A One Building Block Approach for Defect-Enhanced Conjugated Microporous Polymers: Defect Utilization for Recyclable and Catalyt

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A one building block approach for defect- enhanced conjugated microporous polymers: Cite this: J. Mater. Chem. A,2018,6, 15553 defect utilization for recyclable and catalytic † Received 30th June 2018 biomass conversion Accepted 24th July 2018 Kyoungil Cho,a Sang Moon Lee,b Hae Jin Kim,b Yoon-Joo Koc and Seung Uk Son *a DOI: 10.1039/c8ta06273k

rsc.li/materials-a

A one building block approach was studied for preparation of defect- alkynes and can be free from the network-induced suppression enhanced and terminal alkyne-rich hollow conjugated microporous of chemical reactivity. It is noteworthy that defect utilization has polymers (H-TA-CMPs). The enriched terminal alkynes were utilized in been realized in microporous inorganic materials or metal– post-synthetic modiﬁcation of H-TA-CMPs with aliphatic sulfonic organic frameworks.7 Thus, we have devised a synthetic strategy

acids (H-TA-CMP-ASO3H). The obtained H-TA-CMP-ASO3Hshowed to enhance defects in CMPs. excellent reactivity and recyclability in biomass conversion to Infrared absorption (IR) spectroscopy is useful for charac- 5-hydroxymethylfurfural, compared with CMPs with aromatic sulfonic terizing terminal alkynes in CMP materials.8 According to IR

acids (H-control-SO3H). analysis, conventional CMPs showed trace vibration peaks of terminal alkyne groups.8 To induce more defects in CMPs, we have devised a one building block approach using dieth- The representative properties of conjugated microporous poly- ynyldihalo arene (refer to the possible chemical structure of 1 mers (CMPs) are their high surface areas and microporosity. CMPs in Fig. 1). Enriched terminal alkyne groups through Based on these properties, CMPs have been applied as adsor- enhanced defects in CMPs can be utilized to introduce bents for small molecules such as gases and water pollutants.2 To introduce additional functionalities, post-synthetic modi- cation of CMPs has been studied.3 Generally, CMPs have been prepared by the Sonogashira Published on 25 July 2018. Downloaded by Sungkyunkwan University 8/23/2018 8:41:01 AM. coupling of multiethynyl arenes and multihalo arenes.1 Thus, conventional CMPs are rich in alkyne groups. Alkynes are very versatile moieties for chemical reactions including the thiol-yne click reaction.4 Post-synthetic modication of CMPs based on the thiol-yne click reaction has been reported.3a,d,f However, in our studies, functional moieties introduced by this method were not suﬃcient in quantity.5 We speculate that this might be due to two factors. First, diaryl internal alkynes in CMPs may have relatively low reactivity toward the click-based thiol addition. Second, the reactivity of internal alkynes can be sup- pressed in the network due to the so-called network eﬀect.6 We considered that the possible terminal alkyne groups in the defects of the network may have higher reactivity than internal

aDepartment of Chemistry, Sungkyunkwan University, Suwon 16419, Korea. E-mail: [email protected] bKorea Basic Science Institute, Daejeon 34133, Korea cLaboratory of Nuclear Magnetic Resonance, The National Center for Inter-University Research Facilities (NCIRF), Seoul National University, Seoul 08826, Korea † Electronic supplementary information (ESI) available: Experimental procedures, Fig. 1 Synthetic schemes for hollow terminal alkyne-rich CMPs and additional characterization data of CMP materials, recycled CMP materials, (H-TA-CMPs) based on a one building block approach (Synthesis A)

and H-control-SO3H. See DOI: 10.1039/c8ta06273k and CMPs based on a two building block approach (Synthesis B).

