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Efficient Suzuki reaction catalyzed by recyclable clay carbapalladacycle nanocomposite in ionic liquid media
Tetrahedron Letters xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Efficient Suzuki reaction catalyzed by recyclable clay carbapalladacycle nanocomposite in ionic liquid media Amanpreet Kaur, Vasundhara Singh ⇑ Department of Applied Sciences (Chemistry), PEC University of Technology, Chandigarh, India
a r t i c l e
i n f o
Article history: Received 28 November 2014 Revised 6 January 2015 Accepted 7 January 2015 Available online xxxx Keywords: Carbapalladacycle Na+-MMT clay Organic–inorganic hybrid material Suzuki reaction Ionic liquid
a b s t r a c t In this Letter, we report the efficient recyclability and recoverability of ionic tagged carbapalladacycle and its hybrid MMT clay-nanocomposite catalyst in ionic liquid media [TMBA]NTf2 for the Suzuki reaction. It has several distinct advantages which include the use of low levels of catalyst concentration, formation of desired products in high yields and good selectivity using chloro, bromo and iodo substituted aryl halides, and negligible formation of homo coupling products. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Palladium catalyzed Suzuki cross coupling reaction of aryl halides with aryl boronic acids or esters is an important carbon– carbon bond formation reaction for the synthesis of substituted biaryls.1–4 The substituted biaryl moiety is present in many pharmaceutically active compounds, herbicides, polymers, new materials, liquid crystals and ligands5 to mention a few. Over the decades, several homogenous palladium based catalysts have been developed and reported in the literature to promote the Suzuki reaction.6,7 Among these, Najera et al.8 have developed oxime based palladacycle catalysts having unique properties of being thermally robust, air and moisture insensitive and avoid the use of phosphine ligands which get oxidized during the reaction. However, despite the various advantages associated with these catalysts, difficulties are encountered with regard to their separation and recoverability in the reaction process. Further, based on the preference of the chemical industry and in the context of green chemistry, the heterogenization of an active homogenous catalyst is of interest for improved recyclability and recoverability, wherein the catalyst has both an expensive metal and ligand incorporated in it.9 In the past, this heterogenization has been achieved by covalent or ionic immobilization on inorganic support materials such as clays,10 silica,11 zeolites,12 polymers13 and most recently, using ionic14,15 and florous tags16,17 to ⇑ Corresponding author. Tel.: +91 9888222214. E-mail address: [email protected] (V. Singh).
mention a few. Among these, Montmorillonite clay, an inexpensive and naturally occurring material, can act as an excellent host to active homogenous catalysts by ion exchange due to its smectite structure and two dimensional lamellar form.18 This ionic immobilization results in the formation of a stable organic–inorganic hybrid catalytic system, particularly for metal and metal–ligand complex based catalysts.19 The reaction medium used in any reaction is also of great significance and in particular, the use of benign reaction medium such as water20,21 and ionic liquids22,23 has proven to be excellent substitutes to the previously used high boiling solvents, such as DMF in the Suzuki reaction.24 In continuation to our ongoing research program on the development of new recyclable and recoverable heterogeneous catalysts based on ionic liquids25 and solid supports,26,27 we had previously developed a clay based carbapalladacycle nanocomposite catalyst and successfully carried out the Heck and Sonogashira reaction.28 Encouraged by our previous results, we have expanded the application of ammonium tagged oxime carbapalladacycle (1) and its clay nanocomposite (2) as shown in Figure 1, for executing Suzuki reaction in ionic liquid media. The reaction was also tried in aqueous medium but lower yields (65% for model reaction) were obtained. Recyclability of the catalyst has also been carried out upto seven cycles. The IR, NMR, and mass spectral data of catalysts (1) and (2) were comparable with those reported in the literature. The optimization of reaction conditions for model Suzuki reaction as shown in Scheme 1, has been done with respect to catalyst
http://dx.doi.org/10.1016/j.tetlet.2015.01.055 0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Kaur, A.; Singh, V. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.01.055
2
A. Kaur, V. Singh / Tetrahedron Letters xxx (2015) xxx–xxx
Figure 1. Ammonium tagged oxime carbapalladacycle (1) and its clay nanocomposite (2).
