Copper(I)-imine complexes: Synthesis and catalytic activity in olefin cyclopropanation

Different imine-type ligands, prepared by the condensation of anilines or of α-methylbenzylamine with 2-pyridinecarboxaldehyde (pyim1,2) or 2-quinolinecarboxaldehyde (quim1,2) were prepared. These species act as N,N′-bidentate, chelating ligands upon coordination to Cu(I): treatment of [Cu(PPh3)3Cl] with an equimolar amount of the ligands resulted in the displacement of two molecules of PPh3, giving rise to the formation of [Cu(pyim1,2)(PPh3)Cl] (1–2) and [Cu(quim1,2)(PPh3)Cl] (3–4), respectively. The copper derivatives 1–4 proved to be highly active catalysts in olefin cyclopropanation in the presence of ethyl diazoacetate, even using deactivated olefins (namely, 2-cyclohexen-1-one) as substrate. The X-ray structure of complex 2, [Cu(pyim2)(PPh3)Cl], is also reported.

Graphical abstractThe reaction of substituted anilines with pyridinecarboxaldehyde or 2-quinolinecarboxaldehyde afforded the corresponding imine-type species (pyim1−2 or quim1−2), acting as N,N′-bidentate ligands towards copper(I). The resulting complexes ([Cu(pyim1−2)(PPh3)Cl] and [Cu(quim1−2)(PPh3)Cl]) showed high activity in olefin cyclopropanation, in the presence of ethyldiazocetate, even when deactivated substrates were used. The X-ray structure determination of [Cu(pyim2)(PPh3)Cl] is also described.Figure optionsDownload full-size imageDownload as PowerPoint slide