ESR study of radical anions ando-semiquinone metal complexes—5,5′-di-tert-butyl-2,2′-dimethylbiphenyl-3,4,3′,4′-diquinone derivatives

The influence of the nature of the metal (metallofragment) on the spin density distribution in radical anions ando-semiquinone metal complexes (derivatives of sterically hindered 5,5′-di-tert-butyl-2,2′-dimethylbiphenyl-3,4,3′,4′-diquinone) was studied by ESR spectroscopy. Despite the difference in the characters of the spin density distribution between the radical anion derivatives (M=Li, Na, K, and CoCp₂) ando-semiquinone complexes (ML_n=Tl, SnPh₃, TlMe₂, Cu(PPh₃)₂, Cu(CNR)₂, and Mn(CO)₄) in all cases significant delocalization of the spin density of an unpaired electron into theo-quinone ring is observed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 904–907, May, 1998.     

3,6-Di-tert-butyl-o-benzosemiquinone complexes of copper(1) with bidentate bis(diphenylphosphine) ligands. Synthesis, structures, and properties

New mononuclear 3,6-di-tert-butyl-o-benzosemiquinone complexes of copper(1) with bis(diphenylphosphine) ligands were synthesized: (DBSQ)Cu(dppe) (1) (DBSQ=3,6-di-tert-butyl-o-benzosemiquinone and dppe=1,2-bis(diphenylphosphino)ethane), (DBSQ)Cu(dppp) (2) (dppp=1,3-bis(diphenylphosphino)propane), (DBSQ)Cu(dppn) (3) (dppn=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl), and (DBSQ)Cu(dppfc) (4) (dppfc=1,1′-bis(diphenylphosphino)ferrocene). The compositions and structures of complexes1–4 were characterized by elemental analysis and electronic absorption, IR, and ESR spectroscopy. The molecular structures of complexes3 and4 were established by X-ray diffraction analysis. The reactions of elimination and replacement of neutral ligands in the coordination sphere of the complexes were studied by ESR spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2333–2340, November, 1998.     

ESR study of paramagnetic derivatives of sterically hindered di-<Emphasis Type="Italic">o</Emphasis>-quinone with the tetrathiafulvalene bridge

The paramagnetic derivatives of 4,4′,7,7′-tetra-tert-butyl-2,2′-bis-1,3-benzodithiol-5,5′,6,6′-tetraone (1), viz., radical anion salts of the alkali metals (Li, Na, K) and cobaltocenium cations, chelated mono-o-semiquinone complexes with different metal fragments (Tl, TlMe₂, SnPh₃, Mn(CO)₄, Mn(PPh₃)(CO)₃), a number of copper(I) complexes with sterically hindered phosphines as well as binuclear heterometallic derivatives of triphenylantimony(V) o-semiquinone-catecholate with the analogous paramagnetic centers, were studied by ESR spectroscopy. The reaction of di-o-quinone 1 with sodium amalgam resulted in the formation of all reduced forms including quinone-semiquinone, disemiquinone, semiquinone-catecholate, and dicatecholate. A radical cation with the unpaired electron localized on the tetrathiafulvalene (TTF) fragment, which resulted from the oxidation of di-o-quinone 1, was detected by ESR spectroscopy.     

Synthesis, structures, and properties of spiro[6-azaperimidine-2,4′-cyclohexa-2′,5′-dien]-1′-one derivatives

The reaction of 5-amino-4-chloroquinolines with 4-amino-2,6-di-tert-butylphenol yielded derivatives of spiro[6-azaperimidine-2,4′-cyclohexa-2′,5′-dien]-1′-one, which exhibit photo-and thermochromic properties in solutions. The structure of 2′,6′-di-tert-butyl-5,7,9-trimethylspiro[6-aza,-2,3-dihydroperimidine-2,4′-cyclohexa-2′,5′-dien]-1′-one was established by X-ray diffraction study. The ring-chain isomerization of 2′,6′-di-tert-butyl-5,7-dimethyl-and 2′,6′-di-tert-butyl-5,7,8-trimethylspiro[6-aza-2,3-dihydroperimidine-2,4′-cyclohexa-2′,5′-dien]-1′-ones was studied by dynamic NMR spectroscopy. Deceased. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2028–2034, November, 1997.     

