform for Chiral Organocatalysts. Nat. Chem. 2015, 7, 905-912. 22. Shen, C.; Bao, Y.; Wang, Z. Tetraphenyladamantane-based Microporous Polyimide for Adsorption of Carbon Dioxide, Hydrogen, Organic and Water Vapors. Chem. Commun. 2013, 49, 3321-3323. 23. Chen, X.; Addicoat, M.; Jin, E.; Zhai, L.; Xu, H.; Huang, N.; Guo, Z.; Liu, L.; Irle, S.; Jiang, D. Locking Covalent Organic Frameworks with Hydrogen Bonds: General and Remarkable Effects on Crystalline Structure, Physical Properties, and Photochemical Activity. J. Am. Chem. Soc. 2015, 137, 3241-3247. 24. Ding, S.-Y.; Dong, M.; Wang, Y.-W.; Chen, Y.-T.; Wang, H.-Z.; Su, C.-Y.; Wang, W. Thioether-Based Fluorescent Covalent Organic Framework for Selective Detection and Facile Removal of Mercury(II). J. Am. Chem. Soc. 2016, 138, 3031-3037. 25. Li, Z.; Zhang, Y.; Xia, H.; Mu, Y.; Liu, X. A Robust and Luminescent Covalent Organic Framework as a Highly Sensitive and Selective Sensor for the Detection of Cu2+ Ions. Chem. Commun. 2016, 52, 6613-6616. 26. Vyas, V. S.; Vishwakarma, M.; Moudrakovski, I.; Haase, F.; Savasci, G.; Ochsenfeld, C.; Spatz, J. P.; Lotsch, B. V. Exploiting Noncovalent Interactions in 19



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 20 of 23

an Imine-Based Covalent Organic Framework for Quercetin Delivery. Adv. Mater. 2016, 28, 8749-8754. 27. Fang, Q.; Wang, J.; Gu, S.; Kaspar, R. B.; Zhuang, Z.; Zheng, J.; Guo, H.; Qiu, S.; Yan, Y. 3D Porous Crystalline Polyimide Covalent Organic Frameworks for Drug Delivery. J. Am. Chem. Soc. 2015, 137, 8352-8355 28. Jin, S.; Ding, X.; Feng, X.; Supur, M.; Furukawa, K.; Takahashi, S.; Addicoat, M.; El-Khouly, M. E.; Nakamura, T.; Irle, S.; Fukuzumi, S.; Nagai, A.; Jiang, D. Charge Dynamics in A Donor–Acceptor Covalent Organic Framework with Periodically Ordered Bicontinuous Heterojunctions. Angew. Chem., Int. Ed. 2013, 52, 2017-2021. 29. Smith, B. J.; Overholts, A. C.; Hwang, N.; Dichtel, W. R. Insight into the Crystallization of Amorphous Imine-linked Polymer Networks to 2D Covalent Organic Frameworks. Chem. Commun. 2016, 52, 3690-3693. 30. Kandambeth, S.; Shinde, D. B.; Panda, M. K.; Lukose, B.; Heine, T.; Banerjee, R. Enhancement of Chemical Stability and Crystallinity in Porphyrin-Containing Covalent Organic Frameworks by Intramolecular Hydrogen Bonds. Angew. Chem. Int. Ed. 2013, 52, 13052-13056. 31. Shinde, D. B.; Kandambeth, S.; Pachfule, P.; Kumar, R. R.; Banerjee, R. Bifunctional

Covalent

Organic

Frameworks

with

Two

Dimensional

Organocatalytic Micropores. Chem. Commun. 2015, 51, 310-313. 32. Gonḉalves, R. S. B.; de Oliveira, A. B. V.; Sindra, H. C.; Archanjo, B. S.; Mendoza, M. E.; Carneiro, L. S. A.; Buarque, C. D.; Esteves, P. M. Heterogeneous

Catalysis

by

Covalent

Organic

Frameworks

(COF):

Pd(OAc)2@COF-300 in Cross-Coupling Reactions. ChemCatChem 2016, 8, 743-750. 33. Leng, W.; Peng, Y.; Zhang, J.; Lu, H.; Feng, X.; Ge, R.; Dong, B.; Wang, B.; Hu, X.; Gao, Y. Sophisticated Design of Covalent Organic Frameworks with Controllable Bimetallic Docking for a Cascade Reaction. Chem. Eur. J. 2016, 22, 9087-9091. 34. Leng, W.; Ge, R.; Dong, B.; Wang, C.; Gao, Y. Bimetallic Docked Covalent 20


