Engineering a Zirconium MOF through Tandem “Click” Reactions: A

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

pubs.acs.org/IC

Engineering a Zirconium MOF through Tandem “Click” Reactions: A General Strategy for Quantitative Loading of Bifunctional Groups on the Pore Surface Yingfan Zhang,† Bo Gui,† Rufan Chen,† Guiping Hu,† Yi Meng,† Daqiang Yuan,‡ Matthias Zeller,§ and Cheng Wang*,† †

College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, China State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China § Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States ‡

S Supporting Information *

ABSTRACT: Metal−organic frameworks (MOFs) assembled from linkers of identical length but with different functional groups have gained increasing interests recently. However, it is very challenging for precise control of the ratios of different functionalities. Herein, we reported a stable azide- and alkyne-appended Zr-MOF that can undergo quantitative tandem click reactions on the different functional sites, thus providing a unique platform for quantitative loading of bifunctional moieties. As an added advantage, the same MOF product can be obtained via two independent routes. The method is versatile and can tolerate a wide variety of functional groups, and furthermore, a heterogeneous acid−base MOF organocatalyst was synthesized by tandemly introducing both acidic and basic groups onto the predesigned pore surface. The presented strategy provides a general way toward the construction of bifunctional MOFs with a precise control of ratio of different functionalities for desirable applications in future.

■

INTRODUCTION As a new type of novel porous material with high permanent porosity and structural tunability, metal−organic frameworks (MOFs)1,2 have attracted intensive attention over the past two decades for applications in gas absorption,3−7 separation,8−12 catalysis,13−20 sensors,21−23 drug delivery,24−26 energy storage,27−29 etc. Recently, multivariate MOFs (MTV-MOFs), in which a mixture of different linkers or nodes can serve the same structural role throughout MOF crystal and thus may function in a synergistic manner, have triggered substantial interest.30−37 In particular, many efforts have been focused on assembling linkers with identical length but different functional groups into one MOF.34−37 For example, Yaghi and co-workers reported a series of MTV-MOFs containing up to eight different functionalities in one crystalline phase,34 and some of the MTV-MOFs showed substantially better gas-separation properties than their best same-link counterparts. However, while © XXXX American Chemical Society

bringing heterogeneity into an MOF is appealing, it is always difficult to control the proportion of each functionality via direct solvothermal synthesis. Usually, once the initial solution conditions change, their ratio will also change. As a result, the synergistic behavior in the MOF may be affected. To the best of our knowledge, up to this point only one MOF that displayed a magic predefined ratio between the different functionalities has been reported.37 In light of this challenge, the development of a more general strategy for precise control of the ratio of different functionalities in an MTV-MOF is highly desirable. Postsynthetic modification (PSM),38−41 which can introduce new functional groups within the main molecular skeleton after the MOF lattice is formed, has been widely used to functionalize MOFs in recent years. In principle, this approach Received: December 15, 2017

A

DOI: 10.1021/acs.inorgchem.7b03123 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Scheme 1. Synthesis and PSM of UiO-68-N3/CC via Tandem Click Reactions from Two Different Routesa

a

The topology is shown in simplified form as an octahedral cage.

Figure 1. 1H NMR (400 MHz, DMSO-d6) spectra of digested UiO-68-N3/CC and other corresponding Zr-MOFs obtained through PSM.

quantitative, the ratio of incorporated new functionalities cannot keep consistent with that of the initial MOF. Accordingly, the proportion of each functionality is still not controllable, and further improvements are needed. The copper(I)-catalyzed azide−alkyne cycloaddition (CuAAC) “click” reaction, which provides a highly reliable means to quantitatively establish covalent connections between building blocks containing different functional groups, has been widely employed in organic synthesis, medicinal chemistry, material science, etc.43−45 Over the past 10 years, this reaction has proven to be ideally suited for PSM of MOFs, as long as the

can provide a reasonable route to synthesize MTV-MOFs with a precise ratio of different functionalities. Starting from linkers bearing different functional groups that can be further modified, the obtained MTV-MOF with fixed ratio can be used as a platform for precise loading of new functional groups through PSM. For example, by modulating the percentage of aminoand bromo-functionalized ligands used in an MOF synthesis,42 Cohen and co-workers reported a series of mixed-ligand MOFs, which can subsequently undergo PSM reactions on the orthogonal functional sites to generate a wide variety of MTV-MOFs. However, as the yield of PSM reactions is not B

DOI: 10.1021/acs.inorgchem.7b03123 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry pore size is sufficiently large enough to allow the reagents and catalysts to reach the anchor positions inside the MOF.46−49 For example, Zhou et al. reported several highly stable azidetagged zirconium MOFs (Zr-MOFs),48 which offered an ideal platform for quantitative pore surface engineering with a variety of alkynes. Our group reported an alkyne-tagged Zr-MOF,49 which can be functionalized with different azide compounds in quantitative yield. Since the click reaction can proceed efficiently with quantitative yields and high specificity in the presence of various functional groups, if an MTV-MOF bearing both azide and alkyne groups can be obtained, it should provide a unique platform for quantitative loading of different functionalities via tandem PSM. With these considerations in mind, we report herein the design and synthesis of a stable bifunctional Zr-MOF (UiO-68N3/CC, Scheme 1), which has both accessible azide and alkyne groups on the inner pore surface with an ∼1:1 ratio. This Zr-MOF can undergo quantitative tandem click reactions on the tandem functional sites while retaining the framework, thus providing a unique platform for quantitative loading of bifunctional groups. Interestingly, these tandem click reactions can be performed on two independent routes, leading to the same MOF product. Moreover, by using this tandem strategy, we were able to decorate the pore surface with both acidic and basic functionalities, leading to the formation of a heterogeneous acid−base MOF organocatalyst.