Reactions of lithium phenylacetylenide and lithium 3,3-dimethylbut-1-ynide with 3,6-di-tert-butyl-1,2-benzoquinone. Molecular structure of 2,5-di-tert-butyl-8-(3,6-di-tert-butyl-1,2-benzoquinon-4-yl)-8-phenylocta-2,4,6,7-tetraen-1,6-olide

Reactions of 3,6-di-tert-butyl-1,2-benzoquinone with PhC≡CLi and Bu^tC≡CLi are multistage processes. In the first stage, nucleophilic 1,2-addition of the organometallic compound too-benzoquinone occurs to form the corresponding hydroxycyclohexadienone derivative. In polar solvents, the latter undergoes rearrangement through insertion of the oxygen atom into the ring to form a new allenic organolithium compound. The reaction of the newly formed organometallic compound with the initialo-quinone occurs either as a one-electron transfer to yield lithium semiquinolate and a dimerization product,viz., 4,4′-bi(2,5-di-tert-butyl-9,9-dimethyldeca-2,5-dien-7-yn-1,6-olide), or as the 1,4-addition to yield 2,5-di-tert-butyl-8-(3,6-di-tert-butyl-1,2-benzoquinon-4-yl)-8-phenylocta-2,4,6,7-tetraen-1,6-olide. The structure of the latter compound was established by X-ray diffraction analysis and by NMR and IR spectroscopy. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 351–356, February, 1999.     

Synthesis of a Chiral 3,3′-Di- tert -butyl-2,2′-bipyrrole

 Diethyl 3,3′-di-tert-butyl-4,4′-dimethyl-2,2′-bipyrrole-5,5′-dicarboxylate was synthesized in four steps from ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate. The CH₂ hydrogens of the ethyl ester groups of the former are diastereotopic in the ¹H-NMR, consistent with axial chirality of the bipyrrole and restricted rotation about the 2,2′-bipyrrole bond, due to the tert-butyl groups. An X-ray structure of the crystalline target compound shows the pyrrole rings are twisted out of coplanarity by 84.5°.     

Structures of oxidation products of 4,6-di-tert-butylpyrogallol

Oxidation of 4,6-di-tert-butylpyrogallol gave two dimeric products instead of the expected 4,6-di-tert-butyl-3-hydroxy-1,2-benzoquinone (2). It was established by X-ray diffraction analysis that the first product has the structure of tetra-tert-butyl-6, 10a-dihydroxy-1,2-dioxo-3,4a,7,9-1,2,4a, 10a-tetrahydrodibenzo-1,4-dioxine. From this it follows that compound 2 undergoes regio- and stereospecific dimerization according to the [2π+4π]-cycloaddition mechanism,viz, the hetero Diels—Alder reaction. The double intensities of the signals in the¹H NMR spectrum are indicative of a symmetrical structure of the second product, 2,6,4′, 6′-tetra-tert-butyl-4,4′-dihyroxy-3,5,3′,5′-tetraoxo-4,4′-bi(cyclohexene), which is a racemate of enantiomers formed upon recombination (r+r orl+l) of the intermediate of oxidation of pyrogallol, namely, of ther,l-stereogenic 3,5-di-tert-butyl-1-hydroxy-2,6-dioxocyclohex-3-enyl radical. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 139–146, January, 1999.     

Study of the reaction of 4-chloromethylene-2,6-di-<Emphasis Type="Italic">tert</Emphasis>-butylcyclohexa-2,5-dien-1-one with the P(III) acids esters

The main stable products of the reactions 4-chloromethylene-2,6-di-tert-butylcyclohexa-2,5-dien-1-one with triethyl phosphite and ethyl diphenylphosphinite are the phosphorylated phosphorus ylides, 3,3′,5,5′-tetra-tert-butylstilbenequinone, and biphosphorylated sterically hindered phenols.     

Synthesis of a Chiral 3,3′-Di-<Emphasis Type="Italic">tert</Emphasis>-butyl-2,2′-bipyrrole

Summary.  Diethyl 3,3′-di-tert-butyl-4,4′-dimethyl-2,2′-bipyrrole-5,5′-dicarboxylate was synthesized in four steps from ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate. The CH₂ hydrogens of the ethyl ester groups of the former are diastereotopic in the ¹H-NMR, consistent with axial chirality of the bipyrrole and restricted rotation about the 2,2′-bipyrrole bond, due to the tert-butyl groups. An X-ray structure of the crystalline target compound shows the pyrrole rings are twisted out of coplanarity by 84.5°. Corresponding author. E-mail: lightner@scs.unr.edu Received September 2, 2002; accepted September 13, 2002 Published online February 20, 2003     