This journal is © The Royal Society of Chemistry 2018 J. Mater. Chem. A,2018,6, 15553–15557 | 15553 View Article Online Journal of Materials Chemistry A Communication

additional functional groups. For example, aliphatic sulfonic acid can be introduced by the thiol-yne click reaction of CMPs with aliphatic sulfonate thiol. Solid sulfonic acids have been used as Brønsted acid catalysts for carbohydrate-based biomass conversion to 5-hydroxymethylfurfural (HMF) through water abstraction.9 Our research group has studied sulfonated microporous organic polymers10 and their application as catalysts for carbohydrate conversion to HMF. However, we found that although the sulfonated CMPs showed good reactivity in the rst run, they gradually lost their catalytic reactivity in the successive cycles. As well-documented,11 aryl sulfonic acids are not thermally stable in the presence of water to bring about facile cleavage of C–S bonds, leading to poor recyclability of aryl sulfonic acid catalysts. In contrast, it has been known that aliphatic sulfonic acids are thermally stable and show good recyclability in the dehydration reaction of sugar-based biomass to furan derivatives.12 Thus, CMPs with aliphatic sulfonic acids are promising solid catalysts for biomass conversion to HMF. However, as far as we are aware, CMPs with aliphatic sulfonic acids have not been reported yet. In this work, we report a one building block approach for Fig. 2 (a) SEM images of H-TA-CMP and CMP materials prepared for hollow terminal alkyne rich CMPs (H-TA-CMPs), chemical 2, 4, 6, and 12 h by the one building block approach (Synthesis A) and management of enhanced defects to prepare hollow CMPs with two building block approach (Synthesis B), respectively. IR spectra of (b) H-TA-CMP and (c) CMP materials prepared by Syntheses A and B aliphatic sulfonic acids (H-TA-CMP-ASO3H), and their catalytic performance in biomass conversion to HMF. for 4, 6, and 12 h, respectively. Fig. 1 shows the synthetic scheme for H-TA-CMPs. First, we prepared 1,4-dibromo-2,5-diethynylbenzene13 for use as a building block for the one building block approach. To use as (Fig. 2b). Even aer reaction for 12 h, the H-TA-CMPs showed templates, we prepared silica spheres with an average diameter a signicant vibration peak of terminal alkynes, indicating the of 254 nm.14 CMP layers with a thickness of 20–25 nm (vide enhanced defects and the terminal alkyne-rich nature of H-TA- infra) were formed on the silica spheres by the Sonogashira CMPs. In contrast, in the case of Synthesis B, vibration peaks of coupling of 1,4-dibromo-2,5-diethynylbenzene. Etching of silica terminal alkynes in CMPs gradually decreased with the templates resulted in H-TA-CMPs (Synthesis A shown in Fig. 1). increasing reaction time.16 (Fig. 2c) While surface areas of H-TA- For comparison, we tried to prepare comparatively hollow CMP CMPs obtained by Synthesis A for 4, 6, and 12 h were measured À materials using 1,3,5-triethynylbenzene and 1,4-dibromo- to be 677, 661, and 590 m2 g 1, respectively, those of CMPs Published on 25 July 2018. Downloaded by Sungkyunkwan University 8/23/2018 8:41:01 AM. benzene (Synthesis B shown in Fig. 1). obtained by Synthesis B for 4, 6, and 12 h were measured to be À Formation processes of H-TA-CMPs were investigated by 698, 660, and 589 m2 g 1, respectively (Fig. S1 in the ESI†). scanning electron microscopy (SEM), IR spectroscopy, and the Considering the terminal alkyne-rich nature of H-TA-CMP

analysis of N2 sorption isotherm curves. As shown in Fig. 2a, we materials, we introduced aliphatic sulfonic acid by the thiol-

