In 2017, two Mn(I) complexes with chiral pincer ligands were reported as catalysts in the asymmetric hydrogenation of ketones, which is an appealing reaction for industrial application due to the low-toxicity, earth-abundance, and low cost of manganese. Complex 1 is active in ATH and complex 2 in AH [1,2].

We have prepared novel Mn(I) complexes with chiral PNP (3,4) and PNN pincer ligands (5) based on stereogenic phosphorus. We are testing these complexes as catalysts in the AH and ATH of ketones. The hydrogenation of acetophenone with complex 4 as catalyst (1 mol% catalyst, 50 bar H₂, toluene, 100 °C) gives 99% of yield and 48% of ee after 16 h. With the aim of enhancing the enantioselectivity, a more rigid linker will be introduced between the N and P atoms.

[1] A. Zirakzadeh, S. R. M. M. de Aguiar, B. Stöger, M. Widhalm, K. Kirchner, ChemCatChem, 2017, DOI: 10.1002/cctc.201700042.
[2] M. B. Widegren, G. J. Harkness, A.M.Z. Slawin, D. B. Cordes, M. L. Clarke, Angew. Chem. Int. Ed., 2017, DOI: 10.1002/ange.201702406.