Preparation, X-ray Characterization, and Reactivity of the Rod-like and Angular Germanium- and Titanium(IV)-Capped Iron(II) Bis-Clathrochelates and Their Mono- and Bis-Capped (Semi)clathrochelate Precursors.

Transmetalation of the bis{triethylantimony(V)}-capped iron(II) tris-α-dioximate with n-butylboronic acid afforded the mixed antimony, boron cross-linked clathrochelate with single reactive antimony(V)-based apical fragment. This macrobicyclic precursor easily underwent the transmetalation reactions with germanium and titanium(IV) alkoxides to give the rod-like and angular FeII2MIV-trinuclear bis-clathrochelates. Those of the aforementioned diantimony(V)-capped complex with 3- and 4-carboxyphenylboronic acids afforded the monoboron-capped iron(II) semiclathrochelates, undergoing a double-cyclization (macrobicyclization) with germanium- and titanium(IV)-based capping agents. The reactions in the low-temperature range unexpectedly gave the stable 2:1 associates, formed by the bridging of two carboxyl-terminated macrobicyclic molecules of the mixed carboxylboron, triethylantimony-capped iron(II) clathrochelate with a triethylantimony(V)-based linker fragment. The obtained complexes were characterized using elemental analysis, MALDI-TOF, 1H and 13C{1H} NMR and UV-vis spectra, and single-crystal XRD experiments. The encapsulated iron(II) ion in their 3D-molecules is situated almost in the center of its FeN6-coordination polyhedron possessing a truncated trigonal-pyramidal geometry. Fe-N distances fall in the range 1.887(7)-1.945(4) Å characteristic of the low-spin iron(II) complexes. The cross-linking titanium and germanium(IV) ions in the corresponding bis-clathrochelate molecules form the octahedral MIVO6-coordination polyhedra, the MIV-O distances of which vary from 1.946(2) to 1.964(2) Å and from 1.879(7) to 1.907(6) Å, respectively.

Multistep synthesis and X-ray structures of carboxyl-terminated hybrid iron(II) phthalocyaninatoclathrochelates and their postsynthetic transformation into polytopic carboranyl-containing derivatives.

A multistep general synthetic strategy towards polytopic carboranyl-containing (semi)clathrochelate metal complexes, based on the template synthesis, transmetallation, amide condensation and 1,3-dipolar cycloaddition reactions, is developed. Their mono(semi)clathrochelate precursors with a single reactive group were obtained using a transmetallation of the triethylantimony-capped macrobicyclic precursor. The thus obtained carboxyl-terminated iron(II) semiclathrochelate underwent a macrobicyclization with zirconium(IV) phthalocyaninate to form the corresponding phthalocyaninatoclathrochelate. The direct one-pot template condensation of the suitable chelating and cross-linking ligand synthons on the Fe2+ ion as a matrix was also used for its preparation. Further amide condensation of the aforementioned semiclathrochelate and hybrid complexes with propargylamine in the presence of carbonyldiimidazole gave the (pseudo)cage derivatives with a terminal CC bond. Their "click" reaction with an appropriate carboranylmethyl azide afforded the ditopic carboranosemiclathrochelates and the tritopic carboranyl-containing phthalocyaninatoclathrochelates with a flexible spacer fragment between their polyhedral entities. The obtained new complexes were characterized using elemental analysis, MALDI-TOF mass spectrometry, multinuclear NMR, and UV-vis spectroscopy, and by single crystal X-ray diffraction experiments. Their FeN6-coordination polyhedra show a truncated trigonal-pyramidal geometry, while the cross-linking heptacoordinate Zr4+ or Hf4+ cations in the hybrid compounds form the MIVN4O3-coordination polyhedra with the geometry of a capped trigonal prism.

Hybrid iron(II) phthalocyaninatoclathrochelates with a terminal reactive vinyl group and their organo-inorganic polymeric derivatives: synthetic approaches, X-ray structures and copolymerization with styrene.

