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

Novel chiral tetraaza ligands, N1,N2-bis(2-(piperidin-1-yl)benzylidene)cyclohexane-1,2-diamine 1 and N1,N2-bis(2-(piperidin-1-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 [IrHCl2(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.

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(1R,2R)-N1,N2-Bis(2-(piperidin-1-yl)benzylidene)cyclohexane-1,2-diamineC30H40N4[α]D20=+85.5 (c 1.0, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (1R,2R)

(1R,2R)-N1,N2-Bis(2-(piperidin-1-yl)benzyl)cyclohexane-1,2-diamineC30H44N4[α]D20=-55.4 (c 1.0, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (1R,2R)