Figure 2. FT-IR spectra of UiO-68-N3/CC and other corresponding Zr-MOFs obtained through PSM. The disappearance of characteristic peak at ∼3286 cm−1 (alkyne group) and ∼2100 cm−1 (azide group) indicates the complete click reaction.

■

RESULTS AND DISCUSSIONS To design a highly stable azide- and alkyne-appended Zr-MOF with large cavities for quantitative loading of bifunctional groups, we chose the reported 2′,5′-bis(azidomethyl)[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid48 (1) and 2′,5′diethynylterphenyl-4,4″-dicarboxylic acid49 (2) as mixed ligands and ZrCl4 as the metal salts. We aimed to construct Zr-MOFs because of its robustness compared with more commonly used Zn/Cu-centered MOFs.50−52 After the treatment of a reaction mixture containing ZrCl4, ligand 1, ligand 2, acetic acid, and N,N-dimethylformamide (DMF) in a preheated 80 °C oven for 72 h, UiO-68-N3/CC was obtained as octahedron-shaped crystals in reasonable yield.53 The structure and composition of UiO-68-N3/CC were determined by several techniques. As shown in Figure 1 and Figure S1, the 1H NMR spectrum of digested UiO-68-N3/CC is the same as the combination of ligand 1 and ligand 2, indicating the intactness of ligands in the MOF. On the basis of the integrals for the particular resonances of methylene proton and alkyne proton, the ratio of ligand 1 to ligand 2 was calculated to be ∼1:1. The Fourier transform infrared (FT-IR) spectrum of activated UiO-68-N3/CC displayed two peaks at 2100 and 3286 cm−1 (Figure 2), characteristic for the azide and alkyne groups. In addition, UiO68-N3/CC was shown to possess typical UiO-68 structure, with its powder X-ray diffraction (PXRD) pattern identical to that reported for UiO-68-alkyne (Figure 3). Moreover, nitrogen gas sorption at 77 K demonstrated that UiO-68-N3/CC displayed a type I gas sorption isotherm (Figure 4), with a high Brunauer−Emmett−Teller (BET) surface area up to 3260 m2 g−1. The highly porous structure of UiO-68-N3/CC should allow the inside azide and alkynyl groups accessible. To assess this applicability, PSM of UiO-68-N3/CC was performed through independent and tandem click reactions with both azide and alkyne groups. In principle, there are two routes for performing such tandem click reactions, which should lead to

Figure 3. PXRD patterns of UiO-68-alkyne, UiO-68-N3/CC and other corresponding Zr-MOFs obtained through PSM. Obviously, the frameworks were well-retained during PSM process.

Figure 4. N2 sorption properties at 77 K for UiO-68-N3/CC and other corresponding Zr-MOFs obtained through PSM.

the same MOF product (Scheme 1). We first studied the tandem PSM of UiO-68-N3/CC through Route A. After the crystals were treated with phenylacetylene in the presence of catalytic CuI at 60 °C in DMF for 24 h, UiO-68-Ph(1)/CC was isolated with a quantitative yield. From the 1H NMR spectrum of digested UiO-68-Ph(1)/CC (Figure 1 and Figure S5), all the azide groups of ligand 1 in the framework were quantitatively transformed to the corresponding triazole derivative, while ligand 2 was retained. This was further confirmed by the high-resolution electrospray ionization mass (HR-ESI-MS) spectrum of digested sample (Figure S6), which displayed two peaks that can be assigned to the corresponding triazole derivative and ligand 2. In addition, the characteristic IR band for the azide group in UiO-68-N3/CC disappeared completely (Figure 2), indicating a complete click reaction. C

DOI: 10.1021/acs.inorgchem.7b03123 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Scheme 2. Synthesis of UiO-68-Ac/Ba and UiO-68-Es/Ba through PSM of UiO-68-N3/CC

tandem click reactions of UiO-68-N3/CC with but-3-ynoic acid and then (R)-2-(azidomethyl)pyrrolidine. In addition, we also synthesized UiO-68-Es/Ba from methyl propiolate and then (R)-2-(azidomethyl)pyrrolidine, for a control experiment. All of the modified Zr-MOFs shown in Scheme 2 were characterized by several techniques (Figures S11−S15), confirming the successful loading of bifunctional groups with the same ratio (∼1:1) as that of original UiO-68-N3/CC. We then investigated the catalytic performance of UiO-68Ac/Ba, by choosing the aldol addition of cyclohexanone with 4nitrobenzaldehyde as a model reaction (Table 1). To a mixture

