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151.
Rijssenbeek JT Saito T Malo S Azuma M Takano M Poeppelmeier KR 《Journal of the American Chemical Society》2005,127(2):675-681
The related parameters of cation size and valence that control the crystallization of Sr(3)CaRu(2)O(9) into a 1:2 B-site-ordered perovskite structure were explored by cationic substitution at the strontium and calcium sites and by the application of high pressure. At ambient pressures, Sr(3)MRu(2)O(9) stoichiometries yield multiphasic mixtures for M = Ni(2+), Mg(2+), and Y(3+), whereas pseudocubic perovskites result for M = Cu(2+) and Zn(2+). For A-site substitutions, an ordered perovskite structure results for Sr(3-x)Ca(x)CaRu(2)O(9), with 0 = x = 1.5. In contrast, Ba(2+) substitution for Sr(2+) is accompanied by a phase change to a hexagonal BaTiO(3) structure type. At high pressures and temperatures, a 1:2 B-site-ordered perovskite structure is stabilized for Sr(3-x)Ba(x)CaRu(2)O(9), with 0 = x = 3. The scarcity of B-site-ordered perovskite ruthenates at ambient pressure and the metastable nature of the high-pressure phases underscore the strict size and valence requirements that must be met by the constituent cations to achieve these uncommon ordered structures. 相似文献
152.
Michael I. Bruce Andrew Catlow Mark G. Humphrey George A. Koutsantonis Michael R. Snow Edward R.T. Tiekink 《Journal of organometallic chemistry》1980,338(1):59-80
A reinvestigation of the reaction between C2(CO2Me)2 and RuH(PPh3)2(η-C5H5) and some related complexes is reported. Initial cis addition is followed by conversion into the trans isomer. In the case of the bis-(PPh3) complex, isomerisation is followed by chelation of the ester CO group with concomitant displacement of one PPh3ligand. The resulting chelate complex reacts with CO or CNBut to give the (Z)-RuC(CO2Me)CH(CO2Me) complexes; the (E)-isomer of the carbonyl complex is obtained by addition of C2(CO2Me)2to RuH(CO)(PPh3)(η-C5H5). The 1Hand 13C NMR spectra are not a reliable guide to assignment of the stereochemistry of the vinyl group. Other products isolated from the initial reaction are the bis-insertion product CH(CO2Me)} -(PPh3)(η-C5H5) and the 1/2 PPh3/C2(CO2Me)2 adduct. The molecular structures of Ru{(Z)-C(CO2Me)CH(CO2Me)}(CO)(PPh3(η-C5H5) · 0.5EtOH, Ru{(E)-C(C2Me)CH(CO2Me)}(dppe)(η-C5H5) and CH(CO2Me)}(PPh3)(η-C5H5) have been determined. The cis isomer is monoclinic, space group P21,with a 9.328(8), b 17.385(10), c 10.356(7) Å, β 101.78(3)° and Z = 2; 2107 data with I ≥ 2.5σ(I) were refined to R = 0.076 Rw = 0.085. The trans isomer is triclinic, space group P, with a 10.404(7) b 11.221(6), c 13.230(9) Å, α 92.67(5), β 110.56(5), γ 106.21(5)° and Z = 2; 2520 data with I ≥ 2.5σ(I) were refined to R = 0.055 Rw = 0.068. The butadienyl complex is monoclinic, space group P21/a, with a 19.655(8), b 8.674(4), c 21.060(5) Å, β 116.22(3)° and Z = 4; 2724 data with I ≥ 2.5σ(I) were refined to R = 0.042, Rw = 0.047. 相似文献
153.
John T. Shaw Christine E. Brotherton Robert W. Moon Mark D. Winland Mark D. Anderson Keith S. Kyler 《Journal of heterocyclic chemistry》1980,17(1):11-16
A much improved synthesis of the heretofore difficultly obtainable 2,6-diaminopyrazine (4) was afforded by the low-pressure catalytic hydrogenation (palladium on carbon) of 2,6-diazido-pyrazine (2) ; reaction of 2,6-dichloropyrazine (1) and sodium azide gave 2 in 84% yield. The outcome of the reduction was found to be solvent dependent: 1,2-dimethoxyethane containing aqueous ammonia gave 4 in 83% yield; 1,2-dimethoxyethane alone gave 5-aminotetrazolo[1,5-a]-pyrazine (3) in 26% yield. Additional alternative syntheses of 3 and 4 are described. A number of acyl and azo derivatives of 4 were prepared. Reactions of 2 with dimethyl acetylenedicarboxylate and ethyl acetate (base catalyzed) leading to vic-triazole derivatives are also described. 相似文献
154.
