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Synlett 2013; 24(2): 197-200
DOI: 10.1055/s-0032-1317857
letter
© Georg Thieme Verlag Stuttgart · New York

Amphiphilic Viologen: Electrochemical Generation of Organic Reductant and Pd-Catalyzed Reductive Coupling of Aryl Halides in Water

Manabu Kuroboshi*
The Graduate School of Natural Science and Technology, Okayama University, Tsushima-naka 3-1-1, Kita-Ku, Okayama 700-8530, Japan   Fax: +86(255)3424   Email: tanaka95@cc.okayama-u.ac.jp
,
Takashi Yamamoto
The Graduate School of Natural Science and Technology, Okayama University, Tsushima-naka 3-1-1, Kita-Ku, Okayama 700-8530, Japan   Fax: +86(255)3424   Email: tanaka95@cc.okayama-u.ac.jp
,
Hideo Tanaka*
The Graduate School of Natural Science and Technology, Okayama University, Tsushima-naka 3-1-1, Kita-Ku, Okayama 700-8530, Japan   Fax: +86(255)3424   Email: tanaka95@cc.okayama-u.ac.jp
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Further Information

Publication History

Received: 10 October 2012

Accepted after revision: 16 November 2012

Publication Date:
13 December 2012 (online)

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Abstract

Electroreduction of 1,1′-bis(methoxyethoxyethoxyethyl)-4,4′-bipyridinium tosylate generated amphiphilic organic reductants, which promoted the Pd-catalyzed reductive coupling of aryl bromides in water to give the corresponding biaryls. The yields and selectivity of biaryls depended on the length of ethyleneoxy groups and substituents of the aryl bromides.

