EPR study of mono-o-iminobenzosemiquinonato nickel(II) complexes with Ni-C σ-bond

New square-planar (Ph₃P)Ni^II(o-Tol)(ISQ-Prⁱ) (1), (Ph₃P)Ni^II(o-Tol)(ISQ-Me) (2), (Ph₃P)Ni^II(o-Tol)(ISQ-Bu^t) (3) nickel complexes (where ISQ-Prⁱ = 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonate, ISQ-Me = 4,6-di-tert-butyl-N-(2,6-di-methylphenyl)-o-iminobenzosemiquinonate, ISQ-Bu^t = 4,6-di-tert-butyl-N-(2,5-di-tert-butylphenyl)-o-iminobenzosemiquinonate, o-Tol = o-tolyl ligand) have been synthesized. Complexes contain σ-bound o-tolyl and neutral donor ligand Ph₃P. The sterical hindrances of N-aryl in o-iminobenzosemiquinonate ligands lead to the tetrahedral distortion of square-planar configurations of complexes as it was established using EPR spectroscopy.     

Oxidative addition reaction of o-quinones to triphenylantimony: novel triphenylantimony catecholate complexes

New catecholate Sb(V) complexes triphenyl(3,6-di-tert-butylcatecholato)antimony(V) Ph₃Sb(3,6-DBCat) (1) and triphenyl(perchloroxanthrenecatecholato)antimony(V) Ph₃Sb(^OXCat_Cl) (2) were synthesized by the oxidative addition reaction of corresponding o-quinones (3,6-di-tert-butyl-o-benzoquinone and perchloroxanthrenequinone-2,3) with triphenylantimony. Catecholates 1 and 2 can alternatively be synthesized by reacting the appropriate thallium catecholate with triphenylantimony dichloride. The oxidative addition reaction of an equimolar ratio of 4,4′-di-(3-methyl-6-tert-butyl-o-benzoquinone) and triphenylantimony yielded 4-(2-methyl-5-tert-butyl-cyclohexadien-1,5-dion-3,4-yl)-(3-methyl-6-tert-butyl-catecholato)triphenylantimony(V) Ph₃Sb(Cat-Q) (3); in the case of a 1:2 molar ratio, complex 4,4′-di-[(3-methyl-6-tert-butyl-catecholato)triphenylantimony(V)] Ph₃Sb(Cat-Cat)SbPh₃ (4) resulted. Complexes 1-4 were characterized by IR- and ¹H NMR spectroscopy. Molecular structures of 1, 2 and 4 were determined by X-ray crystallography to be a distorted tetragonal-pyramidal.     

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.     

Reaction of ferrocenecarboxylic acid with N,N-disubstituted carbodiimides: synthesis, spectroscopic and X-ray crystallographic analysis of N,N-disubstituted N-ferrocenoylureas and identification of a one-pot coupling reagent for the formation of ferrocenecarboxamides in a non-aqueous solvent

N,N^′-dicyclohexyl-N-ferrocenoylurea 2, N,N^′-diisopropyl-N-ferrocenoylurea 3, N,N^′-di-p-tolyl-N-ferrocenoylurea 4 and N,N^′-di-tert-butyl-N-ferrocenoylurea 5 were obtained by reaction of ferrocenecarboxylic acid 1 with N,N^′-dicyclohexylcarbodiimide (DCC), N,N^′-diisopropylcarbodiimide (DIC), N,N^′-di-p-tolylcarbodiimide 10 and N,N^′-di-tert-butylcarbodiimide 11, respectively. Both N-tert-butyl-N^′-ethyl-N-ferrocenoylurea 6 and N^′-tert-butyl-N-ethyl-N-ferrocenoylurea 7 were obtained by reaction of 1 with N-tert-butyl-N^′-ethylcarbodiimide 12. In all cases a small amount of ferrocenecarboxylic anhydride 8 was formed as a by-product. All compounds were characterized by ¹H NMR, ¹³C NMR, IR and MS. Single crystal X-ray structural analyses were made of 2, 3 and 4. From the consistent results, the reaction products of 1 with carbodiimides appear different from those proposed by some earlier workers. With N-(3-dimethylaminopropyl)-N^′-ethylcarbodiimidehydrochloride 9 ferrocenoylurea was not isolated, but the main product was rather 8. The suitability of 8 as acylation reagent was applied by using 9 to obtain N-(3-triethoxysilyl)-propylferrocenecarboxamide in a one-pot reaction from 1 and 3-(triethoxysilyl)-propylamine.     

