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A 3D In(III) coordination polymer derived from rigid dicarboxylate ligand: Synthesis, crystal structure and catalytic property
Inorganica Chimica Acta 411 (2014) 35–39
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
A 3D In(III) coordination polymer derived from rigid dicarboxylate ligand: Synthesis, crystal structure and catalytic property Jing Xia a, Jifu Zheng b, Jianing Xu a, Li Wang a,⇑, Lu Yang a, Zhandong Su c, Yong Fan a,⇑ a
College of Chemistry, Jilin University, Changchun 130012, Jilin, PR China Key Laboratory of Polymer Ecomaterials, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China c College of Construction Engineering, Jilin University, Changchun 130026, Jilin, PR China b
a r t i c l e
i n f o
Article history: Received 17 July 2013 Received in revised form 6 November 2013 Accepted 13 November 2013 Available online 23 November 2013 Keywords: Indium coordination polymer Crystal structure Lewis acid Heterogeneous catalysis Cyanosilylation
a b s t r a c t A new indium coordination polymer, In(OH)(H2O)(1,4-bdc) (1,4-H2bdc = 1, 4-benzendicarboxylic acid), has been prepared under solvothermal conditions using a mixture of rigid organic linker and inorganic heteropolyacid (12-phosphotungstic acid) template. Single-crystal X-ray diffraction analysis reveals that this new compound possesses a 3D framework with the square-shaped channels constructed from the infinite indium-oxide chains and rigid 1,4-bdc ligands. This compound exhibits good catalytic activity for the cyanosilylation of aromatic aldehydes and can be reused three times without losing activity or significant mass. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction The design and synthesis of coordination polymers are currently interest and great challenge in chemistry and material science due to their fascinating architectures and topologies as well as their potential application as functional materials in many areas, such as magnetism, luminescence and catalysis [1–13]. In order to obtain coordination polymer with desirable topologies and properties, different metal ions were tested. Compared to widely investigated divalent transition metal ions, which are usually four- or six-coordinated, In(III) ions exhibit excellent structural and coordinative flexibility as six-coordinated octahedra MO6, seven-coordinated pentagonal bipyramids MO7, and eight-coordinated polyhedra MO8. Some indium complexes even adopt a high coordination number (e.g. 10) configuration [14]. Moreover, indium coordination polymers with thermally stable framework have been proved to possess interesting catalytic properties in the green chemistry [15,16]. For example, in premise of catalyst and substrate ratio being 0.1%, In2(OH)3(bdc)1.5 with supramolecular 3D framework can be used as efficient Lewis catalysts for hydrogenation of nitroaromatics and oxidation of sulfide reactions and can be recycled in successive runs by a simple filtration, without a significant loss of activity and selectivity [16]. On the other hand, the choice of organic moieties is also very important in the construction and structural tuning of coordination polymers, even small change in flexibility, length, functional group ⇑ Corresponding authors. Tel.: +86 431 88498786; fax: +86 431 85671974. E-mail addresses: [email protected] (L. Wang), [email protected] (Y. Fan). 0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2013.11.014
position, and symmetry of organic ligands can lead to remarkably different materials with diverse architectures and functions. Among various organic ligands, the aromatic dicarboxylate organic ligands are excellent structural builders because they are sterically rigid and chemically robust, leading to frameworks of high thermal stability approaching that of purely inorganic zeolites [17–19]. In particular, the utilization of 1,4-benzendicarboxylic acid (1,4H2bdc) has yielded many new non-interpenetrating frameworks with variable cavities or channels [20–22]. With the aim of preparing the novel coordination polymers, we conducted our studies on the solvothermal synthesis of In-based coordination polymer using rigid 1,4-H2bdc as ligand. Finally, in the presence of 12-phosphotungstic acid (H3PW12O40nH2O) as template, a new In(III) coordination polymer, In(OH)(H2O)(1,4bdc), has been successfully prepared. It possesses a 3D framework with the square-shaped channels that are built up from the infinite –In–OH–In– chains of corner-sharing In(OH)2(H2O)O4 pentagonal bipyramids and 1,4-bdc ligands. Moreover, this compound displays good catalytic activity for the cyanosilylation of aromatic aldehydes. Herein, we report the synthesis, crystal structure and catalytic property of this new In(III)-coordination polymer. 2. Experimental 2.1. Materials and Methods All chemicals were obtained from commercial sources and used without further purification. 12-phosphotungstic acid was
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J. Xia et al. / Inorganica Chimica Acta 411 (2014) 35–39
