Thermodynamic properties of o-semiquinone complex of Co with Di-(2-pyridyl)amine in the temperature range T → 0 to 370 K

The heat capacity of di-(2-pyridyl)amine-bis-(4-methoxy-3,6-di-tert-butyl-o-benzosemiquinone)cobalt in the temperature range from 7 to 370 K was investigated by means of precise adiabatic vacuum calorimetry. It was established that the phase transition associated with the redox-isomeric transformation of the semiquinone-catecholate form of the complex into the bis-semiquinone form is observed above 260 K; this transition is not completed due to thermal destruction that begins at 367 K. The magnetic moment values in the temperature range from 5 to 350 K and the EPR spectra in the temperature range from 130 to 290 K, which confirm the nature of the phase transition, were obtained for the investigated complex. The standard thermodynamic functions C _p ^pO (T), H○(T)-H○(0), S○(T), and G○(T)-H○(0), were calculated from the data on heat capacity in the temperature range from T → 0 to 260 K. Analysis of the low temperature heat capacity on the basis of Debye’s theory of the heat capacity of solids and the multifractional model testifies to the chain-layered structural topology of the investigated complex.     

Synthesis and structures of germanium-containing tungsten carbyne complexes Ph3gec≡w(ch2but)3 and Ph3GeC≡W(CH2SiMe3)3

New germanium-containing tungsten carbyne complexes Ph₃GeC≡W(CH₂R)₃ (R = Bu^t or SiMe₃) were synthesized by the reaction of the alkoxy derivative Ph₃GeC≡W(OBu^t)₃ with alkyllithium reagents RCH₂Li. The new compounds were isolated in individual form as crystals in 95 and 90% yields, respectively, and were characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy, and X-ray diffraction. X-ray diffraction study showed that the coordination environment of the W and Ge atoms in the Ph₃GeC≡ W(CH₂Bu^t)₃ and Ph₃GeC≡W(CH₂SiMe₃)₃ complexes can be described as a distorted tetrahedron. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 213—216, February, 2006.     

Oxidation by oxygen and sulfur of Tin(IV) derivatives containing a redox-active o-amidophenolate ligand

Oxidation of tin(IV) o-amidophenolate complexes [Sn(ap)Ph(2)] (1) and [Sn(ap)Et(2)(thf)] (2) (ap=dianion of 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone (ImQ)) with molecular oxygen and sulfur in toluene solutions was investigated. The reaction of oxygen with 1 at room temperature forms a paramagnetic derivative [Sn(isq)(2)Ph(2)] (3) (isq=radical anion of ImQ) and diphenyltin(IV) oxide [{Ph(2)SnO}(n)]. Interaction of 1 with sulfur gives another monophenyl-substituted paramagnetic tin(IV) complex, [Sn(ap)(isq)Ph] (4), and the sulfide, [Ph(3)Sn](2)S. The oxidation of 2 with oxygen and with sulfur proceeds through the derivative [Sn(isq)(2)Et(2)] (7), which undergoes alkyl elimination to give two new tin(IV) compounds, [Sn(ap)(isq)Et] (5) and [Sn(ap)(EtImQ)Et] (6) (EtImQ=2,4-di-tert-butyl-6-(2,6-diisopropylphenylimino)-3-ethylcyclohexa-1,4-dienolate ligand), respectively, along with the corresponding alkyltin(IV) oxide and sulfide. Complexes 3-5 and 7 were studied by EPR spectroscopy. The structures of 3, 4 and 6 were investigated by X-ray analysis.     

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.     

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.     

New dioxygen-inert triphenylantimony(v) catecholate complexes based on <Emphasis Type="Italic">o</Emphasis>-quinones with electron-withdrawing groups

New triphenylantimony(v) catecholate complexes were synthesized by oxidative addition of sterically hindered o-benzoquinones containing electron-withdrawing substituents in different positions of the carbon ring to triphenylantimony. The complexes were characterized using IR spectroscopy, NMR spectroscopy, and cyclic voltammetry. The oxygen-inertness of the complexes is shown by NMR spectroscopy and electrochemical studies. The introduction of electron-withdrawing substituents to the catecholate ligand shifts the first oxidation potential of the complexes to the electropositive region and thus deactivates the triphenylantimony(v) catecholate complexes in the reaction with molecular oxygen.     

Novel structurally characterized o-semiquinonato PCP-pincer nickel complexes

Structural study of dialkyl (PCP)-pincer o-semiquinonato nickel complexes indicated sloped relative positions of bi- and tri-dentate ligands. It became bright confirmation of propositions made on the base of their EPR spectra followed by molecular modelling.