Template synthesis and structures of bis-ferrocenylboronate macrobicyclic iron(ii) tris-dioximates

Abstract

A series of ferrocenylboron-capped tris-dioximate iron(ii) clathrochelates was synthesized by the template condensation of three molecules of dimethylglyoxime (H2Dm), cyclohexanedione 1,2-dioxime (H2Nx), or cyclooctanedione 1,2-dioxime (H2Ox) and two molecules of ferrocenylboronic acid (FcB(OH)2) on the Fe2+ ion matrix. The yields of the clathrochelate derivatives of alicyclic dioximes were substantially higher than that of their acyclic analog, because the molecules of alicyclic H2Nx and H2Ox α-dioximes have the s-cis-configuration suitable for complex formation, whereas the H2Dm molecules in solution have the s-trans-configuration. The synthesized compounds were characterized using elemental analysis, IR and UV-Vis spectroscopies, MALDI-TOF mass spectrometry, 1H and 13C{1H} NMR and 57Fe Mossbauer spectroscopies, and X-ray diffraction analysis. The crystal of FeDm3(BFc)2·CHCl3 contains two types of crystallographically nonequivalent clathrochelate molecules. The intermolecular contacts C-H⋯Cp formed by the ferrocenyl fragments and cyclooctane carbocycles and the interactions Cp-H⋯O were observed in the crystal of FeOx3(BFc)2. The structural lability of the cyclooctane substituents allows the FeOx3(BFc)2 molecules to arrange by the “bump-into-hollow” mode because of attractive H⋯H interactions between the ribbed substituents of the neighboring molecules. The geometry of the ferrocenylborate iron(ii) clathrochelates is intermediate between a trigonal prism and a trigonal antiprism.