A. I. Poddel’skii

Redox transformations and antiradical activity of triarylantimony(V) 3,6-di- tert -butyl-4,5-dimethoxycatecholates

Triarylantimony(V) catecholate complexes were synthesized by the oxidative addition of 3,6-di-tert-butyl-4,5-dimethoxy-o-benzoquinone to triarylstibines. The electrochemical properties and antiradical activity of the synthesized compounds were studied. According to cyclic viltammetry data, the complexes are oxidized via two consecutive quasi-reversible stages. Introduction of halogen atoms in para-position of phenyl groups at Sb(V) causes anodic shifts of the oxidation potentials and enhances stability of the mono- and dicationic forms of the compounds, which form in the course of electrochemical transformations. Triarylantimony(V) catecholate complexes exhibit appreciable antiradical activity in the auto-oxidation of oleic acid. In was found that the inhibitory activity of the complexes depends on their redox potential.

Quinone imines and aminophenols as precursors of new heterocycles

Cyclization of substituted quinone imines and diazabutadiene derivatives of aminophenols affords 4aH-phenoxazine or 4H-1,4-benzoxazine derivatives, which are finally transformed into the following fused heterocycles: the stable 1,4,6,8-tetra(tert-butyl)phenoxazin-10-yl radical and 7a,14a,15a, 15b-tetrahydro-14,16-dioxa-5,9-diaza-8,15-ethenohexaphene and 5a,6,11a, 12-tetrahydro[1,4]benzoxazino[3,2-b][1,4]benzoxazine derivatives. The influence of the substituents on the pathways of the reactions of intermediate benzoxazines and phenoxazines, such as oxidation, [2+4] dimerization, and the closure of the second ring, was studied. The structures of the fused heterocycles were determined by X-ray diffraction, NMR spectroscopy, and ESR.

Complexes of triphenylantimony( v ) catecholates with ammonium salts. Spectroscopic and electrochemical investigations

The reactions of triphenylantimony(V) catecholates (Cat)SbPh3 with different tetraalkyl-ammonium salts (bromides, iodides, hydroxide anions) in acetonitrile were investigated, and their complexes 8–13 of the general formula [R4N]+[(Cat)SbPh3X]− were synthesized. The molecular structure of complex 8 was determined by X-ray diffraction. The electrochemical oxidation of complexes 8–13 proceeds more easily than the oxidation of the starting catecholates (Cat)SbPh3. The coordination of the bromide anion results in the stabilization of the oxidized forms of the complexes [(SQ)SbPh3X]0 and [(Q)SbPh3X]+ (SQ and Q are the o-benzosemiquinone and o-benzoquinone forms of the redox-active ligand, respectively).

Radical polymerization of methyl methacrylate in the presense of bis[4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-iminobenzosemiquinono]cobalt(II)

Radical polymerization of methyl methacrylate was studied in the presence of initiating systems based on bis[4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-iminobenzosemiquinono]-cobalt(II) and hydrocarbon halo derivatives of different structure. The introduction of amines in the polymerizing system was found to lead to a significant increase in the polymerization rate. The polymerization proceeds via the atom transfer mechanism, which was confirmed by detection of ω-terminal chlorine atoms in the macromolecules by NMR, the linear dependence of the polymer molecular weight on conversion of monomer, and the synthesis of block-copolymers.

Electrochemical transformations of antimony(V) complexes containing tridentate O,N,O-donor ligands

Electrochemical transformations of antimony(V) complexes containing a tridentate redoxactive ligand, N,N-bis-(2-hydroxy-di-3,5-tert-butylphenyl)amine: R3Sb(Cat-NH-Cat) (R = (1) Ph; (2) Et), (3) Et2Sb(Cat-N-Cat)) are studied. Electrochemical oxidation of complexes 1, 2 occurs irreversibly leading to formation of unstable radical cations. The next stage is the chemical process resulting in formation of neutral paramagnetic compounds. The Et2Sb(V)(Cat-N-Cat) complex is characterized by two reversible anodic redox processes corresponding to a change of in the ligand redox level. Stable paramagnetic derivatives are formed as a result of electrochemical oxidation of compounds 1, 3; this allows considering these compounds as potential radical scavengers. Interaction of complex 1 with electrogenerated superoxide radical anion led to formation of paramagnetic reaction products.

