Structure and properties of iron nitrosyl complexes with functionalized sulfur-containing ligands

The review summarizes the results of studies aimed at developing the fundamentals for the design of a new class of nitric oxide donors, viz., iron nitrosyl complexes with functionalized sulfur-containing ligands, which are structural analogs of the active sites of non-heme nitrosyl iron-sulfur proteins. The structures, reactivities, and pharmacological activity in vitro and in vivo of these complexes are considered.     

Electron spin resonance spectroscopy of iron nitrosyl complexes with organic ligands

ESR spectra of liquid and frozen solutions of nitrosyl iron complexes formed in aqueous solution with a variety of mercaptans, dithiocarbamates and azoles have been studied. The hyperfine ¹⁴N splittings from nitrosyl groups and azole nitrogen as well as ¹H splittings in the case of nitrosyl mercaptan complexes have been observed. Structures of these complexes are suggested on the basis of the ESR spectral parameters.     

Electronic structure of dinuclear iron nitrosyl complexes with different ligands at two iron centers

The electronic structures of three dinuclear iron complexes were determined with the DFT method. The complexes contain a {Fe(NO)₂}⁹ unit and thiolate, nitrosyl, carbonyl and amine ligands at the second iron atom. The two iron atoms are bridged by thiolate ligands. In the lowest energy states of these complexes, the iron atoms possess spin S = 1, 3/2 or 5/2, depending on the coordinated ligands and their mutual arrangement. Nitrosyl is coordinated as NO⁻ antiferromagnetically coupled to iron, and the two iron units are antiferromagnetically coupled to each other.     

New class of neutral paramagnetic binuclear sulfur-containing iron nitrosyl complexes

Neutral paramagnetic binuclear iron nitrosyl complexes, whose structures and properties differ from those of the known Roussin"s red salt esters, were synthesized for the first time. The iron nitrosyl complexes [Fe₂(₂-SR)₂(NO)₄]·nH₂O (¹-S, ¹-N; n = 1 or 2; R is 5-amino-1,2,4-triazol-3-yl (1), 1,2,4-triazol-3-yl (2), 1-methyltetrazol-5-yl (3), or benzothiazol-2-yl (4)) were prepared by the exchange reactions of Na₂Fe₂(S₂O₃)₂(NO)₄ with heterocyclic thiols. According to the results of X-ray diffraction analysis, complex 1 has a centrosymmetrical dimeric structure in which the iron atoms are linked through the -N—C—S structural fragment. Each Fe atom is bound to the N atom of one ligand and the S atom of another ligand. The isomer shifts of complexes 1—4 have virtually equal values (_Fe = 0.291(1)—0.304(1) mm s^–1 at T = 85 K), which are twice as large as _Fe for Roussin"s red salt esters. The iron atoms in complexes 1—4 have the low-spin configuration d⁷ (Fe⁺). The ESR spectra of polycrystalline powders of complexes 1—4 consist of a single Lorentzian line with g = 2.032 and a width of 6—10 mT. The temperature dependence of the magnetic susceptibility of complex 1 in the temperature range of 80—300 K is adequately described by the Curie—Weiss law with 8 K; the effective magnetic moment per iron atom is 1.85 B.     

Electronic structure of ferric heme nitrosyl complexes with thiolate coordination

The effect of trans thiolate ligation on the coordinated nitric oxide in ferric heme nitrosyl complexes as a function of the thiolate donor strength, induced by variation of NH-S(thiolate) hydrogen bonds, is explored. Density functional theory (DFT) calculations (BP86/TZVP) are used to define the electronic structures of corresponding six-coordinate ferric [Fe(P)(SR)(NO)] complexes. In contrast to N-donor-coordinated ferric heme nitrosyls, an additional Fe-N(O) sigma interaction that is mediated by the dz2/dxz orbital of Fe and a sigma*-type orbital of NO is observed in the corresponding complexes with S-donor ligands. Experimentally, this is reflected by lower nu(N-O) and nu(Fe-N) stretching frequencies and a bent Fe-N-O moiety in the thiolate-bound case.     

