Synthesis, electrochemical properties, and antioxidant activity of sterically hindered catechols with 1,3,4-oxadiazole, 1,2,4-triazole, thiazole or pyridine fragments.

A series of new RS-, RS-CH- and RN-CH-functionalized сatechols with heterocyclic fragments such as 1,3,4-oxadiazole, 1,2,4-triazole, thiazole, or pyridine were synthesized by the reaction of 3,5-di--butyl--benzoquinone or 3,5-di--butyl-6-methoxymethylcatechol with different heterocyclic thiols. The S-functionalized catechols were prepared by the Michael reaction from 3,5-di--butyl--benzoquinone and the corresponding thiols. The starting reagents such as substituted 1,3,4-oxadiazole-2-thiols and 4-triazole-3-thiols are characterized by thiol-thione tautomerism, therefore their reactions with 3,5-di--butyl-6-methoxymethylcatechol can proceed at the sulfur or nitrogen atom.

Synthesis, Structure, Electrochemical Properties, and Antioxidant Activity of Organogermanium(IV) Catecholate Complexes.

A series of novel organogermanium(IV) catecholates - of the general formula R'Ge(Cat), where R' = Ph, Et, have been synthesized. Compounds were characterized by H, C NMR, IR spectroscopy, and elemental analysis. The molecular structures of -, , and in crystal state were established using single-crystal X-ray analysis.

A Series of Cyclopentadienyl Lanthanum Complexes with Metalloid Germanium Clusters.

A series of cyclopentadienyllanthanum complexes with the disilylated metalloid germanium cluster [Ge(Hyp)] [Hyp = Si(SiMe)] has been prepared and fully characterized. The synthetic procedure is based on the salt metathesis reaction of two different cyclopentadienyllanthanum diiodides CpLaI (Cp: Cp*, pentamethylcyclopentadienyl; Cp, 1,2,4-tri--butylcyclopentadienyl) with K[Ge(Hyp)] in tetrahydrofuran (THF) with a subsequent extraction with -hexane. The composition of the obtained compounds and the mode of coordination of the germanium cluster to the rare-earth metal are strongly influenced by the steric demand of the cyclopentadienyl ligands and the crystallization conditions.

The Synthesis and Biological Activity of Organotin Complexes with Thio-Schiff Bases Bearing Phenol Fragments.

A number of novel di- and triorganotin(IV) complexes - (PhSnL, PhSnL, EtSnL, PhSnL, PhSnL) with mono- or dianionic forms of thio-Schiff bases containing antioxidant sterically hindered phenol or catechol fragments were synthesized. Compounds - were characterized by H, C NMR, IR spectroscopy, and elemental analysis. The molecular structures of complexes and in the crystal state were established by single-crystal X-ray analysis.

Low-Coordinate Mixed Ligand NacNac Complexes of Rare Earth Metals.

We report the synthesis and characterization of two types of new mixed-ligand rare earth complexes: tetracoordinate (NacNac)Ln(BIAN) (Ln = Dy (), Er () and Y ()) and pentacoordinate (NacNac)Ln(AP)(THF) (Ln = Dy (), Er () and Y ()). The first three compounds were prepared by the reaction of [(BIAN)LnI] with potassium β-diketiminate. The salt metathesis of β-diketiminato-supported rare earth dichlorides (NacNac)LnCl(THF) with sodium o-amidophenolate results in compounds -.

Heteroligand α-Diimine-Zn(II) Complexes with O,N,O'- and O,N,S-Donor Redox-Active Schiff Bases: Synthesis, Structure and Electrochemical Properties.

A number of novel heteroligand Zn(II) complexes (-) of the general type (L)Zn(NN) containing O,N,O'-, O,N,S-donor redox-active Schiff bases and neutral N,N'-chelating ligands (NN) were synthesized. The target Schiff bases LH were obtained as a result of the condensation of 3,5-di--butyl-2-hydroxybenzaldehyde with substituted -aminophenols or -aminothiophenol. These ligands with combination with 2,2'-bipyridine, 1,10-phenanthroline, and neocuproine are able to form stable complexes upon coordination with zinc(II) ion.

