Arene Ruthenium(II) Complexes

Arene Ru(II) complexes 1 are stable precursor for the preparation of asymmetric catalysts. For example, BINAP-Ru(II) and Pybox-Ru(II) are prepared from 1 and these catalysts are useful for asymmetric hydrogenation of ketones¹⁾ and asymmetric cyclopropanation of olefins,²⁾ respectively. Recently, R. Noyori and co-workers have found that Ru(II) catalyst 3, which is prepared from 1 and chiral amine 2, is extremely effective for asymmetric hydrogenation. The asymmetric transfer hydrogenation of ketones and imines using chiral Ru(II) catalyst 3 affords chiral alcohols³⁾ and chiral amines,⁴⁾ respectively, in good yield and high enantiomeric purity.

Currently, there are two standard methods for hydrogenation of ketones and imines: catalytic reduction with hydrogen and transfer hydrogenation with alcohols or formic acid as hydrogen donors. The latter method is attractive because of its operational simplicity in that it requires no high pressure autoclave in the chemical procedures.