DOI: 10.1002/chem.201403162

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Template-Induced Diverse Metal–Organic Materials as Catalysts for the Tandem Acylation–Nazarov Cyclization Chao Huang, Ran Ding, Chuanjun Song, Jingjing Lu, Lu Liu, Xiao Han, Jie Wu,* Hongwei Hou,* and Yaoting Fan[a]

Abstract: In our continuing quest to develop a metal–organic framework (MOF)-catalyzed tandem pyrrole acylation–Nazarov cyclization reaction with a,b-unsaturated carboxylic acids for the synthesis of cyclopentenone[b]pyrroles, which are key intermediates in the synthesis of natural product ( )-roseophilin, a series of template-induced Zn-based (1–3) metal-organic frameworks (MOFs) have been solvothermally synthesized and characterized. Structural conversions from non-porous MOF 1 to porous MOF 2, and back to nonporous MOF 3 arising from the different concentrations of template guest have been observed. The anion–p interactions between the template guests and ligands could affect the configuration of ligands and further tailor the frame-

Introduction Metal–organic frameworks (MOFs) are a burgeoning class of functional solid-state materials that are already being explored for use in multiple areas ranging from catalysis[1–3] to surface chemistry,[4] hydrogen storage,[5–9] drug delivery,[10–11] molecular magnetism,[12–13] and biomedical imaging.[10–11] Therein, due to their high crystallinity, uniform pores, and ability to be chemically and physically tuned for specific chemical transformations, MOFs are particularly suited for immobilizing well-defined molecular catalysts, leading to a new generation of solid catalysts with uniform catalytic sites and open channel structures for shape-, size-, chemo-, and enantioselective reactions.[3–15] Although various MOFs have been explored as catalysts for transesterfications,[16] C C bond formations,[17, 18] epoxidations,[14, 19] oxidations[9, 20, 21] and many other reactions,[22, 23] to date, exerting precise control over the physical and chemical properties of the framework to improve catalytic activity and selectivity is still a considerable challenge. These strategies include ways to construct and sustain reagent-accessible chan[a] C. Huang, R. Ding, Prof. C. Song, J. Lu, L. Liu, X. Han, Prof. J. Wu, H. Hou, Prof. Y. Fan The College of Chemistry and, Molecular Engineering Zhengzhou University, Henan 450052 (P.R. China) Fax: (+ 86) 371-67761744 E-mail: [email protected] [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201403162. Chem. Eur. J. 2014, 20, 16156 – 16163

works of 1–3. Futhermore, MOFs 1–3 have shown to be effective heterogeneous catalysts for the tandem acylation– Nazarov cyclization reaction. In particular, the unique structural features of 2, including accessible catalytic sites and suitable channel size and shape, endow 2 with all of the desired features for the MOF-catalyzed tandem acylation–Nazarov cyclization reaction, including heterogeneous catalyst, high catalytic activity, robustness, and excellent selectivity. A plausible mechanism for the catalytic reaction has been proposed and the structure–reactivity relationship has been further clarified. Making use of 2 as a heterogeneous catalyst for the reaction could greatly increase the yield of total synthesis of ( )-roseophilin.

nels, to study framework distortion and characterize large open channels, to quantify substrate diffusion through the MOF channels, and to relate the open channel sizes with catalytic activities/stereoselectivities.[3] Therefore, more rational synthetic strategies to prepare MOFs-based catalysts that allow the control of the channel size and channel geometry are particularly important because the structural features, such as channel size and shape and channel functionalization, have been found to play an important role in designing MOFs as heterogeneous catalysts.[14, 15] Tremendous progress has been made on the theoretical forecast and practical approaches of controlled syntheses of MOF catalysts.[24–26] A current important approach to the rational modification of channel size and channel geometry is the use of templates (or structure-directing agents).[14, 27] When MOFs are synthesized with template molecules, the templates act as placeholders and the structure and chemical properties of guest template molecules can be transcribed into pore shapes and properties.[14, 27, 28] The template guest molecules are not only shape-selective but also site-selective, arising from their interactions with channel surface, such as charge/electron-transfer (CT/ET),[29–31] cation–p,[32] anion–p,[33–35] and XH-p-type (X = O, N, or C) interactions.[36, 37] Conversely, our laboratory has been committed to developing Lewis-catalyzed tandem pyrrole acylation–Nazarov cyclization with a,b-unsaturated carboxylic acids for the syntheses of cyclopentenone[b]pyrroles, which are key intermediates in the synthesis of numerous biologically active molecules, such as natural product roseophilin.[38] However, exploration of this reaction under a variety of catalytic conditions (e.g., [Ti(OiPr)4],

