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Journal of Nanomaterials
Volume 2015, Article ID 674752, 6 pages
http://dx.doi.org/10.1155/2015/674752
Research Article

Mesoporous Silica-Supported Sulfonyldiamine Ligand for Microwave-Assisted Transfer Hydrogenation

1Faculty of Industrial Sciences and Technology, Universiti Malaysia Pahang, 26300 Gambang, Kuantan, Malaysia
2Nanotechnology and Catalysis Research Centre (NanoCat), University of Malaya, Level 3, Block A, IPS Building, 50603 Kuala Lumpur, Malaysia

Received 21 July 2014; Accepted 26 August 2014

Academic Editor: Wei-Chun Chen

Copyright © 2015 Shaheen M. Sarkar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

N-Sulfonyl-1,2-diamine ligands, derived from 1,2-diaminocyclohexane and 1,2-diaminopropane, were immobilized onto mesoporous SBA-15 silica. The SBA-15-supported sulfonyldiamine-Ru complex was prepared in situ under microwave heating at 60 W for 3 min. The prepared sulfonyldiamine-Ru complex was used as an efficient catalyst for the transfer hydrogenation of ketones to the corresponding secondary alcohols. The heterogeneous complex showed extremely high catalytic activity with 99% conversion rate under microwave heating condition. The complexes were regenerated by simple filtration and reused two times without significant loss of activity.

1. Introduction

Catalytic transfer hydrogenation of ketones and imines is an attractive method for the preparation of alcohols or amines [13]. Several homogeneous catalysts have been proposed for the transfer hydrogenation reactions [410]. However, the separation and recycling of homogeneous catalysts are complicated. Therefore, attempts were made to attach the catalyst to an insoluble support to improve the handling and separation of catalyst from the reaction mixture and also its recycling [1113]. Several homogeneous catalysts were immobilized on supports such as dendritic polymers [1416], silica [17], polystyrene [18, 19], biphasic catalysis [20], and Al-SBA-15 materials [21]. However, despite having highly ordered mesoporous structures with uniform pore diameter (6~7 nm) and high surface area, very few catalysts were tested on silica SBA-15 matrix [2224].

Due to well-known silicon chemistry, various organic groups could be robustly anchored in the surface of SBA-15 silica. This strategy would offer practical advantages such as simplified separation, easy recovery, and potential reuse of catalyst over traditional solution-phase chemistry [25]. Our interest in recyclable immobilized catalysts led us to prepare mesoporous SBA-15-supported -sulfonyl-1,2-diaminocyclohexane and 1,2-diaminopropane ligands and their Ru complexes for transfer hydrogenation reaction. Since heterogeneous catalysis typically requires long reaction time, we used here microwave-assisted reactions which occur much faster than conventional heating reactions [2628]. To the best of our knowledge, we described here SBA-15-supported N-sulfonyl-1,2-diaminocyclohexane and 1,2-diaminopropane ligands and their Ru complexes for the heterogeneous transfer hydrogenation of ketones under microwave irradiation conditions for the first time.

2. Experimental

2.1. Preparation of the Mesoporous SBA-15 Silica

Mesoporous silica SBA-15 was synthesized according to Zhao et al. [24]. Briefly, 4 g of Pluronic P123 was dissolved in 30 g of water and 120 g of 2 M HCI solution at room temperature under vigorous stirring. Then 8.5 g of TEOS was added into that solution under stirring. The reaction mixture was maintained at room temperature for 10–12 h and then at 60°C for 48 h and then kept at 120°C for 24 h under static conditions in a Teflon-lined autoclave to generate materials with uniform pore diameter from 4 to 10 nm. The solid product was recovered and washed with DI water.

2.2. Preparation of the Trimethoxysilated N-Sulfonyl-1,2-diamines 2

To a solution of 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (400 mg, 1.23 mmoL) in CH2Cl2 (10 mL) was slowly added a solution of 1,2-diaminocyclohexane 1a (140 mg, 1.23 mmoL) and triethylamine (124 mg, 1.23 mmoL) in CH2Cl2 (7 mL) at −10°C. The reaction mixture was allowed to warm at room temperature and stirred for 2 h. The mixture was diluted with CH2Cl2 and washed with cold water. The organic layer was dried over MgSO4 and concentrated under reduced pressure. The crude product was purified by flash chromatography to give trimethoxysilylated N-sulfonyl-1,2-diaminocyclohexane 2a in 85% yield. Compound 2b was similarly prepared from 1,2-diaminopropane 1b in 78% yield.

