Synthesis and molecular structures of nickel(II) and cobalt(III) complexes with 2-(arylimino)-3-(hydroxyimino)butane

We report new series of NiII and CoIII complexes with nitrogen-donor chelating ligands of the (E,E)-2-(arylimino)-3-(hydroxyimino) butane type (Ar-N∩N-OH). These ligands are characterized by a hydrophilic (OH group) and a hydrophobic region (aryl group). NiII derivatives were obtained either as trimers of formula [Ni3(Ar-N∩N-OH)3Br4(OH)][Br], with the hydrophobic groups oriented on the same side, or as bis(chelated) derivatives with cis geometry, depending on the steric hindrance of the aryl groups. CoIII complexes were obtained only as bis(chelated) derivatives, with the two ligands coplanar. The "iso-oriented" arrangement of ligands in bis(chelated) CoIII complexes is favored by weak interactions between the two ligands, namely O-H⋯O hydrogen bond and stacking interactions between the aryl groups. CoIII complexes might find application as catalysts for living or controlled radical polymerization of polar olefins, and preliminary results are reported. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.