Intramolecular rearrangements of β-diketonates of metals. A non-emprical study of the structure of Y(MDA)<Subscript>3</Subscript> and La(MDA)<Subscript>3</Subscript> complexes

The structure of tris-complexes of yttrium and lanthanum with malonic dialdehyde (MDA = C₃O₂H₃) is studied by a non-empirical Hartree-Fock method and also with taking into account the electron correlation by the second order Möller-Plesset perturbation theory using the effective pseudo-potentials to describe the atomic cores and two-exponent valence basis sets supplemented with polarization functions. Three most probable geometrical configurations of the D ₃, D _3h , and C ₂ nuclei symmetry are considered for each molecule. The D ₃ structure corresponds to the minimum on the potential energy surface. The D _3h and C _2v configurations correspond to the transition states on the path of two most energetically favorable intramolecular rearrangements. Using the results of our previous calculations for the Sc(MDA)₃ molecule, regularities in the change in molecular parameter values of the series Sc(MDA)₃→Y(MDA)₃→La(MDA)₃ are analyzed. The theoretical and experimental structural and spectral data available in the literature are compared.     

Synthesis of (diarylmethyl)amines using Ni-catalyzed arylation of C(sp3)–H bonds

The first nickel catalyzed deprotonative cross coupling between C(sp³)–H bonds and aryl chlorides is reported, allowing the challenging arylation of benzylimines in the absence of directing group or stoichiometric metal activation. This methodology represents a convenient access to the (diarylmethyl)amine moiety, which is widespread in pharmaceutically relevant compounds.     

Synthesis of (±)-cis-Calamenene;

Hydroboration of 4 furnishes a mixture of primary alcohols 5 and 6. The stereochemistry of the crystalline half ester 7 has been established by X-ray studies. While the oxidation of 5 with Jones reagent furnishes the aldehyde 9 in low yield due to the formation of the by product 3, oxidation with Moffatt reagent furnishes the aldehyde 9 in satisfactory yields. cis-Calamenene 1 has been prepared from 9.     

De-protonation of (η4-isoprene)Fe(CO)3; an isoprene anion equivalent

(η⁴-Isoprene)Fe(CO)₃ can be deprotonated with lithium diisopropylamide. The resulting coordinated isoprene anion reacts with electrophiles at low temperature, but rearranges to an isomeric (η⁴-trimethylenemethane)Fe(CO)₃ anion derivative at higher temperatures.     

Electrochemical illumination of intramolecular communication in ferrocene-containing tris-β-diketonato aluminum(III) complexes; cytotoxicity of Al(FcCOCHCOCF3)3

The series of ferrocene-containing tris-β-diketonato aluminum(III) complexes [Al(FcCOCHCOR)(3)] (R = CF(3), 1; CH(3), 2; C(6)H(5), 3; and Fc = ferrocenyl = Fe(η(5)-C(5)H(5))(η(5)-C(5)H(4)), 4) were synthesized and investigated structurally and electrochemically; complex 1 was subjected to cytotoxicity tests. (1)H NMR-spectroscopy distinguished between the mer and fac isomers of 2 and 3. Complex 1 existed only as the mer isomer. A single crystal X-ray crystallographic determination of the structure of a mer-isomer of Al(FcCOCHCOCF(3))(3), 1, (Z = 4, space group P2(1)2(1)2(1)) demonstrated extensive delocalization of all bonds which explained the pronounced electrochemically observed intramolecular communication between molecular fragments. In contrast to electrochemical studies in CH(2)Cl(2)/[N((n)Bu)(4)][PF(6)], the use of the supporting electrolyte [N((n)Bu)(4)][B(C(6)F(5))(4)] allowed identification of all Fc/Fc(+) electrochemical couples by cyclic and square wave voltammetry for 1-4. For R = Fc, formal reduction potentials of the six ferrocenyl groups were found to be E°' = 33, 123, 304, 432, 583, and 741 mV versus free ferrocene respectively. Complex 1 (IC(50) = 10.6 μmol dm(-3)) was less cytotoxic than the free FcCOCH(2)COCF(3) ligand having IC(50) = 6.8 μmol dm(-3) and approximately 2 orders of magnitude less toxic to human HeLa neoplastic cells than cisplatin (IC(50) = 0.19 μmol dm(-3)).     

