We have studied the kinetics of catalytic iodination of acetylene to form trans-1,2-diiodoethylene in the system PdII-NaI-I2-MeOH at 55 °C. The results obtained allow us to hypothesize that the reaction includes a step of iodopalladation of acetylene with intermediate formation of an σ-iodovinyl derivative of palladium, the decomposition of which by reductive elimination yields the end product and regenerates the catalyst.

We have studied the kinetics of catalytic iodination of acetylene to form trans-1,2-diiodoethylene in the system Pd II -NaI-I 2 -MeOH at 55 °C. The results obtained allow us to hypothesize that the reaction includes a step of iodopalladation of acetylene with intermediate formation of an σ-iodovinyl derivative of palladium, the decomposition of which by reductive elimination yields the end product and regenerates the catalyst.

Reaction of the octadentate ligand 2,6-bis{3-[N,N-di(2-pyridylmethyl)amino]propoxy}benzoic acid (LH) with Fe(ClO4)(3) leads to the formation of the tetranuclear complexes [Fe-4(mu-O)(2)(LH)(2)(ClCH2 CO2)(4)](ClO4)(4) (1), [{Fe-2(mu-O)L(R-CO2)}(2)](ClO4)(4) (2 R = C6H5-, 3 R = CH3-, 4, R = ClCH2-). The crystal structures of complexes 1 and 2 reveal that they consist of two Fe-2(III)(mu-O)(mu-RCO2)(2) cores that are linked via the two LH/L ligands to give a "dimer of dimers" structure. Complex I assumes a helical shape, with protonated carboxylic acid moieties of the two ligands forming a hydrogen-bonded pair at the center of the cation. In complexes 2, 3 and 4, central carboxylates of the two ligands bridge the iron ions in each of the two Fe, O units, with an interdimer iron-iron separation of approximately 10 angstrom and an intradimer separation of approximately 3.1 angstrom. The second carboxylate bridge within the Fe2O units is defined by exogenous benzoate (2), acetate (3) or chloroacetate (4) ligands. The aqua complex [{Fe-2(mu-O)L(H2O)(2)}(2)](ClO4)(6) (5) is proposed to have a similar structure, but with the exogenous bridging carboxylates replaced by two terminal water ligands. These complexes exhibit electronic and Mossbauer spectral features that are similar to those of (mu-oxo)diiron(iii) proteins as well as other related (mu-oxo)bis(mu-carboxylato)diiron(III) complexes. This similarity shows that these properties are not significantly affected by the nature of the bridging exogenous carboxylate, and that the octadentate framework ligand is essential in stabilizing the "dimer of dimers" structure. This structural feature remains in highly diluted solution (10(-5) M) as evidenced by electrospray ionization mass-spectroscopy (ES MS). Cyclic voltammetric studies of complexes 2 and 5 showed two irreversible two-electron reductions, indicating that the two Fe2O units of the tetranuclear complexes behave as distinct redox entities. Complexes 2, 3 and, especially, the aqua complex 5 are active alkane oxidation catalysts. Catalytic reactions carried out with alkane substrate molecules and hydrogen peroxide predominantly gave alcohols. High stereospecificity in the oxidation of cis- 1,2-dimethylcyclohexane supports the metal-based molecular mechanism of O-insertion into C-H bonds postulated for non-heme iron enzymes such as methane monooxygenase.

Electrochemistry of a mixture of hydrofullerenes C70H36—46 composed of C70H36, C70H38, C70H44, and C70H46 (50, 20, 14, and 15%, respectively) was studied by cyclic voltammetry in THF and CH2Cl2 in the –43—–13 °C temperature range. Two cathodic peaks, namely, one-electron reversible (E° = –3.16 V (Fc0/+), Fc is ferrocene) and irreversible (Ep = –3.37 V (Fc0/+)) were observed for this mixture in THF. The irreversible broad oxidation peak (Ep = 1.22 V (Fc0/+)) was observed in CH2Cl2. The reversible reduction peak (E° = –3.16 V) and irreversible oxidation peak (Ep = 1.22 V) were attributed to the most stable hydrofullerene C70H36. The irreversible reduction (Ep = –3.37 V) and oxidation (Ep = 1.22 V) peaks were attributed to hydrofullerenes C70H44—46 with a higher degree of hydrogenation. The values of an “electrochemical gap,” which is an analog of the energy gap (HOMO—LUMO), are 4.38 and 4.59 V for C70H36 and C70H44—46, respectively, and indicate that these hydrofullerenes are sufficiently “hard” molecules with low reactivity in redox reactions.

