V. V. Strelets

Synthesis, crystal structures, Mössbauer spectra, and redox properties of binuclear and tetranuclear iron-sulfur nitrosyl clusters

The iron-sulfur nitrosyl complexes A[Fe4S3(NO)7], where A=Na+, NH4+, or N(Bun)4+, and B2[Fe2S2(NO)4], where B=Na+, Cs+, or N(Bun)4+, were synthesized. Their structures and properties were studied by X-ray diffraction analysis, Mössbauer spectroscopy, and cyclic voltammetry. The effect of the crystal packing on the geometry of the tetranuclear NH4[Fe4S3(NO)7]·H2O and binuclear Cs2[Fe2S2(NO)4]·2H2O complexes was analyzed. The changes in the Fe57 Mössbauer spectral parameters of the anion in the B2[Fe2S2(NO)4] series depend on the size of the B cation and agree with variations in the structural parameters of the Fe[S2(NO)2] chromophores as well as in the stretching vibrations of the NO groups caused by changes in intermolecular contacts. The presence of electronic states delocalized through the Fe−Fe bonds explains the fact that the electronic states of the Fea(S3NO) and Feb(S2(NO)2) chromophores in the [Fe4S3(NO)7]− anion are nearly identical. The binuclear clusters are unstable upon storage in the solid phase and decompose in solutions to form the tetranuclear [Fe4S3(NO)7]− complexes, sulfur, and nitrogen oxides. The redox properties of the [Fe4S3(NO)7]− and [Fe2S2(NO4)]2− anions in CH3CN and THF solutions were studied. The mechanism of reduction of the anion in the tetranuclear cluster is proposed.

Synthesis, structure, and properties of a new trinuclear iron cluster, [(MeOH)(H2O)2Fe3(μ3-O)(μ-OOCC6H4OCH2C5H4NH)6] (ClO4)7 · · 8MeOH · 3.5H2O

Reactions of iron(m) salts with a new bidentate ligand, which is potentially capable of forming binuclear iron complexes upon complexation, were studied. Under various conditions, we succeeded in isolating only the trinuclear cationic complex (FeIII3(O2CR)6(μ3-)17+ (1), where RCO2 is 2-(pyrid-2-ylmethoxy)benzoic acid protonated at the pyridyl moiety. The structure of 1 was established by spectral, magnetic, and X-ray structural studies. Cyclic voltammetry in McCN in the temperature range from -35 to 20 °C demonstrated that 1 undergoes successive FeIII→FeII reduction in three one-electron stages, which is indicative of the electronic interaction between iron atoms in the complex.

EFFECT OF SUBSTITUENTS ON THE CATALYTIC PROPERTIES OF BIS(CYCLOPENTADIENYL) ZIRCONOCENE DICHLORIDES IN POLYMERIZATION OF ETHENE

Comparative analysis of catalytic activity of substituted bis(cyclopentadienyl)zirconium dichlorides with the general formula (RnCp)2ZrCl2 (Cp2ZrCl2, (MeCp)2ZrCl2, (PriCp)2ZrCl2, (Pri2Cp)2ZrCl2, (BunCp)2ZrCl2, (BuiCp)2ZrCl2, (ButCp)2ZrCl2, Cp*2ZrCl2 (Cp*=Me5C5), (Me3SiCp)2ZrCl2, (cyclo-C6H11Cp)2ZrCl2, and [(cyclo-C6H11)2Cp]2ZrCl2) in ethene polymerization using polymethylalumoxane as the cocatalyst was performed. The molecular mass characteristics of the polyethylene samples obtained were determined. A linear correlation of the specific activity of the catalysts and the turnover number with the electronic and steric characteristics of substituents at the Cp ring of the complexes was established for the first time. Analysis of the polymerization kinetics and the obtained correlation between the specific activity of the complexes and molecular mass characteristics of the polyethylene samples suggest that alkyl substituents participate in reactions responsible for the restriction of the polymer chain growth and regeneration of the active center. These interactions most likely involve associates of AlMe3 with polymethylalumoxane molecules.

Redox behavior of trinuclear M3(μ-H)(μ3-μ1:μ2:μ2-C2Fe)(Co)9 and tetranuclear RuM3 3(μ-H)(μ4-μ1:μ1:μ1:μ2-C2Fe)(Co)12 (M=Ru or Os; and Fc=ferrocenyl) clusters. Electronic interaction between the ferrocenylacetylide ligand and the metal core of the cluster

The redox properties of the clusters Ru3(CO)12(1), Ru3(μ-H)(μ3-μ1:μ2:μ2-C2Fe)(CO)9 (2), OS3(μ-H)(μ3-μ1:μ2:μ2-C2Fe)(CO)9 (3), Ru4(μ-H)(μ4-μ1:μ1:μ1:μ2-C2Fe)(CO)12 (4), and RuOS3(μ-H)(μ4-μ1:μ1:μ1:μ2-C2Fe)(CO)12 (5) in THF have been studied by cyclic voltammetry in the temperature range from −60 to +20°C. It was demonstrated that reversible one-electron oxidation of the ferrocenyl fragment in clusters 2–5 occurs at more positive potentials (δE0=0.15–0.26 V) than that of free ferrocene. This is indicative of the electron-withdrawing character of the cluster core with respect to the ferrocenylacetylide ligand. The electron-withdrawing effect of the metal core is more pronounced in tetranuclear clusters4 and 5 than in trinuclear clusters2 and3. Unlike complexes1–3, which undergo irreversible reduction, complexes4 and5 undergo reversible one-electron reduction to form the corresponding radical anions4− and5−.