OCH3
Cl
Cl
B(OH)2
+
Catalyst (1/2) 2 equiv K2CO3
OCH3
[TMBA]NTf 2 80oC
I
Scheme 1. General scheme for the model Suzuki reaction using catalyst (1) and (2).
concentration, temperature, reaction time, base and ionic liquid/ aqueous media used in the reaction. Initial assessment of the catalyst (1) was done by optimization of catalyst loading, time, and temperature of reaction between 4iodoanisole and 3-chlorophenylboronic acid as the model reaction with Na2CO3 and [TMBA]NTf2 [tetramethyl butyl ammonium bis (trifluoromethanesulfonyl) imide] as the base and solvent respectively as shown in Table 1. In the reaction carried out over a time period of 12 h, the catalyst concentration was varied from 0.05 mol % to 0.006 mol % (entries 1–4). The lowest concentration of catalyst at which maximum yield was obtained was found to be 0.012 mol % (entry 3). The effect of time of reaction was also studied by reducing it to 6 h for catalyst concentration of 0.025 mol % (entry 5) and 0.012 mol % (entry 6), but a lower yield of 73% and 55%, respectively of the desired product was obtained. Further lowering of reaction temperature to 60 °C resulted in a decrease in yield to 62% (entry 7). Accordingly, a precatalyst loading of 0.012 mol % of Pd was used at 80 °C for 12 h for our subsequent experiments as the optimized reaction conditions.
Further, it is known that nature of base is also a very important factor for determining the efficiency of the Suzuki cross-coupling reaction.29–31 Therefore, the influence of various organic and inorganic bases was investigated for Suzuki coupling reaction of 4iodoanisole and 3-chlorophenylboronic acid in [TMBA]NTf2 and the results are summarized in Table 2. The results show that Na2CO3 (Table 2, entry 1) is the best choice as compared to the other bases. We also explored the possibility of carrying out the model Suzuki reaction with catalyst (1) in water as the reaction media under optimized reaction conditions. The desired biaryl product was obtained in a lower GC–MS yield of 65.87% and the recoverability of the catalyst from the aqueous media also posed a problem. Under the optimized conditions, as determined for catalysts (1) (Pd content 2.39 mmol/1 g of clay as determined by AAS), the reaction was also carried out with catalyst (2) (Pd content 1.178 mmol/ 1 g of clay as determined by AAS) and both the catalysts were further employed for the Suzuki reaction with various phenylboronic acids using 4-iodoanisole and 4-bromoanisole as illustrated in
Table 1 Effect of catalyst loading, time, and temperature on Suzuki reactiona
Table 2 Effect of base on Suzuki reactiona
a
Entry (mol % of Pd)
Catalyst
Time (h)
Temp (°C)
Yieldb (%)
Entry
Base
Yieldb (%)
1 2 3 4 5 6 7
0.05 0.025 0.012 0.006 0.025 0.012 0.012
12 12 12 12 6 6 12
80 80 80 80 80 80 60
98 97 96 47 73 55 62
1 2 3 4 5 6
Na2CO3 CH3COONa3H2O Et3N Morpholine K2CO3 Na3PO412H2O
96 30 67 44 75 83
Reaction condition: 4-iodoanisole (0.1 g, 1 mmol), 3-chlorophenylboronic acid (0.1 g, 1.5 mmol), catalyst (1), Na2CO3 (2 mmol), TMBA]NTf2 (0.5 ml). b Isolated yield.
a Reaction condition: 4-iodoanisole (0.1 g, 1 mmol), 3-chlorophenylboronic acid (0.1 g, 1.5 mmol), catalyst (1) (0.012 mol % of Pd), Base (2 mmol), TMBA]NTf2 (0.5 ml), 80 °C, 12 h. b Isolated yield.
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A. Kaur, V. Singh / Tetrahedron Letters xxx (2015) xxx–xxx Table 3 Optimized results of Suzuki reaction with 4-iodoanisole/4-bromoanisole at 80 °C in 12 h using catalyst (1) and (2) in [TMBA] NTf2a Entry
Boronic acid
Catalyst
Yieldb (%)
TON
TOF (h
1
1
3-Chlorophenylboronic acid
2
3-Nitrophenylboronic acid
3
4-Methoxyphenylboronic acid
4
m-Tolyphenylboronic acid
(1) (2) (1) (2) (1) (2) (1) (2)
96/84 95/83 92/82 93/80 87/89 89/89 90/84 91/83
8000/7000 7916/6916 7666/6833 7750/6666 7250/7416 7416/7416 7500/7000 7583/6916
667/583 660/576 639/569 646/556 604/618 618/618 625/583 632/576
)
a Reaction condition: 4-iodoanisole/4-bromoanisole (0.1 g, 1 mmol), boronic acid (1.5 mmol), catalyst (0.012 mol % of Pd), Na2CO3 (2 mmol), TMBA]NTf2 (0.5 ml), 80 °C, 12 h; b Isolated yield.