found that in the case of the one building block approach yne click reaction to form H-TA-CMP-ASO3H (Fig. 3a). As (Synthesis A), CMP materials were quickly formed on silica described in the introduction part, solid sulfonic acid is an spheres. Aer 4 h, complete hollow CMPs were obtained aer important catalyst for sugar-based biomass conversion to silica etching. In contrast, in the two building block approach HMF.9 It has been known that while aryl sulfonic acids are (Synthesis B) with 1,3,5-triethynylbenzene and 1,4-dibromo- thermally unstable,11 aliphatic sulfonic acids are quite stable.12 benzene, the formation of CMPs was relatively slow and good According to transmission electron microscopy (TEM), aer quality hollow CMPs could not be obtained eventually. Instead, incorporation of aliphatic sulfonic acids into H-TA-CMP, the conventional nonhollow CMPs were obtained aer 12 h original hollow structure was completely retained (Fig. 3b (Fig. 2a). We speculate that the Sonogashira coupling of and c). Elemental mapping based on energy dispersive X-ray 1,4-dibromo-2,5-diethynylbenzene might be more facile than spectroscopy (EDS) showed homogeneous distributions of S

that between 1,3,5-triethynylbenzene and 1,4-dibromobenzene. and O in H-TA-CMP-ASO3H, supporting the successful incor- In the one building block approach, isolated yields of H-TA- poration of aliphatic sulfonic acid into H-TA-CMPs (Fig. 3d).  CMPs obtained a er 2, 4, 6, and 12 h were 127, 179, 173, and According to analysis of N2 sorption isotherm curves based 182%, respectively.15 In contrast, in the two building block on the Brunauer–Emmett–Teller theory, surface areas and À À approach, isolated yields of CMPs obtained aer 2, 4, 6, and micropore volumes decreased from 677 m2 g 1 and 0.20 cm3 g 1 2 À1 3 À1 12 h were 31, 70, 86, and 83%, respectively. (H-TA-CMP) to 387 m g and 0.11 cm g (H-TA-CMP-ASO3H), IR spectra of H-TA-CMPs obtained by Synthesis A showed respectively, through incorporation of aliphatic sulfonic groups, À strong vibration peaks of terminal alkynes at 3295 cm 1 matching well with the observed trends in post-synthetic

15554 | J. Mater. Chem. A,2018,6, 15553–15557 This journal is © The Royal Society of Chemistry 2018 View Article Online Communication Journal of Materials Chemistry A

terminal alkynes at 80 ppm signicantly disappeared (indicated by a green-dotted arrow in Fig. 3g), indicating higher reactivity of terminal alkynes than internal alkynes. New aliphatic 13C – peaks of H-TA-CMP-ASO3H were observed at 50 and 25 31 ppm, indicating successful incorporation of aliphatic sulfonic groups. According to elemental analysis, the content of sulfonic À1 acids in H-TA-CMP-ASO3H was measured to be 0.713 mmol g (S: 4.56 wt%).17 According to powder X-ray diﬀraction studies,

both H-TA-CMP and H-TA-CMP-ASO3H were amorphous, matching well with the conventional properties of CMP materials in the literature1 (Fig. S2 in the ESI†).

Considering aliphatic sulfonic groups in H-TA-CMP-ASO3H, we studied its catalytic activity in the model biomass conversion of fructose to HMF (Fig. 4a). Fig. 4 summarizes the results. In the literature, the conversion of fructose to HMF was mostly studied at a high temperature of 150 C.9 To lower the reaction temperature, we studied the temperature dependent catalytic

activity of H-TA-CMP-ASO3H (2 mol% SO3H to fructose). As

shown in Fig. 4b, while the H-TA-CMP-ASO3H showed good conversion of fructose to HMF (91–92% yields aer 5 h) at 120

Fig. 3 (a) Synthetic scheme for H-TA-CMP-ASO3H by post-synthetic modiﬁcation based on the thiol-yne click reaction. TEM images of (b)

