Abstract
Herein, we provide evidence showing that the long-held major-minor concept for catalytic asymmetric reactions needs to be readdressed. The asymmetric hydrogenation of enamide 1 catalyzed by the chiral Rh(I) complex of (R,R)-BenzP∗ quantitatively yields the corresponding hydrogenated R-product 2 with 89.6% ee. The most abundant catalyst-substrate species in the reaction pool was found to be [Rh((R,R)-BenzP)(Ph(MeCONH)C=CH2)]+SbF6- (5). This species is also the most reactive to hydrogen among the various Rh complexes. Low-temperature hydrogenation experiments showed direct transformation of 5 to 2 with over 98% ee (R). However, the oxidative addition of H2 to 5 would yield the S-product. Computation has now revealed a low-energy R-enantioselective route, whereby H2 addition to 5 is followed by π-bond dissociation, isomerization of nonchelating Rh species, and recoordination of the double bond before C-H bond formation occurs.
Original language | English |
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Pages (from-to) | 2911-2915 |
Number of pages | 5 |
Journal | ACS Catalysis |
Volume | 5 |
Issue number | 5 |
DOIs | |
Publication status | Published - 2015 May 1 |
Keywords
- DFT calculations
- Rh complexes
- asymmetric hydrogenation
- origin of enantioselectivity
- reaction mechanism
ASJC Scopus subject areas
- Catalysis
- Chemistry(all)