Cobalt(II)/(III) Complexes Containingo-Iminothiobenzosemiquinonato(1−) ando-Iminobenzosemiquinonato(1−) π-Radical Ligands

The coordination chemistry of 6-amino-2,4-di-tert-butylthiophenol (H[LSAP]) and of 2-anilino-4,6-di-tert-butylphenol (H[LOAP]) with cobalt(II) ions was investigated in the presence and absence of dioxygen. It was shown that both compounds were redox-non-innocent ligands, existing in different protonation and oxidation levels as: (i) o-aminophenolates(1−) [(LXAP)1−], (ii) o-imidophenolates(2−) [(LXIP)2−], and (iii) one-electron oxidized forms o-iminobenzosemiquinonates(1−) [(LXISQ)1−], which are π-radicals (X = S, O for the sulfur or oxygen derivative). The following complexes were synthesized: [CoII(LSAP)2]2 (1), [CoII(LSISQ)2]2·0.5n-hexane (2·0.5n-hexane), [CoIIII(LSISQ)2] (3), [CoIIII(LOISQ)2] (4), and [CoIIICl(LOISQ)2] (5). The compounds 2·0.5n-hexane, 4, and 5 were structurally characterized by X-ray crystallography. It was shown that the different protonation and oxidation levels of the ligands could readily be identified by X-ray crystallography. Complex 2 could be reversibly oxidized and reduced electrochemically, yielding a monocation and a monoanion, respectively. It was shown that these processes were metal-centered ([CoIII(LSISQ)2]+, [CoII(LSISQ)2], and [CoI(LSISQ)2]−). The electronic structures were elucidated by UV/Vis and EPR spectroscopy and magnetochemistry. Complexes 3, 4, and 5 were shown to be singlet diradicals. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)