2D covalent organic frameworks with built-in amide active sites for efficient heterogeneous catalysis

Article abstract of DOI:10.1039/c9cc07500c

Benzene-1,3,5-tricarboxamides (BTAs) are versatile building blocks for supramolecular assembly due to the strong intermolecular hydrogen bonding. Herein, a BTA based amine, N¹,N³,N⁵-tris(4-aminophenyl)benzene-1,3,5-tricarboxamide (TABTA), was successfully applied to construct two new amide functionalized covalent organic frameworks (COFs) with apparent crystallinity, which were further applied as efficient catalysts for Knoevenagel condensation.

Full text of DOI:10.1039/c9cc07500c

ChemComm
View Article Online
View Journal | View Issue
COMMUNICATION
2
D covalent organic frameworks with built-in
amide active sites for efficient heterogeneous
catalysis†
Cite this: Chem. Commun., 2019,
5, 14538
5
Received 24th September 2019,
Accepted 12th November 2019
Yang Li, Weiben Chen, Ruidong Gao, Ziqiang Zhao, Ting Zhang,
Guolong Xing and Long Chen
*
DOI: 10.1039/c9cc07500c
rsc.li/chemcomm
Benzene-1,3,5-tricarboxamides (BTAs) are versatile building blocks usually suffers from incomplete conversion and relatively poor
for supramolecular assembly due to the strong intermolecular adaptability compared with the bottom-up synthesis.
1
3
5
hydrogen bonding. Herein, a BTA based amine, N ,N ,N -tris-
4-aminophenyl)benzene-1,3,5-tricarboxamide (TABTA), was success- TABTA-COF-2, Scheme 1a) were designed and synthesized via a
Herein, amide functionalized COFs (i.e., TABTA-COF-1 and
(
1
3
5
fully applied to construct two new amide functionalized covalent bottom-up synthesis strategy. N ,N ,N -Tris(4-aminophenyl)-
organic frameworks (COFs) with apparent crystallinity, which were benzene-1,3,5-tricarboxamide (TABTA) comprising three amide
further applied as efficient catalysts for Knoevenagel condensation.
bonds was selected as the building block. Notably, the benzene-
,3,5-tricarboxamide (BTA) core of TABTA is widely used for
Amide functionalized molecules with Lewis alkalinity are often supramolecular assembly due to the strong intermolecular
1
1
–3
12b
used as building units for catalytic porous materials.
For hydrogen bonding interactions. The amide functionalized COFs
instance, many amide based ligands are utilized to construct were synthesized by the condensation of TABTA with benzene-1,4-
4
–9
metal–organic frameworks (MOFs). In addition, polyamides dicarboxaldehyde (BDA) or 1,3,5-tri(4-formylphenyl)benzene
1
3
represent one of the high performance functional polymers (TFPB) and were further characterized by FT-IR, C/CP-MAS
10
featuring prominent thermal and mechanical properties and are NMR, FE-SEM, TEM and PXRD measurements. The as-prepared
11a
widely used in proton exchange membranes. Thus, it is intriguing COFs possessed inherent porosity and built-in alkaline active sites
to introduce amide linkages into functionalized porous organic rendering them with excellent catalytic activities for Knoevenagel
polymers (POPs) by strong covalent bonds, which usually exhibit condensation. Furthermore, the TABTA-COFs can be easily recycled
excellent physicochemical stabilities. For example, Woo and co- with good retention of high stability and catalytic activity.
workers reported a series of nitrogen-rich microporous polymers
The synthetic conditions for TABTA-COFs were systematically
11b
with both imine and amide linkages.
