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.

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.

Size matters, so does shape: Inhibition of transcription of T7 RNA polymerase by iron(II) clathrochelates.

Coordination and organoelement compounds are rarely proposed as the drug candidates despite their vast potential in the area owing to their strictly controlled geometry and rather extensive surface. This is the first example of the inhibition of transcription in the system of T7 RNA polymerase by cage metal complexes. Their IC50 values reach as low as the nanomolar range, placing them among the most potent metal-based transcription inhibitors.

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.

Synthesis and structure of the first clathrochelate iron(II) tris-dioximates with inherent nitrile substituent(s) and new dehalogenation--reduction reaction at a quasi-aromatic macrobicyclic framework.

Monoribbed-substituted mono- and dicyano-functionalized iron(II) macrobicycles were obtained for the first time by the reaction of iron(II) diiodoclathrochelate precursor with copper(I) cyanide-triphenylphosphine complex under mild conditions. The target dinitrile clathrochelate is a minor product of this reaction, whereas the major product contains only one cyano group. The clathrochelates obtained were characterized using elemental analysis, (1)H and (13)C{(1)H} NMR, IR and UV-vis spectroscopy, MALDI-TOF spectrometry and X-ray diffraction crystallography. The geometry of their FeN(6)-coordination polyhedra is intermediate between a trigonal prism (TP) and a trigonal antiprism (TAP); the distortion angles, φ, are 22.6-24.7°. In the molecule of the precursor, the Fe-N distances are close, whereas in the mononitrile macrobicycles those for their functionalized chelate fragments are substantially smaller than the corresponding distances in the α-benzyldioximate moieties. The heights, h, of the TP-TAP coordination polyhedra and the average bite angles, α, (2.33 Å and 39°, respectively) are the same for the X-rayed clathrochelates. The UV-vis spectra indicate a dramatic redistribution of the electron density in the π-conjugated clathrochelate framework caused by functionalization with inherent nitrile substituents. The proposed mechanism of the dehalogenation-reduction reaction of iron(II) diiodoclathrochelate resulting in substitution of their iodine atoms by a cyano group and hydrogen atom includes the anion-radical hydrodehalogenation of this precursor with acetonitrile as a source of hydrogen atom. Then, the monomethinemonoiodine macrobicyclic product underwent a substitution with a cyano group only. The copper(I) cyanide-triphenylphosphine-acetonitrile system is proposed as a tool for the synthesis of nitrile derivatives of electron-withdrawing heterocycles starting from their halogen-containing precursors.

Efficient electrocatalytic hydrogen production from H+ ions using specially designed boron-capped cobalt clathrochelates.

Specially designed hexachlorine-containing cobalt(II) tris-dioximate clathrochelates were found to efficiently electrocatalyze the production of molecular hydrogen from H(+) ions without the overpotential of this process.

1-Pyridine- and 1-quinuclidine-1-boraadamantane as models for derivatives of 1-borabicyclo[2.2.2]octane. Experimental and theoretical evaluation of the B-N fragment as a polar isosteric substitution for the C-C group in liquid crystal compounds.

The suitability of 1-borabicyclo[2.2.2]octane (1) as a structural element for liquid crystals was evaluated using computational methods and experimental studies of two complexes of its close analogue 1-boraadamantane (2). The molecular and crystal structures for 1-pyridine-1-boraadamantane [2-P, C(14)H(20)BN, P2(1)/m, a = 8.4404(13) A, b = 6.8469(10) A, c = 10.5269(16) A, beta = 104.712(3) degrees, Z = 2], 1-quinuclidine-1-boraadamantane [2-Q, C(16)H(28)BN, P2(1)/n, a = 6.6529(3) A, b = 10.6665(6) A, c = 19.3817(10) A, beta = 94.689(3) degrees, Z = 4], and 1-pyridine-trimethylborane [3-P, C(8)H(14)BN, C(cma), a = 6.9875(10) A, b = 15.011(2) A, c = 16.556(2) A, Z = 8] were determined by X-ray crystallography and compared with the results of DFT and MP2 calculations. Gas-phase thermodynamic stabilities of complexes 1-P, 1-Q, 2-P, and 2-Q were estimated using a correlation between theoretical (MP2/6-31+G(d)//MP2/6-31G(d) with B3LYP/6-31G(p) thermodynamic corrections) and experimental data for complexes of BMe(3) (3) with amines lacking N-H bonds. The analysis showed the generally higher thermodynamic stability for the quinuclidine (Q) complexes compared to that of the pyridine (P) analogues in the gas phase and an overall order of stability of 1 > 2 > 3. This order is paralleled by high ring strain energy of 1 (SE = 27 kcal/mol) as compared to that of 1-boraadamantane (2, SE = 16.5 kcal/mol). The chemical stability of 2-P and 2-Q, with respect to hydrolytic and oxidative reagents, is high for the pyridine derivative and satisfactory for the quinuclidine complex at ambient temperature, which implies sufficiently high stability of 1-borabicyclo[2.2.2]octane complexes for materials applications. Molecular dipole moments of 6.2 +/- 0.1 and 6.0 +/- 0.15 D were measured for 2-Q and 2-P, respectively.

Interaction of dichloride iron(II) clathrochelate with dimercaptomaleodinitrile: synthesis of the precursor monoribbed-functionalized phthalocyaninoclathrochelates and the unexpected formation of a new thiophene-containing heterocyclic system in the ribbed chelate fragment of the clathrochelate framework.

Clathrochelate iron(II) FeBd 2(S2C2(CN)2Gm)(BF)2 tris-dioximate with a ribbed vic-dinitrile fragment was synthesized as a precursor of the monoribbed-functionalized hybrid phthalocyaninoclathrochelates by nucleophilic substitution of the vic-dichloride FeBd2(Cl2Gm)(BF)2 clathrochelate (1) with the potassium salt of dimercaptomaleodinitrile. Reaction of nitromethane with this salt was followed by the condensation of the reaction products with 1 to yield the clathrochelate with an annulated previously unknown thiazinothiophene heterocyclic system in the ribbed fragment. Both complexes were characterized on the basis of elemental analysis; MALDI-TOF mass spectrometry; IR, UV-vis, (57)Fe Mössbauer, and NMR spectroscopies; and X-ray crystallography.