Highly enantioselective Ru-catalyzed asymmetric hydrogenation of β-keto ester in ionic liquid/methanol mixtures

Room-Temperature Ionic Liquids: Solvents for Synthesis and Catalysis. 2

“…Ionic liquids have been shown to have striking effects on hydrogenations, even when used as additives. For the Ru-catalyzed asymmetric hydrogenation of β-keto esters both the rate and ee of the reaction in methanol were greatly affected by the addition of ionic liquids, with the ee dropping considerably in the presence of [C 2 C 1 im][NTf 2 ] and increasing slightly when [(HO) 2 C 2 (C 1 ) 3 N][NTf 2 ] was added . This stabilization effect also led to enhanced recyclability of the catalyst system.…”

BINEPINES: chiral binaphthalene-core monophosphepine ligands for multipurpose asymmetric catalysis

“…When the enantioselective hydrogenation of b-ketoesters was run in a homogeneous solution made up of ionic liquids (IL) and methanol, 38 the reaction rate was higher than in pure IL's but the enantioselectivity was lower than that observed in plain methanol. 39 These differences have been attributed to the concurrent formation of ketal and hemiketal that is suppressed to a significant extent in the mixed system IL/methanol.…”

“…Nature and performance of the catalysts heavily depend on the structure of the cationic part of IL. 38 With bis(trifluoromethylsulfonyl)-imide anions [NTf 2 ] À hydroxyalkylammonium salts display the best catalytic activity and the induction time for the generation of the active species is short. In these systems the enantioselectivities were found to be in the same range as for pure methanol (90-96% ee).…”

The Multiple Roles of Imidazolium Ionic Liquids in Transition‐Metal Catalysis: The Palladium‐Catalyzed Telomerization of 1,3‐Butadiene with Acetic Acid

“…[9] In various cases, not only could the role of the ILs be the immobilization of the catalysts [10] but they can also act as modifying and/or stabilizing agents through weak to strong interactions of the cation and/or the anion of the ILs with the catalysts, such as ligand-like effects. [11,12] This is clearly the case, for example, in the selectivity control observed in the partial hydrogenation of benzene [13,14] or 1,3-butadiene [15] by classical heterogeneous Ru catalysts or Pd nanoparticles, respectively, embedded in ILs. Another outstanding example is the enantioselectivity induced by ILs that contain chiral anions [16][17][18] in transition-metal catalysis.…”