Figure 2. Recycling experiments of Suzuki reaction of 4-iodoanisole and 3chlorophenylboronic acid.
% Conversion
Table 3. The yield of products with 4-bromoanisole was slightly lower and in the range of 80 to 89%. GC–MS analysis of the product mixture indicated the absence of formation of Glaser type homocoupling products. The Suzuki reaction was extended to the coupling of chlorobenzene with various phenylboronic acids as shown in Table 4. However, the Suzuki coupling of chlorobenzene was difficult to proceed under optimized conditions and gave very poor yield of the desired products. No change in yield was observed even after increasing the time of reaction to 18 h, temperature to 100 °C and catalyst concentration to 0.025 mol % of Pd. The absence of catalytically active species in the solution leached from the solid was studied for the model reaction using the hot filtration method by filtering the reaction mixture when the reaction had proceeded to nearly 50% completion. The clear filtrate solution was allowed to react for an additional 48 h and the isolated product was analyzed by GC–MS analysis. No further progress of reaction was observed, which confirmed the absence of leaching of palladium. For recycling studies, seven consecutive reactions were carried out with the same catalyst at the same substrate-to-catalyst ratio on the model reaction under optimized conditions, as shown in Scheme 1. Both catalysts exhibit decreasing activities but the immobilized clay nanocomposite performs better even after seven cycles for the Suzuki reaction, as there was no significant decrease in the final conversion of the product formed. No change in selectivity was noticed upto five cycles while in sixth and seventh cycles, 2% decrease in selectivity was observed. The results for the recycling studies are as shown in Figure 2. No precipitation of palladium black was observed indicating the stability of the catalyst (1) in ionic liquid media and catalyst (2) due to immobilization in the interlayers of clay and in ionic liquid media. Kinetics of the reaction was studied using catalyst (1) and (2) under optimized conditions and the results are as shown in Figure 3 indicating comparable behavior of both the catalysts. In conclusion, we have efficiently executed the Suzuki coupling reaction using (1) and (2) catalysts both in homogeneous as well as
Time(h-1)
Figure 3. Kinetic curves of Suzuki reaction of 4-iodoanisole and 3-chlorophenylboronic acid.
heterogeneous phases having the unique properties of being air and moisture insensitive, thermally stable, are used in low concentration, and are both recyclable and recoverable in nature. The ionic liquid used as reaction medium was critical for immobilization of the catalysts and was recyclable also. The inert ammonium
Table 4 Optimized results of Suzuki reaction with chlorobenzene at 80 °C using catalyst (1) and (2) in [TMBA] NTf2a
a b
Entry
Boronic acid
Catalyst
Time (h)
Yieldb (%)
TON
TOF (h
1
3-Chlorophenylboronic acid
2
3-Nitrophenylboronic phenylboronic
3
4-Methoxyphenylboronic acid
4
m-Tolyphenylboronic acid
(1) (2) (1) (2) (1) (2) (1) (2)
12 18 12 12 12 18 12 18
60 55 24 26 58 52 51 50
5000 4483 2000 2166 4833 4333 4250 4166
417 249 167 180 403 241 354 231
Reaction condition: chlorobenzene (0.1 g, 1 mmol), boronic acid (1.5 mmol), catalyst (0.012 mol % of Pd), Na2CO3 (2 mmol), TMBA]NTf2 (0.5 ml), 80 °C, 12–18 h. Isolated yield.
