Chizuko Kabuto

Bio: Chizuko Kabuto is an academic researcher from Tohoku University. The author has contributed to research in topics: Crystal structure & Trimethylsilyl. The author has an hindex of 47, co-authored 383 publications receiving 7953 citations. Previous affiliations of Chizuko Kabuto include Yamagata University & Shinshu University.

Interconversion between syn and anti Conformations of 1,3-Bis(O-cyanomethyl)-p-tert-butylthiacalix[4]arene

Abstract: 1,3-Bis(O-cyanomethyl)-p-tert-butylthiacalix[4]arene (5) has been found to interconvert between syn and anti conformations in solution. The equilibrium shifts toward the anti form with increasing s...

X-Ray Crystal Structure and Dynamic Behavior of Pentafluoro-9,10-disila-9,10-dihydroanthracene Anion Salts Having Transannular 1,4-Fluorine Bridge

Abstract: Potasium-18-crown-6 and tetraethylammonium ion salts of pentafluoro-9,10-disila-9,10-dihydroanthracene anion (5a and 5b) have an unsymmetrical transannular 1,4-fluorine bridge in the solid states. In solution, 5a and 5b show a facile intramolecular fluorine exchange.

Unique inclusion behaviour of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetraaminothiacalix[4]-arene towards small organic molecules

Abstract: Tetraaminothiacalixarene 3, bearing four amino groups instead of the hydroxy groups of p-tert-butylthiacalix[4]arene 2, exhibits inclusion properties different from those of compound 2 towards small organic molecules upon crystallisation from neat solvents or guest solutions. X-ray crystallographic analyses reveal that nitromethane and acetonitrile are included into the cone-shaped cavity of compound 3, as is often seen in inclusion crystals of compound 2, whereas dichloromethane occupies a space between two distal benzene rings of compound 3, adopting a 1,3-alternate conformation. Acetic acid, which forms a dimer, fills a pore surrounded by four host molecules with a pinched cone conformation. Furthermore, guest-free crystals of compound 3 with a 1,3-alternate conformation absorb acetonitrile to give inclusion crystals with the same crystal structure as that obtained by the crystallisation. Thus, compound 3 flexibly changes its conformation according to the structures of guest compounds.

Molecular Structure of Tris(acetylacetonato)technetium(III)

Abstract: The molecular structure of tris(acetylacetonato)technetium(III) was determined by means of the single crystal X-ray diffraction method. The complex has a typical octahedral coordination and the average ∠O–Tc–O is 90.2°. The average Tc–O distance is 2.025 A.

Unusual hexameric structure in the crystal of sodium propylenediaminetetraacetatoeuropium(III)

Abstract: The unique hexameric crystal structure of the title complex, hexasodium bis{cyclotris[propylenediaminetetraacetato-µ-O,O′-diaquaeuropium(III)]}, has been shown by X-ray analysis.

Structure of Graphite Oxide Revisited

Abstract: Graphite oxide (GO) and its derivatives have been studied using 13C and 1H NMR. NMR spectra of GO derivatives confirm the assignment of the 70 ppm line to C−OH groups and allow us to propose a new structural model for GO. Thus we assign the 60 ppm line to epoxide groups (1,2-ethers) and not to 1,3-ethers, as suggested earlier, and the 130 ppm line to aromatic entities and conjugated double bonds. GO contains two kinds of regions: aromatic regions with unoxidized benzene rings and regions with aliphatic six-membered rings. The relative size of the two regions depends on the degree of oxidation. The carbon grid is nearly flat; only the carbons attached to OH groups have a slightly distorted tetrahedral configuration, resulting in some wrinkling of the layers. The formation of phenol (or aromatic diol) groups during deoxygenation indicates that the epoxide and the C−OH groups are very close to one another. The distribution of functional groups in every oxidized aromatic ring need not be identical, and both ...

Catalysis in ionic liquids

Abstract: 2.5. Stabilization of IL Emulsions by Nanoparticles 2623 3. Hydrogenations in ILs 2623 3.1. Hydrogenation on IL-Stabilized Nanoparticles 2623 3.1.1. Hydrogenation of 1,3-Butadiene 2623 3.1.2. Hydrogenation of Alkenes and Arenes 2624 3.1.3. Hydrogenation of Ketones 2624 3.2. Homogeneous Catalytic Hydrogenation in ILs 2624 3.3. Hydrogenation of Functionalized ILs 2625 3.3.1. Selective Hydrogenation of Polymers 2625 3.4. Asymmetric Hydrogenations 2626 3.4.1. Enantioselective Hydrogenation 2626 3.5. Role of the ILs Purity in Hydrogenation Reactions 2628

New Chiral Phosphorus Ligands for Enantioselective Hydrogenation

Abstract: The increasing demand to produce enantiomerically pure pharmaceuticals, agrochemicals, flavors, and other fine chemicals has advanced the field of asymmetric catalytic technologies.1,2 Among all asymmetric catalytic methods, asymmetric hydrogenation utilizing molecular hydrogen to reduce prochiral olefins, ketones, and imines, have become one of the most efficient methods for constructing chiral compounds.3 The development of homogeneous asymmetric hydrogenation was initiated by Knowles4a and Horner4b in the late 1960s, after the discovery of Wilkinson’s homogeneous hydrogenation catalyst [RhCl(PPh3)3]. By replacing triphenylphosphine of the Wilkinson’s catalystwithresolvedchiralmonophosphines,6Knowles and Horner reported the earliest examples of enantioselective hydrogenation, albeit with poor enantioselectivity. Further exploration by Knowles with an improved monophosphine CAMP provided 88% ee in hydrogenation of dehydroamino acids.7 Later, two breakthroughs were made in asymmetric hydrogenation by Kagan and Knowles, respectively. Kagan reported the first bisphosphine ligand, DIOP, for Rhcatalyzed asymmetric hydrogenation.8 The successful application of DIOP resulted in several significant directions for ligand design in asymmetric hydrogenation. Chelating bisphosphorus ligands could lead to superior enantioselectivity compared to monodentate phosphines. Additionally, P-chiral phosphorus ligands were not necessary for achieving high enantioselectivity, and ligands with backbone chirality could also provide excellent ee’s in asymmetric hydrogenation. Furthermore, C2 symmetry was an important structural feature for developing new efficient chiral ligands. Kagan’s seminal work immediately led to the rapid development of chiral bisphosphorus ligands. Knowles made his significant discovery of a C2-symmetric chelating bisphosphine ligand, DIPAMP.9 Due to its high catalytic efficiency in Rh-catalyzed asymmetric hydrogenation of dehydroamino acids, DIPAMP was quickly employed in the industrial production of L-DOPA.10 The success of practical synthesis of L-DOPA via asymmetric hydrogenation constituted a milestone work and for this work Knowles was awarded the Nobel Prize in 2001.3k This work has enlightened chemists to realize * Corresponding author. 3029 Chem. Rev. 2003, 103, 3029−3069