Chiral vanadyl salen complex anchored on supports as recoverable catalysts for the enantioselective cyanosilylation of aldehydes. Comparison among silica, single wall carbon nanotube, activated carbon and imidazolium ion as support |
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Authors: | Carlos Baleizão Bárbara Gigante Avelino Corma |
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Institution: | a INETI, Departamento de Tecnologia das Indústrias Químicas, Estrada Paço do Lumiar 22, 1649-038 Lisboa, Portugal b Instituto de Tecnología Química/CSIC, Universidad Politécnica de Valencia, Avda. de los Naranjos s/n, 46022 Valencia, Spain |
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Abstract: | The activity and enantiomeric excess (ee) (in some cases >85%) obtained for the asymmetric addition of trimethylsilyl cyanide to aldehydes using different heterogeneous chiral catalysts are compared. A library of recoverable catalysts was developed by immobilization of a chiral vanadyl salen complex having a terminal carbon-carbon double bond onto a series of scaffolds including silica, single-wall carbon nanotubes, activated carbon and room-temperature ionic liquids. The covalent linkage has been achieved by radical initiated addition of mercapto groups to C C. The highest enantiomeric excesses, similar to those obtained in the homogeneous phase, were achieved using silica as support or with the homogeneous tetra-tert-butyl salen catalyst dissolved in an imidazolium ionic liquid. The use of silica as support permits an easier separation and reuse of the catalyst from the reaction media. |
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Keywords: | Cyanohydrins Heterogeneous asymmetric catalysis Chiral vanadyl salen complex Silica as support Single-wall carbon nanotubes Activated carbon Ionic liquids |
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