Synthesis and structural characterization of iron complexes bearing N-aryl-phenanthren-o-iminoquinone ligands

Abstract

Treatments of N-aryl-phenanthren-o-iminoquinone (aryl = 2,6-Me₂C₆H₃ (^MeL); 2,6-ⁱPr₂C₆H₃ (^iPrL)) with iron powder in THF at 75 °C generate complexes [η²L]₂Fe[η¹LH] (1a, L = ^MeL; 1b, L = ^iPrL) in moderate yields. The X-ray crystallography analysis reveals that the molecule of 1b consists of a Fe(III) center coordinated by three phenanthren-o-iminosemiquinone ligands, two of which are in an η² fashion while the remaining one is in an η¹ fashion. The analysis of the bond parameters of ligands indicates that the η²-fashioned ligands are radical anions and the η¹-fashioned one is in an aminephenolato form. Reactions of ^MeL and ^iPrL with FeCl₂ in THF produce Fe(III) complexes [L]₂FeCl (2a, L = ^MeL; 2b, L = ^iPrL) with the two ligands in the radical anionic form. However, similar reactions of PIQ ligands with FeCl₂ in CH₂Cl₂ yield ion-pair complexes {[L]₂FeCl}⁺[FeCl₄]⁻ (3a, L = ^MeL; 3b, L = ^iPrL), in which the iron center chelated by two neutral ligands can be formulated as Fe(II). Reduction of 2b with sodium provides a salt-type complex [^iPrL²⁻]₂Fe(II)Na₂ (4), in which a high spin Fe(II) atom is ligated by two amidophenolate ligands, and the sodium atoms attached to the oxygen atoms of ligands are η³-coordinated by the aryl ring in amido moieties.