Direct Asymmetric Ruthenium-Catalyzed Reductive Amination of Alkyl–Aryl Ketones with Ammonia and Hydrogen

The asymmetric ruthenium-catalyzed
reductive amination employing
ammonia and hydrogen to primary amines is described. Here we demonstrate
the capability of our catalyst to perform a chemo- and enantioselective
process while using simple ammonia gas as a reagent, one of the most
attractive and industrially relevant nitrogen sources. The presence
of a catalytic amount of ammonium iodide was essential for obtaining
good yields and enantioselectivities. The mechanism of this reaction
was investigated by DFT and we found a viable pathway that also explains
the trend and magnitude of enantioselectivity through the halide series
in good agreement with the experimental data. The in-depth investigation
of substrate conformers during the reaction turned out to be crucial
in obtaining an accurate prediction of the enantioselectivity. Furthermore,
we report the crystallographic data of the chiral [Ru­(I)­H­(CO)­((S,S)-f-binaphane)­(PPh3)] complex, which we identified as the most efficient catalyst
in our investigation.