Synthesis and structure of new dinuclear palladium complex containing no bridging ligands

Oxidation of the mononuclear semiquinonediimine complex [(NPh)(NH)C₆H₄]₂Pd with silver trifluoromethanesulfonate afforded the diamagnetic dinuclear dicationic palladium complex {[(NPh)(NH)C₆H₄]₂Pd}₂(O₃SCF₃)₂ with a Pd...Pd distance of 3.267(1) . The complex was structurally characterized, and its spectroscopic and electrochemical properties were studied.     

Transition metal complexes with “non-innocent” ligands in the activation of hydrogen sulfide

The reactions of hydrogen sulfide with transition metal complexes containing redox-active ligands are studied. A combination of electrochemical and spectral data indicates that the one-electron process affording the hydrogen sulfide radical and monoanionic complexes is an elementary act for the most part of the reactions studied. The accessibility of the metal center in the Co, Ni, Zn, and Pt complexes allows hydrogen sulfide to preliminary coordinate to the metal followed by the inner-sphere electron transfer in the hydrogen sulfide-metal-organic ligand system. Active intermediates (radical cation, thiyl radical, and proton) formed due to oxidation react with aromatic substrates. The substitution reaction in the aromatic ring produces a mixture of isomeric thiols and dimerization products of organylthiyl radicals (disulfides).     

Redox properties of novel pyrrolidine derivatives containing sterically hindered phenol fragment

The method of cyclic voltammetry on a platinum electrode in acetonitrile is used to study the redox properties of a number of novel pyrrolidine derivatives containing a sterically hindered phenol fragment. It is found that the obtained derivatives of (3,5-di-tert-butyl-4-hydroxyphenyl)pyrrolidine-2-carboxylic acid are irreversibly oxidized in two stages with formation of a phenoxy radical. The structural analogue containing no phenyl fragment is irreversibly oxidized under similar conditions in a single stage. Formation of a stable phenoxy radical from synthesized (3,5-di-tert-butyl-4-hydroxyphenyl)pyrrolidines under PbO₂ oxidation is confirmed by ESR spectroscopy. Application of the synthesized compounds as antioxidant agents has been suggested.     

Synthesis and properties of triphenylantimony(V) dithiolate derivative

Interaction of substituted benzene-1,2-dithiols I–III with triphenylantimony(V) dichloride was studied. As a result of the exchange reaction of 3,6-dichlorobenzene-1,2-dithiol with Ph₃SbCl₂ in the presence of triethylamine triphenylantimony(V) 3,6-dichlorobenzene-1,2-dithiolate IV was obtained. Electrochemical properties of the free dithiols and the complex were explored. According to the cyclic voltammetry, the oxidation of the complex is irreversible and corresponds to one electron transfer with follow-up chemical stage. The antioxidant activity of compounds I–IV was examined in the process of oleic acid autoxidation. A more effective inhibition of the oleic acid oxidation was found at adding dithiol and better protective effect was observed in the presence of Ph₃SbCl₂ compared with the complex IV.     

Oxidative properties of [1,2-b]selenophenes and 4H-selenochromenes and their interaction with hydrogen sulfide

Electrochemical behavior of [1,2-b]selenophenes and 4H-selenochromenes in organic media and their interaction with hydrogen sulfide have been studied. In aprotic solvents (CH₂Cl₂ and CH₃CN), the organoselenium compounds are oxidized at anode to give cation-radicals. In the presence of hydrogen sulfide, at its oxidation potential (1.60 V) [1,2-b]selenophenes and 4H-selenochromenes undergo recyclization into corresponding thiophenes and thiochromenes. The recyclization yielding sulfur analogs have been studied in the presence of organic electromediators, including the transition metal complex with redox-active ligands, as well.     

Oxidative cleavage of the C-C bond in processes involving the heteroaromatization of 9R-sym-nonahydro-10-oxa(chalcogena)anthracenes

The reaction of 9-(2-methoxyphenyl)- and 9-(2-thienyl)-sym-nonahydro-10-selena(thia)anthracenes with trifluoroacetic acid causes their heteroaromatization with the elimination of substituents from the positions of the heterorings. A similar transformation of these compounds, as well as their oxygen and 9-benzyl-substituted analogs, occurs during anode electrochemical oxidation. The stepwise character of the cleavage of the C-C bond, which includes one-electron oxidation of the chalogenapyrans and subsequent fragmentation of the cation-radical intermediates, is substantiated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 900–904, July, 1991.     

Study of the mechanism of redox transformations of sterically hindered <Emphasis Type="Italic">N</Emphasis>-aryl-<Emphasis Type="Italic">o</Emphasis>-iminoquinones

The mechanisms of redox transformations of sterically hindered [¹IBQ]-[³IBQ], 9,10-iminophenanthraquinone [⁴IFQ], and o-aminophenol [⁵AP] have been studied by cyclic voltammetry. It has been shown that the reduction process in tetrahydrofuran consists of two consecutive reversible steps leading to the formation of a radical anion and a dianion. In the case of acetonitrile, only the first redox process is detected, which involves the steps of protonation and electron addition resulting in the formation of a monoanion. Quantum-chemical calculations indicate a lower degree of participation of the six-membered nonaromatic carbon ring in the spin density delocalization in the o-iminosemiquinonate radical anions as compared to o-benzosemiquinonate radical anions. The oxidation of iminoquinones results in the formation of an unstable radical cation, which undergoes further chemical transformations. An increase in the acidity of a medium leads to the formation of protonated forms with the reduction potential being shifted anodically. The introduction of screening groups makes it possible to suppress side reactions of hydrolysis and cyclization of oxidized o-aminophenol [⁵AP] forms. Therefore, the major product of complete electrolysis is o-iminobenzoquinone [²IBQ].