Hybrid metallo(IV)phthalocyaninate-capped tris-dioximate iron(II) complexes (termed as "phthalocyaninatoclathrochelates") with non-equivalent apical fragments and functionalized with one terminal reactive vinyl group were prepared for the first time using three different synthetic approaches: (i) transmetallation (capping group exchange) of the appropriate labile boron,antimony-capped cage precursors, (ii) capping of the initially isolated reactive semiclathrochelate intermediate, and (iii) direct one-pot template condensation of their ligand synthons on the iron(II) ion as a matrix. The obtained polytopic cage complexes were characterized using elemental analysis, 1H NMR, MALDI-TOF MS and UV-vis spectra, and the single-crystal X-ray diffraction experiments. One of the obtained vinyl-terminated iron(II) phthalocyaninatoclathrochelates and its semiclathrochelate precursor were tested as monomers in a copolymerization reaction with styrene as the main component. These vinyl-terminated (semi)clathrochelate iron(II) complexes were found to be successfully copolymerized with this industrially important monomer, affording the intensely colored copolymer products. Because of a low solubility of the tested zirconium(IV) phthalocyaninate-capped tris-nioximate monomer in styrene as a solvent, a molar ratio of 1 : 500 was used. The obtained copolymer products and the kinetics of their formation were studied using GPC, FTIR, UV-vis, TGA and DSC methods. Even at such a low concentration of the Fe,Zr-binuclear metallocomplex component, an increase in the rate of the UV-light degradation of the organo-inorganic products, as well as in their thermal stability, was observed.

Dramatic Effect of A Ring Size of Alicyclic α-Dioximate Ligand Synthons on Kinetics of the Template Synthesis and of the Acidic Decomposition of the Methylboron-Capped Iron(II) Clathrochelates.

Kinetics and thermodynamics of the template synthesis and of the acidic decomposition of the methylboron-capped iron(II) tris-1,2-dioximates-the clathrochelate derivatives of six (nioxime)- and eight (octoxime)-membered alicyclic ligand synthons-were compared. In the case of a macrobicyclic iron(II) tris-nioximate, the plausible pathway of its formation contains a rate-determining stage and includes a reversible formation of an almost trigonal-antiprismatic (TAP) protonated tris-complex, followed by its monodeprotonation and addition of CH3B(OH)2. Thus, the formed TAP intermediate undergoes a multistep rate-determining stage of double cyclization with the elimination of two water molecules accompanied by a structural rearrangement, thus giving an almost trigonal-prismatic (TP) iron(II) semiclathrochelate. It easily undergoes a cross-linking with CH3B(OH)2, resulting in the elimination of H+ ion and in the formation of a macrobicyclic structure. In contrast, the analogous scheme for its macrobicyclic tris-octoximate analog was found to contain up to three initial stages affecting the overall synthesis reaction rate. The rates of acidic decomposition of the above clathrochelates were found to be also affected by the nature of their ribbed substituents. Therefore, the single crystal XRD experiments were performed in order to explain these results. The difference in the kinetic schemes of a formation of the boron-capped iron(II) tris-nioximates and tris-octoximates is explained by necessity of the substantial changes in a geometry of the latter ligand synthon, caused by its coordination to the iron(II) ion, due to both the higher distortion of the FeN6-coordination polyhedra, and the intramolecular sterical clashes in the molecules of the macrobicyclic iron(II) tris-octoximates.

Synthesis and Structure of the Bis- and Tris-Polyhedral Hybrid Carboranoclathrochelates with Functionalizing Biorelevant Substituents-The Derivatives of Propargylamine Iron(II) Clathrochelates with Terminal Triple C≡C Bond(s).