purchased from Sinopharm Chemical Reagent Co., Ltd. Trimethylsilylcyanide was purchased from Alfa. Other reagents were purchased from Beijing chemical agent company. Powder X-ray diffraction (PXRD) data were obtained using SHIMADAZU XRD6000 diffractometer with Cu Ka radiation (k = 1.5418 Å), with the step size and the count time of 0.02° and 4 s, respectively. The elemental analysis was conducted on a Perkin Elmer 2400 elemental analyzer. FT-IR spectrum was recorded on a Nicolet Impact 410 spectrometer between 400 and 4000 cm1 using the KBr pellet method. Thermogravimetric analysis (TGA) was conducted on a Perkin-Elmer TGA 7 thermogravimetric analyzer with a heating rate of 10 °C min1 from room temperature to 800 °C. 1H NMR spectra were measured on a Bruker Avance 300 console at a frequency of 300 MHz. 2.2. Synthesis A mixture of 1,4-H2bdc (0.03 g, 0.18 mmol), InCl34H2O (0.05 g, 0.17 mmol), and H3PW12O40nH2O (0.01 g) were added to 1 ml N,N0 -dimethylformamide (DMF) and 5 ml acetonitrile (CH3CN) in a 23 ml Teflon-lined stainless steel vessel autoclave. The mixture was sealed and heated at 120 °C for 4 days. The colourless block crystals were obtained by filtration and washed by DMF several times. The yield of product was 70% in weight based on indium. The elemental analysis results are listed as follows: Anal. Calc. for In(OH)(H2O)(1,4-bdc): C, 30.61; H, 2.25. Found: C, 30.50; H, 2.16%. IR (KBr pellet, cm1): 3442 (br, m), 2965 (w), 2916 (w), 2058 (w), 1574 (s), 1505(w), 1422 (m), 1160 (s), 1062 (s), 945 (s), 855 (s), 772 (w), 744 (w), 551 (s), 467 (w). 2.3. Crystal structure determination The crystallographic data for In(OH)(H2O)(1,4-bdc) were collected on a Siemens Smart CCD diffractometer with graphitemonochromated Mo Ka (k = 0.71073 Å) radiation at a temperature of 293(2) K. No significant decay was observed during the data collection. Data processing was accomplished with the RAPID AUTO processing program. The structure was solved by direct method and refined by full-matrix least-squares on F2 using the SHELXTL crystallographic software package [23,24]. All indium atoms were located first, and then the oxygen and carbon atoms were subsequently found in difference Fourier maps. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms of ligands were generated geometrically.
3. Results and discussion 3.1. Synthesis Solvothermal synthesis method is widely used in the syntheses of coordination polymers and solvents show a remarkable influence on the terminal structures of coordination polymers. In(OH)(H2O)(1,4-bdc) was synthesized at a relatively low reaction temperature in mixed DMF/CH3CN solvents. When single DMF or CH3CN was used to replace mixed solvents for In(OH)(H2O)(1,4bdc) under the same condition, the same phases were not obtained which can be attributed to different polarity and solubility of solvents. It is found that no phosphotungstic acid was incorporated into the resulting framework of In(OH)(H2O)(1,4-bdc). Moreover, the products could not be obtained from a solution in absence of 12-phosphotungstic acid. In addition, In(OH)(H2O)(1,4-bdc) could not be obtained at the same pH range adjusted by other inorganic acids. This demonstrates that the heteropolyacid additive plays the role of structure-directing agent and pH adjusting agent in the reaction process. 3.2. Characterization The phase purity of In(OH)(H2O)(1,4-bdc) was confirmed by PXRD measurement and PXRD pattern of the as-synthesized sample is very consistent with the simulated one (Fig. 1). The differences in intensity may be owing to the preferred orientation of the powder samples. Thermogravimetric analysis (TGA) of In(OH)(H2O)(1,4-bdc) was conducted under air atmosphere in range from 25 to 800 °C to determine its thermal stability which is deemed an important property for coordination polymers [26]. As shown in Fig. S1, In(OH)(H2O)(1,4-bdc) partially loses the lattice water from 120 to 300 °C and then decomposes rapidly. The weight loss of 61.2% is in agreement with the decomposition of In(OH)(H2O)(1,4-bdc) to InO1.5 (calcd 61.4%). The residue at 800 °C is identified to be In2O3 by PXRD measurement. 3.3. Structural description In(OH)(H2O)(1,4-bdc) crystallizes in the orthorhombic Pnma space group, there are one In(III) ion and one 1,4-bdc ligand in the asymmetric unit. As shown in Fig. 2, the In In(III) ion is
2.4. Catalytic experiment Activation of the catalysts was performed by freeze-drying method [25]: after washing with MeOH and CH2Cl2, the resultant sample was further washed with benzene several times. The suspension of the sample in benzene was then frozen at 0 °C. After three freeze– thaw cycles, the sample cell was placed under dynamic vacuum in an ice/H2O bath for 24 h. The ice/H2O bath was removed and the sample was kept under vacuum at room temperature for another 24 h, and then heated under vacuum at 60 °C for 16 h. A typical cyanosilylation procedure was performed as follows: a quantity of 40 mg (0.12 mmol) of activated catalyst was suspended in dry acetonitrile (5 ml) followed by the addition of the aldehyde or ketone (0.5 mmol) and trimethylsilylcyanide (1.2 mmol). The reaction mixtures were stirred at room temperature under N2. The yields of the reactions were determined by 1H NMR spectroscopy and were calculated based on the carbonyl substrate. Catalytic recyclability was checked for three times with the same batch of catalyst, and no obvious decrease in activity was observed. The observed yields in three consecutive runs were 100%, 97%, and 98%, respectively.
