Direct experimental and computational evidence for the dihydride pathway in TangPHOS-Rh catalysed asymmetric hydrogenation

DFT computations of various possible reaction pathways in asymmetric hydrogenation of methyl (Z-α)acetylaminocinnamate catalysed by Rh-TangPHOS complex revealed the clear preference of the dihydride pathway. This conclusion was explicitly confirmed by the structure of the monohydride intermediate intercepted in the low temperature NMR hydrogenation experiments. DFT analysis of the origin of enantioselection showed that it takes place via obstructing the proper coordination of the double bond in the S-enantioselective pathway.