Copper complexes of chiral tetradentate binaphthyl Schiff-base ligands : Syntheses, X-ray crystal structures and activity in catalytic asymmetric cyclopropanation of alkenes

A number of new chiral monomeric binaphthyl Schiff-base ligands H₂L [where H₂L = 2,2′-bis(3-R¹-5-R²-2-hydroxybenzylideneamino) -1,1′-binaphthyl] and a series of chiral copper(II) complexes [CuL] were prepared in good or nearly quantitative yields. Some of the free ligands and the [CuL] complexes were structurally characterized by X-ray crystallography. Almost all the [CuL] complexes were found to be active catalysts for the asymmetric cyclopropanation of alkenes with ethyl or tert-butyl diazoacetate. Enantioselectivities of up to 77% ee were observed. © Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.