Recyclable LaF3·Pd nanocatalyst in Suzuki coupling: green synthesis of biaryls from haloarenes and phenylboronic acids

Abstract

Herein we prepared the novel LaF₃·Pd nanocatalyst characterized by XRD and TEM analysis. The nanocatalyst was applied in Suzuki coupling reaction for the synthesis of biaryls in aqueous medium from readily available aryl halides (bromides and iodides) and substituted phenylboronic acids in the presence of K₂CO₃ as the base at 70 °C. The present method is capable of giving the C-C coupled product in good to excellent yields (up to 97%). The reactions were conducted under green conditions in aqueous medium and the nanocatalyst used in this study was recyclable. The recyclability and reusability of the catalyst was checked for seven consecutive cycles without significant loss in reactivity.

Fig. 1. Representative examples of biaryls in naturally occurring molecules, catalysts, drugs, and agrochemicals with biaryl scaffolds.

Scheme 1. Preparation of the LaF₃·Pd 5 at % nanoparticles.

Fig. 2. XRD pattern of LaF₃·Pd.

Fig. 3. (a) HRTEM image (b) TEM image (c) SAED pattern (d) histogram of particle size of LaF₃·Pd.

Fig. 4. (a) X-ray photoelectron spectroscopy spectra (b) magnified XPS of LaF₃·Pd.

Scheme 2. Substrate scope for the LaF₃·Pd nanocatalyzed synthesis of biaryls. ^aReaction conditions: 1 (1.0 mmol), 2 (1.5 mmol), LaF₃·Pd (15 mg), K₂CO₃ (2.0 mmol) and H₂O (3.0 mL) were added in a 10 mL round-bottom flask and fitted with reflux condenser. The reaction mixture was stirred vigorously at 70 °C until the completion of the reaction (by TLC monitoring). ^bIn case of 3f the reaction was performed at room temperature. NR: no reaction.

Scheme 3. Gram scale synthesis of 3f.