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191.
Tayagaki T Galet A Molnar G Muñoz MC Zwick A Tanaka K Real JA Bousseksou A 《The journal of physical chemistry. B》2005,109(31):14859-14867
The 1A1 left arrow over right arrow 5T2 spin transition has been investigated in the solid solutions of Fe(x)M(1-x)(pyrazine)[Pt(CN)4] (M = Ni or Co, 0 < or = x < or = 1) having a three-dimensional polynuclear structure. Both Ni and Co dilutions tend to decrease the hysteresis width and smooth the transition curves. The enthalpy (entropy) change associated with the spin transition was found to decrease from 26 kJ mol(-1) (84 J K(-1) mol(-1)) for x = 1 to 12 kJ mol(-1) (47 J K(-1) mol(-1)) for 47% Co dilution and to 15 kJ mol(-1) (54 J K(-1) mol(-1)) for 59% Ni dilution. Raman spectroscopy revealed a mixed one- and two-mode behavior in the solid solutions. For the first time, a correlation between vibrational frequencies exhibiting one-mode behavior and the entropy change, which drives the spin crossover, is established. 相似文献
192.
Isao Kaetsu Hiroshi Okubo Akihiko Ito Koichiro Hayashi 《Journal of polymer science. Part A, Polymer chemistry》1973,11(6):1149-1156
The radiation-induced polymerization of binary systems consisting of glass-forming monomer and glass-forming solvent in supercooled phase was studied. The initial polymerization rates were markedly affected by Tg (glass transition temperature) and Tv of the system (30–50°C higher than Tg), which turned to be functions of the composition. The composition and temperature dependence of initial polymerization rate in binary glass-forming systems were much affected by homogeneity of the polymerization system and the Tg of the glass-forming solvent. The composition and temperature dependences in the glycidyl methacrylate–triacetin system as a typical homogeneous polymerization system were studied in detail, and the polymerizations of hydroxyethyl methacrylate–triacetin and hydroxyethyl methacrylate–isoamyl acetate systems were studied for the heterogeneous polymerization systems; the former illustrates the combination of lower Tg monomer and higher Tg solvent and the latter typifies a system consisting of higher Tg monomer and lower Tg solvent. All experimental results for the composition and temperature dependence of initial polymerization rate in binary glass-forming systems could be explained by considering the product of the effect of the physical effect relating to Tv and Tg of the system and the effect of composition in normal solution polymerization at higher temperature, which was also the product of a dilution effect and a chemical or physical acceleration effect. 相似文献
193.
Previously, an artificial siderophore complex, the iron(III) complex with tris[2-[(N-acetyl-N-hydroxy)glycylamino]ethyl]amine (TAGE), was constructed in order to understand the effect of intramolecular hydrogen bonding interaction on the siderophore function, and its structural characterization in the solid state was reported (Inorg. Chem. 2001, 40, 190). In this paper, the solution behavior of the M(III)-TAGE (M = Fe, Ga) system has been investigated using (1)H NMR, UV-vis, and FAB mass spectroscopies in efforts to characterize the biological implication of hydrogen bonding networks between the amide hydrogens and coordinating aminohydroxy oxygens of the complex. The temperature dependence of (1)H NMR spectra for Ga(III) complex of TAGE indicates that hydrogen bonding networks are maintained in polar solvents such as DMSO-d(6) and D(2)O. The UV-vis spectra of the Fe(III)-TAGE system under various pH conditions have shown that TAGE forms a tris(hydroxamato)iron(III) complex in an aqueous solution in the pH range 4-8. By contrast, tris[2-[(N-acetyl-N-hydroxy)propylamido]ethyl]amine (TAPE; TAGE analogue that is difficult to form intramolecular hydrogen bonding networks), which has been synthesized as a comparison of TAGE, forms both of bis- and tris(hydroxamato)iron(III) complexes in the same pH range. Both the stability constants (log beta(FeTAGE) = 28.6; beta(FeTAGE) = [Fe(III)TAGE]/([Fe(3+)][TAGE(3)(-)])) and pM (-log[Fe(3+)]) value for Fe(III)TAGE (pM 25) are comparable to those of a natural siderophore ferrichrome (log beta = 29.1 and pM 25.2). The kinetic study of the TAGE-Fe(III) system has given the following rate constants: the rate of the ligand exchange reaction between Fe(III)TAGE and EDTA is 6.7 x 10(-4) s(-1), and the removal rates of iron from diferric bovine plasma transferrin by TAGE are 2.8 x 10(-2) and 6.0 x 10(-3) min(-1). These values are also comparable to those of a natural siderophore desferrioxamine B under the same conditions. In a biological activity experiment, TAGE has promoted the growth of the siderophore-auxotroph Gram-positive bacterium Microbacterium flavescens, suggesting that TAGE mimics the activity of ferrichrome. These results indicate that the artificial siderophore with intramolecular hydrogen bonding networks, TAGE, is a good structural and functional model for a natural ferrichrome. 相似文献
194.