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Full Paper BBr3, AlCl3, [Sc(OTf)3], FeCl3, ZnCl2, etc.) usually resulted in no reaction or the acylation product, along with some of the Nazarov cyclization product.[39–40] Encouraged by the merits of MOF-based catalysts, we were interested in exploring whether the MOFs could be used to catalyze tandem acylation–Nazarov cyclization reaction. In our continuing quest to develop new strategies necessary for the rational assembly of MOF platforms, particularly those containing a tunable channel (i.e., confined spaces) and readily amenable to isoreticulation, as robust and selective catalysts for the tandem acylation–Nazarov cyclization, we have applied an approach to the MOFs synthesis with a flexible tetratopic carboxylate ligand 5,5’-(pentane-1,2-diyl)-bis(oxy)diisophthalic (H4pdpa), which is a non-rigid ligand with four diverging tetracarboxylic acid groups by appending two dicarboxylic acid aromatic species through a flexible space entity. It has been anticipated that ligand H4pdpa with an elongated bridging linker, the diverging flexible and polydentate coordination sites may generate stable MOFs with multidimensional architectures and large open channels to transport organic substrates and products of the tandem acylation–Nazarov cyclization reaction. In addition, MOFs constructed with flexible ligands always possess adaptive recognition properties and breathing ability in the solid state.[41] These effects have significant implications in MOF catalysis because it will affect the size and shape of the MOF open channels, which are crucial for mass transport in catalysis.[3] More importantly, to modify channel surface in MOFs and prevent the tendency to form interpenetrated structures, the so-called anion–p interactions between the electrondeficient dicarboxylic acid aromatic cores in H4pdpa and electronegative atoms of template guests were introduced into the synthesis of desired MOF-based catalysts.[35] Herein, as an extension of this methodology, three Zn-based MOFs with the ligand H4pdpa (i.e., {[Zn2(pdpa)(H2O)2]·2 H2O}n (1), {[Zn4(pdpa)2(H2O)8]·H2O}n (2), and {[Zn5(pdpa)2(m3-OH)2(H2O)3]·6H2O·CH3OH}n (3)), have been synthesized under solvothermal conditions. These Zn-MOFs (1–3) were synthesized under the same reaction conditions but simply adding different concentrations of cyclic ethers (1,4-dioxane or THF) as templates. In addition, we demonstrate the catalytic potentials of 1–3 with respect to tandem pyrrole acylation–Nazarov cyclization for the syntheses of cyclopentenone[b]pyrroles and further clarified the mechanism of catalytic reaction and the structure– reactivity relationship through the difference of their frameworks and channel surface. To the best of our knowledge, this is the first report of the application of MOF catalysts into the tandem acylation–Nazarov cyclization reactions.

Results and Discussion Crystal structure of 1 X-ray analysis reveals that 1, which crystallizes in the monoclinic crystal system P21/c, is a 2-fold interpenetrated 3D framework. Each completely deprotonated pdpa4 ligand coordinates four Zn1 ions and three Zn2 ions through its four carboxylate groups (Figure 1 a). The two aromatic rings of pdpa4 Chem. Eur. J. 2014, 20, 16156 – 16163

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Figure 1. a) Coordination environments of the Zn2 + ions in 1. Hydrogen atoms and free water molecule are omitted for clarity; b) View of the 3D 4connected net with {4.5.64}{4.65} topology of 1; c) Ball-and-stick model showing the 2-fold interpenetration of 1 (each color represents an independent molecule).