We then investigated the PSM of UiO-68-Ph(1)/CC with azidomethylbenzene in the presence of CuI at 60 °C in DMF. After 24 h, UiO-68-Ph(1)/Ph(2)-(A) was also isolated in quantitative yield. Similarly, the characteristic IR band for the alkyne group in UiO-68-Ph(1)/CC disappeared (Figure 2), indicating a complete click reaction. From the 1H NMR spectrum of digested UiO-68-Ph(1)/Ph(2)-(A) (Figure 1 and Figure S5), all of the alkyne groups in ligand 2 were also quantitatively transformed to the corresponding triazole derivative, which was further confirmed by HR-ESI-MS experiment (Figure S6). By integrating the resonance peak intensities, both of the corresponding triazole derivatives in UiO-68-Ph(1)/Ph(2)-(A) have the same ratio (∼1:1) as that of UiO-68-N3/CC, indicating the quantitative loading of bifunctional groups. Following the same procedure, we also tested the tandem PSM of UiO-68-N3/CC via Route B (Scheme 1). As confirmed by several different characterization techniques (Figures 1 and 2, Figures S7 and S8), UiO-68-N3/CC can also be quantitatively transformed to first UiO-68-N3/Ph(2) and then to UiO-68-Ph(1)/Ph(2)-(B) via tandem click reactions. Once again, from the 1H NMR spectra (Figure 1), both of the corresponding triazole derivatives in UiO-68Ph(1)/Ph(2)-(B) have a ratio of ∼1:1, the same as that of the starting UiO-68-N3/CC. From the PXRD analysis (Figure 3), all of the modified ZrMOFs shown in Scheme 1 displayed high crystallinity, indicating the frameworks were retained during these PSM processes. In addition, the BET surface area value (Figure 4) for the modified MOFs decreased to 2100 m2 g−1 and then to 1385 m2 g−1 through Route A, whereas in Route B it decreased to 2385 m2 g−1 and then to 1310 m2 g−1, confirming their microporosity. Therefore, via the two independent PSM routes, UiO-68-N3/CC can be quantitatively transformed to the same bifunctional Zr-MOF product, without loss of crystallinity or porosity. More importantly, the ratio of incorporated bifunctional struts is the same as that of the initial UiO-68N3/CC, confirming the quantitative loading. To further demonstrate the potential application of this strategy, we decided to construct a heterogeneous acid−base Zr-MOF, which may function as a synergistic catalyst. By using Route A, we synthesized UiO-68-Ac/Ba (Scheme 2), through

Table 1. Catalytic Studiesa for Aldol Addition of 4Nitrobenzaldehyde and Cyclohexanone with Different ZrMOFs

catalyst

mass (mg)

Mb (% mmol)

yieldc (%)

UiO-68-Ac/CC UiO-68-Es/Ba UiO-68-Ac/Ba

5.1 5.9 6.2

∼1.1 ∼1.0 ∼1.1

13 32 95

Reaction conditions: 40 °C, 60 h, 0.13 mmol of 4-nitrobenzaldehyde, 1.3 mmol of cyclohexanone, 200 μL of H2O. bRelative to 4nitrobenzaldehyde. cDetermined by 1H NMR a

of cyclohexanone, 4-nitrobenzaldehyde, and H2O, a certain amount of UiO-68-Ac/Ba (∼1% based on 4-nitrobenzaldehyde) was added. After the suspension was shaken at 40 °C for 60 h, the expected aldol product was formed with a conversion yield up to 95%, based on the integration of corresponding NMR resonance peak intensities (Figure S19). On the basis of chiral high-performance liquid chromatography (HPLC), four different aldol adduct isomers were determined (Figure S20), with dr-value of 35:65 (syn/anti). In addition, we tested the stability and recyclability of the UiO-68-Ac/Ba catalyst, by subjecting it to three cycles of the aldol reaction. It shows low variation in yields ranging from initially 95% down to 91% after three cycles (Table S3), and the framework was retained during this process (Figure S21). To test the influence of reactant size, we repeated the reaction with a larger molecule, 2D

DOI: 10.1021/acs.inorgchem.7b03123 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

