Deep Eutectic Solvents as Reaction Media for the Palladium‐Catalysed C−S Bond Formation: Scope and Mechanistic Studies

Abstract

A unique jigsaw catalytic system based on deep eutectic solvents and palladium nanoparticles where C−S bonds are formed from aryl boronic acids and sodium metabisulfite, is introduced. The functionalization step is compatible with a broad spectrum of reagents such as nucleophiles, electrophiles or radical scavengers. This versatile approach allows the formation of different types of products in an environmentally friendly medium by selecting the components of the reaction, which engage one with another as pieces in a jigsaw. This simple procedure avoids the use of toxic volatile organic solvents allowing the formation of complex molecules in a one‐pot reaction under mild conditions. Despite the fact that only 1 mol % of metal loading is used, the recyclability of the catalytic system is possible. Kinetic experiments were performed and the reaction order for all reagents, catalyst and ligand was determined. The obtained results were compared to palladium nanocrystals of different known shapes in order to shed some light on the properties of the catalyst.

NCN–Pincer–Pd Complex as Catalyst for the Hiyama Reaction in Biomass-Derived Solvents

“…However, a purification step was required to obtain the pure product, in contrast to the result obtained in glycerol as solvent. Regarding the mechanism of the reaction, it is believed to proceed via Pd (0)/ Pd (II) cycle according to literature precedents, and due to our previous experience in Pd chemistry in DES, 41 we analyzed the crude material by HRTEM trying to find Pd nanoparticles. Nevertheless, no nanoparticles were found (neither in DES nor in glycerol as reaction medium) (Fig S1).…”

Deep eutectic solvents: alternative reaction media for organic oxidation reactions

“…In 2017, Ramòn et al reported the palladium catalyzed C-S bond formation in the presence of sodium metabisulfite as SO 2 source. 53 Exploiting the ability of DESs to dissolve organic substrates, catalyst, ligand and the inorganic salt, the authors obtained an improvement when the reaction was performed in DESs, instead of common organic solvents. The most promising DES was a mixture of ChCl and acetamide (1:2), whereas, 2-(dicyclohexylphosphaneyl)-1-phenylpyridin-1-ium chloride was selected as best ligand.…”

“…Palladium catalyzed C-S bond formation in DESs. 53 In their studies, the authors focused on the C-S coupling keeping the pentyl bromide as the electrophile and investigating the scope of reaction by varying the aryl boronic acid. Aryl boronic acid-based compounds bearing both electro-withdrawing groups (EWGs) and electron-donating groups (EDGs) were tested showing that the reactivity varies from poor to excellent (17-99%).…”

Deep eutectic solvents: cutting-edge applications in cross-coupling reactions

“…Ramón et al reported a unique jigsaw catalytic system based on ChCl:acetamide (1:2) DES and Pd NPs for the C-S bond formation, from aryl boronic acids and sodium metabisulfite as SO 2 source (Scheme 19). 171 Notably, this reaction could be considered as a combination between Suzuki-Miyaura reaction and Ullmann type reaction due to the presence of the aryl boronic acids in substrates and also the formation of carbon-heteroatom bond in the final products. The functionalization step is compatible via three-component reactions with a wide range of reagents such as electrophiles, nucleophiles, or radical scavengers to afford sulfones and aryl sulfides.…”