Abstract

ANJOS, Ademir dos et al. New phenoxyl radical complexes of manganese, gallium, indium and iron based on an H₂bbpen ligand derivative. J. Braz. Chem. Soc. [online]. 2006, vol.17, n.8, pp. 1540-1550. ISSN 0103-5053.  http://dx.doi.org/10.1590/S0103-50532006000800009.

Reported herein are the synthesis and characterization of the hexadentate H₂L pro-ligand (N,N',N,N'-bis[(2-hydroxy-3,5-di-tert -butylbenzyl)(2-pyridylmethyl)]ethylenediamine), as a further derivative of the well known pro-ligand H₂bbpen which contains two phenolate and two pyridyl pendant arms. The phenolate groups in H₂L are suitably protected by bulky substituents (tert-butyl) in the ortho- and para- positions, from which stable phenoxyl radical complexes can be formed. Thus, we have synthesized four new mononuclear complexes with Mn^III, Ga^III, In^III and Fe^III which through electrochemical oxidation generate one- and two-electron oxidized phenoxyl species in solution. These radical species were characterized by UV-Vis, Electronic Paramagnetic Resonance and electrochemical studies. As expected, in the case of the Ga^III, In^III and Fe^III complexes no metal-centered oxidation was observed. However, the manganese complex undergoes metal- and ligand-centered oxidation processes and therefore a phenoxyl radical-Mn^IV complex can be generated in solution. The crystal structures of the [Mn^III(L)]⁺ and [Ga^III(L)]⁺ complexes were determined by X-ray crystallographic analyses revealing monocationic complexes with distorted octahedral geometries.

Keywords : H₂bbpen; trivalent complexes; phenoxyl radical; crystal structures.