X-ray photoelectron spectroscopic studies on initial oxidation of iron and manganese mono-silicides

Initial oxidation of iron and manganese mono-silicides (FeSi and MnSi) surfaces was studied by X-ray photoelectron spectroscopy (XPS). Clean surfaces of these silicides were prepared by fracturing in an ultra high vacuum, and then the fractured surfaces were oxidized by exposing to high-purity oxygen at pressures up to 1.3 Pa. For the clean FeSi surface, positive chemical shifts of the Fe 2p_3/2 and Si 2p peaks from elemental Fe and Si were 0.5 eV and 0.1 eV, respectively. For the clean MnSi surface, a negative chemical shift of the Si 2p peak from elemental Si was 0.1 eV. Iron on the FeSi surface was oxidized at an oxygen pressure of 1.3 Pa, whereas the silicon was oxidized under the pressure of 1.3 × 10⁻⁶ Pa, indicating that oxidation of silicon occurred prior to that of iron. Manganese and silicon on the MnSi were simultaneously oxidized in the range from 1.3 × 10⁻⁶ Pa to 1.3 × 10⁻³ Pa; however, over the pressure of 1.3 Pa, the oxidation of manganese occurs prior to that of silicon. These oxidation behaviors at low oxygen pressures were similar to those of the FeSi and MnSi fractured in air.     

Ring transformation of 6H-cyclopropa[e]pyrazolo[1,5-a]pyrimidine. VI. Substituent effect of 6-substituted 5a-acetyl-6a-ethoxycarbonyl-5a,6a- dihydro-6H-cyclopropa[e]pyrazolo[1,5-a]pyrimidine-3-carbonitriles

Synthesis and reactivity of 6-ethoxycarbonyl-, 6-phenyl- and 6-methyl-5a-acetyl-6a-ethoxycarbonyl-5a,6a-di-hydro-6H-cyclopropa[e]pyrazolo[1,5-a]pyrimidine-3-carbonitriles 4 , 5 , and 7 are described.     

Stereospecific and biomimetic synthesis of CS and C2 symmetric 2,5-disubstituted tetrahydrofuran rings as central building blocks of biogenetically intriguing oxasqualenoids

The enantioselective synthesis of optically active (+)-tetraol 12, corresponding to the C9–C16 subunit of biogenetically and biologically intriguing oxasqualenoids 2–4, has been accomplished by the biomimetic and stereospecific cyclization of diepoxide 22. The experimental details for the preparation of the known meso tetraol 11, corresponding to the C9–C16 subunit of teurilene 1, are also described.     

Structure and electrochemistry of self-organized fullerene-lipid bilayer films

The unique properties of C(60)-bearing artificial lipids with three C(16) (lipid 1), C(14) (lipid 2), or C(12) (lipid 3) alkyl chains have been characterized by a variety of techniques, including (13)C NMR, UV/Vis, and FT-IR spectroscopies, differential scanning calorimetry (DSC), X-ray diffraction, and electrochemistry. The (13)C NMR and UV/Vis spectra show that the lipids 1-3 have a closed aziridine structure at a 6/6-ring junction of C(60). The DSC data reveal that cast films of 1 exhibit two endothermic peaks at temperature ranges of 35-40 degrees C (main transition) and 47-49 degrees C (subtransition) in air, water, and 0.5 M aqueous tetraethylammonium chloride solution, while cast films of 2 and 3 each display one endothermic peak at 50-57 degrees C. The results of temperature-dependent FT-IR and UV/Vis studies of cast films of 1-3, together with the above data, reveal that the main peak in the DSC thermogram of a film of 1 can be attributed to a typical phase transition as seen in lipid bilayer membranes, while the sub-endothermic peak seen with 1 and the peaks for 2 and 3 stem from a change in the orientation of the C(60) moieties. X-ray diffraction patterns of each of the cast films of 1-3 show a diffraction peak corresponding to the (001) plane, suggesting the formation of molecular bilayer membrane structures. Cyclic voltammograms and Osteryoung square-wave voltammograms obtained from cast films of 1-3 on basal plane pyrolytic graphite (BPG) electrodes show strong temperature dependences. Finally, the thermodynamics of the binding of nine different alkylammonium ions and two alkylphosphonium ions to the electrogenerated radical monoanions and dianions of 1-3 cast on electrodes is described.     

Reaction of (bromodifluoromethyl)phenyldimethylsilane with organometallic reagents

A new fluorine-containing organosilicon compound, (bromodifluoromethyl)-phenyldimethylsilane (II), was synthesized by the N-bromosuccinimide (NBS) bromination of difluoromethyl)phenyldimethylsilane (I), which was prepared from phenyldimethylsilyllithium and chlorodifluoromethane. Compound II reacted with dimethyl sulfoxide to give dimethyl sulfide and phenyldimethylfluorosilane in quantitative yield. The reaction of II with nucleophiles, such as sodium ethoxide, Grignard or lithium reagents, afforded products arising from cleavage of the carbonsilicon bond. In contrast, the reaction of II with Grignard reagents in the presence of appropriate catalysts (Group VIII transition metal salts or complexes) afforded the homo-coupling product of II, 1,2-bis-(phenyldimethylsilyl)-1,1,2,2-tetrafluoroethane (IV), in excellent yield. The silver(I) salt-catalyzed reaction of II with ethylmagnesium bromide gave the cross-coupling product, (1,1-difluoropropyl)phenyldimethylsilane (V) as well as III and IV. When cuprous bromide was employed as catalyst, the reaction of II with ethylmagnesium bromide afforded 1-phenyldimethylsilyl-1-propene (VI) and 3-phenyldimethylsilyl-2-pentene (VII) as main products.     

Cp2TiCl2-catalyzed grignard reactions. 3. Reactions with esters: Efficient methodology for the synthesis of secondary alcohols and for the reduction of esters to primary alcohols

Cp₂TiCl₂-catalyzed Grignard reactions with esters provide general methodology for preparation of secondary alcohols or for reduction of esters to the corresponding primary alcohols.     

Preparation of poly(fumaric acid) from poly(di-t-butyl fumarate) and poly(di-trimethylsilyl fumarate)

Polymerization conditions of di-t-butyl fumarate and di-trimethylsilyl fumarate were studied in detail. They cannot be polymerized by either anionic or coordination initiators, but radical and radiation polymerizations are successful. Characterization of poly(di-t-butyl fumarate), obtained thereby, with ¹H-NMR spectrum suggests that the backbone of the chain is stiff. From analysis of thermal properties of poly(di-t-butyl fumarate), it is found to be completely converted to poly(fumaric acid) by pyrolysis around 200°C. Poly(di-trimethylsilyl fumarate), on the other hand, can be quantitatively hydrolyzed with acid to the same polyacid, too. The preliminary measurement of the dissociation behaviors of poly(fumaric acid) was done by potentiometric titration, which shows that the titration curves of poly(fumaric acid) are different from those of poly(acrylic acid) and poly(maleic acid).     

Pd-catalyzed asymmetric allylic amination using aspartic acid derived P-chirogenic diaminophosphine oxides: DIAPHOXs

[reaction: see text] A Pd-catalyzed asymmetric allylic amination using aspartic acid derived P-chirogenic diaminophosphine oxides (DIAPHOXs) is described. Asymmetric allylic amination of both linear and cyclic substrates proceeded at room temperature to give the chiral allylic amines in 72-99% ee.