Synlett 2009(18): 2919-2923  
DOI: 10.1055/s-0029-1218013
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Thieme Journal Awardees - Where Are They Now? On Cobalt-Catalyzed Biaryl Coupling Reactions

Matthias Mayer, Waldemar Maximilian Czaplik, Axel Jacobi von Wangelin*
Department of Chemistry, University of Cologne, Greinstr. 4, 50939 Köln, Germany
Fax: +49(221)4705057; e-Mail: axel.jacobi@uni-koeln.de;
Further Information

Publication History

Received 14 August 2009
Publication Date:
08 October 2009 (online)

Abstract

An operationally simple biaryl coupling reaction has been developed. The underlying domino process involves in situ Grignard formation from aryl bromides and subsequent homocoupling with catalytic CoCl2 and 1 bar synthetic air as terminal oxidant.

10

The current world market prices of palladium (370 USD/oz) and nickel (14.4 USD/lb) are expected to increase due to the request from emerging countries such as China, Russia, India, and Brazil.

19

General Procedure
A 10 mL flask was charged with Mg ribbons (74 mg, 3.0 mmol), fitted with a rubber septum, and purged with argon (1 min). Dry THF (4 mL) and the arylbromide (2.5 mmol) were added via a syringe. The solution was stirred at r.t. for 1-3 h under argon. Cooled to 0 ˚C, a solution of CoCl2 (16.1 mg, 0.12 mmol, 5 mol%) in dry THF (6 mL) was added. Synthetic air (20 mL/min) was added through a needle to the solution. After 0.5-3 h, the reaction was quenched with sat. aq NH4Cl (5 mL), extracted with EtOAc (3 × 10 mL).
The combined organic phases were dried (Na2SO4), concentrated, and subjected to flash chromatography (cyclohexene-EtOAc).
New Compounds
3′,3′′-Difluoro[1,1′:4,1′′:4′,1′′′]quarter-phenyl (2n): mp 182 ˚C. ¹H NMR (300 MHz, CDCl3): δ = 7.75 (d, 4 H, J = 6 Hz), 7.65-7.05 (m, 12 H). ¹³C NMR (75 MHz, CDCl3): δ = 160.0 (d, J = 246 Hz), 140.4 (d, J = 6.8 Hz), 135.3 (d, J = 12.4 Hz), 131.1 (d, J = 3.4 Hz), 128.9, 128.5, 128.1, 122.7, 114.4 (d, J = 24.1 Hz). MS (EI, 70 eV): m/z (%) = 342 (100) [M+], 320 (7), 264 (5), 170 (7), 77 (5). HRMS: m/z = 342.122. IR (ATR): 1550 (m), 1473 (s), 1403 (m), 1246 (m), 1183 (m), 1130 (m), 1040 (m), 911 (s), 823 (s), 766 (s), 695 (s) cm.
3,3′,4,4′-Tetrafluorobiphenyl (2g): mp 83 ˚C; ¹H NMR (300 MHz, CDCl3): δ = 7.39-7.32 (m, 2 H), 7.30-7.25 (m, 4 H). ¹³C NMR (75 MHz, CDCl3): δ = 152.1 (dd, J = 12.7, 23.9 Hz), 148.8 (dd, J = 12.6, 24.8 Hz), 136.2, 123.0 (q, J = 3.4 Hz), 117.8 (d, J = 17.3 Hz), 116.0 (d, J = 17.9 Hz). MS (EI, 70 eV): m/z (%) = 226 (100 [M+], 206 (22), 175 (8), 156 (7), 138 (7), 112 (8). HRMS: m/z = 226.041. IR (ATR): 3064 (w), 1881 (w), 1599 (s), 1495 (s), 1339 (s), 1316 (m), 1265 (s), 1184 (s), 1150 (m), 117 (s), 1028 (m), 943 (m), 909 (m), 885 (m), 865 (s), 805 (s), 766 (s), 739 (s) cm.