On the mechanism of the rhodium catalyzed acrylamide hydrogenation

The hydrogenation of acrylamides using chiral Rh(I) complexes is an attractive method for the enantioselective synthesis of highly functionalized intermediates. It has been employed less frequently than the related Rh(I) catalyzed hydrogenation of enamides and the mechanism of the reaction is not well understood. The parent reaction of acrylamide with a simple Rh(I) bisphosphine complex was studied at the B3LYP/LanL2TZ(f)/6–31++G** level of theory and shows a number of interesting differences compared to the mechanism of the enamide reaction. The minimum energy reaction pathway was found to involve attack of the molecular hydrogen parallel to the C–Rh–P bond, followed by an isomerization at the stage of the dihydride complex to give an altered orientation of the hydride, which is then transferred to the β-carbon.

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