Showing papers in "Bulletin of the Chemical Society of Japan in 2000"
TL;DR: In this paper, the authors reviewed the progress of overall water splitting by photocatalysts and mechanocatalyst and briefly reviewed the recent progress in the understanding of the reaction mechanism.
Abstract: Recent progress of overall water splitting by photocatalysts and mechanocatalysts is briefly reviewed. In photocatalytic reactions, several new materials have been introduced, and the catalyst preparation has also been improved. As a result, a high quantum efficiency for overall water splitting of about 30% has been accomplished. In addition, recent progress in the understanding of the reaction mechanism is briefly introduced. On the other hand, mechano-catalytic overall water splitting reaction has been recently discovered by the authors. The phenomenological aspects of this novel reaction are summarized, and some implications of the reaction mechanism are also described.
301 citations
TL;DR: A composite of polyaniline (PANI) encapsulating titanium oxide (TiO2) with nanometer size has been synthesized by in-situ emulsion polymerization as mentioned in this paper.
Abstract: A composite of polyaniline (PANI) encapsulating titanium oxide (TiO2) with nanometer size has been synthesized by in-situ emulsion polymerization. Particle dimensions have been measured and the nature of the association between the components have been observed using SEM and TEM techniques. The interaction between PANI and TiO2 and the nature of chain growth have been investigated and explained according to the results of FTIR. The improvement of thermal stability and crystallinity of nanocomposites have been evaluated by using TGA and XRD. The mechanism of charge transport in these composites has also been studied by measuring the DC conductivity of all samples and the temperature-conductivity relation. The photoconductivity of PANI-TiO2 composite has been enhanced markedly. This effect is discussed by taking the photoinduced charge transfer between PANI and TiO2 into consideration.
168 citations
TL;DR: In this paper, the single-crystalline cycloreversion reaction of a photochromic diarylethene, bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene, was studied by X-ray singlecrystal structure analysis.
Abstract: The single-crystalline cycloreversion reaction of a photochromic diarylethene, bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene, was studied by X-ray single-crystal structure analysis. The single c...
145 citations
TL;DR: In this paper, structural and physical properties of the Cu salts of a series of π-acceptors N,N′-dicyanobenzoquinonediimines (DCNQIs) are described.
Abstract: Structural and physical properties of the Cu salts of a series of π-acceptors N,N′-dicyanobenzoquinonediimines (DCNQIs) are described. The most notable feature of this system is that 3d electrons in Cu interact with pπ electrons in DCNQI near the Fermi level. This unique feature has provided a lot of interesting solid state properties: the Mott transition triggered by the Peierls transition, the pressure-induced metal-insulator transition, the metal-insulator-metal (reentrant) transition, the three-dimensional Fermi surface, the anomalous isotope effects, the antiferromagnetic transition, the weak ferromagnetism, and the electron mass enhancement. The aim of this account is to give an overview of this unique pπ-d system.
101 citations
TL;DR: In this paper, various oxiranes reacted with carbon dioxide at 100 °C using lithium bromide as a catalyst under atmospheric pressure to afford the corresponding five-membered cyclic carbonates quantitatively.
Abstract: Various oxiranes reacted with carbon dioxide at 100 °C using lithium bromide as a catalyst under atmospheric pressure to afford the corresponding five-membered cyclic carbonates quantitatively. The rate of the reaction increased as the bulkiness of substituents on the oxirane ring was reduced or an electron-withdrawing group was introduced on the oxirane ring. The stereochemistry of the reaction of oxirane and carbon dioxide was retention without loss of optical purity. When substituted phenylethylene carbonates were reacted with benzylamine, the selectivity to afford secondary alcohol increased as the electron-withdrawing ability of the para-substituent increased.
95 citations
TL;DR: The versatility of 1,3-dichloro-1,1,3,3 -tetraisopropylcyclotetrasiloxane (1) as a precursor of cage and ladder siloxanes is presented in this article.