Please cite this article in press as: Kaur, A.; Singh, V. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.01.055
1
)
4
A. Kaur, V. Singh / Tetrahedron Letters xxx (2015) xxx–xxx
tag did not interfere in the course of the reaction and neat products were obtained in high yields and purity. Further studies for optimizing reaction conditions in aqueous media using these catalysts are underway. 1.1. General procedure for Suzuki reaction of aryl halides In a 25 ml round bottom flask, the catalyst (1) (0.1 mg, 0.012 mol % Pd)/ catalyst (2) (0.2 mg, 0.012 mol % Pd) was dissolved in [TMBA]NTf2 (0.5 ml). To this were added, 4-iodoanisole (0.1 g, 1 mmol), 3-chlorophenyl boronic acid (0.1 g, 1.5 mmol), and sodium carbonate (0.09 g, 2 mmol). The mixture was magnetically stirred in a pre-heated oil bath at 80 °C for 12 h. The mixture was allowed to cool, extracted with diethyl ether (5 5 ml), and the ethereal phase was analyzed by GC–MS analysis. Further, the residue from the concentrated ethereal phase was purified by silica gel column chromatography (hexane/ethyl acetate; 9:1) to obtain the desired product. The catalyst and ionic liquid left after the reaction in the reaction flask were dried under vacuum and further subjected to a fresh dose of reactants to assess the recyclability of the catalyst and ionic liquid upto seven cycles. Acknowledgments The authors are thankful to PEC University of Technology, Chandigarh and TEQIP II (World Bank funded project) for fellowship and financial support, RSIC, Chandigarh and NIPER, Mohali for the analytical data. Supplementary data
References and notes 1. Stanforth, S. P. Tetrahedron 1998, 54, 263. 2. Marziale, A. N.; Jantke, D.; Faul, S. H.; Reiner, T.; Herdtweck, E.; Eppinger, J. Green Chem. 2011, 13, 169. 3. Mondal, M.; Bora, U. Green Chem. 1873, 2012, 14. 4. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457. 5. Suzuki, A.; Yamamoto, Y. Chem. Lett 2011, 40, 894. 6. Hayashi, T. J. Organomet. Chem. 2002, 653, 41. 7. Alonsa, D. A.; Najera, C.; Pacheco, M. C. J. Org. Chem. 2002, 67, 5588. 8. Alacid, E.; Alonsa, D. A.; Botella, L.; Najera, C.; Pacheco, M. C. Chem. Rec. 2006, 6, 117. 9. Gladysz, J. A. Pure Appl. Chem. 2001, 73, 1319. 10. Ding, G.; Wang, W.; Jiang, T.; Han, B. Green Chem. 2013, 15, 3396. 11. Baleizao, C.; Corma, A.; Garcia, H.; Leyva, A. Chem. Commun. 2003, 606 12. Guan, Z.; Hu, J.; Gu, Y.; Zhang, H.; Li, G.; Li, T. Green Chem. 1964, 2012, 14. 13. Edwards, G. A.; Trafford, M. A.; Hamilton, A. E.; Buxton, A. M.; Bardeaux, M. C.; Chalker, J. M. J. Org. Chem. 2014, 79, 2094. 14. Corma, A.; Garcia, H.; Leyva, A. Tetrahedron 2004, 60, 8553. 15. Tindale, J. J.; Ragogna, P. J. Can. J. Chem. 2010, 88, 27. 16. Susanto, W.; Chu, C.-Y.; Ang, W. J.; Chou, T.-C.; Lo, L. C.; Lam, Y. J. Org. Chem. 2012, 77, 2729. 17. Susanto, W.; Chu, C.-Y.; Ang, W. J.; Chou, T.-C.; Lo, L.-C.; Lam, Y. Green Chem. 2012, 14, 77. 18. Zhou, C. H. Appl. Clay Sci. 2011, 53, 87. 19. Valkenberg, M. H.; Holderich, W. F. Catal. Rev. 2002, 44, 320. 20. Polshettiwar, V.; Decottignes, A.; Len, C.; Fihri, A. ChemSusChem 2010, 3, 502. 21. Liu, N.; Liu, C.; Jin, Z. Green Chem. 2012, 14, 592. 22. Leadbeater, N. E. Chem. Commun. 2014, 1515 23. Prechtl, M. H. G.; Scholten, J. D.; Dupont, J. Molecules 2010, 15, 344. 24. Li, J.-H.; Zhu, Q.-M.; Xie, Y.-X. Tetrahedron 2006, 62, 10888. 25. Singh, V.; Kaur, S.; Sapehiyia, V.; Singh, J.; Kad, G. L. Catal. Commun. 2005, 6, 57. 26. Singh, V.; Kaur, S.; Ratti, R.; Singh, J.; Kad, G. L. Indian J. Chem. 2010, 493, 611. 27. Singh, V.; Kaur, S.; Ratti, R.; Vaultier, M. Catal. Commun. 2010, 11, 503. 28. Singh, V.; Kaur, S.; Ratti, R. J. Mol. Catal. A: Chem. 2011, 334, 13. 29. Amatore, C.; Jutand, A.; Duc, G. L. Chem. Eur. J. 2011, 17, 2492. 30. Amatore, C.; Jutand, A.; Duc, G. L. Chem. Eur. J. 2012, 18, 6616. 31. Amatore, C.; Duc, G. L.; Jutand, A. Chem. Eur. J. 2013, 19, 10082.
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2015.01. 055.