Key words

electron transfer - palladium - reduction - coupling - arenes
 

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  • 5 Octyl viologen bis(triflimide) and the corresponding quinoid dissolve in organic solvent to promote the reductive homocoupling of aryl halide. See: Kuroboshi M, Kobayashi R, Nakagawa T, Tanaka H. Synlett 2009; 85
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  • 7 Preparation of 1a In a round-bottomed flask were placed 4,4′-bipyridyl (3.531 g, 23 mmol) and 3,6,9-trioxadecyl p-tosylate (14.39 g, 45 mmol). The mixture was stirred at 120 °C for 24 h under argon atmosphere to form a viscous layer. The supernatant was decanted off, and the viscous layer was washed with Et2O and toluene (2 × 10 mL), successively. The viscous liquid layer was concentrated under reduced pressure to give 1,1′-bis(3,6,9-trioxadecyl)-4,4′-bipyridinium bis(p-toluenesulfonate) (1a, 17.14 g, 22 mmol, 96%) as a brown liquid. 1H NMR (200 MHz, CDCl3): δ = 2.28 (s, 6 H), 3.28 (s, 6 H), 3.42–3.53 (m, 16 H), 3.85 (br, 4 H), 4.93 (br, 4 H), 7.11 (d, J = 8.1 Hz, 4 H), 7.69 (d, J = 8.1 Hz, 4 H), 8.71 (d, J = 6.8 Hz, 4 H), 9.24 (d, J = 6.8 Hz, 4 H). 13C NMR (150 MHz, CDCl3): δ = 21.04, 58.69, 61.18, 68.89, 69.91, 70.08, 70.14, 71.56, 125.66, 126.64, 128.71, 1139.42, 143.25, 146.60, 148.87; IR (neat): 3464, 3127, 3059, 2921, 2876, 1638, 1451, 1191, 1122, 822 cm–1.
  • 8 1,1′-Bis(2-methoxyethyl)-4,4′-bipyridinium Bis(p-toluenesulfonate) (1b) Colorless solids. 1H NMR (200 MHz, D2O): δ = 2.13 (s, 6 H), 3.19 (s, 6 H), 3.79 (t, J = 5.0 Hz, 4 H), 4.68 (t, J = 5.0 Hz, 4 H), 7.08 (d, J = 8.3 Hz, 4 H), 7.40 (d, J = 8.3 Hz, 4 H), 8.26 (d, J = 7.0 Hz, 4 H), 8.85 (d, J = 7.0 Hz, 4 H). 13C NMR (50 MHz, CD3OD): δ = 21.3, 59.2, 62.7, 71.3, 126.8, 127.8, 129.8, 141.6, 143.5, 147.5, 151.3. IR (KBr): 3532, 3451, 3134, 3062, 2992, 2864, 1639, 1510, 1448, 1191, 1120, 1035, 568 cm–1. 1,1′-Bis(3,6-dioxaheptyl)-4,4′-bipyridinium Bis(p-toluenesulfonate) (1c) Colorless solids. 1H NMR (200 MHz, D2O): δ = 2.15 (s, 6 H), 3.09 (s, 6 H), 3.32–3.36 (m, 4 H), 3.44–3.49 (m, 4 H), 3.86 (t, J = 4.4 Hz, 4 H), 4.63–4.76 (m, 4 H), 7.11 (d, J = 7.7 Hz, 4 H), 7.42 (d, J = 7.7 Hz, 4 H), 8.30 (d, J = 6.2 Hz, 4 H), 8.89 (d, J = 6.2 Hz, 4 H). 13C NMR (150 MHz, CD3OD): δ = 21.3, 59.1, 62.7, 70.0, 71.2, 72.7, 126.9, 127.7, 129.9, 141.6, 143.7, 147.6, 151.2. IR (KBr): 3509, 3131, 3055, 2879, 1640, 1442, 1192, 1123, 1033, 685 cm–1. 1,1′-Dimethyl-4,4′-bipyridinium Bis(p-toluenesulfonate) (1d) Yellow solids. 1H NMR (200 MHz, D2O): δ = 2.18 (s, 6 H), 4.31 (s, 6 H), 7.13 (d, J = 8.2 Hz, 4 H), 7.45 (d, J = 8.2 Hz, 4 H), 8.25 (d, J = 6.9 Hz, 4 H), 8.81 (d, J = 6.9 Hz, 4 H). 13C NMR (150 MHz, CD3OD): δ = 21.3, 49.0, 126.8, 127.6, 130.0, 141.6, 143.7, 147.8, 150.4. IR (KBr): 3444, 3053, 3020, 2994, 1642, 1509, 1440, 1358, 1208, 1119, 818, 683 cm–1. 1,1′-Dibutyl-4,4′-bipyridinium Bis(p-toluenesulfonate) (1e)Colorless solids. 1H NMR (200 MHz, D2O): δ = 0.71 (t, J = 7.4 Hz, 6 H), 1.13 (sext, J = 7.4 Hz, 4 H), 1.76 (quin, J = 7.4 Hz, 4 H), 2.07 (s, 6 H), 4.40 (t, J = 7.4 Hz, 4 H), 7.01 (d, J = 8.1 Hz, 4 H), 7.32 (d, J = 8.1 Hz, 4 H), 8.16 (d, J = 6.7 Hz, 4 H), 8.77 (d, J = 6.7 Hz, 4 H). 13C NMR (150 MHz, CD3OD): δ = 13.8, 20.4, 21.3, 34.3, 62.9, 126.9, 128.2, 129.9, 141.6, 143.7, 147.0, 151.0. IR (KBr): 3434, 3127, 3054, 2957, 2870, 1643, 1450, 1169, 1120, 1035, 818 cm–1.
  • 9 Viologens V2+ were easily soluble in H2O, whereas the reduced form V0 were soluble in organic solvents. Therefore, viologens were used in a mixed solution of H2O–MeOH or H2O–MeCN. The amphiphilic PEG group would increase the solubility of V2+/V0 as well as the substrates.
  • 10 Recycle use of aqueous viologen/Pd solution was also examined. In the second run, the recovered aqueous solution was placed in the cathodic chamber. The electroreduction was carried out under constant current conditions to generate V0. Though the reaction conditions have not been optimized yet, 4a was obtained in 40% yield.