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.     

Synthesis of magnesium catecholate and <Emphasis Type="Italic">o</Emphasis>-semiquinone complexes by oxidation of the metal with 3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl-<Emphasis Type="Italic">o</Emphasis>-benzoquinone

Oxidation of amalgamated magnesium metal with 3,6-di-tert-butyl-o-benzoquinone (1) in different aprotic organic solvents afforded magnesium catecholate and bis-o-semiquinolate complexes. The catecholate derivatives of magnesium CatMgL₂ (Cat is the 3,6-di-tert-butyl-o-benzoquinone dianion, L = THF or Py) were synthesized in high yields in pyridine and tetrahydrofuran, respectively. The reactions in diethyl ether or dimethoxyethane produced hexacoordinated metal bis-o-semiquinolates SQ₂MgL_n (SQ is the 3,6-di-tert-butyl-o-benzoquinone radical anion, L = Et₂O, n = 2; L = DME, n = 1). The reaction with the use of toluene as the solvent gave a magnesium bis-o-semiquinolate complex containing the coordinated unreduced o-quinone molecule. The molecular structures of the [CatMgPy₂]₂ and SQ₂Mg·DME complexes were established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 92–98, January, 2007.     

Zinc and cadmium complexes based on 3,6-di-tert-butyl-o-benzoquinone

Zinc and cadmium bis-o-semuquinolate and catecholate complexes are synthesized by the reduction of 3,6-di-tert-butyl-o-benzoquinone (3,6-Q) with amalgamated metals in a medium of various solvents. The oxidation of the metal catecholate derivatives results in the corresponding mono-o-semiquinone complexes, which undergo symmetrization to form the metal bis-o-semiquinolates. The molecular structures of the complexes (3,6-SQ)₂Zn · Py, (3,6-SQ)₂Zn · H₂O, and (3,6-SQ)₂Cd · α,α′-Bipy (3,6-SQ is the radical anion of 3,6-Q) are studied by X-ray diffraction analysis. Magnetochemical studies are carried out for the zinc and cadmium bis-o-semiquinone complexes.     

Synthesis, structures, and properties of 3,6-di-tert-butyl-o-benzosemiquinone complexes of copper(i) with 1,5-diaza-3,7-diphosphacyclooctanes

Two new 3,6-di-tert-butyl-o-benzosemiquinone complexes of copper(i) (2a and2b) with 1,3,5,7-tetraphenyl-1,5-diaza-3,5-diphosphacyclooctane (1a) and 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane (1b), respectively, were synthesized. Their structures in solution and in the crystalline state were studied. According to the results of X-ray diffraction analysis, the copper(i) atom in molecules2a and2b is in a pseudotetrahedral environment and is directly coordinated to two P atoms of the diazadiphosphacyclooctane ligand and two O atoms of the benzosemiquinone ligand. In complex2a, ligand1a adopts a chair-boat conformation typical of all complexes with eight-membered cyclic 1,5-donors studied previously. Unlike ligand1a, the ligand in complex2b adopts a chair-chair (crown) conformation identical with that of the free ligand. Both complexes are paramagnetic in the solid state and in solutions. The parameters of the isotropic ESR spectra of complexes2a and2b are typical of four-coordinateo-semiquinone copper(i) complexes with bidentate bisphosphine ligands. Based on analysis of the isotropic ESR spectra, it was suggested that compound2b in solutions exists as two isomers, which differ in the conformation of the eight-membered heterocycle (chair-boat or chair-chair). Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1806–1812, October, 2000.     

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.     

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.     

Quinone complexes of aluminum: Synthesis and structures

Reactions of aluminum metal with 3,6-di-tert-butyl-o-benzoquinone (3,6-Q) in various solvents gave aluminum tris-o-semiquinolate and catecholate. The metal catecholate underwent partial hydrolysis in the presence of water. The dimeric complex [(Cat)Al(OH)Bipy]₂ × 4C₂H₄Cl₂ (Cat is the 3,6-Q dianion and Bipy is 2,2-bipyridyne) with bridging OH groups was isolated and characterized by X-ray diffraction. A reaction of aluminum with o-quinone in the presence of molecular iodine yielded the dimeric catecholate iodide [(Cat)₂Al(Et₂O)₂]AlI₂. The structure of the latter was confirmed by X-ray diffraction. An aluminum catecholato-o-semiquinolate complex was obtained by an exchange reaction between [(Cat)₂Al(Et₂O)₂]AlI₂ and thallium o-semiquinolate.     

