Oxidative Addition of Carbon–Carbon Bonds with a Redox-Active Bis(imino)pyridine Iron Complex

Addition of biphenylene to the bis­(imino)­pyridine iron
dinitrogen
complexes, (iPrPDI)­Fe­(N2)2 and [(MePDI)­Fe­(N2)]2(μ2-N2) (RPDI = 2,6-(2,6-R2C6H3NCMe)2C5H3N; R = Me, iPr), resulted in oxidative addition
of a CC bond at ambient temperature to yield the corresponding
iron biphenyl compounds, (RPDI)­Fe­(biphenyl). The molecular
structures of the resulting bis­(imino)­pyridine iron metallacycles
were established by X-ray diffraction and revealed idealized square
pyramidal geometries. The electronic structures of the compounds were
studied by Mössbauer spectroscopy, NMR spectroscopy, magnetochemistry,
and X-ray absorption and X-ray emission spectroscopies. The experimental
data, in combination with broken-symmetry density functional theory
calculations, established spin crossover (low to intermediate spin)
ferric compounds antiferromagnetically coupled to bis­(imino)­pyridine
radical anions. Thus, the overall oxidation reaction involves cooperative
electron loss from both the iron center and the redox-active bis­(imino)­pyridine
ligand.