Binuclear Triphenylantimony(V) Catecholates through N-Donor Linkers: Structural Features and Redox Properties.

A series of binuclear triphenylantimony(V) bis-catecholato complexes - of the type (Cat)PhSb-linker-SbPh(Cat) was prepared by a reaction of the corresponding mononuclear catecholates (Cat)SbPh with a neutral bidentate donor linker ligands pyrazine (Pyr), 4,4'-dipyridyl (Bipy), bis-(pyridine-4-yl)-disulfide (PySSPy), and diazobicyclo[2,2,2]octane (DABCO) in a dry toluene: Cat = 3,6-di-tert-butyl-catecholate (3,6-DBCat), linker = Pyr (); PySSPy (); Bipy (); DABCO (); Cat = 3,5-di-tert-butyl-catecholate (3,5-DBCat), linker = Bipy (); DABCO (); Cat = 4,5-(piperazine-1,4-diyl)-3,6-di-tert-butylcatecholate (pip-3,6-DBCat), linker = Bipy (); DABCO (); Cat = 4,5-dichloro-3,6-di-tert-butylcatecholate (4,5-Cl-3,6-DBCat), linker = Bipy (); DABCO (); and Cat = 4,5-dimethoxy-3,6-di-tert-butylcatecholate (4,5-(MeO)-3,6-DBCat), linker = Bipy (). The same reaction of (4,5-Cl-3,6-DBCat)SbPh with DABCO in an open atmosphere results in a formation of 1D coordination polymer {[(4,5-Cl-3,6-DBCat)SbPh·HO]·DABCO} (). Bis-catecholate complex PhSb(Cat-Spiro-Cat)SbPh reacts with Bipy as 1:1 yielding a rare macrocyclic tetranuclear compound {PhSb(Cat-Spiro-Cat)SbPh∙(Bipy)} ().

Heteroligand Metal Complexes with Extended Redox Properties Based on Redox-Active Chelating Ligands of o-Quinone Type and Ferrocene.

A combination of different types of redox-active systems in one molecule makes it possible to create coordination compounds with extended redox abilities, combining molecular and electronic structures determined by the features of intra- and intermolecular interactions between such redox-active centres. This review summarizes and analyses information from the literature, published mainly from 2000 to the present, on the methods of preparation, the molecular and electronic structure of mixed-ligand coordination compounds based on redox-active ligands of the o-benzoquinone type and ferrocenes, ferrocene-containing ligands, the features of their redox properties, and some chemical behaviour.

Synthesis and Antioxidant Activity of New Catechol Thioethers with the Methylene Linker.

Novel catechol thio-ethers with different heterocyclic substituents at sulfur atom were prepared by reacting 3,5-di--butyl-6-methoxymethylcatechol with functionalized thiols under acidic conditions. A common feature of compounds is a methylene bridge between the catechol ring and thioether group. Two catechols with the thio-ether group, bound directly to the catechol ring, were also considered to assess the effect of the methylene linker on the antioxidant properties.

Triphenylantimony(V) Catecholates of the Type (3-RS-4,6-DBCat)SbPh-Catechol Thioether Derivatives: Structure, Electrochemical Properties, and Antiradical Activity.

A new series of triphenylantimony(V) 3-alkylthio/arylthio-substituted 4,6-di-tert-butylcatecholates of the type (3-RS-4,6-DBCat)SbPh, where R = n-butyl (), n-hexyl (), n-octyl (), cyclopentyl (), cyclohexyl (), benzyl (), phenyl (), and naphthyl-2 (), were synthesized from the corresponding catechol thioethers and PhSbBr in the presence of a base. The crystal structures of , , , and were determined by single-crystal X-ray analysis. The coordination polyhedron of - is better described as a tetragonal pyramid with a different degree of distortion, while that for - was a distorted trigonal bipyramid ( = 0.

Imine-Based Catechols and -Benzoquinones: Synthesis, Structure, and Features of Redox Behavior.