2.3. Preparation of the SBA-15-Supported Sulfonyldiamines 3

SBA-15 silica (1.0 g) was added to a solution of compound 2a (110 mg, 0.27 mmoL) in toluene (15 mL) and the mixture was refluxed for 18 h. After filtration, the powder was washed several times with methylene chloride and dried under vacuum at 70°C to give SBA-15-supported N-sulfonyldiamine 3a. Weight gain showed that 0.18 mmoL/g of compound 2a was grafted in 1.0 g of SBA-15-silica 3a. The SBA-15-supported N-sulfonyldiamine 3b was also prepared from compound 2b by the same procedure. Weight gain showed that 0.15 mmoL/g of compound 2b was anchored in 1.0 g of the SBA-15 silica 3b.

2.4. Characterization of the SBA-15-Supported Ligand 3

Mesostructures of the synthesized materials were identified by powder X-ray diffractions (XRD). The XRD patterns were obtained by using a Rigaku Multiflex diffractometer with a monochromated high-intensity radiation ( Å). Scanning was performed under ambient conditions over the region of 0.6–4.5° at the rate of 0.1°/min (20 kV, 10 mA). The XRD diffractograms showed three peaks at 100, 110, and 200 which revealed that the synthesized structure was cubic Im3m. The transmission electron microscopy (TEM) was performed with a FEI Tecnai microscope operated at 200 kV. The TEM sample was prepared by placing a few drops of SBA-15 powder dispersed in ethanol on a carbon grid and allowed to dry for 5 min before TEM analysis. Some of the samples, which have big particles, were crushed by submerging them in liquid nitrogen followed by mechanical grinding in a mortar prior to acetone dispersion. The nitrogen adsorption-desorption measurements were performed at −196°C on a Micromeritics ASAP 2020 surface area and porosity analyzer. Approximately, 0.5 g of SBA-15 was degassed at 300°C for 9 h before the measurement. The surface area determination was performed by the Brunauer-Emmett-Teller (BET) method [29] over the relative pressure range of 0.05–0.2, and the pore-size distribution was determined using the Broekhoff-de Boer (BdB) method [30] applied to the adsorption branch. Finally, the total pore volume was calculated from the amount of adsorbed N2 at , and the microporous volume was determined using the -plot method.

2.5. Transfer Hydrogenation of Ketones under Microwave Irradiation

SBA-15-supported ligand 3 (0.03 mmoL) was suspended in water (2 mL) and heated with [Ru(p-cymene)Cl2]2 (6.12 mg, 0.01 mmoL) for 3 min under MW (60 W). Ketone (1 mmoL) and HCO2Na (340 mg, 5 mmoL) were added to the solution and heated under MW (40~60 W) for short reaction time (Table 2) and the conversion was monitored by GC analysis. After completion of the reaction (GC analysis), the mixture was cooled at room temperature and diluted with diethyl ether. The organic layer was washed by brine and dried over MgSO4. The crude product was purified by short column chromatography.

3. Results and Discussion

Preparation of the SBA-15-supported N-sulfonyldiamine 3a and N-sulfonyldiamine 3b was performed in a two-step reaction shown in Scheme 1. Reaction of 1,2-diaminocyclohexane with 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane produced trimethylsilylated N-sulfonyl-1,2-diaminocyclohexane 2a with a yield of 85%. Subsequent condensation of 2a with the surface silanols of SBA-15 silica support in refluxing toluene yielded immobilized N-sulfonyldiamine SBA-15 silica 3a (loading ratio: 0.18 mmoL/g).

Scheme 1: Preparation of the SBA-15-supported N-sulfonyldiamine 3. (i) 2-(4-Chlorosulfonylphenyl)ethyltrimethoxysilane, triethylamine, CH2Cl2  −10°C to room temperature, 2 h; (ii) SBA-15, toluene, 105°C, 18 h.

