A novel method for the synthesis of (Z)-α-selenyl-α,β-unsaturated ketones via acylation of (E)-α-selanylvinylstannanes

The (E)-α-selenylvinylstannanes react with acyl halides in presence of a catalytic amount of Pd(PPh₃)₄ to give the corresponding (Z)-α-selenyl-α,β-unsaturated ketones in good yield.     

The synthesis, structure and reactivity of aldehyde substituted η-allylic complexes of molybdenum

Reaction of cis-[Mo(NCMe)₂(CO)₂(η⁵-L)][BF₄] (L=C₅H₅ or C₅Me₅) with 1-acetoxybuta-1,3-diene gives the cationic complexes [Mo{η⁴-syn-s-cis-CH₂CHCHCH(OAc)}(CO)₂(η⁵-L)][BF₄], which, on reaction with aqueous NaHCO₃/CH₂Cl₂, afford good yields of the anti-aldehyde substituted complexes [Mo{η³-exo-anti-CH₂CHCH(CHO)}(CO)₂(η⁵-L)] 2 (L=C₅Me₅), 4 (L=C₅H₅)]. The corresponding η⁵-indenyl substituted complex 5 was prepared by protonation (HBF₄·OEt₂) of [Mo(η³-C₃H₅)(CO)₂(η⁵-C₉H₇)] followed by addition of CH₂=CHCH=CH(OAc) and hydrolysis (aq. NaHCO₃/CH₂Cl₂). An X-ray crystallographic study of complex 2 confirmed the structure and showed that there is a contribution from a zwitterionic form involving donation of electron density from the molybdenum to the aldehyde carbonyl group. Treatment of 2 and 4, in methanol solution, with NaBH₄ afforded the alcohols [Mo{η³-exo-anti-CH₂CHCHCH₂(OH)}(CO)₂(η⁵-L)] [6 (L=C₅H₅), 8 (L=C₅Me₅)]; however, prolonged (30 h) reaction with NaBH₄/MeOH surprisingly gave good yields of the methoxy-substituted complexes [Mo{η³-exo-anti-CH₂CHCHCH₂(OMe)}(CO)₂(η⁵-L)] [7 (L=C₅H₅), 9 (L=C₅Me₅)], the structure of 7 being confirmed by single crystal X-ray crystallography. This methoxylation reaction can be explained by coordination of the hydroxyl group present in 6 and 8 onto B₂H₆ to form the potential leaving group HOBH₃⁻, which on ionisation affords [Mo(η⁴-exo-buta-1-3-diene)(CO)₂(η⁵-L)]⁺ which is captured by reaction with OMe⁻. Complex 8 is also formed in good yield on reaction of 2 with HBF₄·OEt₂ followed by treatment of the resulting cation [Mo{η⁴-exo-s-cis-syn-CH₂CHCHCH(OH)}(CO)₂(η⁵-C₅Me₅)][BF₄] with Na[BH₃CN]. Reaction of 4 with the Grignard reagents MeMgI, EtMgBr or PhMgCl afforded moderate yields of the alcohols [Mo{η³-exo-anti-CH₂CHCHCH(OH)R}(CO)₂(η⁵-C₅H₅)] [11 (R=Me), 12 (R=Et), 13 (R=Ph)]. Similarly, treatment of 2 with MeLi gave the corresponding alcohol 14. An attempt to carry out the Oppenauer oxidation [Al(OPr′)₃/Me₂CO] of 11 resulted in an elimination reaction and the formation of the η³-s-pentadienyl complex [Mo{η³-exo-anti-CH₂CHCH(CHCH₂)}(CO)₂(η⁵-C₅H₅)], which was structurally identified by X-ray crystallography. Interestingly, oxidation of 6 with [Bu₄ⁿN][RuO₄]/morpholine-N-oxide affords the aldehyde complex, 4 in good yield. Finally, reaction of 11 with [NO][BF₄] followed by addition of Na₂CO₃ affords the fur-3-ene complex [Mo{η²-

(H)Me}(CO)(NO)(η⁵-C₅H₅)].     

Die Kristallstruktur von TlFe3Te3

TlFe₃Te₃ is hexagonal, space groupP6₃/m–C _2h ⁶ ,a=9.350(2) Å,c=4.2230 (7) Å,Z=2. Iron and tellurium atoms occupy the positions 6 (h) withx=0.170,y=0.149 andx=0.046,y=0.357 respectively. Thallium atoms are situated in 2 (d). The structure was determined on the basis of single crystal data obtained form a four circle diffractometer. Refinement yielded andR-value of 4.8% for an asymmetric set of 267 reflections. TlFe₃Te₃ is a new structure type. The structure and its relations to the Mn₅Si_3–, the Nb₃Te₄-and the Tl _x V₆S₈-type are discussed.