Fig. 1. The simulated and experimental powder X-ray diffraction patterns for In(OH)(H2O)(1,4-bdc).
J. Xia et al. / Inorganica Chimica Acta 411 (2014) 35–39
seven-coordinated by four oxygen atoms from 1,4-bdc ligand, two oxygen atoms from two hydroxyl groups, and one from a water molecule to form a approximately pentagonal bipyramidal geometry. The carboxylate anions are completely deprotonated and their oxygen atoms lie in the equatorial plane together with one oxygen atom which is from a coordinated water molecule. The equatorial In–O bond lengths are In(1)–O(3)W = 2.212 Å, In(1)– O(1) = 2.279 Å(2), In(1)–O(2) = 2.309 Å(2), and the shorter axial bond lengths are 2.127 and 2.113 Å. The In(OH)(H2O)O4 units are linked to each other through trans hydroxyl groups and this generates an infinite bent –In–OH–In–OH– chains with In–OH–In angles of 136° running long the a axis (Fig. 3a). The two carboxylate oxygen atoms of 1,4-bdc ligand adopt a bis(chelating) coordination mode to link two indium centers from the different chains (Fig. 3b). The chains are parallel and connected each other through the 1,4-bdc ligands, creating a 3D extended network with one dimensional square-shaped channels delimited by the inorganic chains and the benzene rings of 1,4-bdc ligands (Fig. 4). The utilization of 1,4-bdc ligand has yielded a few of In(III) coordination polymers with variable frameworks [15,16,27–29], but only 6- and 8-coordination numbers of indium centers have been observed. 7-coordination geometry of indium center with the inclusion of one water molecule into the indium coordination sphere is first found in In(OH)(H2O)(1,4-bdc). In(OH)(H2O)(1,4bdc) and the previously reported In(OH)(1,4-bdc) (H2bdc)0.75 [27], both have single zigzag –In–OH–In– chains, but they exhibit the different frameworks that is determined by the geometry of indium center and the organic ligand. The axial oxygen groups of each InO6 unit in In(OH)(1,4-bdc) (H2bdc)0.75 are shared by neighboring octahedra to form a single zigzag –In–OH–In– chain. The two carboxylate groups of 1,4-bdc ligand link two adjacent InO6 octahedra in a bidentate bridging mode with a configuration l4-g1:g1:g1:g1 and the 180° angle between the carboxylate anions in 1,4-bdc results in the characteristic 3D framework with rhombus-shaped channels. In contrast, the indium atoms of In(OH)(H2O)(1,4-bdc) are seven-coordinated to form pentagonal bipyramidal centers. The indium oxide single chains constructed by In(OH)(H2O)O4 units are parallel and connected each other through the 1,4-bdc ligands with bis(chelating) coordination mode to form a 3D extended network with square-shaped channels.
Fig. 2. Coordination environment of In(III) atom in In(OH)(H2O)(1,4-bdc) with the ellipsoids drawn at the 50% probability level. The hydrogen atoms are omitted for clarity.
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Fig. 3. Arrangement of the chain of corner-sharing In(OH)2(H2O)O4 pentagonal bipyramids (a) and crystal packing along the a direction in In(OH)(H2O)(1,4-bdc) (b).
3.4. Property The capability of In(OH)(H2O)(1,4-bdc) as catalyst has been tested in the cyanosilylation of carbonylfunctionalized organic substrates. This reaction provides a convenient route to prepare cyanohydrins, which are key derivatives in the synthesis of fine chemicals and pharmaceuticals [30,31]. Our experiments employed a 1:2.4 M ratio of selected aromatic aldehydes and cyanotrimethylsilane in CH3CN at room temperature. Fig. 5 shows 1H NMR spectra for the cyanosilylation of p-nitrobenzaldehyde. The spectra were taken according to the different reaction time. The peak for CHO proton appears at 10.1 ppm, while peaks for the NO2–oPh–H proton and Ph–CH proton appear at 8.3 and 5.8 ppm, respectively. The gradually disappearing of the peaks at 10.1 and 8.3 ppm and promptly emerging of the peak at 5.8 ppm indicate the catalytic reaction proceeds smoothly. Kinetics results (Table 1) show a loading of 20 mol% of catalyst led to a 100% conversion of p-nitrobenzaldehyde after 94 h. More importantly, removal of catalyst by filtration after only 5 h completely shut down the reaction, affording only 25% total conversion upon standing for 20 h. This demonstrates that no homogeneous catalyst species exists in the reaction solution. In order to further investigate the generality of catalyst, we also study the influence of the different replace groups of aromatic aldehydes on the reaction under the same conditions. When the substrate aldehyde is replaced with o-nitrobenzaldehyde, m-nitrobenzaldehyde or 4-cyanobenzaldehyde, cyanosilylation goes smoothly and the highest conversion rate can reach 98%. When the substrate is p-bromobenzaldehyde, p-chlorobenzaldehyde or p-methoxybenzaldehyde, the reaction rates are all relatively slow. There are still small amount of the raw materials existence in reaction system even the reaction time is prolonged (maximum of 94 h) and the highest conversion yield is only 67%. When the substrate is p-fluorobenzaldehyde, cyanosilylation reaction cannot proceed. The experimental results also show that the solvent has an important effect on the reaction. The catalytic reaction cannot proceed in DMF. This may be attributed to the carbonyl group of DMF molecule being coordinated with metal center which makes the catalyst lose activity. The In(III) centers are also active in presence of dichloromethane, chloroform, tetrahydrofuran or dioxane. But when using tetrahydrofuran or dioxane as solvent, there are obviously side reactions observed in reaction system.