Abstract: The versatility of cis,cis,cis-1,3,5,7-tetrahydroxy-1,3,5,7-tetraisopropylcyclotetrasiloxane (1) as a precursor of cage and ladder siloxanes is presented. Compound 1 reacted with 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane in pyridine to give 1,3,5,5,7,7,9,11,13,13,15,15-cis-cisoid-cis-dodecaisopropyltricyclo[9.5.1.13,9]octasiloxane (2) in 20% yield. The reaction proceeded with retention of the configuration of the silicon atoms, and only syn-type isomer was obtained. The reaction of 1 with 1,1,3,3-tetrachloro-1,3-diisopropyldisiloxane in pyridine produced hexakis(isopropylsilsesquioxane) (T6) (3) in 25% yield. Treatment of 1 with dicyclohexylcarbodiimide (DCC) as dehydrating reagent led to the formation of octakis(isopropylsilsesquioxane) (T8) (4) in 45% yield. The crystal structures of 2, 3, and 4 are reported.
92 citations
TL;DR: In this article, a reagent system consisting of 70% HF/pyridine and an N-halo imide was used to synthesize trifluoromethyl ethers R-OCF3.
Abstract: Trifluoromethyl ethers R-OCF3 are easily synthesized from the corresponding dithiocarbonates R-OCS2Me (R = aryl or primary alkyl) by a reagent system consisting of 70% HF/pyridine and an N-halo imide. When the reaction is applied to R-OCS2Me wherein R = secondary alkyl, tertiary alkyl, or benzylic group, fluorination leading to the corresponding alkyl fluorides R-F is achieved, whereas a combination of 50% HF/pyridine and N-bromosuccinimide affords the corresponding trifluoromethyl ethers R-OCF3 (R = secondary).
78 citations
TL;DR: In this paper, rare earth metal trifluoromethanesulfonates (RE(OTf)3) were found to be efficient catalysts for Friedel-Crafts acylation and alkylation.
Abstract: Rare earth metal trifluoromethanesulfonates (rare earth metal triflates, RE(OTf)3) were found to be efficient catalysts for Friedel-Crafts acylation and alkylation. In the presence of a catalytic amount of RE(OTf)3, acylation of aromatic compounds having electron-donating substituents such as anisole, thioanisole, and mesitylene with acid anhydrides proceeded smoothly to afford the corresponding aromatic ketones in high yields. Although RE(OTf)3 alone is not effective for acylation of less reactive aromatics such as toluene, the combination of RE(OTf)3 and lithium perchlorate (LiClO4) enhanced the catalytic activity dramatically. Friedel-Crafts acylation reactions using rare earth metal perfluoroalkanesulfonates were also successfully performed in supercritical carbon dioxide (scCO2). Moreover, in the presence of a catalytic amount of RE(OTf)3, aromatic compounds reacted with benzyl chloride smoothly to afford the corresponding alkylation products in high yields. In these reactions, RE(OTf)3 could be easi...
76 citations
TL;DR: In this article, the cholesteric phase of resolved indolylfulgides was induced by photo-irradiation of a nematic liquid crystal (5CB) with an enantiomer of resolved (R)-binaphthol-condensed (S)-indolyl fulgides.
Abstract: When an enantiomer of resolved indolylfulgide (1) or either of the (R)-binaphthol-condensed indolylfulgides (2, 3) was mixed with a nematic liquid crystal (5CB), the cholesteric phase was induced. Their cholesteric pitches were reversibly changed by photoirradiation. Whereas the twisting ability of the cholesteric pitch (βM) was larger for the colorless form than for the colored form in the case of 1, it was larger for the colored form than for the colorless form in the cases of 2 and 3. In addition, βM of 1 is generally smaller than that of 2 and 3. These phenomena were explained in terms of the helical conformation of the hexatriene moiety of fulgides and the chirality of the binaphthol moiety. The cholesteric sense of a fulgide-doped liquid crystal was changed between plus and minus reversibly by the pre-doping of the chiral formaldehyde acetal of 1,1′-bi-2-naphthol ((S)-4).