A synthetic strategy for obtaining structurally flexible hybrid iron(II) carboranoclatrochelates functionalized with biorelevant groups, based on a combination of a 1,3-dipolar cycloaddition reaction with nucleophilic substitution of an appropriate chloroclathrochelate precursor, was developed. In its first stage, a stepwise substitution of the dichloroclathrochelate precursor with amine N-nucleophiles of different natures in various solvents was performed. One of its two chlorine atoms with morpholine or diethylamine in dichloromethane gave reactive monohalogenoclathrochelate complexes functionalized with abiorelevant substituents. Further nucleophilic substitution of their remaining chlorine atoms with propargylamine in DMF led to morpholine- and diethylamine-functionalized monopropargylamine cage complexes, the molecules of which contain the single terminal C≡C bond. Their "click" 1,3-cycloaddition reactions in toluene with ortho-carborane-(1)-methylazide catalyzed by copper(II) acetate gave spacer-containing di- and tritopic iron(II) carboranoclatrochelates formed by a covalent linking between their different polyhedral(cage) fragments. The obtained complexes were characterized using elemental analysis, MALDI-TOF mass, UV-Vis, 1H, 1H{11B}, 11B, 11B{1H}, 19F{1H} and 13C{1H}-NMR spectra, and by a single crystal synchrotron X-ray diffraction experiment for the diethylamine-functionalized iron(II) carboranoclathrochelate. Its encapsulated iron(II) ion is situated almost in the center of the FeN6-coordination polyhedron possessing a geometry intermediate between a trigonal prism and a trigonal antiprism with a distortion angle φ of approximately 28°. Conformation of this hybrid molecule is strongly affected by its intramolecular dihydrogen bonding: a flexibility of the carborane-terminated ribbed substituent allowed the formation of numerous C-H…H-B intramolecular interactions. The H(C) atom of this carborane core also forms the intermolecular C-H…F-B interaction with an adjacent carboranoclathrochelate molecule. The N-H…N intermolecular interaction between the diethylamine group of one hybrid molecule and the heterocyclic five-membered 1H-[1,2,3]-triazolyl fragment of the second molecule of this type caused formation of H-bonded carboranoclathrochelate dimers in the X-rayed crystal.

Synthesis and spectral characterization of the first fluorescein-tagged iron(ii) clathrochelates, their supramolecular interactions with globular proteins, and cellular uptake.

A fluorescein-tagged iron(ii) cage complex was obtained in a moderate total yield using a two-step synthetic procedure starting from its propargylamine-containing clathrochelate precursor. An 11-fold decrease in fluorescence quantum yield is observed in passing from the given fluorescein-based dye to its clathrochelate derivative. An excitation energy transfer from the terminal fluorescent group of the macrobicyclic molecule to its quasiaromatic highly π-conjugated clathrochelate framework can explain this effect. The kinetics of the hydrolysis of the acetyl groups of acetylated fluorescein azide and its clathrochelate derivative in the presence of one equivalent of BSA evidenced no strong supramolecular host-guest interactions between BSA and the tested compounds. Study of a chemical stability of the deacetylated iron(ii) clathrochelate suggested the formation of a supramolecular 1 : 1 BSA-clathrochelate assembly. Moreover, an addition of BSA or HSA to its solution caused the appearance of strong clathrochelate-based ICD outputs. The fluorescence emission anisotropy studies also evidenced the supramolecular binding of the fluorescein-tagged iron(ii) clathrochelate to the BSA macromolecule, leading to a high increase in this type of anisotropy. Subcellular uptake of the fluorescein-tagged molecules was visualized using fluorescence microscopy and showed its distribution to be mainly in the cytosol without entering the nucleus or accumulating in any other organelle. An X-rayed crystal of the above propargylamide macrobicyclic precursor with a reactive terminal C[triple bond, length as m-dash]C bond contains the clathrochelate molecules of two types, A and B. The encapsulated iron(ii) ion in these molecules is situated in the center of its FeN6-coordination polyhedron, the geometry of which is intermediate between a trigonal prism (TP) and a trigonal antiprism (TAP). The Fe-N distances vary from 1.8754(6) to 1.9286(4) Å and the heights h of their distorted TP-TAP polyhedra are very similar (2.30 and 2.31 Å); their values of φ are equal to 25.3 and 26.6°. In this crystal, the molecules of types A and B participate in different types of hydrogen bonding, giving H-bonded clathrochelate tetramers through their carboxylic and amide groups, respectively; these tetramers are connected to H-bonded chains.