Yavuz and co-workers screened and optimized including solvent combinations, tempera-
developed ester- and amide-linker-based POPs and these were ture, reaction time, concentration and pressure etc. The crystalline
12a
further used as efficient solid sorbent materials.
and porous materials were obtained in a mixed solvent of mesitylene
Covalent organic frameworks (COFs), with designable topologies and n-butanol or tetrahydrofuran with acetic acid as the catalyst
and permanent porosity, are a burgeoning kind of cystalline (Tables S1 and S2, ESI†). The crystallinities of TABTA-COF-1 and
POPs, which have been extensively explored in electrochemical TABTA-COF-2 were confirmed by powder X-ray diffraction (PXRD)
1
3
14,15
16
energy storage, catalysis,
chemosensors, gas separation analysis (Fig. S4, ESI†). And the optimized parameters of simulated
1
7
and storage, etc. The amide of COFs is generally present in structures for the COFs were acquired by data processing using
1
8
polyimide COFs and amide functionalized COFs. As for amide Materials Studio package. For example, the PXRD pattern of TABTA-
functionalized COFs, amide is often incorporated into the COF-1 displayed a series of diffraction peaks at 2.351, 4.051, 6.951 and
framework by post-modification strategies. A post-synthetic 24.401 which could be assigned to the (100), (200), (300) and (001)
oxidation strategy of transforming the imine COFs to amide facets, respectively. The simulated eclipsed AA stacking of TABTA-
linked COFs was recently developed by Yaghi and others using COF-1 in the hexagonal P6/m was in good agreement with the
1
9,20
sodium chlorite as the oxidant.
Nevertheless, this approach experimental data. And the PXRD profile of TABTA-COF-2 exhibited
different peaks at 3.501, 6.101, 7.051, 9.351 and 24.751, separately
corresponding to the (100), (110), (200), (210) and (001) facets
Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic
Science, School of Science, Tianjin University, Tianjin 300072, P. R. China.
E-mail: long.chen@tju.edu.cn
(Fig. 1a and d). The experimental data of TABTA-COF-2 also fit well
with the AA stacking mode in the hexagonal P6% space group. The
†
Electronic supplementary information (ESI) available: Experimental section, synthesis
and characterization, and supplementary data. See DOI: 10.1039/c9cc07500c
unit cell parameters were further optimized by Pawley refinement
1
4538 | Chem. Commun., 2019, 55, 14538--14541
This journal is ©The Royal Society of Chemistry 2019

View Article Online
Communication
ChemComm
Scheme 1 (a) Synthesis of TABTA-COF-1 and TABTA-COF-2; (b) top and (c) side views of TABTA-COF-1; (d) top and (e) side views of TABTA-COF-2.
p p
(R = 3.04% and Rwp = 3.61% for TABTA-COF-1; R = 3.52% and
Rwp = 4.92% for TABTA-COF-2), (Tables S10 and S11, ESI†).
To verify the chemical structures of these TABTA-COFs, their
Fourier transform infrared (FT-IR) spectra were compared with
the corresponding building blocks (Fig. S5, ESI†). The signals at
À1
3
349 and 3263 cm ascribed to N–H of monomer TABTA nearly
À1
disappeared; meanwhile, a new peak of CQN at 1593 cm
appeared, indicating highly efficient aldimine condensation
between TABTA and the aldehydes. The N–H stretch vibrations
of amide appeared at 3304 cm for TABTA-COF-1 and 3302 cm
for TABTA-COF-2, respectively. The amide II band was observed at
À1
À1
À1
À1
1
513 cm and 1509 cm for each TABTA-COF. The peaks of CQO
for TABTA-COF-1 and for TABTA-COF-2 were clearly centered at
À1
À1
1
667 cm and 1665 cm , respectively. These results concomitantly
suggest that the amide groups were retained in the framework. The
FT-IR spectra of the molecular model compound (TABTA-BA) synthe-
sized by full condensation of benzaldehyde and TABTA were
measured for comparison and further verification (Fig. S8b, ESI†).
