Molecular design and structural pecularities of the 3- and 4-pyridylboron-capped tris-glyoximate and tris-dichloroglyoximate iron(II) clathrochelates with apical donor groups

Abstract

Tris-glyoximate and tris-dichloroglyoximate iron(II) clathrochelates with apical pyridyl groups were obtained through one-pot template condensation of the corresponding α-dioxime with 3- or 4-pyridylboronic acids on the iron(II) ion as a matrix under vigorous reaction conditions using the boiling CF3COOH as a solvent. The initially formed mixtures of mono- and diprotonated clathrochelate species were converted into the target macrobicyclic intracomplexes under basic conditions. These complexes were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–Vis, 1H and 13C NMR spectroscopies, and by single crystal X-ray diffraction as well. In their molecules, the encapsulated iron(II) ion is situated in the center of its FeN6-coordination polyhedron. The geometry of all the FeN6-coordination polyhedra is intermediate between a trigonal prism and a trigonal antiprism with the average distortion angles φ from 16.7 to 17.7°. Their heights h fall from 2.36 to 2.38 Å and the averaged bite angles α vary in a narrow range 78.2–78.4°. Characteristic feature of the 3- and 4-pyridylboron-capped glyoximate clathrochelate molecules, as compared with their aliphatic and aromatic analogs, is shortening of the chelate CC bonds from 1.45 to 1.42 Å. Comparison of the values of a ligand aspect ratio for the obtained new pyridyl-terminated iron(II) clathrochelates with those for their known aliphatic tris-dioximate analogs was performed.