Synthesis, electronic structure and reactivity of bis(imino)pyridine iron carbene complexes: Evidence for a carbene radical

The reactivity of the disubstituted diazoalkane, N₂CPh ₂ with a family of bis(imino)pyridine iron dinitrogen complexes was examined. For the most sterically protected member of the series, ( ^iPrPDI)Fe(N₂)₂ (^iPrPDI = 2,6-(2,6-ⁱPr₂C₆H₃NCMe) ₂C₅H₃N), an S = 1 iron diazoalkane complex was obtained and structurally characterized. Reducing the size of the 2,6-aryl substituents to ethyl or methyl groups resulted in isolation of bis(imino)pyridine iron carbene complexes. Magnetic measurements established S = 1 ground states, demonstrating rare examples of iron carbenes in a weak ligand field. Electronic structure determination using metrical parameters from X-ray diffraction as well as Mössbauer, XAS and computational data established high-spin iron(ii) compounds engaged in antiferromagnetic coupling with redox-active bis(imino)pyridine and carbene radicals.