Novel sterically hindered catechols of the type 3-(RN=CH)-4,6-DBCatH with iminoalkyl or iminoaryl groups in the third position of the aromatic ring have been synthesized and characterized in detail. The -benzoquinones 3-(RN=CH)-4,6-DBBQ have been synthesized by the oxidation of the corresponding catechols. The oxidation of methylimino-substituted catechol with K[Fe(CN)] in alkaline medium leads to the formation of two products: -quinone and diene-dione, the product of the water addition to the corresponding -quinone.

Ferrocene-Containing Tin(IV) Complexes Based on -Benzoquinone and -Iminobenzoquinone Ligands. Synthesis, Molecular Structure, and Electrochemical Properties.

The addition of different substituted -benzoquinones and -iminobenzoquinones to tin(II) bis(-iminophenolates) of the types (Fc-IP)Sn and (Fc-4,6-IP)Sn (where Fc-IP is anion 2-(ferrocenylmethyleneamino)phenolate [Fc-C(H)═N(CH)O] and Fc-4,6-IP is anion 2-(ferrocenylmethyleneamino)-4,6-di--butylphenolate [Fc-C(H)═N(4,6-tBu-CH)O]) in tetrahydrofuran leads to the oxidation of Sn(II) to Sn(IV) with formation of the corresponding tin(IV) catecholates (Fc-4,6-IP)Sn(3,6-Cat) (), (Fc-IP)Sn(3,6-Cat) (), (Fc-4,6-IP)Sn(4-Cl-3,6-Cat) (), (Fc-IP)Sn(4-Cl-3,6-Cat) (), (Fc-4,6-IP)Sn(4,5-Cl-3,6-Cat) (), and (Fc-IP)Sn(4,5-Cl-3,6-Cat) () or the -amidophenolates (Fc-4,6-IP)Sn(AP-Me) (), (Fc-IP)Sn(AP-iPr) (), and (Fc-4,6-IP)Sn(AP-iPr) (). Here ligands 3,6-Cat, 4-Cl-3,6-Cat, and 4,5-Cl-3,6-Cat are dianions 3,6-di--butyl-, 4-chloro-3,6-di--butyl-, and 4,5-dichloro-3,6-di--butylcatecholates, respectively, and AP-Me and AP-iPr are dianions 4,6-di--butyl--(2,6-dimethylphenyl)--amidophenolate and 4,6-di--butyl--(2,6-diisopropylphenyl)--amidophenolate, respectively. Complexes - have been characterized in detail by IR spectroscopy, cyclic voltammetry, and H, C, and Sn NMR spectroscopy.

Polyfunctional Sterically Hindered Catechols with Additional Phenolic Group and Their Triphenylantimony(V) Catecholates: Synthesis, Structure, and Redox Properties.

New polyfunctional sterically hindered 3,5-di--butylcatechols with an additional phenolic group in the sixth position connected by a bridging sulfur atom-(6-(CH-S-tBuPhenol)-3,5-DBCat)H (), (6-(S-tBuPhenol)-3,5-DBCat)H (), and (6-(S-Phenol)-3,5-DBCat)H () (3,5-DBCat is dianion 3,5-di--butylcatecolate)-were synthesized and characterized in detail. The exchange reaction between catechols and with triphenylantimony(V) dibromide in the presence of triethylamine leads to the corresponding triphenylantimony(V) catecholates (6-(CH-S-tBuPhenol)-3,5-DBCat)SbPh () and (6-(S-Phenol)-3,5-DBCat)SbPh (). The electrochemical properties of catechols - and catecholates and were investigated using cyclic voltammetry.

Catechol thioethers with physiologically active fragments: Electrochemistry, antioxidant and cryoprotective activities.

A number of asymmetrical thioethers based on 3,5-di-tert-butylcatechol containing sulfur atom bonding with physiologically active groups in the sixth position of aromatic ring have been synthesized and the electrochemical properties, antioxidant, cryoprotective activities of new thioethers have been evaluated. Cyclic voltammetry was used to estimate the oxidation potentials of thioethers in acetonitrile. The electrooxidation of compounds at the first stage leads to the formation of o-benzoquinones.

Deprotonation of Benzoxazolium Salt: Trapping of a Radical-Cation Intermediate.

