A Cyclobutene-1,2-Bis(imidazolium) Salt as Efficient Precursor of Palladium-Catalyzed Room-Temperature Suzuki-Miyaura Reactions

Abstract

3,3′-[3,4-Bis(dichloromethylene)cyclobut-1-ene-1,2-diyl]bis(1-methyl-1H-imidazolium) bis(tetrafluoroborate), palladium(II)acetate, and sodium tert-butoxide in toluene catalyze effectively Suzuki-Miyaura cross-coupling reactions of aryl bromides, chlorides, and iodides with arylboronic acids at room temperature.

biphenyls - cross-coupling - Suzuki-Miyaura cross-coupling reactions

References and Notes

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18

Typical Procedure for the Synthesis of 3-Methyl-terphenyl (Entry 3) A flame-dried two-necked flask was charged with 4-bromo-biphenyl (1 mmol, 233 mg), 3-methylphenylboronic acid (1.2 mmol, 163.2 mg), salt 2 (1 mol%, 0.01 mmol, 5.6 mg), Pd(OAc)₂ (1 mol%, 0.01 mmol, 2.5 mg), and NaOt-Bu (1.7 mmol, 163.5 mg), capped with a rubber septum, evacuated, and refilled with nitrogen. Evaporation and refilling was repeated three times. Then toluene (5 mL) was added via a syringe. The reaction mixture was stirred at r.t. for 70 min, then diluted with of n-hexane (10 mL), and filtered through a small amount of silica gel. The solvent was then evaporated, and the residue was purified by column chromatography (silica gel). The compound was obtained as colorless solid in 96% yield (234 mg), mp 123-124 ˚C. ^¹H NMR (200 MHz, CDCl₃): δ = 7.65 (s, 5 H), 7.62-7.60 (m, 1 H), 7.48-7.29 (m, 6 H), 7.18-7.17 (m, 1 H), 2.41 (s, 3 H) ppm. ^¹³C NMR (50 MHz, CDCl₃): δ = 140.8, 140.7, 140.3, 140.0, 138.4, 128.8, 128.7, 128.4, 128.1, 127.9, 127.5, 127.4, 127.3, 127.1, 124.2, 21.6 ppm. IR (KBr): 3033, 2974, 2845, 1626, 1585, 1210, 973, 827 cm^-¹. MS: m/z (%) = 244 (100%) [M⁺]. Anal. Calcd for C₁₉H₁₆: C, 93.40; H, 6.60. Found: C, 93.48; H, 6.49.