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Synlett 2006(17): 2747-2750  
DOI: 10.1055/s-2006-950260
LETTER
© Georg Thieme Verlag Stuttgart · New York

Nanocrystalline Magnesium Oxide Stabilized Palladium(0): An Efficient Heterogeneous Catalyst for Heck and Sonogashira Coupling of Aryl Halides [1]

M. Lakshmi Kantam*a, Sarabindu Roya, Moumita Roya, M. S. Subhasa, Pravin R. Likhara, Bojja Sreedhara, B. M. Choudaryb
a Indian Institute of Chemical Technology, Inorganic & Physical Chemistry Division, Hyderabad 500007, India
Fax: +91(40)27160921; e-Mail: mlakshmi@iict.res.in;
b Ogene Systems (I) Pvt. Ltd., Hyderabad 500037, India
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Publication History

Received 30 July 2006
Publication Date:
09 October 2006 (online)

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Abstract

Nanocrystalline magnesium oxide supported palladium(0) catalyst [NAP-Mg-Pd(0)], prepared by the counter-ion stabilization of PdCl4 2- followed by reduction with hydrazine hydrate, was effectively used in the Heck olefination of haloarenes (chloro, bromo, and iodo) to afford good to excellent yields of substituted olefins. This ligand-free heterogeneous NAP-Mg-Pd(0) catalyst was quantitatively recovered from the reaction by a simple filtration and reused for a number of cycles with almost no loss of activity. Moreover, NAP-Mg-Pd(0) efficiently catalyzed the Sonogashira coupling of haloarenes with terminal alkynes without any copper co-catalyst under milder conditions to afford excellent yields of substituted alkynes.

Keywords

nanocrystalline magnesium oxide - palladium - heterogeneous reaction - Heck reaction - Sonogashira reaction

1

IICT communication No. 060818.

1

IICT communication No. 060818.

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Preparation of NAP-Mg-Pd(0) Catalyst: [5c] NAP-MgO (1 g, BET 600 m2/g, purchased from NanoScale Materials Inc., Manhattan, USA) was treated with Na2PdCl4 (294 mg, 1 mmol) dissolved in decarbonated H2O (100 mL) and the resulting mixture was stirred for 12 h under a nitrogen atmosphere to afford the brown colored NAP-Mg-PdCl4. Then the catalyst was filtered, washed with deionized H2O and acetone, and dried. Then NAP-Mg-PdCl4 (1g) was reduced with hydrazine hydrate (1 g, 20 mmol) in anhyd EtOH (20 mL) for 3 h under a nitrogen atmosphere to give the black colored air-stable NAP-Mg-Pd(0) (Pd 0.99
mmol/g).
Heck Coupling of Iodo and Bromoarene: 4-Bromoanisole (2 mmol), styrene (2.2 mol), NaOAc (6 mmol), dimethyl­-acetamide (DMAc, 5 mL), and NAP-Mg-Pd(0) (0.1 mol%) were taken in a 20-mL reaction vessel and stirred under a nitrogen atmosphere at 135 °C (monitored by GC). After completion of the reaction the catalyst was separated by filtration, washed with H2O and acetone, and dried in air. The filtrate was diluted with Et2O and washed with H2O. The organic layer was concentrated to give the crude product, which was purified by column chromatography (hexane-EtOAc, 9:1) to give pure 4-methoxy-trans-stilbene in 94% yield (395 mg); mp 135-137 °C. 1H NMR (300 MHz, CDCl3): δ = 3.84 (s, 3 H), 6.81-7.07 (m, 4 H), 7.17-7.53 (m, 7 H). EI-MS: m/z (%) = 210 (M+), 195, 167, 165, 152. Anal. Calcd for C15H14O: C, 85.68; H, 6.71. Found: C, 85.45; H, 6.83.
Heck Coupling of Chloroarenes: 4-Chloroacetophenone (2 mmol), styrene (2.2 mol), NaOAc (6 mmol), TBAB (2 mmol), DMAc (5 mL), and NAP-Mg-Pd(0) (1.0 mol%) were taken in a 20-mL reaction vessel and stirred under a nitrogen atmosphere at 135 °C (monitored by GC). After completion of the reaction the catalyst was separated by filtration, washed with H2O and acetone, and dried in air. The filtrate was diluted with Et2O and washed with a solution of 1% HCl (to remove the amine formed from decomposition of TBAB) and then a sat. solution of NaCl. Then organic layer was dried over Na2SO4 and concentrated to get the crude product, which was purified by column chromatography (hexane-EtOAc, 8:2) to give pure 4-acetyl-trans-stilbene in 92% yield (408 mg); mp 134-136 °C. 1H NMR (300 MHz, CDCl3): δ = 2.6 (s, 3 H), 7.12 (d, J = 16.6 Hz, 1 H), 7.22 (d, J = 16.6 Hz, 1 H), 7.28-7.41 (m, 3 H), 7.53 (d, J = 6.8 Hz, 2 H), 7.59 (d, J = 8.3 Hz, 2 H), 7.95 (d, J = 8.3 Hz, 2 H). EI-MS: m/z = 222 (M+), 207, 178, 149, 77, 51, 43. Anal. Calcd for C16H14O: C, 86.45; H, 6.35. Found: C, 86.28; H, 6.47.
Sonogashira Reaction: 4-Bromoanisole (0.5 mmol), phenylacetylene (0.6 mol), Et3N (1 mmol), DMF (3 mL), and NAP-Mg-Pd(0) (1.0 mol%) were taken in a 10-mL reaction vessel and stirred under a nitrogen atmosphere at 75 °C (monitored by GC). After completion of the reaction, the catalyst was separated by filtration, washed with H2O and acetone, and dried in air. The filtrate was diluted with Et2O and washed with a sat. solution of NaCl. The organic layer was concentrated to give the crude product, which was purified by column chromatography(hexane) to give pure 4-methoxydiphenylacetylene in 92% yield (96 mg); mp 55-57 °C. 1H NMR (300 MHz, CDCl3): δ = 3.8 (s, 3 H), 6.83 (d, J = 8.3 Hz, 2 H), 7.25-7.35 (m, 3 H), 7.39-7.51 (m, 4 H). EI-MS: m/z = 208 (M+), 194, 167, 166, 140. Anal. Calcd for C15H12O: C, 86.51; H, 5.81. Found: C, 86.39; H, 5.96.