     

η- and η-benzene coordination in [Ag(C6D6)3BF4]

The title complex with one η² and two η¹ deuterobenzene and one monodentate BF₄ ligands was isolated as a by-product in the reaction between [(dppe)RhCl]₂ and EtCl in C₆D₆, in the presence of AgBF₄ and its X-ray crystal structure determined.     

Properties of the perovskites, SrMn1−xFexO3−δ (x=1/3, 1/2, 2/3)

The SrMn_1−xFe_xO_3−δ (x=1/3, 1/2, 2/3) phases have been prepared and are shown by powder X-ray and neutron (for x=1/2) diffraction to adopt an ideal cubic perovskite structure with a disordered distribution of transition-metal cations over the six-coordinate B-site. Due to synthesis in air, the phases are oxygen deficient and formally contain both Fe³⁺ and Fe⁴⁺. Magnetic susceptibility data show an antiferromagnetic transition at 180 and 140 K for x=1/3 and 1/2, respectively and a spin-glass transition at 5, 25, 45 K for x=1/3, 1/2 and 2/3, respectively. The magnetic properties are explained in terms of super-exchange interactions between Mn⁴⁺, Fe^(4+δ)+ and Fe⁽³⁺⁾⁺. The XAS results for the Mn-sites in these compounds indicate small Mn-valence changes, however, the Mn-pre-edge spectra indicate increased localization of the Mn-e_g orbitals with Fe substitution. The Mössbauer results show the distinct two-site Fe⁽³⁺⁾+/Fe^(4+δ)+ disproportionation in the Mn- substituted materials with strong covalency effects at both sites. This disproportionation is a very concrete reflection of a localization of the Fe-d states due to the Mn-substitution.     

Synthesis and some properties of 6-di(tri)fluoromethyl-and 5-di(tri)fluoroacetyl-3-methyl-1-phenylpyrano[2,3-<Emphasis Type="Italic">c</Emphasis>]pyrazol-4(1<Emphasis Type="Italic">H</Emphasis>)-ones

Condensation of 4-acetyl-5-hydroxy-3-methyl-1-phenylpyrazole with R^FCO₂Et (R^F = CF₂H, CF₃) in the presence of LiH affords 4-di(tri)fluoroacetoacetyl-5-hydroxy-3-methyl-1-phenylpyrazoles from which 6-di(tri)fluoromethyl-and 5-di(tri)fluoroacetyl-3-methyl-1-phenylpyrano[2,3-c]pyrazol-4(1H)-ones were synthesized. The reactions of pyrano-pyrazoles with hydrazine hydrate, ethyl mercaptoacetate, or aromatic amines proceed at the C(6) atom with pyrone ring opening and formation of aminoenones, pyrazoles, or thiophenes with the 5-hydroxy-3-methyl-1-phenyl-4-pyrazolyl fragment. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2750–2754, December, 2005.     

Effect of External Pressure on the Excitation Energy Transfer from [Cr(ox)3]3− to [Cr(bpy)3]3+ in [Rh1−xCrx(bpy)3][NaM1−yCry(ox)3]ClO4

Resonant excitation energy transfer from [Cr(ox)₃]^3? to [Cr(bpy)₃]³⁺ in the doped 3D oxalate networks [Rh_1?xCr_x(bpy)₃][NaM^III_1?yCr_y(ox)₃]ClO₄ (ox=C₂O₄^?, bpy=2,2′‐bipyridine, M=Al, Rh) is due to two types of interaction, namely super exchange coupling and electric dipole–dipole interaction. The energy transfer probability for both mechanisms is proportional to the spectral overlap of the ²E→⁴A₂ emission of the [Cr(ox)₃]^3? donor and the ⁴A₂→²T₁ absorption of the [Cr(bpy)₃]³⁺ acceptor. The spin‐flip transitions of (pseudo‐)octahedral Cr³⁺ are known to shift to lower energy with increasing pressure. Because the shift rates of the two transitions in question differ, the spectral overlap between the donor emission and the acceptor absorption is a function of applied pressure. For [Rh_1?xCr_x(bpy)₃][NaM_1?yCr_y(ox)₃]ClO₄ the spectral overlap is thus substantially reduced on increasing pressure from 0 to 2.5 GPa. As a result, the energy transfer probability decreases with increasing pressure as evidenced by a decrease in the relative emission intensity from the [Cr(bpy)₃]³⁺ acceptor.     

