Low temperature structure of FeSr2YCu2O6+δ magnetic superconductor

FeSr₂YCu₂O_6+δ with the tetragonal Ba₂YCu₃O_6+δ-type structure exhibits superconductivity around 60 K, when it is properly annealed in N₂ and subsequently in O₂. This compound also exhibits antiferromagnetic order of Fe around 20 K. We have performed neutron powder diffraction of the FeSr₂YCu₂O_6+δ system at low temperature to investigate the relation between the crystal structure and the physical properties. Neutron diffraction study indicates that this compound does not have the structure phase transition due to the tilt of the FeO₆ octahedron differently from the RuSr₂GdCu₂O₈ magnetic superconductor with the same structure, and that the magnetic order in FeSr₂YCu₂O_6+δ is not long-range order, because we can observe no extra reflection due to the crystal and magnetic superstructure.     

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.     

Regiospecific synthesis of 2‐substituted furanonaphthoquinones

The naturally‐occurring furanonaphthoquinones 1a‐d have been synthesized from 3‐furancarboxylic acid and 2,3‐dimethoxybenzaldehyde via the Birch reduction‐elimination.     

Synthesis of chiral azobenzene-based compounds for use in the photochemical tuning of the helical structure of liquid crystals

We have synthesized azobenzene-based molecules containing either one or two chiral groups. A cholesteric phase can be induced by adding the chiral azobenzene compounds to a host nematic liquid crystal. We investigated the effects of the trans-cis photoisomerization of the chiral azobenzene compounds on the properties of the cholesteric phase, such as the helical pitch length. This can be increased or decreased by the photoisomerization of the chiral azobenzene compounds. We discuss the photochemically driven change in the helical pitch of the cholesteric phase with respect to structural effects involving the chiral groups.     

Cleavage and Formation of Molecular Dinitrogen in a Single System Assisted by Molybdenum Complexes Bearing Ferrocenyldiphosphine

The N?N bond of molecular dinitrogen bridging two molybdenum atoms in the pentamethylcyclopentadienyl molybdenum complexes that bear ferrocenyldiphosphine as an auxiliary ligand is homolytically cleaved under visible light irradiation at room temperature to afford two molar molybdenum nitride complexes. Conversely, the bridging molecular dinitrogen is reformed by the oxidation of the molybdenum nitride complex at room temperature. This result provides a successful example of the cleavage and formation of molecular dinitrogen induced by a pair of two different external stimuli using a single system assisted by molybdenum complexes bearing ferrocenyldiphosphine under ambient conditions.     

Indium-catalyzed enantioselective allylation of aldehydes with β-carbonyl allylstannanes: An efficient synthetic method for chiral α-methylene-γ-lactones

The catalytic enantioselective allylation of aldehydes with β-carbonyl allyltributylstannanes in the presence of chiral indium complexes gave the optically active homoallylic alcohols, which can be converted to the corresponding optically active α-methylene-γ-butyrolactones.     

Transition-metal complex catalyzed polyfluoroalkylation. I. Facile addition of polyfluoroalkyl halides to carbon-carbon multiple bonds

Addition of polyfluoroalkyl halides to alkynes and alkenes bearing a variety of substituents is effected by the catalysis of iron, cobalt and ruthenium carbonyl complexes to give the corresponding adducts in good to excellent yields under mild conditions.     

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).