Aqueous‐Phase, Palladium‐Catalyzed Heck Reaction: The Significant Role of CN‐containing Counter Anion

Abstract

Water‐soluble diol‐functionalized imidazolium ionic liquid 1, prepared from 2,2‐bis(1‐methyl‐methyl‐imidazolium)propane‐1,3‐diol bromide, potassium hydroxide, and malononitrile, was used as an efficient phosphine‐free ligand for palladium‐catalyzed arylation of aryl halides with acrylates in aqueous phase under mild conditions. It was found that the synergistic coordinating action of diol‐functionalized imidazolium cation with CN‐containing anion played the key role in improving the activity and stability of the catalyst.

Investigation on the Coordination Mode of IL‐Supported Diols Used as Phosphine‐Free Ligands for Palladium Catalyzed Heck Reaction

“…With this approach, we extended our efforts to develop novel IL-supported diols (1-9) composed of different cations including pyridinium, piperidinium, and imidazolium (Scheme 1), which were used as the phospine-free ligands in Heck reaction of aryl halides with acrylates. Compared to the IL-supported diols published before, [35][36][37][38] unique structural design of varies cations with different alkyls was introduced into the ionic liquids. The difference in their coordination mode of cations with metal Pd in Heck reaction derived from tuning the composition of IL-supported diols was investigated in detail.…”

“…We have been investigating functionalized ILs of the type IL-supported diols, [35][36][37][38] which were proved to be efficient phosphine-free ligands for Heck reaction under aerobic condition. Despite these advances, opportunities to study relationships between the structure of IL-supported diol ligands and palladium catalyst activity have been rare.…”

Aqueous-Phase, Palladium-Catalyzed Suzuki Reactions under Mild Conditions

“…Our research group has also had a long-standing interest in Pd-catalyzed cross-coupling reactions utilizing functionalized-ionic liquids as phosphine-free ligands. Recently we disclosed a catalyst system, comprised of diol-functionalized ILs, 2,2-bis((1-methylimidazolium)methyl) propane-1,3-diol hexafluorophosphate and 1-(2, 3-dihydroxypropyl)-3-methylimidazolium hexaflu-orophosphate, which showed excellent reactivity for Heck reaction of aryl iodides/bromide and acrylates owing to available multi-coordinating sites in these ligands [15][16][17][18]. In light of these advances, we envisioned that if the use of diol-functionalized ILs could allow Suzuki reaction of aryl iodides/bromides to reach the same efficiencies as Heck reaction.…”