Stable Anilinyl Radicals Coordinated to Nickel: X‐ray Crystal Structure and Characterization

Two anilinosalen and a mixed phenol‐anilinosalen ligands involving sterically hindered anilines moieties were synthesized. Their nickel(II) complexes 1 , 2 , and 3 were prepared and characterized. They could be readily one‐electron oxidized (E_1/2=?0.30, ?0.26 and 0.10 V vs. Fc⁺/Fc, respectively) into anilinyl radicals species 1]⁺ , 2]⁺ , and 3]⁺ , respectively. The radical complexes are extremely stable and were isolated as single crystals. X‐ray crystallographic structures reveal that the changes in bond length resulting from oxidation do not exceed 0.02 Å within the ligand framework in the symmetrical 1]⁺ and 2]⁺ . No quinoid bond pattern was present. In contrast, larger structural rearrangements were evidenced for the unsymmetrical 3]⁺ , with shortening of one C_ortho? C_meta bond. Radical species 1]⁺ and 2]⁺ exhibit a strong absorption band at around 6000 cm^?1 (class III mixed valence compounds). This band is significantly less intense than 3]⁺ , consistent with a rather localized anilinyl radical character, and thus a classification of this species as class II mixed‐valence compound. Magnetic and electronic properties, as well as structural parameters, have been computed by DFT methods.