Setsuo Kashino

Electronic structure of Eu@C60 studied by XANES and UV-VIS absorption spectra

Eu endohedral C60, Eu@C60, has been extracted with aniline from soot prepared by arc-heating of a graphite/Eu2O3 composite rod and obtained at high concentration by combining sublimation and repeated high-performance liquid chromatography. The laser desorption time-of-flight mass spectrum showed a pronounced peak of Eu@C60+. The UV–VIS absorption spectrum of this sample has a red-shift in the onset (>900 nm) in comparison with those for C60 and C70, as expected from electron transfer from the Eu atom to the C60 cage. The valence state of the Eu atom in Eu@C60 has been determined to be +2 by Eu LIII-edge XANES.

Asymmetric reduction of 2-(N-arylimino)-3,3,3-trifluoropropanoic acid esters leading to enantiomerically enriched 3,3,3-trifluoroalanine

Abstract Enantiomerically enriched 3,3,3-trifluoroalanine (1) (up to 62 % ee) has been synthesized by the asymmetric reduction of 2-(N-arylimino)-3,3,3-trifluoropropanoic acid esters with a chiral oxazaborolidine catalyst and subsequent oxidative removal of N-aromatic moiety with retention of the configuration. Detailed optimization studies revealed that the effects of solvents, temperature, and the structural modification of the substrate were drastic on the enantioselectivity. The absolute configuration of 1 was determined to be (R) by X-Ray crystallographic analysis of the corresponding N-(S)-(+)-camphorsulfonyl derivative.

Syntheses, crystal structures and autoreduction behavior of antiferromagnetically coupled dicopper(II) oximato complexes

Abstract Four dicopper(II) oximato complexes of 2-[2-(α-pyridyl)methyl]imino-3-butanone oxime (pmiboH) and 2-[2-(α-pyridyl)ethyl]imino-3-butanone oxime (peiboH), [Cu2(pmibo)2](ClO4)2 (1), [Cu2(pmibo)2](NO3)2·CH3OH (2), [Cu2(peibo)2](ClO4)2·CH3OH (3) and [Cu2(peibo)2(H2O)2](ClO4)2 (4), were prepared and characterized structurally and magnetically. All the dicopper(II) oximato complexes have a common cationic structure in which the two Cu atoms are bridged through two NO bridges of the oximato ligand to afford a dinuclear structure. The cation moieties of 1 and 2 consist of one six-membered Cu2N2O2 chelate ring and four five-membered (CuN2C2 and CuNC2N) chelate rings, providing a planar configuration. The cation moieties of 3 and 4 are also composed of three six-membered (Cu2N2O2 and CuNC3N) chelate rings and two five-membered CuN2C2 chelate rings, giving a twisted-boat configuration. The −2J values (H=−2JS1S2) are 835, 825, 550 and 510 cm−1 for 1, 2, 3 and 4, respectively, indicative of a strong antiferromagnetic interaction in the solid state. All the dicopper(II) oximato complexes show seven 1H NMR signals at 23°C in the range of −0.5 to 30 ppm with the linewidths at half-height, Δν1/2 of 60–1500 Hz, which is characteristic of antiferromagnetic species and indicates that the dinuclear structure is kept in solution. The −2J values reflect the degree of distortion from the planarity of the Cu2 framework. The −2J values roughly correlate with the 1H NMR parameters; the larger the −2J values, the smaller the chemical shifts and linewidths. Complexes 1 and 2 were found to undergo an autoreduction reaction in dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA), and their behaviors were first monitored by UV–Vis and 1H NMR methods.

Intramolecular SN2 reaction at α-carbon of trifluoromethyl group: preparation of optically active 2-trifluoromethylaziridine

Abstract We have succeeded in intramolecular nucleophilic substitution of the hydroxyl group in (S)-1-(alkylamino)-3,3,3-trifluoro-2-propanol. The reaction provides an optically pure (R)-1-benzyl-2-trifluoromethylaziridine in good yield from optically pure (S)-3-(benzylamino)-1,1,1-trifluoro-2-propanol, which was prepared from (S)-3,3,3-trifluoropropene oxide (75% ee).

Structure of the tannin geraniin based on conventional X-ray data at 295 K and on synchrotron data at 293 and 120 K

Geraniin, C41H28O27.7H2O, is the main tannin from Geranium thunbergii Sieb. et Zucc., which is one of the most popular folk medicines and also an official antidiarrheic drug in Japan. Conventional X-ray diffractometer data at 295 K and synchrotron data at 293 and 120 K (at EMBL/DESY Hamburg with a MARRESEARCH imaging plate) were measured. The structure could not be determined with any of the currently distributed direct-methods programs, but was easily solved with DIRDIF using several conformers of the hexahydroxydiphenoyl group as input fragments into a vector-search procedure. A molecular structure was established where a cyclohexenetrione moiety attached to O4 of a central glucose unit was in a hydrated six-membered hemiacetal ring structure, as expected from the NMR study of crystalline geraniin. Owing to the high oligocyclic substitution the glucopyranosyl ring is in the unusual 1C4 conformation. Refinement of the low-temperature synchrotron data allowed identification of almost all the H atoms, even within the seven water molecules, so that a rather complex system of approximately 30 different hydrogen bonds can be studied in some detail.

