Asymmetric Transfer Hydrogenation in Thermomorphic Microemulsions Based on Ionic Liquids

Abstract

A thermomorphic ionic-liquid-based microemulsion system was successfully applied for the Ru-catalyzed asymmetric transfer hydrogenation of ketones. On the basis of the temperature-dependent multiphase behavior of the targeted microemulsion, simple product separation as well as catalyst recycling could be realized. The use of water-soluble ligands improved the immobilization of the catalyst in the microemulsion phase and significantly decreased the catalyst leaching into the organic layer upon extraction of the product. Eventually, the optimized microemulsion system could be applied to a wide range of aromatic ketones that were reduced with good isolated yields (up to 98%) and enantioselectivities (up to 97%), while aliphatic ketones were less successful.

Ru-Catalyzed Asymmetric Addition of Arylboronic Acids to Aliphatic Aldehydes via P-Chiral Monophosphorous Ligands

“…Thus, the invention of methods for the preparing of such chiral aryl alkyl alcohols features an important role in organic synthesis. Classic methods for constructing such chiral molecules include asymmetric hydrogenation of ketones [11][12][13], asymmetric hydrogen transfer reduction of ketones or unsaturated ketones [14][15][16][17][18][19][20][21], along with the asymmetric addition of organometallic reagents to aldehydes [22][23][24]. As an alternative, strategies via the asymmetric homologation reaction [25][26][27][28], tandem Michael-MPV reaction and subsequent reductive desulfurization [29], as well as the asymmetric addition of aldehydes with arylboronic acids were also established [30,31].…”

CO2 and Temperature Control over Nanoaggregates in Surfactant-Free Microemulsion

“…Compared with traditional emulsions, the dispersed droplet diameter of ME is approximately 10–150 nm. Since it was first discovered by Hoar and Schulman in 1943, ME has been widely used in various fields like organic synthesis, drug delivery, − preparation of nanomaterials, , cosmetics carriers, and oil recovery due to its excellent stability and ultrasmall droplet size. However, ordinary MEs require a higher concentration of surfactants, commonly which will cause high costs and potential harms to the environment.…”

Interplay of Polarity and Confinement in Asymmetric Catalysis with Chiral Rh Diene Complexes in Microemulsions

“…Confined reaction spaces provided by micelles and microemulsions have received much attention during the last years [1–12] . Compared to micellar systems, microemulsions are mixtures of two (or more) immiscible solvents, usually at least one polar and one nonpolar, separated at the nanoscale by an amphiphilic film, often consisting of surfactants, which makes them thermodynamically stable.…”

“…Furthermore, the nanometer‐sized domains of hydrophilic and hydrophobic solvents inside microemulsions [8] have been successfully used to accelerate stoichiometric and catalytic reactions of small molecules [9,10] . In contrast, only a few studies have dealt with asymmetric catalysis in microemulsions, such as vitamin B12‐catalyzed isomerization of cyclopentenol, [10] Au‐catalyzed lactonization of allenic acids [11] and asymmetric Ru‐catalyzed transfer‐hydrogenation of ketones [12] …”

“…[9,10] In contrast, only a few studies have dealt with asymmetric catalysis in microemulsions, such as vitamin B12-catalyzed isomerization of cyclopentenol, [10] Aucatalyzed lactonization of allenic acids [11] and asymmetric Rucatalyzed transfer-hydrogenation of ketones. [12] Recently, we investigated the effect of nanoscale confinement comprising a highly dynamic amphiphilic surfactant film by means of the Rh-catalyzed asymmetric 1,2-addition of triphenylboroxine to N-tosylimines utilizing chiral Rh-diene complexes in microemulsions. [17,18] Rh-diene complexes were chosen as benchmark catalysts because they are very versatile and catalyse a large variety of reactions.…”