57Fe Mössbauer and DFT study of the electronic and spatial structures of the iron(II) (pseudo)clathrochelates: the effect of ligand field strength.

Combined experimental 57Fe Mössbauer and theoretical DFT study of a series of iron(II)-centered (pseudo)macrobicyclic analogs and homologs was performed. The field strength of the corresponding (pseudo)encapsulating ligand was found to affect both the spin state of a caged iron(II) ion and the electron density at its nucleus. In a row of the iron(II) tris-dioximates, passing from the non-macrocyclic complex to its monocapped pseudomacrobicyclic analog caused an increase both in the ligand field strength and in the electron density at the Fe2+ ion, and, therefore, a decrease in the isomer shift (IS) value (so-called "semiclathrochelate effect"). Its macrobicyclization, giving the quasiaromatic cage complex, caused a further increase in the two former parameters and a decrease in IS (so-called "macrobicyclic effect"). The trend of their IS values was successfully predicted using the performed quantum-chemical calculations and the corresponding linear correlation with the electron density at their 57Fe nuclei was plotted. A variety of different functionals can be successfully used for such excellent prediction. The slope of this correlation was found to be unaffected by the used functional. In contrast, the predictions of both the sign and the values of quadrupole splitting (QS) for them, based on the theoretical calculations of EFG tensors, were found to be a real great challenge, which could not be solved at the moment even in the case of these C3-pseudosymmetric iron(II) complexes with known XRD structures. The latter experimental data allowed us to deduce a sign of the QSs for them. The straightforwarded molecular design of a (pseudo)encapsulating ligand is proposed to control both the spin state and the redox characteristics of an encapsulated metal ion.

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.

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.

Spectroelectrochemical Properties and Catalytic Activity in Cyclohexane Oxidation of the Hybrid Zr/Hf-Phthalocyaninate-Capped Nickel(II) and Iron(II) tris-Pyridineoximates and Their Precursors.

The in situ spectroelectrochemical cyclic voltammetric studies of the antimony-monocapped nickel(II) and iron(II) tris-pyridineoximates with a labile triethylantimony cross-linking group and Zr(IV)/Hf(IV) phthalocyaninate complexes were performed in order to understand the nature of the redox events in the molecules of heterodinuclear zirconium(IV) and hafnium(IV) phthalocyaninate-capped derivatives. Electronic structures of their 1e-oxidized and 1e-electron-reduced forms were experimentally studied by electron paramagnetic resonance (EPR) spectroscopy and UV-vis-near-IR spectroelectrochemical experiments and supported by density functional theory (DFT) calculations. The investigated hybrid molecular systems that combine a transition metal (pseudo)clathrochelate and a Zr/Hf-phthalocyaninate moiety exhibit quite rich redox activity both in the cathodic and in the anodic region. These binuclear compounds and their precursors were tested as potential catalysts in oxidation reactions of cyclohexane and the results are discussed.

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.

Probing Electronic Communications in Heterotrinuclear Fe-Ru-Fe Molecular Wires Formed by Ruthenium(II) Tetraphenylporphyrin and Isocyanoferrocene or 1,1'-Diisocyanoferrocene Ligands.

Two new heterotrinuclear Fe-Ru-Fe complexes of ruthenium(II) tetraphenylporphyrin axially coordinated with a pair of isocyanoferrocene ((FcNC)2RuTPP, 1) or 1,1'-diisocyanoferrocene (([C5H4NC]2Fe)2RuTPP, 2) ligands [Fc = ferrocenyl, TPP = 5,10,15,20-tetraphenylporphyrinato(2-) anion] were synthesized and characterized by UV-vis, magnetic circular dichroism, NMR, and FTIR spectroscopies as well as by electrospray ionization mass spectrometry and single-crystal X-ray diffraction. Isolation of insoluble polymeric {([C5H4NC]2Fe)RuTPP}n molecular wires (3) was also achieved for the first time. The redox properties of the new trinuclear complexes 1 and 2 were probed using electrochemical (cyclic voltammetry and differential pulse voltammetry), spectroelectrochemical, and chemical oxidation methods and correlated to those of the bis(tert-butylisocyano)ruthenium(II) tetraphenylporphyrin reference compound, (t-BuNC)2RuTPP (4). In all cases, the first oxidation process was attributed to the reversible oxidation of the Ru(II) center. The second and third reversible oxidation processes in 1 are separated by ∼100 mV and were assigned to two single-electron Fe(II)/Fe(III) couples, suggesting a weak long-range iron-iron coupling in this complex. Electrochemical data acquired for 2 are complicated by the interaction between the axial η(1)-1,1'-diisocyanoferrocene ligand and the electrode surface as well as by axial ligand dissociation in solution. Spectroelectrochemical and chemical oxidation methods were used to elucidate the spectroscopic signatures of the [1](n+), [2](n+), and [4](n+) species in solution. DFT and time-dependent DFT calculations aided in correlating the spectroscopic and redox properties of complexes 1, 2, and 4 with their electronic structures.