Fabrication of multilayer ceramic structure for fuel cell based on La(Sr)Ga(Mg)O<Subscript>3</Subscript>–La(Sr)Fe(Ga)O<Subscript>3</Subscript> cathode

Fabrication by co-sintering method of a multilayer pore-free electrode–electrolyte structure promising for use in solid-oxide fuel cell and its characteristics have been studied. A material with high ionic conductivity of La_0.88Sr_0.12Ga_0.82Mg_0.18O_3–δ (LSGM) served as electrolyte. The composite electrode was formed from a 1: 2 mixture of LSGM and LSFG (La_0.7Sr_0.3Fe_0.95Ga_0.05O_3–δ). The maximum temperature of the materials co-sintering ability is 1250°C. It was shown by the impedance spectroscopy that the polarization resistance of the LSGM–LSFG electrode is 0.14 Ω cm² at 800°C.     

Synthesis of solvates of the copper(II) complex with chiral caryophyllane-type morpholino oxime (HL). Structure of Cu(HL)Cl<Subscript>2</Subscript> · CHCl<Subscript>3</Subscript>

Paramagnetic Cu(HL)Cl₂ · 0.25CHCl₃ (I) and Cu(HL)C1₂ · 0.25CH₂C1₂ (II), where HL is the optically active morpholino oxime obtained from the terpenoid caryophyllene, were synthesized. The crystals of Cu(HL)Cl₂ · CHCl₃ (III) were isolated. According to X-ray diffraction data, the crystals of III are composed of acentric mononuclear complex molecules Cu(HL)Cl₂ and solvate molecules CHCl₃. In the complex molecules, the Cu ion coordinates two N atoms of the bidentate chelating ligand HL and two C1 atoms at the vertices of a distorted tetrahedron. The translationally identical molecules of the complex combined by H-bonds form chains along the axis x.     

Thermal Stability of newberyite Mg(PO<Subscript>3</Subscript>OH)·3H<Subscript>2</Subscript>O

The mineral newberyite Mg(PO₃OH)·3H₂O is a mineral that has been found in caves such as the Skipton Lava Tubes (SW of Ballarat, Victoria, Australia), Moorba Cave, (Jurien Bay, Western Australia) and in the Petrogale Cave (Madura, Eucla, Western Australia). Since these minerals contain water, the minerals lend themselves to thermal analysis. The mineral newberyite is found to decompose at 145 °C with a water loss of 31.96%, a result which is very close to the theoretical value. The result shows that the mineral is not stable in caves where the temperature exceeds this value. The implication of this result rests with the removal of kidney stones, which have the same composition as newberyite. Point heating focussing on the kidney stone results in the destruction of the kidney stone.     

Oxidation of Fe(III) to Fe(VI) by the Fe(CN)<Stack><Subscript>6</Subscript><Superscript>3−</Superscript></Stack> ion in strong solution of alkalis

Ferricyanide ions oxidize Fe(III) up to Fe(VI) in 7–11 M KOH solutions and 10–16 M NaOH solutions. The completeness of the oxidation increases with increasing alkali and ferricyanide concentrations. The presence of KNO₂, KAc, and K₂C₂O₄ in 7 M KOH solution increases the Fe(VI) yield. Potassium fluoride in the concentration of 0.02 M does not hinder Fe(VI) formation, but in the concentration of 0.1 M completely suppresses Fe(III) oxidation. The attempt to oxidize Fe(VI) up to Fe(VIII) by the disproportionation of Fe(VI) or by the action of Fe(CN)₆³⁻ and ozone was unsuccessful due to a high oxidation potential of the Fe(VIII)/(VI) couple.     

Bis(4‐picoline‐κN)gold(I) dibromidoaurate(I) and bis(4‐picoline‐κN)gold(I) dichloridoaurate(I): space‐group ambiguity?

Bis(4‐picoline‐κN)gold(I) dibromidoaurate(I), [Au(C₆H₇N)₂][AuBr₂], (I), crystallizes in the monoclinic space group P2₁/n, with two half cations and one general anion in the asymmetric unit. The cations, located on centres of inversion, assemble to form chains parallel to the a axis, but there are no significant contacts between the cations. Cohesion is provided by flanking anions, which are connected to the cations by short Au...Au contacts and C—H...Br hydrogen bonds, and to each other by Br...Br contacts. The corresponding chloride derivative, [Au(C₆H₇N)₂][AuCl₂], (II), is isotypic. A previous structure determination of (II), reported in the space group P with very similar axis lengths to those of (I) [Lin et al. (2008). Inorg. Chem. 47 , 2543–2551], might be identical to the structure presented here, except that its γ angle of 88.79 (7)° seems to rule out a monoclinic cell. No phase transformation of (II) could be detected on the basis of data sets recorded at 100, 200 and 295 K.     

