Isolable Iron(II)–Porphycene Derivative Stabilized by Introduction of Trifluoromethyl Groups on the Ligand Framework

Abstract

Abstract Two iron porphycene complexes having four trifluoromethyl groups, chloro-2,7,12,17-tetraethyl-3,6,13,16-tetrakis(trifluoromethyl)porphycenatoiron(III) [FeIIIClEtio(CF3)4Pc] and its μ-oxo dimer [{FeIIIEtio(CF3)4Pc}2(μ-O)], were characterized. The μ-oxo dimer was easily converted into the monomeric iron(II) complex via the Fe–O bond cleavage in pyridine. This is the first study to obtain a stable iron(II) species in a series of porphycene iron complexes. The iron(II) species crystallized in the monoclinic system C2⁄m, and the Fe–Npyridyl (2.007 Å) and Fe–Npyrrolyl (1.958 Å) bonds were remarkably short distances among the bispyridine-coordinated iron(II) porphyrins and porphyrinoids. To evaluate the influences of the CF3 substituents and framework structure on the autoreduction, we compared the reactivity of [{FeIIIEtio(CF3)4Pc}2(μ-O)] in pyridine with the reference iron porphycene and porphyrins. Autoreduction of [{FeIIIEtio(CF3)4Pc}2(μ-O)] smoothly proceeded at 20 °C in pyridine, whereas the reaction of the μ-oxo-bis{2,7,12,17-tetraethyl-3,6,13,16-tetramethylporphycenatoiron(III)} [{FeIIIEtio(CH3)4Pc}2(μ-O)] was converted into the monomeric iron(III) complex, and the iron(II) species was not available. In contrast, the μ-oxo-bis{1,3,5,7-tetrakis(trifluoromethyl)-2,4,6,8-tetraethylporphyrinatoiron(III)}[{FeIIIEtio(CF3)4Por}2(μ-O)] as a structural isomer of [{FeIIIEtio(CF3)4Pc}2(μ-O)] allowed the autoreduction, although the reaction was very slow and took over one month. These results indicate that the introduction of strong electron-withdrawing groups at the pyrrole β-carbons exhibits a unique reactivity of the iron complex.