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排序方式: 共有554条查询结果,搜索用时 383 毫秒
91.
92.
Paul‐Michael Pellny Vladimir V. Burlakov Wolfgang Baumann Anke Spannenberg Uwe Rosenthal 《无机化学与普通化学杂志》1999,625(6):910-918
The reactions of the bis(trimethylsilyl)acetylene permethylmetallocene complexes CpM(η2‐Me3SiC2SiMe3) (M = Ti ( 1 ), M = Zr ( 2 )) with H2O and CO2 were studied and compared to those of the corresponding metallocene complexes Cp2M(L)(η2‐Me3SiC2SiMe3) (M = Ti ( 3 ), L = – ; M = Zr, L = THF ( 4 )) to understand the influence of the ligands Cp(η5‐C5H5) and Cp*(η5‐C5Me5) as well as the metals titanium and zirconium on the reaction pathways and the obtained products. In the reaction of the permethyltitanocene complex 1 with water the dihydroxy complex CpTi(OH)2 ( 5 ) was formed. This product differs from the well‐known titanoxane Cp2TiOTiCp2 which was obtained by the reaction of the corresponding titanocene complex 3 with water. The reaction of the permethylzirconocene complex 2 with water gives the mononuclear alkenyl zirconocene hydroxide 6 . An analogous product was assumed as the first step in the reaction of the corresponding zirconocene complex 4 with water which ends up in a dinuclear zirconoxane. In the conversion of the permethylzirconocene complex 2 with carbon dioxide the mononuclear insertion product 7 was formed by coupling of carbon dioxide and the acetylene. In contrast, the corresponding zirconocene complex 4 affords, by an analogous reaction, a dinuclear complex. In additional experiments the known complex CpZr(η2‐PhC2SiMe3) ( 8 ) was prepared, starting from CpZrCl2 and Mg in the presence of PhC≡CSiMe3. This complex reacts with carbon dioxide resulting in a mixture of the regioisomeric zirconafuranones 9 a and 9 b . From these in the complex 9 a , having the SiMe3 group in β‐position to the metal, the Zr–C bond was quickly hydrolyzed by water to give the complex CpZr(OH)OC(=O)–C(SiMe3)=CHPh ( 10 a ) compared to complex ( 9 b ) which gives slowly the complex CpZr(OH)OC(=O)–CPh=CH(SiMe3) ( 10 b ). 相似文献
93.
Dirk Lützenkirchen‐Hecht Ralph Wagner Ulrich Haake Anke Watenphul Ronald Frahm 《Journal of synchrotron radiation》2009,16(2):264-272
The hard X‐ray beamline BL8 at the superconducting asymmetric wiggler at the 1.5 GeV Dortmund Electron Accelerator DELTA is described. This beamline is dedicated to X‐ray studies in the spectral range from ~1 keV to ~25 keV photon energy. The monochromator as well as the other optical components of the beamline are optimized accordingly. The endstation comprises a six‐axis diffractometer that is capable of carrying heavy loads related to non‐ambient sample environments such as, for example, ultrahigh‐vacuum systems, high‐pressure cells or liquid‐helium cryostats. X‐ray absorption spectra from several reference compounds illustrate the performance. Besides transmission measurements, fluorescence detection for dilute sample systems as well as surface‐sensitive reflection‐mode experiments have been performed. The results show that high‐quality EXAFS data can be obtained in the quick‐scanning EXAFS mode within a few seconds of acquisition time, enabling time‐resolved in situ experiments using standard beamline equipment that is permanently available. The performance of the new beamline, especially in terms of the photon flux and energy resolution, is competitive with other insertion‐device beamlines worldwide, and several sophisticated experiments including surface‐sensitive EXAFS experiments are feasible. 相似文献
94.
95.
We report new chiral bisimidazolium salts synthesized from naturally occurring l-amino acids. They served as precursors for bidentate N-heterocyclic carbene metal complexes. The chiral imidazoles could be synthesized in good yields via a one-pot ring closing reaction, followed by esterification. The methylene bridged bisimidazolium iodide salts are accessible in moderate yields. Corresponding palladium(II)- and platinum(II)-NHC complexes could be synthesized and fully characterized, but do not show optical activity. We also report a solid state structure of one of the synthesized palladium(II) biscarbene compounds derived from alanine. 相似文献
96.
