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Synlett 2008(2): 255-259  
DOI: 10.1055/s-2008-1000874
LETTER
© Georg Thieme Verlag Stuttgart · New York

Polyionic Heterogeneous Phenylating Agent for Base-Free Suzuki-Miyaura Coupling Reaction

Basudeb Basu*, Sajal Das, Sekhar Kundu, Bablee Mandal
Department of Chemistry, North Bengal University, Darjeeling 734013, India
e-Mail: basu_nbu@hotmail.com;
Further Information

Publication History

Received 26 July 2007
Publication Date:
21 December 2007 (online)

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Abstract

A new polyionic resin-bound tetraphenylborate has been prepared, which can serve as efficient phenylating agent in Pd-catalyzed Suzuki-Miyaura (SM) coupling with aryl halides in the absence of any base. The conditions are mild, operationally simple and the polyionic resin can be recharged and reused for several runs.

Key words

polyionic resins - tetraphenylborate - Suzuki-Miyaura coupling - base-free conditions - biphenyls

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Amberlite® IRA-900 resin (chloride form; 2.50 g) was stirred with aq NaBPh4 (1.73 g) until complete exchange as judged by Cl- loss (AgNO3). The exchanged resin was washed with H2O, acetone and dried to give the tetra­-phenylborate-form resin (3.92 g). The mass difference between product and starting materials (ca. 310 mg) was comparable with the calculated difference (296 mg). The resulting borate-bound resin thus contained a 1.14 mmol g-1 loading of the borate ions and was used directly in the SM coupling reactions.

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Representative Procedure for Suzuki-Miyaura Reaction: A mixture of 3-iodotoluene (218 mg, 1 mmol), Amberlite resin (Ph4B- form) (1 g, 1.14 mmol) and Pd(OAc)2 (4.5 mg, 2 mol%) was taken in DMF (2 mL) and heated in an oil bath at 85 °C for 2 h. After cooling, the reaction mixture was diluted with H2O (5 mL) and the resin was filtered off. The filtrate was extracted with Et2O (3 × 15 mL) and the combined organic layers were dried over anhyd Na2SO4. Removal of the solvent left an oily residue, which was passed through a short column of silica gel (60-120 mesh) eluting with light petroleum to afford 3-phenyltoluene as a colorless liquid (161 mg, yield 96%). IR (neat): 3031, 2900, 1604 cm-1. 1H NMR (300 MHz, CDCl3): δ = 7.84-7.87 (m, 2 H), 7.56-7.71 (m, 6 H), 7.42 (d, J = 7.2 Hz, 1 H), 2.67 (s, 3 H). 13C NMR (75 MHz, CDCl3): δ = 141.3, 141.2, 138.2, 128.7, 128.6, 127.94, 127.89, 127.2, 127.1, 124.2, 21.5.

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After the first run, the resin beads were filtered off, washed with MeOH, then with H2O and finally rinsed again with aq NaBPh4 solution. The resulting borate-bound resin could be reused for the SM reaction. Employing the recovered and recharged resin (tetraphenylborate form) for SM coupling with 3-iodotoluene (1 mmol scale), provided the desired biaryl in 95% yield. The three subsequent runs gave the biaryl in 92%, 92% and 88% yields.