Palladium-Catalyzed Cross-Coupling Reaction of Silicone with Aryl Chlorides

Abstract

The palladium-catalyzed cross-coupling reaction of silicone, poly(diorganosiloxane), with aryl chlorides in the presence of K₂CO₃/H₂O as an activator proceeds to afford the biaryl derivatives in moderate to excellent yields. A wide range of aryl chlorides bearin­g an electron-donating or electron-withdrawing substituent on the aromatic ring are tolerated. The amount of K₂CO₃ relative to silicone significantly influences the reaction. Treatment of silicone with K₂CO₃/H₂O at r.t. for 1 hour prior to the addition of the palladium catalyst and an aryl chloride is necessary.

Key words

palladium - cross coupling - silicone - aq potassium carbona­te - aryl chlorides

References

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  Average mol. wt of 1 employed is ca. 2500-2700.

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8

Typical Experimental Procedure for the Cross-Coupling Reaction: To a toluene (3 mL) solution of [Ph(Me)SiO]_n (1, 204 mg, 1.5 mmol) was added K₂CO₃ (414 mg, 3.0 mmol) in water (0.5 mL). After stirring at r.t. for 1 h, 1-chloro-4-methoxybenzene (2a, 43 mg, 0.3 mmol) and PdCl₂(PCy₃)₂ (11 mg, 0.015 mmol) were added and then the resulting yellow mixture was stirred at 120 °C for 39 h. After cooling the mixture to r.t., the organic layer was separated and aqueous layer was extracted with Et₂O (2 × 10 mL). The combined organic layer was washed with 1 M HCl (10 mL), sat. aq NaHCO₃ (10 mL), and brine (10 mL) and then dried over anhyd MgSO₄. Removal of the solvent left a crude oil, which was purified by chromatography on silica gel (reverse phase, MeOH-H₂O = 3:1) to yield 52.5 mg of 4-methoxy-biphenyl (95%).