73 citations
TL;DR: The fatigue mechanism of photochromic 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene was studied in hexane solution as discussed by the authors.
Abstract: The fatigue mechanism of photochromic 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene was studied in hexane solution. Upon irradiation with ultraviolet light, two kinds of by-products were produced in addition to normal photochromic reactions. The major by-product was isolated by HPLC, and was characterized by 1H NMR and absorption spectroscopies and X-ray crystallographic analysis. A minor by-product was also isolated and analyzed with a mass spectrometer. Based on the molecular structural analysis a possible photofatigue mechanism of the dithienylethene was proposed.
70 citations
TL;DR: The use of trifluoroacetate as an efficient and nonhygroscopic catalyst for the alcoholysis, hydrolysis, and acetolysis of epoxides was studied in this article.
Abstract: Iron(III) trifluoroacetate was used as an efficient and nonhygroscopic catalyst for the alcoholysis, hydrolysis, and acetolysis of epoxides. The addition of chloride, bromide, iodide, and nitrate ions to epoxides to produce the corresponding 2-halo and 2-nitratoalkanols and also the conversion of epoxides to acetonides and thiiranes were also performed efficiently in the presence of this catalyst.
TL;DR: In this paper, the authors calculated the bare V of the highest occupied molecular orbitals (HOMO) of BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) is calculated for various molecular geometries.
Abstract: Intermolecular Coulomb repulsion, V, of the highest occupied molecular orbitals (HOMO) of BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) is calculated for various molecular geometries. The bare V is a quantity that is easily estimated under the point charge approximation. As far as the screened V in actual crystals is proportional to the calculated bare V, the usual θ-phase prefers the horizontal or diagonal stripe, whereas the vertical stripe becomes comparatively stable in the limit of the small dihedral angle (in the metallic limit). The phase diagrams of the θ-phase are discussed under the combination of the static charge distribution (the atomic limit) and the Stoner model (the extended Stoner model). The model contains two order parameters: the spin polarization, Sz, and the charge order, n-1/2. This model explains why the insulating state of the Rb salt below 190 K is a paramagnetic charge-ordered state, while the Cs salt has a different insulating phase below 20 K. The lattice dimerization of th...
TL;DR: In this article, a mixture of CuCN and N-benzylbenzenesulfonamide catalyzes the 1,4-addition of dialkylzincs or diarylizincs to α,β-unsaturated ketones to give, after aqueous workup, the corresponding β-substituted ketones in nearly quantitative yields.
Abstract: A mixture of CuCN and N-benzylbenzenesulfonamide catalyzes the 1,4-addition of dialkylzincs or diarylzincs (Cu : Zn = 1 : 200 to 1 : 10000) to α,β-unsaturated ketones to give, after aqueous workup, the corresponding β-substituted ketones in nearly quantitative yields. A range of cyclic enones having s-cis or s-trans geometries as well as conformationally flexible acyclic enones are usable as substrates. The ethyl group migrates more readily than the methyl and phenyl groups. CuOTf, CuO-t-C4H9, and mesitylcopper can be used in place of CuCN. The in situ-formed alkylzinc enolate, prior to aqueous workup, further undergoes an aldol reaction with aldehydes or Pd(0)-assisted coupling with allyl acetate, resulting in regio-controlled, vicinal carbacondensation products. A catalytic cycle is proposed on the basis of a kinetic study and a structural analysis of the zinc enolate product by NMR and molecular weight measurements.
TL;DR: In this article, two types of silver-triphenylphosphine complexes with 2-mercaptonicotinic acid (H2mna) were obtained by single-crystal X-ray diffraction.