Electrochemical potentials, optical transitions, and frontier orbitals of non-bridged and bridged bent sandwich zirconocene complexes

A linear correlation between the electrochemical gap values (G=Eox−Ered) and the energies of optical transition in the UV-vis region was found and justified for a series of non-bridged and bridged bent-sandwich zirconocene complexes with the general formula R(η5-L)2ZrX2, where L=cyclopentadienyl (Cp), indenyl (Ind), fluorenyl (Flu); X=Cl, Me; the bridging group R=SiMe2, (CH2)2.

Electrochemical behavior and parameters of hydrofullerene C60H36

Electrochemistry of hydrofullerene C60H36 was studied by cyclic voltammetry in THF and CH2Cl2 in the −47–14 °C temperature range. Hydrofullerene undergoes reversible one-electron reduction to form a radical anion in THF (E0=−3.18 V (Fc0/Fc+), Fc=ferrocene) and irreversible one-electron oxidation in CH2Cl2 (Epa=1.22 V (Fc0/Fc+)). The reduction potential was used to estimate electron affinity of hydrofullerene as EA=−0.33 eV. It was suggested that C60H36 is an isomer withT-symmetry in which 12 double bonds form four isolated benzenoid rings located in vertices of an imaginary inscribed tetrahedron on the molecular surface. For hydrofullerene, the “electrochemical gap” is an analog of the energy gap (HOMO−LUMO), equal to (EOx−ERed)=4.4 V, and indicates that C60H36 is a sufficiently “hard” molecule with a low reactivity in redox reactions.

Redox-induced ?5 ? ?3 haptotropy of the fluorenyl ligand in 9-substituted ?5-fluorenylmanganesetricarbonyl complexes

It has been shown by cyclic voltammetry in THF within the −90 to 40 °C temperature range that fluorenyl (η5-9-R-C13H8)Mn(CO)3 complexes (R=But (3) and Ph (4)) undergo two-electron reduction to form allyl type [(η3-9-R-C13H8)Mn(CO)3]2− dianions as final products. At low temperatures complexes3 and4 are reduced in two one-electron steps according to the EEC-scheme. The first step is reversible and corresponds to the formation of 19ē-radical anions 3−. and 4−.. TheE0 values for redox pairs30/−. and40/−. are −1.88 and −1.73 V, respectively. The further reduction of radical anions3−. and4−. at more negative potentials is accompanied by fast η5 → η3 haptocoordination of the fluorenyl ligand to form 18ē-dianions [(η3-9-R-C13H8)Mn(CO)3]2−. These dianions obtained by the reduction of complexes3 and4 by the radical anion of pyrene are stable at −80 °C and are characterized by their IR spectra. At room temperature the η5 ⇔ η3 hapticity change is a fast and reversible process occurring at the step of 19ē-radical anions3−. and4−. and leading to the electron deficient 17ē-species [(η3-9-R-C13H8)Mn(CO)3]−., which are reduced easier than the initial complexes. As a result, complexes3 and4 are reduced to the corresponding dianions [(η3-9-R-C13H8)Mn(CO)3]2− at room temperature in one reversible two-electron step according to the ECE-scheme. Reactivities of 19e−-species of the isomeric η5- and η6-fluorenylmanganesetricarbonyl complexes are compared.

Oxidation of isomeric η6- and η5-fluorenylchromiumtricarbonyl anions

The oxidation of the carbon-centered [(η6-C13H9)Cr(CO)3]− anion (1−) results in formation of (μ-η6:η6-9,9′-bifluorenyl)bis-chromiumtricarbonyl (3) due to coupling of the intermediate carbon-centered radical (1.). The oxidation of the metal-centered anion [(η5-C13H9)Cr(CO)3]− (2−), which is isomeric to the 1− anion, gives an equilibrium mixture of the chromium-centered radical {(η5-C13H9)Cr(CO)3}. (2.) and its dimer [(η5-C13H9)Cr(CO)3]2 (6). Radical2. readily reacts with MeI and the solvent (THF); the resulting derivatives, (η5-C13H9)Cr(CO)3R (R=Me (10); R=H (7)), undergo fast ricochet inter-ring η5→η6 rearrangements into (η6-9R-C13H9)Cr(CO)3 (R=CH3 (9); R=H (4)).

Electron-transfer induced haptotropic isomerization of fluorenylmanganesetricarbonyl complexes: electrocatalytic and chain mechanisms

The electrochemical reduction of (η6-C13H9)Mn(CO)3 (1, where C13H9—fluorenyl) has been studied in THF by cyclic voltammetry and preparative controlled potential electrolysis. One-electron reduction of1 to the corresponding 19-electron radical anion1.− is accompanied by the haptotropic isomerization of the latter to the radical anion (η5-C13H9)Mn(CO)3.− (2.−), which is oxidized at the electrode to neutral complex2. Electron-transfer induced isomerization1 →2 is an electrocatalytic process with current efficiency of 600%, which can be also promoted by catalytic amounts (≤20%) of the chemical reducing agents (benzophenone radical anion or sodium amalgam). If the reaction is chemically induced, the radical anion2.− is oxidized by initial complex1; as a result the electron-transfer induced isomerization1 →2 proceeds by a chain mechanism. The influence of the electronic state (18e−/19e−) of η6- and η5-fluorenyl complexes on the position of the equilibrium of the intra-ring haptotropic isomerization reaction is discussed.

Redox-induced hydrogen transfer from hydrofullerene C60H36 to fullerene C60

The possibility of hydrogen transfer from hydrofullerene C60H36 to electrogenerated radical anion C60.− or dianion C602− in propylene carbonate-toluence (3∶2, v/v) was demonstrated by cyclic voltammetry. The process affords C60H2 as the product. The reaction found is the typical redox-induced process.