β‐cyclodextrin‐capped palladium nanoparticle‐catalyzed ligand‐free Suzuki and Heck couplings in low‐melting β‐cyclodextrin/NMU mixtures

Abstract

Low-melting β-cyclodextrin/N-methylurea (NMU) mixture, an efficient catalytic system for ligand-free Suzuki and Heck couplings in the presence of fresh native β-CD-capped Pd 0 nanoparticles, has been successfully reported. This natural and convenient system can be performed in air and could afford the corresponding cross-coupled products in good to excellent isolated yields after a simple workup under every low Pd loading (0.05 mol%). Remarkably, the catalytic system can be recycled and reused without loss of catalytic activity.

Recent advances in the application of deep eutectic solvents as sustainable media as well as catalysts in organic reactions

“…Suzuki, Heck, and Sonogashira reactions as well as the Huisgen 1,3-dipolar cycloaddition, have been extensively investigated by the research group from König in 2009 40. In these kinds of reactions, most of catalyst-solvent systems could be reused without significant loss of their catalytic activity.Recently, Zhao et al improved Suzuki-Miyaura and Heck reactions by using low-melting β-cyclodextrin (CD)/NMU mixture as reaction media in the presence of β-CD supported Pd nanoparticles (Scheme 79) 137. The reactions could be performed in air without any ligand at 85 o C and afforded the corresponding cross-coupled products in good to excellent isolated yields after a simple workup under every low Pd loading (0.05 mol%).…”

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

“…Afterward, PdCl 2 in combination with cationic pyridiniophosphine ligands in ChCl:gly (1:2) as DES was used for the reaction between aryl iodides and methyl acrylate to synthesize the corresponding products in reasonable yields. 119 In 2014, Zhao et al introduced a deep eutectic or low-melting mixture based on -CD and N-methylurea (3:7) 135 via a ligand-free Mizoroki-Heck process in the presence of fresh native -CD-capped Pd 0 nanoparticles. This eco-friendly medium could be prepared in air, with the ability to produce the cross-coupled products in good to excellent yields at a low amount of Pd catalyst loading (0.05 mol%), and via a simple workup (Scheme 6).…”

Prospects and Applications of Palladium Nanoparticles in the Cross‐coupling of (hetero)aryl Halides and Related Analogues

“…High interest in cyclodextrins in the present era reveals their extensive applications in organic synthesis and stabilization of transition metal nanoparticles for CÀ C bond formations. [32,[49][50][51][52] In this regard, Zhao and coworkers [33] investigated β-cyclodextrin-capped palladium nanoparticle-catalyst, which provided yields of coupled products according to the relative strength of the CÀ X bond of the aryl halide substrates (Scheme 7). While the reaction of aryl iodides with styrenes (27 and 28) provides 90-96 % yields within 2 h, treating aryl bromides (26) with methyl or ethyl acrylates (29) gave products 32 in 55-76 % yield at a much longer time (10 h).…”