Isolable iron(II)-porphycene derivative stabilized by introduction of trifluoromethyl groups on the ligand framework

Two iron porphycene complexes having four trifluoromethyl groups, chloro-2,7,12,17-tetraethyl-3,6,13,16-tetrakis- (trifluoromethyl) porphycenatoiron(III) [Fe^IIIClEtio(CF₃)₄Pc] and its μ-oxo dimer [{Fe^IIIEtio(CF3)4Pc}2(/U,-Oj], were characterized. The μ,-oxo dimer was easily converted into the monomelic iron(II) complex via the Fe-O bond cleavage in pyridine. This is the first study to obtain a stable iron(ll) species in a series of porphycene iron complexes. The iron(II) species crystallized in the monoclinic system C2/m, and the Fe-N_pyridyl (2.007 A) and Fe-Np_pyrrolyl (1.958 A) 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 [{Fe^IIIEtio(CF)₄Pc}₂(μ-0)] in pyridine with the reference iron porphycene and porphyrins. Autoreduction of [{FemEtio(CF₃)₄Pc)₂(μ-0)] 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)} [{Fe _IIIEtio(CH₃)₄Pc}₂(μ-0)] was converted into the monomeric iron(III) complex, and the iron(II) species was not available. In contrast, the μ-oxo-bis{l,3,5,7-tetrakis(trifluoromethyl)-2,4, 6,8-tetraethylporphyrinatoiron(III)}[{Fe^IIIEtio(CF₃) ₄Por}2(μ-0)] as a structural isomer of [{Fe ^IIIEtio(CF₃)₄Pc}₂(μ-0)] 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.