pubs.acs.org/Langmuir © 2009 American Chemical Society
Layered Transition Metal Carboxylates: Efficient Reusable Heterogeneous Catalyst for Epoxidation of Olefins Rupam Sen,† Susmita Bhunia,† Dasarath Mal,† Subratanath Koner,*,† Yoshitaro Miyashita,‡ and Ken-Ichi Okamoto‡ †
Department of Chemistry, Jadavpur University, Kolkata 700 032, India, and ‡Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan Received February 25, 2009. Revised Manuscript Received September 24, 2009
Layered metal carboxylates [M(malonato)(H2O)2]n (M=Ni(II) and Mn(II)) that have a claylike structure have been synthesized hydrothermally and characterized. The interlayer separation in these layered carboxylates is comparable to that of the intercalation distance of the naturally occurring clay materials or layered double hydroxides (LDHs). In this study, we have demonstrated that, instead of intercalating the metal complex into layers of the clay or LDH, layered transition metal carboxylates, [M(malonato)(H2O)2]n, as such can be used as a recyclable heterogeneous catalyst in olefin epoxidation reaction. Metal carboxylates [M(malonato)(H2O)2]n exhibit excellent catalytic performance in olefin epoxidation reaction.
Introduction Oxidative transformations,1 especially epoxidation of alkenes, are the key chemical processes in biology,2 in synthetic organic chemistry, and in the chemical industry.3-5 In recent years, considerable advances have been made in the development of atom-efficient catalytic methods employing tert-butyl hydroperoxide (tert-BuOOH).6 The byproduct, tert-BuOH, generated from tert-butyl hydroperoxide can be separated by distillation or recycled for other industrial production, for example, methyl tert-butyl ether (MTBE). There is an ever-growing interest in the application of reusable catalysis for the synthesis of fine chemicals, including enantioselective reactions,7,8 which could reduce the large amounts of waste products often formed in noncatalytic organic synthesis. Immobilization of metal complexes into solid silica, aluminosilicate, or clay to design olefin epoxidation catalysts which allows *To whom correspondence should be addressed. E-mail: snkoner@ chemistry.jdvu.ac.in. (1) Backvall, J.-E., Ed. Modern Oxidation Methods; Wiley-VCH: Weinheim, Germany, 2004. (2) Wu, A. J.; Penner-Hahn, J. E.; Pecoraro, V. L. Chem. Rev. 2004, 104, 903. (3) (a) Lane, B. S.; Burgess, K. Chem. Rev. 2003, 103, 2457. (b) Sheldon, R. A.; Kochi, J. K. Metal-Catalyzed Oxidations of Organic Compounds; Academic Press: New York, 1981. (c) Brinksma, J.; de Boer, J. W.; Hage, R.; Feringa, B. L. In Modern Oxidation Methods; B€ackvall, J.-E., Ed.; Wiley-VCH: Weinheim, Germany, 2004; Chapter 10, p 295. (d) Noyori, R.; Aoki, M.; Sato, K. Chem. Commun. 2003, 1977. (e) Katsuki, T. Chem. Soc. Rev. 2004, 33, 437. (f) Punniyamurthy, T.; Velusamy, S.; Iqbal, J. Chem. Rev. 2005, 105, 2329. (4) Kolb, H. C.; Van Nieuwenhze, M. S.; Sharpless, K. B. Chem. Rev. 1994, 94, 2483. (5) (a) Nelson, D. W.; Gypser, A.; Ho, P. T.; Kolb, H. C.; Kondo, T.; Kwong, H.-L.; McGrath, D. V.; Rubin, A. E.; Norrby, P.-O.; Gable, K. P.; Sharpless, K. B. J. Am. Chem. Soc. 1997, 119, 1840. (b) Katsuki, T.; Sharpless, K. B. J. Am. Chem. Soc. 1980, 102, 5974. (c) Sato, K.; Aoki, M.; Ogawa, M.; Hashimoto, T.; Noyori, R. J. Org. Chem. 1996, 61, 8310. (d) Herrmann, W. A.; Fischer, R. W.; Marz, D. W. Angew. Chem., Int. Ed. Engl. 1991, 30, 1638. (6) Bregeault, J.-M. Dalton Trans. 2003, 3289. (7) (a) See for a recent review: Fraile, J. M.; Garcı´ a, J. I.; Mayoral, J. A. Chem. Rev. 2009, 109, 360. (b) Baiker, A.; Blaser H. U. Handbook of Heterogeneous Catalysis; Ertl, G., Kn€ozinger, H., Weitkamp, J., Eds.; VCH: Weinheim, 1997; Vol. 5, p 2432. (8) (a) See for a review: Thomas, J. M.; Raja, R. Acc. Chem. Res. 2008, 41, 708. (b) Bellocq, N.; Abramson, S.; Lasperas, M.; Brunel, D.; Moreau, P. Tetrahedron: Asymmetry 1999, 10, 3229. (c) Bae, S.-J.; Kim, S.-W.; Hyeon, T.; Kim, B.-M. Chem. Commun. 2000, 31.
