Ekaterina G. Lebed

Synthesis and X-ray structure of methyl esters of the dicarboxyphenylsulfide iron(II) clathrochelates

Abstract All six constitutional isomers of the dimethoxy-terminated clathrochelate FeBd2((CH3OOCC6H4S)2Gm)(BF)2 (where Bd2− is α-benzildioxime dianion, Gm is glyoxime residue, and BF is fluoroboron capping group) were obtained under mild reaction conditions by nucleophilic substitution of their dichloroclathrochelate precursor with the corresponding methyl ester of carboxyphenylthiolate anion generated in situ in the presence of triethylamine. In the case of homodifunctionalized cage complexes with equivalent ortho-, meta-, or para-substituted arylsulfide groups, 1.5-fold excess of methyl ester of the corresponding mercaptobenzoic acid was added. In the case of their heterodifunctionalized macrobicyclic analogs, subsequent addition of one equivalent of the first nucleophilic agent and one equivalent of the second nucleophile was used. The complexes were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–vis, 1H and 13C{1H} NMR spectra, and by single-crystal X-ray diffraction. In all these molecules, the encapsulated iron(II) is situated in the center of FeN6-coordination polyhedron, the geometry of which is intermediate between a trigonal prism and a trigonal antiprism with the average distortion angles φ from 24.7 to 25.2°. The absence of strong intermolecular interactions and the substantial sterical clashes hampering a rotation around the single C–S bonds, resulted in different orientations of the functionalizing arylsulfide substituents at a cage framework.

Extension and functionalization of an encapsulating macrobicyclic ligand using palladium-catalyzed Suzuki–Miyaura and Sonogashira reactions of iron(ii) dihalogenoclathrochelates with inherent halogen substituents

A new approach for performing Suzuki–Miyaura and Sonogashira reactions of iron(II) dihalogenoclathrochelates, optimizing their reaction conditions (such as temperature, solvent and a palladium-containing catalyst) and the nature of other reagents (such as arylboron components) is elaborated. These palladium-catalyzed reactions are very sensitive to the nature of the macrobicyclic substrates. The reactivity of the leaving halogen atoms correlates with their ability to undergo an oxidative addition, decreasing in the order: I > Br > Cl, and iron(II) diiodoclathrochelate underwent these C–C cross-couplings under their “classical” conditions. Phenylboronic, 4-carboxyphenylboronic and 6-ethoxy-2-naphthylboronic acids, and the diethyl ether of 4-(ethoxycarbonyl)boronic acid were tested as components of Suzuki–Miyaura reactions in DMF and in THF. The highest yields of the target products were obtained in DMF, while the highest activation was observed with sodium and potassium carbonates. The Suzuki–Miyaura reaction of a diiodoclathrochelate with 6-ethoxy-2-naphthylboronic acid gave the mono- and difunctionalized clathrochelates resulting from the tandem hydrodeiodination – C–C cross-coupling and double C–C cross-coupling reactions, respectively. Its Sonogashira reactions with trimethylsilylacetylene and acetylenecarboxylic acid in THF and in DMF were tested. This palladium-catalyzed reaction with a (CH3)3Si-containing active component gave the target products in a high total yield. The complexes obtained were characterized using elemental analysis, MALDI-TOF, UV-Vis, 1H and 13C{1H} NMR spectroscopy, and by single crystal XRD. Despite the non-equivalence of the ribbed α-dioximate fragments of their molecules, the encapsulated iron(II) ion is situated almost in the centre of its FeN6-coordination polyhedron, the geometry of which is almost intermediate between a trigonal prism and a trigonal antiprism.

Clathrochelate iron(II) tris-nioximates with non-equivalent capping groups and their precursors: synthetic strategies, X-ray structure, and reactivity

Abstract Template cross-linking of nioxime using equimolar amounts of boric and 4-vinylphenylboronic acids on an iron(II) ion as a matrix gave a mixture of mono- and divinyl-terminated clathrochelate products, which were chromatographically isolated in moderate yields and characterized by X-ray diffraction. The target complex FeNx3(BOCH3)(4-BC6H4CH=CH2) with non-equivalent capping groups was also obtained in a low yield using a transmetallation (re-boronation) of its dimethoxyboron-capped clathrochelate precursor. Re-boronation of the monomethoxyboron-capped cage complex with benzene-1,4-diboronic acid as a bifunctional Lewis-acidic agent afforded mainly the clathrochelate product of its 1:1 re-boronation having a terminal B(OH)2 group. The iron(II) clathrochelate with labile triethylantimony capping groups underwent a transmetallation on the surface of silica gel giving an immobilized Sb, Si-capped macrobicyclic intermediate. Its desorption with 4-vinylphenylboronic acid unexpectedly gave the monovinyl-terminated iron(II) semiclathrochelate as the major product, isolated in a high yield; it was X-ray structurally characterized. The geometry of FeN6-coordination polyhedra of the above semi- and clathrochelates is intermediate between a trigonal prism and a trigonal antiprism; that of the monocapped iron(II) semiclathrochelate is more TAP-distorted and its pseudoencapsulated iron(II) ion is shifted from the center of this polyhedron by 0.02 Å in the direction of the capping boron atom.