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991.
992.
Carsten von Hänisch Birgit Rolli 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4-5):749-757
The reaction of GaEt3 with H2PSiMe2R (R = CMe2] initially yields the cyclic compound [(Et2Ga)2{P(H)SiMe2R}2] 1. 1 appears as a mixture of cis and trans isomers and has been characterized by 31P NMR spectroscopy, IR spectroscopy, and mass spectrometry. 1 decomposes at 180°C under elimination of ethane during 1 h to form the cage-like compound [EtGaPSiMe2R]4 (2). Central structural motif of 2 is a Ga4P4 heterocubane cage. 相似文献
993.
994.
995.
996.
Marcus Frings Iuliana Atodiresei Dr. Yutian Wang Jan Runsink Dr. Gerhard Raabe Prof. Dr. Carsten Bolm Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4577-4587
Vinylogous Mukaiyama‐type aldol reactions have been catalyzed by a combination of Cu(OTf)2 and readily available C1‐symmetric aminosulfoximines. After a fine‐tuning of the reaction conditions and an optimization of the modularly assembled ligand structure, high stereoselectivities and excellent yields have been achieved in catalyzed reactions involving various electrophile/nucleophile combinations. The relative and absolute configurations of two products were assigned by X‐ray single crystal structure analysis and a comparison of calculated and experimental CD spectra. 相似文献
997.
998.
The coordination of (R,R)-tetramethylcyclohexane-1,2-diamine derivatives with stereogenic nitrogen centers to zinc and mercury halides is investigated. It is shown that the resulting complexes display one specific configuration at the stereogenic nitrogen centers. This fact is unusual due to the fast inversion of nitrogen centers but highly desirable as the stereoinformation of the ligands is brought closer to the metal centers of the potential catalysts. A combination of NMR studies and quantum chemical calculations gives insight into the selective formation of one specific configuration at the stereogenic nitrogen centers of the zinc complexes. 相似文献
999.
Wet iron-sulfur minerals have been shown to be ideal environments to allow for simple chemical reactions to occur in nature, for instance, in the framework of prebiotic chemistry. Yet, not much is known about such water/mineral interfaces beyond those involving pyrite, FeS(2), which is, however, chemically rather inert. In contrast, mackinawite is chemically reactive and consists of a layered crystal structure comprising FeS sheets that can be easily cleaved. Here, the properties of water confined between such sheets in lamella-like setups is investigated in the spirit of surface science model systems. The properties of this intercalated water are found to depend significantly on the interlayer distance and change from "arrested water" (in the limit of small interlayer distances) to liquid-like behavior. 相似文献
1000.
Reuter S Amado E Busse K Kraska M Stühn B Tschierske C Kressler J 《Journal of colloid and interface science》2012,372(1):192-201
Langmuir films of facial T-shaped amphiphilic liquid crystals were studied at the air-water interface. The liquid crystals were composed of three incompatible segments: a central rigid rodlike p-terphenyl (TP) group, two flexible hydrophobic n-alkyl terminal chains of identical length linked through ether bonds, and one hydrophilic lateral chain of three ethylene oxide units with a carboxyl end group. In order to determine the influence of the alkyl chain length on the characteristics of condensed films three TPs having n-alkyl chains with eight (TP8/3), ten (TP10/3) or 16 (TP16/3) carbon atoms were investigated. Surface pressure - mean molecular area isotherms revealed clear differences. TP8/3 and TP10/3 exhibit an extended plateau region where a phase transition from monolayer to multilayer takes place. On the other hand, the TP16/3 isotherm showed a distinct maximum ('spike') corresponding to a surprising surface crystallization process which is reported for the first time for a Langmuir film of a liquid crystal. Brewster angle microscopy clearly confirmed these differences: TP8/3 and TP10/3 formed circular domains with liquid crystalline order, while TP16/3 formed well-defined two-dimensional polycrystalline spherulites which are fractured after further compression. The film thickness determined by X-ray reflectivity measurements correlated with a multilayer formation for TP10/3. The morphology of Langmuir-Blodgett (LB) films transferred onto silicon wafers and studied by atomic force microscopy also confirmed the striking different behavior (multilayer formation vs. 2D crystallization) of the TPs under investigation. 相似文献