The [ n -Bu 4 N] 2 [Fe 2 (μ-S 2 O 3 ) 2 (NO) 4 ] complex was studied using X-ray diffraction analysis, cyclic voltammetry, and EPR spectroscopy, and its crystal structure was determined. The redox properties of the [Fe 2 (μ-S 2 O 3 ) 2 (NO) 4 ] 2– anion in CH 3 CN and CH 2 Cl 2 solutions were studied. An addition of excess reducer (sodium thiosulfate) to the thiosulfate complex was shown to produce an EPR signal with g = 2.03 typical of the mononuclear iron dinitrosyl complexes. The mechanism for [Fe 2 (μ-S 2 O 3 ) 2 (NO) 4 ] 2– reduction was suggested.

A linear relationship was found between the first reduction potentials (E°red) and electron affinities (EA) for fullerenes C60 and C70, their hydro- and fluoro-derivatives, and aromatic hydrocarbons: E°red = –3.04 + 0.81·EA. This equation was used to estimate the unknown values of EA = 2.45 eV for C60H2, 2.47 eV for C70H2, –0.15 eV for C70H36—38, –0.41 eV for C70H44—46, and E°red = –1.74—–1.91 V (vs. Fc0/+) for C60H18.

Emphasis is given to redox, photophysical, and photochemical properties of homologous bent metallocenes of group 4 transition metals. Comparative analysis of a variety of electron-transfer induced transformations and ligand-to-metal charge-transfer excited states is performed for bent metallocene complexes upon systematic variation of the identity of the metal ion (Ti, Zr or Hf), ancillary pi- and monodentate sigma- (Cl, Me) ligands. For such organometallic pi -complexes, linear correlations exist between energies of optical and redox HOMO-to-LUMO electron transitions. It is suggested that combination of spectroscopic and electrochemical techniques provides important diagnostics to determine "ionisation potential" and "electron affinity" in solution (relative energies of frontier molecular orbitals obtained as redox potentials) and the energy gap in metallocene complexes. Some of earlier instructive cases of direct relationship between optical transition energies and differences in redox potentials revealed for inorganic and coordination compounds are discussed.

Electrochemistry of hydrofullerene C 60 H 36 was studied by cyclic voltammetry in THF and CH 2 Cl 2 in the −47–14 °C temperature range. Hydrofullerene undergoes reversible one-electron reduction to form a radical anion in THF ( E 0 =−3.18 V (Fc 0 /Fc + ), Fc=ferrocene) and irreversible one-electron oxidation in CH 2 Cl 2 ( E p a =1.22 V (Fc 0 /Fc + )). The reduction potential was used to estimate electron affinity of hydrofullerene as EA=−0.33 eV. It was suggested that C 60 H 36 is an isomer with T -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 ( E Ox − E Red )=4.4 V, and indicates that C 60 H 36 is a sufficiently “hard” molecule with a low reactivity in redox reactions.

