Constructing Robust Covalent Organic Frameworks viaMulticomponent ReactionsPeng-Lai Wang, San-Yuan Ding,* Zhi-Cong Zhang, Zhi-Peng Wang, and Wei Wang*

State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University,Lanzhou, Gansu 730000, China

*S Supporting Information

ABSTRACT: Methodology development of robust link-ages is fundamentally important for the synthesis andapplication of covalent organic frameworks (COFs). Wereport herein a new strategy based on multicomponentreactions (MCRs) to construct ultrastable COFs. Withthe one-pot formation of five covalent bonds in each cyclicjoint, a series of imidazole-linked COFs were robustlyconstructed through the Debus−Radziszewski MCR fromthree easily available components. By reaching a higherlevel of complexity and precision in covalent assembly,this research explores a new direction in integratingsophisticated reversible/irreversible reactions to constructcrystalline porous frameworks.

Covalently linked from organic building blocks, covalentorganic frameworks1 (COFs) have been receiving much

research interest in recent years.2,3 One of the most importantaspects in this area is therefore how to construct robustlinkages.4,5 An effective strategy for improving the structuralrobustness is to form the cyclic joints throughout the COFframeworks. Indeed, the cyclic triazine,6 phenazine,7 benzox-azole,8 dioxin,9 benzothiazole,8c,10 quinoline,11 and benzimi-dazole12 joints have been ingeniously constructed toward thesynthesis of crystalline and ultrastable COFs. In this context,the dynamic covalent chemistry employed for the constructionof cyclic linkages is rather limited, which hampers to a largeextent the diversification of COF materials. Aiming to improvethe generality, feasibility, and diversity of the syntheticmethodology, we present herein a new approach to constructrobust COFs via multicomponent reactions (MCRs).Having been extensively used in classic organic synthesis to

improve the synthetic efficiency and diversity,13,14 MCRsprecisely deliver a single product via the one-pot formation ofseveral dif ferent covalent bonds among at least threecomponents. We noticed that the cyclic structures could beconveniently constructed in many MCRs which delicatelycombine a series of reversible/irreversible covalent assemblies.For example, the classic synthesis of imidazole rings could befacilely achieved via the Debus−Radziszewski reaction15 fromthree components (Figure 1a). The synthetic philosophyparallels the ancient assembly of the robust Kongming lock(joint)16 from multiple mortises and tenons (Figure 1b). Weaccordingly adapt this MCR strategy to construct a series ofimidazole-linked ultrastable COFs (Figure 1c). Note that, byutilizing multicomponent reactions to form cyclic linkages, this

strategy is conceptually different from those to constructmultivariate (multiple component) COFs with mixed linkers17

or with orthogonal reactions.18 The potential advantages are(i) Generality. The paradigms of dynamic covalent chemistry inCOF synthesis have therefore been extended from reversibleassembly to reversible/irreversible MCRs; the precise for-mation of cyclic joints via MCRs may provide additional

Received: October 2, 2019

Figure 1. (a) Classic example of multicomponent reactions (MCRs):formation of 2-methylimidazole from glyoxal, ammonia, andacetaldehyde via Debus−Radziszewski reaction. (b) Ancient wisdomto assemble the Kongming lock (joint) from multiple mortises andtenons. (c) Our mortise-and-tenon proposal for one-pot constructionof imidazole-linked COFs by in situ formation of five-membered cycliclinkages.

Communication

pubs.acs.org/JACSCite This: J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

© XXXX American Chemical Society A DOI: 10.1021/jacs.9b10625J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Dow

nloa

ded

via

WE

STE

RN

SY

DN

EY

UN

IV o

n N

ovem

ber

4, 2

019

at 2

1:55

:18

(UT

C).

