Synthetic Pathways Towards the Monodentate 3D-Shaped Clathrochelate Ligands: Preparation and XRD Characterization of the Monopyridyl-Containing Linear and Angular Macrobicyclic Iron(II) Tris-Nioximates

The titled 4- and 3-monopyridyl-terminated cage complexes, as the promising N-donor structurally rigid 3D-shaped ligands were prepared starting from the bis(triethylantimony(V))-capped iron(II)-centered macrobicyclic precursor, is known to easily undergo the stepwise mono- or di-centered capping group exchange (transmetallation) reaction(s) in the presence of silica gel as their heterogeneous catalyst. Its reaction in a low-temperature range with 3-pyridylboron acid gave the mixed antimony,boron-capped 3-pyridine-terminated iron(II) tris-nioximate possessing an angular geometry of its N-donor fragment. Transmetallation reaction of its triethylantimony,n-butylboron-capped macrobicyclic analog with 4-pyridylboronic acid afforded the monopyridyl-terminated linear diboron-capped iron(II) clathrochelate with non-equivalent cross-linking groups. The prepared monopyridyl-terminated iron(II) cage complexes were characterized using elemental analysis, MALDI-TOF mass, 1H and 13C{1H} NMR, and UV-vis spectra, and by the single-crystal XRD experiments.