To compare the catalytic effect of the active center of nitrogenase (iron-molybdenum cofactor (FeMoco)) under nonenzymatic conditions with the behavior of FeMoco incorporated in a protein, the kinetics of C 2 H 2 reduction with Zn and Eu amalgams was examined in the presence of the cofactor extracted from the MoFe protein of nitrogenase (the specific activity of the extracted FeMoco after its integration into the cofactordeficient MoFe protein of Kp 5058 was 200 ± 20 mol of C 2 H 4 (mol of Mo) -1 min -1 . It was found that under exposure to reducing agents of different strength—Zn amalgam (I) (−0.84 V with respect to a normal hydrogen electrode (NHE)) and Eu amalgam (II) (−1.4 V with respect to NHE)—different reduction states of FeMoco were produced. They differed in the number and properties of substrateand inhibitor-coordinating active sites. For I, the rate of ethylene formation was described by a hyperbolic function of substrate concentration ( K M = 0.045 atm). Carbon monoxide reversibly inhibited the reduction of acetylene (K i - 0.05). For II, a sigmoid relationship between the rate of accumulation of C 2 H 4 or C 2 H 6 and substrate concentration was found. This relationship was explained by the occurrence of three interrelated sites of acetylene coordination and reduction with the apparent constant K M = 0.08 atm in the FeMoco cluster reduced by europium amalgam. In this case, the specific activity was 40–60 mol of C 2 H 4 (mol of Mo) −1 min −1 . For the system with Eu (Hg), the CO inhibition constants were 0.004 and 0.009 atm for the formation of ethylene and ethane, respectively. The behavior of FeMoco as a catalyst for acetylene reduction and the inhibition of this reaction by carbon monoxide in various reducing protein and nonprotein media were compared. This comparison demonstrated that typical features of the catalytic behavior of FeMoco depend primarily on its composition and structure and only secondarily on the type of the reducing agent and on the reaction medium.

It was shown by cyclic voltammetry and preparative electrolysis that electrochemical deposition of alkali fullerides in aprotic media leads to the formation of the conducting films on such electrode supports as Pt, Ni, ITO glass, carbon fibres etc., possessing ordered cubic type structures.

The linear relationship between the redox and optical HOMO-to-LUMO electron transitions are reported for complex molecules with π-ligands for the first time. Linear correlations between electrochemical (redox) gaps and absorption charge-transfer energies have been noted for Ti(IV), Zr(IV), and Hf(IV) bis(cyclopentadienyl) dichlorides. A similar correlation was also observed for the fourth ionization potentials of the corresponding Group IVB metals. The correlation between absorption charge-transfer energies and redox gaps was justified for a series of ansa- and unbridged zirconocene dichlorides and dimethyls with variable sandwich ligands.

A linear correlation between the electrochemical gap values (G=E ox−E red) 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.

The iron-sulfur nitrosyl complexes A[Fe4S3(NO)7], where A=Na+, NH4 +, or N(Bu n )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.

Electrochemistry of hydrofullerene C60H36 has been studied by cyclic voltammetry in THF, CH2Cl2 and MeCN in the - 47 - +14 degrees C temperature range. It has been shown that hydrofullerene undergoes the reversible one-electron reduction to the radical anion in THF [E-0=-3.18 V (Fc(0/+)), Fc = ferrocene] and is irreversibly oxidized in CH2Cl2 [E-p(a) = +1.22 V (Fc(0/+))]. The value of the reduction potential has been used for the estimation of electron affinity of hydrofullerene (EA= - 0.33 eV). It has been suggested that C60H36 is the most probably an isomer with the T-symmetry, in which 12 double bonds form four isolated benzenoid rings located in the tetragonal positions of the molecular surface. Being the analog of the energy gap (HOMO - LUMO) an "electrochemical gap" is equal to (E-0x - E-red) = 4.4 V for hydrofullerene and indicates that C60H36 is a rather "hard", almost non-reactive molecule towards redox reactions.

The electrochemical behavior of citral at Hg, Au, Pt, Cu, and glassy carbon electrodes was studied by cyclic voltammetry in DMF solutions containing acetic acid. Electrocatalytic hydrogenation of citral is the predominant reaction route at Pt and Cu electrodes.

It was shown by cyclic voltammetry and preparative electrolysis that electron transfer induced deposition of solvated fullerene C-60 in aprotic media, such as mixtures of toluene with acetonitrile, dimethylsulfoxide and dimethylformamide leads to the formation of the conducting films on such electrode supports as Pt, Ni, ITO glass, carbon fibres etc. From an Electron Beam Diffraction study, existence of ordered cubic type structures was proposed for the coatings of formal stoichiometry KC60.

The possibility of hydrogen transfer from hydrofullerene C 60 H 36 to electrogenerated radical anion C 60 .− or dianion C 60 2− in propylene carbonate-toluence (3∶2, v/v) was demonstrated by cyclic voltammetry. The process affords C 60 H 2 as the product. The reaction found is the typical redox-induced process.