Similarly, immobilized N-sulfonyldiamine 3b (loading ratio: 0.15 mmoL/g) was obtained from 1,2-diaminopropane. The loading ratios for the SBA-15-supported N-sulfonyldiamines were determined by measuring weight gain. The TEM images are obtained after the modification of the parent SBA-15 silica which showed that the hexagonal symmetry of the pore arrays is conserved after immobilization of organic moiety onto the SBA-15 silica (Figure 1). The hexagonal symmetry of the pore arrays also appeared in XRD analysis (Figure 2).

Figure 1: TEM images of parent SBA-15- and SBA-15-supported ligands 3a and 3b.
Figure 2: XRD pattern of modified SBA-15.

The BET surface area and pore diameter of the SBA-15 silica were measured before and after immobilizing the ligand (Table 1 and Figure 3). It was clearly observed that both the surface area and pore diameter were significantly decreased following the modifications.

Table 1: Structural information of the SBA-15-supported sulfonyldiamine 3.
Table 2: Microwave-assisted transfer hydrogenation in the presence of 3a.
Figure 3: Nitrogen adsorption-desorption isotherms.

The SBA-15-supported Ru(II) complexes were prepared in situ by MW-assisted heating of a mixture of [Ru(p-cymene)Cl2]2 and the supported ligand 3 in H2O at 1 : 3 ratio. With the SBA-15-supported N-sulfonyldiamine ligand 3a, we first performed microwave-assisted transfer hydrogenation of acetophenone (1 mmoL) as a model substrate using [Ru(p-cymene)Cl2]2 (0.01 mmoL) and 0.03 mmoL of ligand 3a in aqueous HCO2Na under 80 W microwave irradiation. The catalyst showed high activity and provided corresponding alcohol in a quantitative yield within 30 min reaction time (Table 2, entry 1). Surprisingly, the catalyst showed outstanding catalytic activity to give the corresponding alcohol when the microwave power decreased to 60 W (entries 2, 3). When the MW power was further decreased to 50–40 W, the conversion was also decreased (entries 4, 5). The propiophenone and -tetralone were smoothly converted into the corresponding alcohol with excellent yield (entries 7, 8).

Recently, Baruwati et al. [31] reported magnetically recoverable supported ruthenium catalyzed transfer hydrogenation of carbonyl compounds in isopropanol at 100°C under microwave irradiation conditions. In this study, we performed hydrogen transfer reaction in pure water under mild reaction condition, which is safer, more economical, more convenient, and greener for industrial applications.

Finally, we examined the transfer hydrogen reaction of 3-chloroacetophenone and 2-acetylnaphthalene substrates and excellent results were obtained under the same microwave irradiation conditions (entries 9–12). The MW-assisted reaction reached completion with quantitative conversion within 25 min with a TOF of up to 245 h−1 in presence of SBA-15-supported ligand 3a (entry 9). The conversions seemed to be insensitive to substituent or structure of the substrates. It is noteworthy that the Ru catalyst could be reused with consistent catalytic activity (entry 3). The SBA-15-supported ligand 3b also showed similar catalytic activity to ligand 3a under similar reaction conditions (entries 6, 10).

4. Conclusion

We have prepared recyclable SBA-15-supported N-sulfonyl-1,2-diamine ligands from 1,2-diaminocyclohexane and 1,2-diaminopropane. Microwave-assisted heating was employed for heterogeneous Ru-catalyzed transfer hydrogenation of ketones. The immobilized N-sulfonyldiamine Ru-complex showed extremely high catalytic activity (TOF 245 h−1) under microwave heating condition. Moreover, the catalyst could be reused without significant loss of activity.

Conflict of Interests

All authors declare that this paper does not have any content with conflict of interests.

Acknowledgment

The authors acknowledge the Universiti Malaya Fund no. RP005A-13AET to Md. Eaqub Ali.