See

http

s://p

ubs.

acs.

org/

shar

ingg

uide

lines

for

opt

ions

on

how

to le

gitim

atel

y sh

are

publ

ishe

d ar

ticle

s.

driving force for covalent crystallization. (ii) Feasibility. Thedesigned synthesis of building blocks becomes easier becausethe structural restriction has been degraded to morecomponents. (iii) Diversity. The component scopes areexpanded and, therefore, the diversity of COFs in structureand functionality can be realized.Involving the covalent assemblies among diketone, ammo-

nia, and aldehyde, the Debus−Radziszewski reaction15 isgenerally conducted in acetic acid under reflux conditions.After looking into the assembly mechanism (see SupportingInformation), we start out to adapt this MCR to constructcrystalline and porous frameworks. As shown in Figure 1c, theimidazole-linked COFs were eventually synthesized undersolvothermal conditions from tertbutylpyrene tetraone (1),ammonium acetate (2), and aldehydes (3a−d). Note that allthe components are easily available on a large scale (seeSupporting Information). The optimized conditions (FiguresS3 and S4) were established as crystallization at 150 °C for 5days in dioxane/mesitylene. The observed powder X-raydiffraction (PXRD) patterns of LZU-501 (Figure 2a, black),

LZU-506 (Figure 2b, black), LZU-508 (Figure S35), andLZU-512 (Figure S47) indicated that they are microcrystallinematerials. Simulation of their PXRD patterns with MaterialsStudio19 suggested that these COFs possess preferably theeclipsed stacking arrangement (Figure 2 and Figures S34, S46).The phase purity was further confirmed by scanning electronmicroscopy (SEM): only one morphology was observed foreach COF (Figures S10, S21, S32, and S44). Nitrogenadsorption−desorption measurements at 77 K derived theBrunauer−Emmett−Teller (BET) surface areas of LZU-501(Figure S7), LZU-506 (Figure S17), LZU-508 (Figure S28),and LZU-512 (Figure S40) as 815, 757, 506, and 689 m2 g−1,

respectively, and the total pore volumes (P/P0 = 0.99) as 0.58,0.55, 0.29, and 0.36 cm3 g−1, respectively.Formation of the imidazole linkages was verified by FT-IR

and solid-state NMR spectroscopy. The FT-IR spectra showedtypical bands for the imidazole moieties at ca. 1618 and 3434cm−1 (Figures S8, S18, S29, and S41), which are similar tothose found for the model imidazole compound (Figure S2).The 13C cross-polarization/magic-angle spinning (CP/MAS)NMR spectra of LZU-501 (Figure 3a), LZU-506 (Figure S19),

LZU-508 (Figure S30), and LZU-512 (Figure S42) exhibitedsignals at ca. 161, 138, and 127 ppm, which correspond to thecarbon atoms of the imidazole moieties.20 The 13C non-quaternary suppression (NQS) MAS NMR measurement(Figure 3b) further confirmed that these signals are indeedoriginated from the quaternary carbon atoms located at thecyclic joints. Moreover, the 15N CP/MAS NMR spectrum of15N-labeled LZU-501 (synthesized from 15NH4OAc, seeSupporting Information) exhibited signals at 244 and 144ppm, which are characteristic21 for the nitrogen atoms at theimidazole rings (Figure 4a).With the robust imidazole linkages throughout the frame-

works, the synthesized COFs are insoluble and ultrastable incommon solvents, such as water, N,N-dimethylformamide(DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF),acetone, and trichloromethane. Moreover, these COFs showedhigh chemical stability under harsh conditions, such as upon 3-day treatment in aqueous NaOH (9 M) and HCl (9 M). Afterthe treatment, the 13C CP/MAS NMR spectra (Figure S51)and PXRD patterns (Figure 5a and 5b) remained unchanged,indicating the retention of the atomic-level connectivity andcrystallinity. The N2 adsorption−desorption analysis (Figure5c and 5d) indicates negligible decrease in BET surface areas.The residual weight percentages of LZU-501 and LZU-506were 94%, 95% and 90%, 89% after 3-day treatments in NaOH(9 M) and HCl (9 M), respectively (Figures S49 and S60).The SEM images showed that the morphology was alsoretained (Figures S50 and S61). Thermogravimetric analysis(TGA) indicated that they are thermally stable up to 400 °C(Figures S9, S20, S31, and S43).

Figure 2. Indexed experimental (black), Pawley-refined (red), andpredicted (blue) PXRD patterns of LZU-501 (a) and LZU-506 (b).The difference plots are presented in green. Top inset: eclipsedstructures proposed for LZU-501 and LZU-506. C, gray; N, red; F,blue; H atoms have been omitted for clarity.