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.

Binuclear Triphenylantimony(V) Catecholate Based on Redox-Active Bis-o-Benzoquinone, a Bis-Catechol-Aldimine Derivative

The oxidative addition of bis-o-benzoquinone Q–(CH=N–N=CH)–Q (L), in which two 3,5-ditert-butyl-o-benzoquinones are linked to each other in positions 6 via the CH=N–N=CH group, to triphenylstibine gave a new binuclear triphenylantimony(V) bis-catecholate complex, Ph3Sb(Cat–(CH=N–N=CH)–Cat)SbPh3 (I). Recrystallization of I from a methanol–trichloromethane mixture resulted in an additional coordination of a methanol molecule to each antimony atom to give the binuclear complex, (CH3OH)Ph3Sb(Cat–(CH=N–N=CH)–Cat)SbPh3(CH3OH) (I · 2CH3OH), the crystals of which (I · 2CH3OH) · 2CH3OH · CHCl3 (II) contain additionally two methanol solvate molecules, which fix the geometry of the nitrogen-containing bridging group, and a trichloromethane molecule. The molecular structure of compound II in the crystalline state was determined by X-ray diffraction (CIF file CCDC no. 1560840).

Complex of triphenylantimony(v) catecholate with 5-(2,6-dimethylphenyl)-3-(4-pyridyl)-1-phenylformazan

The complex of triphenylantimony(V) 3,6-di-tert-butylcatecholate with 5-(2,6-dimethylphenyl)-3-(4-pyridyl)-1-phenylformazan was synthesized and characterized by spectroscopic and electrochemical methods and by X-ray diffraction. In the crystal structure, there are intermolecular hydrogen bonds between the formazan ligands of adjacent molecules. The electrochemical transformations of the complex were investigated by cyclic voltammetry. It was shown that both the formazan and catecholate moieties are involved in redox processes.

Electron density distribution in crystals of the antimony(V) spiroendoperoxide complexes

The experimental and theoretical electron densities in complexes [6-(2,6-di-iso-propylphenyl)imino-2,4-di-tert-butylcyclohexa-2,4-diene-1-peroxo-1-olato-N,O,O′]tris(p-chlorophenyl)antimony(V), (p-Cl–C6H4)3Sb(2,6-iso-Pr–Ph–AP) · O2 (I), and [6-(2,6-dimethylphenyl)imino-2,4-di-tert-butylcyclohexa-2,4-diene-1-peroxo-1-olato-N,O,O′]tris(p-chlorophenyl)antimony(V), (p-Cl–C6H4)3Sb(2,6-Me–Ph–AP) · O2 (II), where AP is 4,6-di-tert-butyl-N-o-iminobenzoquinone dianion, are studied on the basis of high-resolution X-ray diffraction data and theoretical calculations using the density functional theory (B3LYP/DGDZVP). The nature of chemical bonds and the charge distribution on atoms are studied, and the energy of molecular oxygen addition to the Sb(V) o-aminophenolate complexes is estimated. The structures are deposited with the Cambridge Crystallographic Data Centre (CIF files CCDC nos. 1560600 (spherical refinement) and 1560601 (multipole refinement) for complex I; 1560602 (spherical) and 1560603 (multipole) for complex II).

Synthesis, structure, and properties of a new multiredox-active Sn(IV) complex based on 3,6-di- tert -butyl- o -benzoquinone and ferrocenylaldimine phenol

A new mixed-ligand tin(IV) complex 2 derived from 3,6-di-tert-butyl-o-benzoquinone and ferrocenylaldimine phenol 1 has been prepared and characterized by different physicochemical methods (IR, 1HNMR, and 119Sn NMR spectroscopies). Electrochemical transformations of complex 2 have been studied by cyclic voltammetry. Catecholate and ferrocenyl groups have been found to take part in the redox transformations. Chemical oxidation of complex 2 with silver triflate in a dichloromethane solution has been studied. Formation of monocationic complex 2+ has been detected by EPR spectroscopy. The catecholate ligand has been found to be the primary redox center subjected to oxidation.