Phase diagram and local environment of Sn and Te: SnTeBi and SnTeBi2Te3 systems

From thermal analyses and X-ray diffraction the phase diagram of the BiSnTe and SnTeBi₂Te₃ sections was determined. The local environment of Sn and Te atoms was studied by ¹¹⁹Sn and ¹²⁵Te Mössbauer spectroscopy. The BiSnTe section showed a eutectic reaction at 267 °C and 20 % mole SnTe–80 % mole Bi. No intermediate compound was detected. The SnTeBi₂Te₃ section is characterized by a eutectic reaction at 585 °C and 40 % mole SnTe–60% mole Bi₂Te₃ and a peritectic reaction at 600 °C and 50 % mole SnTe–50% mole Bi₂Te₃. It corresponds to the compound SnBi₂Te₄, which has a rhombohedral layered structure with unit cell parameters a=4.3954(4) Å and c=41.606(1) Å. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASSnTe / Bi / Bi₂Te₃ / phase diagram / Mössbauer     

Optimization of the chemoenzymatic mono-epoxidation of linoleic acid using D-optimal design

Mono-epoxied linoleic acid 9(12)-10(13)-monoepoxy 12(9)-octadecanoic acid (MEOA) was synthesized and optimized by immobilized Candida antarctica lipase (Novozym 435®) using D-optimal design. For optimizing the reaction, response surface methodology (RSM) was employed with four reaction variables such as the effect of amount of hydrogen peroxide (μL), amount of enzyme (w) and reaction time (h). At optimum conditions the experiment to obtain a higher yield% with a medium OOC% of MEOA was predicted at an amount of H₂O₂ μL of 15, Novozym 435® of 0.12 g and 7 h of reaction time. At this condition, the yield of MEOA was 82.14%, 4.91% of OOC and 66.65 mg/g of iodine value (IV). The observed value was reasonably close to the predicted value. Hydrogen peroxide was found to have the most significant effect on the degree of epoxidation OOC% and yield%. The epoxy ring opening (–C–O–C–) has been observed by Fourier Transform Infrared Spectroscopy (FTIR) at 820 cm⁻¹ and the double band (–CC–) at 3009 cm⁻¹. ¹H NMR analyses confirmed that the oxirane ring (–CH–O–CH–) of MEOA at 2.92–3.12 ppm and four signals of methane (–CHCH–) was at 5.38–5.49 ppm while the ¹³C NMR showed the oxirane ring (–C–O–C–) at 54.59–57.29 ppm and the olefinic carbons at 124.02–132.89 ppm.     

Direct determination of the equilibrium constant and thermodynamic parameters in the reaction of pentadienyl radicals with O2

Reaction of pentadienyl radicals (C₅H₇) with O₂ has been studied by a combination of pulsed laser photolysis and photoionization mass spectrometry. These radicals could be generated either by the photolysis of 1,3-pentadiene or by the two-step reaction of carbon tetrachloride photolysis followed by the H-atom abstraction reaction of Cl atom with 1,4-pentadiene. The equilibrium between pentadienyl radicals, O₂ and pentadienylperoxy radicals could be observed over the range 268–308 K. An analysis of the temporal signal of pentadienyl radicals was used to evaluate the equilibrium constant. Third-law analysis was used to evaluate the enthalpy change for the reaction C₅H₇ + O₂ ⇌ C₅H₇O₂. The observed CO bond energy in the C₅H₇O₂ adduct was found to be 56.0 ± 2.2 kJ·mol^–1, which is lower than the values of peroxy radicals formed with allyl and cyclohexenyl radicals which have an allylic resonance structure.     

