Asymmetric hydrogenation of ketimines with minimally different alkyl groups.

Asymmetric catalysis allows the synthesis of optically active compounds, often requiring the differentiation between two substituents on prochiral substrates 1 . Despite decades of development of mainly noble metal catalysts, achieving differentiation between substituents with similar steric and electronic properties remains a significant challenge 2,3 . Here, we introduce a class of earth-abundant manganese catalysts for the asymmetric hydrogenation of dialkyl ketimines to give a range of chiral amine products. These catalysts distinguish between pairs of minimally differentiated alkyl groups bound to the ketimine, such as methyl and ethyl, and even subtler distinctions, like ethyl and n-propyl. The degree of enantioselectivity can be adjusted by modifying the components of the chiral manganese catalyst. This reaction demonstrates a wide substrate scope and achieves a turnover number (TON) of up to 107,800. Our mechanistic studies indicate that the exceptional stereoselectivity arises from the modular assembly of confined chiral catalysts and cooperative non-covalent interactions between the catalyst and the substrate.