have a dihedral angle of 77.19 8. Pairs of Zn2 + ions connect four carboxylate groups to generate a dinuclear Zn2 + as secondary building unit (SBU) with a Zn···Zn separation of 3.482 . Each SBU is linked with four pdpa4 ligands and each ligand also connects with four Zn2 + SBUs, leading to a 3D network (Figure 1 b). Topologically, taking both the binuclear zinc SBU and the pdpa4 ligands as 4-connected nodes, compound 1 can be regarded as a 4-connected net with the topological

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Full Paper point symbol of {4.5.64}{4.65} (Figure 1 c). Because of the elongated pdpa4 ligand, compound 1 adopts a two-fold interpenetrated structure, which reduces the interior void space of the framework. Crystal structure of 2 As expected, catenation isomerism can be controlled by introducing guest templates, which act as placeholders to modify the framework, pore shapes, and properties.[3] We hypothesized that the anion–p interactions between the electron-deficient dicarboxylic acid aromatic cores in H4pdpa and electronegative oxygen atoms of templates (1,4-dioxane or THF) can favor the formation of the non-interpenetrated structure. Compound 2 was obtained under the conditions of 1, except with the addition of 1,4-dioxane or THF as templates (1:9 Vtemplate/Vprior solvents). X-ray analysis reveals that 2, which crystallizes in the triclinic space group P-1, is a 2D open-framework with 36membered macrocycles. Four oxygen atoms from two carboxylate groups and two independent Zn2 + ions construct a {Zn2(CO2)2} SBU, which can be regarded as a four-connected node (Figure 2 a). Each pdpa4 ligand connects four {Zn2(CO2)2} SBUs. Therefore, the {Zn2(CO2)2} SBUs are extended by pdpa4 ligands to build a 2D layer framework with bimetallic macrocycle running along the a axis (Figure 2 b).The non-interpenetrated framework has many large open channel dimensions of  16  9 2 along the b axis. Furthermore, the 2D networks, stacked by p···p interactions with a distance of approximately 3.7  between two phenyl rings, form supermolecules with an open-framework (Figure 2 c). Moreover, the addition of templates (1,4-dioxane or THF) bring about the change of the configuration of ligand. Compared with the distorted pdpa4 ligands of 1, the dihedral angle of two phenyl moieties of a pdpa4 ligand in 2 is 0.9 8, which further modify the surface of the channel in the structure. Crystal structure of 3 Complex 3 was obtained under the conditions of 2, except that the ratio of templates and the prior solvents was increased to 4:1. X-ray analysis reveals that 3, which is a 3D framework, crystallizes in the monoclinic crystal system P21/c. Five adjacent Zn2 + ions are connected by one water molecule and two m3-hydroxyl oxygen atoms, showing a pentanuclear zinc cluster (Figure 3 a). All carboxyl groups from H4pdpa Figure 2. a) Coordination environments of the Zn2 + ions in 2. Hydrogen atoms and free water molecule are omitted for clarity; b) View of the 2D network along the b axis; c) A space-filling view of the porous network along the b axis, showing the channels of 2.

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Full Paper are deprotonated and adopt a bridging coordination mode to bridge pentazinc SBU, generating a 3D framework. The 3D framework is further stabilized by the p···p interaction with a distance of approximately 3.7  between the two phenyl rings. There are two crystallographically different pdpa4 ligands in this complex and both of them could be regarded as four-connected nodes. As a result, compound 3 adopts a 4,8connected net with a topological point symbol of {410.615.83}{45.6}2 (Figure 3 b).Interestingly, with the increasing of template concentration, the pdpa4 ligands in 3 are distorted and the dihedral angles between two phenyl rings are approximately 78.7 8, which is tremendously different to that of 2. Due to the pentanuclear zinc cluster and the flexible and twisted pdpa4 ligands reducing the open channel sizes, compound 3 exhibits a compact structure with the open channel of  8  4  along the b axis (Figure 3 c). The effect of the template guest