Pulse radiolysis of aqueous diphenyloxide

Pulse radiolysis of aqueous diphenyloxide (DPO) has been performed under various experimental conditions. The OH radicals react with DPO on various positions of the molecule with a rate constant, k=2.1×10¹⁰ l mol⁻¹ s⁻¹. The major reaction step appears to be a cleavage of the C–O bond of DPO resulting into C₆H₄OH (λ=285 nm) and C₆H₅O(λ=325 nm) radicals in addition to DPO–OH adducts. They disappear according to a second-order reaction. In the presence of air or in a gas mixture of N₂O:O₂=4:1 the DPO–OH adducts are scavenged by oxygen, resulting into peroxyl radicals, which are long-lived species. For the reaction of e_aq⁻ with DPO a rate constant, k=2×10¹⁰ l mol⁻¹ s⁻¹ was found.     

Versatile Ru-based metathesis catalysts designed for both homogeneous and heterogeneous processes

The synthesis of new ruthenium-based catalysts applicable for both homogeneous and heterogeneous metathesis is described. Starting from the Hoveyda-Grubbs first generation (1) and the Hoveyda-Grubbs second generation (2) catalysts the homogeneous catalysts [RuCl((RO)₃Si–C₃H₆–N(R′)–CO–C₃F₆–COO)(CH–o-O–iPr–C₆H₄)(SIMes)] (4: R = Et, R′ = H; 5: R = R′ = Me) (SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) were prepared by substitution of one chloride ligand with trialkoxysilyl functionalized silver carboxylates (RO)₃Si–C₃H₆–N(R′)–CO–C₃F₆–COOAg (3a: R = Et, R′ = H; 3b: R = R′ = Me). These homogeneous ruthenium-species are among a few known examples with mixed anionic ligands. Exchange of both chloride ligands afforded the catalysts [Ru((RO)₃Si–C₃H₆–N(R′)–CO–C₃F₆–COO)(CH–o-O–iPr–C₆H₄)(SIMes)] (9: R = Et, R′ = H; 11: R = R′ = Me) and [Ru((RO)₃Si–C₃H₆–N(R′)–CO–C₃F₆–COO)(CH–o-O–iPr–C₆H₄)(PCy₃)] (8: R = Et, R′ = H; 10: R = R′ = Me). The reactivity of the new complexes was tested in homogeneous ring-closing metathesis (RCM) of N,N-diallyl-p-toluenesulfonamide and TONs of up to 5000 were achieved. Heterogeneous catalysts were obtained by reaction of 4, 5 and 8–11 with silica gel (SG-60). The resultant supported catalysts 4a, 5a, 8a–11a showed reduced activity compared to their homogenous analogues, but rival the activity of similar heterogeneous systems.     

An FT-IR study of the isomerization of 1-butoxy radicals under atmospheric conditions

Relative rate-studies of the reactions of 1-butoxy radicals have been carried out using a 47 L static reactor with detection of end products by FT-IR spectroscopy. Experiments were performed at 700 torr total pressure and over the temperature range 253–295 K. The chemistry of 1-butoxy is characterized by a competition between reaction with oxygen CH₃CH₂CH₂CH₂O + O₂ → n-C₃H₇CHO + HO₂ (R2), which yields butanal and isomerization CH₃CH₂CH₂CH₂O → CH₂CH₂CH₂CH₂OH (R3), to form a hydroxylated carbonyl-product. A reference spectrum attributed to the product of 1-butoxy isomerization was obtained and used to determine the competition between 1-butoxy isomerization versus reaction with oxygen. The results indicate that isomerization is the dominant fate of 1-butoxy radicals at ambient temperature and pressure and that its importance decreases with decreasing temperature. The rate-coefficient ratio k₃/k₂ (molecule cm⁻³) = 5.5 × 10²³ exp[(−25.1 ± 0.9 kJmol⁻¹)/RT] was obtained. This agrees with other estimates based on methods without monitoring of the isomerization product.     

