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

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.