Volker Huch

Sol-Gel Synthesis of Nano-Scaled BaTiO3, BaZrO3 and BaTi0.5Zr0.5O3 Oxides via Single-Source Alkoxide Precursors and Semi-Alkoxide Routes

Sol-gel synthesis of nano-sized BaTiO3, BaZrO3 and BaTi0.5Zr0.5O3 ceramics using alkoxide and semi-alkoxide routes has been investigated and the pervoskites obtained have been compared with respect to crystallisation temperature, crystallite size and compositional purity. Heterometal alkoxides containing two (for BaTiO3 and BaZrO3) and three (for BaTi0.5Zr0.5O3) different metals were used as single-source precursors in the alkoxide route while semi-alkoxide synthesis was performed by reacting barium hydroxide or acetate with Ti and/or Zr alkoxides. Semi-alkoxide synthesis also produces stoichiometric and phase-pure oxides, however, at temperatures higher than 1000°C. At temperatures below 1000°C, BaCO3 and small amounts of other undesired phases (e.g., BaTi2O4) were present in the oxides derived from semi-alkoxide synthesis. Thermal behaviour, studied by TGA/DTA measurements, shows that thermal decomposition occurs in three major steps and depends on the educt composition and the synthesis route. Among alkoxide derived powders, crystalline BaTi0.5Zr0.5O3 phase is formed at 400°C while complete crystallisation of BaMO3 ceramics occurs around 600°C. The cubic to tetragonal phase transition for BaTiO3 is clearly observed at relatively low-temperature of 800°C. The stoichiometry and phase homogeneity of the obtained powders were demonstrated by energy dispersive X-ray analysis and powder diffractometry. The averaged crystallite size of the obtained nano-ceramics was evaluated using the FormFit programme. SEM and TEM observations revealed a high microstructural uniformity.

Equilibrium between a cyclotrisilene and an isolable base adduct of a disilenyl silylene

In organic chemistry, compounds with adjacent alkene and carbene functionalities (vinyl carbenes) are studied widely as fleeting intermediates and in the coordination sphere of transition metals. Stable derivatives of vinyl carbenes remain elusive, including the corresponding heavier group 14 homologues. Here we report the isolation and full characterization of a base-stabilized silicon version of a vinyl carbene that features a silicon-silicon double bond as well as a silylene functionality, coordinated by an N-heterocyclic carbene (NHC). In solution, the intensely green disilenyl silylene adduct exists in equilibrium with the corresponding silicon analogue of a cyclopropene and free NHC, which was quantified by nuclear magnetic resonance spectroscopy and ultraviolet-visible spectroscopy. The reversibility of this process raises exciting possibilities for the preparation of extended conjugated π systems of silicon.

One-dimensional arrangements of metal atoms in transition metal carbonyl complexes of mixed main group metal alkoxides

Abstract Mixed metal alkoxides containing main group elements with n s 2 electron configurations of the general formula M(O t Bu) 3 M′ (M = In, Tl; M′ = Ge, Sn, Pb), M′(O t Bu) 3 M(O t Bu) 3 M′ (M = divalent metal atom, M′ = Ge, Sn) and (O t Bu)M′(O t Bu) 2 M(O t Bu) 2 M′(O t Bu) (M = Co, Ni; M′ = Ge, Sn) can be reacted with simple metal carbonyls. The products obtained are composed of a one-dimensional array of metal atoms held together by direct metal-metal bonds or by bridging alkoxide groups. The following compounds have been isolated and characterized by IR and NMR spectroscopy and X-ray diffraction (M′ = Ge, Sn, Pb; M = In, Tl; M T = transition metal): M′(O t Bu) 3 M−M T (CO) n , (CO) n M T −M(O t Bu) 3 M′−M T (CO) n , M′(O t Bu) 3 M−M T (CO) n M(O t Bu) 3 M′, (CO) n M T −M′(O t Bu) 3 M(O t Bu) 3 M′−M T (CO) n , (CO) n M T −M′[O t Bu](O t Bu) 2 M(O t Bu) 2 M(O t Bu) 2 [O t Bu]M′−M T (CO) n and (CO) n M T −M′(O t Bu) 3 M−M T (CO) n M(O t Bu) 3 M′−M T (CO) n . In addition, an oligomeric species of the general formula [Sn(O t Bu) 3 In−Mo(CO) 4 ] n −Sn(O t Bu) 3 In−Mo(CO) 5 with n ≈ 9, 10 has been isolated.