Features of the decomposition of the nitrosyl iron complex with thiourea ligands under aerobic conditions: experiment and kinetic and quantum chemical modeling

The reaction of oxygen with the nitrosyl iron complex [Fe(SC(NH₂)₂)₂(NO)₂]⁺ (complex 1) was studied. According to the results obtained, three main directions of transformation of complex 1 under aerobic conditions can be distinguished: (i) reversible binding of complex 1 with oxygen leading to a sharp decrease in the oxygen concentration at the initial moment, (ii) irreversible spontaneous transformation of complex 1 without participation of oxygen accompanied by the elimination of thio ligands and NO groups, and (iii) irreversible reaction of complex 1 with oxygen to form oxygen coordination products (at the iron atom, Fe-N bond, and two N atoms of nitrosyl ligands), which then reversibly transform into oxidation products. The latter process is accompanied by an increase in the absorbance in the experimental UV spectra and the formation of nitrates and nitrites in the reaction system.

     

Cationic metal nitrosyl complexes. IV. Polymerization of olefins with dinitrosyl iron complexes

The polymerization of styrene was performed with new cationic iron complexes, (Fe(N-O)₂S_n)⁺PF₆^?(BF₄^?, CIO₄^?), where S_n represents solvent molecules such as CH₂Cl₂, THF, and MeCN. Kinetic experiments showed a first-order dependence of (R_p)₀ on the monomer and iron complex concentrations. The molecular weight determinations suggested that the termination process is fast and occurs by chain transfer to monomer. An extension of this polymerization to α-methylstyrene, isobutene, tetrahydrofuran, and styrene-methylmethacrylmate system emphasized the cationic nature of the reaction.     

Formation of paramagnetic mononuclear iron nitrosyl complexes from diamagnetic di- and tetranuclear iron-sulphur nitrosyls: characterisation by EPR spectroscopy and study of thiolate and nitrosyl ligand exchange reactions

The diamagnetic Roussin esters Fe₂(SR)₂(NO)₄ readily underwent exchange with thiols R′SH to yield Fe₂(SR′)₂(NO)₄: the exchange was faster in polar, coordinating solvents where paramagnetic, mononuclear complexes of types [Fe(NO)₂(solvent)₂]⁺ and Fe(NO) ₂(SR)(solvent) were formed. With the corresponding thiolate anions RS^-, the esters Fe₂(SR)₂(NO)₄ formed the mononuclear complexes [Fe(SR)₂(NO)₂]^-, which were fully characterised by EPR spectroscopy for R = H, Me, Et, i-Pr, t-Bu and PhCH₂: assignments of hyperfine couplings were confirmed by use of ¹⁵N. With Fe₂(SR)₂(NO)₄ and a different set of thiolate anion, R′S ^-, in excess, thiol exchange occurred to give [Fe(SR′)₂(NO)₂]^-. A mechanism for formation of Fe₂(SR′)₂(NO)₄ from Fe₂(SR)₂(NO)₄ has been proposed. The paramagnetic mononuclear complexes [Fe(SR)₂(NO)₂] were also readily formed from the diamagnetic clusters [Fe₄S₃(NO)₇]^- and Fe₄S₄(NO)₄, together with [Fe(SR)₃(NO)]^-, and additionally from [Fe(CO)₃NO]^-. [Fe(SMe)₂(NO)₂]^-. was found to be a precursor of isolable Fe₂(SMe)₂(NO)₄, and [Fe(SH)₂ (NO)₂]^- to be the common precursor of both Roussin′s red anion [Fe₂S₂(NO)₄]^- and Roussin's black anion [Fe₄S₃ (NO)₇]^- interconvertible by appropriate adjustment of pH. The nitrosyl groups in these complexes were freely labile, and mononitrosyliron and dinitrosyliron fragments were readily interconvertible: FE(NO) fragments were favoured by the dimethyldithiocarbamate ligand (Me₂NCS ₂) and Fe(NO)₂ fragments by thiolate ligands, RS^-, regardless of the origin of the Fe(NO)_x(x = 1,2) fragment: both mono- and dinitrosyliron complexes persisted with [(i-PrO)₂S₂]^- as ligand. Isotopic labelling showed the occurrence of rapid exchange of nitrogen between nitrosyl ligands and added nitrite in Fe(NO)(S₂CNMe₂)₂ and [Fe(SR)₂(NO)₂]^-     

Kinetic regularities of NO donation by binuclear dinitrosyl iron complexes with thiolate ligands based on thiophenol derivatives in the presence of red blood cells

