The first example of the alkoxy-containing iron(ii) tris-dioximate clathrochelate: synthesis, structure, and properties

Abatract  The reaction of the dichloride iron(ii) tris-dioximate clathrochelate with triethyl orthoformate in the presence of metallic sodium afforded the diethoxy-substituted macrobicyclic complex. The first alkoxy-containing clathrochelate was characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-Vis, ¹H and ¹³C{¹H} NMR spectroscopy, and X-ray diffraction analysis. Dedicated to the 90th anniversary of the L. Ya. Karpov Institute of Physical Chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1283–1288, June, 2008.     

Multistep synthesis,reactivity and X-ray structure of the anisole-terminated iron(II) polyhalogenoclathrochelates and their monoribbed-functionalized macrobicyclic derivatives

Multistep synthetic pathway towards a series of the anisoleboron-capped ribbed-functionalized iron(II) cage complexes was developed. Their hexachloroclathrochelate precursor was obtained by the template condensation of three dichloroglyoximate chelating ligand synthons with two molecules of 4-methoxyphenylboronic acid as a Lewis-acidic cross-linking agent on the iron(II) ion as a matrix. It easily underwent a stepwise nucleophilic substitution with S₂- and O₂-dinucleophilic aliphatic (ethanedithiolate) or aromatic (pyrocatecholate) agents, forming the stable X₂ (X?=?S or O)-six-membered ribbed substituent(s) at a quasiaromatic cage framework. Performing these reactions under the different reaction conditions (i.e., at various hexachloroclathrochelate-to-nucleophile molar ratios, a wide range of temperatures and a series of the solvents) allowed to control a predominant formation of its mono-, di- or triribbed-substituted macrobicyclic derivatives. Thus obtained iron(II) di- and tetrachloroclathrochelates can undergo their post-synthetic transformations with active nucleophilic agents. The latter complexes underwent a further nucleophilic substitution with the anionic derivative of n-butanthiol, thus giving the hexasulfide macrobicyclic compound with two functionalizing n-alkyl substituents in one of its three chelate α-dioximate fragments and two apical biorelevant anisole substituents. The obtained iron(II) clathrochelates, possessing a low-spin electronic d⁶ configuration, were characterized using elemental analysis, MALDI-TOF mass spectrometry, UV–Vis, ¹H and ¹³C{¹H} NMR spectroscopies, and by the single-crystal X-ray diffraction experiments for the hexachloroclathrochelate precursor, its dichlorotetrasulfide macrobicyclic derivative and the monoribbed-functionalized hexasulfide cage complex. In all their molecules, the encapsulated iron(II) ion is situated in the centre of its FeN₆-coordination polyhedron, the geometry of which is intermediate between a trigonal prism and a trigonal antiprism with the distortion angles φ from 21.4 to 23.4°. Halogen bonding between the polyhalogenoclathrochelate molecules in their crystals is observed.

Graphical abstract

     

Ribbed-functionalized iron(ii) tris-dioximate clathrochelates with pendant fragments of various types: synthetic pathways,structures, and properties

Nucleophilic substitution of chlorine atoms in the iron(ii) hexachloride clathrochelate on treatment with thiolate anions afforded hexafunctionalized tris-dioximate complexes with the pendant n-butyl-, n-octylsulfide, silatrane, and captopryl functionalizing groups. These complexes were characterized by elemental analysis, IR, UV-Vis, ¹H and ¹³C NMR, and ⁵⁷Fe Mössbauer spectroscopies, and plasma-desorption mass spectrometry. The crystal and molecular structures of the n-butylsulfide and silatrane clathrochelates were established by X-ray diffraction analysis. Cyclic voltammetry study demonstrated that the Fe²⁺/Fe³⁺ redox process of the encapsulated iron ion is responsible for the electrochemical behavior of the prepared compounds in solution.     

Template synthesis and structures of apically functionalized iron(ii) clathrochelates

Template condensation of three nioxime or dichloroglyoxime molecules with monosubstituted boronic acids on an iron(ii) ion matrix afforded apically functionalized tris-nioximate clathrochelates and hexachloride precursors of apically-ribbed functionalized clathratochelates, respectively. The macrobicyclic tris-nioximates containing apical o-dimethoxyphenyl, p-bromophenyl, phenylethynyl, biphenylyl, 6-pyrimidinyl, or tert-butyl substituents and the dibenzothienyl-containing hexachloroglyoximate clathrochelate thus obtained were characterized by elemental analysis and IR, UV-Vis, ¹H and ¹³C NMR, ⁵⁷Fe Mössbauer and PD mass spectroscopies. The structures of o-dimethoxyphenyl- and phenylethynyl-containing iron(ii) tris-nioximates and the dibenzothienyl precursor were established by X-ray diffraction analysis.     