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


Organic Frameworks with High Catalytic Performance Towards Tandem Reactions. RSC Adv. 2016, 6, 37403-37406. 35. Ullmann’s Encyclopedia of Industrial Chemistry, 5th ed.; VCH: Weinheim, Germany, 1985; p 469. 36. Zhan, G.; Hong, Y.; Lu, F.; Ibrahim, A.-R.; Du, M.; Sun, D.; Huang, J. Kinetics of Liquid Phase Oxidation of Benzyl Alcohol with Hydrogen Peroxide over Bio-reduced Au/TS-1 Catalysts. J. Mol. Catal. A 2013, 366, 215-221. 37. Tahira, M. N.; Nielsena, T. T.; Larsen, K. L. β-Cyclodextrin Functionalized on Glass Micro-particles: A Green Catalyst for Selective Oxidation of Toluene to Benzaldehyde. Appl. Surf. Sci. 2016, 389, 1108-1112. 38. Balaga, V.; Pedada, J.; Friedrich, H. B.; Singh, S. Tuning Surface Composition of Cs Exchanged Phosphomolybdic Acid Catalysts in C-H Bond Activation of Toluene to Benzaldehyde at Room Temperature. J. Mol. Catal. A: Chem 2016, 425, 116-123. 39. Keane, M. A. Gas Phase Reaction of Hydrogen with Carboxyl and Carbonyl Functions in Aromatic Systems over Ni/SiO2. J. Mol. Catal. A: Chem 1999, 138, 197-299. 40. Islam, S. M.; Roy, A. S.; Mondal, P.; Paul, S.; Salam, N. A Recyclable Polymer Anchored Copper(II) Catalyst for Oxidation Reaction of Olefins and Alcohols with Tert-butylhydroperoxide in Aqueous Medium. Inorg. Chem. Commun. 2012, 24, 170-176. 41. Zhao, Q.; Bai, C.; Zhang, W.; Li, Y.; Zhang, G.; Zhang, F.; Fan, X. Catalytic Epoxidation of Olefins with Graphene Oxide Supported Copper (Salen) Complex. Ind. Eng. Chem. Res. 2014, 53, 4232-4238. 42. Tang, Q.; Wang, Y.; Zhang, J.; Qiao, R.; Xie, X.; Wang, Y.; Yang, Y. Cobalt(II) Acetylacetonate Complex Immobilized on Aminosilane-modified SBA-15 as an Efficient Catalyst for Epoxidation of Trans-stilbene with Molecular Oxygen. Appl. Organomet. Chem. 2016, 30, 435-440. 43. Mungse, H. P.; Verma, S.; Kumar, N.; Sain, B.; Khatri, O. P. Grafting of Oxo-vanadium Schiff base on Graphene Nanosheets and its Catalytic Activity for 21



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 22 of 23

the Oxidation of Alcohols. J. Mater. Chem. 2012, 22, 5427-5433. 44. Esnaashari,

F.;

Moghadam,

M.;

Mirkhani,

V.;

Tangestaninejad,

S.;

Mohammadpoor-Baltork, I.; Khosropour, A. R.; Zakeri, M. Multi-wall Carbon Nanotubes Supported Molybdenyl Acetylacetonate: Efficient and Highly Reusable Catalysts for Epoxidation of Alkenes with Tert-butyl Hydroperoxide. Mater. Chem. Phys. 2012, 137, 69-75. 45. Cancino, P.; Paredes-García, V.; Aguirre P.; Spodine, E. A Reusable CuII based Metal–organic Framework as a Catalyst for the Oxidation of Olefins. Catal. Sci. Technol. 2014, 4, 2599-2607. 46. Sun, J.; Kan, Q.; Li, Z.; Yu, G.; Liu, H.; Yang, X.; Huo, Q.; Guan, J. Different Transition Metal (Fe2+, Co2+, Ni2+, Cu2+ or VO2+) Schiff Complexes Immobilized onto Three-dimensional Mesoporous Silica KIT-6 for the Epoxidation of Styrene. RSC Adv. 2014, 4, 2310-2317. 47. Ding, X.; Han, B. H.; Metallophthalocyanine-Based Conjugated Microporous Polymers as Highly Efficient Photosensitizers for Singlet Oxygen Generation. Angew. Chem. Int. Ed. 2015, 54, 6536–6539; Angew. Chem. 2015, 127, 6636-6639. 48. Zhang, Z.; Zhang, X.; Zheng, T.; Yu, H.; Liu, Q. Structural Study of Compartmental Complexes of Europium and Copper. J. Mol. Struct. 1999, 478, 23-27.

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Two-Dimensional Imine-Linked Covalent Organic Frameworks as a

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