À1
À1
The vibrations at 3269 cm (N–H stretch), 1653 cm (CQO stretch)
À1
and 1507 cm (amide II stretch) are unambiguously assigned to the
21
amide group in the BTA core, which further illustrates the reten-
tion of amide groups in TABTA-COFs. More detailed chemical
structure information was confirmed by solid-state nuclear magnetic
resonance (NMR) spectroscopy (Fig. S7, ESI†). The chemical shifts at
165 ppm for TABTA-COF-1 and 164 ppm for TABTA-COF-2 further
confirmed the existence of amide groups (Fig. S8a, ESI†). Meanwhile,
the signals of imine CQN bond linkages for the TABTA-COF-1 and
TABTA-COF-2 were located at 158 and 159 ppm, respectively.
Elemental analysis of TABTA-COFs revealed that the C, H, and N
contents were well fitted with the theoretical values calculated based
on an infinite network structure (Table S3, ESI†). The morphology
Fig. 1 (a and d) The experimental PXRD patterns (blue: TABTA-COF-1;
red: TABTA-COF-2), their difference (yellow) with corresponding Pawley
refinement (black), simulated staggered AB (green) and eclipsed AA
(
magenta) modes. The extended structures of AA stacking modes for (b)
TABTA-COF-1 and (e) TABTA-COF-2; the extended structures of AB
stacking modes for (c) TABTA-COF-1 and (f) TABTA-COF-2.
This journal is ©The Royal Society of Chemistry 2019
Chem. Commun., 2019, 55, 14538--14541 | 14539

View Article Online
ChemComm
Communication
TABTA-COF-2 (Fig. 3 inset). These results were in good agree-
ment with the values of d-spacing that were recorded from the
PXRD patterns for TABTA-COF-1 at 2y = 2.351 (3.76 nm) and
TABTA-COF-2 at 2y = 3.501 (2.53 nm).
Physicochemical stabilities represent one of the paramount
parameters for applications of COFs, especially in hetergeneous
catalysis aspects. The thermostability of TABTA-COFs was checked
by thermogravimetric analysis under nitrogen atmosphere, and
the results indicated that TABTA-COF-1 and TABTA-COF-2 were
thermally stable up to ca. 410 and 487 1C, respectively (Fig. S10,
ESI†). The ordered framework structure of TABTA-COF-2 could be
maintained at least at 400 1C (Fig. S11, ESI†). Although the crystal-
linity of TABTA-COF-1 decreases with increasing temperature, the IR
spectrum of TABTA-COF-1 indicates that the chemical structure
remains stable at elevated temperatures even up to 400 1C (Fig. S12,
ESI†). In addition, both TABTA-COFs were insoluble and stable in
conventional solvents (such as THF, toluene, and water) and strong
Fig. 2 Representative SEM images of (a) TABTA-COF-1 and (c) TABTA-
COF-2; TEM images of (b) TABTA-COF-1 and (d) TABTA-COF-2.
of both TABTA-COFs displayed a laminar microstructure, which acidic/basic conditions (Fig. S13 and S14, ESI†), etc. Moreover, the
was recorded by field-emission scanning electron microscopy –NH moiety of amide is an appealing active site with Lewis
2
2
(
FE-SEM, Fig. 2 and Fig. S9, ESI†). Interestingly, the transmis- alkalinity. Therefore, the amide functionalized TABTA-COFs are
22,24
sion electron microscopy (TEM) images further indicated that expected to be heterogeneous alkaline catalysts.
both TABTA-COFs displayed fringes of periodicity corres-
To verify the catalytic activity of the TABTA-COFs, Knoevenagel
ponding to the stacked 2D layers which could be assigned to condensation reaction was selected. Malonitrile was chosen as
the (001) facet (Fig. 2).
the typical nucleophilic reagent and various benzaldehydes were
25
The porosity of the TABTA-COFs was unveiled by Nitrogen tested as substrates to evaluate the catalytic performance and
adsorption/desorption measurements at 77 K. The Brunauer– generality of TABTA-COFs toward Knoevenagel condensation.