Please cite this article in press as: Kaur, A.; Singh, V. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.01.055
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Efficient Suzuki reaction catalyzed by recyclable clay carbapalladacycle nanocomposite in ionic liquid media Amanpreet Kaur, Vasundhara Singh ⇑ Department of Applied Sciences (Chemistry), PEC University of Technology, Chandigarh, India
a r t i c l e
i n f o
Article history: Received 28 November 2014 Revised 6 January 2015 Accepted 7 January 2015 Available online xxxx Keywords: Carbapalladacycle Na+-MMT clay Organic–inorganic hybrid material Suzuki reaction Ionic liquid
a b s t r a c t In this Letter, we report the efficient recyclability and recoverability of ionic tagged carbapalladacycle and its hybrid MMT clay-nanocomposite catalyst in ionic liquid media [TMBA]NTf2 for the Suzuki reaction. It has several distinct advantages which include the use of low levels of catalyst concentration, formation of desired products in high yields and good selectivity using chloro, bromo and iodo substituted aryl halides, and negligible formation of homo coupling products. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Palladium catalyzed Suzuki cross coupling reaction of aryl halides with aryl boronic acids or esters is an important carbon– carbon bond formation reaction for the synthesis of substituted biaryls.1–4 The substituted biaryl moiety is present in many pharmaceutically active compounds, herbicides, polymers, new materials, liquid crystals and ligands5 to mention a few. Over the decades, several homogenous palladium based catalysts have been developed and reported in the literature to promote the Suzuki reaction.6,7 Among these, Najera et al.8 have developed oxime based palladacycle catalysts having unique properties of being thermally robust, air and moisture insensitive and avoid the use of phosphine ligands which get oxidized during the reaction. However, despite the various advantages associated with these catalysts, difficulties are encountered with regard to their separation and recoverability in the reaction process. Further, based on the preference of the chemical industry and in the context of green chemistry, the heterogenization of an active homogenous catalyst is of interest for improved recyclability and recoverability, wherein the catalyst has both an expensive metal and ligand incorporated in it.9 In the past, this heterogenization has been achieved by covalent or ionic immobilization on inorganic support materials such as clays,10 silica,11 zeolites,12 polymers13 and most recently, using ionic14,15 and florous tags16,17 to ⇑ Corresponding author. Tel.: +91 9888222214. E-mail address: [email protected] (V. Singh).
mention a few. Among these, Montmorillonite clay, an inexpensive and naturally occurring material, can act as an excellent host to active homogenous catalysts by ion exchange due to its smectite structure and two dimensional lamellar form.18 This ionic immobilization results in the formation of a stable organic–inorganic hybrid catalytic system, particularly for metal and metal–ligand complex based catalysts.19 The reaction medium used in any reaction is also of great significance and in particular, the use of benign reaction medium such as water20,21 and ionic liquids22,23 has proven to be excellent substitutes to the previously used high boiling solvents, such as DMF in the Suzuki reaction.24 In continuation to our ongoing research program on the development of new recyclable and recoverable heterogeneous catalysts based on ionic liquids25 and solid supports,26,27 we had previously developed a clay based carbapalladacycle nanocomposite catalyst and successfully carried out the Heck and Sonogashira reaction.28 Encouraged by our previous results, we have expanded the application of ammonium tagged oxime carbapalladacycle (1) and its clay nanocomposite (2) as shown in Figure 1, for executing Suzuki reaction in ionic liquid media. The reaction was also tried in aqueous medium but lower yields (65% for model reaction) were obtained. Recyclability of the catalyst has also been carried out upto seven cycles. The IR, NMR, and mass spectral data of catalysts (1) and (2) were comparable with those reported in the literature. The optimization of reaction conditions for model Suzuki reaction as shown in Scheme 1, has been done with respect to catalyst
http://dx.doi.org/10.1016/j.tetlet.2015.01.055 0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Kaur, A.; Singh, V. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.01.055
2
A. Kaur, V. Singh / Tetrahedron Letters xxx (2015) xxx–xxx
Figure 1. Ammonium tagged oxime carbapalladacycle (1) and its clay nanocomposite (2).