Charge density analysis of abiraterone acetate.

A high-resolution single-crystal X-ray diffraction study of abiraterone acetate (1) has been carried out. The charge density distribution in the crystal of this anticancer drug is reconstructed from experimental data. The nature and the contributions of various intermolecular interactions to the total crystal energy are studied by means of the quantum theory `Atoms-in-Molecules', a non-covalent interactions method and energy framework plots. In general, dispersion C-H...H-C and C-H...π interactions play the main role in crystal packing of 1. The Voronoi tessellation analysis of 1 confirmed that contribution of hydrophobic and hydrophilic interactions to the molecular surface is close to their contribution to the total crystal energy. Similar analysis of abiraterone complexes with the cytochrome P450 family demonstrated that contribution of the C-H...H-C and C-H...π interactions to the molecular surface of the drug remains unchanged to fit the binding pocket, despite the presence of water and heme molecules, and hydrophilic groups within the pocket.

Intermolecular Interactions in Crystal Structures of Imatinib-Containing Compounds.

Imatinib, one of the most used therapeutic agents to treat leukemia, is an inhibitor that specifically blocks the activity of tyrosine kinases. The molecule of imatinib is flexible and contains several functional groups able to take part in H-bonding and hydrophobic interactions. Analysis of molecular conformations for this drug was carried out using density functional theory calculations of rotation potentials along single bonds and by analyzing crystal structures of imatinib-containing compounds taken from the Cambridge Structural Database and the Protein Data Bank. Rotation along the N-C bond in the region of the amide group was found to be the reason for two relatively stable molecular conformations, an extended and a folded one. The role of various types of intermolecular interactions in stabilization of the particular molecular conformation was studied in terms of (i) the likelihood of H-bond formation, and (ii) their contribution to the Voronoi molecular surface. It is shown that experimentally observed hydrogen bonds are in accord with the likelihood of their formation. The number of H-bonds in ligand-receptor complexes surpasses that in imatinib salts due to the large number of donors and acceptors of H-bonding within the binding pocket of tyrosine kinases. Contribution of hydrophilic intermolecular interactions to the Voronoi molecular surface is similar for both conformations, while π...π stacking is more typical for the folded conformation of imatinib.

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.

Family of Polynuclear Nickel Cagelike Phenylsilsesquioxanes; Features of Periodic Networks and Magnetic Properties.

A new family of bi-, tetra-, penta-, and hexanickel cagelike phenylsilsesquioxanes 1-6 was obtained by self-assembly and transmetalation procedures. Their crystal structures were established by single-crystal X-ray analysis, and features of crystal packing relevant to the network formation were studied by a topological analysis. Compounds 1, 2, and 4 are isolated architectures, while 3, 5, and 6 present extended 1D and 3D networks. The investigation of magnetic properties revealed the presence of ferro- (1 and 3-5) or antiferromagnetic (2 and 6) interactions between Ni(II) ions, giving rise in the most cases (1, 2, and 4-6) to the presence of a slow relaxation of the magnetization, which can originate from the spin frustration.

A New Series of Cobalt and Iron Clathrochelates with Perfluorinated Ribbed Substituents.

The study tackles one of the challenges in developing platinum-free molecular electrocatalysts for hydrogen evolution, which is to seek for new possibilities to ensure large turnover numbers by stabilizing electrocatalytic intermediates. These species are often much more reactive than the initial electrocatalysts, and if not properly stabilized by a suitable choice of functionalizing substituents, they have a limited long-time activity. Here, we describe new iron and cobalt(II) cage complexes (clathrochelates) that in contrast to many previously reported complexes of this type do not act as electrocatalysts for hydrogen evolution. We argue that the most probable reason for this behavior is an excessive stabilization of the metal(I) species by perfluoroaryl ribbed groups, resulting in an unprecedented long-term stability of the metal(I) complexes even in acidic solutions.

