Structure, spectral and electrochemical properties of the 2,6-di-tert-butylphenol-functionalized iron and cobalt(II) clathrochelates and their phenylsulfide analogs

Abstract

The iron and cobalt(II) clathrochelates were functionalized with one, two and six 2,6-di-tert-butylphenolsulfide and phenylsulfide ribbed substituents by nucleophilic substitution of their chlorine-containing clathrochelate precursors. The cycloaddition of the corresponding phenol-containing α-dioxime to the macrocyclic iron(II) bis-α-benzyldioximate afforded the clathrochelate with only one ribbed inherent phenol substituent. The cage complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–Vis, 1H and 13C{1H} NMR, 57Fe Mössbauer spectroscopies, and X-ray crystallography. As it follows from the X-ray data for three iron(II) clathrochelates obtained, the geometry of their macrobicyclic frameworks is intermediate between a trigonal prism and a trigonal antiprism, and the nature of the ribbed sulfide substituents did not affect this geometry. The EPR spectra for the radical clathrochelate species, which were obtained by an oxidation with PbO2, contain the hyperfine splittings resulted from the interaction of the unpaired electron with the protons of the phenoxyl fragment as well as with the adjacent nitrogen atom of the corresponding α-dioximate chelate cycle. The parameters of the 57Fe Mössbauer spectra of the iron macrobicycles are characteristic of the low-spin iron(II) complexes and are in a good agreement with the X-ray data. The electrochemical properties of the complexes obtained were studied by cyclic voltammetry. The electrochemically generated reduced forms of the clathrochelate complexes are stabilized by the electron-withdrawing phenylsulfide substituents, in contrast to the electron-donating 2,6-di-tert-butylphenolsulfide groups; the stability of the oxidized clathrochelate species depends on the nature and number of their ribbed substituents.