Synthesis and X-ray structure of a Cu(II) complex of N,N′-bis(2-pyridylmethylidene)-(R,R)-1,2-diaminocyclohexane and its catalytic application for asymmetric Henry reaction

The reaction of N,N′-bis(2-pyridylmethylidene)-(R,R)-1,2-diaminocyclohexane (L) with Cu(ClO4)2 · 6H2O was carried out and resulted in the formation of a new chiral tetradentate Cu(II) complex. The structure of Cu(L)(NCCH3)(ClO4)2 was determined by X-ray diffraction method. This result revealed that Cu2+ ion in the complex was coordinated by four nitrogen atoms of the chiral Schiff base ligand and one nitrogen atom of NCCH3 in a distorted trigonal bipyramid geometry. The yields of asymmetric Henry reaction between benzaldehyde and nitromethane in the presence of triethylamine or diiospropylethylamine by using the complex as a catalyst were high (⩾94%), however, the enantiomeric excesses were not (ca. 30%).

The reaction of N,N′-bis(2-pyridylmethylidene)-(R,R)-1,2-diaminocyclohexane (L) with Cu(ClO4)2 · 6H2O afforded a new chiral Cu(L)(NCCH3)(ClO4)2. The X-ray crystal structure revealed that the geometry around Cu2+ ion was a distorted square-planar geometry. The complex was evaluated as a catalyst for asymmetric Henry reaction between benzaldehyde and nitromethane in the presence of triethylamine or diiospropylethylamine (yield: ⩾94%; ee: cat. 30%).Figure optionsDownload as PowerPoint slide