Figure 3. a) Coordination environments of the Zn2 + ions in 3. Hydrogen atoms and free water molecule are omitted for clarity; b) View of the 3D 4,8connected net with a topological point symbol of {410.615.83}{45.6}2 ; c) View of the packing of 3 along b axis. Chem. Eur. J. 2014, 20, 16156 – 16163

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The modification of the structural and chemical properties of MOFs is very topical in the area of materials chemistry.[24, 27, 42–46] To date, it remains a considerable challenge to obtain certain MOFs designed as platforms with controlled pore size, shape, and functionality for specific applications. It is even more difficult to predict the final MOF topology by using flexible ligand H4pdpa due to conformational flexibility of ligand, influence of guest/solvent molecules, and reaction conditions. To achieve a framework design for heterogeneous catalysts with H4pdpa, the anion–p interactions between the electron-deficient aromatic cores in H4pdpa and electronegative oxygen atoms of template guest (1,4-dioxane or THF) were exploited because the electron-deficient p systems could operate as receptors capable of binding an anion or molecule with electronegative atoms and the anion–p interactions could play an important role in designing MOFs.[27, 35] By introducing a template guest (1,4-dioxane or THF), a series of Zn-based MOFs (1–3) have been successfully synthesized and their structures depend on the concentration of template. The template guests could affect the dihedral angle between two aromatic rings of ligand and further influence the frameworks of the structure. Without a template guest, compound 1 shows a 2-fold interpenetrated 3D framework and the ligands are distorted with the dihedral angle between two aromatic rings being 77.19 8. The addition of a low concentration of the template (1:9 Vtemplate/Vprior solvents) leads to the formation of 2, which shows a 2D open-framework with 36-membered macrocycles. The templates bring about the change of the configuration of ligand. Compared with the distorted pdpa4 ligands in 1, the ligands in 2 are almost planar and the dihedral angles of two phenyl moieties are near 0 8. However, a high concentration of templates (4:1 Vtemplate/Vprior solvents) results in the generation of 3, which exhibits a compact 3D framework with pentanuclear zinc clusters. The ligands return to a distorted position in which the dihedral angles of two phenyl moieties are 78.7 8. It has been well demonstrated that the solvent templates, as the ligands or guests, can affect the coordination assemblies of specific reactants from both thermodynamic and

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Full Paper kinetic aspects, yielding diverse crystalline products. However, the examples shown in this work, in which the solvent templates (1,4-dioxane or THF) are not present in the products but actually influence the crystal growth, crystalline morphology, and lattice structure of the final solid, the so-called structuredirecting effect, are really rare.[47]

Table 1. MOFs 1–3-catalyzed tandem acylation–Nazarov cyclization.

Analysis of thermal stability of 1–3 To investigate the thermal stability of 1–3, the thermogravimetric analysis (TGA) experiments were carried out (the Supporting Information, Figure S1). The result of 1 shows a weight loss of 11.0 % (calcd 11.4 %) in the range of 50–290 8C attributed to the release of four water molecules, and then the main framework of 1 begins to collapse at 400 8C. The curve of 2 reveals that a preliminary weight loss of 11.9 % (calcd 12.6 %) beginning at 50 to 350 8C is attributed to the release of water molecules. After that, the expulsion of H4pdpa ligands occurs at 420 8C. As for 3, the initiatory weight loss of 9.20 % (calcd. 9.91 %) in the 50–370 8C range is due to the departure of six lattice water molecules and one uncoordinated methanol molecule, and the H4pdpa ligands of 3 are released at a temperature of 380 8C. The catalytic effect of 1–3

Entry

Catalyst

1 2 3 4 5 6

a,b-Unsaturated carboxylic acids

Yield [%] of isolated 9 b–c

Yield [%] of isolated 10 b–c

1 2 3

33 98 48

35 n.o.[a] 10

1 2 3

30 85 25

30 n.o.[a] 5

[a] n.o. = not observed.

