ABSTRACT

The use of ruthenium tertiary bisphosphine complexes as catalysts for the homogeneous hydrogenation of imines (at 1000 psi H2 in MeOH) is discussed; the systems are active even at ≤ 1 mM [Ru]. The air-stable Ru2Cl5(PP)2 complexes are more active than the commonly used Ru2(IIJI) systems to which they give rise in situ (PP = a chelating ditertiary phosphine, including chiral systems). Asymmetric induction in prochiral imines was consistent (but to only 15% e.e.) within a series of neutral, diop complexes, implying a common catalyst intermediate. A maximum of only 27% e.e. is found for reduction of PhCH2N=C(Me)Ph (using Ru2Cl5(chiraphos)2).