OCH3
Cl
Cl
B(OH)2
+
Catalyst (1/2) 2 equiv K2CO3
OCH3
[TMBA]NTf 2 80oC
I
Scheme 1. General scheme for the model Suzuki reaction using catalyst (1) and (2).
concentration, temperature, reaction time, base and ionic liquid/ aqueous media used in the reaction. Initial assessment of the catalyst (1) was done by optimization of catalyst loading, time, and temperature of reaction between 4iodoanisole and 3-chlorophenylboronic acid as the model reaction with Na2CO3 and [TMBA]NTf2 [tetramethyl butyl ammonium bis (trifluoromethanesulfonyl) imide] as the base and solvent respectively as shown in Table 1. In the reaction carried out over a time period of 12 h, the catalyst concentration was varied from 0.05 mol % to 0.006 mol % (entries 1–4). The lowest concentration of catalyst at which maximum yield was obtained was found to be 0.012 mol % (entry 3). The effect of time of reaction was also studied by reducing it to 6 h for catalyst concentration of 0.025 mol % (entry 5) and 0.012 mol % (entry 6), but a lower yield of 73% and 55%, respectively of the desired product was obtained. Further lowering of reaction temperature to 60 °C resulted in a decrease in yield to 62% (entry 7). Accordingly, a precatalyst loading of 0.012 mol % of Pd was used at 80 °C for 12 h for our subsequent experiments as the optimized reaction conditions.
Further, it is known that nature of base is also a very important factor for determining the efficiency of the Suzuki cross-coupling reaction.29–31 Therefore, the influence of various organic and inorganic bases was investigated for Suzuki coupling reaction of 4iodoanisole and 3-chlorophenylboronic acid in [TMBA]NTf2 and the results are summarized in Table 2. The results show that Na2CO3 (Table 2, entry 1) is the best choice as compared to the other bases. We also explored the possibility of carrying out the model Suzuki reaction with catalyst (1) in water as the reaction media under optimized reaction conditions. The desired biaryl product was obtained in a lower GC–MS yield of 65.87% and the recoverability of the catalyst from the aqueous media also posed a problem. Under the optimized conditions, as determined for catalysts (1) (Pd content 2.39 mmol/1 g of clay as determined by AAS), the reaction was also carried out with catalyst (2) (Pd content 1.178 mmol/ 1 g of clay as determined by AAS) and both the catalysts were further employed for the Suzuki reaction with various phenylboronic acids using 4-iodoanisole and 4-bromoanisole as illustrated in
Table 1 Effect of catalyst loading, time, and temperature on Suzuki reactiona
Table 2 Effect of base on Suzuki reactiona
a
Entry (mol % of Pd)
Catalyst
Time (h)
Temp (°C)
Yieldb (%)
Entry
Base
Yieldb (%)
1 2 3 4 5 6 7
0.05 0.025 0.012 0.006 0.025 0.012 0.012
12 12 12 12 6 6 12
80 80 80 80 80 80 60
98 97 96 47 73 55 62
1 2 3 4 5 6
Na2CO3 CH3COONa3H2O Et3N Morpholine K2CO3 Na3PO412H2O
96 30 67 44 75 83
Reaction condition: 4-iodoanisole (0.1 g, 1 mmol), 3-chlorophenylboronic acid (0.1 g, 1.5 mmol), catalyst (1), Na2CO3 (2 mmol), TMBA]NTf2 (0.5 ml). b Isolated yield.
a Reaction condition: 4-iodoanisole (0.1 g, 1 mmol), 3-chlorophenylboronic acid (0.1 g, 1.5 mmol), catalyst (1) (0.012 mol % of Pd), Base (2 mmol), TMBA]NTf2 (0.5 ml), 80 °C, 12 h. b Isolated yield.
Please cite this article in press as: Kaur, A.; Singh, V. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.01.055
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A. Kaur, V. Singh / Tetrahedron Letters xxx (2015) xxx–xxx Table 3 Optimized results of Suzuki reaction with 4-iodoanisole/4-bromoanisole at 80 °C in 12 h using catalyst (1) and (2) in [TMBA] NTf2a Entry
Boronic acid
Catalyst
Yieldb (%)
TON
TOF (h
1
1
3-Chlorophenylboronic acid
2
3-Nitrophenylboronic acid
3
4-Methoxyphenylboronic acid
4
m-Tolyphenylboronic acid
(1) (2) (1) (2) (1) (2) (1) (2)
96/84 95/83 92/82 93/80 87/89 89/89 90/84 91/83
8000/7000 7916/6916 7666/6833 7750/6666 7250/7416 7416/7416 7500/7000 7583/6916
667/583 660/576 639/569 646/556 604/618 618/618 625/583 632/576
)
a Reaction condition: 4-iodoanisole/4-bromoanisole (0.1 g, 1 mmol), boronic acid (1.5 mmol), catalyst (0.012 mol % of Pd), Na2CO3 (2 mmol), TMBA]NTf2 (0.5 ml), 80 °C, 12 h; b Isolated yield.