Nazarov cyclization reaction catalyzed by the Zn-based MOFs had been proposed tentatively (Scheme 1). Mixed anhydride formation gives I. Activation of the carbonyl group from the initial a,b-unsaturated acid by coordination to the Zn catalyst makes it more electrophilic, which is attacked by N-tosylpyrrole to provide pyrrolylvinylketone II. Finally, Nazarov cyclization generates cyclopenta[b]pyrrole IV. In particular, when 2 was used as heterogeneous catalyst, the yield of 9 c was less than that of 9 b under the same reaction conditions, which may be due to the fact that 9 c was obtained from the more bulky carboxylic acids (8 c). To further investigate the effect of the substrate size in this reaction, we carried out the process catalyzed by 2 with a series of a,b-unsaturated carboxylic acids (8 a–d) as substrates. Treatment of N-tosylpyrrole with a,b-unsaturated carboxylic acids (8 a–d) and TFAA in the present of 2 as a heterogeneous catalyst at reflux for 4 h, the tandem reaction proceeded successfully and gave cyclopentenone[b]pyrroles (9 a–d), which were isolated in good yields. As shown in Table 2, the yields decrease in the

Phase purity of the bulky crystalline samples of MOFs 1–3 was confirmed by an excellent match between the experimental and simulated PXRD patterns (the Supporting Information, Figure S2). The solvent-resistance property of 1–3 was examined by suspending samples in 1,2-dichloroethane (DCE) for 48 h because DCE would be chosen as reaction solvent in the catalytic reaction. It was found that 1–3 could keep original shapes in boiling DCE for more than 48 h. To study the potential of MOFs 1–3 as heterogeneous catalysts in the tandem acylation–Nazarov cyclization reaction, we compared their activities with the homogeneous ZnCl2 by keeping the Zn content the same (30 %). According to the previously optimized reaction conditions,[39] the catalytic activities of 1–3 were initially evaluated in 1,2-dichloroethene (DCE) at reflux for 4 h, with N-tosylpyrrole, trifluoroacetic anhydride (TFAA), and a,b-unsaturated carboxylic acids (8 b and 8 c) as substrates. As shown in Table 1, MOFs 1 and 3 can promote the catalytic tandem acylation–Nazarov cyclization reaction, leading to 9 b and 9 c with moderate selectivity of the cyclization product, along with some of the acylation product (entries 1, 3, 4, and 6 of Table 1). In comparison, ZnCl2 as a homogeneous catalyst gave Nazarov cyclization products 9 b and 9 c in yields of 53 and 61 %, respectively. More importantly, compound 2 obviously shows superior activity over ZnCl2, 1, and 3, with 98 and 85 % yields for 9 b and 9 c, respectively (entries 2 and 5 of Table 1). The Nazarov cyclization products were formed as the sole products when 2 was used as the heterogeneous catalyst, whereas the acylation products have not been detected. The mechanism for the tandem acylation– Scheme 1. The suggested mechanism. Chem. Eur. J. 2014, 20, 16156 – 16163

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Full Paper Table 2. MOF 2-catalyzed tandem acylation–Nazarov cyclization for the synthesis of cyclopentenone[b]pyrroles.[a] Entry

Catalyst a,b-Unsaturated Product carboxylic acids

Yield of the isolated product [%]

1 2

ZnCl2 2

43 98

3 4

ZnCl2 2

53 98

5 6

ZnCl2 2

61 85/97[b]