Preparation, X-ray Structures, Spectroscopic, and Redox Properties of Di- and Trinuclear Iron-Zirconium and Iron-Hafnium Porphyrinoclathrochelates.

The first hybrid di- and trinuclear iron(II)-zirconium(IV) and iron(II)-hafnium(IV) macrobicyclic complexes with one or two apical 5,10,15,20-tetraphenylporphyrin fragments were obtained using transmetalation reaction between n-butylboron-triethylantimony-capped or bis(triethylantimony)-capped iron(II) clathrochelate precursors and dichlorozirconium(IV)- or dichlorohafnium(IV)-5,10,15,20-tetraphenylporphyrins under mild conditions. New di- and trinuclear porphyrinoclathrochelates of general formula FeNx3((Bn-Bu)(MTPP)) and FeNx3(MTPP)2 [M = Zr, Hf; TPP = 5,10,15,20-tetraporphyrinato(2-); Nx = nioximo(2-)] were characterized by one-dimensional (1H and 13C{1H}) and two-dimensional (COSY and HSQC) NMR, high-resolution electrospray ionization mass spectrometry, UV-visible, and magnetic circular dichroism spectra, single-crystal X-ray diffraction experiments, as well as elemental analyses. Redox properties of all complexes were probed using electrochemical and spectroelectrochemical approaches. Electrochemical and spectroelectrochemical data suggestive of a very weak, if any, long-range electronic coupling between two porphyrin π-systems in FeNx3(MTPP)2 complexes. Density functional theory and time-dependent density functional theory calculations were used to correlate spectroscopic signatures and redox properties of new compounds with their electronic structures.

Novel Cage-Like Hexanuclear Nickel(II) Silsesquioxane. Synthesis, Structure, and Catalytic Activity in Oxidations with Peroxides.

New hexanuclear nickel(II) silsesquioxane [(PhSiO1.5)12(NiO)6(NaCl)] (1) was synthesized as its dioxane-benzonitrile-water complex (PhSiO1,5)12(NiO)6(NaCl)(C4H8O2)13(PhCN)2(H2O)2 and studied by X-ray and topological analysis. The compound exhibits cylinder-like type of molecular architecture and represents very rare case of polyhedral complexation of metallasilsesquioxane with benzonitrile. Complex 1 exhibited catalytic activity in activation of such small molecules as light alkanes and alcohols. Namely, oxidation of alcohols with tert-butylhydroperoxide and alkanes with meta-chloroperoxybenzoic acid. The oxidation of methylcyclohexane gave rise to the isomeric ketones and unusual distribution of alcohol isomers.

Clathrochelates meet phosphorus. New thio- and phosphorylation reactions of an iron(II) dichloroclathrochelate precursor and preparation of its first phosphorus(III)-containing macrobicyclic derivative.