Figure 3. (a) 13C CP/MAS and (b) NQS MAS NMR spectra ofLZU-501. Asterisks denote spinning sidebands. The assignments forthe 13C chemical shifts are shown in the chemical structure. Thepresence of the quaternary-carbon signals at 161, 138, and 127 ppm in(b) indicates the successful formation of the imidazole linkages. Bothspectra were obtained at a 13C Larmor frequency of 100.61 MHz.

Journal of the American Chemical Society Communication

DOI: 10.1021/jacs.9b10625J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

B

The excellent stability of these imidazole-linked COFs hasprovided further possibilities for postmodification. Forexample, the ethyl-, benzyl-, pyridine-, and morpholine-modified LZU-501 (denoted as LZU-501-FGs) could bedirectly obtained by a one-step N-alkylation reaction underNaH/THF/65 °C (Scheme 1). A comparison of the PXRDpatterns of LZU-501 and LZU-501-FGs (Figure S76) revealedthat the crystalline structures were well maintained afterpostmodification. The 13C CP-TOSS (total suppression ofsidebands) MAS NMR spectra (Figures S72−S75) confirmedthe successful formation of modified imidazole structures.Furthermore, the 15N CP/MAS NMR signal at 144 ppm of15N-labeled LZU-501 (Figure 4a) was changed to that at 164ppm in 15N-labeled LZU-501-Et (Figure 4b), demonstrating

the successful postmodification via N-ethylation. Therefore,the imidazole-linked COFs could be used not only asfunctional materials directly but also as stable scaffolds tofurther introduce diversified functionalities.In conclusion, we developed a new strategy to construct

robust COFs via multicomponent reactions. As a proof ofconcept, a series of imidazole-linked COFs have beenconstructed via the Debus−Radziszewski reaction, one of therepresentative MCRs. By realizing the in situ formation of fivecovalent bonds in each cyclic imidazole ring, this research setsa new level for precise covalent assembly to crystalline COFs.The formation of cyclic joints not only strengthens the skeletalrobustness but also provides additional driving forces forcovalent crystallization. Given that various types of MCRs(such as Passerini, Ugi, Doebner, and Mannich reactions) havebeen established to construct cyclic moieties in classic organicchemistry, we expect that our approach will boost the researchon employing sophisticated reversible/irreversible combina-tions to diversely construct robust COFs.

■ ASSOCIATED CONTENT*S Supporting InformationThe Supporting Information is available free of charge on theACS Publications website at DOI: 10.1021/jacs.9b10625.

Detailed synthetic procedures, FT-IR spectra, 13C CP/MAS NMR spectra, TGA traces, gas adsorption data,SEM images, TEM images, PXRD patterns, andmodeling details (PDF)

■ AUTHOR INFORMATIONCorresponding Authors*wang_wei@lzu.edu.cn*dingsy@lzu.edu.cnORCIDSan-Yuan Ding: 0000-0003-2160-4092Wei Wang: 0000-0002-9263-7927NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThis work was financially supported by the National NaturalScience Foundation of China (Nos. 21632004 and 21871120)and the Natural Science Foundation of Gansu Province (No.18JR4RA003).

■ REFERENCES(1) Cote, A. P.; Benin, A. I.; Ockwig, N. W.; O’Keeffe, M.; Matzger,A. J.; Yaghi, O. M. Porous, crystalline, covalent organic frameworks.Science 2005, 310, 1166.(2) (a) Feng, X.; Ding, X.; Jiang, D. Covalent organic frameworks.Chem. Soc. Rev. 2012, 41, 6010. (b) Colson, J. W.; Dichtel, W. R.

Figure 4. 15N CP/MAS NMR spectra of 15N-labeled LZU-501 (a)and LZU-501-Et (b). The assignments for the 15N chemical shifts areindicated in the imidazole ring. The minor signals at 309 and 97 ppmare attributed to the terminal nitrogen atoms. Both spectra wereobtained at a 15N Larmor frequency of 60.82 MHz. Note that the 15NCP/MAS NMR experiments may not be quantitative because thepeak intensity depends on the strength of the 1H−15N dipole couplinginteraction.