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recycling of the catalyst and easy separation of the products attracts considerable attention.9-11 Clay minerals such as montmorillonite and kaolinite, and layered double hydroxides (LDHs) that afford space between the layers are found to be suitable for intercalation of a planar transition metal complex catalyst containing porphyrin, phthalocyanine, or Schiff-base ligands.12 The approach of performing heterogeneous enantioselective conversions under the spatial restrictions imposed by the cavities within which the reactions occur has spawned the design of numerous immobilized catalysts.9-13 The efficacy of homogeneous salenbased catalysts in olefin epoxidations was reported by Jacobsen et al.14 and Katsuki et al.15 in the early 1990s. This led to an extensive effort in the design of their heterogeneous analogues using porous solid as a matrix16 Anderson and co-workers used LDHs to intercalate metal-salen complexes to obtain catalysts for heterogeneous olefin epoxidation.17 Herein we demonstrate that instead of intercalating metal complex into layers of the clay or LDH, layered transition metal carboxylates as such can be used as heterogeneous catalysts in olefin epoxidation reaction. Metal carboxylates have rarely been used, so far, in heterogeneous catalytic oxidations.18 Interestingly, (9) (a) Thomas, J. M. Angew. Chem., Int. Ed. 1999, 38, 3588. (b) De Vos, D. E.; Dams, M.; Sels, B. F.; Jacobs, P. A. Chem. Rev. 2002, 102, 3615. (c) De Vos, D. E.; Sels, B. F.; Jacobs, P. A. Adv. Synth. Catal. 2003, 345, 457. (10) Corma, A.; Moliner, M.; Dı´ az-Caban~as, M. J.; Serna, P.; Femenia, B.; Primo, J.; Garcı´ a, H. New J. Chem. 2008, 32, 1338. (11) Holbach, M.; Weck, M. J. Org. Chem. 2006, 71, 1825. (12) (a) Bedioui, F. Coord. Chem. Rev. 1995, 144, 39. (b) Pinnavaia, T. J. Science 1983, 220, 365. (13) (a) Parton, R. F.; Vankelecom, I.; Bezoukhanova, C. P.; Casselman, M.; Uytterhoeven, J.; Jacobs, P. A. Nature 1994, 370, 541. (b) Jana, S.; Dutta, B.; Bera, R.; Koner, S. Langmuir 2007, 23, 2492 and references therein . (14) Jacobsen, E. N.; Zhang, W.; Muci, A. R.; Ecker, J. R.; Dent, L. J. Am. Chem. Soc. 1991, 113, 7063. (15) Irie, R.; Noda, K.; Ito, Y.; Matsumoto, N.; Katsuki, T. Tetrahedron: Asymmetry 1991, 2, 481. (16) (a) Li, C. Catal. Rev. 2004, 46, 419. (b) Li, C.; Zhang, H.; Jiang, D.; Yang, Q. Chem. Commun. 2007, 547. (c) Balezao, C.; Garcia, H. Chem. Rev. 2006, 106, 3987. (17) (a) Bhattacharjee, S.; Anderson, J. A. Chem. Commun. 2004, 554. (b) Bhattacharjee, S.; Dines, T. J.; Anderson, J. A. J. Phys. Chem. C 2008, 112, 14124. (18) (a) Alaerts, L.; Wahlen, J.; Jacobs, P. A.; De Vos, D. Chem. Commun. 2008, 1727. (b) Cho, S.-H.; Ma, B.; Nguyen, S. T.; Hupp, J. T.; Albrecht-Schmitt, T. E. Chem. Commun. 2006, 2563. (c) Alkordi, M. H.; Liu, Y.; Larsen, R. W.; Eubank, J. F.; Eddaoudi, M. J. Am. Chem. Soc. 2008, 130, 12639.
