Synthesis, structural and electrochemical features of alicyclic and aromatic α,α′-N2- and-S2-dioximate macrobicyclic cobalt(II,III) and ruthenium(II) tris-complexes

The triribbed-functionalized cobalt(II,III) and ruthenium(II) clathrochelate derivatives of the vic-dioximes with two nitrogen or sulfur atoms in α-positions to π-conjugated diazomethine chelate fragments of a macrobicyclic framework were obtained in moderate yields under mild and high dilution conditions by nucleophilic substitution of six reactive chlorine atoms of the boron-capped macrobicyclic cobalt and ruthenium(II) precursors with N2- and S2-dinucleophiles (ethylenediamine and the corresponding α-dithiols in the presence of triethylamine, respectively). The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–Vis, 1H and 13C{1H} NMR and EPR spectroscopies, magnetochemistry and X-ray crystallography. The MN6-coordination polyhedra of all the X-ray studied clathrochelates possess a slightly distorted trigonal prismatic geometry. The encapsulated cobalt(II) ions are shifted from the centers of the cavities formed by the macrobicyclic ligand due to the Jahn–Teller distortion, while the ruthenium and iron(II) ions in their clathrochelate analogs do occupy these centers. The main geometrical parameters of the macrobicyclic frameworks vary with Shannon radius of an encapsulated metal ion. In the case of the tris-ethylenediamine cobalt(III) clathrochelate, the field strength of the macrobicyclic amine ligand is essentially lower than those for their aromatic and aliphatic analogs because of the negative σpara-effect of the ribbed alkylamine substituents. The magnetometry and EPR data confirmed the low-spin character of the cobalt(II) complexes synthesized. The electrochemically generated oxidized cobalt clathrochelates are stable in the CVA time scale, whereas their ruthenium- and iron-containing analogs as well as the reduced forms of all the cobalt, ruthenium and iron complexes obtained are unstable.

Nucleophilic substitution of the chlorine atoms of the macrobicyclic hexahalogen-containing cobalt and ruthenium(II) precursors with ethylendiamine, 1,2-ethanedithiolate and 1,2-benzenedithiolate anions afforded the low-spin hexamine cobalt(III) and hexasulfide cobalt and ruthenium(II) triribbed-functionSalized clathrochelates with a distorted trigonal-prismatic geometry. The encapsulated cobalt(II) ions are shifted from the center of their CoN6-polyhedra due to the Jahn–Teller effect.Figure optionsDownload as PowerPoint slideResearch highlights
► Tris-N2- and S2-dioximate cobalt and ruthenium clathrochelates were obtained.
► Cobalt and ruthenium(II) precursors undergo substitution with N2- and s2-dinucleophiles.
► The structures of the cobalt(II) clathrochelates undergo Jahn–Teller distortion.
► Oxidized cobalt clathrochelates are stable in the CVA time scale.
► Oxidized Ru and Fe macrobicycles and reduced Co, Ru and Fe clathrochelates are unstable.