Figure 2. Recycling experiments of Suzuki reaction of 4-iodoanisole and 3chlorophenylboronic acid.
% Conversion
Table 3. The yield of products with 4-bromoanisole was slightly lower and in the range of 80 to 89%. GC–MS analysis of the product mixture indicated the absence of formation of Glaser type homocoupling products. The Suzuki reaction was extended to the coupling of chlorobenzene with various phenylboronic acids as shown in Table 4. However, the Suzuki coupling of chlorobenzene was difficult to proceed under optimized conditions and gave very poor yield of the desired products. No change in yield was observed even after increasing the time of reaction to 18 h, temperature to 100 °C and catalyst concentration to 0.025 mol % of Pd. The absence of catalytically active species in the solution leached from the solid was studied for the model reaction using the hot filtration method by filtering the reaction mixture when the reaction had proceeded to nearly 50% completion. The clear filtrate solution was allowed to react for an additional 48 h and the isolated product was analyzed by GC–MS analysis. No further progress of reaction was observed, which confirmed the absence of leaching of palladium. For recycling studies, seven consecutive reactions were carried out with the same catalyst at the same substrate-to-catalyst ratio on the model reaction under optimized conditions, as shown in Scheme 1. Both catalysts exhibit decreasing activities but the immobilized clay nanocomposite performs better even after seven cycles for the Suzuki reaction, as there was no significant decrease in the final conversion of the product formed. No change in selectivity was noticed upto five cycles while in sixth and seventh cycles, 2% decrease in selectivity was observed. The results for the recycling studies are as shown in Figure 2. No precipitation of palladium black was observed indicating the stability of the catalyst (1) in ionic liquid media and catalyst (2) due to immobilization in the interlayers of clay and in ionic liquid media. Kinetics of the reaction was studied using catalyst (1) and (2) under optimized conditions and the results are as shown in Figure 3 indicating comparable behavior of both the catalysts. In conclusion, we have efficiently executed the Suzuki coupling reaction using (1) and (2) catalysts both in homogeneous as well as
Time(h-1)
Figure 3. Kinetic curves of Suzuki reaction of 4-iodoanisole and 3-chlorophenylboronic acid.
heterogeneous phases having the unique properties of being air and moisture insensitive, thermally stable, are used in low concentration, and are both recyclable and recoverable in nature. The ionic liquid used as reaction medium was critical for immobilization of the catalysts and was recyclable also. The inert ammonium
Table 4 Optimized results of Suzuki reaction with chlorobenzene at 80 °C using catalyst (1) and (2) in [TMBA] NTf2a
a b
Entry
Boronic acid
Catalyst
Time (h)
Yieldb (%)
TON
TOF (h
1
3-Chlorophenylboronic acid
2
3-Nitrophenylboronic phenylboronic
3
4-Methoxyphenylboronic acid
4
m-Tolyphenylboronic acid
(1) (2) (1) (2) (1) (2) (1) (2)
12 18 12 12 12 18 12 18
60 55 24 26 58 52 51 50
5000 4483 2000 2166 4833 4333 4250 4166
417 249 167 180 403 241 354 231
Reaction condition: chlorobenzene (0.1 g, 1 mmol), boronic acid (1.5 mmol), catalyst (0.012 mol % of Pd), Na2CO3 (2 mmol), TMBA]NTf2 (0.5 ml), 80 °C, 12–18 h. Isolated yield.
