RUTHENIUM(II) COMPLEXES CONTAINING OPTICALLY-ACTIVE HEMILABILE P,N,O-TRIDENTATE LIGANDS - SYNTHESIS AND EVALUATION IN CATALYTIC ASYMMETRIC TRANSFER HYDROGENATION OF ACETOPHENONE BY PROPAN-2-OL

The trifunctional ligands phino)-2-((1R,2S,5R)-menthoxy)-1-(2-pyridyl) ethane (2R), phino)-2-((1R,2S,5R)-menthoxy)-1-(2-pyridyl)ethane (25), and (S)-(phenyl(2-anisyl)phosphino)(2-pyridyl)methane (3) have been sy nthesized, as well as the corresponding RuCl2(PPh(3))(L) complexes. Th e complexes RuCl2(PPh(3))(2R) (5) and RuCl2(PPh(3))(2S) (6) were isola ted as mixtures of two isomers, 5a and 5b and 6a and 6b, respectively. In each of these isomers, the ligands 2 are eta(3)-(P,N,O) bound. The y differ by the position of the triphenylphosphine, which is either in a trans position relative to the pyridyl ring (5a or 6a) or in a tran s position relative to the ether function (5b or 6b). Variable tempera ture NMR experiments have shown that the hemilabile character in solut ion of the ligands 2 is through their pyridyl arm in the isomers a or their ether arm in b. The complexes 6b and RuCl2(PPh(3))(3) (9) were c haracterized by X-ray diffraction. The complexes 5, 6, and 9 are very active catalysts for the transfer hydrogenation of acetophenone by pro pan-2-ol in basic media, the higher activity being observed for 9 (tur novers frequency 48 900 h(-1)). The enantioselectivity is modest and d ependent on the reactions conditions. The best result has been observe d for 5, with an ee of 60%.