Issue 1, 2018

The molecular design of cage metal complexes for biological applications: pathways of the synthesis, and X-ray structures of a series of new N2-, S2- and O2-alicyclic iron(ii) di- and tetrachloroclathrochelates

Abstract

The synthesis of new metal(II) di- and tetrahalogenoclathrochelates with apical functionalizing substituents as reactive macrobicyclic precursors is a key stage of the molecular design of cage metal complexes – prospective biological effectors. We found that the most convenient multistep synthetic pathway for their preparation includes (i) direct template condensation of a dihalogeno-α-dioxime with an appropriately functionalized boronic acid on the corresponding metal ion as a matrix, giving an apically functionalized metal hexahalogenoclathrochelate in a high yield; and (ii) its stepwise nucleophilic substitution with S2-, N2- or O2-bis-nucleophiles, forming stable six-membered alicyclic ribbed fragments, thus allowing obtaining the corresponding apically functionalized di- and tetrahalogenoclathrochelates. The latter reaction of an iron(II) hexachloroclathrochelate with different N2-, S2- and O2-bis-nucleophilic agents afforded chloroclathrochelate complexes with equivalent and non-equivalent alicyclic ribbed substituents, such as N2-, S2 or O2-containing six-membered cycles. In the case of anionic forms of pyrocatechol and 1,2-ethanedithiol as O2- and S2-bis-nucleophiles, generated in situ in the presence of triethylamine, such substitution proceeds easily and in a high yield. In the case of anionic derivatives of ethylenediamine as N2-bis-nucleophiles, only a mono-N2-alicyclic iron(II) tetrachloroclathrochelate was obtained in a moderate yield. The S2-alicyclic iron(II) tetrachloroclathrochelate underwent a further nucleophilic substitution of one of the two dichloroglyoximate fragments, giving its N2, S2-alicyclic dichloroclathrochelate derivative with three non-equivalent ribbed chelate fragments. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, and IR, UV-vis, 1H and 13C{1H} NMR spectroscopies, and by single crystal X-ray diffraction (XRD). As follows from XRD data for four O2-, S2- and N2-ribbed-functionalized iron(II) clathrochelates, the geometry of their FeN6-coordination polyhedra is intermediate between a trigonal prism and a trigonal antiprism. UV-vis spectra of these cage complexes are indicative of a dramatic redistribution of the electron density in a quasiaromatic clathrochelate framework caused by its ribbed functionalization with six-membered O2-, S2- and/or N2-alicyclic substituent(s).

Graphical abstract: The molecular design of cage metal complexes for biological applications: pathways of the synthesis, and X-ray structures of a series of new N2-, S2- and O2-alicyclic iron(ii) di- and tetrachloroclathrochelates

Supplementary files

Article information

Article type
Paper
Submitted
18 Aug 2017
Accepted
09 Nov 2017
First published
27 Nov 2017

New J. Chem., 2018,42, 56-66

The molecular design of cage metal complexes for biological applications: pathways of the synthesis, and X-ray structures of a series of new N2-, S2- and O2-alicyclic iron(II) di- and tetrachloroclathrochelates

G. E. Zelinskii, A. S. Belov, I. G. Belaya, A. V. Vologzhanina, V. V. Novikov, O. A. Varzatskii and Y. Z. Voloshin, New J. Chem., 2018, 42, 56 DOI: 10.1039/C7NJ03051G

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