First example of perfluoroalkylation of a quasi-aromatic encapsulating ligand: 2,5-Dithiahexane-assisted reaction of the iron(II) diiodoclathrochelate with trifluoromethylcopper(I)

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.

A new approach for performing Suzuki and Sonogashira reactions of iron(ii) dihalogenoclathrochelates, optimizing their reaction conditions, is elaborated.

The molecular design of cage metal complexes for biological applications: pathways of the synthesis, and X-ray structures of a series of new N2-, S2- and O2-alicyclic iron(ii) di- and tetrachloroclathrochelates

New iron(ii) di- and tetrahalogenoclathrochelates with apical functionalizing substituents were prepared and characterized.

First iron and cobalt(II) hexabromoclathrochelates: structural, magnetic, redox, and electrocatalytic behavior

Template condensation of dibromoglyoxime with n-butylboronic acid on the corresponding metal ion as a matrix under vigorous reaction conditions afforded iron and cobalt(ii) hexabromoclathrochelates. The paramagnetic cobalt clathrochelate was found to be a low-spin complex at temperatures below 100 K, with a gradual increase in the effective magnetic moment at higher temperatures due to the temperature 1/2↔3/2 spin crossover and a gap caused by the structure phase transition. The multitemperature X-ray and DSC studies of this complex and its iron(ii)-containing analog also showed temperature structural transitions. The variation of an encapsulated metal ion's radius, electronic structure and spin state caused substantial differences in the geometry of its coordination polyhedron; these differences increase with the decrease in temperature due to Jahn-Teller distortion of the encapsulated cobalt(ii) ion with an electronic configuration d(7). As follows from CV and GC data, these cage iron and cobalt complexes undergo both oxidation and reduction quasireversibly, and showed an electrocatalytic activity for hydrogen production in different producing systems.

Large, heterometallic coordination cages based on ditopic metallo-ligands with 3-pyridyl donor groups

Ditopic N-donor ligands with terminal 4-pyridyl groups are omnipresent in coordination-based self-assembly. The utilization of ligands with 3-pyridyl donor groups is significantly less common, because the intrinsic conformational flexibility of these ligands tends to favor the formation of small aggregates. Here, we show that large Pd6L1212+ cages can be obtained by reaction of Pd(ii) salts with metallo-ligands L bearing terminal 3-pyridyl groups. The easy-to-access metallo-ligands contain an Fe(ii) clathrochelate core. These sterically demanding clathrochelate complexes prevent the formation of smaller aggregates, which is observed for less bulky analogous building blocks. The cages were shown to bind BF4- and BPh4- anions in aqueous solvent mixtures, whilst the lateral size of the clathrochelate significantly affects their guest encapsulation behavior.

Recent advances in biological applications of cage metal complexes

This review highlights advances in biochemical and medical applications of cage metal complexes (clathrochelates) and related polyhedral compounds.

Molecular design of cage iron(ii) and cobalt(ii,iii) complexes with a second fluorine-enriched superhydrophobic shell

Pentafluorophenylboron-capped iron and cobalt(ii) hexachloroclathrochelate precursors undergo nucleophilic substitution giving the fluorine-enriched cage complexes.

Apically linked iron(II) α-dioximate and α-oximehydrazonate bis-clathrochelates: synthesis, structure and electrocatalytic properties

Iron(II) α-oximehydrazonate and α-dioximate bis-clathrochelates with apical hydrocarbon linkers were obtained by template condensation on an iron(II) ion followed by H(+)-catalyzed macrobicyclization of the bis-semiclathrochelate precursor with formaldehyde and triethyl orthoformate, and by transmetallation of the triethylantimony-containing clathrochelate precursor with diboron-containing bifunctional Lewis acids, respectively. The geometry of the para-phenylenediboron-capped iron(II) bis-clathrochelate studied by single-crystal X-ray diffraction is intermediate between a trigonal prism and a trigonal antiprism with a distortion angle of 20.4°; the rigidity of its C6H4 linker results in the presence of the expected three-fold pseudo-rotational B···Fe···B···B···Fe···B axis and a staggered conformation of the cyclohexane-containing chelate moieties. The cyclic voltammograms (CVs) for the oximehydrazonate bis-clathrochelates contain single one-electron (for each metallocentre, and therefore, two electrons per molecule) quasi-reversible reduction waves assigned to the redox-processes of Fe(2+/+), and no interaction is observed between the two encapsulated iron(I)-containing metallocenters; six strong electron-withdrawing ethoxy substituents in the 1,3,5-triazacyclohexane capping fragments substantially affect the potential of this reduction. The corresponding waves for the dioximate complexes are irreversible: due to the structural rigidity of the caging tris-dioximate ligands, their reduced dianionic forms are unstable on the CV time scale. The CV for the hexaethoxy bis-clathrochelate complex contains one two-electron reversible oxidation wave assigned to the metal-centered oxidation of Fe(2+/3+), whereas those for its dioximate analogs are quasi-reversible. The relative lability of the ligand cavity in binuclear oximehydrazonates causes a stabilization of both the oxidized and the reduced forms; the reduced iron(I)-containing species are highly electrocatalytically active in the hydrogen-producing 2H(+)/H2 reaction. Their higher activity as compared with that for dioximate bis-clathrochelates was explained by the higher availability of the catalytically active metallocentres for H(+) ions.