Computational Design of SCS Nickel Pincer Complexes for the Asymmetric Transfer Hydrogenation of 1-Acetonaphthone

Inspired by the active site structures of lactate racemase and recently reported sulphur- carbon-sulphur (SCS) nickel pincer complexes, a series of scorpion-like SCS nickel pincer complexes with an imidazole tail and asymmetric claws was proposed and examined computationally as potential catalysts for the asymmetric transfer hydrogenation of 1-acetonaphthone. Density functional theory calculations reveal a proton-coupled hydride transfer mechanism for the dehydrogenation of (R)-(+)-1-phenyl-ethanol and the hydrogenation of 1-acetonaphthone to produce (R)-(+)-1-(2-naphthyl)ethanol and (S)-(-)-1-(2-naphthyl)ethanol. Among all proposed Ni complexes, 1(Ph) is the most active one with a rather low free energy barrier of 24 kcal/mol and high enantioselectivity of near 99% enantiomeric excess (ee) for the hydrogenation of prochiral ketones to chiral alcohols.