On the kinetics and thermodynamics of S–X (X = H,CH<Subscript>3</Subscript>, SCH<Subscript>3</Subscript>, COCH<Subscript>3</Subscript>, and CN) cleavage in the formation of self-assembled monolayers of alkylthiols on Au(111)

Abounding potential technological applications is one of the many reasons why adsorption of aliphatic thiols on gold surface is a subject of intense research by many research groups. Understanding and exploring the nature of adsorbed species, the site of adsorption and the nature of interaction between adsorbed species and the gold surface using experimental and theoretical investigations is an active area of pursuit. However, despite a large number of investigations to understand the atomistic structures of thiols on Au(111), some of the basic issues are still unaddressed. For instance, there is still no clear information about the mechanism of adsorption of alkylthiol on gold surface. Furthermore, the reactivity and mechanism of adsorption of alkylthiol is likely to differ when gold adatoms and/or vacancies in the gold layers are considered. In this work, we have tackled these issues by computing the stationary states involved in the thiols adsorption in order to shed light on the kinetics aspects of adsorption process. In this respect, we have considered a variety of thiols into consideration such as methylthiol, dimethylsulfide, dimethyldisulfide, thioacetates, and thiocyanates. We have also considered the cleavage mechanism in the clean and the reconstructed surface scenario and the structure, energetics and spin densities have been computed using electronic structure calculations. For all the studied cases, an homolytic cleavage of CH₃S–X (X = H, CH₃, SCH₃, CN, and COCH₃) bond has been found to occur upon adsorption on the gold surface.     

Transport and Electrochemical Properties of SrFe(Al,Mo)O<Subscript>3–δ</Subscript>

In this work, effects of molybdenum doping on the crystal structure, stability, electrical conductivity, oxygen permeability and thermomechanical properties of Sr(Fe,Al)O_3–δ-based perovskites, were studied. The electrochemical performance of model anodes of solid oxide fuel cells (SOFCs), made of SrFe_0.7Mo_0.3O_3–δ, was assessed. Whilst the introduction of Mo cations improves structural stability with respect to the oxygen vacancy ordering processes, excessive molybdenum content leads to a worse phase and mechanical stability under oxidizing conditions. Mo-doping was shown to decrease the thermal and chemical expansivity, to reduce p-type electronic conductivity and to increase n-type electronic conduction. The oxygen permeation fluxes through gas-tight Sr_0.97Fe_0.75Al_0.2Mo_0.05O_3–δ membranes are determined by both the bulk oxygen diffusion and surface exchange kinetics. The role of the latter factor increases on decreasing temperature and reducing oxygen partial pressure. Due to a relatively high electrical conductivity and moderate thermal expansion coefficients in reducing conditions, SrFe_0.7Mo_0.3O_3–δ-based anodes show a substantially high electrochemical activity.     

Effect of P-Containing Ligands on the Structural and Optical Properties of (CdSe)<Subscript>n</Subscript> (n = 3, 6, 10) Clusters

The effect of phosphorus-containing ligands on the structure, energetics and properties of the (CdSe)_n clusters (n = 3, 6, and 10) with different number of PH₃ and PMe₃ ligands were studied by using density functional theory calculations. The P atom in the ligand interacts with Cd and forms a strong Cd–P coordination bond. The introduction of ligands does not change the cluster architecture, but leads to considerable changes in Cd–Se bondlength, charge distribution, binding energy, HOMO–LUMO gap and optical absorption. The ligand influence is enhanced with increasing ligand coverage. A blueshift in absorption band was predicted for the clusters with increasing ligands, resulting from the electron donating characteristics of the ligands that hamper electron transition from Se to Cd. As P-containing ligands are often used in the preparation of CdSe nanocrystals, our calculations reveal the influence of ligand-cluster interaction on the cluster geometrical and electronic properties, which would be helpful for the nanocrystal design and synthesis.     

Formation of Trinuclear Rhodium‐Hydride Complexes [{Rh(PP*)H}3‐ (μ2‐H)3(μ3‐H)][anion]2—During Asymmetric Hydrogenation?