Figure 5. PXRD patterns (a, b) and N2 adsorption (filled shapes) anddesorption (open shapes) isotherms (c, d) measured after 3-daytreatment of LZU-501 and LZU-506: pristine (green), in DMF(blue), in water (red), in 9 M NaOH (purple), and in 9 M HCl(black).

Scheme 1. Postmodification of LZU-501 on the ImidazoleLinkages via a One-Step N-Alkylation Reactiona

aFG represents the functional group.

Journal of the American Chemical Society Communication

DOI: 10.1021/jacs.9b10625J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

C

Rationally synthesized two-dimensional polymers. Nat. Chem. 2013,5, 453. (c) Ding, S. Y.; Wang, W. Covalent organic frameworks(COFs): From design to applications. Chem. Soc. Rev. 2013, 42, 548.(d) Diercks, C. S.; Yaghi, O. M. The atom, the molecule, and thecovalent organic framework. Science 2017, 355, 923. (e) Jin, Y. H.;Hu, Y. M.; Zhang, W. Tessellated multiporous two-dimensionalcovalent organic frameworks. Nat. Rev. Chem. 2017, 1, 0056.(f) Beuerle, F.; Gole, B. Covalent organic frameworks and cagecompounds: Design and applications of polymeric and discreteorganic scaffolds. Angew. Chem., Int. Ed. 2018, 57, 4850. (g) Lohse, M.S.; Bein, T. Covalent organic frameworks: Structures, synthesis, andapplications. Adv. Funct. Mater. 2018, 28, 1705553. (h) Kandambeth,S.; Dey, K.; Banerjee, R. Covalent organic frameworks: Chemistrybeyond the structure. J. Am. Chem. Soc. 2019, 141, 1807.(3) For selected examples see: (a) Wan, S.; Guo, J.; Kim, J.; Ihee, H.;Jiang, D. A belt-shaped, blue luminescent, and semiconductingcovalent organic framework. Angew. Chem., Int. Ed. 2008, 47, 8826.(b) Furukawa, H.; Yaghi, O. M. Storage of hydrogen, methane, andcarbon dioxide in highly porous covalent organic frameworks for cleanenergy applications. J. Am. Chem. Soc. 2009, 131, 8875. (c) Wan, S.;Gandara, F.; Asano, A.; Furukawa, H.; Saeki, A.; Dey, S. K.; Liao, L.;Ambrogio, M. W.; Botros, Y. Y.; Duan, X.; Seki, S.; Stoddart, J. F.;Yaghi, O. M. Covalent organic frameworks with high charge carriermobility. Chem. Mater. 2011, 23, 4094. (d) Ding, S. Y.; Gao, J.; Wang,Q.; Zhang, Y.; Song, W. G.; Su, C. Y.; Wang, W. Construction ofcovalent organic framework for catalysis: Pd/COF-LZU1 in Suzuki-Miyaura coupling reaction. J. Am. Chem. Soc. 2011, 133, 19816.(e) Kandambeth, S.; Mallick, A.; Lukose, B.; Mane, M. V.; Heine, T.;Banerjee, R. Construction of crystalline 2D covalent organicframeworks with remarkable chemical (acid/base) stability via acombined reversible and irreversible route. J. Am. Chem. Soc. 2012,134, 19524. (f) Bertrand, G. H. V.; Michaelis, V. K.; Ong, T. C.;Griffin, R. G.; Dinca, M. Thiophene-based covalent organicframeworks. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 4923.(g) Calik, M.; Auras, F.; Salonen, L. M.; Bader, K.; Grill, I.;Handloser, M.; Medina, D. D.; Dogru, M.; Lobermann, F.; Trauner,D.; Hartschuh, A.; Bein, T. Extraction of photogenerated electronsand holes from a covalent organic framework integrated hetero-junction. J. Am. Chem. Soc. 2014, 136, 17802. (h) Stegbauer, L.;Schwinghammer, K.; Lotsch, B. V. A hydrazone-based covalentorganic framework for photocatalytic hydrogen production. Chem. Sci.2014, 5, 2789. (i) Lin, S.; Diercks, C. S.; Zhang, Y. B.; Kornienko, N.;Nichols, E. M.; Zhao, Y.; Paris, A. R.; Kim, D.; Yang, P.; Yaghi, O. M.;Chang, C. J. Covalent organic frameworks comprising cobaltporphyrins for catalytic CO2 reduction in water. Science 2015, 349,1208. (j) Wang, X.; Han, X.; Zhang, J.; Wu, X.; Liu, Y.; Cui, Y.Homochiral 2D porous covalent organic frameworks for heteroge-neous asymmetric catalysis. J. Am. Chem. Soc. 2016, 138, 12332.(k) Sun, Q.; Aguila, B.; Perman, J.; Earl, L. D.; Abney, C. W.; Cheng,Y.; Wei, H.; Nguyen, N.; Wojtas, L.; Ma, S. Postsynthetically modifiedcovalent organic frameworks for efficient and effective mercuryremoval. J. Am. Chem. Soc. 2017, 139, 2786. (l) Ma, Y.-X.; Li, Z.-J.;Wei, L.; Ding, S.-Y.; Zhang, Y.-B.; Wang, W. A dynamic three-dimensional covalent organic framework. J. Am. Chem. Soc. 2017, 139,4995. (m) Lin, G.; Ding, H.; Chen, R.; Peng, Z.; Wang, B.; Wang, C.3D porphyrin-based covalent organic frameworks. J. Am. Chem. Soc.2017, 139, 8705. (n) Jiang, L.; Tian, Y.; Sun, T.; Zhu, Y.; Ren, H.;Zou, X.; Ma, Y.; Meihaus, K. R.; Long, J. R.; Zhu, G. A crystallinepolyimide porous organic framework for selective adsorption ofacetylene over ethylene. J. Am. Chem. Soc. 2018, 140, 15724. (o) Guo,Z.; Zhang, Y.; Dong, Y.; Li, J.; Li, S.; Shao, P.; Feng, X.; Wang, B. Fastion transport pathway provided by polyethylene glycol confined incovalent organic frameworks. J. Am. Chem. Soc. 2019, 141, 1923.(p) Li, Y.; Chen, Q.; Xu, T.; Xie, Z.; Liu, J.; Yu, X.; Ma, S.; Qin, T.;Chen, L. De novo design and facile synthesis of 2D covalent organicframeworks: A two-in-one strategy. J. Am. Chem. Soc. 2019, 141,13822.(4) (a) Waller, P. J.; Gandara, F.; Yaghi, O. M. Chemistry ofcovalent organic frameworks. Acc. Chem. Res. 2015, 48, 3053.