Abstract: Two types of silver(I)-triphenylphosphine complexes with 2-mercaptonicotinic acid (H2mna) were prepared as [Ag(Hmna)(PPh3)n] (1, n = 2; 2, n = 3); their crystal structures determined by single-crystal X-ray diffraction. These complexes were obtained from reactions of the precursor, [Ag(Hmna)]n, with less excess (3 equiv) and large excess (20 equiv) amounts of PPh3, respectively. Complex 1 was also obtained from a reaction among another precursor [AgCl(PPh3)3], H2mna and aqueous NaOH. The coordination geometry of 1 was a trigonal pyramid with an AgSP2 core; there was a weak interaction between the silver(I) center and the pyridine nitrogen atom, while that of 2 was a distorted tetrahedron with an AgSP3 core. In both 1 and 2, the carboxyl group was protonated and its oxygen atoms did not participate in the coordination. In contrast to the formation of 1 and 2, a related complex, [Ag(Hmba)(PPh3)3] 4 (H2mba = 2–mercaptobenzoic acid), has been obtained from a reaction of [Ag(Hmba)]n with a stoichiometric amoun...
TL;DR: In this paper, the homo-coupling reactions of an alkenyl- or arylsilane readily occur with a copper(I) salt in an aprotic polar solvent such as N, N-dimethylformamide or dimethyl sulfoxide under an aerobic condition to give the corresponding conjugated dienes or biaryls, respectively.
Abstract: Homo-coupling reactions of an alkenyl- or arylsilane readily occur with a copper(I) salt in an aprotic polar solvent such as N, N-dimethylformamide or dimethyl sulfoxide under an aerobic condition to give the corresponding conjugated dienes or biaryls, respectively. Optimization of a copper salt and a solvent for the homo-coupling reaction is discussed. The formation of the organocopper intermediates is evidenced by trapping experiments with iodine and by a conjugate addition to methyl vinyl ketone.
TL;DR: It was essential for the successful synthesis of this compound to utilize a new removal method for the chiral source with a combination of tetrabutylammonium hydroxide and hydrogen peroxide to utilize the desired product in high yield with high optical purity.
Abstract: (R)-2-Propyloctanoic acid has been developed as a novel therapeutic agent for Alzheimer's disease. A large-scale synthesis of this candidate was achieved by using Oppolzer's camphorsultam as a chiral auxiliary under improved conditions. It was essential for the successful synthesis of this compound to utilize a new removal method for the chiral source with a combination of tetrabutylammonium hydroxide and hydrogen peroxide. The present process afforded the desired product in high yield with high optical purity.
TL;DR: In this paper, the reaction of dimethyl(phenyl)silanol with butyl acrylate in the presence of a stoichiometric amount of Pd(OAc)2 or by a combined use of 0.1 molar amount of Cu(OAC)2/LiOAc (molar ratio 3/2) gave butyl cinnamate in 76% or 57% yield, respectively.
Abstract: The reaction of dimethyl(phenyl)silanol with butyl acrylate in the presence of a stoichiometric amount of Pd(OAc)2 or by a combined use of 0.1 molar amount of Pd(OAc)2 and Cu(OAc)2/LiOAc (molar ratio 3/2) gave butyl cinnamate in 76% or 57% yield, respectively. The similar reaction with tributyl(phenyl)tin also proceeded in 77% yield. The organotin compound was shown to react faster than the silanol, although the tin reagent sometimes induced undesirable homo-coupling, while the reaction with silanol did not give such by-product.
TL;DR: In this article, the structural effects on the alkyl substitutions at the close 3 position in hydrotris(pyrazolyl)borates play an important role in modifying the coordination environment about a copper(II) center and their physicochemical properties.