Published on Web 10/29/2009
DOI: 10.1021/la902945x
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zeolite-like three-dimensional carboxylate-based metal organic frameworks have been used to encapsulate metalloporphyrin in a recent study.18c This zeotype compound is capable of catalyzing oxidation of cyclohexane in heterogeneous medium. Nevertheless, to our knowledge, the present study is the first example of using of layered transition metal carboxylates as heterogeneous catalysts in olefin epoxidation.
Experimental Section Materials. Nickel nitrate hexahydrate, manganese nitrate tetrahydrate, malonic acid, sodium hydroxide, cyclooctene, styrene, trans-β-methyl styrene, 1-octene, 1-hexene, and tertbutyl hydroperoxide (70% aqueous) were purchased from Aldrich and were used as received, and solvents were purchased from Merck (India). The solvents were distilled and dried before use. Physical Measurements. Fourier transformed infrared spectra of KBr pellets were measured on a Shimadzu S-8400 FTIR spectrometer. The metal content of the sample was estimated on a PerkinElmer A-Analyst 200 atomic absorption spectrometer (sensitivity up to parts per billion). The powder X-ray diffraction (XRD) patterns of the samples were recorded with a Scintag XDS-2000 diffractometer using Cu KR radiation. The products of the catalytic reactions were identified and quantified by using a Varian CP-3800 gas chromatograph with a CP-Sil 8 CB capillary column. Other instruments used in this study were the same as reported earlier.13b Synthesis of [Ni(Malonate)(H2O)2]n (1) and [Mn(Malonate)(H2O)2]n (2). Complexes [Ni(malonato)(H2O)2]n (1) and
[Mn(malonato)(H2O)2]n (2) were prepared hydrothermally; complex 1 was grown as a green block crystal in a Teflon-lined Parr acid digestion bomb at 120 °C for 3 days, followed by slow cooling at the rate of 5 °C/h to room temperature. For digestion, Ni(NO3)2, malonic acid, NaOH, and Milli-Q water were added in the molar ratio of 1:1:2:550. Initially, the pH of the reaction mixture was 6.5. The pH was found to be 6 after the reaction was over. The crystals thus formed were filtered off, washed with a little amount of ethyl alcohol, and dried in air. Complex 2 was prepared in a similar manner by using Mn(NO3)2 instead of Ni(NO3)2 with the same molecular ratio of reactants as that of the nickel analogue. Compound 2 crystallized as light pink needles. Yields were ca. 45% and 58% (based on metal) for 1 and 2, respectively. For preliminary characterization of the compounds, elemental analysis and IR spectroscopic study were undertaken. AAS analysis shows that compound 1 contains 29.9% nickel (calcd. 29.83%) and compound 2 contains 28.6% manganese (calcd. 28.47%). Anal. Calcd. for [Ni(malonate)(H2O)2] 1: C=18.35, H=3.20; found C=18.30, H=3.04. Selected IR peaks (KBr disk, cm-1): 1623, 1577 [υas (CO2-)], 1406 [υs (CO2-)], 1284, 1176 [υs (C-O)], and 3500-3200 [υ(O-H); s.br]. Anal. Calcd. for [Mn(malonate)(H2O)2] 2: C=18.67, H=3.13; found C=18.47, H=3.20. Selected IR peaks (KBr disk, cm-1): 1669, 1573 [υas (CO2-)], 1449 [υs (CO2-)], 1284, 1178 [υs (C-O)], and 3500-3200 [υ(O-H); s.br]. Catalytic Reactions. The catalytic reactions were carried out in a glass batch reactor according to the following procedure. Substrate, solvent, and finely powdered catalysts were first mixed. The mixture was then equilibrated to 70 °C in an oil bath. After addition of tert-BuOOH, the reaction mixture was stirred continuously for 24 h. The products of the epoxidation reactions were collected at different time intervals and were identified and quantified by gas chromatography and verified by GCMS.