Template synthesis and structures of bis-ferrocenylboronate macrobicyclic iron(ii) tris-dioximates

A series of ferrocenylboron-capped tris-dioximate iron(ii) clathrochelates was synthesized by the template condensation of three molecules of dimethylglyoxime (H₂Dm), cyclohexanedione 1,2-dioxime (H₂Nx), or cyclooctanedione 1,2-dioxime (H₂Ox) and two molecules of ferrocenylboronic acid (FcB(OH)₂) on the Fe²⁺ ion matrix. The yields of the clathrochelate derivatives of alicyclic dioximes were substantially higher than that of their acyclic analog, because the molecules of alicyclic H₂Nx and H₂Ox α-dioximes have the s-cis-configuration suitable for complex formation, whereas the H₂Dm molecules in solution have the s-trans-configuration. The synthesized compounds were characterized using elemental analysis, IR and UV-Vis spectroscopies, MALDI-TOF mass spectrometry, ¹H and ¹³C{¹H} NMR and ⁵⁷Fe Mössbauer spectroscopies, and X-ray diffraction analysis. The crystal of FeDm₃(BFc)₂·CHCl₃ contains two types of crystallographically nonequivalent clathrochelate molecules. The intermolecular contacts C-H?Cp formed by the ferrocenyl fragments and cyclooctane carbocycles and the interactions Cp-H?O were observed in the crystal of FeOx₃(BFc)₂. The structural lability of the cyclooctane substituents allows the FeOx₃(BFc)₂ molecules to arrange by the “bump-into-hollow” mode because of attractive H?H interactions between the ribbed substituents of the neighboring molecules. The geometry of the ferrocenylborate iron(ii) clathrochelates is intermediate between a trigonal prism and a trigonal antiprism.     

Synthesis, structure, properties and immobilization on a gold surface of the monoribbed-functionalized tris-dioximate cobalt(II) clathrochelates and an electrocatalytic hydrogen production from H+ ions

The cycloaddition of the mono- and dichloroglyoximes to the cobalt(II) bis-α-benzyldioximate afforded the cobalt(II) mono- and dichloroclathrochelates in moderate yields (40-60%). These complexes undergo nucleophilic substitution of their reactive chlorine atoms with aliphatic amines, alcohols and thiolate anions. In the case of ethylenediamine and 1,2-ethanedithiol, only the macrobicyclic products with α,α'-N(2)- and α,α'-S(2)-alicyclic six-numbered ribbed fragments were obtained. The cobalt(II) cage complexes with terminal mercapto groups were synthesized using aliphatic dithiols. The crystal and molecular structures of the six cobalt(II) clathrochelates were obtained by X-ray diffraction. Their CoN(6)-coordination polyhedra possess a geometry intermediate between a trigonal prism and a trigonal antiprism, and the encapsulated cobalt(II) ions are shifted from their centres due to the structural Jahn-Teller effect with the Co-N distances varying significantly (by 0.10-0.26 ?). The electrochemistry of the complexes obtained was studied by cyclic voltammetry (CV). The anodic waves correspond to the quasi-reversible Co(2+/3+) oxidations, whereas the cathodic ranges contain the quasi-reversibile waves assigned to the Co(2+/+) reductions; all the cobalt(i)-containing clathrochelate anions formed are stable in the CV time scale. The electrocatalytic properties of the cobalt complexes obtained were studied in the production of hydrogen from H(+) ions: the addition of HClO(4) resulted in the formation of the same catalytic cathodic reduction Co(2+/+) waves. The controlled-potential electrolysis with gas chromatography analysis confirmed the production of H(2) in high Faraday yields. The efficiency of this electrocatalytic process was enhanced by an immobilization of the complexes with terminal mercapto groups on a surface of the working gold electrode.     

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

All six constitutional isomers of the dimethoxy-terminated clathrochelate FeBd₂((CH₃OOCC₆H₄S)₂Gm)(BF)₂ (where Bd^2? 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.     

Hexakis(dimethylformamide)iron(II) complex cation in hexahalorhenate(IV)-based salts: synthesis,X-ray structure and magnetic properties

Abstract

Two iron(II)-rhenium(IV) compounds of general formula [Fe^II(dmf)₆][Re^IVX₆] [X = Cl (1) and Br (2); dmf = N,N-dimethylformamide] have been prepared and characterized. X-ray powder diffraction measurements on samples of 1 and 2 support the same structure for both systems. The crystal structure of 1 was determined by single-crystal X-ray diffraction. 1 crystallizes in the triclinic system with space group Pī. Each iron(II) is six-coordinate and bonded to six oxygens from six dmf molecules building a distorted octahedral environment. Rhenium(IV) is six-coordinate by six halide anions in an almost regular octahedral geometry. The magnetic properties were investigated from variable-temperature magnetic susceptibility measurements performed on microcrystalline samples of 1 and 2, whose experimental data were reproduced by a model of two isolated paramagnetic centers [S = 2 (Fe^II) and S = 3/2 (Re^IV)] with large values of zero-field splitting (zfs) parameter.     

