Mechanistic insights into asymmetric transfer hydrogenation of pyruvic acid catalysed by chiral osmium complexes with formic acid assisted proton transfer.

A density functional theory study of the asymmetric transfer hydrogenation of pyruvic acid to ł- and d-lactic acids catalysed by a chiral osmium complex OsH[(R,R)TsNCH(Ph)CH(Ph)NH2](η6-p-cymene) reveals a formic acid assisted enantio-determining proton-coupled hydride transfer mechanism. Activation strain model analysis indicates that the C-H/π interaction between η6-arene and carboxyl ligands has a significant influence on the enantioselectivity. The replacement of p-cymene by 4-isopropyl biphenyl or phenyl is highly likely to improve the catalytic performance of the complex.