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Fig. 4. Crystal packing along the c direction showing square-shaped channels in In(OH)(H2O)(1,4-bdc).
Table 1 Cyanosilylation of aromatic aldehydes catalyzed by In(OH)(H2O)(1,4-bdc).
.
Entry
Ar
Reaction time (h)
Conversion (%)
1 2 3 4 5 6 7 8 9 10 11
p-nitrophenyl p-nitrophenyl p-nitrophenyl p-nitrophenyl o-nitrophenyl m-nitrophenyl p-cyanophenyl p-bromophenyl p-chlorophenyl p-methoxyphenyl p-fluorophenyl
0.5 5 20 94 94 94 94 94 94 94 120
2.5 25 52 100 98 98 98 67 60 53 trace
and the results show no change in the structure of the catalyst before and after reaction. 4. Conclusion
Fig. 5. 1H NMR spectrum for the cyanosilylation of p-nitrobenzaldehyde.
This new Lewis heterogeneous catalyst is stable in both water and organic solvents, being easily recovered by centrifugal separation and reused at least in three cycles without loss of yield or selectivity. The stability of the solid catalyst was checked by PXRD
In summary, a new In(III)-coordination polymer has been successfully prepared under solvothermal conditions using a mixture of rigid organic linker and inorganic heteropolyacid template. This new solid material exhibits chemical stability in various solvents, as well as good Lewis acid catalytic ability for cyanosilylation of aromatic aldehyde by virtue of its coordinatively unsaturated metal sites. Further investigations on such a new trivalent indium catalyst will be applied to a-amino acids synthetic reaction in our future work.
J. Xia et al. / Inorganica Chimica Acta 411 (2014) 35–39
Acknowledgements We thank the National Science Foundation of China (No. 20901028, 21201077, 21171065) and the Fundamental Research Funds for the Central Universities (No. 201103099) for financial support. Appendix A. Supplementary material CCDC 928050 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ 10.1016/j.ica.2013.11.014. References [1] [2] [3] [4] [5] [6] [7] [8]
M.H. Mir, S. Kitagawa, J.J. Vittal, Inorg. Chem. 47 (2008) 7728. Q.G. Zhai, C.Z. Lu, X.Y. Wu, S.R. Batten, Cryst. Growth Des. 7 (2007) 2332. S.R. Batten, R. Robson, Angew. Chem., Int. Ed. 37 (1998) 1460. M. Eddaoudi, D.B. Moler, H.L. Li, B.L. Chen, T.M. Reineke, M. O’Keeffe, O.M. Yaghi, Acc. Chem. Res. 34 (2001) 319. L. Carlucci, G. Ciani, D.M. Proserpio, Coord. Chem. Rev. 246 (2003) 247. P. Lama, A. Aijaz, E.C. Sañudo, P.K. Bharadwaj, Cryst. Growth Des. 10 (2010) 283. K. Koh, A.G. Wong-Foy, A.J. Matzger, J. Am. Chem. Soc. 131 (2009) 4184. M. Dinca˘, J.R. Long, Angew. Chem., Int. Ed. 47 (2008) 6766.