Synthesis and structure of the ferrocenylboron-capped clathrochelate iron(ii) oximehydrazonates

The direct template macrocyclization of 2,3-butanedione monooxime hydrazone (HDXO) with ferrocenylboronic acid on the iron(ii) ion matrix afforded the ferrocenylboron-capped semiclathrochelate iron(ii) oximehydrazonate. The H⁺ ion-catalyzed macrocyclization of this precursor with an excess of triethyl orthoformate gave the clathrochelate complex with syn,syn,syn-orientation of the ethoxy substituents relative to the 1,3,5-triazacyclohexane ring. The complexes synthesized were characterized using elemental analysis, IR and UV—Vis spectroscopies, MALDI-TOF mass spectrometry, ¹H and ¹³C{¹H} NMR, ⁵⁷Fe Mössbauer spectroscopies, and X-ray diffraction analysis.     

A spectrometric,separation and voltammetric study of the complexation reactions of bromazepam with iron(ii),copper(ii) and cobalt(ii)

Bromazepam, in the form of a cationic iron(II) chelate, can be determined spectrophotometrically at 588 nm with a limit of detection of ca. 10^-6 M. When this chelate is ion-paired with perchlorate, it can be extracted into organic solvents such as 1,2-dichloroethane and 4-methyl-2-pentanone, and determined by atomic absorption spectrometry with a limit of detection of 1.5 × 10^-5 M bromazepam at the iron resonance 248.3-nm line. Ion-pairs involving the Fe(II), Cu(II) and Co(II) chelates and perchlorate can be separated by h.p.l.c. using a C₁₈ reverse-phase column and a mobile phase of 4:1 water—methanol, with a u.v. detector at 242 nm. This approach allowed for the determination of iron(II) ions in aqueous solution with a limit of detection of 10^-8 M. The h.p.l.c. method could also be used to quantify bromazepam spiked in plasma in the concentration range 1–10 μg ml^-1, following extraction of bromazepam from plasma and subsequent formation of the iron(II) ion-pair. Copper(II) forms a labile chelate with bromazepam in pH 4.8 acetate buffer which, when subjected to differential pulse voltammetry at the hanging mercury drop electrode, gives rise to a catalytic phenomenon which can be utilised for the determination of bromazepam in the concentration range 10^-5–10^-9 M.     

Reactions of dichloro-substituted iron(ii) clathrochelate with 1,4-dioxane radical derivatives: synthesis, structure, and spectral characteristics of the dioxane ring opening product in the ribbed fragment of the macrobicyclic ligand

A free-radical substitution for the chlorine atoms with the 1,4-dioxan-2-yl fragment in the tris-dichloro-substituted dioximate iron(II) clathrochelate is accompanied by the oxidative dioxane ring opening as a side process. The compound obtained was characterized by elemental analysis data, 1D and 2D ¹H and ¹³C{¹H} NMR spectroscopy (in solution), MALDI TOF mass spectrometry, as well as by single-crystal X-ray diffraction.     

Synthesis,structure, and reactivity of siloxides and germyloxides of iron(ii) and cobalt(ii)

Iron and cobalt siloxides and germyloxides [(Me₃Si)₃SiO]₂M (M = Fe (1), Co (2)), (Me₅Si₂O)₂Fe (3), (Prⁱ ₃SiO)₂M (M = Fe (4), Co (5)), (Prⁱ ₃GeO)₂Fe (6), (Ph₃SiO)₂Fe (7), (Me₃SiO)₂Fe (8), (Prⁱ ₃GeO)₂Fe(bpy) (9), and [(Me₃Si)₂NFe(-OSi₂Me₅)₂]₂Fe·C₆H₆ (10) were synthesized by the reactions of metal silylamides [(Me₃Si)₂N]₂M (M = Fe, Co) with the corresponding silanols or triisopropylgermanol. The reaction of pentamethyldisilanol with iron(ii) silylamide affords either polymeric complex 3 or coordination oligomer 10, depending on the ratio of the reactants. The structures of complexes 9 and 10 were established by X-ray diffraction analysis. The interaction of the prepared compounds with carbon oxides was studied. Low-coordination cobalt siloxide is the only among all prepared compounds that absorbs CO (2 mol) at room temperature and under 1 atm to form an unstable cluster. Compounds 1, 2, and 4—8 react with CO₂ to form carbonate complexes, and their reactivity decreases with a decrease in the electron-donating ability of the substituents at the central atom: (Me₃Si)₃SiO > Prⁱ ₃GeO Prⁱ ₃SiO > Me₃SiO Ph₃SiO.     

