Cobalt(II)/(III) complexes containing o-iminothiobenzosemiquinonato(1-) and o-iminobenzosemiquinonato(1-) π-radical ligands

The coordination chemistry of 6-amino-2,4-di-tert- butylthiophenol (H[L-S(AP)]) and of 2-anilino-4,6-di-tert- butylphenol (H[L-O(AP)]) with cobalt(II) ions was investigated in the presence and absence of dioxygen. It was shown that both compounds were redox-non-innocont ligands, existing in different protonation and oxidation levels as: (i) o- aminophenolates(1-) [(L-X(AP))(1-)], (ii) o-imidophenolates(2-) [(L-X(IP))(2-)] , and (iii) one-electron oxidized forms o- iminobenzosemiquinonates(1-) [(L-X(ISQ))(1-)], which are pi- radicals (X = S, O for the sulfur or oxygen derivative). The following complexes were synthesized: [Co-II(L-S(AP))(2)](2) (1), [Co-II(L-S(ISQ))(2)](2).0.5n-hexane (2.0.5n-hexane), [Co- III(L-S(ISQ))(2)] (3), [(CoI)-I-III(L-O(ISQ))(2)] (4), and [(CoCl)-Cl-III(L-O(ISQ))(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 ([Co-III(L-S(ISQ))(2)](+), [Co- II(L-S(ISQ))(2)], and [Co-I(L-S(ISQ))(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. ((C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)