Specific features of the synthesis and structures of the complexes of Group 14 elements (Si, Ge, Sn, Pb) with o-iminoquinone ligands are discussed. The chemical reactions of the above indicated compounds accompanied by the transformation of the redox-active ligand in the coordination sphere of the complex- forming agent are considered.

Chemistry of Complexes of Group 14 Elements Based on Redox-Active Ligands of the o-Iminoquinone Type

The reactivity of o-amidophenolate indium(III) complexes towards different oxidants was investigated. The oxidation reactions were found to proceed through the stage of paramagnetic o-iminobenzosemiquinonato indium(III) derivative formation. The monoradical intermediates undergo symmetrization. The final products of the oxidation processes are corresponding biradical o-iminobenzosemiquinonato indium(III) complexes. In order to understand the reasons for the symmetrization processes steric factors (G-parameters) were evaluated for all intermediates and final products by a method based on the ligand solid angle approach.

The reactivity of o-amidophenolate indium(III) complexes towards different oxidants

Antiradical and antiand prooxidant activities of the newly obtained triphenylantimony(V) catecholate complexes derived from gallic acid esters of the general formulas (RO(O)C–Cat)SbPh3 (R = Me (1), C8H17 (2), C12H25 (3)) and (MeO(O)C–(OH•NEt3)Cat)SbPh3 (4) were studied. The comparative study involving gallic acid esters of the general formula RO(O)C–GallH3 (R = Me (5), C8H17 (6), C12H25 (7)) was performed in order to evaluate the effect of organic ligands on the properties of the antimony(V) compounds. The values of EC50, the number of converted molecules of stable radical (nDPPH), as well as the relative content of oleic acid hydroperoxides confirm the antiradical and antioxidant activity of triphenylantimony(V) complexes in reactions with diphenylpicrylhydrazyl radicals and in the antioxidation of oleic acid. The influence of more active compounds 1 and 4 and ester 5 on lipid peroxidation of the rat liver homogenate of male Wistar line was determined. The membraneprotective properties were evaluated for induced hemolysis of erred blood cells as an example, and catalase activity of erythrocyte hemolysate was studied.

Anti- and prooxidant activity of triphenylantimony(V) catecholates derived from alkyl gallates

Characteristic features of synthesis of various polymers with participation of the tin complex imSQSnBut2Cl, where imSQ is the 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone radical anion, were studied. It was shown that for a number of monomers, this complex acts as an iniferter, i.e., it can not only initiate the polymerization, but can also regulate the chain growth of macromolecules. The effect of the conditions of the process on the possibility of obtaining macromolecular products with a narrow polydispersity was estimated.

o-Iminosemiquinone complex of tin(iv) with tert-butyl substituents in the polymer synthesis

New paramagnetic tin(IV) derivatives containing the radical-anion of 2,4,6,8-tetra-tert-butylphenoxazin-1-one redox-active ligand (phenox-imQ) are synthesized and studied by EPR spectroscopy. Complexes I–V are paramagnetic in the crystalline state and in solution. The geometry of the obtained paramagnetic species and spin density distribution in them are studied by the Density functional theory. Diamagnetic complex VI is synthesized from the phenox-imQ dianion, and its one-electron oxidation is studied. The molecular structure of complex VI · ТHF is determined by X-ray diffraction analysis (CIF file CCDC no. 2000962 (VI · ТHF)).

Specific Features of EPR Spectroscopy of Organotin Compounds with Paramagnetic Ligands of the o-Iminobenzosemiquinone Type

1.

Disappearance of the free valence in organometallic derivatives of o-semiquniones with IVB group metals linked with elimination of one of the radicals on the IVB group element, proceeds by a bimolecular mechanism with participation of an external acceptor of the radical. The case in which a stable radical is formed as a result of elimination constitutes an exception.




2.

Examples of acceptors contributing to radical elimination are atoms of metals, organometallic and organic radicals, and neutral molecules.

Mechanism of homolysis of M-C bonds in group IVB organometallic derivatives of o-semiquinones

1.

Disappearance of the free valence in Group IVB semiquinolates, independent of their method of preparation, occurs as the result of their disproportionation into quinone and bis (triorganoelementoxy)benzene derivatives and elimination of the alkyl group from the Group IVB element under the influence of radical acceptors.




2.

The concrete ratio of the transformation paths is determined by the nature of the elementoorganic fragment of the semiquinone: the probability of its dealkylation increases with decrease in the energy of the M-C bond.

Some rules in transformations of Group IVB o-semiquinolates

1.

The products of the oxidative 1,4-addition formed in the reaction of diheteroorganic compounds with sterically hindered o-quinones react readily with organic oxidants.




2.

The types of reactions of o-hemiquinolates of Group IVB elements are determined by the tendency to eliminate alkyl and aryl groups from the heteroatom under the influence of the unpaired electron of the free-radical ligand.

Oxidative addition products in reactions of heteroorganic compounds with substituted o-quinones

ConclusionsTrimethylsilicon 3,5-di-tert-butyl-o-benzosemiquinolate disproportionates to the quinone and 1,2-bis-(trimethylsiloxy)-3,5-di-tert-butylbenzene.

V. A. Tsaryapkin

Papers

Mechanism of homolysis of M-C bonds in group IVB organometallic derivatives of o-semiquinones

Some rules in transformations of Group IVB o-semiquinolates

Oxidative addition products in reactions of heteroorganic compounds with substituted o-quinones

Disproportionation of trimethylsilicon 3,5-di-tert-butyl-o-benzosemiquinolate