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

• Published in: Chemistry : a European journal Vol. 19; no. 49; pp. 16707 - 16721
• Main Authors: Kochem, Amélie, Gellon, Gisèle, Leconte, Nicolas, Baptiste, Benoit, Philouze, Christian, Jarjayes, Olivier, Orio, Maylis, Thomas, Fabrice
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 02.12.2013; WILEY‐VCH Verlag; Wiley Subscription Services, Inc; Wiley-VCH Verlag
• Subjects: aminyl; aniline; Aniline Compounds - chemistry; Chemical Sciences; Chemistry; Coordination Complexes - chemistry; Crystallography, X-Ray; Ethylenediamines - chemistry; Ligands; Models, Molecular; nickel; Nickel - chemistry; or physical chemistry; Oxidation-Reduction; Phenols - chemistry; radicals; Theoretical and; X-ray diffraction; X-ray diffraction; ligands; nickel; aminyl; aniline; radicals; Aminyl; Ligands; Nickel; Aniline; Radicals
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201303228

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 (E1/2=−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 CorthoCmeta 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. Nickel(II)‐anilinyl radical complexes from N4‐anilinosalen ligands are remarkably stable; depending on the ligand structure, the radical complexes belong to either class II or class III mixed‐valence compounds (see figure). Solid‐state structure and DFT calculations reveal striking differences between anilinyl and isoelectronic phenoxyl radicals.