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[9] B.L. Chen, S.Q. Ma, F. Zapata, F.R. Fronczek, E.B. Lobkovsky, H.C. Zhou, Inorg. Chem. 46 (2007) 1233. [10] D.N. Dybtsev, A.L. Nuzhdin, H. Chun, K.P. Bryliakov, E.P. Talsi, V.P. Fedin, K. Kim, Angew. Chem., Int. Ed. 45 (2006) 916. [11] Christoph Janiak, Angew. Chem., Int. Ed. 36 (1997) 1431. [12] Christoph. Janiak, Dalton Trans. (2003) 2781. [13] Christoph. Janiak, Jana K. Vieth, New J. Chem. 34 (2010) 2366. [14] B.F.T. Cooper, C.L.B. Macdonald, J. Organomet. Chem. 693 (2008) 1707. [15] B. Gómez-Lor, E. Gutiérrez-Puebla, M. Iglesias, M.A. Monge, C. Ruiz-Valero, N. Snejko, Chem. Mater. 17 (2005) 2568–2573. [16] B. Gómez-Lor, E. Gutiérrez-Puebla, M. Iglesias, M.A. Monge, C. Ruiz-Valero, N. Snejko, Inorg. Chem. 41 (2002) 2429–2432. [17] J.S. Seo, D. Whang, H. Lee, S.I. Jun, J. Oh, Y.J. Jeon, K. Kim, Nature 4 (2004) 982. [18] S.T. Zheng, F. Zuo, T. Wu, B. Irfanoglu, C. Chou, R.A. Nieto, P.Y. Feng, X.H. Bu, Angew. Chem., Int. Ed. 50 (2011) 1849. [19] S. Huh, T.H. Kwon, N. Park, S.J. Kim, Y. Kim, Chem. Commun. (2009) 4953. [20] H. Eddaudi, H.L. Li, O.M. Yaghi, J. Am. Chem. Soc. 122 (2000) 1391. [21] S.S.Y. Chui, S.M.F. Lo, J.P.H. Charmant, A.G. Orpen, I.D. Williams, Science 283 (1999) 1148. [22] H. Kumagai, M. Akita-Tanaka, K. Inoue, M. Kurmoo, J. Mater. Chem. 11 (2001) 2146. [23] G.M. Sheldrick, SHELXTL-NT, Version 5.1, Bruker AXS Inc., Madison, WI, 1997. [24] D.T. Cromer, J.T. Weber, International Tables for X-ray Crystallography, Vol. 4, Kynoch Press, Birmingham, Al, 1974 (Table 2.2A). [25] L.Q. Ma, A. Jin, Z.G. Xie, W.B. Lin, Angew. Chem., Int. Ed. 48 (2009) 9905. [26] D.X. Xue, Y.Y. Lin, X.N. Cheng, X.M. Chen, Cryst. Growth Des. 7 (2007) 1332. [27] E.V. Anokhina, M. Vougo-Zanda, X. Wang, A.J. Jacobson, J. Am. Chem. Soc. 127 (2005) 15000. [28] J. Sun, L. Weng, Y. Zhou, J. Chen, Z. Chen, Z. Liu, D. Zhao, Angew. Chem., Int. Ed. 41 (2002) 4471. [29] M. Vougo-Zanda, X.Q. Wang, A.J. Jacobson, Inorg. Chem. 46 (2007) 8819. [30] R.J.H. Gregory, Chem. Rev. 99 (1999) 3649. [31] M. North, Tetrahedron: Asymmetry 14 (2003) 147.
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
A 3D In(III) coordination polymer derived from rigid dicarboxylate ligand: Synthesis, crystal structure and catalytic property Jing Xia a, Jifu Zheng b, Jianing Xu a, Li Wang a,⇑, Lu Yang a, Zhandong Su c, Yong Fan a,⇑ a
College of Chemistry, Jilin University, Changchun 130012, Jilin, PR China Key Laboratory of Polymer Ecomaterials, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China c College of Construction Engineering, Jilin University, Changchun 130026, Jilin, PR China b
a r t i c l e
i n f o
Article history: Received 17 July 2013 Received in revised form 6 November 2013 Accepted 13 November 2013 Available online 23 November 2013 Keywords: Indium coordination polymer Crystal structure Lewis acid Heterogeneous catalysis Cyanosilylation
a b s t r a c t A new indium coordination polymer, In(OH)(H2O)(1,4-bdc) (1,4-H2bdc = 1, 4-benzendicarboxylic acid), has been prepared under solvothermal conditions using a mixture of rigid organic linker and inorganic heteropolyacid (12-phosphotungstic acid) template. Single-crystal X-ray diffraction analysis reveals that this new compound possesses a 3D framework with the square-shaped channels constructed from the infinite indium-oxide chains and rigid 1,4-bdc ligands. This compound exhibits good catalytic activity for the cyanosilylation of aromatic aldehydes and can be reused three times without losing activity or significant mass. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction The design and synthesis of coordination polymers are currently interest and great challenge in chemistry and material science due to their fascinating architectures and topologies as well as their potential application as functional materials in many areas, such as magnetism, luminescence and catalysis [1–13]. In order to obtain coordination polymer with desirable topologies and properties, different metal ions were tested. Compared to widely investigated divalent transition metal ions, which are usually four- or six-coordinated, In(III) ions exhibit excellent structural and coordinative flexibility as six-coordinated octahedra MO6, seven-coordinated pentagonal bipyramids MO7, and eight-coordinated polyhedra MO8. Some indium complexes even adopt a high coordination number (e.g. 10) configuration [14]. Moreover, indium coordination polymers with thermally stable framework have been proved to possess interesting catalytic properties in the green chemistry [15,16]. For example, in premise of catalyst and substrate ratio being 0.1%, In2(OH)3(bdc)1.5 with supramolecular 3D framework can be used as efficient Lewis catalysts for hydrogenation of nitroaromatics and oxidation of sulfide reactions and can be recycled in successive runs by a simple filtration, without a significant loss of activity and selectivity [16]. On the other hand, the choice of organic moieties is also very important in the construction and structural tuning of coordination polymers, even small change in flexibility, length, functional group ⇑ Corresponding authors. Tel.: +86 431 88498786; fax: +86 431 85671974. E-mail addresses: [email protected] (L. Wang), [email protected] (Y. Fan). 