calculate the BET surface area were subject to the consistency criteria detailed by Walton and Snurr.56 FT-IR spectra were recorded on a Bruker TENSOR-27 infrared spectrometer using KBr pellets. Enantiomeric excesses were determined by HPLC analysis (Daicel Chiralcel AD-H column) in comparison with racemic products. The absolute configurations of the products were determined by comparison with compounds previously published.57 MOFs Activation. The MOF crystals were allowed to immerse in DCM several times to replace and remove DMF and were then evacuated in oil pump vacuum at room temperature. MOFs Digestion and 1H NMR Study. In a typical procedure, ∼5 mg of activated MOF was digested with heating in ∼1 mL of deuterated dimethyl sulfoxide (DMSO-d6) and 20 μL of DCl aqueous solution. The digested solution was used directly for 1H NMR, and a big peak from solvent was observed from approximately 4.8 to 5.2 ppm. Synthesis of UiO-68-N3/CC. ZrCl4 (17.7 mg, 0.076 mmol), ligand 1 (17.2 mg, 0.040 mmol), ligand 2 (14 mg, 0.038 mmol), and acetic acid (680 μL) were ultrasonically dissolved in DMF (2.4 mL) and then placed in a preheated 80 °C oven for 72 h. Single crystals with octahedral shape were harvested with a yield of ∼28 mg. The crystals were rinsed with DMF to remove unreacted starting materials and then kept in DMF for further use. From the 1H NMR spectrum of digested sample (Figure 1 and Figure S1), the ratio of ligands 1 and 2 was determined to be ∼1:1. In addition, both ligands 1 and 2 can be found in HR-ESI-MS spectrum of digested sample (Figure S2). By using the same method, we also synthesized several MOFs starting from ligand 1 and ligand 2 with different ratios. These MOFs were also characterized by several techniques (Figures S3 and S4), and the ratio of two ligands was determined (Table S1) from the 1H NMR spectra of digested samples. Synthesis of UiO-68-Ph(1)/CC. Phenylacetylene (0.1 mL, 0.9 mmol) was added to a mixture of UiO-68-N3/CC (∼60 mg) and CuI (5.0 mg) in DMF (4.0 mL). The reaction mixtures were kept at 60 °C under N2 atmosphere for 24 h without stirring. The resultant octahedral crystals were collected, washed with DMF, and then kept in DMF for further modification. From 1H NMR spectrum of digested sample (Figure 1 and Figure S5), UiO-68-Ph(1)/CC was obtained in quantitative yield. Moreover, both components can be found in the HR-ESI-MS spectrum of digested sample (Figure S6). Synthesis of UiO-68-Ph(1)/Ph(2)-(A). Azidomethylbenzene (0.1 mL, 0.8 mmol) was added to a mixture of activated UiO-68-Ph(1)/ CC (∼50 mg) and CuI (4.0 mg) in DMF (4.0 mL). The reaction mixtures were kept at 60 °C under N2 atmosphere for 24 h without stirring. The resultant octahedral crystals were collected by centrifugation and then washed with DMF. From 1H NMR spectrum (Figure 1 and Figure S5) of digested sample, UiO-68-Ph(1)/Ph(2)(A) was obtained in quantitative yield. Moreover, the HR-ESI-MS spectrum (Figure S6) of digested sample showed a major peak that should be assigned to both components, as they have same molecular weight. Synthesis of UiO-68-N3/Ph(2). Azidomethylbenzene (0.1 mL, 0.8 mmol) was added to a mixture of UiO-68-N3/CC (∼60 mg) and CuI (5.0 mg) in DMF (4.0 mL). The reaction mixtures were kept at 60 °C under N2 atmosphere for 24 h without stirring. The resultant octahedral crystals were collected, washed with DMF, and then kept in DMF for further modification. From 1H NMR spectrum of digested sample (Figure 1 and Figure S7), UiO-68-N3/Ph(2) was obtained in quantitative yield. Moreover, both components can be found in the HR-ESI-MS spectrum of digested sample (Figure S8). Synthesis of UiO-68-Ph(1)/Ph(2)-(B). Azidomethylbenzene (0.1 mL, 0.9 mmol) was added to a mixture of activated UiO-68-N3/Ph(2) (∼50 mg) and CuI (4.0 mg) in DMF (4.0 mL). The reaction mixtures were kept at 60 °C under N2 atmosphere for 24 h without stirring. The resultant octahedral crystals were collected by centrifugation and then washed with DMF. From the 1H NMR spectrum of digested sample, UiO-68-Ph(1)/Ph(2)-(B) was obtained in quantitative yield (Figure 1 and Figure S7). Moreover, the HR-ESI-MS spectrum of digested sample (Figure S8) showed a major peak that should be assigned to both components, as they have the same molecular weight.

naphthaldehyde instead of 4-nitrobenzaldehyde, under otherwise identical conditions. Only a low conversion of ca. 9% was observed after reaction for 7 d (Figure S22), demonstrating that the catalytic reaction with the smaller 4-nitrobenzaldehyde did indeed occur within the pores of UiO-68-Ac/Ba. To prove that the catalytic behavior of UiO-68-Ac/Ba was ascribed to the cooperation of the acid sites and base sites, we performed several control experiments, by studying the catalytic performance of UiO-68-Ac/CC and UiO-68-Es/Ba under the same reaction condition. As shown in Table 1, UiO-68-Ac/ CC with acid sites gave a yield of only 13%, where UiO-68Es/Ba with base sites showed a slightly higher yield of 32%, respectively. Therefore, the high catalytic activity of UiO-68Ac/Ba can be ascribed to the incorporation of both acidic sites and basic sites into UiO-68-N3/CC through tandem click reactions, indicating the powerful promise of this unique strategy.

■

CONCLUSION In conclusion, we have synthesized a highly stable bifunctional Zr-MOF (UiO-68-N3/CC), with accessible azide and alkyne groups, in an ∼1:1 ratio. This Zr-MOF can provide a unique platform for anchoring bifunctional groups with precise ratio control (∼1:1) on the pore surface, via tandem click reactions on the tandem functional sites. As an added advantage, the same bifunctional MOF product can be obtained through two independent PSM routes. Since a series of Zr-MOFs with different ratios of azide and alkyne groups can be synthesized by modulating the initial ratio utilized in the solvothermal synthesis,53 we also envision that it is possible for quantitative loading of bifunctional groups with other ratios in an MOF. Moreover, acid and base groups have been tandemly introduced onto the predesigned pore surface from this platform, leading to the formation of a heterogeneous acid− base MOF organocatalyst. Therefore, we strongly believe our design strategy provides a general way toward the construction of bifunctional MOF with a precise control of the ratio of different functionalities for desirable applications. The construction of other bifunctional MOFs with cooperative functionality for other applications is ongoing in our lab.

