Cationic BINAP-Ru(II) Halide Complexes: Highly Efficient Catalysts for Stereoselective Asymmetric Hydrogenation of .alpha.- and .beta.-Functionalized Ketones

Cationic ruthenium-BINAP complexes 5, 7, and 10 of the formula [RuX((S)-BINAP)(arene)]Y, where X=Cl, Br, I; Y=Cl, Br, I, BF 4 , B(C 6 H 5 ) 4 ; arene=benzene, p-cymene, ethyl benzoate, and their enantiomers have been prepared by the reaction of arene-ruthenium halide complexes 4, 6, and 9 with (S)-BINAP or (R)-BINAP. Structures of the complexes were established by spectroscopy, conductivity, and a single-crystal X-ray analysis (5d: orthorhombic, P2 1 2 1 2; a=20.141(2) A, b=18.504(1) A, c=12.241(1) A, V=4562.0(7) A 3 , Z=4, R=0.078 for unique 4177 reflections). BINAP derivatives with various substituents at the para and meta positions of four phenyl rings on phosphorous atoms and their cationic Ru(II) complexes have also been synthesized. These BINAP-Ru (II) complexes have been used as catalysts for the asymmetric hydrogenation of various unsaturated organic compounds such as α- and β-keto esters, allylic alcohols, and α,β-unsaturated carboxylic acids in excellent diastereo- and/or enantioselectivities. Catalytic activities and stereoselectivities depend highly on reaction conditions such as solvent, temperature, and additives. Variation of halogen ligands bound to ruthenium atom and substituents on four phenyl rings of BINAP also have exerted remarkable effects on the efficiency of the catalysis. Asymmetric hydrogenation of methyl (∓)-2-(benzamidomethyl)-3-oxobutanoate catalyzed by the species derived from 9c and 3,5-(tBu) 2 -BINAP afforded the corresponding syn-(2S,3R)-17 in 98% de and 99% ee