Unexpected Product of the Reaction of Iron(II) Dichloroclathrochelate with the [Fe₂(μ-S)₂(CO)₆]^2– Cluster Dianion: Synthesis and X-ray Diffraction Structure of the First Cage Complex with Thiol Groups Inherently Bonded to a Macrobicyclic Framework

An attempt to prepare a hybrid clusteroclathrochelate by nucleophilic substitution of iron(II) dichloroclathrochelate by substitution of its chlorine atoms with the [Fe₂(μ-S)₂(CO)₆]^2– cluster dianion as a nucleophilic agent generated in situ by the reduction of Fe₂(μ-S₂)(CO)₆ with lithium triethylborohydride unexpectedly gave the macrobicyclic complex with two inherent thiol groups as the single clathrochelate product. Obviously, the initial iron-sulfide cluster underwent a complete decomposition during the reaction, thus acting only as a source of HS^– and S^2– anions. The composition and the structure of the complex obtained were confirmed by elemental analysis, MALDI-TOF mass spectrometry, ¹H and ¹³C{¹H} NMR spectroscopy, and single crystal X-ray diffraction (CIF file CCDC 1585112). The encapsulated iron(II) ion is located at the centre of its FeN₆ coordination polyhedron possessing the geometry intermediate between a trigonal prism (the distortion angle φ = 0°) and a trigonal antiprism (φ = 60°) with φ ≈ 25°; the height of this polyhedron is 2.33 Å. The presence of two thiol groups in the vicinal positions of the same ribbed moiety of the macrobicyclic molecule substantially affects the crystal packing of the molecular crystal containing clathrochelate dimers formed by four hydrogen bonds of two types (i.e., two S–H···O and two S–H···N bonds). The obtained cage complex and its deprotonated forms seem to be promising cis-disulfide bridging or chelating ligand synthons for the synthesis of new types of polynuclear complexes and coordination polymers as well.