The kinetics of nitrogen oxide release by binuclear dinitrosyl iron complexes (B-DNICs) with thiolate ligands based on thiophenol and its several oxy, amino, and nitro derivatives was studied using a suspension of red blood cells simulating the internal medium of a blood vessel. The NO donating ability of the complexes was estimated by the kinetic parameters of first-order equation, which described the formation of intra-erythrocytic methemoglobin. Three typical kinetic profiles of NO donation were distinguished: pseudosaturation donation and donation with prolonged and explosive profiles. In the case of first-type NO donation typical of complexes with thiophenol and its nitro derivatives, the curves display a fast coming to saturation long before the complete release of all NO groups contained in the structure of the starting complex into a solution. Such a type of donation is likely due to the formation of long-lived nitrosyl intermediates in the system. The prolonged type of NO donation shown by the complex with hydroxyphenyl ligand is characterized by virtually constant rate of NO release into a solution without pronounced transition to saturation during experiment (10–12 min). In the case of explosive-type donation characteristic of the complex with aminophenyl ligands, a considerable portion of NO was fast released into a solution within 1–3 min. All complexes under study caused hemolysis of a 0.2% suspension of red blood cells. The complex with aminophenyl ligands exhibited the highest hemolytic activity.

     

Preparation, characterization, and catalytic properties of ruthenium nitrosyl complexes with polypyrazolylmethane ligands

Ruthenium(II) nitrosyl complexes with polypyrazolylmethanes, [(Bpm)Ru(NO)Cl₃] [Bpm = bis(1-pyrazolyl)methane, 1], [(Bpm^∗)Ru(NO)Cl₃] [Bpm^∗ = bis(3,5-dimethyl-1-pyrazolyl)methane, 2], [(Tpm)Ru(NO)Cl₂][PF₆] [Tpm = tris(1-pyrazolyl)methane, 3], and [(Tpm^∗)Ru(NO)Cl₂][PF₆] [Tpm^∗ = tris(3,5-dimethyl-1-pyrazolyl)methane, 4], have been synthesized and characterized. The solid-state structures of [(Bpm^∗)Ru(NO)Cl₃] (2) and [(Tpm^∗)Ru(NO)Cl₂][PF₆] (4) were determined by single-crystal X-ray crystallographic analyses. These complexes have been tested as catalysts in the transfer hydrogenation of several ketones under mild conditions.     

Indenyl complexes of ruthenium containing thiolate ligands. Structure of IndRu(dppe)SPh

The indenyl ruthenium thiolate complexes IndRu(PPh₃)₂SR, (1) [Ind = η⁵-C₉H₇; R = Pr ⁿ (a), Ph (b), CH₂Ph(c)] were prepared directly by reacting the thiolate anions (RS⁻) with IndRu(PPh₃)₂Cl. The one-pot reaction of IndRu(PPh₃)₂Cl, thiolate anions and dppa ligands gave IndRu(dppa)SR [dppa= bis(diphenylphosphino)ethane: dppe (2); bis(diphenylphosphino)methane: dppm (3)]. Complexes (1) readily react with NOBF₄ in THF at room temperature to give [IndRu(PPh₃)(NO)SR]BF₄, (4). Complexes (1)–(4) have been characterized by spectroscopic techniques (i.r.,¹H-n.m.r., ³¹P-n.m.r.) and by elemental analysis. The crystal structure of IndRu(dppe)SC₆H₅, (2b) has been determined by X-ray analysis.     

Coordination complexes of silicon and germanium halides with neutral ligands

The coordination chemistry of silicon(IV) and (II) and germanium(IV) and (II) halides with neutral donor ligands from groups 15 (N, P or As) and 16 (O, S or Se) is reviewed; N-heterocyclic carbene complexes are also included. The focus is mainly on results published after 1990 and illustrates that significant recent developments have been made in the coordination chemistry of low-valent silicon and germanium halide complexes in particular; this is expected to pave the way for much new reaction chemistry both from a fundamental and application-driven perspective.     