Abstract: New mononuclear nitratocopper(II) complexes ([Cu(NO3){HB(3,5-iPr2pz)3}] (1) and [Cu(NO3){HB(3-tBu-5-iPrpz)3}] (3)) and a novel mononuclear hydroxocopper(II) complex ([Cu(OH){HB(3-tBu-5-iPrpz)3}] (4)) have been prepared. These complexes were characterized by X-ray analysis and IR, UV-vis, and EPR spectroscopies. Except for the dinuclear complex ([{Cu[HB(3,5-iPr2pz)3]}2(μ-OH)2] (2)), the complexes are mononuclear structures having square-pyramidal (1), trigonal-pyramidal (3), and distorted tetrahedral (4) geometry. In comparison with these structures and their physicochemical properties, the structural effects on the alkyl substitutions at the close 3-position in hydrotris(pyrazolyl)borates play an important role in modifying the coordination environment about a copper(II) center and their physicochemical properties.
TL;DR: In this paper, the peroxidase was used as a catalyst for the enzymatic oxidative polymerization of phenol using a mixture of alcohol and buffer, and hydrogen peroxide (oxidizing agent) was added to the reaction mixture.
Abstract: Enzymatic oxidative polymerization of phenol using peroxidase as catalyst has been carried out in a mixture of alcohol and buffer. Hydrogen peroxide (oxidizing agent) was added dropwise to the reaction mixture. Effects of the reaction parameters have been systematically investigated. The polymer solubility strongly depended on the buffer pH and content, and a polymer soluble in N,N-dimethylformamide (DMF) was obtained in good yields under appropriate reaction conditions. The solvent composition also affected the regioselectivity of the polymer. Purity and amount of the enzyme also affected the polymerization behaviors. By changing the concentration and addition rate of hydrogen peroxide, the molecular weight and solubility of the polymer could be controlled. Some solid properties of the resulting polyphenol were evaluated. From thermal analysis, the polymer was found to possess relatively high thermal stability.
TL;DR: In this article, the authors present from density functional theory calculations how a reactive surface species is generated upon decomposition of dinitrogen oxide (N2O) and propose a possible form of α-oxygen on Fe-ZSM-5 zeolite, a surface oxygen species responsible for high reactivity in oxidation of methane and benzene.
Abstract: The so-called ``α-oxygen" on Fe-ZSM-5 zeolite, a surface oxygen species responsible for high reactivity in oxidation of methane and of benzene, has been investigated. We present from density-functional-theory (DFT) calculations how such a reactive surface species is generated upon decomposition of dinitrogen oxide (N2O) and propose a possible form of ``α-oxygen" on Fe-ZSM-5 zeolite. In the initial stages of the reactions, a complex involving an Fe(ON2) moiety is formed, followed by dissociation into an iron-oxo species and N2. The activation energy for the decomposition of N2O on a possible iron active site model of Fe-ZSM-5 zeolite is predicted to be 2.4 kcal mol-1 at the B3LYP level of theory. Therefore the decomposition of N2O is expected to take place easily at a coordinatively unsaturated iron active center supported on zeolite. The iron-oxo species thus formed should play an essential role in the direct hydroxylation of methane, benzene, and other hydrocarbons if it involves a coordinatively unsatur...
TL;DR: In this article, the authors developed optical oxygen sensors based on the luminescence intensities of four different europium(III) complexes, ((1,10-phenanthroline)tris(thenoyltrifluoroacetonato)europium-III dihydrate ([Eu(tta)3]·2H2O), tris(1, 1,1, 2,2,3,3-heptafluoro-7, 7-dimethyl-4,6-octanedionato) europ
Abstract: New optical oxygen sensors based on the luminescence intensities of four different europium(III) complexes, ((1,10-phenanthroline)tris(thenoyltrifluoroacetonato)europium(III) complex ([Eu(tta)3phen]), tris(thenoyltrifluoroacetonato)europium(III) dihydrate ([Eu(tta)3]·2H2O), tris(1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedionato)europium(III) complex ([Eu(pta)3]·2H2O) and tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionato)europium(III) complex ([Eu(fod)3]·2H2O)) immobilized in poly(styrene-co-2,2,2-trifluoroethyl methacrylate) (poly-(styrene-co-TFEM)) films were developed. The luminescence intensity of the europium(III) complex films decreased with increasing the oxygen concentration. Stern-Volmer plots of the europium(III) complex films exhibited considerable linearity. The KSV values of [Eu(tta)3phen], [Eu(tta)3]·2H2O, [Eu(pta)3]·2H2O and [Eu(fod)3]·2H2O in films were estimated to be 0.015, 0.005, 0.002 and 0.003 %-1, respectively. The large KSV value of the [Eu(tta)3phen] film was obtained compa...