0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2013.11.014
position, and symmetry of organic ligands can lead to remarkably different materials with diverse architectures and functions. Among various organic ligands, the aromatic dicarboxylate organic ligands are excellent structural builders because they are sterically rigid and chemically robust, leading to frameworks of high thermal stability approaching that of purely inorganic zeolites [17–19]. In particular, the utilization of 1,4-benzendicarboxylic acid (1,4H2bdc) has yielded many new non-interpenetrating frameworks with variable cavities or channels [20–22]. With the aim of preparing the novel coordination polymers, we conducted our studies on the solvothermal synthesis of In-based coordination polymer using rigid 1,4-H2bdc as ligand. Finally, in the presence of 12-phosphotungstic acid (H3PW12O40nH2O) as template, a new In(III) coordination polymer, In(OH)(H2O)(1,4bdc), has been successfully prepared. It possesses a 3D framework with the square-shaped channels that are built up from the infinite –In–OH–In– chains of corner-sharing In(OH)2(H2O)O4 pentagonal bipyramids and 1,4-bdc ligands. Moreover, this compound displays good catalytic activity for the cyanosilylation of aromatic aldehydes. Herein, we report the synthesis, crystal structure and catalytic property of this new In(III)-coordination polymer. 2. Experimental 2.1. Materials and Methods All chemicals were obtained from commercial sources and used without further purification. 12-phosphotungstic acid was
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purchased from Sinopharm Chemical Reagent Co., Ltd. Trimethylsilylcyanide was purchased from Alfa. Other reagents were purchased from Beijing chemical agent company. Powder X-ray diffraction (PXRD) data were obtained using SHIMADAZU XRD6000 diffractometer with Cu Ka radiation (k = 1.5418 Å), with the step size and the count time of 0.02° and 4 s, respectively. The elemental analysis was conducted on a Perkin Elmer 2400 elemental analyzer. FT-IR spectrum was recorded on a Nicolet Impact 410 spectrometer between 400 and 4000 cm1 using the KBr pellet method. Thermogravimetric analysis (TGA) was conducted on a Perkin-Elmer TGA 7 thermogravimetric analyzer with a heating rate of 10 °C min1 from room temperature to 800 °C. 1H NMR spectra were measured on a Bruker Avance 300 console at a frequency of 300 MHz. 2.2. Synthesis A mixture of 1,4-H2bdc (0.03 g, 0.18 mmol), InCl34H2O (0.05 g, 0.17 mmol), and H3PW12O40nH2O (0.01 g) were added to 1 ml N,N0 -dimethylformamide (DMF) and 5 ml acetonitrile (CH3CN) in a 23 ml Teflon-lined stainless steel vessel autoclave. The mixture was sealed and heated at 120 °C for 4 days. The colourless block crystals were obtained by filtration and washed by DMF several times. The yield of product was 70% in weight based on indium. The elemental analysis results are listed as follows: Anal. Calc. for In(OH)(H2O)(1,4-bdc): C, 30.61; H, 2.25. Found: C, 30.50; H, 2.16%. IR (KBr pellet, cm1): 3442 (br, m), 2965 (w), 2916 (w), 2058 (w), 1574 (s), 1505(w), 1422 (m), 1160 (s), 1062 (s), 945 (s), 855 (s), 772 (w), 744 (w), 551 (s), 467 (w). 2.3. Crystal structure determination The crystallographic data for In(OH)(H2O)(1,4-bdc) were collected on a Siemens Smart CCD diffractometer with graphitemonochromated Mo Ka (k = 0.71073 Å) radiation at a temperature of 293(2) K. No significant decay was observed during the data collection. Data processing was accomplished with the RAPID AUTO processing program. The structure was solved by direct method and refined by full-matrix least-squares on F2 using the SHELXTL crystallographic software package [23,24]. All indium atoms were located first, and then the oxygen and carbon atoms were subsequently found in difference Fourier maps. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms of ligands were generated geometrically.