Among the polyhedral [closo-BnHn]2- ion series (n = 5-12 inclusive) the aromatic [closo-B10H10]2- ion is both readily available and quite reactive. Among its many reactions which retain its cage structure one finds the oxidative dimerization reaction in which two [closo-B10H12]2- ions each formally lose a hydride ion and undergo dimerization of the resulting [closo-B10H9]- ions to produce the [trans-B20H18]2- ion. The two-component [closo-B10H9]- ions of the latter are linked together by a pair of unique B-B-B bonds which provide unprecedented reactivity to the structure. Among these reactions are the two-electron reduction to a set of three interconvertible [B20H18]4- ions having intercage B-B bonds and the related reductive substitution reaction in which [trans-B20H18]2- undergoes attack by nucleophile, L, to produce [B20H18L]2-. The latter species is formally a substituted [B20H19]3- (L = H) ion formed by B-B bond protonation of one of the isomeric [B20H18]4- ions. These and a variety of novel reactions are described here along with interrelated reaction mechanisms considered for the first time. 相似文献
155.
Mark Salomon 《Journal of solution chemistry》1990,19(12):1225-1236
Conductivity data are used to determine thermodynamic complex formation constants for cases in which both the initial electrolyte and the complexed electrolyte form ion pairs. Using the method described in the text, the complex formation constants of Li+, Na+ and K+ with the crown ether 18-crown-6 and of Li+ with the ligand triphenylphosphine oxide in propylene carbonate have been evaluated from conductance data. The complexation of AgBr in propylene carbonate solutions of n-etrabutylammonium bromide has also been studied by the measurement of molar conductivities. The results of these studies indicate that ion pairing should not be neglected, even in high permittivity solvents such as propylene carbonate, and that the ion pair association constants correlate well with structural studies on cation-crown ether molecular conformations. 相似文献
156.
Hydrocarbon oxidation vs C-C bond-forming approaches for efficient syntheses of oxygenated molecules
[Reaction: see text] A hydrocarbon oxidation approach has been applied to the construction of several linear (E)-allylic alcohols that have served as intermediates in the synthesis of natural products and natural product-like molecules. In the original syntheses, these intermediates were constructed using a standard Wittig-type olefination approach. We report here that routes to these same intermediates designed around a hydrocarbon oxidation approach are more efficient both in the total number of functional group manipulations (FGMs) and overall steps, as well as in the overall yield. 相似文献
157.
158.
The asymmetric total synthesis of (-)-reveromycin A is described. The key steps involved a Lewis acid catalyzed inverse electron demand hetero-Diels-Alder reaction followed by hydroboration/oxidation to afford the spiroketal core 4 in a highly stereoselective manner and introduction of the C18 hemisuccinate by high-pressure acylation. 相似文献
159.
Irina G. Gazaryan Maya Yu. Rubtsova Yuri L. Kapeliuch José Neptuno Rodriguez-Lopez L. Mark Lagrimini Roger N. F. Thorneley 《Photochemistry and photobiology》1998,67(1):106-110
The properties of a newly isolated anionic tobacco peroxidase from transgenic tobacco plants overexpressing the enzyme have been studied with respect to the chemiluminescent reaction of luminol oxidation. These were compared to the properties of horseradish peroxidase in the cooxidation of luminol and p -iodophenol, the enhanced chemiluminescence reaction. The pH, luminol and hydrogen peroxide concentrations were optimized for maximum sensitivity using the tobacco enzyme. The detection limit for the latter under the optimal conditions (2.5 m M luminol, 2 m M hydrogen peroxide, 100 m M Naborate buffer, pH 9.3) was about 0.1 p M , which is at least five times lower than that for horseradish peroxidase in enhanced chemiluminescence with p -iodophenol. The rate constants for the elementary steps of the enzyme-catalyzed reaction have been determined: k 1 = 4.9 × 106 M −1 s1 , k 2 = 7.3 × 106 M −1 s−1 , k 3 = 2.1 × 106 M −1 s−1 (pH 9.3). The similarity of these rate constants is unusual for plant peroxidases. The high catalytic activity of tobacco peroxidase in the luminescent reaction is explained by the high reactivity of its Compound II toward luminol and the high stability of the holoenzyme with respect to heme dissociation. This seems to be a unique property of this particular enzyme among other plant peroxidases. 相似文献
160.
Synthesis and NMR-Spectroscopic Structure Determination of Novel 7,7′-Diphenyl-7,7′-diapocarotenoids
Wittig reaction of crocetindial ( 1 ) and benzylidenetripenylphosphorane ( 2 ) gave (7E, 7′Z)-7,7′-diphenyl-7-7′-diapocarotene ( 3 ), instead of the previously reported (7E, 7′E)-isomer. Similar reaction of 8,9-didehydrocrocetindial ( 4 ) with 2 yielded the three acetylenic isomers 5a–c which differ in the configuration of the terminal double bonds. Structures were established by 1D- and 2D-NMR studies. Illustrative spectra and their interpretation are presented. Most chemical shifts of corresponding protons in 3 and 5 and nearly identical, but 13C shifts differ considerably. 相似文献