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New heteroligand cobalt(III) bis-3,6-di-tert-butyl-o-benzosemiquinone complexes with 1-(p-X-phenyl)-3,5-diphenylformazan ligands Co(3,6-SQ)2LX (Х is fluorine (I), chlorine (II), bromine (III), iodine (IV), and methyl (V)) are synthesized. The molecular structures of compounds I, II, and IV are determined by X-ray structure analysis (CIF files CCDC nos. 2060727 (I), 2052592 (II), and 2060728 (IV)). The coordination environment of the central cobalt ion in the studied complexes is a weakly distorted octahedron, and the degree of distortion insignificantly changes depending on the substituent. According to the X-ray structure data and results of magnetic and spectral studies, compounds I–V are low-spin complexes of cobalt(III) bound to two radical anion o-semiquinone ligands and one formazan anion. The magnetic behavior of complexes I–V in a temperature range of 50–300 K is characterized by the predomination of intramolecular exchange interactions of the antiferromagnetic type, whereas in the range lower than 50 K complexes II–V exhibit ferromagnetic ordering caused by intermolecular exchange interactions between the paramagnetic ligands.

Heterometallic chromium(III) CrIII[(SQ-Cat)SbPh3]3 (I), copper(II) CuII[(SQ-Cat)SbPh3]2 (II), and zinc I2Zn(Q-Cat)SbPh3 (III) and IZn(SQ-Cat)SbPh3 (IV) complexes, where SQ is the corresponding o-semiquinone radical anion, and Cat is the catecholate dianion (mono- and direduced forms of the quinone fragment), are synthesized on the basis of the mononuclear triphenylantimony(V) quinone-catecholate complex (Q-Cat)SbPh3, which was derived from 4,4'-di-(6-tert-butyl-3-methylbenzo-1,2-quinone) (Q-Q). The one-electron oxidation and one-electron reduction of chromium complex I afford the paramagnetic derivatives [CrIII[(Q-Cat)SbPh3][(SQ-Cat)SbPh3]2]+ (I+) and [CrIII[(Cat-Cat)SbPh3][(SQ-Cat)SbPh3]2]– (I–), respectively, which are easily detected by EPR spectroscopy. The EPR spectroscopy data and measurements of the temperature dependence of the magnetic susceptibility of copper complex II indicate in favor of the localization of the lone electron on the organic ligand, which can be explained by the antiferromagnetic metal–ligand exchange in this complex (J(SQ-Cu) = –157 cm–1, J(SQ-SQ) = –10.0 cm–1). The coordination of (Q-Cat)SbPh3 as neutral o-quinone to zinc iodide with the formation of complex III increases significantly the oxidation ability of the quinone fragment in this complex (ERed1 = 0.43 V for III and –0.45 V for (Q-Cat)SbPh3 vs. Ag/AgCl/KCl(sat.)), and the complex can oxidize the iodide anion to iodine with the formation of paramagnetic derivative IV, whose EPR spectrum is characteristic of complexes of the M(SQ-Cat) type. The redox properties of complexes I and III are studied by cyclic voltammetry.

A series of triarylantimony(V) complexes with p-dimethylaminopyridine and р-cyanopyridine of the general formulas [(Cat)SbAr3(р-Me2N–Py)] (complexes I–IV) and [(Cat)SbAr3(р-CN–Py)] (complexes V–VII) has been synthesized. Their molecular structures and electrochemical properties have been studied. 3,6-Di-tert-butyl-o-benzoquinone, 4,5-piperazine-1,4-diyl-3,6-di-tert-butyl-o-benzoquinone, and 4,5-dichloro-3,6-di-tert-butyl-o-benzoquinone are used as redox-active ligands. The molecular structures of several complexes in the crystalline state are determined by X-ray diffraction analysis (CIF files CCDC nos. 1974173 (I ⋅ 0.5toluene), 1974174 (II ⋅ 2toluene), 1974175 (V), 1974176 (VI ⋅ hexane), and 1974177 (VII)). All complexes have a distorted octahedral structure, and an additional neutral pyridine ligand occupies one of the apical positions. Electrochemical transformations of the complexes are studied by cyclic voltammetry in a dichloromethane solution. The introduction of substituted pyridine into the molecule of the complex does not change the electrooxidation mechanism of the complexes. For all complexes with р-dimethylaminopyridine, both oxidation potentials are shifted to the cathodic region (0.13–0.21 V for the potential of the first oxidation process and to 0.3–0.4 V for the potential of the second oxidation process). A similar shift for the complex with p-cyanopyridine is less pronounced (0.05 V for the potential of the first oxidation process of complex V as compared to that of complex I).