TL;DR: In this article, dark-brown planar dianionic planar complexes of O(μ-O)VO 4+ with the general formula (VOL)2O were isolated from reactions of bis(acetylacetonato)oxovanadium(IV) and aroylhydrazones of salicylaldehyde or of 5-methoxysalicylylaldehyde (H2L, two H stand for the dissociable protons at the phenol and amide functionalities) in acetonitrile.
Abstract: Dark-brown complexes of {OV(μ-O)VO}4+ with the general formula [(VOL)2O] were isolated from reactions of bis(acetylacetonato)oxovanadium(IV) and aroylhydrazones of salicylaldehyde or of 5-methoxysalicylaldehyde (H2L, two H stand for the dissociable protons at the phenol and the amide functionalities) in acetonitrile. The infrared spectra of these complexes are consistent with the dianionic form of the ligands. The electronic spectral profiles are very similar and display strong absorptions in the range 425—263 nm due to ligand-to-metal charge transfer and intraligand transitions. The proton NMR spectra suggest that in solution the two ligands in each complex are magnetically equivalent. The complexes are redox active and display a reduction response in the potential range -0.28—0.47 V (vs. Ag/AgCl). The molecular structures of the complexes were determined by X-ray crystallography. The deprotonated dianionic planar ligands coordinate the metal ions through the phenolate-O, the imine-N, and the amide-O ato...
TL;DR: Copper(II) complexes of several new N3O-type tripodal ligands, including 2,4-di(t-butyl)-6-{[bis(2-pyridyl)methyl]aminomethyl}phenol (HtbuL), 2, 4-di-tbutyl-6- {[(1-methyl-2-imidazolyl)methyl][(6-methyl)-2-polymorphic]methyl]amino-acetyl]-phenol(Mepy) RE
Abstract: Copper(II) complexes of several new N3O-type tripodal ligands, 2,4-di(t-butyl)-6-{[bis(2-pyridyl)methyl]aminomethyl}phenol (HtbuL), 2,4-di(t-butyl)-6-{[(6-methyl-2-pyridyl)methyl](2-pyridylmethyl)aminomethyl}phenol (HtbuL(Mepy)), 2,4-di(t-butyl)-6-{bis[(6-methyl-2-pyridyl)methyl]aminomethyl}phenol (HtbuL(Mepy)2), and 2,4-di(t-butyl)-6-{[(1-methyl-2-imidazolyl)methyl][(6-methyl-2-pyridyl)methyl]aminomethyl}phenol (HtbuL(im)(Mepy)), were prepared. They were structurally characterized by the X-ray crystallographic method to have a square-pyramidal structure with a weakly coordinating group at an apical position. The phenol moiety of [CuCl(tbuL(Mepy))] (2), [CuCl(tbuL(Mepy)2)] (3), and [CuCl(tbuL(im)(Mepy))] (4) was revealed to be coordinated equatorially; it was converted to the phenoxyl radical upon oxidation with Ce(IV), giving a new absorption peak at 405—420 nm. ESR measurements at low temperatures and resonance Raman spectra established that the radical species has a Cu(II)-phenoxyl radical bond. The cy...
TL;DR: A pyrazine bridged dimer of triruthenium clusters [{RuIII2RuII(μ3-O)(μ-CH3CO2)6(CO)(abco)}2(μ-pz)] gave an inter-cluster mixed valence state upon one electron reduction as mentioned in this paper.