Please cite this article in press as: Kaur, A.; Singh, V. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.01.055
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tag did not interfere in the course of the reaction and neat products were obtained in high yields and purity. Further studies for optimizing reaction conditions in aqueous media using these catalysts are underway. 1.1. General procedure for Suzuki reaction of aryl halides In a 25 ml round bottom flask, the catalyst (1) (0.1 mg, 0.012 mol % Pd)/ catalyst (2) (0.2 mg, 0.012 mol % Pd) was dissolved in [TMBA]NTf2 (0.5 ml). To this were added, 4-iodoanisole (0.1 g, 1 mmol), 3-chlorophenyl boronic acid (0.1 g, 1.5 mmol), and sodium carbonate (0.09 g, 2 mmol). The mixture was magnetically stirred in a pre-heated oil bath at 80 °C for 12 h. The mixture was allowed to cool, extracted with diethyl ether (5 5 ml), and the ethereal phase was analyzed by GC–MS analysis. Further, the residue from the concentrated ethereal phase was purified by silica gel column chromatography (hexane/ethyl acetate; 9:1) to obtain the desired product. The catalyst and ionic liquid left after the reaction in the reaction flask were dried under vacuum and further subjected to a fresh dose of reactants to assess the recyclability of the catalyst and ionic liquid upto seven cycles. Acknowledgments The authors are thankful to PEC University of Technology, Chandigarh and TEQIP II (World Bank funded project) for fellowship and financial support, RSIC, Chandigarh and NIPER, Mohali for the analytical data. Supplementary data
References and notes 1. Stanforth, S. P. Tetrahedron 1998, 54, 263. 2. Marziale, A. N.; Jantke, D.; Faul, S. H.; Reiner, T.; Herdtweck, E.; Eppinger, J. Green Chem. 2011, 13, 169. 3. Mondal, M.; Bora, U. Green Chem. 1873, 2012, 14. 4. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457. 5. Suzuki, A.; Yamamoto, Y. Chem. Lett 2011, 40, 894. 6. Hayashi, T. J. Organomet. Chem. 2002, 653, 41. 7. Alonsa, D. A.; Najera, C.; Pacheco, M. C. J. Org. Chem. 2002, 67, 5588. 8. Alacid, E.; Alonsa, D. A.; Botella, L.; Najera, C.; Pacheco, M. C. Chem. Rec. 2006, 6, 117. 9. Gladysz, J. A. Pure Appl. Chem. 2001, 73, 1319. 10. Ding, G.; Wang, W.; Jiang, T.; Han, B. Green Chem. 2013, 15, 3396. 11. Baleizao, C.; Corma, A.; Garcia, H.; Leyva, A. Chem. Commun. 2003, 606 12. Guan, Z.; Hu, J.; Gu, Y.; Zhang, H.; Li, G.; Li, T. Green Chem. 1964, 2012, 14. 13. Edwards, G. A.; Trafford, M. A.; Hamilton, A. E.; Buxton, A. M.; Bardeaux, M. C.; Chalker, J. M. J. Org. Chem. 2014, 79, 2094. 14. Corma, A.; Garcia, H.; Leyva, A. Tetrahedron 2004, 60, 8553. 15. Tindale, J. J.; Ragogna, P. J. Can. J. Chem. 2010, 88, 27. 16. Susanto, W.; Chu, C.-Y.; Ang, W. J.; Chou, T.-C.; Lo, L. C.; Lam, Y. J. Org. Chem. 2012, 77, 2729. 17. Susanto, W.; Chu, C.-Y.; Ang, W. J.; Chou, T.-C.; Lo, L.-C.; Lam, Y. Green Chem. 2012, 14, 77. 18. Zhou, C. H. Appl. Clay Sci. 2011, 53, 87. 19. Valkenberg, M. H.; Holderich, W. F. Catal. Rev. 2002, 44, 320. 20. Polshettiwar, V.; Decottignes, A.; Len, C.; Fihri, A. ChemSusChem 2010, 3, 502. 21. Liu, N.; Liu, C.; Jin, Z. Green Chem. 2012, 14, 592. 22. Leadbeater, N. E. Chem. Commun. 2014, 1515 23. Prechtl, M. H. G.; Scholten, J. D.; Dupont, J. Molecules 2010, 15, 344. 24. Li, J.-H.; Zhu, Q.-M.; Xie, Y.-X. Tetrahedron 2006, 62, 10888. 25. Singh, V.; Kaur, S.; Sapehiyia, V.; Singh, J.; Kad, G. L. Catal. Commun. 2005, 6, 57. 26. Singh, V.; Kaur, S.; Ratti, R.; Singh, J.; Kad, G. L. Indian J. Chem. 2010, 493, 611. 27. Singh, V.; Kaur, S.; Ratti, R.; Vaultier, M. Catal. Commun. 2010, 11, 503. 28. Singh, V.; Kaur, S.; Ratti, R. J. Mol. Catal. A: Chem. 2011, 334, 13. 29. Amatore, C.; Jutand, A.; Duc, G. L. Chem. Eur. J. 2011, 17, 2492. 30. Amatore, C.; Jutand, A.; Duc, G. L. Chem. Eur. J. 2012, 18, 6616. 31. Amatore, C.; Duc, G. L.; Jutand, A. Chem. Eur. J. 2013, 19, 10082.
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2015.01. 055.
Please cite this article in press as: Kaur, A.; Singh, V. Tetrahedron Lett. (2015), http://dx.doi.org/10.1016/j.tetlet.2015.01.055