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Temperature‐tuned enantioselectivity in transfer hydrogenation : preparation and catalytic property of amino acid‐modified benzimidazole
Author(s) -
Li XiaoNa,
Zhou HongYong,
Feng Lei,
Duan Kai,
Wang JiaXi
Publication year - 2012
Publication title -
applied organometallic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 71
eISSN - 1099-0739
pISSN - 0268-2605
DOI - 10.1002/aoc.2823
Subject(s) - chemistry , acetophenone , enantiomeric excess , catalysis , transfer hydrogenation , benzimidazole , substrate (aquarium) , medicinal chemistry , solvent , asymmetric hydrogenation , stereochemistry , enantioselective synthesis , organic chemistry , ruthenium , oceanography , geology
A series of l ‐amino acid‐modified benzimidazoles have been synthesized and their application in Ru‐catalysed asymmetric transfer hydrogenation (ATH) of ketones has been evaluated using i‐propanol as hydrogen donor as well as solvent. The enantioselectivity of the product was sensitive to the reaction conditions and showed reversed temperature effect. Better reaction activity and enantioselectivity were obtained at higher reaction temperature and higher molar ratio of substrate to catalyst (S/C). At an S/C of 2000:1 and 5000:1, the turnover frequency (TOF) and the enantiomeric excess (ee) value of the ATH of acetophenone promoted by the combination of l ‐proline benzimidazole 7c and [RuCl 2 ( p ‐cymene)] 2 were up to 6880, 13 000 h −1 and 67%, 51% respectively. The ee value dropped off after the reaction reached equilibrium. The high activity and enantioselectivity of [RuCl 2 ( p ‐cymene)] 2 / 7c was primarily influenced by the ( S , R ) configuration, whereas the ( S , S ) configuration had low activity and enantioselectivity. Copyright © 2012 John Wiley & Sons, Ltd.