New semiquinone-catecholate rhodium complex with 2,2′-dipyridyl

A new semiquinone rhodium complex,viz., (2,2′-dipyridyl)(3,6-di-tert-butyl-o-benzosemiquinone)(3,6-di-tert-butylcatecholate)rhodium(III) (1), which is a structural analog of the known redox-isomeric cobalt complex, was prepared, isolated in the individual state, and characterized by X-ray analysis, magnetochemistry, and IR and ESR spectroscopy. At room temperature, compound1, unlike the cobalt analog, is a complex of trivalent low-spin rhodium with one catecholate and one semiquinone ligand. However, broadening of the lines in the ESR spectra both of a solution and a powder of complex1 with increasing temperature indicates that the redox-isomeric transformation occurs in this case as well. The equilibrium of this transformation is virtually completely shifted toward the low-spin semiquinone-, catecholate isomer. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1784–1788, September, 1999.     

New lead(II) catecholate and o-semiquinone complexes

Lead(II) catecholate complexes were prepared by reduction of 3,6-di-tert-butyl-o-benzoquinone and its derivatives with lead metal in THF. The molecular structure of the (CatPb)₄·(PbO)₂·6C₃H₆O complex (Cat is the dianion of 3,6-di-tert-butylcatechol), which was synthesized by hydrolysis of lead 3,6-di-tert-butylcatecholate in acetone, was established by X-ray diffraction. A series of lead(II) o-semiquinone complexes, which were prepared by the addition of the phenoxyl radical to lead catecholates or by oxidation of the latter with mercury(II), copper(II), or silver(I) halides, were studied by the ESR method. Lead(II) mono-o-semiquinolate complexes undergo symmetrization to form stable bis-o-semiquinolates, which were isolated and characterized in individual state. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1103–1111, July, 2006.     

Solid-phase oxidation of 2,4-Di-tert-butylphenol and 3,6-Di-tert-butylpyrocatechol in the presence of alkali and alkaline earth metal halides under elastic deformation

Solid-phase oxidation of 2,4-di-tert-butylphenol to give 2,2′,4,4′-tert-butyl-6,6′-bisphenol and of 3,6-di-tert-butylpyrocatechol to afford 3,6-di-tert-butyl-l,2-benzoquinone was performed in the presence of alkali and alkaline earth metals halides under conditions of modified extrusion. The formation of the corresponding metal 3,6-di-tert-butylsemiquinolates was registered by ESR method. The different behavior of chlorides, bromides, and iodides was observed and rationalized basing on the dissimilar complexing ability of halogens. The mechanism of activated oxidation was assumed. The study was carried out under financial support of the Russian Foundation for Basic Research (grant no. 96-03-33253a). Deceased.     

<Emphasis Type="Italic">o</Emphasis>-Semiquinone metal complexes as derivatives of sterically hindered di-<Emphasis Type="Italic">o</Emphasis>-quinone

ESR spectroscopy was used to study a series of mono- and binuclear o-semiquinone metal complexes, viz., derivatives of sterically hindered di-o-quinone 1,2-bis(2,5-di-tert-butylcyclohexadiene-1,5-dion-3,4-yl)ethane (1). Hindered rotation was found in the o-semiquinone moiety of the generated complexes. Magnetochemical measurements for polymeric bis(o-semiquinolate)copper(II) based on di-o-quinone 1 showed two antiferromagnetic channels of interaction between the paramagnetic centers. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1580–1584, July, 2005.     

Hypercoordinated gold(I) compounds

A hypercoordinated 2,2′-diaurated 4-tert-butylbiphenyl derivative, which contains an intramolecular Au...Au secondary bond, was first synthesized by the reaction of 2,2′-dilithio-4-tert-butylbiphenyl with ClAuPPh₃. The structure of the complex was established by X-ray structural analysis,¹H and³¹P NMR spectroscopy, and fast-atom bombardment mass spectrometry. For Part 3, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2244–2247, December, 1997.     

Functionalization of sterically hindered <Emphasis Type="Italic">o</Emphasis>-benzoquinones: amino-substituted 3,6-di(<Emphasis Type="Italic">tert</Emphasis>-butyl)-<Emphasis Type="Italic">o</Emphasis>-benzoquinones

New sterically hindered functionalized o-quinones were synthesized by the 1,4-nucleophilic addition of secondary cyclic amines to 3,6-di(tert-butyl)-o-benzoquinone. The ability of these o-quinones to form o-semiquinone complexes with transition and main-group metals was studied by ESR spectroscopy in solution. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1786–1793, September, 2007.     

