Synthesis, X-ray structure and redox properties of the macrobicyclic iron(II) N2- and S2-containing vic-dioximates

Abstract

Abstract Nucleophilic substitution of the reactive chlorine atoms of the boron-capped macrobicyclic vic-di- and hexahalogen-containing iron(II) precursors with 1,2-ethanedithiol and 1,2-benzenedithiol in dichloromethane as a solvent in the presence of triethylamine as a strong organic base afforded the corresponding di- and hexasulfide mono- and triribbed-functionalized clathrochelates, respectively, in relatively high yields. In the case of the low-reactive tin-capped clathrochelate [Fe(Cl2Gm)3(SnCl3)2]2− dianion this reaction was performed in DMF with the potassium salt of 1,2-benzenedithiol. The reaction of the dichlorine-containing FeBd2(Cl2Gm)(BF)2 precursor with an excess of ethylenediamine in DMF led to the clathrochelate with N2-containing vic-dioximate ribbed fragment. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–vis, 1H and 13C{1H} NMR, 57Fe Mossbauer spectroscopies, and X-ray crystallography. The nature and number of the ribbed substituents affect the geometry of a clathrochelate framework, first of all, the distortion of the trigonal prismatic–trigonal antiprismatic iron(II) coordination polyhedra, whereas the apical substituents at the capping boron atoms influe on the B–O distances in the apical RBO3 fragments. The geometry of the tin-capped hexasulfide clathrochelate complex was deduced from EXAFS data using the scattering both on the encapsulated iron(II) and capping tin(IV) ions. The electrochemical properties of the iron(II) complexes obtained were studied by cyclic voltammetry. The electrochemically generated unstable reduced anionic forms are destabilized by the electron-donating ribbed substituents, whereas the oxidation led to the formation of the cationic macrobicycles, the stability of which depends on the nature of the apical capping groups and ribbed substituents as well. The pseudo-aromatic disulfide ribbed fragments stabilize the oxidized forms of the clathrochelate complexes.