Phosphorylation reactions of an iron(II) dichloroclathrochelate FeBd2(Cl2Gm)(BF)2 (where Bd(2-) and Cl2Gm(2-) are α-benzildioxime and dichloroglyoxime dianions, respectively) with diphenylphosphine oxide and diethyl thiophosphite were performed under phase-transfer conditions. In the case of diethyl thiophosphite as a P-nucleophile, the best yields were obtained in the dichloromethane-50% NaOH aqueous solution-5 mol% triethylbenzylammonium chloride (TEBAC) system. The use of different molar ratios of a macrobicycle precursor and this thiophosphorylating agent allowed us to obtain both the mono- and the diphosphorylated cage complexes. Nucleophilic substitution with diphenylphosphine oxide was performed in the K2CO3-acetonitrile-5 mol% TEBAC system, giving only the corresponding monophosphorylated iron(II) complex in high yield even in the presence of an excess of this P-nucleophile. The phosphorus(v)-containing clathrochelate product was reduced with an excess of silicoform to give an iron(II) macrobicycle with an inherent diphenylphosphine group in an almost quantitative yield, which was then characterized by (31)P{(1)H} NMR and single-crystal X-ray diffraction; it easily undergoes re-oxidation to the initial clathrochelate. The synthesized phosphorus(v)-containing cage complexes were characterized using elemental analysis, MALDI-TOF mass, IR, UV-Vis, (1)H, (11)B, (13)C{(1)H}, (19)F{(1)H} and (31)P{(1)H} NMR spectra, and by single-crystal X-ray diffraction.

Synthesis and Temperature-Induced Structural Phase and Spin Transitions in Hexadecylboron-Capped Cobalt(II) Hexachloroclathrochelate and Its Diamagnetic Iron(II)-Encapsulating Analogue.

Template condensation of dichloroglyoxime with n-hexadecylboronic acid on the corresponding metal ion as a matrix under vigorous reaction conditions afforded n-hexadecylboron-capped iron and cobalt(II) hexachloroclathrochelates. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-vis, (1)H and (13)C{(1)H} NMR, (57)Fe Mössbauer spectroscopies, SQUID magnetometry, electron paramagnetic resonance, and cyclic voltammetry (CV) and by X-ray crystallography. The multitemperature single-crystal X-ray diffraction, SQUID magnetometry, and differential scanning calorimetry experiments were performed to study the temperature-induced spin-crossover [for the paramagnetic cobalt(II) complex] and the crystal-to-crystal phase transitions (for both of these clathrochelates) in the solid state. Analysis of their crystal packing using the molecular Voronoi polyhedra and the Hirshfeld surfaces reveals the structural rearrangements of the apical long-chain alkyl substituents resulting from such phase transitions being more pronounced for a macrobicyclic cobalt(II) complex. Its fine-crystalline sample undergoes the gradual and fully reversible spin transition centered at approximately 225 K. The density functional theory calculated parameters for an isolated molecule of this cobalt(II) hexachloroclathrochelate in its low- and high-spin states were found to be in excellent agreement with the experimental data and allowed to localize the spin density within a macrobicyclic framework. CV of the cobalt(II) complex in the cathodic range contains one reversible wave assigned to the Co(2+/+) redox couple with the reduced anionic cobalt(I)-containing species stabilized by the electronic effect of six strong electron-withdrawing chlorine substituents. The quasireversible character of the Fe(2+/+) wave suggests that the anionic iron(I)-containing macrobicyclic species undergo substantial structural changes and side chemical reactions after such metal-centered reduction.

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.

