Synthesis and characterisation of Cu(II) complexes bearing N,N'-di(methoxybenzy1)-(R,R)-1,2-diaminocyclohexane as catalysts for the asymmetric nitroaldol reaction

Enantiopure Cu(II) complexes with N,N'-di(p-methoxybenzyl)-(R,R)-1,2-diaminocyclohexane (L-1), 101'di(m-methoxybenzy1)-(R,R)-1,2-diaminocyclohexane (L-2), and N,N'-di(m-methoxybenzyI)-(R,R)-1.2diaminocyclohexane (L-3) ligands were synthesised and characterised. The X-ray crystal structures of Cu(II) complexes containing 1.1 and L3 were determined. The geometry around the Cu(II) centre for (L-1)CuCl2 was distorted square-planar. The crystal structure of (L-3)CuCl2 revealed a square-pyramidal structure with a strong interaction between the Cu and O of the methoxy group. Their double catalytic activation with diisopropylethylamine in the asymmetric nitroaldol reaction of benzaldehyde and nitromethane was examined. The reaction yield was moderate with an enantiomeric excess of up to 87%. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.