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991.
Frech CM Blacque O Schmalle HW Berke H Adlhart C Chen P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(12):3325-3338
The reaction of [Re(H)(NO)2(PR3)2] complexes (1 a: R = PCy3; 1 b: R = PiPr3) with [H(OEt2)2][BAr(F)4] ([BAr(F)4] = tetrakis{3,5-bis(trifluoromethyl)phenyl}borate) in benzene at room temperature gave the corresponding cations [Re(NO)2(PR3)2][BAr(F)4] (2 a and 2 b). The addition of phenyldiazomethane to benzene solutions of 2 a and 2 b afforded the moderately stable cationic rhenium(I)-benzylidene-dinitrosyl-bis(trialkyl)phosphine complexes 3 a and 3 b as [BAr(F)4]- salts in good yields. The complexes 2 a and 2 b catalyze the ring-opening metathesis polymerization (ROMP) of highly strained nonfunctionalized cyclic olefins to give polymers with relatively high polydispersity indices, high molecular weights and over 80 % Z configuration of the double bonds in the chain backbone. However, these complexes do not show metathesis activity with acyclic olefins. The benzylidene derivatives 3 a and 3 b are almost inactive in ROMP catalysis with norbornene and in olefin metathesis. NMR experiments gave the first hints of the initial formation of carbene complexes from [Re(NO)2(PR3)2][BAr(F)4] (2 a and 2 b) and norbornene. In a detailed mechanistic study ESI-MS/MS measurements provided further evidence that the carbene formation is initiated by a unique reaction sequence where the cleavage of the strained olefinic bond starts with phosphine migration forming a cyclic ylide-carbene complex, capable of undergoing metathesis with alternating rhenacyclobutane formation and cycloreversion reactions ("ylide" route). However, even at an early stage the ROMP propagation route is expected to merge into an "iminate" route by attack by the ylide function on one of the N(NO) atoms followed by phosphine oxide elimination. The formation of phosphine oxide was confirmed by NMR spectroscopy. The proposed mechanism is supported further by detailed DFT calculations. 相似文献
992.
Yan Y Hoffmann H Drechsler M Talmon Y Makarsky E 《The journal of physical chemistry. B》2006,110(11):5621-5626
Intermediate structures of the aggregates in the aqueous solution of an ABA-type silicone surfactant and in the process of an SDS-induced vesicle-micelle transition are reported. In single ABA silicone surfactant aqueous solutions, large multilamellar vesicles (MLV), small single lamellar vesicles (SLV), threadlike micelles (TLM), and spheroidal micelles were observed. Interestingly, a large amount of TLMs were found entrapped into the large MLVs, but not in SLVs. Disintegration of the small vesicles inside the MLVs indicates that the entrapped TLM are from the disintegrated membrane of the entrapped small vesicles. Addition of SDS induced a transition from vesicles or threadlike micelles to spheroidal micelles. The intermediate structures, such as the appearance of small holes in the vesicle membrane, the budding of threadlike micelles from the membrane fracture, and the clusters of spheroidal micelles, were observed with increase of the SDS concentration. The electrical conductivity measurements indicated that complex micelles of SDS and silicone surfactant were formed in the solution due to the interaction between the SDS and PEO part of the silicone surfactant. 相似文献
993.
Langhals H El-Shishtawy R von Unold P Rauscher M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(17):4642-4645
The synthesis of methoxyperylene bisimides and perylene lactame imides with aliphatic N-substituents is described. Both classes of dyes exhibit fluorescence in the bathochromic region of visible light so that red light is obtained. The lightfastness of the dyes is very high, thus, there is special interest for diverse applications. 相似文献
994.
