β-Nitro Derivatives of Iron Corrolates

Two different methods for the regioselective nitration
of different meso-triarylcorroles leading to the
corresponding β-substituted
nitrocorrole iron complexes have been developed. A two-step procedure
affords three Fe­(III) nitrosyl productsthe unsubstituted corrole,
the 3-nitrocorrole, and the 3,17-dinitrocorrole. In contrast, a one-pot
synthetic approach drives the reaction almost exclusively to formation
of the iron nitrosyl 3,17-dinitrocorrole. Electron-releasing substituents
on the meso-aryl groups of the triarylcorroles induce
higher yields and longer reaction times than what is observed for
the synthesis of similar triarylcorroles with electron-withdrawing
functionalities, and these results can be confidently attributed to
the facile formation and stabilization of an intermediate iron corrole
π-cation radical. Electron-withdrawing substituents on the meso-aryl groups of triarylcorrole also seem to labilize
the axial nitrosyl group which, in the case of the pentafluorophenylcorrole
derivative, results in the direct formation of a disubstituted iron
μ-oxo dimer complex. The influence of meso-aryl
substituents on the progress and products of the nitration reaction
was investigated. In addition, to elucidate the most important factors
which influence the redox reactivity of these different iron nitrosyl
complexes, selected compounds were examined by cyclic voltammetry
and thin-layer UV–visible or FTIR spectroelectrochemistry in
CH2Cl2.