Akiko Sekine

Photocatalytic CO2 Reduction Using Cu(I) Photosensitizers with a Fe(II) Catalyst

Photocatalytic systems developed from complexes with only abundant metals, i.e., Cu(I)(dmp)(P)2(+) (dmp =2,9-dimethyl-1,10-phenanthroline; P = phosphine ligand) as a redox photosensitizer and Fe(II)(dmp)2(NCS)2 as a catalyst, produced CO as the main product by visible light irradiation. The best photocatalysis was obtained using a Cu(I) complex with a tetradentate dmp ligand tethering two phosphine groups, where the turnover number and quantum yield of CO formation were 273 and 6.7%, respectively.

Relation between photochromic properties and molecular structures in salicylideneaniline crystals

The crystal structures of the salicylideneaniline derivatives N-salicylidene-4-tert-butyl-aniline (1), N-3,5-di-tert-butyl-salicylidene-3-methoxyaniline (2), N-3,5-di-tert-butyl-salicylidene-3-bromoaniline (3), N-3,5-di-tert-butyl-salicylidene-3-chloroaniline (4), N-3,5-di-tert-butyl-salicylidene-4-bromoaniline (5), N-3,5-di-tert-butyl-salicylidene-aniline (6), N-3,5-di-tert-butyl-salicylidene-4-carboxyaniline (7) and N-salicylidene-2-chloroaniline (8) were analyzed by X-ray diffraction analysis at ambient temperature to investigate the relationship between their photochromic properties and molecular structures. A clear correlation between photochromism and the dihedral angle of the two benzene rings in the salicylideneaniline derivatives was observed. Crystals with dihedral angles less than 20° were non-photochromic, whereas those with dihedral angles greater than 30° were photochromic. Crystals with dihedral angles between 20 and 30° could be either photochromic or non-photochromic. Inhibition of the pedal motion by intra- or intermolecular steric hindrance, however, can result in non-photochromic behaviour even if the dihedral angle is larger than 30°.

X-ray Analysis of Successive Reaction in Crystalline State Photoisomerization of Cobaloxime Complexes

Abstract The γ-cyanopropyl group bonded to the cobalt atom in some cobaloxime complexes was isomerized to the α-cyanopropyl group through β-cyanopropyl group on exposure to visible light in the solid state. For the complex with 1-phenylethylamine as an axial base ligand almost chiral α-cyanopropyl group was produced with retention of the single crystal form. The mechanism is discussed on the basis of the structural change.

Crystalline-state β—α photoisomerization of cobaloxime complexes, part 1 generation of asymmetry in chiral crystal environment

Abstract The β -cyanoethyl groups bonded to the cobalt atoms in [ β -cyanoethyl](3-methylpyridine)bis(dimethylglyoximato)cobalt(III) and [ β -cyanoethyl](4-methylpyridine)bis(dimethylglyoximato)cobalt(III) are isomerized to the α -cyanoethyl groups, at room temperature and at 346 K respectively, on exposure to visible light with retention of the single crystal form. The produced α -cyanoethyl group has a chiral carbon atom bonded to the cobalt atom. The crystal structures of the 3-methylpyridine complex before and after the irradiation, which were determined by X-rays, revealed that the ratio of the R and S configurations of the produced α -cyanoethyl group in one site was not 1:1 but about 4:7. On the other hand, the α -cyanoethyl group only had the R configuration in one site of the 4-methylpyridine complex crystal. The difference in shape of the reaction cavities for the produced α -cyanoethyl groups of the two complex crystals well explains the reason why such different degrees of asymmetry were generated in the produced α -cyanoethyl groups.

Direct observation of various reaction pathways of arylnitrenes in different crystal environments caused by acid-base complex formation.

The structures of reaction intermediates, arylnitrenes and their final products have been successfully analyzed by X-rays using acid-base complex formation. The acid-base complexes of 2-azidobenzoic acid (2a), 3-azidobenzoic acid (3a) and 4-azidobenzoic acid (4a) were made with dibenzylamine (db), N-benzyl-2-phenylethylamine (bp) and dicyclohexylamine (dc). For the complex crystals of (3a) and db (3a-db), and (4a) and db (4a-db) two forms of (I) and (II) were obtained. Eight types of complex crystals, (2a-db), (3a-db-I), (3a-db-II), (3a-dc), (4a-db-I), (4a-db-II), (4a-bp) and (4a-dc), suitable for X-ray analysis were obtained. When the crystals were irradiated with UV light at low temperatures, the reactions proceeded keeping the single-crystal form in the five crystals (2a-db), (3a-db-I), (3a-db-II), (3a-dc) and (4a-bp). Less than 25% of each azidobenzoic acids was transformed into an arylnitrene and dinitrogen. In three crystals the arylnitrenes produced gave new final products; 2,1-benzisoxazolone was observed for (2a-db) and trans-azobenzenes (i.e. dimerized nitrenes) were obtained for (3a-db-II) and (4a-bp). For (3a-db-I) and (3a-dc) the intermediate arylnitrenes were observed but did not transform to new products. All the structural changes were directly observed by X-ray analysis because the incomplete reactions occurred with retention crystallinity. The crystal environment, including the hydrogen bonding between the benzoic acid and the amine, places restrictions on the movement of the arylnitrene and influences the reaction pathway followed for conversion of the arylnitrene to its final product.