Structure and electronic properties of Dy@C82 studied by UV–VIS absorption, X-ray powder diffraction and XAFS

Abstract Two isomers of Dy@C 82 were separated by high performance liquid chromatography (HPLC), and their UV–VIS absorption spectra were measured to characterize these isomers. The crystalline powder of Dy@C 82 was obtained by removing the solvent (toluene) at 250°C under vacuum. The X-ray diffraction pattern can be indexed with fcc crystal lattice, as that in La@C 82 . The lattice constant a at 298 K, 15.86(1) A, is close to that of La@C 82 , 15.78 A. The distances between Dy and the first and second nearest C atoms are determined to be 2.52(2) and 2.86(2) A, respectively, on the basis of Dy L III -edge EXAFS. The XANES shows that the valence of the Dy atom in Dy@C 82 is +3.

Antiferromagnetism induced by successive protonation of terminal phenol groups of a bis(μ-phenoxide)-bridged dicopper(II,II) complex

The reaction of a tripodal ligand (H2L = N,N-bis(2-hydroxybenzyl)-N′,N′-dimethylethylenediamine) with Cu(NO3)2·3H2O and Cu(ClO4)2·6H2O in methanol yielded [Cu2(HL)2](NO3)2·H2O (1) and [Cu2(HL)2](ClO4)2 (1′), respectively. When H2L was allowed to react with CuSO4·5H2O in the presence of triethylamine (1 ∶ 1 ∶ 2) in methanol, the neutral dicopper(II,II) complex [Cu2(L)2] (2) was obtained. The monopositive species [Cu2(L)(HL)]ClO4·CH3OH·H2O (3) crystallized on mixing 1′ and 2 (1 ∶ 1) in methanol–dichloromethane. The crystal structures of 1, 2, and 3 were determined by X-ray crystallography. All of the complexes consist of a discrete dinuclear molecule with bis(μ-phenoxide)-bridges. The tripodal ligand functions as a tetradentate ligand and one of the phenolic oxygen atoms serves as a bridging ligand. Protonation/deprotonation takes place at the terminal phenol moiety and as the phenol group is deprotonated the coordination geometry changes from a distorted square pyramid to a distorted trigonal bipyramid. The two copper ions in 1–3 are antiferromagnetically coupled with 2J = −714 (1), −19.9 (2), and −277 cm−1 (3). The results clearly demonstrate that protonation/deprotonation causes a change in coordination geometry, which in turn drastically affects magnetic exchange interactions.

Synthesis, structures and properties of the dinuclear copper(II) complexes triply bridged by two oximato and one pyrazolato or one phthalazine

Abstract The triply (two oximato and one pyrazolato or one phthalazine) bridged dinuclear copper(II) complexes [Cu2(L1)2(pz)]ClO4 (1) and [Cu2(L1)2(phta)](ClO4)2 (2) (HL1=2-[2-(α-pyridyl)ethyl]imino-3-butanone oxime, pz=pyrazolate anion, phta=phthalazine) were synthesized and characterized; the crystal structures of 1 and 2 were determined by X-ray crystallography. Magnetic susceptibility measurements from liquid helium temperature to room temperature showed a weak antiferromagnetic exchange coupling between two copper(II) ions (2J=−17 cm−1) for l, on the other hand, a very strong antiferromagnetic interaction for 2 was observed (2J=−760 cm−1).

Structure of La2@C80 studied by La K-edge XAFS

Abstract The structure of La2@C80 is studied by La K-edge XAFS from 40 to 295 K. The distances between the La atom and the first nearest C atoms have been determined to be 2.42(1) A at 40 K and 2.44(2) A at 295 K, and those between the La atom and the second nearest C atoms to be 2.97(2) A at 40 K and 2.98(3) A at 295 K. The La–La distance has been determined to be 3.90(1) A at 40 K and 3.88(2) A at 295 K. The temperature dependence of the mean-square displacement of La–C is also studied to get an insight into the dynamical behavior of two La atoms in the C80 cage.

1: 2 complexes of chloranilic acid with pyrazole and imidazole, and the acetonitrile solvate of a 1:1 complex with imidazole

2,5-Dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid) forms X-H.Y (X, Y = N or O) and C-H.Cl hydrogen bonds with pyrazole and imidazole to afford bis(pyrazolium) dichloroanilate and bis(imidazolium) dichloroanilate, (I) and (II), both 2C(3)H(5)N(2)(+).C(6)Cl(2)O(4)(2-), and imidazolium chloroanilate acetonitrile solvate, C(3)H(5)N(2)(+).C(6)HCl(2)O(4)(-).C(2)H(3)N, (III). Their crystal structures demonstrate three novel supramolecular architectures based on supramolecular synthons to build a ladder, (I), a two-dimensional network, (II), and a flat ribbon, (III).