‘Pincer’ pyridyl- and bipyridyl-N-heterocyclic carbene analogues of the Grubbs’ metathesis catalyst

The ‘pincer’ pyridine-dicarbene and bipyridyl-carbene ruthenium benzylidene complexes, Ru(C–N–C)Cl₂(CHPh) and Ru(C–N–N)Cl₂(CHPh), (C–N–C) = 2,6-bis(DiPP-imidazol-2-ylidene)pyridine, (C–N–N) = (DiPP-imidazol-2-ylidene)bipyridine, have been prepared and characterised by spectroscopic and diffraction methods. They exhibit moderate metathesis activity. Non-symmetrical linear tridentate ether-functionalised N-heterocyclic carbene pro-ligands are also described.     

Molecular structure of caffeine as determined by gas electron diffraction aided by theoretical calculations

The molecular structure of caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) was determined by means of gas electron diffraction. The nozzle temperature was 185 °C. The results of MP2 and B3LYP calculations with the 6-31G⁷ basis set were used as supporting information. These calculations predicted that caffeine has only one conformer and some of the methyl groups perform low frequency internal rotation. The electron diffraction data were analyzed on this basis. The determined structural parameters (r_g and ∠_α) of caffeine are as follows: <r(NC)_ring> = 1.382(3) Å; r(CC) = 1.382(←) Å; r(CC) = 1.446(18) Å; r(CN) = 1.297(11) Å; <r(NC_methyl)> = 1.459(13) Å; <r(CO)> = 1.206(5) Å; <r(CH)> = 1.085(11) Å; ∠N₁C₂N₃ = 116.5(11)°; ∠N₃C₄C₅ = 121. 5(13)°; ∠C₄C₅C₆ = 122.9(10)°; ∠C₄C₅N₇ = 104.7(14)°; ∠N₉–C₄=C₅ = 111.6(10)°; <∠NCH_methyl> = 108.5(28)°. Angle brackets denote average values; parenthesized values are the estimated limits of error (3σ) referring to the last significant digit; left arrow in parentheses means that this parameter is bound to the preceding one.     

Nickel-catalysed asymmetric SN2′ substitution chemistry of Baylis–Hillman derived allylic electrophiles

Unsymmetrical PhCHCH(CH₂X)(CO₂Me) (X = Cl, OAc) undergoes regioselective α-substitution with AlMe₃ to afford (E)-PhCHCH(Et)(CO₂Me) under Ni(acac)₂ catalysis. On the addition of planar chiral Ferrophite ligands [(R)-CpFe(1,2-C₅H₃Ar{P(OR)₂}) (Ar = Ph, 4-CF₃Ph, 3,5-Me₂Ph, 1-naphthyl; (OR)₂ = 1,1′-binaphthylene, 1,1′-biphenylene)] regioselective methylation γ to the leaving group is possible. It is proposed that the bulky Ferrophite ligand leads to an intermediate nickel allyl species Ni^II(Me)(Ferrophite){η³-PhCHCHCH(CO₂Me)} that adopts a configuration whereby the PhCH terminus of the π-allyl and the Ni–Me are syn leading to good regio (up to 6.4:1) and stereo (up to 94% ee) selectivities.     

Synthesis,molecular structure and reactivity of new π-conjugated diyne with ferrocenyl and phenyl units

New π-conjugated butadiynyl ligand FcC(CH₃)₂Fc′–CC–CC–Ph (L₁) has been synthesized and its reaction with Co₂(CO)₈ has been studied. New clusters [FcC(CH₃)₂Fc′–CC–CC–Ph][Co₂(CO)₆]_n [(1): n = 1; (2): n = 2] and [Fc–CC–CC–Ph][Co₂(CO)₆]_n [(3): n =  1; (4): n = 2] were obtained by the reaction of ligands FcC(CH₃)₂Fc′–CC–CC–Ph (L₁) and Fc–CC–CC–Ph (L₂) with Co₂(CO)₈ respectively and the composition and structure of the clusters and ligands have been characterized by elemental analysis, FTIR, ¹H and ¹³C NMR and MS. The crystal structures of compounds L₁, L₂, 2 and 4 have been determined by X-ray single crystal analysis.     