References

  1. E. N. Jacobsen, A. Pfaltz, and H. Yamamoto, Eds., Comprehensive Asymmetric Catalysis, Springer, Berlin, Germany, 1999.
  2. M. J. Palmer and M. Wills, “Asymmetric transfer hydrogenation of C = O and C = N bonds,” Tetrahedron Asymmetry, vol. 10, no. 11, pp. 2045–2061, 1999. View at Publisher · View at Google Scholar · View at Scopus
  3. S. Gladiali and E. Alberico, “Asymmetric transfer hydrogenation: chiral ligands and applications,” Chemical Society Reviews, vol. 35, no. 3, pp. 226–236, 2006. View at Publisher · View at Google Scholar · View at Scopus
  4. W. Baratta, J. Schütz, E. Herdtweck, W. A. Herrmann, and P. Rigo, “Fast transfer hydrogenation using a highly active orthometalated heterocyclic carbene ruthenium catalyst,” Journal of Organometallic Chemistry, vol. 690, no. 24-25, pp. 5570–5575, 2005. View at Publisher · View at Google Scholar · View at Scopus
  5. R. Noyori and S. Hashiguchi, “Asymmetric transfer hydrogenation catalyzed by chiral ruthenium complexes,” Accounts of Chemical Research, vol. 30, no. 2, pp. 97–102, 1997. View at Publisher · View at Google Scholar · View at Scopus
  6. R. A. W. Johnstone, A. H. Wilby, and I. D. Entwistle, “Heterogeneous catalytic transfer hydrogenation and its relation to other methods for reduction of organic compounds,” Chemical Reviews, vol. 85, no. 2, pp. 129–170, 1985. View at Publisher · View at Google Scholar · View at Scopus
  7. S. Horn, C. Gandolfi, and M. Albrecht, “Transfer hydrogenation of ketones and activated olefins using chelating NHC ruthenium complexes,” European Journal of Inorganic Chemistry, vol. 18, no. 2, pp. 2863–2868, 2011. View at Google Scholar
  8. W. Ye, M. Zhao, and Z. Yu, “Ruthenium(II) pyrazolyl-pyridyl-oxazolinyl complex catalysts for the asymmetric transfer hydrogenation of ketones,” Chemistry, vol. 18, no. 35, pp. 10843–10846, 2012. View at Publisher · View at Google Scholar
  9. M. D. Le Page and B. R. James, “Nickel bromide as a hydrogen transfer catalyst,” Chemical Communications, no. 17, pp. 1647–1648, 2000. View at Google Scholar · View at Scopus
  10. R. Kadyrov and T. H. Riermeier, “Highly enantioselective hydrogen-transfer reductive amination: catalytic asymmetric synthesis of primary amines,” Angewandte Chemie, vol. 115, no. 44, pp. 5630–5632, 2003. View at Publisher · View at Google Scholar
  11. P. N. Liu, P. M. Gu, F. Wang, and Y. Q. Tu, “Efficient heterogeneous asymmetric transfer hydrogenation of ketones using highly recyclable and accessible silica-immobilized Ru-TsDPEN catalysts,” Organic Letters, vol. 6, no. 2, pp. 169–172, 2004. View at Publisher · View at Google Scholar
  12. C. Saluzzo and M. Lamaire, “Homogeneous-supported catalysts for enantioselective hydrogenation and hydrogen transfer reduction,” Advanced Synthesis & Catalysis, vol. 344, no. 9, pp. 915–928, 2002. View at Publisher · View at Google Scholar
  13. X. Li, X. Wu, W. Chen, E. F. Hancock, F. King, and J. Xiao, “Asymmetric transfer hydrogenation in water with a supported Noyori−Ikariya catalyst,” Organic Letters, vol. 6, no. 19, pp. 3321–3324, 2004. View at Publisher · View at Google Scholar
  14. Y.-C. Chen, T.-F. Wu, J.-G. Deng et al., “Dendritic catalysts for asymmetric transfer hydrogenation,” Chemical Communications, no. 16, pp. 1488–1489, 2001. View at Google Scholar · View at Scopus
  15. Y.-C. Chen, T.-F. Wu, J.-G. Deng et al., “Multiple dendritic catalysts for asymmetric transfer hydrogenation,” Journal of Organic Chemistry, vol. 67, no. 15, pp. 5301–5306, 2002. View at Publisher · View at Google Scholar · View at Scopus
  16. Y.-C. Chen, T.-F. Wu, L. Jiang et al., “Synthesis of dendritic catalysts and application in asymmetric transfer hydrogenation,” Journal of Organic Chemistry, vol. 70, no. 3, pp. 1006–1010, 2005. View at Publisher · View at Google Scholar · View at Scopus