(b) Lyle, S. J.; Waller, P. J.; Yaghi, O. M. Covalent organicframeworks: Organic chemistry extended into two and threedimensions. Trends Chem. 2019, 1, 172.(5) For selected examples see: (a) Waller, P. J.; Lyle, S. J.; OsbornPopp, T. M.; Diercks, C. S.; Reimer, J. A.; Yaghi, O. M. Chemicalconversion of linkages in covalent organic frameworks. J. Am. Chem.Soc. 2016, 138, 15519. (b) Zhuang, X.; Zhao, W.; Zhang, F.; Cao, Y.;Liu, F.; Bi, S.; Feng, X. A two-dimensional conjugated polymerframework with fully sp2-bonded carbon skeleton. Polym. Chem. 2016,7, 4176. (c) Jin, E.; Asada, M.; Xu, Q.; Dalapati, S.; Addicoat, M. A.;Brady, M. A.; Xu, H.; Nakamura, T.; Heine, T.; Chen, Q.; Jiang, D.Two-dimensional sp2 carbon-conjugated covalent organic frame-works. Science 2017, 357, 673. (d) Liu, H.; Chu, J.; Yin, Z.; Cai, X.;Zhuang, L.; Deng, H. Covalent organic frameworks linked by aminebonding for concerted electrochemical reduction of CO2. Chem. 2018,4, 1696. (e) Zhao, C.; Diercks, C. S.; Zhu, C.; Hanikel, N.; Pei, X.;Yaghi, O. M. Urea-linked covalent organic frameworks. J. Am. Chem.Soc. 2018, 140, 16438. (f) Lyu, H.; Diercks, C. S.; Zhu, C.; Yaghi, O.M. Porous crystalline olefin-linked covalent organic frameworks. J.Am. Chem. Soc. 2019, 141, 6848. (g) Acharjya, A.; Pachfule, P.;Roeser, J.; Schmitt, F. J.; Thomas, A. Vinylene-linked covalent organicframeworks by base-catalyzed Aldol condensation. Angew. Chem., Int.Ed. 2019, 58, 14865. (h) Xu, J.; He, Y.; Bi, S.; Wang, M.; Yang, P.;Wu, D.; Wang, J.; Zhang, F. An olefin-linked covalent organicframework as a flexible thin-film electrode for a high-performancemicro-supercapacitor. Angew. Chem., Int. Ed. 2019, 58, 12065.(i) Jadhav, T.; Fang, Y.; Patterson, W.; Liu, C. H.; Hamzehpoor,E.; Perepichka, D. F. 2D poly(arylene vinylene) covalent organicframeworks via aldol condensation of trimethyltriazine. Angew. Chem.,Int. Ed. 2019, 58, 13753.(6) (a) Kuhn, P.; Antonietti, M.; Thomas, A. Porous, covalenttriazine-based frameworks prepared by ionothermal synthesis. Angew.Chem., Int. Ed. 2008, 47, 3450. (b) Liu, M.; Jiang, K.; Ding, X.; Wang,S.; Zhang, C.; Liu, J.; Zhan, Z.; Cheng, G.; Li, B.; Chen, H.; Jin, S.;Tan, B. Controlling monomer feeding rate to achieve highlycrystalline covalent triazine frameworks. Adv. Mater. 2019, 31,1807865.(7) Guo, J.; Xu, Y.; Jin, S.; Chen, L.; Kaji, T.; Honsho, Y.; Addicoat,M. A.; Kim, J.; Saeki, A.; Ihee, H.; Seki, S.; Irle, S.; Hiramoto, M.;Gao, J.; Jiang, D. Conjugated organic framework with three-dimensionally ordered stable structure and delocalized π clouds.Nat. Commun. 2013, 4, 2736.(8) (a) Pyles, D. A.; Crowe, J. W.; Baldwin, L. A.; McGrier, P. L.Synthesis of benzobisoxazole-linked two-dimensional covalent organicframeworks and their carbon dioxide capture properties. ACS MacroLett. 2016, 5, 1055. (b) Wei, P. F.; Qi, M. Z.; Wang, Z. P.; Ding, S. Y.;Yu, W.; Liu, Q.; Wang, L. K.; Wang, H. Z.; An, W. K.; Wang, W.Benzoxazole-linked ultrastable covalent organic frameworks forphotocatalysis. J. Am. Chem. Soc. 2018, 140, 4623. (c) Waller, P. J.;AlFaraj, Y. S.; Diercks, C. S.; Jarenwattananon, N. N.; Yaghi, O. M.Conversion of imine to oxazole and thiazole linkages in covalentorganic frameworks. J. Am. Chem. Soc. 2018, 140, 9099. (d) Seo, J. M.;Noh, H. J.; Jeong, H. Y.; Baek, J. B. Converting unstable imine-linkednetwork into stable aromatic benzoxazole-linked one via post-oxidative cyclization. J. Am. Chem. Soc. 2019, 141, 11786.(9) (a) Zhang, B.; Wei, M.; Mao, H.; Pei, X.; Alshmimri, S. A.;Reimer, J. A.; Yaghi, O. M. Crystalline dioxin-linked covalent organicframeworks from irreversible reactions. J. Am. Chem. Soc. 2018, 140,12715. (b) Guan, X.; Li, H.; Ma, Y.; Xue, M.; Fang, Q.; Yan, Y.;Valtchev, V.; Qiu, S. Chemically stable polyarylether-based covalentorganic frameworks. Nat. Chem. 2019, 11, 587.(10) Haase, F.; Troschke, E.; Savasci, G.; Banerjee, T.; Duppel, V.;Dorfler, S.; Grundei, M. M. J.; Burow, A. M.; Ochsenfeld, C.; Kaskel,S.; Lotsch, B. V. Topochemical conversion of an imine- into athiazole-linked covalent organic framework enabling real structureanalysis. Nat. Commun. 2018, 9, 2600.(11) Li, X.; Zhang, C.; Cai, S.; Lei, X.; Altoe, V.; Hong, F.; Urban, J.J.; Ciston, J.; Chan, E. M.; Liu, Y. Facile transformation of imine