Hydrogenation of Imines Catalyzed by Trisphosphine‐Substituted Molybdenum and Tungsten Nitrosyl Hydrides and Co‐Catalytic Acid 下载免费PDF全文
Dr. Subrata Chakraborty Dr. Olivier Blacque Dr. Thomas Fox Prof. Heinz Berke 《化学:亚洲杂志》2014,9(10):2896-2907
Hydride complexes Mo,W(CO)(NO)H(mer‐etpip) (iPr2PCH2CH2)2PPh=etpip) ( 2 a,b(syn) , syn and anti of NO and Ph(etpip) orientions) were prepared and probed in imine hydrogenations together with co‐catalytic [H(Et2O)2][B(C6F5)4] (140 °C, 60 bar H2). 2 a,b(syn) were obtained via reduction of syn/anti‐Mo,W(NO)Cl3(mer‐etpip) and syn,anti‐Mo,W(NO)(CO)Cl(mer‐etpip). [H(Et2O)2][B(C6F5)4] in THF converted the hydrides into THF complexes syn‐[Mo,W(NO)(CO)(etpip)(THF)][B(C6F5)4]. Combinations of the p‐substituents of aryl imines p‐R1C6H4CH=N‐p‐C6H4R2 (R1,R2=H,F,Cl,OMe,α‐Np) were hydrogenated to amines (maximum initial TOFs of 1960 h?1 ( 2 a(syn) ) and 740 h?1 ( 2 b(syn) ) for N‐(4‐methoxybenzylidene)aniline). An ‘ionic hydrogenation’ mechanism based on linear Hammett plots (ρ=?10.5, p‐substitution on the C‐side and ρ=0.86, p‐substitution on the N‐side), iminium intermediates, linear P(H2) dependence, and DKIE=1.38 is proposed. Heterolytic splitting of H2 followed by ‘proton before hydride’ transfers are the steps in the ionic mechanism where H2 ligand addition is rate limiting. 相似文献
995.
Wenzel SC Williamson RM Grünanger C Xu J Gerth K Martinez RA Moss SJ Carroll BJ Grond S Unkefer CJ Müller R Floss HG 《Journal of the American Chemical Society》2006,128(44):14325-14336
Feeding experiments with isotope-labeled precursors rule out hydroxypyruvate and TCA cycle intermediates as the metabolic source of methoxymalonyl-ACP, the substrate for incorporation of "glycolate" units into ansamitocin P-3, soraphen A, and other antibiotics. They point to 1,3-bisphosphoglycerate as the source of the methoxymalonyl moiety and show that its C-1 gives rise to the thioester carbonyl group (and hence C-1 of the "glycolate" unit), and its C-3 becomes the free carboxyl group of methoxymalonyl-ACP, which is lost in the subsequent Claisen condensation on the type I modular polyketide synthases (PKS). d-[1,2-(13)C(2)]Glycerate is also incorporated specifically into the "glycolate" units of soraphen A, but not of ansamitocin P-3, suggesting differences in the ability of the producing organisms to activate glycerate. A biosynthetic pathway from 1,3-bisphosphoglycerate to methoxymalonyl-ACP is proposed. Two new syntheses of R- and S-[1,2-(13)C(2)]glycerol were developed as part of this work. 相似文献
996.
Dynamics of alkyl ammonium intercalants within organically modified montmorillonite: Dielectric relaxation and ionic conductivity 总被引:1,自引:0,他引:1
Jacobs JD Koerner H Heinz H Farmer BL Mirau P Garrett PH Vaia RA 《The journal of physical chemistry. B》2006,110(41):20143-20157
The low-frequency (0.01 Hz-10 MHz) dynamic characteristics of alkyl quaternary ammonium exchanged montmorillonite (SC20A) were investigated to determine the correlation between temperature-dependent changes in the interlayer structure and collective mobility of the surfactant. From 25 to 165 degrees C, SC20A exhibits two interlayer transitions, one ascribed to the melting of the intercalated alkyl chains of the surfactant (20-40 degrees C) and another associated with an abrupt decrease in the interlayer's coefficient of thermal expansion (100 degrees C). For this temperature range, the excess surfactant and residual electrolytes present in commercially manufactured SC20A enhance the direct current conductivity and increase low-frequency space-charge polarization, which is believed to occur across percolation paths established by the surfaces of the SC20A crystallites. In contrast, a higher-frequency relaxation, which was less sensitive to process history and impurity content, is ascribed to relaxation within the interlayer at the surfactant-aluminosilicate interface electrostatic couple. The temperature dependence of these dielectric relaxations indicated a drastic increase in mobility as the interlayer organic phase transitions from static and glasslike into molten and mobile. Overall, SC20A displayed features of alternating current universality, including time-temperature superposition, common in other types of disordered ion-conducting media. The presence of long-range transport and its sensitivity to low amounts of impurities imply that from a dynamic perspective the local environment of the surfactants are substantially diverse and a minority fraction, such as at the edge of the crystallite (gallery and aluminosilicate layer), may dominate the lower-frequency dielectric response. 相似文献
997.