Efficient immobilization of 9,10-anthraquinonyl moiety at solid interfaces through 2-(bromomethyl)anthraquinone one-electron cleavage

We report here a new and very efficient method for the coverage of different carbon materials with 9,10-anthraquinone attached via a methylene linker. The method is based on one-electron reduction of 2-(bromomethyl)anthraquinone (AQ-CH₂-Br) to a free radical AQ–CH₂ which was readily achieved using propylene carbonate (PC) as solvent containing tetrabutylammonium iodide. This way, the radical AQ–CH₂ adds to the abovementioned carbons forming very stable and dense covalently bound anhraquinonyl methane layers (Г ≈ 2 × 10^− 9 mol cm^− 2). The grafting could be performed by constant potential electrolyses (q < 0.5 × 10^− 3 C mm^− 2).     

Cationic organoiron mixed-sandwich hydrazine complexes: Reactivity toward aldehydes,ketones, β-diketones and dioxomolybdenum complexes

This review covers comprehensively the authors work during the present decade based on the chemistry of ionic organometallic hydrazines formulated as [(η⁵-Cp′)Fe(η⁶-Ar-NHNH₂)]⁺PF₆^? (Cp′ = C₅H₅, C₅Me₅; Ar = aryl), that could be considered as a new generation of hydrazines owing to the changes provoked by the coordination of the 12-electron Cp′Fe⁺ fragment both in the electronic properties of the aromatic ring and in the hydrazine group. The reactivity of this new class of hydrazine is obviously centered, as in the classic Fischer's organohydrazines, Ar-NHNH₂, on the –NHNH₂ functional unit which is able to react with aldehydes, RCH(O) (R = alkyl, aryl, ferrocenyl (Fc)) and ketones, RR′CO (R = alkyl, aryl; R′ = alkyl, aryl, Fc), to afford ionic organometallic hydrazones. Likewise, the mixed-sandwich hydrazine precursors react with β-diketones Me–C(O)–CH₂–C(O)–Me to afford ionic organometallic pyrazoles, and with cis-dioxo-molybdenum complexes, e.g. [MoO₂(S₂CNEt₂)₂], to afford ionic organometallic mono-organodiazenido complexes in which the two metal centers are connected by a μ,η⁶:η¹-aryldiazenido bridge. While some ionic hydrazones exhibit NLO properties, the ionic organodiazenido hybrid complexes exhibit charge-transfer features.     

Reaction of isocyanides with iminophosphorane-based carbene ligands: Synthesis of unprecedented ketenimine–ruthenium complexes

The RuC bond of the bis(iminophosphorano)methandiide-based ruthenium(II) carbene complexes [Ru(η⁶-p-cymene)(κ²-C,N-C[P{NP(O)(OR)₂}Ph₂]₂)] (R = Et (1), Ph (2)) undergoes a C–C coupling process with isocyanides to afford ketenimine derivatives [Ru(η⁶-p-cymene)(κ³-C,C,N-C(CNR′)[P{NP(O)(OR)₂}Ph₂]₂)] (R = Et, R′ = Bz (3a), 2,6-C₆H₃Me₂ (3b), Cy (3c); R = Ph, R′ = Bz (4a), 2,6-C₆H₃Me₂ (4b), Cy (4c)). Compounds 3–4a–c represent the first examples of ketenimine–ruthenium complexes reported to date. Protonation of 3–4a with HBF₄ · Et₂O takes place selectively at the ketenimine nitrogen atom yielding the cationic derivatives [Ru(η⁶-p-cymene)(κ³-C,C,N-C(CNHBz)[P{NP(O)(OR)₂}Ph₂]₂)][BF₄] (R = Et (5a), Ph (6a)).     