Published on 25 July 2018. Downloaded by Sungkyunkwan University 8/23/2018 8:41:01 AM. H-TA-CMPs and (c) H-TA-CMP-ASO3H. (d) SEM and TEM-EDS elemental mapping images of H-TA-CMP-ASO3H. (e) N2 adsorption– desorption isotherm curves obtained at 77 K, inset: pore size distri- bution diagrams (based on the DFT method), (f) IR absorption spectra, and (g) solid state 13C NMR spectra of H-TA-CMPs and H-TA-CMP-

ASO3H.

modication of CMP materials in the literature.3 (Fig. 3e) While H-TA-CMPs showed major vibration peaks at 3295, 1460, and À 886 cm 1, corresponding to terminal alkyne and aromatic C]C – and C H vibrations, respectively, H-TA-CMP-ASO3H showed new À strong vibration peaks at 3442, 1633, and 1203 cm 1, corre- – ] sponding to vibrations of O H(SO3H), C C (alkene neigh- 8 boring sulde), and S]O(SO3H), respectively (Fig. 3f). Solid state 13C nuclear magnetic resonance spectroscopy Fig. 4 (a) Scheme of catalytic fructose conversion to HMF by H-TA- 13 CMP-ASO3H. (b) Temperature dependent catalytic conversion of (NMR) of H-TA-CMPs showed aromatic C peaks at 136 and fructose to HMF by H-TA-CMP-ASO H (2 mol% SO H to fructose). 13 3 3 125 ppm (Fig. 3g). In addition, two kinds of alkyne C peaks Biphenyl was used as an internal standard. (c) Recyclability tests of H- were clearly observed at 93 and 80 ppm, corresponding to TA-CMP-ASO3H and H-control-SO3H (temperature: 100 C, time: 5 h internal and terminal alkyne moieties, respectively, indicating for H-TA-CMP-ASO3H and 2 h for H-control-SO3H, 2 mol% SO3Hto the terminal alkyne rich-nature of H-TA-CMPs. fructose). H-Control-SO3H with aromatic SO3H was prepared by 13 direct sulfonation of H-TA-CMPs with ClSO3H (refer to the Experi- Interestingly, in the C NMR spectrum of H-TA-CMP-ASO3H, mental section in the ESI†). (d) TGA curves of H-TA-CMP-ASO H and 13 3 while the C peak of internal alkynes at 93 ppm was mostly H-control-SO3H. (e) SEM images of H-TA-CMP-ASO3H retrieved retained (indicated by a black-dotted arrow in Fig. 3g), that of before and after ﬁve successive reactions.

This journal is © The Royal Society of Chemistry 2018 J. Mater. Chem. A,2018,6, 15553–15557 | 15555 View Article Online Journal of Materials Chemistry A Communication

and 140 C, it maintained good catalytic activity (85% yield of C. D. Wood, H. Niu, J. T. A. Jones, Y. Z. Khimyak and HMF aer 5 h) at 100 C. It is noteworthy that microporous A. I. Cooper, J. Am. Chem. Soc., 2008, 130, 7710–7720. organic polymers with sulfonic groups have been recently 2 Reviews: (a) S. Das, P. Heasman, T. Ben and S. Qiu, Chem. developed as solid catalysts for fructose conversion to HMF, Rev., 2017, 117, 1515–1563; (b) N. Chaoui, M. Trunk, showing catalytic turnover numbers (TONs) of 5.83 and 6.11 at R. Dawson, J. Schmidt and A. Thomas, Chem. Soc. Rev., 18 120 and 140 C. In comparison, the H-TA-CMP-ASO3H showed 2017, 46, 3302–3321; (c) L. Tan and B. Tan, Chem. Soc. Rev., superior TONs of 42.5 and 45.5 at 100 and 120 C, respectively. 2017, 46, 3322–3356; (d) Y. Xu, S. Jin, H. Xu, A. Nagai and