Nicolas Pradeille Anthony Linden Heinz Heimgartner 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(5):o249-o252
The title compounds, O‐benzyl‐N‐(benzyloxycarbonyl)threonyl‐2,N‐dimethylalaninanilide, C30H35N3O5, and methyl (4R)‐4‐benzyloxy‐N‐(benzyloxycarbonyl)valyl‐2‐(methylalanyl)prolinate, C30H39N3O7, were obtained from the `azirine coupling' of the corresponding protected amino acids with 2,2,N‐trimethyl‐2H‐azirin‐3‐amine and methyl (4R)‐4‐(benzyloxy)‐N‐(2,2‐dimethyl‐2H‐azirin‐2‐yl)prolinate, respectively. The Aib unit in each molecule has the greatest turn‐ or helix‐inducing effect on the molecular conformation. Intermolecular N—H⋯O interactions link the molecules of the tripeptide into sheets and those of the dipeptide into extended chains. 相似文献
998.
Synthesis of Z‐Protected Aib‐ and Phe(2Me)‐Containing Pentapeptides and Their Crystal Structures 下载免费PDF全文
A series of pentapeptide derivatives containing α,α‐disubstituted α‐amino acids have been prepared by a combination of the ‘azirine/oxazolone method’ and segment condensations. X‐Ray crystal‐structure determinations of the molecular structures confirmed the presence of helical conformations stabilized by β‐turns of type III or III′. Pentapeptides containing (R)‐Phe(2Me) form a right‐handed helix, whereas those containing (S)‐Phe(2Me) adopt a left‐handed helical structure. 相似文献
999.
Rami A. Abdel-Rahem Martin Reger Matthias Hloucha Heinz Hoffmann 《Journal of Dispersion Science and Technology》2014,35(1):64-75
Aqueous solutions containing sodium lauryl ether sulphate (SLES) and cocamidopropyl Betaine (CAPB) with a constant total surfactant concentration (10 wt%) but different volume mixing ratios were prepared. A remarkable increase in the solutions’ viscosity at a volume mixing ratio of 34 v/v% SLES to 66 v/v% CAPB was observed. By increasing the volume ratio of SLES (r-value) in the binary mixture, the viscosity of 10 wt% SLES, which is close to that of water, increases to a maximum, but then drops down drastically at high r values (>45 v/v%). The maximum viscosity (Vmax) is 2.8 Pas, whereas the minimum is 2 mPas. The rheological behavior at Vmax has the remarkable feature of a simple Maxwell fluid over a large frequency range with one relaxation time. By adding a microemulsion (Plantasil Micro), the value of Vmax decreases extremely, whereas adding cosurfactants like isodecyltrietheleneoxide (IT3) or salts, like calcium chloride, leads to a pronounced increase in the value of Vmax. At 0.76 wt% CaCl2, Vmax is 140 Pas and 150 Pas in the presence of 1 wt% IT3. By increasing the SLES volume mixing ratio in the solution the maximum viscosity is shifted to higher CaCl2 amounts. The increasing viscosity can be explained by a transformation of the micelle shape from spherical to rod-like. Whereas adding cosurfactants or salts leads to an increased entanglement between the rod-like micelles. Consequently, higher microemulsion amounts can be added before reaching the minimum viscosity. 相似文献
1000.
Grzegorz Mlosto Marcin Jasiski Anthony Linden Heinz Heimgartner 《Helvetica chimica acta》2006,89(7):1304-1316
The reaction of 1,4,5‐trisubstituted 1H‐imidazole‐3‐oxides 1 with 2,2‐bis(trifluoromethyl)ethene‐1,1‐dicarbonitrile ( 7 , BTF) yielded the corresponding 1,3‐dihydro‐2H‐imidazol‐2‐ones 10 and 2‐(1,3‐dihydro‐2H‐imidazol‐2‐ylidene)malononitriles 11 , respectively, depending on the solvent used. In one example, a 1 : 1 complex, 12 , of the 1H‐imidazole 3‐oxide and hexafluoroacetone hydrate was isolated as a second product. The formation of the products is explained by a stepwise 1,3‐dipolar cycloaddition and subsequent fragmentation. The structures of 11d and 12 were established by X‐ray crystallography. 相似文献