Structure and oxygenase activity of the iron(ii) complex with pyridylcarboxamide ligand

A reaction of Fe(ClO₄)₂·6H₂O or Fe(OTf)₂(MeCN)₂ with one equivalent of the tetradentate ligand bis(2-pyridyl)methyl-2-pyridylcarboxamide (Py₂CHNHCOPy, tpcaH) furnished dimeric iron(II) complexes [Fe(tpcaH)]₂X₄ (X = ClO₄ ^? (1a), OTf^? (1b)). According to the X-ray diffraction data for the complex 1a, each iron atom is bound to the two pyridyl fragments of one ligand and the pyridylcarboxamide pair of the other one. Complex 1a is a dimer in the crystalline state, while in MeCN solution according to the mass spectrometric data with the electrospray ionization, ¹H NMR spectroscopic data, and quantum chemical calculations, it is apparently in the equilibrium with monomers of different structures. Complex 1 catalyzes selective oxidation of saturated hydrocarbons with hydrogen peroxide presumably involving the perferryl intermediate, which has an N,N,O-facial coordination of potentially tetradentate ligand tpcaH structurally modeling the 2-histidine-1-carboxylate-facial triad of the nonheme oxygenases.     

Hydrothermal synthesis, crystal structure, and luminescence of a novel tetranuclear zinc(ii) complex

A new tetranuclear zinc(II) complex [Zn₄(tmphen)₄(tbip)₄(H₂O)₄] (1, tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, H₂tbip = 5-tert-butyl isophthalic acid) is hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction, elemental analysis, and IR spectroscopy. In complex 1, four tbip^2? ligands act as bridges between four neighboring Zn atoms to form an unusual tetranuclear zinc cluster. The clusters are further connected by two types of O-H…O and C-H…O hydrogen bonds, generating a three-dimensional supramolecular structure. Meanwhile, π-π stacking interactions and C-H…π interactions further consolidate the three-dimensional supramolecular framework of 1. In addition, the luminescence measurements reveal that complex 1 exhibits strong fluorescent emissions in the solid state at room temperature.     

Synthesis and structure of binuclear iron(ii) complex with the cage-like ligand as a model of methane monooxygenase

A binuclear iron(II) complex, [Fe^II ₂L(OTf)₂](OTf) (1), with the cage-like ligand LH = [(PyCH₂)₂N(CH₂)₃O]₂C₆H₃COOH containing an immobilized carboxylate was synthe-sized and characterized in order to model an active center of soluble methane monooxygenase (sMMO). Studies on the oxidation of cyclohexane with hydrogen peroxide or O₂ involving this complex showed that the complex 1 does not catalyze the indicated reactions. Consideration of crystal structure of complex 1 gives an explanation of its inactivity in the reaction of O₂ activation.     

Synthesis and structure of antiferromagnetic dinuclear iron(ii) pivalate with a Chinese-lantern-like structure

Russian Chemical Bulletin -     

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 ? 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.     

The first hexanuclear copper(I) carboxylate: X-ray crystal structure and reactivity in solution and gas-phase reactions

The carboxylate ligand-exchange reaction of copper(I) trifluoroacetate by 3,5-difluorobenzoate yielded a new product, [Cu(O2C(3,5-F)2C6H3)] (1). Single crystals of 1 suitable for X-ray structural characterization were obtained by sublimation-deposition procedures at 230 degrees C. An X-ray diffraction study revealed a remarkable planar hexanuclear copper(I) core supported by bridging carboxylates, the first such structural type among other known copper(I) carboxylates. The Cu...Cu distances within the core range from 2.7064(8) to 2.8259(8) A and fall into the category of cuprophillic interactions. The hexacopper unit remains intact upon gas-phase deposition with a planar polyarene, coronene (C24H12), to give [Cu6(O2C(3,5-F)2C6H3)6](C24H12) (2). Density functional theory calculations suggest the latter compound to be a cocrystallization product having electrostatic interactions between the hexacopper complex and coronene. However, cocrystallization affects the photophysical properties of 2. While copper(I) 3,5-difluorobenzoate (1) exhibits photoluminescence at ca. 554 nm (lambda(ex) = 350 nm) in the solid state, compound 2 is nonluminescent at room temperature in the visible region. Gas-phase and solution reactions of 1 with alkyne ligands, diphenylacetylene (C14H10) and 1,4-bis(p-tolylethynyl)benzene (C24H18), result in the rupture of the [Cu6] core to afford dinuclear organometallic copper(I) complexes. The latter have a dimetal core cis-bridged by two carboxylate groups with acetylene ligands eta(2)-coordinated to each copper(I) center.