Photolytic decarbonylation of o-benzoquinones

It was established that photodecarbonylation of o-benzoquinones occurs by irradiation not only by UV-light, but visible light (λ>520 nm) too. Study of the series of 4,5-di-substituted 3,6-di-tert-butyl-o-benzoquinones detected that the only product of photoreaction is the corresponding 3,4-di-substituted 2,5-di-tert-butyl-cyclopentadienone, which is formed in a yield close to quantitative. NMR monitoring of reaction of photodecarbonylation of o-benzoquinones detected that this is a two-stage process. In the first stage the photoexcited molecule of quinone rearranges into bicyclo compound (bicyclo[1.3.0]hexa-3-en-2,6-dione) containing five- and three- membered cycles, which spontaneously decomposes during the following dark stage into cyclopentadienone and a molecule of CO.     

Hexacoordinate triphenylantimony(V) complex with tridentate bis-(3,5-di-tert-butyl-phenolate-2-yl)-amine ligand: Synthesis,NMR and X-ray study

The oxidative addition reaction of 4,6-di-tert-butyl-N-(2-hydroxy-3,5-di-tert-butyl-phenyl)-o-iminobenzoquinone (IBQ) to triphenylantimony(III) proceeds with the migration of hydroxyl-proton to a nitrogen atom to form tridentate O,N,O′-coordinated bis-(3,5-di-tert-butyl-phenolate-2-yl)-amine ligand. In accordance with ¹H, ¹³C, DEPT NMR data, the new hexacoordinate complex [bis-(3,5-di-tert-butyl-phenolate-2-yl)-amine]triphenylantimony(V), [(AP-AP)H]SbPh₃ (1) in solution has a C_s symmetry plane leading to the equivalence of two O,N-chelate o-aminophenolato moieties. The molecular structure of 1 · acetone was studied by a single-crystal X-ray. Compound 1 was found to be air-stable both in solid and in solution. Its oxidation by PbO₂ leads to paramagnetic [4,6-di-tert-butyl-N-(3,5-di-tert-butyl-phenolate-2-yl)-o-iminobenzosemiquinolato]triphenylantimony(V), [(AP-ISQ)]SbPh₃ (2).     

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.     

Thermodecomposition ofo-benzoquinone complexes of transition metals

Thermodecomposition of 3,5- and 3,6-di-tert-butyl-o-benzoquinone complexes of Cu, Fe, Co, Cr, Mo, and W has been investigated in the solid phase by the thermogravimetric method. The relative stability of a series of complexes has been determined from the temperatures at which their decomposition begins. Detachment of a neutral electron-donor ligand takes place in the first stage. Detachment of ano-quinone ligand and decomposition of theo-benzoquinone formed occur in the next stage. Thermodecomposition of Fe, Co, Cr, Mo, and W complexes gives oxides or carbides, while copper complexes decompose to pure metal.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 327–329, February, 1994.     

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.     

Synthesis, structure, and antioxidant activity of hybrid N-substituted salicylic acid amides

Sterically hindered phenols, 3-tert-butyl-N-(3,5-di-tert-butyl-4-hydroxyphenyl)-5-ethyl-2-hydroxybenzamide and N-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propyl]-2-hydroxybenzamide, were synthesized as potential antioxidants, and the formation of hydrogen bonds by their molecules was shown by UV and IR spectroscopy.     

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.     

Condensations of N-arylhydroxylamines for the preparation of 5,5′-di-tert-butyl-2,2′-dihydroxydiphenylamine

Acid-promoted condensation of 4-tert-butyl-2-hydroxylaminoanisole with p-tert-butylphenol resulted in the formation of 5,5′-di-tert-butyl-2,2′-dihydroxydiphenylamine upon demethylation with BBr₃. Protection of the acidic phenol unit was required to isolate the acid labile N-arylhydroxylamine intermediate.     