Emmett–Teller (BET) specific surface areas of TABTA-COF-1 and The conversion efficiency was monitored by a gas chromatography-
2
À1
2
À1
TABTA-COF-2 were determined to be 246 m g and 368 m g
,
mass spectrometer (GC-MS) analyzer at different intervals of
respectively (Fig. 3). CO sorption isotherms were further recorded reaction time (Fig. S17, ESI†). The products were further analyzed
2
1
at 195 K to evaluate the porosity of the TABTA-COFs. Similar BET and validated by H NMR measurements (Fig. S20–S24, ESI†). As
2
À1
surface areas were obtained as 264 m g for TABTA-COF-1 and shown in Fig. 4, almost all the benzaldehydes were converted to
2
À1
22
4
32 m g for TABTA-COF-2 (Fig. S6, ESI†). The amide linked the corresponding products within a short time. The catalytic
conjugated porous polymers were reported to exhibit low surface conversion efficiencies of different substrates are summarized in
area because of the unfavorable interactions between the polymer Tables S4 and S5 (ESI†). It can be concluded that the substrates
11b
skeleton and guest gas molecules. This might also be the reason with electron-withdrawing substituents showed higher yields
that causes the decrement in the specific surface areas for TABTA- than the counterparts bearing electron donating groups. And in
COFs. And a similar phenomenon has also been reported by
1
9,23
others.
In addition, the pore size distribution simulated by
the nonlocal density functional (NLDFT) method based on
nitrogen adsorption suggested uniform mesopore distribution
with a diameter of 3.68 nm for TABTA-COF-1 and 2.32 nm for
Fig. 3 (a) Nitrogen sorption isotherms of TABTA-COF-1 at 77 K (inset:
photograph of the pore size distribution of TABTA-COF-1); (b) nitrogen
sorption isotherms of TABTA-COF-2 at 77 K (inset: photograph of the pore
size distribution of TABTA-COF-2).
Fig. 4 Catalytic performance of TABTA-COFs toward Knoevenagel con-
densation of malonitrile with various aldehydes after one hour.
1
4540 | Chem. Commun., 2019, 55, 14538--14541
This journal is ©The Royal Society of Chemistry 2019

View Article Online
Communication
ChemComm
all cases, the TABTA-COFs exhibited great robustness with well
retained crystallinity and chemical composition after treatments
under catalytic Knoevenagel condensation conditions (magenta
lines in Fig. S13 and S14, ESI†). To investigate the possible effect
of the imine bonds of TABTA-COFs on the catalytic activity, a
control experiment using TFPB-TAPB-COF as the catalyst with
a similar structure but without amides linkages was carried
out (Fig. S15 and Table S7, ESI†). The low catalytic efficiency
indicated that the amides play vital roles while the imines exert
less effect on the catalysis.
The recyclability of the catalysts is another significant metric
for practical applications. The reusability of TABTA-COF-2 with
better stability for catalyzing Knoevenagel condensation was
investigated in detail. Taking the Knoevenagel condensation
between benzaldehyde and malonitrile as an example, TABTA-
2 R.-R. Cheng, S.-X. Shao, H.-H. Wu, Y.-F. Niu, J. Han and X.-L. Zhao,
Inorg. Chem. Commun., 2014, 46, 226–228.
3
R. S. Forgan, R. J. Marshall, M. Struckmann, A. B. Bleine, D. Long,
M. C. Bernini and D. Fairen-Jimenez, CrystEngComm, 2015, 17,
299–306.