Anke Flemming Martin Köckerling Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(14):2605-2608
Complete exchange : [M6X12] type cluster compounds with an octahedral M6 metal atom arrangement, which is completely surrounded by alcoholato ligands, were unknown until now. The first representatives are prepared containing a [Nb6(OR)12]4+ unit (R=CH3 or C2H5). They are accessible at elevated temperatures from strongly basic alcoholate solutions of [Nb6Cl12]2+‐containing precursors. C gray, H white, K turquoise, Nb blue, O red.
97.
Nienhaus GU Nienhaus K Hölzle A Ivanchenko S Renzi F Oswald F Wolff M Schmitt F Röcker C Vallone B Weidemann W Heilker R Nar H Wiedenmann J 《Photochemistry and photobiology》2006,82(2):351-358
EosFP is a fluorescent protein from the coral Lobophyllia hemprichii that changes its fluorescence emission from green to red upon irradiation with near-UV light. Here we present the spectroscopic properties of wild-type EosFP and a variety of monomeric and dimeric mutants and provide a structural interpretation of its oligomerization and photoconversion, which is based on X-ray structure analysis of the green and red species that we reported recently. Because functional expression of the monomeric EosFP variant is limited to temperatures of 30 degrees C, we have developed a tandem dimer. This construct, in which two EosFP subunits are connected by a flexible 12 amino acid linker, expresses well after fusion with the androgen and endothelin A receptors at 37 degrees C. A variety of applications in cellular imaging, developmental biology and automated high-content screening applications are presented, which demonstrate that EosFP is a powerful tool for in vivo monitoring of cellular processes. 相似文献
98.
Holz J Zayas O Jiao H Baumann W Spannenberg A Monsees A Riermeier TH Almena J Kadyrov R Börner A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(19):5001-5013
A set of 16 new and closely related bisphospholane ligands have been prepared by using a highly flexible and convergent approach. Each synthesis can be performed on an industrially relevant scale. The bisphosphines differ in the nature of the bridge connecting both phospholane units. Bridges are formed by three-, four-, five- and six-membered heterocyclic or alicyclic rings. Bisphospholanes and their Rh-precatalysts have been investigated by using results of theoretical calculations (DFT) and analytic measurements ((31)P and (103)Rh NMR spectroscopy, X-ray structure analysis). The studies showed that catalysts based on ligands with maleic anhydride or maleimide bridges give constantly superior enantioselectivities in methanol as the solvent. This may account for optimised steric and electronic effects. However, by changing the solvent catalysts with other backbones can give rise to excellent results. This gives proof that simple correlations between steric and electronic properties and results in the enantioselective hydrogenation frequently claimed in literature are not general. 相似文献
99.
Anke Rückert 《Tetrahedron letters》2006,47(45):7977-7981
A concise, enantioselective synthesis of (+)-dumetorine is described, giving the natural product in six steps and a 27% overall yield from a readily available precursor. Among the key steps used, the synthesis entails a high-yielding ring-rearrangement metathesis (RRM), using the commercially available first generation Grubbs catalyst 2 in combination with Ti(Oi-Pr)4 as a co-catalyst. This constitutes the first enantioselective total synthesis of the alkaloid from a known chiral intermediate, and hence a confirmation of its absolute stereochemistry. 相似文献
100.
Gärtner F Denurra S Losse S Neubauer A Boddien A Gopinathan A Spannenberg A Junge H Lochbrunner S Blug M Hoch S Busse J Gladiali S Beller M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(11):3220-3225
Novel phenylazole ligands were applied successfully in the synthesis of cyclometalated iridium(III) complexes of the general formula [Ir(phenylazole)(2)(bpy)]PF(6) (bpy=2,2'-bipyridine). All complexes were fully characterized by NMR, IR, and MS spectroscopic studies as well as by cyclic voltammetry. Three crystal structures obtained by X-ray analysis complemented the spectroscopic investigations. The excited-state lifetimes of the iridium complexes were determined and showed to be in the range of several hundred ns to multiple μs. All obtained iridium complexes were active as photosensitizers in catalytic hydrogen evolution from water in the presence of triethylamine as a sacrificial reducing agent. Applying an in situ formed iron-based water reduction catalyst derived from [HNEt(3)](+) [HFe(3)(CO)(11)](-) and tris[3,5-tris-(trifluoromethyl)-phenyl]phosphine as the ligand, [Ir(2-phenylbenz-oxazole)(2)-(bpy)]PF(6) proved to be the most efficient complex giving a quantum yield of 16% at 440 nm light irradiation. 相似文献