Synthesis of 4<Emphasis Type="Italic">H</Emphasis>-imidazole-5-carbaldoxime 3-oxides and 4<Emphasis Type="Italic">H</Emphasis>-imidazole-5-carbonitrile 3-oxides

The condensation of 3-hydroxyamino-3-methylbutan-2-one or 3-ethyl-3-hydroxyamino-pentan-2-one with aldehydes and ammonia afforded a series of new 1-hydroxy-4-methyl-2,5-dihydroimidazoles, whose oxidation gave rise to the corresponding 5-methyl-4H-imidazole 3-oxides. The latter, like 1-hydroxy-4-methyl-2,5-dihydroimidazoles, react with PrⁱONO in the presence of bases to form 4H-imidazole-5-carbaldoxime 3-oxides, which are transformed into 4H-imidazole-5-carbonitrile 3-oxides in the reaction with TsCl in the presence of Et₃N. The by-products produced in different steps of the synthesis were isolated and characterized. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1487–1503, July, 2008.     

New results in the ammonolysis of hexafluoro-cyclo-triphosphazene: Crystal structure of P3N3F5–NH–P3N3F4NH2

The reaction of hexafluoro-cyclo-triphosphazene P₃N₃F₆ with ammonia in acetonitrile has been studied. New compounds, (2-imino-2,4,4,6,6-pentafluoro-2λ⁵,4λ⁵,6λ⁵-cyclo-triphosphaza-1,3,5-trienyl)-2-amino-4,4,6,6-tetrafluoro-2λ⁵,4λ⁵,6λ⁵-cyclo-triphosphaza-1,3,5-triene, P₃N₃F₅–NH–P₃N₃F₄NH₂ (2) and cis and trans isomers of non-gem-2,4-diamino-2,4,6,6-tetrafluoro-2λ⁵,4λ⁵,6λ⁵-cyclo-triphosphaza-1,3,5-triene, P₃N₃F₄(NH₂)₂ (4, 5)_, were detected by GC/MS, and ³¹P NMR spectroscopy in reaction mixtures. X-ray diffraction analysis of P₃N₃F₅–NH–P₃N₃F₄NH₂ (2) revealed two conformational polymorphs, 2A and 2B, the latter being built up of two different conformers that were further denoted as 2B_a (the same as the single conformer in 2A) and 2B_b. The compound 2 was characterized by spectroscopic methods and its 2D potential energy surface (PES) was described by density functional theory computations depending on two dihedral angles. The calculated PES spans over 30 kJ/mol in energy including 8 local minima and all first and second order saddle points. The occurrence of the two experimentally observed conformers 2B_a and 2B_b seems to be governed by crystal packing effects.     

Macroscopic and spectroscopic characterization of selenate, selenite, and chromate adsorption at the solid–water interface of γ-Al2O3

The interaction of selenate, selenite, and chromate with the hydrated surface of γ-Al₂O₃ was studied using a combination of macroscopic pH edge data, electrophoretic mobility measurements, and X-ray absorption spectroscopic analyses. The pH edge data show generally increased oxyanion adsorption with decreasing pH, and indicate ionic strength-(in)dependent adsorption of chromate and selenate across the pH range 4–9, and ionic strength-(in)dependent adsorption of selenite in this pH range. The adsorption of chromate peaks at pH 5.0, whereas for selenate and selenite no pH adsorption maxima are observed. Electrophoretic mobility measurements show that all three oxyanions decrease the zeta potential of γ-Al₂O₃ upon adsorption; however, only selenite decreased the pH_PZC of the γ-Al₂O₃ sorbent. EXAFS data indicate that selenite ions are coordinated in a bridging bidentate fashion to surface AlO₆ octahedra, whereas no second-neighbor Al scattering was observed for adsorbed selenate ions. Combined, the results presented here show that pH is a major factor in determining the extent of adsorption of selenate, selenite, and chromate on hydrated γ-Al₂O₃. The results point to substantial differences between these anions as to the mode of adsorption at the hydrated γ-Al₂O₃ surface, with selenate adsorbing as nonprotonated outer-sphere complexes, chromate forming a mixture of monoprotonated and nonprotonated outer-sphere adsorption complexes, and selenite coordinating as inner-sphere surface complexes in bridging configuration.     