Journal of the American Chemical Society Communication

DOI: 10.1021/jacs.9b10625J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

D

covalent organic frameworks into ultrastable crystalline porousaromatic frameworks. Nat. Commun. 2018, 9, 2998.(12) (a) Das, P.; Mandal, S. K. In-depth experimental andcomputational investigations for remarkable gas/vapor sorption,selectivity, and affinity by a porous nitrogen-rich covalent organicframework. Chem. Mater. 2019, 31, 1584. (b) Ranjeesh, K. C.;Illathvalappil, R.; Veer, S. D.; Peter, J.; Wakchaure, V. C.;Goudappagouda; Raj, K. V.; Kurungot, S.; Babu, S. S. Imidazole-linked crystalline two-dimensional polymer with ultrahigh proton-conductivity. J. Am. Chem. Soc. 2019, 141, 14950.(13) Toure, B. B.; Hall, D. G. Natural product synthesis usingmulticomponent reaction strategies. Chem. Rev. 2009, 109, 4439.(14) (a) Kakuchi, R. Multicomponent reactions in polymersynthesis. Angew. Chem., Int. Ed. 2014, 53, 46. (b) Qin, W.; Yang,Z.; Jiang, Y.; Lam, J. W. Y.; Liang, G.; Kwok, H. S.; Tang, B. Z.Construction of efficient deep blue aggregation-induced emissionluminogen from triphenylethene for nondoped organic light-emittingdiodes. Chem. Mater. 2015, 27, 3892.(15) (a) Debus, H. Ueber die einwirkung des ammoniaks aufglyoxal. Ann. Chem. Pharm. 1858, 107, 199. (b) Radzisewski, B. Ueberglyoxalin und seine homologe. Ber. Dtsch. Chem. Ges. 1882, 15, 2706.(16) Wyatt, E. M. Puzzles in Wood; Bruce Publishing Co:Milwaukee, WI, US, 1928.(17) (a) Huang, N.; Zhai, L.; Coupry, D. E.; Addicoat, M. A.;Okushita, K.; Nishimura, K.; Heine, T.; Jiang, D. Multiple-componentcovalent organic frameworks. Nat. Commun. 2016, 7, 12325.(b) Pang, Z. F.; Xu, S. Q.; Zhou, T. Y.; Liang, R. R.; Zhan, T. G.;Zhao, X. Construction of covalent organic frameworks bearing threedifferent kinds of pores through the heterostructural mixed linkerstrategy. J. Am. Chem. Soc. 2016, 138, 4710. (c) Zhang, J.; Han, X.;Wu, X.; Liu, Y.; Cui, Y. Multivariate chiral covalent organicframeworks with controlled crystallinity and stability for asymmetriccatalysis. J. Am. Chem. Soc. 2017, 139, 8277.(18) Zeng, Y.; Zou, R.; Luo, Z.; Zhang, H.; Yao, X.; Ma, X.; Zou, R.;Zhao, Y. Covalent organic frameworks formed with two types ofcovalent bonds based on orthogonal reactions. J. Am. Chem. Soc.2015, 137, 1020.(19) Materials Studio v.7.0; Accelrys Software: San Diego, 2013.(20) Zhao, Y.-C.; Wang, T.; Zhang, L.-M.; Cui, Y.; Han, B.-H.Microporous spiro-centered poly(benzimidazole) networks: Prepara-tion, characterization, and gas sorption properties. Polym. Chem. 2015,6, 748.(21) Solum, M. S.; Altmann, K. L.; Strohmeier, M.; Berges, D. A.;Zhang, Y.; Facelli, J. C.; Pugmire, R. J.; Grant, D. M. 15N chemicalshift principal values in nitrogen heterocycles. J. Am. Chem. Soc. 1997,119, 9804.

Journal of the American Chemical Society Communication

DOI: 10.1021/jacs.9b10625J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

E