The deprotonation of N-2,6-diisopropylphenyl-substituted benzoxazolium tetrafluoroborate 1 with NaH results in the formation of electron-rich diaminodioxaethylene 2. The radical cation salt 2·BF is found to be an intermediate product in the redox reaction leading from 1 to 2.

Heteroligand o-Semiquinonato-Formazanato Cobalt Complexes.

Two novel heteroligand o-semiquinonato-formazanato cobalt complexes [Co(3,6-SQ)(Form)] (1) and [Co(3,6-SQ)2(Form)] (2) (3,6-SQ is 3,6-di-tert-butyl-o-benzosemiquinonate radical anion; Form is 1,3,5-triphenylformazanate anion) were synthesized and characterized in detail. The molecular structures of [Co(3,6-SQ)(Form)] and [Co(3,6-SQ)2(Form)] were determined by X-ray analysis. Magnetic susceptibility measurements and spectroscopic studies have shown that square-planar complex 1 is diamagnetic with a residual paramagnetism due to antiferromagnetic exchange metal-ligand.

Ferrocene-o-benzosemiquinonato tin(IV) electron-transfer complexes.

The interaction of ferrocene with tin(IV) o-benzosemiquinonato complexes in acetonitrile results in a reversible electron transfer (ET) from ferrocene to the redox-active ligand with the formation of electron-transfer complexes [(3,6-Cat)SnBr3](-)[Cp2Fe](+) (1) and [(3,6-Cat)(3,6-SQ)SnCl2](-)[Cp2Fe](+) (2), where 3,6-Cat is the 3,6-di-tert-butyl-catecholate dianion and 3,6-SQ is the 3,6-di-tert-butyl-o-benzosemiquinonato radical anion. The ET process and the solvent effect in the system "ferrocene-o-benzosemiquinonato tin(IV) complexes" were investigated on the basis of a combination of spectroscopic and X-ray diffraction methods. The molecular structures of 1 and 2 were confirmed by X-ray analysis.

Reversible binding of molecular oxygen to catecholate and amidophenolate complexes of SbV: electronic and steric factors.

Edge of reactivity: The reactions of reversible binding of molecular oxygen to catecholate and amidophenolate complexes of Sb(V) are investigated by analyzing the position of electronic (E(HOMO)) and steric (G-parameter) factors. The optimal electronic and steric parameters for such type reactions are found.

Experimental and theoretical investigation of topological and energetic characteristics of Sb complexes reversibly binding molecular oxygen.

The experimental distribution of electron density in Ph(3)(4,5-OMe-3,6-Bu(t)-Cat)Sb·MeCN (1*) and Ph(3)(4,5-N(2)C(4)H(6)-3,6-Bu(t)-Cat)Sb·MeOH (2*) complexes was studied. According to atoms in molecules theory, the Sb-C(Ph), Sb-O(catecholate), and Sb···N(O) bonds are intermediate, whereas the O-C and C-C bonds are covalent, respectively. The energy of the Sb···N(MeCN) and Sb···O(MeOH) bonds are 7.

Triphenylantimony(v) catecholates and o-amidophenolates: reversible binding of molecular oxygen.

Novel neutral antimony(V) complexes were isolated as crystalline materials and characterized by IR and NMR spectroscopy: o-amidophenolate complexes [4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-amidophenolato]triphenylantimony(V) (Ph3Sb[AP-Me], 1) and [4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolato]triphenylantimony(v) (Ph3Sb[AP-iPr], 2); catecholate complexes (3,6-di-tert-butyl-4-methoxycatecholato)triphenylantimony(V) (Ph3Sb[(MeO)Cat], 3), its methanol solvate 3CH3OH (4); (3,6-di-tert-butyl-4,5-di-methoxycatecholato)triphenylantimony(V) (Ph3Sb[(MeO)2Cat], 5) and its acetonitrile solvate 5CH3CN (6). Complexes 1-7 were synthesized by oxidative addition of the corresponding o-iminobenzoquinones or o-benzoquinones to Ph3Sb. In the case of the phenanthrene-9,10-diolate (PhenCat) ligand, two different complexes were isolated: Ph3Sb[PhenCat] (7) and [Ph4Sb]+[Ph2Sb(PhenCat)2]- (8).