[chemical reaction: see text]. Diorganophosphide anions, which usually function as nontransferable ligands on mixed cuprates, undergo smooth 1,2-migration on ate-type copper carbenoids. Phosphinodisilylmethylcoppers prepared by this protocol are converted into the corresponding phosphines, which can be used as bulky, highly basic and air-stable ligands. 相似文献
195.
Fujita K Yorimitsu H Shinokubo H Oshima K 《Journal of the American Chemical Society》2004,126(21):6776-6783
Zirconocene-olefin complexes Cp(2)Zr(H(2)C=CHR), prepared in benzene-THF at 0 degrees C, react with acid chlorides to provide homoallylic alcohols. The key is an equilibrium between the zirconocene-olefin complexes and the corresponding zirconocene allyl hydride complexes via allylic C-H bond cleavage of the coordinating alkenes. Furthermore, the zirconocene-olefin complexes are also available for the reaction with 1,4-diketone to afford anti-1,4-diols with excellent diastereoselectivity. Thus, Cp(2)Zr(H(2)C=CHR) serves as a donor of both hydride and an allylic group. These reactions also proceed efficiently by using zirconocene-olefin complexes, derived from Cp(2)ZrCl(2), Mg metal, and 1-alkenes. 相似文献
196.
Nerol is cyclized to terpinyl chloride or bromide in the presence of TiX4-PhNHMe (1:1) complex in dichloromethane at ?23 °C, while cyclization of ()-allylic alcohols CH2=CR-CH2CH2CMe=CHCH2OH (R = H, Me, Cl) produces seven-membered ring products in fair yields. 相似文献
197.
Me2AlSPh or Me2AlSeMe adds to α,β-unsaturated carbonyl compounds in 1,4-fashion. The resulting aluminium enolates react with aldehydes effectively to afford the adducts of the title anion after formal PhSH (or MeSeH)-elimination. 相似文献
198.
Koichi Takakura Koichiro Hayashi Seizo Okamura 《Journal of polymer science. Part A, Polymer chemistry》1966,4(7):1731-1745
Cyclic ethers such as trioxane and 3,3-bis(chloromethyl)oxetane have been polymerized easily in the presence of maleic anhydride by the irradiation of γ-rays and ultraviolet light. The polymer formed is a homopolymer of cyclic ether. The rate of polymerization is accelerated by suitable amounts of oxygen which is required to form some active species at the initiation step. The polymerization is inhibited by the addition of a small amount of radical scavenger, thus suggesting a radical initiating mechanism. In addition, the polymerization is easily initiated by benzoyl peroxide even in vacuo at or above 50°C. Diaroyl and diacyl peroxides are also effective, and polymerization also proceeds in the presence of chloromaleic anhydride, exactly in the same manner as in maleic anhydride. On the other hand, it is well known that polymerization of these cyclic monomers rarely occurs with radical catalysts and easily with cationic catalysts in the absence of maleic anhydride. From these results, it may be concluded that the polymerization is brought about by means of a radical–cationic species. 相似文献
199.
Cobalt/N-heterocyclic carbene system or cobalt/diamine combination effectively catalyzes sequential cyclization/cross-coupling reactions of 6-halo-1-hexene derivatives with trialkylsilylmethyl, 1-alkynyl, and aryl Grignard reagents. The sequential cyclization/cross-coupling reactions are applied to the synthesis of 1,3-diols starting from siloxy-tethered 6-halo-1-hexene derivatives. 相似文献
200.
Radical reactions mediated by Schwartz reagent and zirconocene(alkene) complex are firstly described. Schwartz reagent is a promising alternative to tributyltin hydride and the first transition metal hydrido complex used as a radical mediator in organic synthesis. A zirconocene(alkene) complex effects single electron transfer to alkyl halide to generate the corresponding alkyl radical. Secondly, serendipitous allylic C-H bond activation of the coordinating alkene of zirconocene(alkene) complex and its application to organic synthesis are summarized. By utilizing equilibrium between zirconocene(alkene) and zirconocene 2-alkenyl hydride, reaction of acid chloride with zirconocene(alkene) provides the corresponding homoallylic alcohol by sequential attacks of the hydride and 2-alkenyl moieties. A set of hydride and 2-alkenyl attacks on 1,4-diketone yields 6-heptene-1,4-diol derivative in high yield with high stereoselectivity. Selective capture of the hydride with diisopropyl ketone gives zirconocene 2-alkenyl alkoxide, which is a useful reagent for stereoselective allylation of aldehyde and imine. alpha-Halo carbonyl compounds undergo radical allylation with the zirconocene 2-alkenyl alkoxide which serves as a substitute for allyltin. 相似文献