Oxidation and Reduction of Bis(imino)pyridine Iron Dicarbonyl Complexes

The oxidation and reduction of a redox-active aryl-substituted bis(imino)pyridine iron dicarbonyl has been explored to determine whether electron-transfer events are ligand- or metal-based or a combination of both. A series of bis(imino)pyridine iron dicarbonyl compounds, [((PDI)-P-iPr)Fe(CO)(2)](-), ((PDI)-P-iPr)Fe(CO)(2), and [((PDI)-P-iPr)Fe(CO)(2)](+) [(PDI)-P-iPr = 2,6-(2,6-(2C6H3N)-C-iPr=CMe)(2)C5H3N], which differ by three oxidation states, were prepared and the electronic structures evaluated using a combination of spectroscopic techniques and, in two cases, [((PDI)-P-iPr)Fe(CO)(2)](+) and [((PDI)-P-iPr)Fe(CO)(2)], metrical parameters from X-ray diffraction. The data establish that the cationic iron dicarbonyl complex is best described as a low-spin iron(I) compound (S-Fe = (1)/(2)) with a neutral bis(imino)pyridine chelate. The anionic iron dicarbonyl, [((PDI)-P-iPr)Fe(CO)(2)], is also best described as an iron(I) compound but with a two-electron-reduced bis(imino)pyricline. The covalency of the neutral compound, ((PDI)-P-iPr)Fe(CO)(2), suggests that both the oxidative and reductive events are not ligand- or metal-localized but a result of the cooperativity of both entities.