Abstract: A pyrazine bridged dimer of triruthenium clusters [{RuIII2RuII(μ3-O)(μ-CH3CO2)6(CO)(abco)}2(μ-pz)] (abco =1-azabicyclo[2,2,2]octane, pz = pyrazine) gives an inter-cluster mixed valence state upon one electron reduction. The splitting of the reduction waves in cyclic voltammetry, ΔE, was 470 mV. This corresponds to a comproportionation constant for formation of the mixed valence state of 9.0 × 107. The IR spectrum of the mixed valence species in the ν(CO) region, measured by reflectance IR spectroelectrochemistry, showed a completely coalesced ν(CO) band. This represents delocalized redox behavior on the infrared vibrational timescale. The rate constant for intramolecular electron transfer was estimated to be 1 × 1012 s-1 at -18 °C by simulating the ν(CO) absorption bandshape. The mixed valence complex showed an intervalence charge transfer (ICT) band at 12500 cm-1. Hush analysis provides a spectroscopic estimate of HAB to be 2490 cm-1. Crystal structures of [{RuIII2RuII(μ3-O)(μ-CH3CO2)6(CO)(abco)}2(μ-pz)]...
TL;DR: In this article, the coordination of a triple bond to Lewis acids is proposed as a key step for the Lewis acid catalyzed reactions, and it is well known that transition metal catalyzed hydrometalations and carbometalations, in general, proceed in a cis-manner.
Abstract: Hydrosilylation, hydrostannation, carbosilylation, and carbostannation of unactivated alkynes with organosilanes, or organostannanes proceed effectively in the presence of catalytic amounts of Lewis acids to produce the corresponding vinylsilyl or vinylstannyl compounds in a highly regio- and stereoselective way. Although it is well known that transition metal catalyzed hydrometalations and carbometalations, in general, proceed in a cis-manner, the Lewis acid-catalyzed reactions proceed in a trans-manner exclusively. The coordination of a triple bond to Lewis acids is proposed as a key step for the Lewis acid catalyzed reactions.
TL;DR: In this paper, optically active hydroxamic acids bearing a 1,1′-binaphthyl group were prepared as ligands in a vanadium-catalyzed asymmetric epoxidation.
Abstract: New optically active hydroxamic acids bearing a 1,1′-binaphthyl group were prepared as ligands in a vanadium-catalyzed asymmetric epoxidation. The feature of these hydroxamic acids is a sterically hindered ligand. The asymmetric epoxidation with good selectivity and reactivity can be established by using VO(O-i-Pr)3 (5 mol%) and a small excess amount of ligand (7.5 mol%) with triphenylmethyl hydroperoxide (TrOOH) in toluene at -20 °C. Disubstituted allyl alcohols were epoxidized more rapidly than mono- or tri-substituted allyl alcohols, and were obtained in good to high enantioselectivities (48—94%ee). The transition state based on X-ray crystal structure of 1e is discussed.
TL;DR: In this article, the porphyrin moiety of meso-tetraphenylporphyrins (H2T(4-X)PP, X = H, Cl, CH3, CH(CH3)2, OCH3), H4TPP2+Cl2+H4P2+C 2+C2+OCH3+C 3 ) was found to be bonded from above and below the mean porphrin plane to the lone electron pairs of the pyrrolenine nitrogens of the tetraphen
Abstract: Different para-substituted meso-tetraphenylporphyrins (H2T(4-X)PP, X = H, Cl, CH3, CH(CH3)2, OCH3) react with various molar ratios of tetracyanoethylene (TCNE) in dichloromethane or benzene and produce only the 1 : 2 molecular complex, (TCNE)2H2T(4-X)PP. The remarkable agreement between the corresponding 1H, 13C solution (CDCl3) NMR resonances of the porphyrin moiety in these complexes with those of tetraphenylporphyrin dication, H4TPP2+, and also the strong resemblance between their UV-vis spectra and the spectra of the related diprotonated porphyrins indicates similar out-of-plane distorted porphyrin core structure in all of them. Based on these close spectral correspondences among the various molecular complexes and the related diprotonated porphyrins, and also consideration of the known structure of H4TPP2+Cl2- species, it is proposed that the two TCNEs in (TCNE)2H2T(4-X)PP complexes are bonded from above and below the mean porphyrin plane to the lone electron pairs of the pyrrolenine nitrogens of the...