We think that the excellent performance of H-TA-CMP-ASO3His D. Jiang, Chem. Soc. Rev., 2013, 42, 8012–8031; (e) F. Vilela, attributable to its microporosity and thin hollow structure.19 K. Zhang and M. Antonietti, Energy Environ. Sci., 2012, 5, – Importantly, the H-TA-CMP-ASO3H showed excellent recycla- 7819 7832; (f) R. Dawson, A. I. Cooper and D. J. Adams, bility in the ve successive catalytic reactions with 85, 84, 85, 83, Prog. Polym. Sci., 2012, 37, 530–563; (g) N. B. McKeown and and 82% yields of HMF for the rst, second, third, fourth, and P. M. Budd, Chem. Soc. Rev., 2006, 35, 675–683. h run, respectively (Fig. 4c). According to thermogravimetric 3(a) X. Han, M. Xu, S. Yang, J. Qian and D. Hua, J. Mater.

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ESI†). SEM and IR analysis showed that the H-TA-CMP-ASO3H Commun., 2017, 53, 8778–8781; (c) K. Thiel, R. Zehbe, recovered aer the h run maintained its original hollow J. Roeser, P. Strauch, S. Enthaler and A. Thomas, Polym. structure and aliphatic sulfonic acids (Fig. 4e and S4 in the Chem., 2013, 4, 1848–1856; (d) H. Urakami, K. Zhang and ESI†). F. Vilela, Chem. Commun., 2013, 49, 2353–2355; (e) In comparison, we prepared hollow aromatic sulfonic acids T. ˙Islamo˘glu, M. G. Rabbani and H. M. El-kaderi, J. Mater.

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shown in Fig. 4c and d, the H-control-SO3H with aromatic SO3H D. Yuan, R. Krishna, Z. Wei and H.-C. Zhou, Angew. Chem., showed poor recyclability,20 poor thermal stability, and Int. Ed., 2012, 51, 7480–7484; (h) P. A. Kerneghan, a gradual desulfonation in IR analysis (Fig. S6 in the ESI†), S. D. Halperin, D. L. Bryce and K. E. Maly, Can. J. Chem., matching with the thermal instability of aromatic sulfonic acids 2011, 89, 577–582; (i) H. Lim and J. Y. Chang, in the literature.12 Macromolecules, 2010, 43, 6943–6945. In conclusion, this work shows that defects can be enhanced 4 Reviews: (a) A. B. Lowe, Polymer, 2014, 55, 5517–5549; (b) and utilized for functionalization of CMP materials. Versatile R. Hoogenboom, Angew. Chem., Int. Ed., 2010, 49, 3415–3417. defective terminal alkynes can be incorporated into CMP 5 J. Y. Jang, H. T. T. Duong, S. M. Lee, H. J. Kim, Y.-J. Ko, materials by the Sonogashira coupling of 1,4-dibromo-2,5- J. H. Jeong, D. S. Lee, T. Thambi and S. U. Son, Chem. diethynybenzene. Aliphatic sulfonic acids can be easily intro- Commun., 2018, 54, 3652–3655. duced into H-TA-CMPs by the thiol-yne click reaction of 6 M. H. Kim, J. Choi, K. C. Ko, K. Cho, J. H. Park, S. M. Lee,

