Transition states of binap-rhodium(I)-catalyzed asymmetric hydrogenation: theoretical studies on the origin of the enantioselectivity.
By using the hybrid IMOMM(B3LYP:MM3) method, we examined the binap-Rh(I)-catalyzed oxidative-addition and insertion steps of the asymmetric hydrogenation of the enamide 2-acetylamino-3-phenylacrylic acid. We report a path that is energetically more favorable for the major enantiomer than for the minor enantiomer. This path follows the "lock-and-key" motif and leads to the major enantiomeric product via an energetically favorable binap-dihydride-Rh(III)-enamide complex. Our theoretical results are consistent with the mechanism that takes place via Rh(III) dihydride formation, that is, oxidative addition of H2 followed by enamide insertion.
Mori
Seiji
S
Faculty of Science, Ibaraki University, Bunkyo, Mito 310-8512, Japan. smori@mx.ibaraki.ac.jp
Vreven
Thom
T
Morokuma
Keiji
K