TL;DR: In this paper, the authors present theoretical analyses for the conversion of methane to methanol on a diiron model of soluble methane monooxygenase (sMMO) and on dicopper models of particulate methyl migration via a three-centered transition state (TS2) using the hybrid density functional theory B3LYP method.
Abstract: We present theoretical analyses for the conversion of methane to methanol on a diiron model of soluble methane monooxygenase (sMMO) and on dicopper models of particulate methane monooxygenase (pMMO) using the hybrid density-functional-theory B3LYP method. Methane is proposed to be reasonably converted into methanol in a two-step concerted manner on the dinuclear enzyme models. The first step in our proposal is concerted H atom abstraction of methane via a four-centered transition state (TS1) and the second step is concerted methyl migration via a three-centered transition state (TS2). The general features of the electronic process are identical to those of the gas-phase process for the methane-methanol conversion by the bare FeO+ complex. The concerted H atom abstraction and the direct H atom abstraction via a transition state with a linear C-H-O(Fe) array are compared using the dinuclear models. The transition state for the direct H atom abstraction (TSd) on the diiron model is found in the spin undecet ...
TL;DR: The gelators of organic solvents are classified into two categories on the basis of their basic intermolecular forces as discussed by the authors : hydrogen-bonded or non-hydrogen bonded.
Abstract: The gelators of organic solvents are classified into two categories on the basis of their basic intermolecular forces: hydrogen-bonded or nonhydrogen-bonded. To utilize these two interactions cooperatively for organogel formation we newly synthesized seven gelators (1—7) and two reference compounds (8 and 9) which have both a cholesterol moiety and a saccharide moiety within one molecule. The solubility of 1—7 changed drastically from totally insoluble one to very soluble one depending on the saccharide absolute configuration. In general, the gelator became very insoluble when it includes many equatorial OH groups, whereas it became very soluble when it includes many axial OH groups. Gelators 2 and 5 bearing two equatorial OH groups and one axial OH group acted as good gelators and in several cases the sol-gel phase-transition temperatures (measured in a sealed tube) were higher than the boiling points. The SEM observations of the xerogels established that the stable gels contain the entangled fibrous net...
TL;DR: In this article, dispersions of these bimetallic nanoclusters with different composition ratios are extensively examined as catalysts for the hydrogenation of various nitrobenzene derivatives: i.e., p-nitrotoluene, 1-nitronaphthalene, etc.
Abstract: Poly(N-vinyl-2-pyrrolidone)-protected Ni/Pd bimetallic colloidal nanoparticles, prepared by the polyol reduction method, have been proved to have a nanometer-sized alloy structure with both metals at zerovalent state by our previous study of TEM, XRD, EXAFS, and XPS analyses. Here, dispersions of these bimetallic nanoclusters with different composition ratios are extensively examined as catalysts for the hydrogenation of various nitrobenzene derivatives: i.e., p-nitrotoluene, p-nitroanisole, 1-nitronaphthalene, p-nitrobenzonitrile, and methyl p-nitrobenzoate, at 30 °C under an atmospheric pressure of hydrogen. These bimetallic nanoclusters exhibit excellent catalytic properties for the reduction of a nitro group to an amino group with high selectivity. The catalytic activity strongly depends on the metal composition of the particles. The maximum catalytic activity can be observed at a certain intermediate composition ratio, being 3—4 times greater than that of a monometallic colloidal Pd catalyst. A bimet...