New catecholate complexes of triphenylantimony(V), (Etgly-3,6-DBCat)SbPh3 (I), (Propgly-3,6-DBCat)SbPh3 (II), and (Cat-3,6-DBCat)SbPh3 (III), based on analogs of sterically hindered 3,6-di-tert-butyl-o-benzoquinone, 5,8-di-tert-butyl-2,3-dihydrobenzo[b][1,4]dioxine-6,7-dione (L1), 6,9-di-tert-butyl-2,3-dihydrobenzo[b][1,4]dioxepine-7,8-dione (L2), and 1,4-di-tert-butyl-dibenzo[b,e][1,4]dioxine-2,3-dione (L3), which are the 2,3-dihydrobenzo[b][1,4]dioxine, 2,3-dihydrobenzo[b][1,4]dioxepine, and dibenzo[1,4]dioxine derivatives, respectively, have been synthesized. At room temperature catecholates I and II react with molecular oxygen adding an O2 molecule to form the corresponding spiroendoperoxides IV and V. Catecholate III reacts with oxygen with the deep oxidation of the complex and formation of neutral o-benzoquinone. The molecular structures of complexes I and III are determined by X-ray diffraction analysis (CIF files CCDC nos. 1840299 (I · toluene) and 1840300 (III)).

The reactivity of ferrocene derivatives with respect to p-quinones in acid media has been studied. A tentative mechanism of oxidation of ferrocene with p-qionone in acid media including two-step reduction of p-quinone to hydroquinone is proposed.

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).

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).

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.

The electrochemical transformations of triphenylantimony(V) catecholate complexes containing fragments of alkyl gallates (RO(O)C–(OH)Cat)SbPh3 (R = CH3 (1), C8H17 (2), and C12H25 (3)); (RO(O)C–(OH ∙ NEt3)Cat)SbPh3 (4); and ROC(O)GallH3 (R = CH3 (5), C8H17 (6), and C12H25 (7)) in acetonitrile were studied. The electrochemical oxidation of alkyl gallates 5–7 proceeds in two irreversible stages and leads to formation of o-quinoid products. At the first stage, the oxidation of antimony(V) compounds is electrochemically quasi-reversible and leads to the formation of unstable cationic complexes. The second irreversible redox transfer results in ligand decoordination and destruction of the compounds. Three redox stages were observed for complex 4. The triethylamine-deprotonated hydroxy group is oxidized at the first electrochemical step that leads to a further intramolecular transfer, forming a stable intermediate, whose oxidation occures in quasireversible manner.

We studied the effect of bis[4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-ortho-iminobenzosemi-quinono]cobalt(II) on the kinetics of the bulk polymerization of methyl methacrylate at 70°C and on the molecular-weight characteristics of the polymer synthesized. The effective chain transfer constant in the polymerization of methyl methacrylate in the presence of the complex in benzene at 70°C was determined by the Mayo method and by linearizing the macromolecule chain length distribution. The constants obtained were compared with the same parameters available from the literature for a number of known chain-transfer agents, viz., dodecyl mercaptan and cobalt porphyrin and oxime complexes.

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.

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).

tert-Butyl hydroperoxide reacts with the tetra-tert-butoxychromium by oxidizing the latter to chromyl CrV=O (C6H6, 20°C). At t-BuOOH-Cr(OBu-t)4 ratio of 2: 1 or higher, oxygen is released. The occuring processes include the formation of chromium-containing peroxides and peroxytrioxydes. The t-BuOOH-Cr(OBu-t)4 system oxidizes aromatic hydrocarbons of various structures (anthracene, 9,10-dimethylanthracene, 1,1-diphenylethylene, alkylarenes), as well as primary and secondary alcohols. Depending on the structure of the substrate, the oxidants are: in situ generated oxygen including that in the singlet state, peroxy radicals, or chromium-containing peroxides.

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.

Photolysis of [4-(2-methyl-5-tert-butyl-cyclohexadiene-1,5-dion-3,4-yl)-3-methyl-6-t-butyl-catecholato] triphenylantimony(V) in toluene by irradiation with the light of wavelength 546 nm leads to excitation of the molecule of parent compound which reacts with a molecule of Ph3SbCatQ affording 4,4′-di-(3-methyl-6-tert-butyl-o-benzoquinone) and 4,4′-di[(3-methyl-6-tert-butyl-catecholato)triphenylantimony(V)]. The formed compounds react with each other returning the system into the initial state. Action of light of wavelength 313 and 405 nm on the initial reaction mixture leads to the formation of carbon monoxide, Ph3SbCatCatSbPh3 and the products of photolytic transformation of 4,4′-di(3-methyl-6-tert-butyl-o-benzoquinone).

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.