■

EXPERIMENT SECTION

General Methods. 4-Methoxyl carbonylphenylboronic acid, 1,4dibromo-2,5-dimethylbenzene, sodium azide, N-bromosuccinimide, phenylacetylene, methyl propiolate, but-3-ynoic acid, and benzoylperoxide were purchased from AK Scientific, Inc. Pd(PPh3)4 was bought from Aladdin. Zirconium(IV) chloride was purchased from Alfa Aesar. Triisopropylsilane and copper(I) iodide were purchased from Adamas. Ligand 1,48 ligand 2,49 (R)-2-(azidomethyl)pyrrolidine,54 and azidomethy benzene55 were synthesized according to the literature procedure. 1 H and 13C NMR spectra were measured on a Bruker Fourier 400 M spectrometer. High-resolution mass spectra were collected on Bruker Daltonics Inc. APEXII FT-ICR mass spectrometer, which was equipped with EI, ESI, and MALDI as ionization source. PXRD data were recorded on a Rigaku Smartlab 9KW diffractometer operated at 45 kV, 200 mA for Cu Kα (λ = 1.5406 Å) with a scan speed of 5°/min and a step size of 0.01° in 2θ at ambient temperature and pressure. Thermogravimetric analysis from 30 to 800 °C was performed on a DTA-60 Simultaneous DTG-TG Apparatus (Shimadzu) in air atmosphere using a 10 °C/min ramp without equilibration delay. The nitrogen adsorption and desorption isotherms were measured at 77 K using a Quantachrome Nova 4200e surface area and pore size analyzer. Before measurement, the samples were degassed under vacuum at room temperature for 12 h. The isotherm points chosen to E

DOI: 10.1021/acs.inorgchem.7b03123 Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

■

Synthesis of UiO-68-Ac/CC. But-3-ynoic acid (50 mg, 0.6 mmol) was added to a mixture of UiO-68-N3/CC (∼60 mg) and CuI (5.0 mg) in DMF (4.0 mL) in a glass tube. The reaction mixtures were kept at 60 °C under N2 atmosphere for 30 h without stirring. The resultant octahedral crystals were collected, washed with DMF, and then kept in DMF for further use. From the 1H NMR spectrum of digested sample (Figure S11), UiO-68-Ac/CC was obtained in quantitative yield. Moreover, both components can be found in the HR-ESI-MS spectrum of digested sample (Figure S12). Synthesis of UiO-68-Ac/Ba. (R)-2-(Azidomethyl)pyrrolidine (0.1 mL, 0.9 mmol) was added to a mixture of UiO-68-Ac/CC (∼50 mg) and CuI (5.0 mg) in DMF (4.0 mL) in glass tube. The reaction mixtures were kept at 60 °C under N2 atmosphere for 24 h without stirring. The resultant octahedral crystals were collected, washed with DMF, and then kept in DMF for further use. From the 1H NMR spectrum of digested sample (Figure S11), UiO-68-Ac/Ba was obtained in quantitative yield. Moreover, both components can be found in the HR-ESI-MS spectrum of digested sample (Figure S12). Synthesis of UiO-68-Es/CC. Methyl propiolate (0.1 mL, 1.1 mmol) was added to a mixture of UiO-68-N3/CC (∼60 mg) and CuI (5.0 mg) in DMF (4.0 mL) in a glass tube. The reaction mixtures were kept at 60 °C under N2 atmosphere for 30 h without stirring. The resultant crystals were collected, washed with DMF, and then kept in DMF for further use. From the 1H NMR spectrum of digested sample (Figure S13), UiO-68-Es/CC was obtained in quantitative yield. Moreover, both components can be found in the HR-ESI-MS spectrum of digested sample (Figure S14). Synthesis of UiO-68-Es/Ba. (R)-2-(Azidomethyl)pyrrolidine (0.1 mL, 0.9 mmol) was added to a mixture of UiO-68-Es/CC (∼50 mg) and CuI (5.0 mg) in DMF (4.0 mL) in glass tube. The reaction mixtures were kept at 60 °C under N2 atmosphere for 24 h without stirring. The resultant crystals were collected, washed with DMF, and then kept in DMF for further use. From the 1H NMR spectrum of digested sample (Figure S13), UiO-68-Es/Ba was obtained in quantitative yield. Moreover, both components can be found in the HR-ESI-MS spectrum of digested sample (Figure S14). General Catalysis Procedure. To test their catalytic performance, all the catalytic Zr-MOFs kept in DMF were first exchanged with H2O several times. Then, the reactions were performed as follows: cyclohexanone (100 μL, 1.0 mmol), 4-nitrobenzaldehyde (20 mg, 0.13 mmol), and a certain amount of MOF crystals (∼1% based on 4nitrobenzaldehyde) were loaded in a vial containing H2O (200 μL), which was then shaken at 40 °C for 60 h. After that period, ethanol (1 mL) was added, and then the solvent was pipetted off. This process was repeated five times, the extracts were combined, and the solvents were removed under vacuum to provide the crude product. From the 1 H NMR spectra, the yield and diastereomeric selectivity were determined.57 The crystals were collected and dried in an oven to weigh the recovered amounts of catalysts. Determination of ee-Value. For determination of enantiomeric excess (ee) by chiral HPLC, the crude product obtained by using UiO68-Ac/Ba as catalyst was further purified by flash chromatography in ethyl acetate/n-hexane mixture (1/1.1) to obtain the pure product. The ee was determined by HPLC analysis. Recyclability of UiO-68-Ac/Ba. At the end of each reaction cycle, ethanol (1 mL) was added, and then the solvent was pipetted off. This process was repeated five times. The crystals were collected, exchanged with H2O, and reused as catalysts for the next cycle under the otherwise identical reaction conditions. The yields and devalue of UiO-68-Ac/Ba in the three cycles is shown in Table S3. Control Experiment. Cyclohexanone (100 μL, 1.0 mmol), 2naphthaldehyde (20 mg, 0.13 mmol), and UiO-68-Ac/Ba crystals (∼6.0 mg, ∼1% based on 4-nitrobenzaldehyde) were loaded in a glass vial containing H2O (200 μL). After that, the reaction mixture was shaken at 40 °C for 7 d. From the 1H NMR spectrum (Figure S22), only a small amount (9%) of the product was obtained.

