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Synlett 2011(3): 369-372  
DOI: 10.1055/s-0030-1259310
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

In Situ Generation of Palladium Nanoparticles: Reusable, Ligand-Free Heck Reaction in PEG-400 Assisted by Focused Microwave Irradiation

Zhengyin Du*a, Wanwei Zhoua, Lin Bai*b, Fen Wanga, Jin-Xian Wanga
a Key Laboratory of Eco-Environment Related Polymer Materials of Ministry of Education, Key Laboratory of Polymer Materials of Gansu Province & College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou 730070, P. R. of China
Fax: +86(931)7971989; e-Mail: zhengyin_du@nwnu.edu.cn;
b School of Chemistry and Environmental Sciences, Lanzhou City University, Lanzhou 730070, P. R. of China
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Publication History

Received 13 October 2010
Publication Date:
13 January 2011 (online)

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In Situ Generation of Palladium Nanoparticles: Reusable, Ligand-Free Heck Reaction in PEG-400 Assisted by Focused Microwave IrradiationSynlett 2011; 2011(19): 2905-2905
DOI: 10.1055/s-0031-1289897

Abstract

A rapid and efficient Heck coupling reaction of aryl iodides with terminal olefins was conducted in PEG-400 at 120 ˚C in the presence of potassium carbonate and palladium nanoparticles formed in situ from palladium chloride under focused microwave irradiation. High to excellent product yields were achieved. The reaction medium and catalyst could be easily recycled at least five times without significant loss in reactivity.

Key words

Heck reaction - ligand-free palladium catalysis - palladium nanoparticles - focused microwave irradiation - PEG-400 - green chemistry

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General Procedure for the Heck Coupling Reactions of Aryl Iodides with Terminal Olefins: In a 10-mL glass tube were placed aryl iodide (0.5 mmol), terminal olefin (0.6 mmol), K2CO3 (1.0 mmol), PdCl2 (0.005 mmol), PEG-400 (3 mL), and a magnetic stir bar. The vessel was sealed with a septum and placed into the microwave cavity. Microwave irradiation of 10 W was used, and the temperature was ramped from r.t. to 120 ˚C. Once the temperature of
120 ˚C was reached, the reaction mixture was held at this temperature for 12 min. After cooling the mixture to r.t., the reaction vessel was opened, the contents were extracted with Et2O (5 × 5 mL; for substrates with carboxyl group, acidification using hydrochloric acid was needed before extraction) and the combined organic layers were dried over anhyd MgSO4. The solvent was removed by evaporation under reduced pressure to afford the crude products, which were further purified by recrystallization or by column chromatography on silica gel using petroleum ether and EtOAc as eluent. The catalyst system (Pd-PEG) was recycled by the evaporation of Et2O and H2O under reduced pressure and could be reused directly in the next run.
Selected Data for Compound 1a: white crystal; mp 133-134 ˚C. ¹H NMR (400 MHz, CDCl3): δ = 12.13 (s, 1 H), 7.82 (d, J = 16.0 Hz, 1 H), 7.54-7.56 (m, 2 H), 7.39-7.43 (m, 3 H), 6.47 (d, J = 16.0 Hz, 1 H). ¹³C NMR (100 MHz, CDCl3): δ = 172.75, 147.12, 133.99, 130.75, 128.95, 128.36, 117.30. MS (EI): m/z = 148 [M+], 105, 77. IR: 1682, 1628, 1419, 767, 705 cm-¹. Anal. Calcd for C9H8O2 (148.05): C, 72.96; H, 5.44. Found: C, 72.64; H, 5.38.