Novel chiral tetraaza ligands: synthesis and application in asymmetric transfer hydrogenation of ketones

Abstract

Novel chiral tetraaza ligands, N-1,N-2-bis(2-(piperidin-1-yl)benzylidene)cyclohexane-1,2-diamine 1 and N-1,N-2-bis(2-(piperidin1-yl)benzyl)cyclohexane-1,2-diamine 2, have been synthesized and fully characterized by analytical and spectroscopic methods. The structure of (R,R)-1 has been established by X-ray crystallography. Asymmetric transfer hydrogenation of aromatic ketones with the catalysts prepared in situ from [lrHCl(2)(COD)](2) and the chiral tetraaza ligands in 2-propanol gave the corresponding optically active secondary alcohols in high conversions and good ees (up to 91%) under mild reaction conditions. (c) 2007 Published by Elsevier Ltd.