7 8

ZnCl2 2

43 65

[a] Reaction conditions: 30 mol % catalyst, TFAA, DCE, heat at reflux, 4 h. [b] Reaction time was 12 h

order 8 a (98 %)  8 b (98 %) > 8 c (85 %) > 8 d (65 %), corresponding to the increase of substrate sizes. To eliminate the possibility of the different activities of 8 a–d leading to such tendency, further experiments were carried out with zinc chloride as the catalyst under the same reaction conditions. Substrates 8 a–d under the catalysis of ZnCl2 gave yields of 43, 53, 61, and 43 %, respectively, which do not follow the decrease order of 2. It indicated that the channel size of MOFs and substrate size play a vital role in the heterogeneous catalyzed reaction. For a MOF to function as an effective heterogeneous catalyst, it needs to possess enough large open channels to transport organic substrates and products. In addition, when we extended the reaction time from 4 to 12 h for 8 c in the presence of 2 as the heterogeneous catalyst, the yield could increase from 85 to 97 % (entry 6 of Table 2). It showed that the increase of the substrate size leads to a decline of reaction rate but has no effect on the reaction selectivity. The high catalytic activity of 2 may be attributed to its specific frameworks and channel surface. Single-crystal structural analysis reveals that the mesh size of 2 is  16  9 . The large open channels can facilitate the transport of organic substrates and products. In addition, the two aromatic rings of the pdpa4 ligand in 2 are coplanar, which further form a planiform channel surface in the structure. We hypothesized that the planiform channel surface could stabilize the flat intermediates produced in the Nazarov cyclization process and provide a platform to perform reactions in the channels and display shapeselective catalytic capability. Thirdly, the planiform channel surface is occupied by the coordinated water molecules, which are good leaving groups and will favor making contact of substrates with the catalytic active sites in the catalytic process. On the contrary, from the single-crystal structural analysis we Chem. Eur. J. 2014, 20, 16156 – 16163

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know that 1 and 3 are nonporous. Compound 1, in particular, shows a 2-fold interpenetrated 3D framework. Such interpenetrations can severely reduce or even eliminate the interior void space of the MOFs, which is unfavorable to catalytic activity owing to its inability to transport the substrates through the small channels. Compound 3 exhibits a compact 3D framework with pentanuclear zinc cluster and flexible and twisted pdpa4 ligands, which reduce the open channel sizes and prevent the heterogeneous catalytic reaction. Therefore, for 1 and 3, the catalytic sites might only exist on the outer surface and could not possess size- and shape-selective catalytic capability, leading to the formation of both the acylation product and Nazarov cyclization product. In contrast, compound 2 could work as a more efficient heterogeneous catalyst for the tandem pyrrole acylation–Nazarov cyclization reaction with a,b-unsaturated carboxylic acids due to the fact that it could provide a platform to perform reactions in the channels, display size- and shape-selective catalytic capability, yielding Nazarov cyclization product as the sole product. In addition, compared with the previous used homogeneous Lewis acid catalysts for the reaction ([Ti(OiPr)4], AlCl3, [Sc(OTf)3], FeCl3, and ZnCl2),[39] compound 2 as a heterogeneous catalyst could yield several principal advantages, such as recyclability for reuse, higher catalytic activity arising from its ability to stabilize the intermediates, enhanced catalyst stability due to the spatial separation of single catalytic sites, and most evidently its pore sizes, and thus its shape and size selectivity for the Nazarov cyclization product. To further confirmed that the catalytic reactions proceeded within the crystal voids, experiments were carried out with large crystals of 2 (  0.3  0.3  0.2 mm3) without grinding and stirring, eliminating the possibility of catalytic activity resulting from the surface metal sites of very tiny particles. The Nazarov cyclization reaction of 8 b gave cyclization product in a yield of 60 % and no acylation product after 4 h. The result provided unambiguous evidence for the substrates to enter the interior of the crystals and access the catalytic active sites in the interior of the MOF crystals, because big crystals own too few surface metal sites to account for the catalytic reaction. Second, to investigate whether the catalytic reactions are heterogeneous or homogeneous, we carried out a filtrations experiment based on the former. At the 10 % conversion of the N-tosylpyrrole in the presence of large crystals of 2 without grinding and stirring for 30 min, the reaction mixture was passed through a sand core funnel to remove the catalyst, and the supernatant was allowed to react for 4 h. It was found that the conversion of the supernatant almost unchanged during the time. Based on the filtration experiment, we believe that the reaction is basically heterogeneous. We have also examined the recyclability of 2 for this catalytic reaction with 8 b. In the recyclability experiments, compound 2 was readily recovered from the catalytic reaction via centrifugation, and the recovered catalyst showed only slight deterioration in four runs (the Supporting Information, Figure S3). Moreover, the PXRD patterns of the crystallites of 2 after the fourth catalytic reactions closely matched those of single crystals of 2 and showed no signs of framework collapse and decomposition, which indicates that the framework could

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Full Paper remain intact after at least four runs (the Supporting Information, Figure S4).

