The development of sustainable, more efficient and selective organic synthesis is one of the fundamental research goals in chemistry. In this respect, catalysis is a key technology. However, most catalytic reactions today rely on precious metals such as ruthenium, rhodium, iridium, or palladium. Accordingly, to develop greener, safer, and more cost-effective chemical processes, it is highly important to replace precious metal catalysts by earth abundant non-precious (base) metal catalysts (Fe, Mn, Co, Ni etc). Chiral N-heterocyclic structures are ubiquitous in natural products and artificial bioactive molecules. Transition metal-catalyzed asymmetric hydrogenation of N-heteroaromatics is one of the most straightforward and environmentally friendly methods for the synthesis of this class of structures, and a number of chiral noble metal catalysts have been developed for this purpose. However, this field is still less explored with base metal catalysts. Herein, we introduced a new class of well-defined chiral pincer Mn catalysts for highly efficient and enantioselective hydrogenation of N-Heteroarenes with either molecular hydrogen or ammonia borane as reducing agent. The present system works well in the reduction of both quinolines and quinoxalines and tolerates a broad range of functional groups. Interestingly, mirror enantiomer of saturated heterocycle was produced under the catalysis of the same manganese complex, using H2 and NH3.BH3 as reductant, respectively. Mechanistic studies were performed to understand the observation.

Enantiodivergent asymmetric hydrogenation of N-heteroarenes with well-defined manganese catalysts

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