Synthesis, X-ray structure and reactivity of the vinyl-terminated iron(II) clathrochelate precursors and their cage derivatives with non-equivalent capping groups

Abstract

A novel vinyl-terminated boron, antimony-capped iron(II) tris-dimethylglyoximate with labile triethylantimony cross-linking group was prepared using two-step synthetic procedure including template condensation of dimethylglyoxime and triethylantimony(V) dibromide on an iron(II) ion as a matrix followed by transmetallation with 4-vinylphenyl boronic acid. This labile clathrochelate precursor and its bis-methoxyboron-capped analog underwent the same capping group exchange (transmetallation) reactions with more strong Lewis acids, such as trigonal boron compounds or hafnium(IV) phthalocyaninate (HfPc), giving the macrobicyclic iron(II) tris-dimethylglyoximates with non-equivalent capping groups and a binuclear HfPc-capped phthalocyaninoclathrochelate, respectively. The complexes obtained were characterized using elemental analysis, 1H and 13C{1H} NMR, MALDI-TOF MS, IR and UV–vis data as well as by single crystal X-ray diffraction. The number, positions and multiplicity of the signals in the solution 1H and 13C{1H} NMR spectra of these clathrochelates as well as the ratios of their integral intensities in 1H NMR spectra confirmed the composition and symmetry of the macrobicyclic molecules, suggesting the presence of their molecular C3 symmetry pseudoaxis. In the 1H NMR spectrum of a hybrid phthalocyanine-capped cage complex, the π-electron current in its apical macroheterocyclic fragment caused the substantial high-field shifts of the signals of protons of the ribbed methyl substituents because their nuclei are located in its shielding region. Single crystal X-ray diffraction data for the monovinyl-terminated mixed Sb, B- and Hf, B-capped iron(II) cage complexes suggest that their FeN6-coordination polyhedra possess the geometry of a rotationally distorted truncated trigonal pyramid that is close to intermediate between a trigonal prism and a trigonal antiprism with slightly expanded trigonal bases, which are connected with a heavy (Sb or Hf) atom. The encapsulated iron(II) ion is slightly shifted from the center of these polyhedra in the direction of such capping atom.