61478-28-2Relevant academic research and scientific papers
Chiral rhodium complexes covalently anchored on carbon nanotubes for enantioselective hydrogenation
Gheorghiu,Machado,Salinas-Martinez De Lecea,Gouygou,Roman-Martinez,Serp
, p. 7455 - 7463 (2014/05/20)
Chiral rhodium hybrid nanocatalysts have been prepared by covalent anchorage of pyrrolidine-based diphosphine ligands onto functionalized CNTs. This work constitutes the first attempt at covalent anchoring of homogeneous chiral catalysts on CNTs. The catalysts, prepared with two different chiral phosphines, were characterized by ICP, XPS, N2 adsorption and TEM, and have been tested in the asymmetric hydrogenation of two different substrates: methyl 2-acetamidoacrylate and α-acetamidocinnamic acid. The hybrid nanocatalysts have shown to be active and enantioselective in the hydrogenation of α-acetamidocinnamic acid. A good recyclability of the catalysts with low leaching and without loss of activity and enantioselectivity was observed. This journal is the Partner Organisations 2014.
Transition-Metal-Catalyzed Asymmetric Organic Synthesis via Polymer-Attached Optically Active Phosphine Ligands. 5. Preparation of Amino Acids in High Optical Yield via Catalytic Hydrogenation
Baker, Gregory L.,Fritschel, Scott J.,Stille, John R.,Stille, John K.
, p. 2954 - 2960 (2007/10/02)
Two new optically active phosphinopyrrolidine monomers were prepared by the reaction of (2S,4S)-4-(diphenylphosphino)-2-pyrrolidine and (2R,4R)-4-(diphenylphosphino)-2-pyrrolidine with acryloyl chloride to give N-acryloyl-(2S,4S)-4-(diphenylphosphino)-2-pyrrolidine (1) and N-acryloyl-(2R,4R)-4-(diphenylphosphino)-2-pyrrolidine (2).Copolymerization of 1 and 2 with hydrophilic comonomers and a divinyl monomer provided cross-linked insoluble polymers containing 3-5percentof 1 or 2 that would swell in polar solvents.Exchange of rhodium (I) onto the polymer gave catalysts which were active for the asymmetric hydrogenation of N-acyl α-amino acids in high optical yields, the phosphine derived from the enantiomer of the naturally occurring 4-hydroxyproline giving (S)-amino acids.The catalysts could be reused with no loss in selectivity by simple filtration.
Asymmetric Hydrogenation of Prochiral Olefins Catalyzed by Rhodium Complexes with Chiral Pyrrolidinodiphosphines. Crucial Factors for the Effective Asymmetric Induction
Ojima, Iwao,Kogure, Tetsuo,Yoda, Noriko
, p. 4728 - 4739 (2007/10/02)
Remarkable effects of hydrogen pressure on the stereoselectivity were observed in the asymmetric hydrogenations of itaconic acid, α-(acylamino)acrylic acid, and their derivatives catalyzed by rhodium complexes of chiral pyrrolidinodiphosphines.Effects of added triethylamine on the pressure dependency of stereoselectivity were also studied.Marked differences in the direction of asymmetric induction were found in the asymmetric hydrogenations of the methylsuccinic acid precursors itaconic acid, citraconic acid, and mesaconic acid.This result clearly indicates that the chiral recognition by the rhodium catalyst is extremely sensitive to the stereochemistry of the prochiral olefins.Possible mechanisms are discussed on the basis of these results. 31PNMR studies on the key intermediates in asymmetric hydrogenations have revealed that the mode of the bidentate complexation of the prochiral substrates is extremely regioselective.The "induced-fit" phenomena of the chiral rhodium complex were observed.A possible mechanism for the chiral recognition of enantiofaces in the chiral coordination sphere is proposed.