Article

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b03123. Characterization details and catalytic experiments (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Daqiang Yuan: 0000-0003-4627-072X Cheng Wang: 0000-0003-0326-2674 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We gratefully acknowledge the financial support from the National Natural Science Foundation of China (21572170, 21772149), the Research Fund for the Doctoral Program of Higher Education of China (20130141110008), the Funds for Creative Research Groups of Hubei Province (2017CFA002), and the Beijing National Laboratory for Molecular Sciences.

■

REFERENCES

(1) Zhou, H.-C.; Long, J. R.; Yaghi, O. M. Introduction to metal− organic frameworks. Chem. Rev. 2012, 112, 673−674. (2) Furukawa, H.; Cordova, K. E.; O’Keeffe, M.; Yaghi, O. M. The chemistry and applications of metal-organic frameworks. Science 2013, 341, 1230444. (3) Peng, Y.; Krungleviciute, V.; Eryazici, I.; Hupp, J. T.; Farha, O. K.; Yildirim, T. Methane storage in metal−organic frameworks: current records, surprise findings, and challenges. J. Am. Chem. Soc. 2013, 135, 11887−11894. (4) Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.; Bae, T.-H.; Long, J. R. Carbon dioxide capture in metal−organic frameworks. Chem. Rev. 2012, 112, 724−781. (5) Li, B.; Wen, H.-M.; Wang, H.; Wu, H.; Tyagi, M.; Yildirim, T.; Zhou, W.; Chen, B. A porous metal−organic framework with dynamic pyrimidine groups exhibiting record high methane storage working capacity. J. Am. Chem. Soc. 2014, 136, 6207−6210. (6) Kim, H.; Yang, S.; Rao, S. R.; Narayanan, S.; Kapustin, E. A.; Furukawa, H.; Umans, A. S.; Yaghi, O. M.; Wang, E. N. Water harvesting from air with metal-organic frameworks powered by natural sunlight. Science 2017, 356, 430−434. (7) Rieth, A. J.; Yang, S.; Wang, E. N.; Dincă, M. Record atmospheric fresh water capture and heat transfer with a material operating at the water uptake reversibility limit. ACS Cent. Sci. 2017, 3, 668−672. (8) Li, J.-R.; Sculley, J.; Zhou, H.-C. Metal−organic frameworks for separations. Chem. Rev. 2012, 112, 869−932. (9) Cadiau, A.; Adil, K.; Bhatt, P. M.; Belmabkhout, Y.; Eddaoudi, M. A metal-organic framework−based splitter for separating propylene from propane. Science 2016, 353, 137−140. (10) Cui, X.; Chen, K.; Xing, H.; Yang, Q.; Krishna, R.; Bao, Z.; Wu, H.; Zhou, W.; Dong, X.; Han, Y.; Li, B.; Ren, Q.; Zaworotko, M. J.; Chen, B. Pore chemistry and size control in hybrid porous materials for acetylene capture from ethylene. Science 2016, 353, 141−144. (11) Gao, Q.; Xu, J.; Cao, D.; Chang, Z.; Bu, X.-H. A rigid nested metal−organic framework featuring a thermoresponsive gating effect dominated by counterions. Angew. Chem., Int. Ed. 2016, 55, 15027− 15030. (12) Engel, E. R.; Jouaiti, A.; Bezuidenhout, C. X.; Hosseini, M. W.; Barbour, L. J. Activation-dependent breathing in a flexible metal− organic framework and the effects of repeated sorption/desorption cycling. Angew. Chem., Int. Ed. 2017, 56, 8874−8878. F

