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, [(iPrPDI)Fe(CO)2]−, (iPrPDI)Fe(CO)2, and [(iPrPDI)Fe(CO)2]+ [iPrPDI = 2,6-(2,6-iPr2C6H3NCMe)2C5H3N], which differ by three oxidation states, were prepared and the electronic structures evaluated using a combination of spectroscopic techniques and, in two cases, [(iPrPDI)Fe(CO)2]+ and [(iPrPDI)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 (SFe = 1/2) with a neutral bis(imino)pyridine chelate. The anionic iron dicarbonyl, [(iPrPDI)Fe(CO)2]−, is also best described as an iron(I) compound but with a two-electron-reduced bis(imino)pyridine. The covalency of the neutral compound, (iPrPDI)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.