A new method to radical anions derived from s-Indacene organobimetallic complexes, their ESR characterization

The following organobimetallic radical anions derived from 2,6-diethyl-4,8-dimethyl-s-indacene (s-Ic′): [CODRh(s-Ic′)RhCOD]− (IIa), [Cp∗Ru(s-Ic′)RuCp∗]− (IIb), [Cp∗Ru(s-Ic′)RhCOD] − (IIc), [Cp∗Ru(s-Ic′)NiCp∗]− (IId) [(CO)3Mn(s-Ic′)NiCp∗]− (IIe) and [Cp∗Fe(s-Ic′)NiCp∗]− (IIf) (COD = 1,5-cyclooctadiene; Cp∗ = pentamethylcyclopentadienyl) were prepared by reduction of the parent complexes using a monoelectronic transfer from an electron rich olefin. The radical anions were fully characterized by ESR spectroscopy which usually gave a well resolved hyperfine coupling structure, indicating that the spin distribution in the symmetrical radical anions (IIa, IIb) affects mainly the organic spacer whereas in the unsymmetrical ones (IIc–f) it is displaced towards the most electronegative metal center and its ligands. This effect is most pronounced in IId, IIe and IIf. The calculated g tensor values of the radical anions are in good agreement with the experimental values. In heterobimetallic radical anions, the dissymmetric spin distribution shows that the two metals present different electrophile properties leading to potentially different catalytic activities.