DOI: 10.1021/acs.inorgchem.7b03123 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (13) Liu, J.; Chen, L.; Cui, H.; Zhang, J.; Zhang, L.; Su, C.-Y. Applications of metal−organic frameworks in heterogeneous supramolecular catalysis. Chem. Soc. Rev. 2014, 43, 6011−6061. (14) Zhang, T.; Lin, W. Metal−organic frameworks for artificial photosynthesis and photocatalysis. Chem. Soc. Rev. 2014, 43, 5982− 5993. (15) Mondloch, J. E.; Katz, M. J.; Isley Iii, W. C.; Ghosh, P.; Liao, P.; Bury, W.; Wagner, G. W.; Hall, M. G.; DeCoste, J. B.; Peterson, G. W.; Snurr, R. Q.; Cramer, C. J.; Hupp, J. T.; Farha, O. K. Destruction of chemical warfare agents using metal−organic frameworks. Nat. Mater. 2015, 14, 512−516. (16) Zhao, M.; Yuan, K.; Wang, Y.; Li, G.; Guo, J.; Gu, L.; Hu, W.; Zhao, H.; Tang, Z. Metal−organic frameworks as selectivity regulators for hydrogenation reactions. Nature 2016, 539, 76−80. (17) Ji, P.; Manna, K.; Lin, Z.; Feng, X.; Urban, A.; Song, Y.; Lin, W. Single-site cobalt catalysts at new Zr12(μ3-O)8(μ3-OH)8(μ2-OH)6 metal−organic framework nodes for highly active hydrogenation of nitroarenes, nitriles, and isocyanides. J. Am. Chem. Soc. 2017, 139, 7004−7011. (18) Lian, X.; Fang, Y.; Joseph, E.; Wang, Q.; Li, J.; Banerjee, S.; Lollar, C.; Wang, X.; Zhou, H.-C. Enzyme−MOF (metal−organic framework) composites. Chem. Soc. Rev. 2017, 46, 3386−3401. (19) Xia, Q.; Li, Z.; Tan, C.; Liu, Y.; Gong, W.; Cui, Y. Multivariate metal−organic frameworks as multifunctional heterogeneous asymmetric catalysts for sequential reactions. J. Am. Chem. Soc. 2017, 139, 8259−8266. (20) Duan, H.; Zeng, Y.; Yao, X.; Xing, P.; Liu, J.; Zhao, Y. Tuning synergistic effect of Au−Pd bimetallic nanocatalyst for aerobic oxidative carbonylation of amines. Chem. Mater. 2017, 29, 3671−3677. (21) Liu, S.-Y.; Qi, X.-L.; Lin, R.-B.; Cheng, X.-N.; Liao, P.-Q.; Zhang, J.-P.; Chen, X.-M. Porous Cu(I) triazolate framework and derived hybrid membrane with exceptionally high sensing efficiency for gaseous oxygen. Adv. Funct. Mater. 2014, 24, 5866−5872. (22) Hu, Z.; Lustig, W. P.; Zhang, J.; Zheng, C.; Wang, H.; Teat, S. J.; Gong, Q.; Rudd, N. D.; Li, J. Effective detection of mycotoxins by a highly luminescent metal−organic framework. J. Am. Chem. Soc. 2015, 137, 16209−16215. (23) Lustig, W. P.; Mukherjee, S.; Rudd, N. D.; Desai, A. V.; Li, J.; Ghosh, S. K. Metal−organic frameworks: functional luminescent and photonic materials for sensing applications. Chem. Soc. Rev. 2017, 46, 3242−3258. (24) He, C.; Liu, D.; Lin, W. Nanomedicine applications of hybrid nanomaterials built from metal−Ligand coordination bonds: nanoscale metal−organic frameworks and nanoscale coordination polymers. Chem. Rev. 2015, 115, 11079−11108. (25) Meng, X.; Gui, B.; Yuan, D.; Zeller, M.; Wang, C. Mechanized azobenzene-functionalized zirconium metal-organic framework for oncommand cargo release. Sci. Adv. 2016, 2, e1600480. (26) Wu, M.-X.; Yang, Y.-W. Metal−organic framework (MOF)based drug/cargo delivery and cancer therapy. Adv. Mater. 2017, 29, 1606134. (27) Zhou, J.; Li, R.; Fan, X.; Chen, Y.; Han, R.; Li, W.; Zheng, J.; Wang, B.; Li, X. Rational design of a metal−organic framework host for sulfur storage in fast, long-cycle Li−S batteries. Energy Environ. Sci. 2014, 7, 2715−2724. (28) Wang, L.; Feng, X.; Ren, L.; Piao, Q.; Zhong, J.; Wang, Y.; Li, H.; Chen, Y.; Wang, B. Flexible solid-state supercapacitor based on a metal−organic framework interwoven by electrochemically-deposited PANI. J. Am. Chem. Soc. 2015, 137, 4920−4923. (29) Wang, L.; Han, Y.; Feng, X.; Zhou, J.; Qi, P.; Wang, B. Metal− organic frameworks for energy storage: batteries and supercapacitors. Coord. Chem. Rev. 2016, 307, 361−381. (30) Burrows, A. D. Mixed-component metal−organic frameworks (MC-MOFs): enhancing functionality through solid solution formation and surface modifications. CrystEngComm 2011, 13, 3623− 3642. (31) Brozek, C. K.; Dincă, M. Ti3+-, V2+/3+-, Cr2+/3+-, Mn2+-, and Fe2+-substituted MOF-5 and redox reactivity in Cr- and Fe-MOF-5. J. Am. Chem. Soc. 2013, 135, 12886−12891.