Synthesis of Bis‐Heterocyclic 1H‐Imidazole 3‐Oxides from 3‐Oxido‐1H‐imidazole‐4‐carbohydrazides

The reaction of 1H‐imidazole‐4‐carbohydrazides 1 , which are conveniently accessible by treatment of the corresponding esters with NH₂NH₂?H₂O, with isothiocyanates in refluxing EtOH led to thiosemicarbazides (=hydrazinecarbothioamides) 4 in high yields (Scheme 2). Whereas 4 in boiling aqueous NaOH yielded 2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thiones 5 , the reaction in concentrated H₂SO₄ at room temperature gave 1,3,4‐thiadiazol‐2‐amines 6 . Similarly, the reaction of 1 with butyl isocyanate led to semicarbazides 7 , which, under basic conditions, undergo cyclization to give 2,4‐dihydro‐3H‐1,2,4‐triazol‐3‐ones 8 (Scheme 3). Treatment of 1 with Ac₂O yielded the diacylhydrazine derivatives 9 exclusively, and the alternative isomerization of 1 to imidazol‐2‐ones was not observed (Scheme 4). It is important to note that, in all these transformations, the imidazole N‐oxide residue is retained. Furthermore, it was shown that imidazole N‐oxides bearing a 1,2,4‐triazole‐3‐thione or 1,3,4‐thiadiazol‐2‐amine moiety undergo the S‐transfer reaction to give bis‐heterocyclic 1H‐imidazole‐2‐thiones 11 by treatment with 2,2,4,4‐tetramethylcyclobutane‐1,3‐dithione (Scheme 5).     

O-Tosylaminobenzaldehyde aminals in the synthesis of 1,3-disubstituted propargylamines,derivatives of 3H-2-vinylidene-3-aminoindoline and quinoline

o-Tosylaminobenzaldehyde aminals react with propargyl alcohol and its phenyl ether on heating in acetonitrile in the presence of CuI to yield 3H-2-vinylidene-3-aminoindoline derivatives. Analogous reactions with phenylacetylene and dimethylethynylcarbinol result in 1,3-disubstituted propargylamines. The possibility of using the latter compounds in synthesis of quinoline derivatives was shown: cyclization of 1-(o-tosylaminophenyl)-1-morpholino-3-phenylprop-2-yne in the presence of H₂SO₄ and KOH gave 2-phenylquinoline and 2-phenyl-4-morpholinoquinoline, respectively. 3H-2-Phenoxymethylvinylidene-3-morpholinoindoline was studied by X-ray diffraction spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2236–2240, November. 1995.     

Reactions of nickelocene with lithium and magnesium alkyls containing β-hydrogen atoms

The reaction of nickelocene with BrMgR, where R=CH₂CH(CH₃)C₆H₅, C₂H₅, (CH₂)₇CH₃ and CH₂CH₂CH₃, have been studied. It was found that the presence of β-hydrogen in R did not cause the total splitting of the carbon–nickel bond but alkylidynetrinickel clusters were formed. It is the first example of the synthesis of alkylidynetrinickel clusters (NiCp)₃CR′ from the organonickel species possessing β-hydrogen. Besides trinickel clusters, the following compounds were always formed in all the studied reactions: (NiCp)₄H₂, (NiCp)₆, CpNi(η³-C₅H₇) and (NiCp)₂(μ-C₅H₆). The structure of (NiCp)₃CCH(CH₃)Ph has been determined by a single-crystal X-ray diffraction study.     

Synthesis and ac susceptibility of YCa2Cu3O7−δ

The bulk superconducting YCa₂Cu₃O_7−δ compounds are prepared at an ordinary pressure of oxygen by conventional solid-state reaction method. The formation of sample is tested by means of XRD and is studied for their ac susceptibility below room temperature up to 77.5 K. The samples are found single-phase orthorhombic structure and found superconducting at 83.5 K. It is shown that the analysis is consistent with published data on YBa₂Cu₃O_7−δ oxide superconductor.     

Preparation, characterization and the standard enthalpy of formation of La0.95MnO3+δ and Sm0.95MnO3+δ

Among the perovskites, the rare earth manganites find application in several electrochemical devices because of their enhanced thermodynamic stability. In this paper, we present the results obtained on the preparation and characterization of La_0.95MnO_3+δ and Sm_0.95MnO_3+δ which were prepared by the solid state and sol–gel methods. XRD characterization of the manganites indicated that the crystal structure depends on the method of preparation and heat treatments. The ratio of Mn³⁺ to Mn⁴⁺ in these samples also depended on the method of preparation and heat treatments, as indicated by thermogravimetric (TG) and temperature programmed reduction (TPR) studies in Ar + 5% H₂ atmosphere. The standard molar enthalpy of formation, which is a measure of the thermodynamic stability of these compounds were determined using an isoperibol calorimeter.     

