Carbon dioxide, supercritical metal catalyzed

Although numerous advantages are associated with the use of supercritical carbon dioxide (scC02) as an ecologically benign and user friendly reaction medium, systematic applications to metal-catalyzed processes are still rare. A notable exception is a recent report on the use of scC02 for the formation of industrially relevant polymers by ROMP and the eyelization of various dienes or enynes via RCM [7]. Both Schrock s molybdenum alkylidene complex 24 and the ruthe-... 

Langanke J, Leitner W (2008) Regulated Systems for Catalyst Immobilisation Based on Supercritical Carbon Dioxide. 23 91-108 Larock R (2005) Palladium-Catalyzed Annulation of Alkynes. 14 147-182 Larrow JF, Jacobsen EN (2004) Asymmetric Processes Catalyzed by Chiral (Salen)Metal Complexes 6 123-152... 

Transition-metal-catalyzed hydroboration, a reduction using B H bonds, of styrene derivatives has been demonstrated to occur in supercritical carbon dioxide using tunable Rh(I) complexes as catalysts. In the case of vinyl anisole (eq. 2.5), significantly higher regioselectivities were reported for the reaction in this medium than in THF or perfluoro(methylcyclohexane) (Carter et ah, 2000). 

Heterogeneously catalyzed hydrogenation reactions can be run in batch, semibatch, or continous reactors. Our catalytic studies, which were carried out in liquid, near-critical, or supercritical C02 and/or propane mixtures, were run continuously in oil-heated (200 °C, 20.0 MPa) or electrically heated flow reactors (400 °C, 40.0 MPa) using supported precious-metal fixed-bed catalysts. The laboratory-scale apparatus for catalytic reactions in supercritical fluids is shown in Figure 14.2. This laboratory-scale apparatus can perform in situ countercurrent extraction prior to the hydrogenation step in order to purify the raw materials employed in our experiments. Typically, the following reaction conditions were used in our supercritical fluid hydrogenation experiments catalyst volume, 2-30 mL total pressure, 2.5-20.0 MPa reactor temperature, 40-190 °C carbon dioxide flow, 50-200 L/h ... 

The present contribution highlights recent developments in the application of compressed (liquid or supercritical) carbon dioxide as a solvent for chemical reactions. After a brief introduction to the basic physical properties of SCCO2, some practical aspects of the use of compressed gases are discussed. A survey of successful applications of compressed and particularly supercritical CO2 in organic synthesis is provided with an emphasis on metal-catalyzed reactions. 

Compressed liquid or supercritical carbon dioxide has been recognized as a useful alternative reaction medium for radical and ionic polymerization reactions (see Chapter 4.5). Many of the benefits associated with the use of SCCO2 in these processes apply equally well to polymerizations relying on a metal complex as the chain-carrying species. However, the solubility of the metal catalyst and hence the controlled initiation of chain growth add to the complexity of the systems under study. Furthermore, many of the environmental benefits would be diminished if subsequent conventional purification steps were needed to remove the metal from the polymer. Nevertheless, the interest in metal-catalyzed polymerizations is increasing, and some promising systems have been described. 

Hydrogenation Reactions in Supercritical CO2 Catalyzed by Metal Nanoparticles in a Water-in-Carbon Dioxide Microemulsion... 

Supercritical carbon dioxide (SCCO2) has been shown to be a powerful medium for performing catalysis and separating the products from the metallic center [89]. Good performances have been reported in hydrogenation reactions [90,91] in palladium-catalyzed carbon-carbon bond formation [92,93], and more recently in platinum-catalyzed enantioselective hydrogenation [94]. Darr and Poliakoff [95], with Jessop et al. [96], reviewed extensively the characteristic of co-ordination chemistry and catalysis in SCCO2. 

T. J. de Vries, Late Transition State Metal Catalyzed Polymerizations of Olefins in Supercritical Carbon Dioxide, PhD thesis, Technische Universiteit Eindhoven,... 

Li, J.-H., Jia, L.-Q. and Jiang, H.-R (2000) Transition metal-catalyzed reactions in supercritical carbon dioxide. Youji Huaxue, Chinese J. Org. Chem., 20, 293-8 Chem. Abstr., 133, 90955 (2000) remark wrong citations of names are given in this review. 

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