Synthesis and thermal transformations of molecular complexes of bis[tris(trifluoromethyl)germyl]mercury(ii witho-quinones

Stable molecular complexes of bis[tris(trifluoromethyl)germyl]mercury(II) Hg[(CF₃)₃Ge]₂ (1) witho-quinones (3,6-di-tert-butylbenzoquinone-1,2 (2), 3,6-di-tert-butyl-4,5-dimethoxybenzoquinone-1,2 (3), and 1,4,5,7-tetra-tert-butyldibenzo[1,4]dioxin-2,3-dione (4)) have been synthesized and characterized by elemental analysis and IR and electronic absorption spectroscopies. Depending on the ratio between the starting reactants, the reactions ofo-quinones with1 gave complexes of the composition R₂Hg · Q (5,7,9) or R₂Hg · Q₂ (6,8,10), where Q=2 (5,6),3 (7,8),4 (9,10); R=Ge(CF₃)₃. According to the spectral data, the molecule ofo-quinone in R₂Hg · Q acts as a neutral ligand, whereas the second molecule ofo-quinone in R₂Hg · Q₂ is not coordinated to1. It has been found by ESR that thermolysis of polycrystalline samples of complexes6 and10 involves intermediate formation of radical pairs and finally yields paramagnetico-semiquinone complexes, SQGe(CF₃)₃, which are typical products of one-electron oxidation of Organometallic compounds byo-quinones.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1568–1573, August, 1995.The authors wish to thank M. A. Lopatin for his help in recording the electronic absorption spectra.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No. 93-03-18369).     

Kinetics of the formation and dissociation of complexes of cobalt(II) with <Emphasis Type="Italic">meso</Emphasis>-Phenylocta(methyl)porphyrin derivatives in organic solvents

The influence of the deformation of the tetrapyrrole aromatic macrocycle and the electronic effects of substituents on the kinetic parameters in the formation and dissociation reactions of cobalt complexes of porphyrins are discussed on the basis of a study of the kinetics of the formation and dissociation of cobalt complexes with meso-phenyl octa(methyl)porphyrin derivatives: 5,10,15-triphehyl octa(methyl) porphyrin; 5,15-bis-(3′,5′-di-tert-butyl phenyl) octa(methyl)porphyrin; 5,10,15-tris-(3′,5′-di-tert-butyl phenyl) octa(methyl)porphyrin; and 5,10,15,20-tetrakis-(3′,5′-di-tert-butyl phenyl) octa(methyl)porphyrin in acetic acid and pyridine.     

Investigation of radical pairs produced upon pulse action of elastic waves on the 3,6-di-tert-butylcatechol-3,6-di-tert-butyl-o-benzoquinone-sulfur system

The pulse action of elastic waves on polycrystalline mixtures of 3,6-di-tert-butylcatechol and 3,6-di-tert-butyl-o-benzoquinone produces radical pairs stable at room temperature, and the addition of polycrystalline sulfur considerably increases their yield. The dependences of formation and decay rates of paramagnetic centers on the composition of the mixture were studied. The threshold character of formation of paramagnetic centers at various powers of elastic wave pulse was established.Translated fromIzvestiya Akademii Nauk. Seriva Khimicheskaya, No. 4, pp. 864–868, April, 1996.     

Formation and stabilization of radical pairs in the quinone-pyrocatechol-polymer system

The formation of radical pairs (RP) in solid mixtures of 3,6-di-tert-butyl-o-quinones (Q) and 3,6-di-tert-butylpyrocatechol (QH₂) under the action of shock-wave (SW) pulses was studied by ESR and IR spectroscopy. The radical pairs are formed only when a threshold value of SW power is achieved. The generation of RP is preceded by the formation of hydrogen-bonded associates QH₂…Q upon intimate mixing and fine dispergation of the reagents in a SW field. The incorporation of the reagents into a polymeric matrix favors the formation of associates and stabilization of the pairs, which leads to a decrease in the SW power threshold. Deceased. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1464–1467, August, 1997.     

Synthesis of 2,2′-diamino-7-tert-butyl-9,9′-spirobifluorene starting from 4,4′-di-tert-butylbiphenyl

Abstract  

A novel spirobifluorene diamine monomer, 2,2′-diamino-7-tert-butyl-9,9′-spirobifluorene, was obtained starting from the readily available reagent 4,4′-di-tert-butylbiphenyl. The key step of the synthesis is the introduction of a nitro group into the 2-position of the spirobifluorene through the loss of tert-butyl at the 2-position.