Manganese(I)-catalyzed asymmetric (transfer) hydrogenation of ketones: An insight into the effect of chiral PNN and NN ligands
A new type of (RC,SP)-1-(2-diphenylphosphino)ferrocenylethylamine N-substituted with a (RC)-5,6,7,8-tetrahydroquinolinyl group (LPNN-1) was successfully employed as a chiral chelating ligand in both Mn-catalyzed asymmetric transfer hydrogenation (ATH) and asymmetric hydrogenation (AH) of a broad range of ketonic substrates (39 examples), leading to high conversions and excellent enantioselectivities for their product alcohols. In particular, PNN-pincer complex Mn-1 and its NN-bidentate analogue Mn-2 have been isolated and their comparative performance as catalysts studied with Mn-1 proving more effective in both ATH and AH. Moreover, Mn-1 generally imparted higher degrees of enantiomeric excess (ee) in both hydrogenation processes which can reach up to 99% in ATH and 93% in AH for propiophenone-type substrates. DFT calculations highlight the importance of π-π interactions and steric hindrance between catalyst and substrate which manifests itself in enhancements in ee for propiophenone over acetophenone substrates. Furthermore, a possible mechanism for the Mn-catalyzed ATH has been proposed on the basis of a joint DFT and experimental investigation.
We acknowledge the support from the National Natural Science Foundation of China (21871275), the Nature Science Foundation of Hebei Province (B2022205020, B2022204020 and B2019205149) and Talent Introduction Foundation of Hebei Agricultural University (YJ201931), Discipline Group Construction Foundation of Forestry College of Hebei Agricultural University (XK1008601519), Research project of Fundamental Scientific Research Business Expenses of provincial colleges and universities in Hebei Province (KY2021028). G.A.S. is grateful to the Chinese Academy of Sciences for a President’s International Fellowship for Visiting Scientists.
Author affiliationDepartment of Chemistry, University of Leicester
- AM (Accepted Manuscript)