  17. P. N. Liu, J. G. Deng, Y. Q. Tu, and S. H. Wang, “Highly efficient and recyclable heterogeneous asymmetric transfer hydrogenation of ketones in water,” Chemical Communications, vol. 10, no. 18, pp. 2070–2071, 2004. View at Publisher · View at Google Scholar · View at Scopus
  18. D. J. Bayston, C. B. Travers, and M. E. C. Polywka, “Synthesis and evaluation of a chiral heterogeneous transfer hydrogenation catalyst,” Tetrahedron Asymmetry, vol. 9, no. 12, pp. 2015–2018, 1998. View at Publisher · View at Google Scholar · View at Scopus
  19. R. Ter Halle, E. Schulz, and M. Lemaire, “Heterogeneous enantioselective catalytic reduction of ketones,” Synlett, vol. 1997, no. 11, pp. 1257–1258, 1997. View at Publisher · View at Google Scholar · View at Scopus
  20. T. J. Geldbach and P. J. Dyson, “A versatile ruthenium precursor for biphasic catalysis and its application in ionic liquid biphasic transfer hydrogenation: conventional vs task-specific catalysts,” Journal of the American Chemical Society, vol. 126, no. 26, pp. 8114–8115, 2004. View at Publisher · View at Google Scholar · View at Scopus
  21. M. J. Gracia, J. M. Campelo, E. Losada, R. Luque, J. M. Marinas, and A. A. Romero, “Microwave-assisted versatile hydrogenation of carbonyl compounds using supported metal nanoparticles,” Organic and Biomolecular Chemistry, vol. 7, no. 23, pp. 4821–4824, 2009. View at Publisher · View at Google Scholar · View at Scopus
  22. A. P. Wright and M. E. Davies, “Design and preparation of organic−inorganic hybrid catalysts,” Chemical Reviews, vol. 102, no. 10, pp. 3589–3614, 2002. View at Publisher · View at Google Scholar
  23. J. Y. Ying, C. P. Mehnert, and M. S. Wong, “Synthesis and applications of supramolecular-templated mesoporous materials,” Angewandte Chemie International Edition, vol. 38, pp. 56–77, 1999. View at Google Scholar
  24. D. Zhao, Q. Huo, J. Feng, B. F. Chemlka, and G. D. Stucky, “Nonionic triblock and star diblock copolymer and oligomeric surfactant syntheses of highly ordered, hydrothermally stable, mesoporous silica structures,” Journal of the American Chemical Society, vol. 120, pp. 6024–6036, 1998. View at Publisher · View at Google Scholar
  25. N. E. Leadbeater and M. Marco, “Preparation of polymer-supported ligands and metal complexes for use in catalysis,” Chemical Reviews, vol. 102, no. 10, pp. 3217–3274, 2002. View at Publisher · View at Google Scholar · View at Scopus
  26. C. O. Kappe, “Controlled microwave heating in modern organic synthesis,” Angewandte Chemie International Edition, vol. 43, no. 46, pp. 6250–6284, 2004. View at Publisher · View at Google Scholar
  27. T. Marimuthu and H. B. Friedrich, “Microwave-assisted transfer hydrogenation of ketones by Ru(xantphos) arene complexes,” ChemCatChem, vol. 4, no. 12, pp. 2090–2095, 2012. View at Publisher · View at Google Scholar · View at Scopus
  28. A. Bengtson, A. Hallberg, and M. Larhed, “Fast synthesis of aryl triflates with controlled microwave heating,” Organic Letters, vol. 4, no. 7, pp. 1231–1233, 2002. View at Publisher · View at Google Scholar · View at Scopus
  29. S. Brunauer, P. H. Emmett, and E. Teller, “Adsorption of gases in multimolecular layers,” Journal of the American Chemical Society, vol. 60, no. 2, pp. 309–319, 1938. View at Publisher · View at Google Scholar · View at Scopus
  30. W. W. Lukens Jr., P. Schmidt-Winkel, D. Zhao, J. Feng, and G. D. Stucky, “Evaluating pore sizes in mesoporous materials: a simplified standard adsorption method and a simplified Broekhoff-de Boer method,” Langmuir, vol. 15, no. 16, pp. 5403–5409, 1999. View at Publisher · View at Google Scholar · View at Scopus
  31. B. Baruwati, V. Polshettiwar, and R. S. Varma, “Magnetically recoverable supported ruthenium catalyst for hydrogenation of alkynes and transfer hydrogenation of carbonyl compounds,” Tetrahedron Letters, vol. 50, no. 11, pp. 1215–1218, 2009. View at Publisher · View at Google Scholar · View at Scopus