Biotransformation of 3-azidomethyl-4-phenyl-3-buten-2-one and analogs by Saccharomyces cerevisiae: New evidence for an SN2′ mechanism

(Z)-3-XCH₂-4-(C₆H₅)-3-buten-2-one enones (X = SCN, N₃, SO₂Me, OC₆H₅) were synthesized and submitted to biotransformations using whole Saccharomyces cerevisiae cells. The enone (X = SCN) produced (R)-4-(phenyl)-3-methylbutan-2-one (R)-6 with 93% ee and enones (X = N₃, SO₂Me, OC₆H₅) yielded a mixture of (R)-6 and the corresponding CC bond reduction products. Biotransformation with enone (X = N₃) mediated by Saccharomyces cerevisiae resulted in two products via two different routes: (i) the ketone (R)-4-azido-3-benzylbutan-2-one in 28% yield and with >99% ee by CC bond reduction; (ii) ketone (R)-6 in 51% yield and with 95% ee via cascade reactions beginning with azido group displacement by the formal hydride from flavin mononucleotide in an S_N2′ type reaction followed by reduction of the newly formed CC bond.     

Double cyclometallation of bridging 3,6-bis(2-thienyl)-1,2,4,5-tetrazine in a dinuclear mesityl(dimethylsulfoxide)platinum(II) complex: Structure and properties

3,6-Bis(2-thienyl)-1,2,4,5-tetrazine (bttz) reacts with trans-Pt(dmso)₂(mes)₂, mes = mesityl = 2,4,6-trimethylphenyl, under twofold cyclometallation to yield structurally characterized (μ-bttz-2H⁺)[Pt(dmso)(mes)]₂ with uncoordinated thiophene sulfur atoms and bttz deprotonated in the 3,3′ positions. The structural features include cis-positioned carbanionic ligands, twisted mesityl substituents, S-coordinated dmso ligands with the SO bonds lying in the molecular plane, shortened inter-ring bonds, and rather short Pt–C bonds at 1.998(9)/2.00(1) Å (Pt–C_mes) and 1.985(9)/1.99(1) Å (Pt–C_bttz-2H+). Reversible reduction to {(μ-bttz-2H⁺)[Pt(dmso)(mes)]₂}^? causes a high-energy shift of the charge transfer bands and the appearance of an unresolved EPR signal at g = 1.9905.     

A general route for the stereoselective synthesis of (E)-(1-propenyl)phenyl esters by catalytic CC bond isomerization

A general and efficient procedure for the stereoselective synthesis of (E)-(1-propenyl)phenyl esters from readily accessible allylphenols has been developed. The process involves a two-step sequence consisting of the initial acylation of the allylphenols with an acid chloride, followed by catalytic CC bond isomerization in the resulting allylphenyl esters. The latter step was performed in methanol at 80 °C using catalytic amounts (0.5 mol %) of the commercially available bis(allyl)-ruthenium(IV) dimer [{RuCl(μ-Cl)(η³:η³-C₁₀H₁₆)}₂] (C₁₀H₁₆=2,7-dimethylocta-2,6-diene-1,8-diyl). Reactions proceeded in high yields (68–93%) and short times (4–9 h) with complete E-selectivity.     

Reactions of β-diketiminatoaluminum hydrides with tert-butyl hydrogenperoxide – Facile formation of dialuminoxanes containing Al–O–Al groups

Treatment of diphenyl-β-diketiminatoaluminum dihydride, LAlH₂ [1, L = {H₅C₆–NC(Me)}₂CH] with neopentyl- or trimethylsilylmethyllithium afforded the corresponding alkylderivatives LAlH(R) [R = CH₂–SiMe₃ (2), CH₂–CMe₃ (3)] by the precipitation of lithium hydride. Deprotonation of a methyl group instead of salt elimination occurred by the similar reaction of the more basic alkyllithium compound LiC(SiMe₃)₃. The reactions of the hydrides 1–3 with tert-butyl hydrogenperoxide did not yield the expected peroxo derivatives, instead the dialuminoxanes LAl(R)–O–Al(R)L [R = OCMe₃ (5), CH₂SiMe₃ (6), CH₂CMe₃ (7)] were isolated in high yields. Their Al–O–Al bridges deviated from linearity and had Al–O–Al bond angles of about 155° on average.