Ultrasonication Accelerates the Suzuki Coupling Reaction
The Suzuki Cross-Coupling (also known as Suzuki-Miyaura Coupling) is an organic reaction with the aim to synthesize biphenyl derivatives, vinyl aromates (e.g. styrenes), poly-olefins, as well as alkyl bromides. The reaction base materials are an aryl- or vinyl-boronic acid with an aryl- or vinyl-halide catalyzed by a palladium(0) complex, which can also be in the form of a nanomaterial-based catalyst.
For the Suzuki Coupling reaction, ultrasound has been found to accelerate the whole reaction. This article gives an overview about the results of various studies concerning the ultrasonic improvement of the Suzuki Coupling reaction.
The study of Zhang et al. (2008) proved that ultrasound facilitates the heterogeneous reaction of Suzuki coupling of phenylboronic acid with arylhalides in the presence of TBAB by means of easily obtained ligand-free cyclopalladated ferrocenylimines in neat water. For the coupling of arylchlorides, the achievement of moderate to good yields has been reported. In comparison with conventional heating, the ultrasonically-assisted coupling reaction was accelerated drastically. Further, this reaction improving method has the great advantage of using a nontoxic, nonflammable solvent that facilitates and secures the preparation.
Rajagopal et al. examines in their work that the palladium catalyzed Suzuki cross-coupling reactions of halobenzenes including chlorobenzenes with phenylboronic acid have been achieved at ambient temperature (30 °C) in the absence of a phosphine ligand using the ionic liquid 1,3-di–butylimidazolium tetrafluoroborate [bbim][BF4] with methanol as co-solvent under ultrasonic irradiation. [Rajagopal et al. 2002, p. 616]
Sonogashira cross-coupling reaction
Ultrasound has also found to promote the Sonogashira coupling reaction very effectively. The Sonogashira cross-coupling is palladium-catalyzed too and is used for the organic synthesis of carbon-carbon (C-C) bonds under mild conditions, such as at room temperature, in aqueous media and using a mild base. It is widely used in the pharmaceutical and chemical industry to synthesize complex molecules.
A convenient ligand-, copper-, and amine-free palladium-catalyzed one-pot synthesis of benzo[b]furans/nitro benzo[b]furans via Sonogashira coupling-5-endo-dig-cyclization using ultrasonication at ambient temperature. The reaction has been influenced very positively by sonochemical effects. [cf. Palimkar et al. 2008]
- Oxley, J. D.; Prozorov, T.; Suslick, K. S. (2003): Sonochemistry and Sonoluminescence of Room-Temperature Ionic Liquids. In: Journal of American Chemical Society 125/2003. pp. 11138-11139.
- Palimkar, S. S.; More, V. S.; Srinivasan, K. V. (2008): Ultrasound promoted copper-, ligand- and amine-free synthesis of benzo[b]furans/nitro benzo[b]furans via Sonogashira coupling-5-endo-dig-cyclization. In: Ultrasonics Sonochemistry 15/2008. pp. 853-862.
- Rajagopal, R.; Jarikote, D. V.; Srinivasan, K. V. (2002): Ultrasound promoted Suzuki cross-coupling reactions in ionic liquid at ambient conditions. In: Chemical Communications 6/2002. pp. 616-617.
- Zhang, J.; Yang, F,; Ren, G.; Mak, Th. C. W.; Song, M.; Wu, Y. (2008): Ultrasonic irradiation accelerated cyclopalladated ferrocenylimines catalyzed Suzuki reaction in neat water. In: Ultrasonics Sonochemistry 15/2008. pp. 115-118.