terminal alkyne groups. The resultant H-TA-CMP-ASO3H H. J. Kim, Y.-J. Ko, J. Y. Lee and S. U. Son, Chem. Commun., showed recyclable catalytic performance in fructose conversion 2018, 54, 5134–5137. Published on 25 July 2018. Downloaded by Sungkyunkwan University 8/23/2018 8:41:01 AM. to HMF. We believe that more diverse functional groups can be 7 Recent reviews: (a) S. Dissegna, K. Epp, W. R. Heinz, incorporated by the reaction of terminal alkynes of H-TA-CMPs G. Kieslich and R. A. Fischer, Adv. Mater., 2018, 10, with tailored functional reactants. 1704501; (b) J. Ren, M. Ledwaba, N. M. Musyoka, H. W. Langmi, M. Mathe, S. Liao and W. Pang, Coord. ﬂ Chem. Rev., 2017, 349, 169–197; (c) L. Yuan, M. Tian, J. Lan, Con icts of interest X. Cao, X. Wang, Z. Chai, J. K. Gibson and W. Shi, Chem. 54 – There are no conicts to declare. Commun., 2018, , 370 373; (d) B. Peng, H. Zou, L. He, P. Wang, Z. Shi, L. Zhu, R. Wang and Z. Zhang, CrystEngComm, 2017, 19, 7088–7094. Acknowledgements 8(a) B. Kim, N. Park, S. M. Lee, H. J. Kim and S. U. Son, Polym. Chem., 2015, 6, 7363–7367; (b) J. Chun, J. H. Park, J. Kim, “ This work was supported by Next Generation Carbon Upcycling S. M. Lee, H. J. Kim and S. U. Son, Chem. Mater., 2012, 24, ” Project (Project No. 2017M1A2A2043146) through the National 3458–3463. Research Foundation (NRF) funded by the Ministry of Science 9(a) B. Liu and Z. Zhang, ACS Catal., 2016, 6, 326–338; (b) and ICT, Republic of Korea. B. R. Caes, R. E. Teixeira, K. G. Knapp and R. T. Raines, ACS Sustainable Chem. Eng., 2015, 3, 2591–2605; (c) Notes and references M. Hara, Energy Environ. Sci., 2010, 3, 601–607. 10 N. Park, Y. N. Lim, S. Y. Kang, S. M. Lee, H. J. Kim, Y.-J. Ko, 1(a) J.-X. Jiang, F. Su, A. Trewin, C. D. Wood, N. L. Campbell, B. Y. Lee, H.-Y. Jang and S. U. Son, ACS Macro Lett., 2016, 5, H. Niu, C. Dickinson, A. Y. Ganin, M. J. Rosseinsky, 1322–1326. Y. Z. Khimyak and A. I. Cooper, Angew. Chem., Int. Ed., 11 C. Vogel, J. Meier-Haack, A. Taeger and D. Lehmann, Fuel 2007, 46, 8574–8578; (b) J.-X. Jiang, F. Su, A. Trewin, Cells, 2004, 4, 320–327.

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12 M. Balakrishnan, E. R. Sacia and A. T. Bell, ChemSusChem, 17 Acid-base titration of H-TA-CMP-ASO3H with 0.10 M NaOH 2014, 7, 1078–1085. conrmed the same amount of sulfonic acids in the 13 D. Wang and T. Michinobu, J. Polym. Sci., Part A: Polym. materials. Chem., 2011, 49,72–81. 18 S. Mondal, J. Modal and A. Bhaumik, ChemCatChem, 2015, 7, 14 W. Stober,¨ A. Fink and E. Bohn, J. Colloid Interface Sci., 1968, 3570–3578. 26,62–69. 19 K. Cho, J. Yoo, H.-W. Noh, S. M. Lee, H. J. Kim, Y.-J. Ko, 15 The quantitative yield (100%) was dened assuming H.-Y. Jang and S. U. Son, J. Mater. Chem. A, 2017, 5, 8922– complete and nondefective networking. 8926. 16 For H-TA-CMPs, intensity ratios of the terminal alkyne peaks 20 When we tested the hollow microporous organic polymer À À at 3295 cm 1 to vibration peaks at 1468 cm 1 were 0.76 (4 h), with aryl sulfonic acids in ref. 10 as a catalyst for fructose 0.63 (6 h), and 0.55 (12 h). In comparison, for CMP materials, conversion to HMF, it also showed poor recyclability due À intensity ratios of the terminal alkyne peaks at 3296 cm 1 to to desulfonation.12. À vibration peaks at 1484 cm 1 were 0.52 (4 h), 0.36 (6 h), and 0.27 (12 h). Published on 25 July 2018. Downloaded by Sungkyunkwan University 8/23/2018 8:41:01 AM.