Redox reactions involving the indium(III) catecholate complexes

Indium catecholate complexes 3,6-CatInR (3,6-Cat is the 3,6-di-tert-butyl-o-benzoquinone dianion (3,6-Q), R = Me (I) and Et (II)) are synthesized by the exchange reaction between RInI₂ and thallium catecholate 3,6-CatTl₂. Compounds I and II are trimeric in both the solution and crystalline state. The oxidation of compound I and earlier described complex [3,6-CatInI(THF)]₂ (THF is tetrahydrofuran) by various substrates (iodine, 3,6-Q, and tetramethylthiuram disulfide) is studied. Different indium(III) o-semiquinone complexes are the reaction products, depending on the reaction conditions.     

Photolysis of 2-(Triorganostannyloxy)-3,6-di-tert-butyl-benzquinone-1,4 in Alkanes Solution

Abstract

Photolysis of 2-(trimethylstannyloxy)-3,6-di-tert-butyl-benzquinone-1,4 (I), 2-(triphenylstannyloxy)-3,6-di-tert-butyl-benzquinone-1,4 (II), and 2-(tribenzylstannyloxy)-3,6-di-tert-butyl-benzquinone-1,4 (III) by light with the wavelength 436 nm leads to the evolution of carbon mono- and dioxide and the formation of hydrocarbon radicals with their consequent recombination.

GRAPHICAL ABSTRACT     

Synthesis,structure, and properties of 2-(triphenylstannyloxy)-3,6-di-tert butyl-1,4-benzoquinone

2-(Triphenylstannyloxy)-3,6-di-tert-butyl-1,4-benzoquinone (1) was obtained from the potassium salt of 3,6-di-tert-butyl-2-hydroxy-1,4-benzoquinone and triphenyltin bromide in methanol and characterized by x-ray diffraction analysis, electronic, IR, and NMR spectroscopy. According to x-ray diffraction data, the single crystal of1 has the structure of a chain metal polymer with bridging hydroxy-para-quinone ligands; the coordination number of tin is six. Complex1 is reduced by cobaltocene to the corresponding radical anion. In solutions,1 reacts with metal-centered radicals , and with formation of paramagnetic binuclearortho-semiquinone complexes.Institute of Organometallic Chemistry, Russian Academy of Sciences, 603600 Nizhnii Novgorod. A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2798–2804, December, 1992.     

Low-temperature oxidation of 3,6-di-tert-butyl-o-benzoquinone and 3,6-di-tert-butylpyrocatechol with tert-butyl hydroperoxide in the presence of aluminum, titanium, and zirconium tert-butylates

Systems consisting of metal (Al, Ti, Zr) tert-butylate and tert-butyl hydroperoxide oxidize 3,6-di-tert-butyl-o-benzoquinone under mild conditions (room temperature, benzene). With (t-BuO)₃Al and (t-BuO)₄Zr, the major reaction products are 5-hydroxy-3,6-di-tert-butyl-2,3-epoxy-p-benzoquinone, and with (t-BuO)₄Ti, 2-hydroxy-3,6-di-tert-butyl-p-benzoquinone. Under the conditions of this reaction, 3,6-di-tert-butylpyrocatechol initially transforms into 3,6-di-tert-butyl-o-benzoquinone. The reactions involve metalcontaining peroxides.     

ESR study of the reaction of decacarbonyidimanganese with thallium(i) 3,6-di-tert-butyl-o-benzosendquinolate in solutions

The reaction of decacarbonyldimanganese Mu₂(CO)₁₀ (1) With thallium(t) 3,6-di-tert-butyl-o-benzosemiquinolate (2) in solution was studied by ESR spectroscopy. Irradiation of solutions containing1 and2 in organic solvents with visible light at 220–280 K leads totrinuclear MnTlMn complex (3). An analysis of hyperfine structure parameters indicates that3 is a semiquinone complex of thallium. A possible mechanism of the formation of complex3 and its molecular structure was discussed.Translated fromIzveshya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 95–98, January, 1996.     

