A new thioglycolic ester β-cyclodextrin/PdCl2 in water: An accessible catalyst for the Suzuki-Miyaura coupling reaction

Abstract

A novel, easily prepared and accessible water-soluble supramolecular catalyst for the Suzuki-Miyaura CC coupling reaction was synthesized and characterized by FTIR, NMR, XRD, SEM, and HR-TEM. An inexpensive Pd(II) source added to the resulting aqueous solution of thioglycolic ester β-cyclodextrin (1-TGA-SH-β-CD/PdCl₂) showed Pd nanoclusters and efficient catalytic activity for Suzuki-Miyaura CC coupling reactions of aryl halides with aryl boronic acids, employing K₂CO₃ as base, in an environmentally benign aqueous solution prepared in open flasks. Organic aryl halides including chlorides can produce moderate to excellent yields with aryl boronic acids and a small catalytic amount (0.01 mol%) of 1-TGA-SH-β-CD/PdCl₂. This hydro-soluble catalyst stock solution was stable for long periods (more than three months) and could be reused in two runs until showing loss of catalytic activity. Some experiments to understand the mechanism were performed, with the results suggesting incorporation of aryl halide in the catalytic cavity.

Keywords: Aqueous Suzuki-Miyaura cross-coupling; Eco-friendly catalysts; Inclusion complex; Palladium complex; Thioglycolic ester β-cyclodextrin.