Pathways of directed synthesis of iron(II) clathrochelates and polyclathrochelates with non-equivalent capping groups starting from antimony- and germanium-containing precursors

摘要

Alternative methods for directed syntheses of clathrochelates and polyclathrochelates with two non-equivalent capping fragments using semiclathrochelate precursors and capping group reactions are described. The lability of antimony-capped iron(II) clathrochelates in remetallation (a capping group exchange) reactions allowed to obtain of mono- and bis-clathrochelates of a general formula FeNx(3)X(1)X(2) and (FeNx(3)X(1))(2)X-2 (where Nx(2-) is cyclohexanedione-1,2-dioxime dianion; X-1, X-2 are different capping groups). The first and unique dioximate [Fe(HNX)(3)(Sb(C6H5)(3))](ClO4) semiclathrochelate was isolated and characterized. The reaction of this complex with differing mono- and bifunctional cross-linking agents (Lewis acids) led to the formation of clathrochelates molecules with non-equivalent capping groups. The clathrochelates with a labile triethylantimony capping group underwent remetallation in the presence of silicon dioxide as a catalyst. The first stage led to the formation of a surface-immobilized mixed SbSi-capped clathrochelate, which under the action of another capping agent desorbed from the surface gives a mono- or bis-clathrochelate depending on the nature of this agent. An alternative pathway using the bis-capping agents has been implemented for synthesis of bis-clathrochelates when reactive fragments of an initial azomethine ligand demonstrate essentially different chemical properties. The oximehydrazonate germanium-capped iron(II) bis-clathrochelate was synthesized starting from a bis-semiclathrochelate, which was initially isolated with bis-capping germanium(IV) tetraethoxide. A further H+-catalyzed macrocyclization with triethyl orthoformate produced germanium-capped bis-clathrochelate. The obtained mono- and bis-clathrochelates have been characterized using elemental analysis, PD mass, IR, UV-Vis and H-1 and C-13 NMR spectra, and X-ray crystallography (for FeNx(3)(Sb(C2H5)(3))(2) complex), as well as by cyclic voltammograms. The distortion angle phi values and the main distances in the clathrochelate frameworks have been deduced using Fe-57 Mossbauer parameters, and EXAFS data and molecular mechanics calculations, respectively. (C) 2004 Elsevier B.V. All rights reserved.