Electrochemical transformations of catecholate and <Emphasis Type="Italic">o</Emphasis>-amidophenolate complexes with triphenylantimony(V)

The electrochemical properties of catecholate and o-amidophenolate complexes with triphenylantimony(V) with various substituents in the aromatic ring were examined. Introduction of electron-donating groups into the catecholate ligand or replacement of an O atom (in catecholate) by a N atom (o-amidophenolate) stabilizes the monocationic forms of the complexes obtained by one-electron oxidation. Complexes with electron-withdrawing substituents undergo irreversible two-electron oxidation resulting in the elimination of o-quinone. Complexes containing electron-withdrawing ligands do not form o-semiquinones and are inert to atmospheric oxygen. According to electrochemical data, oxygen can be bound reversibly by catecholate complexes containing the electron-donating methoxy groups in the 3,6-di-tert-butylcatecholate ligand and o-amidophenolate derivatives with half-wave oxidation potentials lower than or equal to 0.70 V (vs. Ag/AgCl), which form relatively stable cationic complexes upon the oxidation.     

New polydentate ligands based on sterically hindered o-benzoquinones (pyrocatechols) containing the 1,4-diazadiene group

New bifunctional ligands containing the 1,4-diazadiene and 1,2-benzoquinone groups were synthesized by the reactions of 4-amino-3,6-di-tert-butylpyrocatechol with glyoxal and its derivatives. Their o-semiquinone complexes with transition and nontransition metals were studied in solution by the ESR method.     

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.     

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.     

Reaction of 3,6-di-tert-butyl-o-benzoquinone with dimedone. Functionalized derivatives of hinderedo-quinones and catechols

The reaction of 3,6-di-tert-butyl-o-benzoquinone with dimedone in the presence of a catalytic amount of Et₃N occurs as repeated 1,4-nucleophilic addition-oxidation and isomerization of a tricyclic quinone into quinomethane. The intermediate products were isolated and characterized. Semiquinone complexes of quinones were studied by ESR in solution. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2206–2209, December, 1997.     

The reaction of 3,6-di-tert-butyl-1,2-benzoquinone and 3,6-di-tert-butylcatechol withtert-butyl hydroperoxide

Reaction of 3,6-di-tert-butyl-1,2-benzoquinone and 3,6-di-tert-butylcatechol withtert-butyl hydroperoxide in aprotic solvents leads to the generation of semiquinone (SQ^.H), alkylperoxy (ROO^.), and alkyloxy radicals. The reaction of SQ^.H and ROO^. produces 2,5-di-tert-butyl-6-hydroxy-1,4-benzoquinone, 3,6-di-tert-butyl-1-oxacyclohepta-3,5-diene-2,7-dione, and 2,5-di-tert-butyl-3,6-dihydroxy-1,4-benzoquinone. The radical generated from solvent attacks SQ^.H at position 4 with C−C bond formation. 4-Benzyl-2,5-di-tert-butyl-6-hydroxycyclohexa-2,5-diene-1-dione produced in this way is transformed into 4-benzyl-3,6-di-tert-butyl-1,2-benzoquinone under the reaction conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 943–946, May, 1999.     

Photooxygenolysis of 3,6-di-tert-butyl-o-benzoquinone

The photolysis of 3,6-and 3,5-di-tert-butyl-o-benzoquinones in benzene (λ > 380 nm, inert atmosphere) involves decarbonylation of the compounds to furnish respectively 2,5-and 2,4-di-tert-butylcyclopentadienones. The 2,5-isomer is stable, and the 2,4-di-tert-butylcyclopentadienone suffers a conversion into a Diels-Alder adduct. The participation of oxygen inhibited the decarbonylation and changed the direction of the photolysis: Here the products of the 3,5-di-tert-butyl-o-benzoquinones conversion were a di-tert-butylmuconic anhydride and dipivalylethylene. It was concluded that a singlet oxygen was involved in the process which formed by a triplet-triplet annihilation at the interaction of ³O₂ with a triplet-excited initial quinone.     

Tin oxidation with 3,6-di-tert-butyl-o-benzoquinone

The kinetics of tin oxidation with 3,6-di-tert-butyl-o-benzoquinone (3,6-Q) in toluene was studied. The scheme of formation of tin o-quinone complexes during metal oxidation with 3,6-Q in different aprotic solvents was suggested on the basis of the kinetic, EPR, and IR data.