(32) Helal, A.; Yamani, Z. H.; Cordova, K. E.; Yaghi, O. M. Multivariate metal-organic frameworks. Natl. Sci. Rev. 2017, 4, 296− 298. (33) Huang, Y. B.; Liang, J.; Wang, X. S.; Cao, R. Multifunctional metal-organic framework catalysts: synergistic catalysis and tandem reactions. Chem. Soc. Rev. 2017, 46, 126−157. (34) Deng, H.; Doonan, C. J.; Furukawa, H.; Ferreira, R. B.; Towne, J.; Knobler, C. B.; Wang, B.; Yaghi, O. M. Multiple functional groups of varying ratios in metal-organic frameworks. Science 2010, 327, 846− 850. (35) Kong, X.; Deng, H.; Yan, F.; Kim, J.; Swisher, J. A.; Smit, B.; Yaghi, O. M.; Reimer, J. A. Mapping of functional groups in metalorganic frameworks. Science 2013, 341, 882−885. (36) Manna, K.; Zhang, T.; Greene, F. X.; Lin, W. Bipyridine- and phenanthroline-based metal−organic frameworks for highly efficient and tandem catalytic organic transformations via directed C−H activation. J. Am. Chem. Soc. 2015, 137, 2665−2673. (37) Sue, A. C.-H.; Mannige, R. V.; Deng, H.; Cao, D.; Wang, C.; Gándara, F.; Stoddart, J. F.; Whitelam, S.; Yaghi, O. M. Heterogeneity of functional groups in a metal−organic framework displays magic number ratios. Proc. Natl. Acad. Sci. U. S. A. 2015, 112, 5591−5596. (38) Cohen, S. M. Postsynthetic methods for the functionalization of metal−organic frameworks. Chem. Rev. 2012, 112, 970−1000. (39) Roy, P.; Schaate, A.; Behrens, P.; Godt, A. Post-synthetic modification of Zr-metal−organic frameworks through cycloaddition reactions. Chem. - Eur. J. 2012, 18, 6979−6985. (40) Marshall, R. J.; Forgan, R. S. Postsynthetic modification of zirconium metal-organic frameworks. Eur. J. Inorg. Chem. 2016, 2016, 4310−4331. (41) Cohen, S. M. The postsynthetic renaissance in porous solids. J. Am. Chem. Soc. 2017, 139, 2855−2863. (42) Kim, M.; Cahill, J. F.; Prather, K. A.; Cohen, S. M. Postsynthetic modification at orthogonal reactive sites on mixed, bifunctional metalorganic frameworks. Chem. Commun. 2011, 47, 7629−7631. (43) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Click chemistry: diverse chemical function from a few good reactions. Angew. Chem., Int. Ed. 2001, 40, 2004−2021. (44) Wu, P.; Feldman, A. K.; Nugent, A. K.; Hawker, C. J.; Scheel, A.; Voit, B.; Pyun, J.; Fréchet, J. M. J.; Sharpless, K. B.; Fokin, V. V. Efficiency and fidelity in a click-chemistry route to triazole dendrimers by the copper(I)-catalyzed ligation of azides and alkynes. Angew. Chem., Int. Ed. 2004, 43, 3928−3932. (45) Li, P.-Z.; Wang, X.-J.; Liu, J.; Lim, J. S.; Zou, R.; Zhao, Y. A triazole-containing metal−organic framework as a highly effective and substrate size-dependent catalyst for CO2 conversion. J. Am. Chem. Soc. 2016, 138, 2142−2145. (46) Goto, Y.; Sato, H.; Shinkai, S.; Sada, K. Clickable” metal− organic framework. J. Am. Chem. Soc. 2008, 130, 14354−14355. (47) Gadzikwa, T.; Farha, O. K.; Malliakas, C. D.; Kanatzidis, M. G.; Hupp, J. T.; Nguyen, S. T. Selective bifunctional modification of a non-catenated metal−organic framework material via “click” chemistry. J. Am. Chem. Soc. 2009, 131, 13613−13615. (48) Jiang, H. L.; Feng, D.; Liu, T. F.; Li, J. R.; Zhou, H. C. Pore surface engineering with controlled loadings of functional groups via click chemistry in highly stable metal-organic frameworks. J. Am. Chem. Soc. 2012, 134, 14690−14693. (49) Li, B.; Gui, B.; Hu, G.; Yuan, D.; Wang, C. Postsynthetic modification of an alkyne-tagged zirconium metal-organic framework via a ″click″ reaction. Inorg. Chem. 2015, 54, 5139−5141. (50) Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti, C.; Bordiga, S.; Lillerud, K. P. A new zirconium inorganic building brick forming metal organic frameworks with exceptional stability. J. Am. Chem. Soc. 2008, 130, 13850−13851. (51) Bai, Y.; Dou, Y.; Xie, L.-H.; Rutledge, W.; Li, J.-R.; Zhou, H.-C. Zr-based metal-organic frameworks: design, synthesis, structure, and applications. Chem. Soc. Rev. 2016, 45, 2327−2367. (52) Gao, C.; Ai, J.; Tian, H.; Wu, D.; Sun, Z.-M. An ultrastable zirconium-phosphonate framework as bifunctional catalyst for highly G

DOI: 10.1021/acs.inorgchem.7b03123 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry active CO2 chemical transformation. Chem. Commun. 2017, 53, 1293− 1296. (53) It should be mentioned here, by modulating the percentage of ligand 1 and ligand 2 in the initial reaction mixture, a series of ZrMOFs with different ratio of two ligands can also be obtained (Figure S3 and Table S1). (54) Dahlin, N.; Bøgevig, A.; Adolfsson, H. N-Arenesulfonyl-2aminomethylpyrrolidines - novel modular ligands and organocatalysts for asymmetric catalysis. Adv. Synth. Catal. 2004, 346, 1101−1105. (55) Maury, J.; Feray, L.; Bertrand, M. P.; Kapat, A.; Renaud, P. Unexpected conversion of alkyl azides to alkyl iodides and of aryl azides to N-tert-butyl anilines. Tetrahedron 2012, 68, 9606−9611. (56) Walton, K. S.; Snurr, R. Q. Applicability of the BET method for determining surface areas of microporous metal−organic frameworks. J. Am. Chem. Soc. 2007, 129, 8552−8556. (57) Kutzscher, C.; Nickerl, G.; Senkovska, R.; Bon, V.; Kaskel, S. Proline functionalized UiO-67 and UiO-68 type metal−organic frameworks showing reversed diastereoselectivity in aldol addition reactions. Chem. Mater. 2016, 28, 2573−2580.

H

DOI: 10.1021/acs.inorgchem.7b03123 Inorg. Chem. XXXX, XXX, XXX−XXX