Stereoselective Synthesis of Enantiomerically Pure β-Fluoroalkyl γ-Butyrolactones by Sulfoxide-Directed Lactonization

Enantiomerically pure α,α-dichloro β-fluoroalkyl γ-p-tolylthio γ-butyrolactones trans-6a–c have been obtained with excellent stereocontrol (> 98:2) and enantiomeric purity (> 98:2) by sulfoxide-directed lactonization (Marinos annu-lation reaction) of β-fluoroalkyl vinyl sulfoxides (R)-(E)-5a–c with dichloroketene. Highly chemoselective dechlorination and desulfurization reactions performed on trans-6c efficiently provided the β-chlorodifluoromethyl γ-butyrolactone (S)-8c, the absolute stereochemistry of which was determined by X-ray diffraction analysis of its γ-p-tolylthio precursor (2R,3S)-7c.

QUANTITATIVE COMPARISON OF PHOTOISOMERIZATION OF THREE COBALOXIME COMPLEXES IN THE SOLID AND CRYSTALLINE STATES

Abstract The β-cyanoethyl group bonded to the cobalt atom in cobaloxime complexes with 3-methyl-, 3-chloro- and 3-bromopyridines as axial base ligands was found, on exposure to a xenon lamp, to be isomerized to the α-cyanoethyl group with retention of the single-crystal form. The reaction rate of each compound was estimated from the change of unit-cell dimensions on a diffractometer (crystalline state) and from the change of the IR spectra of the powdered sample (the solid state). The reaction rates thus obtained were compared with the volumes of the reaction cavities for the cyanoethyl groups in the crystal structures of the three cobaloxime complexes. A quantitative relationship was observed between structure and reactivity.

Absolute chirality of the γ-polymorph of glycine: correlation of the absolute structure with the optical rotation

Crystal specimens of the γ-polymorph of achiral glycine which crystallize in space groups P31 and P32 as determined by the anomalous X-ray scattering method are shown to be laevorotatory and dextrorotatory, respectively, as determined by optical rotation of the crystals.

Four polymorphs of a cobaloxime complex with different solid-state photoisomerization rates

The complex (2-cyanoethyl)bis(dimethylglyoximato)(triphenylphosphine)cobalt(III), [Co(C4H7N2O2)2(C3H4N){P(C6H5)3}], when it was crystallized rapidly from an aqueous methanol solution, has four crystal forms, three of which were obtained separately from different solvents in large amounts. The crystal structures of the four forms were determined by X-rays. The molecular structures in the four forms have different conformations around the Co—C and Co—P bonds. The packing energy calculation indicated that the four forms have approximately the same energy. The 2-cyanoethyl group of this complex was isomerized to the 1-cyanoethyl group when the powdered sample of the complex was irradiated with a xenon lamp. For three crystal forms prepared separately, the solid-state photoisomerization rates were measured from the change in the IR spectra, assuming first-order kinetics. A quantitative relationship between the rate constant and the size of the reaction cavity for the 2-cyanoethyl group has been obtained for the three crystal forms.

Mechanism of asymmetric photocyclization of α-oxoamides

The molecules of N,N-diisopropylarylglyoxylamides, 1, are converted into the corresponding β-lactams, 2, on exposure to UV light in the solid state. However, the chemical and optical yields of the photocyclization are quite different among the crystals. The crystal structures of the three positional isomers 1a–c as reactants and the photoproduct 2b derived from 1b are determined by X-ray structure analysis: (1a)o-chlorophenyl-N,N: diisopropylglyoxylamide; (1b)m-chlorophenyl-N,N-diisopropylglyoxylamide; (1c)p-chlorophenyl-N,N-diisopropylglyoxylamide; (2b) 3-(m-chlorophenyl)-3-hydroxy-N-isopropyl-4,4-dimethylazetidin-2-one. The reactivity and enantioselectivity of the reactions are discussed on the basis of the structures and the packing potential energy calculated.