An iron(II) complex with a tetradentate peptide ligand, cis-C6H10(CO-Cys-Pro-Leu-Cys-OMe)2-1,2, as a model of reduced rubredoxin
Abstract
The complexes [NEt4]2[Fe{cis-C6H10(CO-Cys-OMe)2-1,2}2]1 and [NEt4]2[Fe{cis-C6H10(CO-Cys-Pro-Leu-Cys-OMe)2-1,2}]2 were synthesised by ligand-exchange reaction of [NEt4]2[Fe(SBut)4] with the corresponding free peptide. In the 1H NMR spectra the Cys CβH2 protons of 1 and 2 were observed between δ 200 and 270 in CD3CN at 30 °C. The temperature dependence of these signals indicate that high-spin mononuclear iron(II) complexes are formed. Complexes 1 and 2 exhibit redox potentials at –0.60 and –0.78 V respectively vs. saturated calomel electrode in dimethyl sulfoxide. These negatively shifted redox potentials are explained by the difficulty in forming an intramolecular NH ⋯ S hydrogen bond involving the Leu residue in 2, confirmed by the 2H NMR spectrum.