4
5
B. Zheng, H. Wang, Z. Wang, N. Ozaki, C. Hang, X. Luo, L. Huang,
W. Zeng, M. Yang and J. Duan, Chem. Commun., 2016, 52, 12988–12991.
O. Benson, I. Da Silva, S. P. Argent, R. Cabot, M. Savage, H. G. W.
Godfrey, Y. Yan, S. F. Parker, P. Manuel, M. J. Lennox, T. Mitra,
T. L. Easun, W. Lewis, A. J. Blake, E. Besley, S. Yang and M. Schr ¨o der,
J. Am. Chem. Soc., 2016, 138, 14828–14831.
2
6
6
7
8
9
X.-J. Hong, Q. Wei, Y.-P. Cai, S.-R. Zheng, Y. Yu, Y.-Z. Fan, X.-Y. Xu
and L.-P. Si, ACS Appl. Mater. Interfaces, 2017, 9, 4701–4708.
Z. Lu, J. Zhang, H. He, L. Du and C. Hang, Inorg. Chem. Front., 2017,
4, 736–740.
P.-Z. Li, X.-J. Wang, J. Liu, H. S. Phang, Y. Li and Y. Zhao, Chem.
Mater., 2017, 29, 9256–9261.
B. Zheng, L. Huang, X. Cao, S. Shen, H. Cao, C. Hang, W. Zeng and
Z. Wang, CrystEngComm, 2018, 20, 1874–1881.
10 K. Marchildon, Macromol. React. Eng., 2011, 5, 22–54.
COF-2 can effectively catalyze the reaction after at least 5 recycling 11 (a) L. Ma, J. Li, J. Xiong, G. Xu, Z. Liu and W. Cai, Polymers, 2017,
9
, 703; (b) N. Manoranjan, D. H. Won, J. Kim and S. I. Woo, J. CO
2
processes under identical experimental conditions (Table S9, ESI†).
Meanwhile, both the crystallinity and chemical structure of the
sample were also well retained after 5 cycles (Fig. S18 and S19, ESI†).
On the other hand, the condensation between malononitrile
and benzaldehyde showed very low conversion (24%) even after
Util., 2016, 16, 486–491.
2 (a) R. Ullah, M. Atilhan, B. Anaya, S. Al-Muhtaseb, S. Aparicio,
H. Patel, D. Thirion and C. T. Yavuz, ACS Appl. Mater. Interfaces,
1
2016, 8, 20772–20785; (b) T. F. A. De Greef, M. M. J. Smulders,
M. Wolffs, A. P. H. J. Schenning, R. P. Sijbesma and E. W. Meijer,
Chem. Rev., 2009, 109, 5687–5754.
1
h in the absence of COF catalysts (Table S6, ESI†), suggesting 13 D. B. Shinde, H. B. Aiyappa, M. Bhadra, B. P. Biswal, P. Wadge,
S. Kandambeth, B. Garai, T. Kundu, S. Kurungot and R. Banerjee,
J. Mater. Chem. A, 2016, 4, 2682–2690.
a high catalytic activity of the TABTA-COFs. The reusability of
TABTA-COF-1 is also summarized in Table S8 and Fig. S16
1
4 (a) X. Li, Z. Wang, J. Sun, J. Gao, Y. Zhao, P. Cheng, B. Aguila, S. Ma,
Y. Chen and Z. Zhang, Chem. Commun., 2019, 55, 5423–5426; (b) Q. Sun,
B. Aguila and S. Ma, Mater. Chem. Front., 2017, 1, 1310–1316; (c) Y. Song,
Q. Sun, B. Aguila and S. Ma, Adv. Sci., 2019, 6, 1801410.
(ESI†). The mesopores facilitating the mass transfer of sub-
strates along with the densely arranged amide functional groups
are beneficial to the catalytic performance.
1
1
1
1
5 P. Pachfule, S. Kandambeth, D. D ´ı az D ´ı az and R. Banerjee, Chem.
Commun., 2014, 50, 3169–3172.
6 F.-Z. Cui, J.-J. Xie, S.-Y. Jiang, S.-X. Gan, D.-L. Ma, R.-R. Liang,
G.-F. Jiang and X. Zhao, Chem. Commun., 2019, 55, 4550–4553.
7 N. Huang, X. Chen, R. Krishna and D. Jiang, Angew. Chem., Int. Ed.,
2015, 54, 2986–2990.