3. Results and discussion 3.1. Synthesis Solvothermal synthesis method is widely used in the syntheses of coordination polymers and solvents show a remarkable influence on the terminal structures of coordination polymers. In(OH)(H2O)(1,4-bdc) was synthesized at a relatively low reaction temperature in mixed DMF/CH3CN solvents. When single DMF or CH3CN was used to replace mixed solvents for In(OH)(H2O)(1,4bdc) under the same condition, the same phases were not obtained which can be attributed to different polarity and solubility of solvents. It is found that no phosphotungstic acid was incorporated into the resulting framework of In(OH)(H2O)(1,4-bdc). Moreover, the products could not be obtained from a solution in absence of 12-phosphotungstic acid. In addition, In(OH)(H2O)(1,4-bdc) could not be obtained at the same pH range adjusted by other inorganic acids. This demonstrates that the heteropolyacid additive plays the role of structure-directing agent and pH adjusting agent in the reaction process. 3.2. Characterization The phase purity of In(OH)(H2O)(1,4-bdc) was confirmed by PXRD measurement and PXRD pattern of the as-synthesized sample is very consistent with the simulated one (Fig. 1). The differences in intensity may be owing to the preferred orientation of the powder samples. Thermogravimetric analysis (TGA) of In(OH)(H2O)(1,4-bdc) was conducted under air atmosphere in range from 25 to 800 °C to determine its thermal stability which is deemed an important property for coordination polymers [26]. As shown in Fig. S1, In(OH)(H2O)(1,4-bdc) partially loses the lattice water from 120 to 300 °C and then decomposes rapidly. The weight loss of 61.2% is in agreement with the decomposition of In(OH)(H2O)(1,4-bdc) to InO1.5 (calcd 61.4%). The residue at 800 °C is identified to be In2O3 by PXRD measurement. 3.3. Structural description In(OH)(H2O)(1,4-bdc) crystallizes in the orthorhombic Pnma space group, there are one In(III) ion and one 1,4-bdc ligand in the asymmetric unit. As shown in Fig. 2, the In In(III) ion is
2.4. Catalytic experiment Activation of the catalysts was performed by freeze-drying method [25]: after washing with MeOH and CH2Cl2, the resultant sample was further washed with benzene several times. The suspension of the sample in benzene was then frozen at 0 °C. After three freeze– thaw cycles, the sample cell was placed under dynamic vacuum in an ice/H2O bath for 24 h. The ice/H2O bath was removed and the sample was kept under vacuum at room temperature for another 24 h, and then heated under vacuum at 60 °C for 16 h. A typical cyanosilylation procedure was performed as follows: a quantity of 40 mg (0.12 mmol) of activated catalyst was suspended in dry acetonitrile (5 ml) followed by the addition of the aldehyde or ketone (0.5 mmol) and trimethylsilylcyanide (1.2 mmol). The reaction mixtures were stirred at room temperature under N2. The yields of the reactions were determined by 1H NMR spectroscopy and were calculated based on the carbonyl substrate. Catalytic recyclability was checked for three times with the same batch of catalyst, and no obvious decrease in activity was observed. The observed yields in three consecutive runs were 100%, 97%, and 98%, respectively.
Fig. 1. The simulated and experimental powder X-ray diffraction patterns for In(OH)(H2O)(1,4-bdc).
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seven-coordinated by four oxygen atoms from 1,4-bdc ligand, two oxygen atoms from two hydroxyl groups, and one from a water molecule to form a approximately pentagonal bipyramidal geometry. The carboxylate anions are completely deprotonated and their oxygen atoms lie in the equatorial plane together with one oxygen atom which is from a coordinated water molecule. The equatorial In–O bond lengths are In(1)–O(3)W = 2.212 Å, In(1)– O(1) = 2.279 Å(2), In(1)–O(2) = 2.309 Å(2), and the shorter axial bond lengths are 2.127 and 2.113 Å. The In(OH)(H2O)O4 units are linked to each other through trans hydroxyl groups and this generates an infinite bent –In–OH–In–OH– chains with In–OH–In angles of 136° running long the a axis (Fig. 3a). The two carboxylate oxygen atoms of 1,4-bdc ligand adopt a bis(chelating) coordination mode to link two indium centers from the different chains (Fig. 3b). The chains are parallel and connected each other through the 1,4-bdc ligands, creating a 3D extended network with one dimensional square-shaped channels delimited by the inorganic chains and the benzene rings of 1,4-bdc ligands (Fig. 4). The utilization of 1,4-bdc ligand has yielded a few of In(III) coordination polymers with variable frameworks [15,16,27–29], but only 6- and 8-coordination numbers of indium centers have been observed. 7-coordination geometry of indium center with the inclusion of one water molecule into the indium coordination sphere is first found in In(OH)(H2O)(1,4-bdc). In(OH)(H2O)(1,4bdc) and the previously reported In(OH)(1,4-bdc) (H2bdc)0.75 [27], both have single zigzag –In–OH–In– chains, but they exhibit the different frameworks that is determined by the geometry of indium center and the organic ligand. The axial oxygen groups of each InO6 unit in In(OH)(1,4-bdc) (H2bdc)0.75 are shared by neighboring octahedra to form a single zigzag –In–OH–In– chain. The two carboxylate groups of 1,4-bdc ligand link two adjacent InO6 octahedra in a bidentate bridging mode with a configuration l4-g1:g1:g1:g1 and the 180° angle between the carboxylate anions in 1,4-bdc results in the characteristic 3D framework with rhombus-shaped channels. In contrast, the indium atoms of In(OH)(H2O)(1,4-bdc) are seven-coordinated to form pentagonal bipyramidal centers. The indium oxide single chains constructed by In(OH)(H2O)O4 units are parallel and connected each other through the 1,4-bdc ligands with bis(chelating) coordination mode to form a 3D extended network with square-shaped channels.
