Département de chimie moléculaire

Five tetradentate ligands based on the N,N'-bis(2-amino-3,5-di-tert-butylphenyl)-o-phenylenediamine backbone were prepd., with different substituents at positions 4 and 5 (CH3 (3a), p-CH3O-C6H4 (3b), H (3c), Cl (3d), F (3e)). Their reaction with a nickel(II) salt in air affords the neutral species 4(a-e), which were isolated as single crystals. 4(A-e) feature two antiferromagnetically exchange-coupled diiminosemiquinonate moieties, both located on peripheral rings, and a diamidobenzene bridging unit. Oxidn. of 4(a-e) with 1 equiv of AgSbF6 yields the cations 4(a-e)+, which harbor a single diiminosemiquinonate radical. Significant structural differences were obsd. within the series. 4B+ is mononuclear and contains a localized diiminosemiquinonate moiety. In contrast, 4c+ is a dimer wherein the diiminosemiquinonate radical is rather delocalized over both peripheral rings. 4D+ represents an intermediate case where the complex is mononuclear, but the radical is fully delocalized. Oxidn. of 4(a-e) with 2 equiv of AgSbF6 produces the corresponding mononuclear dications. X-ray diffraction data on 4(b-d)2+ reveals that the bridging ring retains its diamidobenzene character, whereas both peripheral rings were oxidized into diiminobenzoquinone moieties. All the complexes were characterized by electrochem., EPR, and UV-visible-NIR spectroscopy. Remarkably, the electronic structures of the complexes differ from those reported by Wieghardt et al. for copper and zinc complexes of a related ligand involving a mixed N2O2 donor set. The easier oxidn. of phenylenediamine moieties in comparison to aminophenols is proposed to account for the difference. [on SciFinder(R)]