Recently described and fully characterized trinuclear rhodium‐hydride complexes [{Rh(PP*)H}₃(μ₂‐H)₃(μ₃‐H)][anion]₂ have been investigated with respect to their formation and role under the conditions of asymmetric hydrogenation. Catalyst–substrate complexes with mac (methyl (Z)‐ N‐acetylaminocinnamate) ([Rh(tBu‐BisP*)(mac)]BF₄, [Rh(Tangphos)(mac)]BF₄, [Rh(Me‐BPE)(mac)]BF₄, [Rh(DCPE)(mac)]BF₄, [Rh(DCPB)(mac)]BF₄), as well as rhodium‐hydride species, both mono‐([Rh(Tangphos)‐ H₂(MeOH)₂]BF₄, [Rh(Me‐BPE)H₂(MeOH)₂]BF₄), and dinuclear ([{Rh(DCPE)H}₂(μ₂‐H)₃]BF₄, [{Rh(DCPB)H}₂(μ₂‐H)₃]BF₄), are described. A plausible reaction sequence for the formation of the trinuclear rhodium‐hydride complexes is discussed. Evidence is provided that the presence of multinuclear rhodium‐hydride complexes should be taken into account when discussing the mechanism of rhodium‐promoted asymmetric hydrogenation.     

Reduction of Oxide Mixtures of (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + CuO) and (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) by Low-Temperature Hydrogen Plasma

The paper presents experimental results pertaining to the reduction of oxide mixtures namely (Fe₂O₃ + CuO) and (Fe₂O₃ + Co₃O₄), by low-temperature hydrogen plasma in a microwave hydrogen plasma set-up, at microwave power 750 W and hydrogen flow rate 2.5 × 10^?6 m³ s^?1. The objective was to examine the effect of addition of CuO or Co₃O₄, on the reduction of Fe₂O₃. In the case of the Fe₂O₃ and CuO mixture, oxides were reduced to form Fe and Cu metals. Enhancement of reduction of iron oxide was marginal. However, in the case of the Fe₂O₃ and Co₃O₄ mixture, FeCo alloy was formed within compositions of Fe₇₀Co₃₀, to Fe₃₀Co₇₀. Since the temperature was below 841 K, no FeO formed during reduction and the sequence of Fe₂O₃ reduction was found to be Fe₂O₃ → Fe₃O₄ → Fe. Reduction of Co₃O₄ preceded that of Fe₂O₃. In the beginning, the reduction of oxides led to the formation of Fe–Co alloy that was rich in Co. Later Fe continued to enter into the alloy phase through diffusion and homogenization. The lattice strain of the alloy as a function of its composition was measured. In the oxide mixture in which excessive amount of Co₃O₄ was present, all the Co formed after reduction could not form the alloy and part of it appeared as FCC Co metal. The crystallite size of the alloy was in the range of 22–30 nm. The crystal size of the Fe–Co alloy reduced with an increase in Co concentration.     

Total Synthesis of 3 (R)-Panaxynol

Panaxynol1,asacommonconstituentofmanyplantparts',wasfirstdescribedbyTakahashietal.2in1964asaconstituentofPanaxyginseng.C.A.MeyershowedinhisBioassayshowedthatpanaxynolhadselectiveinvitrocytotoxicityagainstL-1210',MKI,B-16,andL-929cancercelllinescomparedtonormalcellcultures4.TheabsoluteconfigurationhadbeenestablishedbyLarsenetal.5tobe3R.Hereinwereportthefirsttotalstereoselectivesynthesisofpanaxynol(l).C'-CIafragmentofpanaxynol1wasobtainedaccordingtothefollowingsequencefReagentsandconditio…     

Note: Helix or No Helix of β‐Peptides Containing β3hAla(αF) Residues?

A remote ⁴J(F,H) coupling (F? C(α)? C(O)? N? H) of up to 4.2 Hz in α‐fluoro amides with antiperiplanar arrangement of the C? F and the C?O bonds (dihedral angle F? C? C?O ca. 180°) confirms that previous NMR determinations, using the XPLOR‐NIH procedure, of the secondary structures of β‐peptides containing β³hAla(αF) and β³hAla(αF₂) residues were correct. In contrast, molecular‐dynamics (MD) simulations, using the GROMOS program with the 45A3 force field, led to an incorrect conclusion about the relative stability of secondary structures of these β‐peptides. The problems encountered in NMR analyses and computations of the structures of backbone‐F‐substituted peptides are briefly discussed.