Asymmetric addition of trimethylsilylcyanide to N-benzylimines catalyzed by recyclable chiral dimeric V(V) salen complex

Chiral dimeric vanadium (V) salen complex (10 mol%) derived from 5,5-Methylene di-[(S,S)-{N-(3-tert-butyl salicylidine)-N′-(3′,5′-di-tert-butyl salicylidene)]-1,2-cyclohexanediamine] with vanadyl suphate followed by auto oxidation was used as efficient catalyst for enantioselective Strecker reaction of N-benzylimines with TMSCN at −30 °C. Excellent yield (92%) of α-aminonitrile and high chiral induction was achieved (ee up to 94%) in case of 2-methoxy substituted N-benzylimines in 10 h. The catalytic system worked well up to four cycles with retention of enantioselectivity.     

Reactions of isomeric 3,6- and 3,5-di-tert-butyl-ortho-benzoquinones with NH3

The interaction of 3,6-di-tert-butyl-ortho-benzoquinone (1) and 3,5-di-tert-butyl-ortho-benzoquinone (2) with NH₃ in water—alcohol medium and with (NH₄)₂CO₃ in a solid phase has been studied. Redox processes with participation of a nucleophile of the medium take place for1, while2 reacts with NH₃ at the carbonyl group with transformation of the quinone imide. The mechanism of redox transformation of1 has been proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1789–1793, September, 1995.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No. 94-03-08653).     

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.     

N,N,N,N-Tetramethyl-1,3-propanediamine as the catalyst of choice for the Baylis-Hillman reaction of cycloalkenone: rate acceleration by stabilizing the zwitterionic intermediate via the ion-dipole interaction

N,N,N^′,N^′-Tetramethyl-1,3-propanediamine (TMPDA) can be used as an efficient catalyst for the Baylis-Hillman reaction of cycloalkenones. The increased reaction rate was thought be derived from the stabilizing effect of the zwitterionic intermediate via the ion-dipole interaction.     

A novel one-pot synthesis of hydroximoyl chlorides and 2-isoxazolines using N-tert-butyl-N-chlorocyanamide

Treatment of aldoximes with N-tert-butyl-N-chlorocyanamide gave hydroximoyl chlorides in quantitative yields in less than a minute, which on dehydrohalogenation in the presence of triethylamine gave the corresponding nitrile oxides. The nitrile oxides underwent 1,3-dipolar addition to dipolarophiles and gave 2-isoxazolines in excellent yields under mild conditions.     

5-{5-(bicyclo[2.2.1]hept-2-enyl)hydroxymethyl}-3,6-di-<Emphasis Type="Italic">tert</Emphasis>-butyl<Emphasis Type="Italic">o</Emphasis>-benzoquinone and related polymers. Synthesis and some properties

A norbornene-containing ortho-quinone, 5-{5-(bicyclo[2.2.1]hept-2-enyl)hydroxymethyl)-3,6-ditert-butyl-o-benzoquinone, was synthesized by the nucleophilic addition of 5-(hydroxymethyl)bicyclo[2.2.1] hept-2-ene to 3,6-di-tert-butyl-o-benzoquinone. The structure of the compound was established by the X-ray analysis. The monomer obtained undergoes metathesis polymerization in the presence of Grubbs catalyst of the third generation with the formation of polynorbornene containing quinone fragments in the side chains.     

Group II metal complexes with the N-(2-oxy-3,5-di-tert-butylphenyl)-4,6-di-tert-butyl-o-iminobenzoquinone ligand: an ESR study

The Group II metal (Mg, Ca, Sr, Ba, Zn, Cd) complexes based on the paramagnetic N-(2-oxy-3,5-di-tert-butylphenyl)-4,6-di-tert-butyl-o-iminobenzoquinone ligand were generated in solutions and studied by ESR spectroscopy. The magnesium, zinc, and cadmium complexes with trialkylphosphine ligands were prepared. Their molecular structures and electron density distribution were studied by ESR spectroscopy and DFT calculations.     

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.