Conclusion Herein, we demonstrated a rare example of template-induced isomerism and controlled channel geometry in a series of Znbased MOFs 1–3. The structures of 1–3 could be systematically tuned by changing the concentration of introduced templates. The interactions between the oxygen atoms of template guest (1,4-dioxane or THF) and electron-deficient dicarboxylic acid aromatic cores in H4pdpa, the so-called anion–p interactions could influence the configuration of ligand H4pdpa. Furthermore, systematically tuning the frameworks and the cavity shapes of MOFs were achieved only by changing the concentration of introduced templates. In addition, with the large channels (  16  9 ), compound 2 could work as an efficient heterogeneous catalyst for the Lewis-catalyzed tandem pyrrole acylation–Nazarov cyclization reaction with a,b-unsaturated carboxylic acids, provide a platform to perform reactions in the channels, display size- and shape-selective catalytic capability and recyclability, leading to the formation of cyclopentenone[b]pyrroles in good yield.

Experimental Section Materials and physical measurements All reagents and solvents were commercially available and used as received without further purification. FTIR spectra were recorded on a Bruker-ALPHA spectrophotometer with KBr pellets in the 400– 4000 cm 1 region. Elemental analyses (C and H) were carried out on a FLASH EA 1112 elemental analyzer. PXRD patterns were recorded using CuKa1 radiation on a PANalyticalX’Pert PRO diffractometer. Thermal analyses were performed on a Netzsch STA 449C thermal analyzer at a heating rate of 10 8C min 1 in air. 1H and 13 C NMR spectra were obtained with Bruker Avance-400 spectrometers. High-resolution mass spectra (HRMS-ESI) were obtained on a Micro Q-TOF mass spectrometer.

Syntheses {[Zn2(pdpa)(H2O)2]·2 H2O}n (1): A mixture of [Zn(NO3)2]·6 H2O (0.059 g, 0.2 mmol), H4pdpa (0.043 g, 0.1 mmol), NaOH (0.016 g, 0.4 mmol), H2O (8 mL), and CH3OH (2 mL) was placed in a 25 mL Teflon-lined stainless steel container. The mixture was sealed and heated at 130 8C for three days. After the mixture was cooled to ambient temperature at a rate of 5 8C h 1, colorless crystals of 1 were obtained with a yield of 39 % (based on Zn). IR (KBr): n˜ = 3255 (w), 2948 (m), 2167 (w), 1614 (w), 1542 (m), 1455 (m), 1413 (w), 1380 (s), 1324 (w), 1264 (m), 1134 (m), 1041 (m), 933 (w), 887 (w), 774 (s), 720 (m), 671 (w), 598 cm 1 (w); elemental analysis calcd (%) for C21H24Zn2O14 : C 39.96; H 3.83; found: C 40.11; H 3.75. {[Zn4(pdpa)2(H2O)8]·H2O}n (2): A mixture of [Zn(NO3)2]·6 H2O (0.059 g, 0.2 mmol), H4pdpa (0.043 g, 0.1 mmol), NaOH (0.016 g, 0.4 mmol), H2O/CH3OH 4:1 (9 mL), and 1,4-dioxane (or THF) (1 mL) was placed in a 25 mL Teflon-lined stainless steel container. The mixture was sealed and heated at 130 8C for three days. After the mixture was cooled to ambient temperature at a rate of 5 8C h 1, colorless crystals of 2 were obtained in 64 % yield (based on Zn). IR Chem. Eur. J. 2014, 20, 16156 – 16163