Results and Discussion Synthesis of Complexes 1 and 2. Synthesis of complexes 1 and 2 through a nonhydrothermal process has been reported in 13668 DOI: 10.1021/la902945x
the literature.19,20 In the present study, we used the hydrothermal technique to synthesize 1 and 2. The hydrothermal method is traditionally used to grow high quality phase pure single crystals. This method has been used extensively for the preparation of zeolites and mesoporous silica,21 and it is now being used as an effective and routine technique for synthesizing inorganic coordination polymers in crystalline form. We used the method to enhance the crystallinity of the compounds. The crystal sizes we obtained in the hydrothermal process were typically ca. 1.5 1.5 1.1 mm3 for compound 1 and 1.5 0.5 0.5 mm3 for compound 2, which were much larger than those were obtained in the nonhydrothermal process.19,20 The crystals were ground to fine powder before using them in catalytic reactions. Structural Similarities between Compounds 1 and 2 and Clay. The molecular structure of both the compounds was determined by single crystal X-ray diffraction measurement. The X-ray crystal structure of 1 has been reported by Delgado et al. in a previous study, while structure of 2 was reported by Lis and Matuszewski.19,20 Both of the complexes feature a twodimensional layered structure. Metal ions have an exclusive MO6 [M=Ni(II) and Mn(II)] octahedral coordination environment. All four oxygen atoms of the malonato ligand are coordinated to metal centers in the basal plane; the other two coordination sites of the octahedron are occupied by the oxygen atom of the H2O molecule to give rise to a coordination environment, MO6. All the metal ions are bridged to each other through carboxylato ligands to form the layer. However, MO6 octahedrons do not share edges or corners with each other. Layers are stacked along the crystallographic a-axis in complex 1, while they are stacked along the b-axis in complex 2 (see Supporting Information Figures S1 and S2). Though in the earlier study complexes were prepared through a nonhydrothermal route, there were practically no differences in the crystal structure with the present complexes (see Supporting Information Tables S1 and S2). The separation between the two consecutive layers in 1 is around 3.131 A˚ (Ni-Ni=5.441 A˚), while in the case of 2 layers are separated by a distance of 2.187 A˚ (Mn-Mn=5.391 A˚). Both 1 and 2 have close similarity with the layered structure of clay (Figure 1). The intercalation distance of clay (for example, intercalation distance in montmorillonite is 2.4-3.0 A˚) is comparable to the separation between two consecutive layers in compounds 1 and 2. Epoxidation Reactions. Olefin epoxidation reactions catalyzed by nickel and manganese complexes in homogeneous and heterogeneous medium and the mechanism involved in these reactions are well established.24-26 Epoxidation of olefins (19) Delgado, F. S.; Hernandez-Molina, M.; Sanchiz, J.; Ruiz-Perez, C.; Rodrı´ guezMartı´ n, Y.; Lopez, T.; Lloret, F.; Julve, M. CrystEngComm 2004, 6, 106. (20) Lis, T.; Matuszewski, J. Acta Crystallogr. 1979, 35B, 2212. (21) (a) Barrer, R. M. Hydrothermal Chemistry of Zeolites; Academic Press: London, 1982. (b) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S. Nature 1992, 359, 710. (c) Asefa, T.; MacLachlan, M. J.; Coombs, N.; Ozin, G. A. Nature 1999, 402, 867. (c) Kumar, R.; Bhaumik, A.; Ahedi, R. K.; Ganapathy, S. Nature 1996, 381, 298. (22) Molecular graphics software DIAMOND 3.1 was used for polyhedral drawing. Bergerhoff, G.; Berndt, M.; Brandenburg, K. J. Res. Natl. Inst. Stand. Technol. 1996, 101, 221. (23) Gruner, W. J. Z. Kristallogr. 1932, 83, 75. (24) See for a review: (a) Deubel, D. V.; Frenking, G.; Gisdakis, P.; Herrmann, W. A.; R€osch, N.; Sundermeyer, J. Acc. Chem. Res. 2004, 37, 645. (b) Joergensen, K. A. Chem. Rev. 1989, 89, 431. (25) (a) Feiters, M. C.; Metselaar, G. A.; Wentzel, B. B.; Nolte, R. J. M.; Nikitenko, S.; Sherrington, D. C.; Joly, Y.; Yu, G.; Antonina, S.; Kravtsova, N.; Soldatov, A. V. Ind. Eng. Chem. Res. 2005, 44, 8631. (b) Ramanathan, A.; Archipov, T.; Maheswari, R.; Hanefeld, U.; Roduner, E.; Gl€aser, R. J. Phys. Chem. C 2008, 112, 7468. (26) (a) Mirkhani, V.; Moghadam, M.; Tangestaninejad, S.; MohammadpoorBaltork, I.; Shams, E.; Rasouli, N. Appl. Catal., A 2008, 334, 106. (b) Jhung, S. H.; Lee, J.-H.; Cheetham, A. K.; Ferey, G.; Chang, J.-S. J. Catal. 2006, 239, 97.
