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Synlett 2010(15): 2271-2274  
DOI: 10.1055/s-0030-1258018
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Copper-Free Sonogashira Coupling in Water with Linear Polystyrene-Stabilized PdO Nanoparticles

Takuto Teratania, Atsushi Ohtaka* a, Takahiro Kawashimaa, Osamu Shimomuraa, Ryôki Nomura*a,b
a Department of Applied Chemistry, Faculty of Engineering, Osaka Institute of Technology, 5-16-1 Ohmiya, Asahi, Osaka 535-8585, Japan
Fax: +81(6)69572135; e-Mail: otaka@chem.oit.ac.jp;
b Nanomaterials and Microdevices Research Center, Osaka Institute of Technology, 5-16-1 Ohmiya, Asahi, Osaka 535-8585, Japan
Fax: +81(6)69544604; e-Mail: nomura@chem.oit.ac.jp;
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Publication History

Received 26 May 2010
Publication Date:
06 August 2010 (online)

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Abstract

Linear polystyrene-stabilized PdO nanoparticles generated by thermal decomposition of palladium acetate have high catalytic activity for Sonogashira coupling in water under copper-free conditions. The catalyst was recovered and reused at least four times without any loss of catalytic activity.

Key words

polystyrene - water - PdO nanoparticles - Sonogashira coupling

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Preparation of Polystyrene-Stabilized PdO Nanoparticles (1) Linear polystyrene-stabilized palladium nanoparticles 1 was prepared according to our previous publication.¹² To a screw-capped vial with a stirring bar were added polystyrene (9.0 mg, 85 µmol of styrene unit), Pd(OAc)2 (5.5 mg, 25 µmol), and 1.5 M aq K2CO3 solution (3 mL). After stirring at 90 ˚C for 1 h, the reaction mixture was cooled to r.t. by immediately immersing the vial in H2O (ca. 20 ˚C) for about 10 min. Subsequently, the aqueous phases were removed, and recovered catalyst was washed with H2O (5 × 1.0 mL) and MeOH (5 × 1.0 mL).

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Compound 1 (2.9 mg) was placed in a screw-capped vial and then added 13 M nitric acid (5 mL). The mixture was heated at 80 ˚C to dissolve completely. After cooled to r.t., the solution was adjusted to 50 mL by H2O and then measured the amount of Pd metal by ICP-AES analysis (15.3 ppm).

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General Procedure for Sonogashira Coupling (Table   [ ² ] , Entry 1) To a screw-capped vial with a stirring bar were added iodobenzene (52.0 mg, 0.5 mmol), phenylacetylene (56.2 mg, 0.55 mmol), 1 (2.9 mg, 1.5 mol% of Pd), Et3N (152 mg, 1.5 mmol), and H2O (1.0 mL). After stirring at 80 ˚C for 6 h, the reaction mixture was cooled to r.t. by immediately immersing the vial in H2O (ca. 20 ˚C) for about 10 min. Subsequently, the aqueous phases were removed, and recovered catalyst was washed with H2O (5 × 3.0 mL) and Et2O (5 × 3.0 mL), which were then added to the aqueous phase. The aqueous phase was extracted eight times with Et2O. The combined organic extracts were dried over MgSO4 and concentrated under reduced pressure. The recovered 1 was dried in vacuo and reused. The resulting product was analyzed by ¹H NMR.