In summary, two new BTA-derived 2D COFs bearing amide
built-in functional groups were synthesized via a bottom-up strategy.
TABTA-COFs possessed crystallinity and exhibited high catalytic
activity toward Knoevenagel condensation with a broad substrate
scope and excellent recyclability. Further oxidation of the imine
bond linkages in TABTA-COF-1 to amide groups resulting in a fully
8 (a) L. Jiang, Y. Tian, T. Sun, Y. Zhu, H. Ren, X. Zou, Y. Ma, K. R.
Meihaus, J. R. Long and G. Zhu, J. Am. Chem. Soc., 2018, 140,
1
5724–15730; (b) Q. Fang, Z. Zhuang, S. Gu, R. B. Kaspar,
J. Zheng, J. Wang, S. Qiu and Y. Yan, Nat. Commun., 2014, 5, 4503;
c) K. Liu, H. Qi, R. Dong, R. Shivhare, M. Addicoat, T. Zhang,
2D polyamide network with complete amide linkages is currently
(
underway in our laboratory. It could be envisioned that the intro-
duction of amide groups into the scaffolds could expand the scope
of functional COFs and the application of COF-based materials.
This work was financially supported by the National Key
Research and Development Program of China (2017YFA0207500),
the National Natural Science Foundation of China (51973153) and
the Natural Science Foundation of Tianjin City (17JCJQJC44600).
H. Sahabudeen, T. Heine, S. Mannsfeld, U. Kaiser, Z. Zheng and
X. Feng, Nat. Chem., 2019, 11, 994–1000; (d) M. S. Lohse and T. Bein,
Adv. Funct. Mater., 2018, 28, 1705553.
9 P. J. Waller, S. J. Lyle, T. M. Osborn Popp, C. S. Diercks, J. A. Reimer
and O. M. Yaghi, J. Am. Chem. Soc., 2016, 138, 15519–15522.
0 X. Han, J. Huang, C. Yuan, Y. Liu and Y. Cui, J. Am. Chem. Soc., 2018,
140, 892–895.
1
2
2
2
2
1 S. Cantekin, T. F. de Greef and A. R. Palmans, Chem. Soc. Rev., 2012,
41, 6125–6137.
2 V. M. Suresh, S. Bonakala, H. S. Atreya, S. Balasubramanian and
T. K. Maji, ACS Appl. Mater. Interfaces, 2014, 6, 4630–4637.
3 (a) A. Rehman and S. Park, Bull. Korean Chem. Soc., 2017, 38,
Conflicts of interest
1
285–1292; (b) R. Khatioda, D. Talukdar, B. Saikia, K. K. Bania
There are no conflicts to declare.
and B. Sarma, Catal. Sci. Technol., 2017, 7, 3143–3150.
2
4 J. Park, J. Li, Y. Chen, J. Yu, A. A. Yakovenko, Z. U. Wang, L. Sun,
P. B. Balbuena and H. Zhou, Chem. Commun., 2012, 48, 9995–9997.
5 S. Hasegawa, S. Horike, R. Matsuda, S. Furukawa, K. Mochizuki,
Y. Kinoshita and S. Kitagawa, J. Am. Chem. Soc., 2007, 129, 2607–2614.
Notes and references
2
1
S. Yuan, L. Feng, K. Wang, J. Pang, M. Bosch, C. Lollar, Y. Sun,
J. Qin, X. Yang, P. Zhang, Q. Wang, L. Zou, Y. Zhang, L. Zhang, 26 L. Zhai, N. Huang, H. Xu, Q. Chen and D. Jiang, Chem. Commun.,
Y. Fang, J. Li and H. Zhou, Adv. Mater., 2018, 30, 1704303. 2017, 53, 4242–4245.
This journal is ©The Royal Society of Chemistry 2019
Chem. Commun., 2019, 55, 14538--14541 | 14541