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over a variety of nickel and manganese containing clay catalysts under heterogeneous conditions have been studied in the recent past.27-30 Nevertheless, reports on heterogeneous catalytic reactions over metal-organic frameworks (MOFs) are scarce in the literature. Horcajada et al. employed a hydrothermally synthesized iron(III) carboxylate zeotype metal-organic framework in Friedel-Crafts benzylation catalysis.31 Metalloporphyrin encapsulated into zeolite-like three-dimensional metal-organic frameworks efficiently catalyze oxidation of cyclohexane with tert-BuOOH.18c Cd containing MOF catalyzes the Knoevenagel condensation in heterogeneous medium.32 Notably, this catalytic system shows size selectivity of the reactants. Recently Corma et al. reported heterogeneous catalytic oxidation of tetralin with molecular oxygen using copper-based MOFs.33 However, metal carboxylate catalyzed epoxidation reactions, in heterogeneous medium, have never been explored. In this study, layered metal carboxylates are found to be catalytically active in epoxidation reactions of olefins with tert-BuOOH in heterogeneous conditions. Aromatic and aliphatic alkenes react with tert-BuOOH to produce epoxides with remarkable selectivity and in good yield using [Ni(malonate)(H2O)2]n 1 and [Mn(malonate)(H2O)2]n 2 in acetonitrile (Table 1). Epoxides are very useful and versatile
intermediates for the synthesis of many commodity and fine chemicals as well as pharmaceuticals and agrochemicals. Alkyl-hydroperoxides are used on a large scale in industrial epoxidation, for example, in Halcon-Arco and Sumitomo processes.6,34 Recycling of coproducts, for example, tert-BuOH has been realized in the Sumitomo process. The results of the catalytic epoxidation of different substrates, undertaken in the present study, are summarized in Table 1. The epoxidation of cyclooctene goes smoothly, showing an excellent conversion (90% and 93% for 1 and 2, respectively) to form cyclooctene oxide with 100% selectivity. Epoxidation of cyclooctene usually does not show such a level of selectivity in homogeneous medium. For example, in oxidation of cyclooctene catalyzed by metal complexes in homogeneous medium, epoxide was not the sole product; along with the desired epoxide, cyclooctane-1,2-diol was also generated.35 Oxidation of cyclooctene was studied over Mn(II) Schiff-base intercalated montmorillonite clay (natural clay, Zenith-N) catalysts using 30% H2O2 as oxidant which shows a conversion of ca. 58%.29 Epoxide conversion in this reaction improves substantially (85%) on intercalation of the Mn(II) salen complex into montmorillonite K-10.36 In the latter case, iodosylbenzene (PhIO) was used as oxidant. Recycling of the catalysts could not be realized if PhIO is used, because it is impossible to completely free the catalyst from PhIO2, a disproportionate product of PhIO.37 Recently, Trujillano et al. reported epoxidation of cyclooctene over different nickel(II) containing saponite clay catalysts using 70% H2O2 and obtained a maximum olefin conversion of ca. 20%.27 Oxidation of styrene over various types of silicate or clay catalysts has been receiving intense attention for a long time.27-29 Choudary et al. studied epoxidation of styrene over different Mn(II)-salen immobilized clay catalysts which showed up to 90% conversion with a maximum turnover of 240.36 However, the catalysts suffer extensive leaching of the manganese complex. Styrene conversion was only 12% in the case of Mn(II) Schiff-base intercalated montmorillonite clay (natural clay, Zenith-N) catalyst.29 Although a remarkable improvement of conversion of styrene has been obtained in the case of Mn(III) Schiff-base intercalated pillared clay catalysts, the yield of epoxide was not impressive (