Orthorhombic–orthorhombic phase transitions in Nd2NiO4+δ (0.067≤δ≤0.224)

Variation of the phases of Nd₂NiO_4+δ with the excess oxygen concentration δ has been examined at room temperature in the range 0.067≤δ≤0.224 using the X-ray powder diffraction technique. The phases observed at room temperature are orthorhombic-I (0.21<δ≤0.224), orthorhombic-IV (0.175<δ≤0.21), orthorhombic-II (0.15<δ≤0.175), orthorhombic-II+quasi-tetragonal-I (0.10<δ≤0.15), and quasi-tetragonal-I (0.067<δ≤0.10).     

Continuous Dehydrogenation of n‐Pentanol over a Cr Modified Cu/γ‐Al2O3‐La2O3 Catalyst

The oxidant‐free dehydrogenation of n‐pentanol over copper based catalysts was investigated in this paper. The effect of metal modification on the activity and stability of the copper catalyst supported on γ‐Al₂O₃ and La₂O₃ (Cu/γ‐Al₂O₃‐La₂O₃) was clarified and a Cr modified Cu/Al₂O₃‐La₂O₃ (Cu‐Cr/γ‐Al₂O₃‐La₂O₃) showed the best catalytic performance. The conversion of n‐pentanol was 70.0% and the selectivity for n‐pentanal increased to 97.1% over Cu‐Cr/γ‐Al₂O₃‐La₂O₃. X‐ray diffraction and temperature programmed reduction of H₂ indicated that the addition of Cr favors the formation and reduction of the copper oxide, and the dispersion of the active Cu⁰ species, accounting for the good activity and stability of this catalyst. Furthermore, the lower amount of acidic sites in Cu‐Cr/γ‐Al₂O₃‐La₂O₃ is suggested to suppress the dehydration in oxidant‐free dehydrogenation of n‐pentanol, accounting for the higher selectivity for n‐pentanal.     

Synthesis, Structure, and Physical Studies of the New β-LiVOAsO4 Compound

Two new compounds of the A_xMOXO₄ family, β-LiVOAsO₄ and β-VOAsO₄, have been synthesized by solid state reaction and electrochemical lithium deintercalation from β-LiVOAsO₄, respectively. Both compounds are isostructural and are built like other β-VOXO₄ (X=S, P) by (VO₅)_∞ chains of distorted VO₆ octahedra connected via corner-shared AsO₄ tetrahedra. For β-LiVOAsO₄ the additional Li⁺ ions occupy chains of edge-shared octahedra running perpendicularly to the (VO₅)_∞ chains. The one-dimensional antiferromagnetic behavior suggested by the structure has been experimentaly confirmed. It is shown that lithium deintercalation occurs through a first-order transition at 4.02 V vs Li⁺/Li⁰. From chemical bond considerations it is shown why the redox potential of a given transition element M in a six-fold coordination involving (M=O)^m+ units lies between those observed in oxides and in M₂(XO₄)₃ compounds with (XO₄)ⁿ⁻ oxo anions (X=S, P, As).     

Transition‐Metal π‐Ligation of a Tetrahalodiborane

The reaction of tetraiododiborane (B₂I₄) with trans‐[Pt(BI₂)I(PCy₃)₂] gives rise to the diplatinum(II) complex [{(Cy₃P)(I₂B)Pt}₂(μ₂:η³:η³‐B₂I₄)], which is supported by a bridging diboranyl dianion ligand [B₂I₄]^2?. This complex is the first transition‐metal complex of a diboranyl dianion, as well as the first example of intact coordination of a B₂X₄ (X=halide) unit of any type to a metal center.     

Synthesis and Characterization of β‐Diketiminate Aluminum Compounds and Their Use in the Ring‐Opening Polymerization of ε‐Caprolactone

Four aluminum alkyl compounds, [CH{(CH₃)CN‐2,4,6‐MeC₆H₂}₂AlMe₂] ( 1 ), [CH{(CH₃)CN‐2,4,6‐MeC₆H₂}₂AlEt₂] ( 2 ), [CH{(CH₃)CN‐2‐iPrC₆H₄}₂AlMe₂] ( 3 ), and [CH{(CH₃)CN‐2‐iPrC₆H₄}₂AlEt₂] ( 4 ), bearing β‐diketiminate ligands [CH{(Me)CN‐2,4,6‐MeC₆H₂}]₂ (L¹H) and [CH{(Me)CN‐2‐ⁱPrC₆H₄}]₂ (L²H) were obtained from the reactions of trimethylaluminum, triethylaluminum with the corresponding β‐diketiminate, respectively. All compounds were characterized by ¹H NMR and ¹³C NMR spectroscopy, single‐crystal X‐ray structural analysis, and elemental analysis. Compounds 1 – 4 were found to catalyze the ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) with good activity.