Enantioselective Catalysis, XII. Synthesis of Bis(phosphane) Palladium and Rhodium Complexes on a Polyethylene Oxide Grafted Polystyrene Matrix (TentaGel) and the Catalytic Behavior of the Rhodium Complexes

1996 ◽  
Vol 129 (7) ◽  
pp. 815-821 ◽  
Author(s):  
Ulrich Nagel ◽  
Joachim Leipold
Keyword(s):  
Polyethylene Oxide ◽  
Enantioselective Catalysis ◽  
Rhodium Complexes ◽  
Catalytic Behavior ◽  
Polystyrene Matrix

Asymmetrische Katalysen, 13 [1]. Chelat-Liganden und ihre Rhodium-Komplexe mit seitlichen Asymmetriezentren und ihre Anwendung in der enantioselektiven Katalyse / Asymmetric Catalyses. 13 [1]. Chelate Ligands and their Rhodium Complexes with Lateral Asymmetrie Centers and their Use in Enantioselective Catalysis

1983 ◽  
Vol 38 (11) ◽  
pp. 1332-1338 ◽  
Author(s):  
Henri Brunner ◽  
A. F. M. Mokhlesur Rahman
Keyword(s):  
Cinnamic Acid ◽  
Asymmetric Hydrogenation ◽  
Optically Active ◽  
Enantioselective Catalysis ◽  
Rhodium Complexes ◽  
Chelate Ligands

Abstract The chelate ligands 1-3 with lateral asymmetric centers at the nitrogen atoms were prepared and characterized. In the Rh complexes 4 and 5 the asymmetric centers directly interact with those coordination positions where during enantioselective catalysis pro-chiral substrates are converted into optically active products. The compounds 4 and 5, as well as the in situ catalysts [Rh(COD)Cl]2/2 were used in the asymmetric hydrogenation of α-N[acetamino]cinnamic acid and in the asymmetric hydrosilylation of acetophenone with diphenylsilane. The low optical inductions obtained result from the catalyst loosing its chiral information during catalysis due to racemization or fragmentation.

Structures Formed by Cryoprotective Agents Used in Freezc-Etching

1971 ◽  
Vol 29 ◽  
pp. 448-449
Author(s):  
G. G. Cocks ◽  
C. E. Cluthe
Keyword(s):  
Aqueous Solution ◽  
Polyethylene Oxide ◽  
Liquid Nitrogen Temperature ◽  
Ice Crystals ◽  
Etching Technique ◽  
Structural Constituent ◽  
Cryoprotective Agents ◽  
Quick Freezing ◽  
Freeze Etching ◽  
Fractured Surface

The freeze etching technique is potentially useful for examining dilute solutions or suspensions of macromolecular materials. Quick freezing of aqueous solutions in Freon or propane at or near liquid nitrogen temperature produces relatively large ice crystals and these crystals may damage the structures to be examined. Cryoprotective agents may reduce damage to the specimem, hut their use often results in the formation of a different set of specimem artifacts.In a study of the structure of polyethylene oxide gels glycerol and sucrose were used as cryoprotective agents. The experiments reported here show some of the structures which can appear when these cryoprotective agents are used.Figure 1 shows a fractured surface of a frozen 25% aqueous solution of sucrose. The branches of dendritic ice crystals surrounded hy ice-sucrose eutectic can be seen. When this fractured surface is etched the ice in the dendrites sublimes giving the type of structure shown in Figure 2. The ice-sucrose eutectic etches much more slowly. It is the smooth continuous structural constituent surrounding the branches of the dendrites.

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