Phase selective deposition and microstructure control in iron oxide films obtained by single-source CVD

Iron(III) tert-butoxide, [Fe(O t Bu) 3 ] 2 , was used as a single source for iron and oxygen to obtain nanocrystalline hematite (Fe 2 O 3 ) or magnetite (Fe 3 O 4 ) films by low-pressure (LP) CVD. The decomposition profile of the molecular precursor and the crystallization temperature of iron oxide were derived from thermogravimetry/differential thermal analysis (TG/DTA). The substrate temperature was found to markedly influence the morphology and Fe/O stoichiometry in the deposited films. The morphological features and phase identification of the grown films were obtained by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The compositional identity of the phases was determined by the X-ray photoelectron spectroscopy (XPS) of the CVD deposits. Annealing the films ex-situ under reducing or oxidizing conditions allows selective interconversion (Fe 2 O 3 ↔ Fe 3 O 4 ) among the deposited phases with no particle size variation. The interplay between the rate of precursor delivery and substrate temperature controlled the mean particle size in the films. Magnetite film with a mean particle size of 10 nm was obtained on silicon at 450 °C. Formation of larger grains and grain clusters was observed at higher temperatures. High coercivity (4000 Oe) and small saturation magnetization (0.3 emu g -1 ) of the Fe 3 O 4 film confirmed superparamagnetic behavior due to small particle size. Absorption spectra of magnetite and hematite films deposited on glass show them to be transparent to the visible light. The sheet resistance of nanocrystalline Fe 3 O 4 and Fe 2 O 3 films was found to be 2.4 kΩ and 2 MΩ, respectively.

Total Synthesis of Myrtucommulone A

reported that 1 is highly active against Gram-positive bacteria. Three years later Lounasmaa and co-workers isolated myrtucommulone A from other members of the myrtacea family. After that, interest in myrtle died down until 2002 when Appendino and co-workers re-examined extracts of this Mediterranean shrub and described additional myrtucommulones and their anti-oxidative properties. Shaheen et al. recently isolated the myrtucommulones C to E and other natural products from Myrtus communis. Quinn and coworkers examined extracts from Corymbia scabrida and could identify 1 and the myrtucommulones F to I. We became interested in the myrtucommulones when it was reported that these compounds show very significant antiinflammatory activity as well as highly selective apoptosisinducing activity. For detailed studies of the pharmacological activities of these compounds it seemed reasonable to develop a synthetic strategy leading to myrtucommulone A (1) and the other myrtucommulones. Here, we report on our total synthesis of myrtucommulone A (1), myrtucommulone F (13), myrtucommulone C (16), and three analogues thereof. Based on the constitutional symmetry of 1 the retrosynthetic disconnection shown in Scheme 1 seems reasonable. It should be possible to synthesize 1 from isobutyryl phloroglucinol (2), isobutyraldehyd (3), and syncarpic acid (4) in one step. Isobutyryl phloroglucinol (2) is readily available through Friedel–Crafts acylation of phloroglucinol (5) in 70–80% yield (Scheme 2). Syncarpic acid (4) is described in the

A straightforward approach towards cyclic peptides via ring-closing metathesis—scope and limitations†‡

N- and C-terminal diallylated peptides are obtained by several approaches, such as peptide Claisen rearrangement, N- and O- allylation, and the Ugi reaction of allyl-protected components. These diallylated peptides are suitable substrates for ring-closing metathesis and the success of this cyclisation was investigated with respect to the ring size, the position of the allyl moieties and the reaction parameters. In general, excellent yields are obtained for cyclisation of allyl glycine subunits and N-allylated amides, while allyl esters and allyl carbamates often presented serious problems. However, yields of up to 73% were obtained under optimised conditions, and the new generated double bond is formed with excellent trans-selectivity.

