Iron complexes containing the ligand N,N'-bis(6-methyl-2-pyridylmethyl)N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine:: Structural, spectroscopic, and electrochemical studies, reactivity with hydrogen peroxide and the formation of a low-spin Fe-OOH complex

The ligand N,N'-bis(6-methyl-2-pyridylmethyl)-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine (L(6)(2)2M) has allowed to prepare the new Fe-II complex [(L(6)(2)2M)FeCl2] (1), and to compare its structural and spectroscopic characteristics with [(L(6)(2)2M)FeCl]PF6 (2). The molecular structure of 1, resolved by X-ray diffraction, exhibits the ligand tetracoordinated with the two non-methylated pyridine rings coordinated. As shown by UV/Vis spectroscopy and cyclic voltammetry, upon dissolution in methanol or acetonitrile, one chloride ion is released and replaced by a pyridine group. Therefore, complexes I and 2 adopt identical structures in solution, i.e. [(L(6)(2)2M)FeCl+. However, upon oxidation complex 1 gives several ferric complexes with the ligand L(6)(2)2M pentacoordinated, or tetracoordinated with two chloride ions. This peculiar behaviour is due to the presence of chloride ions in solution in the case of 1. Upon reaction with H2O2 in methanol, complex 2 leads to the formation of low-spin [(L(6)(2)2M)Fe-III (OOH)(2+), whereas it is not observed in the case of 1. Based on the presence or not of chloride ions in solution, a mechanism is proposed for the reactivity of complexes I and 2 toward H2O2 ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).