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

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 Mössbauer 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.