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(KBr): n˜ = 3336 (m), 2951 (w), 2167 (w), 2043 (w), 1617 (w), 1551 (s), 1454 (m), 1415 (w), 1376 (s), 1323 (w), 1263 (m), 1133 (m), 1040 (m), 929 (w), 887 (w), 809 (w), 774 (s), 712 (m), 672 cm 1 (w); elemental analysis calcd (%) for C42H50Zn4O29 : C 39.40; H 3.94; found: C 39.26; H 3.99. {[Zn5(pdpa)2(m3-OH)2(H2O)3]·6 H2O·CH3OH}n (3): A mixture of [Zn(NO3)2]·6 H2O (0.059 g, 0.2 mmol), H4pdpa (0.043 g, 0.1 mmol), NaOH (0.016 g, 0.4 mmol), H2O/CH3OH 4:1 (2 mL) and 1,4-dioxane (or THF) (8 mL) was placed in a 25 mL Teflon-lined stainless steel container. The mixture was sealed and heated at 130 8C for three days. After the mixture was cooled to ambient temperature at a rate of 5 8C h 1, colorless crystals of 3 were obtained in 58 % yield (based on Zn). IR (KBr): n˜ = 3377 (m), 2942 (w), 2862 (w), 2168 (w), 1616 (w), 1552 (s), 1454 (m), 1416 (m), 1369 (s), 1265 (m), 1129 (m), 1041 (m), 889 (w), 864 (w), 774 (m), 742 cm 1 (m); elemental analysis calcd (%) for C43H56Zn5O32 : C 36.58; H 4.00; found: C 36.69; H 3.85.

Crystal data collection and refinement The data of the 1–3 were collected on a Rigaku Saturn 724 CCD diffractomer (MoKa, l = 0.71073 ) at temperature of (20  1) 8C. Absorption corrections were applied by using numerical program. The data were corrected for Lorentz and polarization effects. The structures were solved by direct methods and refined with a fullmatrix least-squares technique based on F2 with the SHELXL-97 crystallographic software package.[48, 49] The hydrogen atoms were placed at calculated positions and refined as riding atoms with isotropic displacement parameters. Crystallographic crystal data and structure processing parameters for 1–3 and parts of complexes under specific conditions are summarized in Table S1 (the Supporting Information). Selected bond lengths and bond angles for 1–3 and parts of complexes under specific conditions are listed in Table S2 (the Supporting Information), respectively. CCDC-993992, CCDC-993993, and CCDC-993994 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Typical procedure of a tandem acylation–Nazarov cyclization reaction for the synthesis of cyclopentenone[b]pyrroles Trifluoroacetic anhydride (TFAA, 4.0 mmol, 4.0 equiv) and catalyst (0.3 equiv calculated according to the content of Zn) were added to a mixture of N-tosylpyrrole (1.0 mmol, 1.0 equiv) and a,b-unsaturated carboxylic acid (2.0 mmol, 2.0 equiv) in dry DCE (20 mL). The solution was then stirred under reflux for 4 h. The bulk of the cool solvent was evaporated in vacuo and then the residue was partitioned between EtOAC (20 mL) and H2O (20 mL). The organic phase was washed by saturated aqueous NaHCO3 and saturated aqueous NaCl, dried by Na2SO4, filtered and evaporated in vacuo. The crude residue was purified by column chromatography on silica gel with an appropriate eluting solvent system. The 1H/ 13 C NMR spectra, and HRMS of the pure products were consistent with our previous literature report.[39] .

Acknowledgements This work was financially supported by the National Natural Science Foundation (Nos. 21201152, 21371155, and 91022013) and Research Found for the Doctoral Program of Higher Education of China (20124101110002).

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Received: April 18, 2014 Published online on October 10, 2014

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Template-induced diverse metal-organic materials as catalysts for the tandem acylation-Nazarov cyclization.

In our continuing quest to develop a metal-organic framework (MOF)-catalyzed tandem pyrrole acylation-Nazarov cyclization reaction with α,β-unsaturate...
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