From Disilene (SiSi) to Phosphasilene (SiP) and Phosphacumulene (PCN)

The generation of heavier double-bond systems without by- or side-product formation is of considerable importance for their application in synthesis. Peripheral functional groups in such alkene homologues are promising in this regard owing to their inherent mobility. Depending on the steric demand of the N-alkyl substituent R, the reaction of disilenide Ar2Si=Si(Ar)Li (Ar = 2,4,6-iPr3C6H2) with ClP(NR2)2 either affords the phosphinodisilene Ar2 Si=Si(Ar)P(NR2)2 (for R = iPr) or P-amino functionalized phosphasilenes Ar2(R2N)Si=Si(Ar)=P(NR2) (for R = Et, Me) by 1,3-migration of one of the amino groups. In case of R = Me, upon addition of one equivalent of tert-butylisonitrile a second amino group shift occurs to yield the 1-aza-3-phosphaallene Ar2(R2N)Si=Si(NR2)(Ar)-P=C=NtBu with pronounced ylidic character. All new compounds were fully characterized by multinuclear NMR spectroscopy as well as single-crystal X-ray diffraction and DFT calculations in selected cases.

Bendigoles D–F, bioactive sterols from the marine sponge-derived Actinomadura sp. SBMs009

Marine derived actinomycetes have become an important source of bioactive natural products. Here we report the structure and bioactivity of the bendigoles D-F (1-3), 3-keto sterols isolated from the new marine sponge derived bacterium, Actinomadura sp. SBMs009. The isolation of these compounds was guided by a novel high-content screen for NF-κB and glucocorticoid receptor (GR) activity, and cytotoxicity assays. The structures of 1-3 were determined by detailed analysis of NMR, MS, and single crystal X-ray diffraction data. Interestingly, 1 displayed cytotoxicity against the L929 (mouse fibroblast) cell line with an IC(50) approximated to 30 μM and was the most active inhibitor of GR-translocation, while 3 was the most effective inhibitor of NF-κB nuclear translocation with an IC(50) of 71 μM.

Synthesis of IR‐sensitive photoswitchable molecules: photochromic 9′‐ styrylquinolinedihydroindolizines

New mono- (5a–t, w) and biphotochromic (5u, v) 9′-styrylquinolinespirodihydroindolizines (DHIs) with IR-absorbing colored forms (4) were prepared. The conformation and configuration of these new DHIs were investigated by NMR studies and the structure was proved by x-ray analysis. The kinetics of the fast cyclizing process of betaine 4 to DHI 5 takes place in the millisecond range and were studied by flash photolysis. The absorption bands of the betaines 4 were recorded at low temperature by FT-UV/VIS/near-IR spectroscopy. Large solvent effects on the absorption maxima of betaines 4 were observed. Copyright

Spezielle Silazanderivate von Digallan( 4) und Diindan( 4) mit Ga-Ga- bzw. In-In-Bindung *

Al, Ga and In can easily be incorporated in the cyclic silazane (MeSi)2(NtBu)4H2(LH2) through formal substitution of the hydrogen atoms by the metallic elements. LAlMe, LAlCl, LGaCl, LInCl as well as the side product L(H)InCl2 are obtained in high yields. X-ray structure determinations confirm the molecules LAlMe and L(H)InCl2 to be polycyclic and the metallic atoms to be four-coordinated by intramolecular nitrogen donors. When LAlCl, LGaCl and LInCl are reduced by sodium naphthalene, in the two latter cases the formation of LGaGaL and LInInL is observed. An X-ray structure determination of LInInL shows an InIn bond of 2.768(1) A with the two indium atoms being coordinated by three nitrogen atoms each (InN ranging from 2.12(1)−2.298(7) A). LGaGaL and LInInL can be considered as the first amides of GaII and InII.