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Synlett 2010(13): 1990-1996  
DOI: 10.1055/s-0029-1219816
CLUSTER
© Georg Thieme Verlag Stuttgart ˙ New York

Immobilization of Pd on Nanosilica Dendrimer as SILC: Highly Active and Sustainable Cluster Catalyst for Suzuki-Miyaura Reaction

Hisahiro Hagiwara*a, Hirokazu Sasakia, Norio Tsubokawab, Takashi Hoshib, Toshio Suzukib, Tetsuya Tsudac, Susumu Kuwabatac
a Graduate School of Science and Technology, Niigata University, 8050, 2-Nocho, Ikarashi, Niigata 950-2181, Japan
Fax: +81(25)2627368; e-Mail: hagiwara@gs.niigata-u.ac.jp;
b Faculty of Engineering, Niigata University, 8050, 2-Nocho, Ikarashi, Niigata 950-2181, Japan
c Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
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Publikationsverlauf

Received 26 January 2010
Publikationsdatum:
16. April 2010 (online)

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Abstract

Palladium acetate was noncovalently immobilized as a supported ionic liquid catalyst (SILC) in a nanosilica dendrimer, PAMDMAM, with the aid of an ionic liquid to form a cluster catalyst of palladium nanoparticles. The pseudo-homogeneous hetero­genized catalyst, Pd-nanoPAMDMAM-SILC, was effective for Suzuki-Miyaura reactions of ortho-substituted aryl bromides or aryl triflates without a ligand in 50% aqueous ethanol in air at room temperature. The catalyst could be re-used up to five times in 93% average yield after simple centrifugation. TON reached 176,000.

Key words

dendrimers - heterogeneous catalysis - supported catalysis - palladium - cross-coupling

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Hagiwara, H.; Kuroda, T.; Hoshi, T.; Suzuki, T. unpublished results.

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Preparation of Pd-nanoPAMDMAM-SILC 5
NanoPAMDMAM 3 (200 mg) powder was added to a solution of [bmim]PF6 (19 mg, 10 wt%) and Pd(OAc)2
(36 mg, 0.16 mmol) in THF (2 mL) in open air. The homogeneous solution was stirred at r.t. for 4 h, and evaporated to dryness under reduced pressure. The resulting powder was rinsed with Et2O (2 mL) five times. Each time, the ether solution was stirred for 10 min, centrifuged for 10 min, and decanted to leave the powder. Evaporation of ether provided Pd-nanoPAMDMAM-SILC 5 as a pale yellow powder (247 mg, 0.5-0.6 mmol/g of Pd).

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4-Phenylacetophenone (8a)
Potassium carbonate (138 mg, 1.0 mmol) and Pd-nanoPAMDMAM-SILC 5 (8 mg, 0.005 mmol) were added to a solution of 4-bromoacetophenone (6a, 100 mg, 0.50 mmol) and phenylboronic acid (7a, 85 mg, 0.70 mmol) in 50% aq EtOH (2 mL) in open air. The solution was stirred at r.t. for 30 min, then centrifuged for 10 min. After decantation of the organic layer, the powder was rinsed with Et2O-EtOH (1:1, 5 mL) five times. Each time, the resulting homogeneous solution was centrifuged to precipitate the SILC. The combined organic layer was evaporated to dryness under reduced pressure. Purification by column chromatography (EtOAc-n-hexane = 1:10) provided
4-phenylacetophenone (8a, 102 mg) quantitatively.

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4-(2-Phenylphenyl)acetophenone (8c)
Potassium carbonate (138 mg, 1.0 mmol) and Pd-nanoPAMDMAM-SILC 5 (8 mg, 0.005 mmol) were added to a solution of 4-bromoacetophenone (6a, 100 mg, 0.50 mmol) and (2-phenyl)phenylboronic acid (7c, 85 mg, 0.70 mmol) in 50% aq EtOH (2 mL) in open air. The solution was stirred at r.t. for 30 min, then centrifuged for 10 min. After decantation of the organic layer, the powder was rinsed with Et2O-EtOH (1:1, 5 mL) five times. Each time, the resulting homogeneous solution was centrifuged to precipitate the SILC. The combined organic layer was evaporated to dryness under reduced pressure. Purification by column chromatography (EtOAc-n-hexane = 1:10) provided 4-(2-phenylphenyl)acetophenone (8c, 134 mg) in 98% yield.

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4-(4-Methoxyphenyl)acetophenone (8d) Potassium carbonate (138 mg, 1.0 mmol) and Pd-nanoPAMDMAM-SILC 5 (8 mg, 0.005 mmol) were added to a solution of 4-bromoacetophenone (6a, 101 mg, 0.50 mmol) and 4-methoxyphenylboronic acid (7d, 106 mg, 0.70 mmol) in 50% aq EtOH (2 mL) in open air. The solution was stirred at r.t. for 30 min, then centrifuged for 10 min. After decantation of the organic layer, the powder was rinsed with Et2O-EtOH (1:1, 5 mL) five times. Each time, the resulting homogeneous solution was centrifuged to precipitate the SILC. The combined organic layer was evaporated to dryness under reduced pressure. Purification by column chromatography (EtOAc-n-hexane = 1:3) provided 4-(4-methoxyphenyl)acetophenone (8d, 104 mg) in 90% yield.