Chromatographic study of186Re complexes with various ligands

Thin-layer and paper chromatography have been used for the determination of radiochemical yields of¹⁸⁶Re complexation with three selected ligands methylenediphosphonic acid (MDP), ethylenediamminotetraacetic acid (EDTA), and citrate convenient for the radiopharmaceutical applications. The combination of selected two chromatographic systems has been chosen due to the satisfactory separation of free perrhenate, corresponding complex with¹⁸⁶Re and reduced hydrolyzed rhenium. Rhenium complexes with studied ligands were prepared by reduction of perrhenate at presence of suitable ligand. Stannous chloride together with ascorbic acid (antioxidant) was used for perrhenate reduction. The effect of pH of reaction mixture, reaction time and concentration of reducing agent on the radiochemical yield of complexation is described and the optimal conditions for synthesis of rhenium complexes with MDP, EDTA and citrate have been found. Under optimal condition the radiochemical yield of complexation¹⁸⁶Re-MDP,¹⁸⁶Re-EDTA and¹⁸⁶Re-citrate reached more than 90%, 80%, and 80%, respectively.     

过氧化环丙基甲酰在不同类型溶剂中的热分解

本文报道过氧化环丙基甲酰(1)在不同类型溶剂中的化学行为。首先,我们建立了五个热解主要产物:环丙基甲酸环丙酯(4)、环丙基甲酸(5)、双环丙烷(6)、环丙烷(7)及二氧化碳的色谱定量分析方法,然后在不同类型的溶剂中测定1热分解产物的分布。结果表明,在非极性碳氢溶剂中,以自由基型的单分子均裂过程为主;在极性溶剂中则可能伴有诱导分解。我们的结果还表明,产物4,6,7主要生成于笼外,与文献报道的不同。更有趣的发现是,在HMPA中,1的分解可能主要是通过它与溶剂间的电子转移来实现的.     

The thermal decomposition of transition-metal complexes containing heterocyclic ligands: 2.Benzoxazole complexes

Enthalpies of the overall decomposition reactions

and of the intermediate reactions involving stepwise loss of ligand, L, where M is Mn, Co, Ni, Cu, or Cd, X is Cl or Br, and L is benzoxazole, 2-methylbenzoxazole, or 2,5-dimethylbenzoxazole have been measured by use of a differential scanning calorimeter. Specific heats of CoCl₂(2-methylbenzoxazole)₂, and CoBr₂(2-methylbenzoxazole)₂ are reported together with enthalpies of sublimation of CoCl₂(2-methylbenzoxazole)₂, CoBr₂(2-methyl-benzoxazole)₂, CoCl₂(2,5-dimethylbenzoxazole)₂ and CoBr₂(2,5-dimethylbenzoxazole)₂. Enthalpies of decomposition of benzoxazole complexes are found to be greater than those of the corresponding pyridine complexes, but less than those of the analogous benzothiazole complexes. However, the mean bond dissociation energies of the cobalt—nitrogen and cobalt—oxygen bonds in these complexes are all in the region 33±2 kcal mol^?.     

The thermal decomposition of transition-metal complexes containing heterocyclic ligands: I. Benzothiazole complexes

Enthalpies of the decomposition reactions MX₂L₂(c)→MX₂(c) + 2L (g), where M is Mn, Co, Ni, Cu, or Cd, X is Cl and/or Br, and L is benzothiazole or 2-methyl-benzothiazole have been measured by use of a differential scanning calorimeter. Specific heats and enthalpies of sublimation of some of the complexes have been obtained.     

Extraction of europium complexes with 1,2,4,5-benzenetetracarboxylic acid and neutral ligands

Extraction of mixed-ligand europium complexes with 1,2,4,5-benzenetetracarboxylic (pyromellitic) acid and neutral ligands was studied. The complexation of europium with the ligands is discussed on the basis of data on europium distribution in extraction systems, as well as IR and luminescent spectroscopy data of extracts. Crystalline polynuclear europium complexes with pyromellitic acid and 1,10-phenanthroline and tris(hydroxymethyl)aminomethane were isolated from the extracts. The composition of pyrolysis products of extracts was studied. It was shown that nanosized bulk samples of europium oxide can be obtained by the pyrolysis of saturated extracts. Differences in the morphology of europium oxide nanoparticles were revealed in the samples obtained by pyrolysis of extracts differing in composition at the same temperature and time.     

Thermal decomposition of metal complexes: III. Uranyl nitrate adducts with N-donor ligands

The thermal decomposition of some uranyl nitrate adducts with neutral N-donor ligands was investigated in order to correlate the “activation energy” , E^*₂, of the first step, whose shape depends on the kind of the neutral ligand, with the anti-symmetric stretching vibration ν₃ of the O—U—O group. The linear relationship

was found.Some considerations about the identification of the symmetric stretching band ν₁ have been drawn.