Improved Ru Catalyst for Enantioselective Hydrogenation of Ketones

Significance

The new Ru(II) catalyst (1) shows improved enantioselectivity compared to its BINAP counterpart in the asymmetric hydrogenation of ketones (R. Noyori and coworkers J. Am. Chem. Soc. 1995, 117, 2675-2676; J. Am. Chem. Soc. 1998, 120, 13529-13530). In addition to its ease of preparation, it showed higher enan­tioselectivity than BINAP-Ru or Tol-BINAP-Ru catalysts for all cases of o-, m-, or p-substituted acetophenones. The chiral control by (1S,2S)-1,2-diphenylethylenediamine (DPEN) led to the formation of enantiomerically pure complex 1 and the X-ray analysis showed that the benzophenone skeleton of the DPBP ligand adopts a chiral propeller conformation. This application adds to the emerging concept of enantiomeric discrimination of conformational chirality of achiral ligands (see reviews below).