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 were obtained by the one-pot template condensation of dichloroglyoxime with pentafluorophenylboronic acid on iron and cobalt(II) ions under vigorous reaction conditions in trifluoroacetic acid media. These reactive precursors easily undergo nucleophilic substitution with (per)fluoroarylthiolate anions, giving (per)fluoroarylsulfide macrobicyclic complexes with encapsulated iron and cobalt(II) ions; nucleophilic substitution of the cobalt(II) hexachloroclathrochelate precursor with a pentafluorophenylsulfide anion gave the target hexasulfide monoclathrochelate and the mixed-valence Co(III)Co(II)Co(III) bis-clathrochelate as a side product. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-Vis, (57)Fe Mössbauer (for the X-rayed iron complexes), (1)H, (11)B, (13)C and (19)F NMR spectroscopies and by X-ray diffraction; their redox and electrocatalytic behaviors were studied using cyclic voltammetry and gas chromatography. As can be seen from the single-crystal X-ray diffraction data, the second superhydrophobic shell of such caged metal ions is formed by fluorine atoms of both the apical and ribbed (per)fluoroaryl peripheral groups. The main bond distances and chelate N=C-C=N angles in their molecules are similar, but rotational elongation (contraction) along the molecular C3-pseudoaxes, accompanied by changes in the geometry of the corresponding MN6-coordination polyhedra from a trigonal prism to a trigonal antiprism, allowed encapsulating Fe(2+), Co(2+) and Co(3+) ions. The nature of an encapsulated metal ion and its oxidation state affect the M-N bond lengths, and, for cobalt(ii) clathrochelate with an electronic configuration d(7) the Jahn-Teller structural effect is observed as an alternation of the Co-N distances. Pentafluorophenylboron-capped hexachloroclathrochelate precursors, giving stable catalytically active metal(I)-containing intermediates due to the electron-withdrawing effect of their six ribbed chlorine substituents, were found to show moderate electrocatalytic activity in a 2H(+)/H2 hydrogen-forming reaction. In the case of their ribbed-functionalized sulfide derivatives, the strong electron-withdrawing (per)fluoroaryl groups do not stabilize the reduced electrocatalytically active metal(i)-containing species as their mesomeric effect is absent or substantially decreased by steric hindrances between them.

Copper(I)- and copper(0)-promoted homocoupling and homocoupling-hydrodehalogenation reactions of dihalogenoclathrochelate precursors for C-C conjugated iron(II) bis-cage complexes.

Iron(II) dibromo- and diiodoclathrochelates undergo copper(I)-promoted reductive homocoupling in HMPA at 70-80 °C leading to C-C conjugated dibromo- and diiodo-bis-clathrochelates in high yields. Under the same conditions, their dichloroclathrochelate analog does not undergo the same homocoupling reaction, so the target dichloro-bis-cage product was obtained in high yield via dimerization of its heterodihalogenide iodochloromonomacrobicyclic precursor. The use of NMP as a solvent at 120-140 °C gave the mixture of bis-clathrochelates resulting from a tandem homocoupling-hydrodehalogenation reaction: the initial acetonitrile copper(I) solvato-complex at a high temperature underwent re-solvatation and disproportionation leading to Cu(II) ions and nano-copper, which promoted the hydrodehalogenation process even at room temperature. The most probable pathway of this reaction in situ includes hydrodehalogenation of the already formed dihalogeno-bis-clathrochelate via the formation of reduced anion radical intermediates. As a result, chemical transformations of the iron(II) dihalogenoclathrochelates in the presence of an acetonitrile copper(I) solvato-complex were found to depend both on the nature of halogen atoms in their ribbed chelate fragments and on reaction conditions (i.e. solvent and temperature). The C-C conjugated iron(II) dihalogeno-bis-clathrochelates easily undergo nucleophilic substitution with various N,S-nucleophiles giving ribbed-functionalized bis-cage species. These iron(II) complexes were characterized by elemental analysis, MALDI-TOF mass spectrometry, IR, UV-Vis, (1)H and (13)C NMR spectroscopy, and by X-ray diffraction; their electrochemical properties were studied by cyclic voltammetry. The isomeric shift values in (57)Fe Mössbauer spectra of such cage compounds allowed identifying them as low-spin iron(II) complexes, while those of the quadrupole splitting are the evidence for a significant TP distortion of their FeN6-coordination polyhedra. As follows from CV data, the C-C conjugated iron(II) bis-clathrochelates undergo stepwise electrochemical reduction and oxidation giving mixed-valence Fe(II)Fe(I) and Fe(II)Fe(III) bis-cage intermediates.

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.

Iron vs. cobalt clathrochelate electrocatalysts of HER: the first example on a cage iron complex.

New macrobicyclic 2-thiopheneboron-capped iron and cobalt(II) tris-dioximates showed high electrocatalytic activity for hydrogen production from H(+) ions. This is the first example of the hydrogen evolution reaction electrocatalyzed by a clathrochelate iron complex, which catalyzes the hydrogen production at low overpotential.