924278-01-3Relevant academic research and scientific papers
LIGAND, METHOD FOR PRODUCING THE SAME, AND CATALYST USING THE LIGAND
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Page/Page column 24, (2009/01/20)
Disclosed is a novel asymmetric ligand which can be synthesized by a short process at low cost and is capable of exhibiting higher catalytic activity and enantioselectivity than the conventional ligands derived from sugars. Also disclosed are a method for producing such an asymmetric ligand, and a catalyst using such an asymmetric ligand. Specifically disclosed is a ligand represented by the general formula I below or the like. (In the formula, R1 and R2 independently represent 0-5 substituents; X represents P, As or N; m represents an integer of 0-7; n represents an integer of 0-3; A1-A4 independently represent hydrogen, fluorine, chlorine, bromine, benzoyl or acetyl, or alternatively A2 and A3 combine together to form a ring.)
Key role of the Lewis base position in asymmetric bifunctional catalysis: Design and evaluation of a new ligand for chiral polymetallic catalysts
Fujimori, Ikuo,Mita, Tsuyoshi,Maki, Keisuke,Shiro, Motoo,Sato, Akihiro,Furusho, Sanae,Kanai, Motomu,Shibasaki, Masakatsu
, p. 16438 - 16439 (2007/10/03)
New chiral ligands for asymmetric polymetallic catalysts were designed on the basis of the assumption that the higher-order assembly structure is stabilized by modifying the modular unit. The designed ligands 6 and 7 contained a scaffolding cyclohexane ring with a Lewis base phosphine oxide directly attached to the scaffold. A module in the polymetallic complex contains two metals per ligand, and a stable 6-, 5-, 5-membered fused chelation ring system should be generated. Synthesis of these ligands is simple and high yielding, using a catalytic dynamic kinetic resolution promoted by the Trost catalyst as a key step. Ligand function was assessed in a catalytic asymmetric ring-opening reaction of meso-aziridines with TMSCN, a useful reaction for the synthesis of optically active β-amino acids. The Gd complex generated from Gd(OiPr)3 and the ligand was a highly active and enantioselective catalyst in this reaction. Enantioselectivity was reversed compared to the previously reported d-glucose-derived catalyst containing the same chirality of the individual module. ESI-MS analysis and X-ray crystallographic studies indicate that the assembly state of the modules in the polymetallic catalysts differs depending on the chiral ligand. The difference in the higher-order structure stems from a subtle change (one carbon) in the position of the Lewis base relative to the Gd metal. The change in the higher-order structure of the polymetallic complex led to a dramatic reversal of the enantioselectivity and increased catalyst activity. Copyright