Fig. 2. Coordination environment of In(III) atom in In(OH)(H2O)(1,4-bdc) with the ellipsoids drawn at the 50% probability level. The hydrogen atoms are omitted for clarity.
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Fig. 3. Arrangement of the chain of corner-sharing In(OH)2(H2O)O4 pentagonal bipyramids (a) and crystal packing along the a direction in In(OH)(H2O)(1,4-bdc) (b).
3.4. Property The capability of In(OH)(H2O)(1,4-bdc) as catalyst has been tested in the cyanosilylation of carbonylfunctionalized organic substrates. This reaction provides a convenient route to prepare cyanohydrins, which are key derivatives in the synthesis of fine chemicals and pharmaceuticals [30,31]. Our experiments employed a 1:2.4 M ratio of selected aromatic aldehydes and cyanotrimethylsilane in CH3CN at room temperature. Fig. 5 shows 1H NMR spectra for the cyanosilylation of p-nitrobenzaldehyde. The spectra were taken according to the different reaction time. The peak for CHO proton appears at 10.1 ppm, while peaks for the NO2–oPh–H proton and Ph–CH proton appear at 8.3 and 5.8 ppm, respectively. The gradually disappearing of the peaks at 10.1 and 8.3 ppm and promptly emerging of the peak at 5.8 ppm indicate the catalytic reaction proceeds smoothly. Kinetics results (Table 1) show a loading of 20 mol% of catalyst led to a 100% conversion of p-nitrobenzaldehyde after 94 h. More importantly, removal of catalyst by filtration after only 5 h completely shut down the reaction, affording only 25% total conversion upon standing for 20 h. This demonstrates that no homogeneous catalyst species exists in the reaction solution. In order to further investigate the generality of catalyst, we also study the influence of the different replace groups of aromatic aldehydes on the reaction under the same conditions. When the substrate aldehyde is replaced with o-nitrobenzaldehyde, m-nitrobenzaldehyde or 4-cyanobenzaldehyde, cyanosilylation goes smoothly and the highest conversion rate can reach 98%. When the substrate is p-bromobenzaldehyde, p-chlorobenzaldehyde or p-methoxybenzaldehyde, the reaction rates are all relatively slow. There are still small amount of the raw materials existence in reaction system even the reaction time is prolonged (maximum of 94 h) and the highest conversion yield is only 67%. When the substrate is p-fluorobenzaldehyde, cyanosilylation reaction cannot proceed. The experimental results also show that the solvent has an important effect on the reaction. The catalytic reaction cannot proceed in DMF. This may be attributed to the carbonyl group of DMF molecule being coordinated with metal center which makes the catalyst lose activity. The In(III) centers are also active in presence of dichloromethane, chloroform, tetrahydrofuran or dioxane. But when using tetrahydrofuran or dioxane as solvent, there are obviously side reactions observed in reaction system.
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Fig. 4. Crystal packing along the c direction showing square-shaped channels in In(OH)(H2O)(1,4-bdc).
Table 1 Cyanosilylation of aromatic aldehydes catalyzed by In(OH)(H2O)(1,4-bdc).
.
Entry
Ar
Reaction time (h)
Conversion (%)
1 2 3 4 5 6 7 8 9 10 11
p-nitrophenyl p-nitrophenyl p-nitrophenyl p-nitrophenyl o-nitrophenyl m-nitrophenyl p-cyanophenyl p-bromophenyl p-chlorophenyl p-methoxyphenyl p-fluorophenyl
0.5 5 20 94 94 94 94 94 94 94 120
2.5 25 52 100 98 98 98 67 60 53 trace
and the results show no change in the structure of the catalyst before and after reaction. 4. Conclusion
Fig. 5. 1H NMR spectrum for the cyanosilylation of p-nitrobenzaldehyde.
This new Lewis heterogeneous catalyst is stable in both water and organic solvents, being easily recovered by centrifugal separation and reused at least in three cycles without loss of yield or selectivity. The stability of the solid catalyst was checked by PXRD
In summary, a new In(III)-coordination polymer has been successfully prepared under solvothermal conditions using a mixture of rigid organic linker and inorganic heteropolyacid template. This new solid material exhibits chemical stability in various solvents, as well as good Lewis acid catalytic ability for cyanosilylation of aromatic aldehyde by virtue of its coordinatively unsaturated metal sites. Further investigations on such a new trivalent indium catalyst will be applied to a-amino acids synthetic reaction in our future work.
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Acknowledgements We thank the National Science Foundation of China (No. 20901028, 21201077, 21171065) and the Fundamental Research Funds for the Central Universities (No. 201103099) for financial support. Appendix A. Supplementary material CCDC 928050 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ 10.1016/j.ica.2013.11.014. References [1] [2] [3] [4] [5] [6] [7] [8]
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